Such pressure corresponds to the atomic concentration of hydrogen nD ≈ 2952 1022 at.Нcm3 at its density pD ≈ 0:0494 g cm3 (see monograph [20]). Only a manganin foil was placed in the HHPC chamber, and there was no Pd-rod inside. The chamber irradiation was carried out during 14 h (5.04 104 s). The electron beam energy was equal to 9.7 MeV at the average current (20–21)μА. During opening of the HHPC, it spilled out eight small particles about 1 mm in size. Some of them were dark, and the other was of light color. When being photographed with a special tool, all of the particles turned out to be transparent.

The photos in Figure 14 obtained using a special photomicrography tool show the "light" (a) and "dark" (b) particles at about the same scale.

Figure 15 shows SEM images of a dark particle with a size about 703 μm to 628 μm (a) and of its lengthy "tail" (b). Afterwards, this tail was broken during the studies. In regions 17 (a) and 18 (b) from Figure 15a and b, X-ray microprobe spectrometer (XRMPS) was used.

Table 5 provides the element compositions measured in regions 17 (Figure 15a) and 18 for a dark particle from Figure 15b. Note that both parts of the dark particle contain only light elements, such as 6C, 7N↑, 8O, 9F↑, 10Ne↑, 11Na, 12Mg, 13Al, 14Si, 15P, 16S, 17Cl, 18Ar↑, 19K, 20Ca, and a heavier metal 29Cu. Here is a series of elements with a nucleus charge change by ΔZ = 1 from Z = 6 (carbon) to Z = 20 (calcium), where the volatile elements 7N↑, 9F↑, 10Ne↑, 18Ar↑, which could not have formed any chemical compounds, were not detected. The same refers to the elements which are lighter than carbon and have a nucleus charge Z < 6, i.e., such elements as 1D, 2He, 3Li, 4Be and 5B, since they cannot be registered by an X-ray microprobe spectrometer.

Figure 14. Photos of the "light" (a) and "dark" (b) particles obtained in H2 gas experiment.

carbon layer, with the carbon concentration reaching 80.94 at.%, a rhenium concentration of

Because of some doubts concerning to our results with deuterium-Me systems, by some typical nuclear physicists, analogous investigations aimed at studying the possibilities of nuclear reactions were carried out using hydrogen high pressure chambers (HHPC) in presence of palladium [6] and tin rods, as well as with hydrogen only without any metallic samples inside [15], under irradiation with 10 MeV braking γ-rays. The phenomenological-model approaches for the description of the obtained experimental data on the basis of nuclear fission reactions

only 4.92 at.% and relatively high concentration of osmium up to 0.84 at.%.

Table 4. Elements and it concentration in Re specimen in places shown in Figure 13.

Figure 13. The surface structure of a Re-rod with marked patches for XMA analysis.

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Element Ca Fe Re Os Initial — — 100 — Point 1 — — 16.07 0.84 Point 2 — 0.16 4.92 0.28 Point 3 — — 11.91 0.77 Point 4 1.15 — 6.48 —

Element C O Mg S K Initial — — — — Point 1 65.65 17.44 — — Point 2 80.94 13.35 0.25 0.10 Point 3 72.95 14.37 — — Point 4 72.22 18.90 0.87 0.39 —

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in

5. Induced effects in pure gases

5.2. Results of synthesis of new particles and structures in dense deuterium using the

Shown in Figure 3a modified high-pressure chamber was used for the deuterium experiment with the initial pressure 2.2 kbar with a relative deuterium purity ≈106 (see Ref. [4]). The experiment was repeated under a pressure of 3.05 kbar with element 8 made of beryllium bronze. The modification of the DНРС consisted in the replacement of the viton sealing with the metalto metal one (beryllium bronze (CuBe2)). This allowed to limit the chemical elements inside the high-pressure chambers filled with gases H2, D2 and He (HHPC, DHPC and HeHPC) only to Cu and Be. The initial pressure was constant before irradiation during 2 weeks. The atomic density nD2 ≈ 2:1 1022 mol:D cm3 and the mass density pD2 ≈ 0:13 g cm3 [20]. The integrated electron fluence at the target was ≈ 2.5 1019 е during the whole experiment. After the irradiation procedure the pressure in the chamber remained constant during 1 month, so

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The irradiation time was t = 1.76 105 s at the electron current 20–21μА. During the irradiation at the stationary state, due to growing temperature an increase of deuterium pressure in the chamber was noted, from initial pressure po ≈ 2.085 kbar at Т0 = 293К to pstat ≈ 2.697 kbar at Тstat. = 343 K, which means "by jump": Δp ≈ 612 bar. Here, the temperature Tstat was measured at the surface of the pressure chamber made of beryllium bronze (Figure 3, position 6) inside

Taking into consideration the known ideal gases rule [20], the calculated pressure should be:

Thus, the pressure change ought to be Δpcal = pcalc po = 356 bar, as opposed to direct measurement yielding the value Δpmeas = 612 bar. In this situation we can suppose that the temperature inside the beryllium bronze chamber was higher, attaining the value: Tstat,cal = T0 pstat/po ≈ 379К. That means it was 36 K higher. The interpretation of this difference can be based on the supposition that some nuclear reactions took place during our experiment, It should be noted that in the case of the experiment with hydrogen the calculated growth of pressure during the irradiation was in proper relation to the temperature measured at the

An accurate SEM and XRMPA observation of the inner surface of the high-pressure chamber and inner surface of the split sleeve and closing element revealed 26 different objects which are described in a preprint published by the Joint Institute of Nuclear Research. Here we will

Eight interesting objects were found and only two are presented in Figure 16. Figure 16a shows a curious multiple objects in the form of small pillars, which element composition is

describe only the most interesting and representative results which can be interpreted.

The object found on the inner surface of the window plug (Figure 3, p. 4).

surface of the pressure chamber made of beryllium bronze (Figure 3, position 6).

the protecting sleeve (Figure 3, position 11) made from stainless steel.

DHPC under the action of γ-rays with 10 MeV energy

leakage of gas was not observed.

pcalc = 2.441 kbar.

5.3. Results of measurements

given in Table 5.

Figure 15. SEM images with a general view of a dark micro particle (a) and its right part with a "tail" (b).

Table 5. The element compositions measured for the marked areas in Figures 15, 16, 18–20.

### 5.2. Results of synthesis of new particles and structures in dense deuterium using the DHPC under the action of γ-rays with 10 MeV energy

Shown in Figure 3a modified high-pressure chamber was used for the deuterium experiment with the initial pressure 2.2 kbar with a relative deuterium purity ≈106 (see Ref. [4]). The experiment was repeated under a pressure of 3.05 kbar with element 8 made of beryllium bronze.

The modification of the DНРС consisted in the replacement of the viton sealing with the metalto metal one (beryllium bronze (CuBe2)). This allowed to limit the chemical elements inside the high-pressure chambers filled with gases H2, D2 and He (HHPC, DHPC and HeHPC) only to Cu and Be. The initial pressure was constant before irradiation during 2 weeks. The atomic density nD2 ≈ 2:1 1022 mol:D cm3 and the mass density pD2 ≈ 0:13 g cm3 [20]. The integrated electron fluence at the target was ≈ 2.5 1019 е during the whole experiment. After the irradiation procedure the pressure in the chamber remained constant during 1 month, so leakage of gas was not observed.

The irradiation time was t = 1.76 105 s at the electron current 20–21μА. During the irradiation at the stationary state, due to growing temperature an increase of deuterium pressure in the chamber was noted, from initial pressure po ≈ 2.085 kbar at Т0 = 293К to pstat ≈ 2.697 kbar at Тstat. = 343 K, which means "by jump": Δp ≈ 612 bar. Here, the temperature Tstat was measured at the surface of the pressure chamber made of beryllium bronze (Figure 3, position 6) inside the protecting sleeve (Figure 3, position 11) made from stainless steel.

Taking into consideration the known ideal gases rule [20], the calculated pressure should be: pcalc = 2.441 kbar.

Thus, the pressure change ought to be Δpcal = pcalc po = 356 bar, as opposed to direct measurement yielding the value Δpmeas = 612 bar. In this situation we can suppose that the temperature inside the beryllium bronze chamber was higher, attaining the value: Tstat,cal = T0 pstat/po ≈ 379К. That means it was 36 K higher. The interpretation of this difference can be based on the supposition that some nuclear reactions took place during our experiment, It should be noted that in the case of the experiment with hydrogen the calculated growth of pressure during the irradiation was in proper relation to the temperature measured at the surface of the pressure chamber made of beryllium bronze (Figure 3, position 6).

### 5.3. Results of measurements

Figure 15. SEM images with a general view of a dark micro particle (a) and its right part with a "tail" (b).

Table 5. The element compositions measured for the marked areas in Figures 15, 16, 18–20.

Figure 15a Figure 15b Figure 16a Figure 18b Figure 19a Figure 19b Figure 21, p. 3 Figure 21b El. wt.% at.% wt.% at.% wt.% at.% wt.% at.% wt.% at.% wt.% at.% wt.% at.% wt.% at.% C 13.0 17.40 25 32.02 47 64.48 43.3 69.30 11.2 17.15 47 66.95 34.2 46.54 25.6 42.44 N 8.1 9.45 5.16 7.34 O 76.7 77.35 68 65.09 26.6 27.31 12.9 15.47 58 66.42 23.1 24.66 37 38.13 26.1 32.65 F — — — — —— Na 2.49 1.75 1.05 0.70 ———— 0.62 0.49 — — 0.23 0.16 — — Mg — — 0.03 0.02 1.76 1.19 — — 6.21 4.68 — — 0.06 0.04 0.51 0.25 Al 0.19 0.11 0.17 0.10 0.24 0.15 0.03 0.02 0.27 0.18 0.11 0.07 0.07 0.04 2.87 2.25 Si 0.22 0.13 0.11 0.06 1.42 0.83 1.03 0.71 1.27 0.83 0.05 0.03 0.10 0.06 — — P 0.16 0.08 0.06 0.03 — — 0.39 0.24 0.02 0.01 0.04 0.02 0.23 0.12 0.30 0.20 S — — 0.03 0.02 0.14 0.07 — — 0.16 0.09 0.12 0.06 0.28 0.14 0.48 0.30 Cl 4.12 1.88 0.45 0.20 0.18 0.08 — — 0.50 0.26 0 .07 0.03 0.91 0.42 0.89 0.50 K 1.88 0.78 1.37 0.54 0.23 0.09 — — 0.37 0.17 — — 0.80 0.33 0.89 0.46 Ca 1.29 0.52 2.18 0.84 0.21 0.09 1.44 0.69 21.0 9.60 1.91 0.82 0.17 0.07 0.87 0.43 Cr —————— 0.31 0.12 ————— — —— Mn —————— 0.35 0.12 ————— — —— Fe —————— 35.7 12.32 0.32 0.11 0.40 0.12 0.14 0.04 7.51 2.68 Cu — — 1.68 0.41 22.1 5.72 2.37 0.72 — — 17.0 4.56 17.3 4.44 25.0 7.83 Zn —————————— 10.24 2.68 — — —— Sn —————— 1.20 0.19 ————— — —— Pb —————— 1.03 0.10 ————— — ——

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An accurate SEM and XRMPA observation of the inner surface of the high-pressure chamber and inner surface of the split sleeve and closing element revealed 26 different objects which are described in a preprint published by the Joint Institute of Nuclear Research. Here we will describe only the most interesting and representative results which can be interpreted.

The object found on the inner surface of the window plug (Figure 3, p. 4).

Eight interesting objects were found and only two are presented in Figure 16. Figure 16a shows a curious multiple objects in the form of small pillars, which element composition is given in Table 5.

Figure 16. SEM image of the objects found on the window-plug in D2 experiment.

### 5.3.1. The object found on the inside surface of the split sleeve: a container for expected products of nuclear reactions

Figure 17 gives a view of the inner surfaces of the first and second halves of the sleeve. We can see dark places on the light surfaces. The element compositions at these places are presented in Table 6. In the second case, we can observe a small amount of Cu, which can be interpreted as a large thickness of this object. MPRA used in our experiments collects information from the depth no greater than 4 μm.

### 5.3.2. The effects observed on the surface of the closing disk made of pure copper

Shown in Figure 18a is an image of the closing disc. One can see here similar dark stains as on the surface of the sleeve half (a). Figure 18b is a triangular structure on the surface of this disk with a large amount of iron (see Table 5).

5.3.3. The synthesized structures found during demounting of the pressure chamber, from the left and

Element Z wt.% at.% wt.% at.%

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C 6 24.9 3.9 54.92 57 12 65.94 O 8 11.1 1.8 18.36 39 11 33.20 Si 14 0.18 0.04 0.17 — — Cu 29 63.8 1.8 26.54 3.97 0.45 0.86

Table 6. The element compositions at the dark spots on the CuBe2 sleeve surfaces, (a) and (b), in the marked areas from

Area A B

As mentioned above, many different large particles were found after the irradiation. Here we are going to present only two typical ones. One particle, with a large amount of oxygen and of a rather regular shape, is shown in Figure 19a, and its element composition is given in Table 5. Another particle, with a large amount of carbon and of a rather non-regular shape, is shown in

Optical Studies of the Black Oily Foils Synthesized in HeHPC under the Action of Braking γ-

Upon opening of the chamber, black foils with reinforcing needles were observed at the junction of the entrance window and reaction chamber (see Figure 3, pos. 5). Part of the needles protruded from the foils as lengthy white rods of uniform thickness. The foils were then placed on a clean sheet of (tracing) paper. In the place where the black foils were found, the tracing paper was soaked with exudation from the foils. Such exudation resembled synthetic oil or liquid hydrocarbons. In Figure 20, the photos obtained using a special device for photomicrography show an array of round black foils which acquired this shape due to the

Figure 19b; and its element component is given in Table 5, too.

Figure 18. The view of the surface of the closing disk (a) and the found structure (b).

cylindrical symmetry of the reaction chamber's entrance window.

right parts of the pressure chamber

Figure 17.

rays at Pressure 1.1 kbar.

Figure 17. The observed dark stains on the inner surface of the CuBe2 half sleeve, (a) and (b) in the D2 irradiation experiment.

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Table 6. The element compositions at the dark spots on the CuBe2 sleeve surfaces, (a) and (b), in the marked areas from Figure 17.

5.3.1. The object found on the inside surface of the split sleeve: a container for expected products of

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in

5.3.2. The effects observed on the surface of the closing disk made of pure copper

Figure 16. SEM image of the objects found on the window-plug in D2 experiment.

Figure 17 gives a view of the inner surfaces of the first and second halves of the sleeve. We can see dark places on the light surfaces. The element compositions at these places are presented in Table 6. In the second case, we can observe a small amount of Cu, which can be interpreted as a large thickness of this object. MPRA used in our experiments collects information from the

Shown in Figure 18a is an image of the closing disc. One can see here similar dark stains as on the surface of the sleeve half (a). Figure 18b is a triangular structure on the surface of this disk

Figure 17. The observed dark stains on the inner surface of the CuBe2 half sleeve, (a) and (b) in the D2 irradiation

nuclear reactions

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experiment.

depth no greater than 4 μm.

with a large amount of iron (see Table 5).

### 5.3.3. The synthesized structures found during demounting of the pressure chamber, from the left and right parts of the pressure chamber

As mentioned above, many different large particles were found after the irradiation. Here we are going to present only two typical ones. One particle, with a large amount of oxygen and of a rather regular shape, is shown in Figure 19a, and its element composition is given in Table 5. Another particle, with a large amount of carbon and of a rather non-regular shape, is shown in Figure 19b; and its element component is given in Table 5, too.

Optical Studies of the Black Oily Foils Synthesized in HeHPC under the Action of Braking γrays at Pressure 1.1 kbar.

Upon opening of the chamber, black foils with reinforcing needles were observed at the junction of the entrance window and reaction chamber (see Figure 3, pos. 5). Part of the needles protruded from the foils as lengthy white rods of uniform thickness. The foils were then placed on a clean sheet of (tracing) paper. In the place where the black foils were found, the tracing paper was soaked with exudation from the foils. Such exudation resembled synthetic oil or liquid hydrocarbons. In Figure 20, the photos obtained using a special device for photomicrography show an array of round black foils which acquired this shape due to the cylindrical symmetry of the reaction chamber's entrance window.

Figure 19. SEM images of the large and regular-shape particles with large amounts of oxygen (a) and with a small amount of oxygen (b) obtained in the D2 experiment.

5.3.4. The objects found on the inner surfaces of the CuBe2 window-plug (Figure 3, position 4)

Figure 21. Large particles found near the screw surface obtained in the He experiment.

potassium (8.33 at.%).

Table 5.

5.3.5. The objects observed on the Cu0.98Be0.02 cylinder

prior to irradiation in the second He experiment.

At the surface we have observed three interesting objects, one of them being of pyramidal form. These objects are composed mainly of carbon (26.5 at.%), oxygen (62.31 at.%) and

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On the surface of the cylinder (divided into two equal parts) we could observe 27 different objects. Three of them, of large dimensions and complicated form, located on the wall, are presented in Figure 21 and their element compositions, in p. 3 and rectangular, are given in

An example of deposition on a wall and an object of complicated form are shown in Figure 22.

Figure 20 summarizes the element compositions measured for different objects. The curves are given for two experiments with account of the mean values for the element compositions obtained using the MPRA method. Presented curves are different but have a similar character, i.e., a regular decreasing tendency of atomic concentration with a rising atomic number. In

Figure 22. SEM images of the inside surface of the CuBe2 sleeve. Here, we can see specific surface structures and a particle of complex shape. The chemical composition of the particle at p. 4 (in at.%) is as follows: C—39.58, N—9.99, O—39.35, Na—0.69, Cl—1.49, Ca—0.32 and Cu—6.69. In the middle, there is a photo of the respective inside surface of the sleeve

In the middle, there is a photo of the respective surface before irradiation.

Figure 20. Illustration of the performed experiments with helium carried out using almost the same gamma irradiation procedure. Squares and the red line present first experiment data (p = 1.1 kb); stars and the dotted line correspond to the second experiment (p = 3 kb). On the right the largest object obtained in the first experiment, shown as an example.

Paper [18] (Figures 2 and 6) describes other black particles of complex shape obtained in the first experiment. Using the element compositions measured at some points, it was possible to determine some regularities with the help of their mean values (see Figure 20).

In a second helium experiment we observed another kind of inhomogeneities. Namely, the main products of synthesis of similar chemical content that covered the surface of the split sleeve surface which is presented in Figure 21. This experiment is described in paper [13], here only some, most interesting and representative facts are considered.

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Figure 21. Large particles found near the screw surface obtained in the He experiment.

### 5.3.4. The objects found on the inner surfaces of the CuBe2 window-plug (Figure 3, position 4)

At the surface we have observed three interesting objects, one of them being of pyramidal form. These objects are composed mainly of carbon (26.5 at.%), oxygen (62.31 at.%) and potassium (8.33 at.%).

### 5.3.5. The objects observed on the Cu0.98Be0.02 cylinder

Paper [18] (Figures 2 and 6) describes other black particles of complex shape obtained in the first experiment. Using the element compositions measured at some points, it was possible to

Figure 20. Illustration of the performed experiments with helium carried out using almost the same gamma irradiation procedure. Squares and the red line present first experiment data (p = 1.1 kb); stars and the dotted line correspond to the second experiment (p = 3 kb). On the right the largest object obtained in the first experiment, shown as an example.

Figure 19. SEM images of the large and regular-shape particles with large amounts of oxygen (a) and with a small

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in

amount of oxygen (b) obtained in the D2 experiment.

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In a second helium experiment we observed another kind of inhomogeneities. Namely, the main products of synthesis of similar chemical content that covered the surface of the split sleeve surface which is presented in Figure 21. This experiment is described in paper [13], here

determine some regularities with the help of their mean values (see Figure 20).

only some, most interesting and representative facts are considered.

On the surface of the cylinder (divided into two equal parts) we could observe 27 different objects. Three of them, of large dimensions and complicated form, located on the wall, are presented in Figure 21 and their element compositions, in p. 3 and rectangular, are given in Table 5.

An example of deposition on a wall and an object of complicated form are shown in Figure 22. In the middle, there is a photo of the respective surface before irradiation.

Figure 20 summarizes the element compositions measured for different objects. The curves are given for two experiments with account of the mean values for the element compositions obtained using the MPRA method. Presented curves are different but have a similar character, i.e., a regular decreasing tendency of atomic concentration with a rising atomic number. In

Figure 22. SEM images of the inside surface of the CuBe2 sleeve. Here, we can see specific surface structures and a particle of complex shape. The chemical composition of the particle at p. 4 (in at.%) is as follows: C—39.58, N—9.99, O—39.35, Na—0.69, Cl—1.49, Ca—0.32 and Cu—6.69. In the middle, there is a photo of the respective inside surface of the sleeve prior to irradiation in the second He experiment.

"upstream" nuclear reactions with synthesis of heavier elements and "downstream" reactions with asymmetric fission, with the formation of both light elements from carbon to iron and heavier elements (Ag, Zr, Ba, Ta, W, Pb, Pt, Au) were formed. To interpret these results several models were used. From the authors' point of view, to achieve an accurate description of these effects it is important to elaborate on new approaches to fission and fusion nuclear reactions. Because of volume limit of the chapter, problems including how to explain "protuberation," macro mass changes, so called "Dubna Oscillation," [31] how to realize third step of Tsar bomb

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Many thanks to Teresa Wilczyńska-Kitowska for her close, long time and fruitful cooperation. All experiments were carried out according to International (PL-RF) Scientific Cooperation in very efficient, friendly atmosphere, during many years of close cooperation between Polish and Russian teams (presented by Author and Alexander Yu. Didyk) and were financed by both sides.

[1] Yu DA, Wiśniewski R, Wilczyńska T. Joint Protocol JINR-IAE 2009-2011 and JINR-NCNR

[2] Baranowski B, Wiśniewski R. Synteza wodorku niklu z metalicznego niklu i gazowego wodoru. Bulletin de l'Academie Polonaise des Sciences, Serie des Sciences Chimiques.

[3] Wiśniewski R. High pressure apparatus for Gaseous Hydrogen (Deuterium) up to 25 kilobar and temperature range 50C – +100C. Review of Scientific Instruments. 1970;41

[4] Didyk AY, Wiśniewski R. Nuclear reaction, induced by γ quanta, in palladium saturated with deuterium saturated surrounded by dense deuterium gas. Europhysics Letters. 2012;

(using it for public welfare) author decided to publish it later.

\*Address all correspondence to<EMAIL_ADDRESS>
2 National Centre of Nuclear Research, Otwock-Świerk, Poland

3 Physics Faculty, Warsaw University of Technology, Warsaw, Poland

1 Joint Institute for Nuclear Research, Dubna, Russia

2012-2014. Poland: NCNR; Archives. 2013

Acknowledgements

Author details

References

1966;14(4):1273-1275

(3):455-464

99:22001-22006

Roland Wiśniewski1,2,3\*

Figure 23. Creation of the stabilized transmolecule of the Carbon 12Ctr. Red point means the α particle [41, 42].

those experiments, inside the HeHPC there was either spectrally pure helium under different pressures or a palladium rod in such helium atmosphere.

All of the three synthesized particles here are the largest objects shown in Figures 21 and 22 (see also Refs. [12, 13]), and have dielectric properties. According to the X-ray structural analysis, these articles have amorphous structures with a complex hydrocarbon composition that is absent in the reference library of the X-ray analysis. Due to its importance and for the purpose of greater reliability of the data, the structure of synthesized particles was analyzed using microscopes and X-ray micro-analyzers at two independent analytical centers. The mechanical properties of the large particles were not investigated. But there is a most intriguing problem with the electrical properties of the carbon-based structures which we obtained during all the helium experiments. The latest measurements of object shown in Figure 22 (right upper corner) [30] have shown a very large electrical resistivity r = 105 μΏm, relative dielectric constant ɛ = 3–4, low density d = (1.2 0.2)g/cm3 , appeared large paramagnetic properties, having main chemical content C62, O31, Mn3 wt.%, structure-open problem. In the compression probe we have noted its micro elastic-brittle state with strength 10 MPa (approximate value) and temperature stability bellow 400C. To interpret these results, phenomenological model of deuteron photo-disintegration with Oppenheimer's reaction, atomic processes of γ-ray scattering on atoms, formation of a di-nuclear system, quasi-classical approach with a two-hump ion potential, internal conversion in solids using a third charged particle, stabilization of nuclei in respect to the β-decay with occupied electronic shells, interpretation of cluster radioactivity, synthesis of elements in astrophysics and element abundance in the Universe were tested in other publications [21–29]. The induced effect in case of helium, referred to multi nuclear reactions in condensed (under high pressure) helium. This process could be considered as cold transmutation of nuclei of chemical elements phenomena, where the unusual detection of transmolecule 12C could be explained as seen in Figure 23 [30].

### 6. Conclusions

Induced effects of gamma irradiation at different energies (10 and 23 MeV) were presented in different pure elements and in more complicated systems in details, the results indicated "upstream" nuclear reactions with synthesis of heavier elements and "downstream" reactions with asymmetric fission, with the formation of both light elements from carbon to iron and heavier elements (Ag, Zr, Ba, Ta, W, Pb, Pt, Au) were formed. To interpret these results several models were used. From the authors' point of view, to achieve an accurate description of these effects it is important to elaborate on new approaches to fission and fusion nuclear reactions. Because of volume limit of the chapter, problems including how to explain "protuberation," macro mass changes, so called "Dubna Oscillation," [31] how to realize third step of Tsar bomb (using it for public welfare) author decided to publish it later.

## Acknowledgements

Many thanks to Teresa Wilczyńska-Kitowska for her close, long time and fruitful cooperation.

All experiments were carried out according to International (PL-RF) Scientific Cooperation in very efficient, friendly atmosphere, during many years of close cooperation between Polish and Russian teams (presented by Author and Alexander Yu. Didyk) and were financed by both sides.

## Author details

those experiments, inside the HeHPC there was either spectrally pure helium under different

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in

Figure 23. Creation of the stabilized transmolecule of the Carbon 12Ctr. Red point means the α particle [41, 42].

All of the three synthesized particles here are the largest objects shown in Figures 21 and 22 (see also Refs. [12, 13]), and have dielectric properties. According to the X-ray structural analysis, these articles have amorphous structures with a complex hydrocarbon composition that is absent in the reference library of the X-ray analysis. Due to its importance and for the purpose of greater reliability of the data, the structure of synthesized particles was analyzed using microscopes and X-ray micro-analyzers at two independent analytical centers. The mechanical properties of the large particles were not investigated. But there is a most intriguing problem with the electrical properties of the carbon-based structures which we obtained during all the helium experiments. The latest measurements of object shown in Figure 22 (right

having main chemical content C62, O31, Mn3 wt.%, structure-open problem. In the compression probe we have noted its micro elastic-brittle state with strength 10 MPa (approximate value) and temperature stability bellow 400C. To interpret these results, phenomenological model of deuteron photo-disintegration with Oppenheimer's reaction, atomic processes of γ-ray scattering on atoms, formation of a di-nuclear system, quasi-classical approach with a two-hump ion potential, internal conversion in solids using a third charged particle, stabilization of nuclei in respect to the β-decay with occupied electronic shells, interpretation of cluster radioactivity, synthesis of elements in astrophysics and element abundance in the Universe were tested in other publications [21–29]. The induced effect in case of helium, referred to multi nuclear reactions in condensed (under high pressure) helium. This process could be considered as cold transmutation of nuclei of chemical elements phenomena, where the unusual detection of

Induced effects of gamma irradiation at different energies (10 and 23 MeV) were presented in different pure elements and in more complicated systems in details, the results indicated

μΏm, relative dielectric

, appeared large paramagnetic properties,

pressures or a palladium rod in such helium atmosphere.

constant ɛ = 3–4, low density d = (1.2 0.2)g/cm3

upper corner) [30] have shown a very large electrical resistivity r = 105

transmolecule 12C could be explained as seen in Figure 23 [30].

6. Conclusions

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Roland Wiśniewski1,2,3\*

### References

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rays with maximum energy of 10MeV in condensed deuterium at a pressure of 2.2 kbar. Preprint P15-2018- 3. Dubna: JINR, RF, Particles and Nuclei, Letters 2018, in press. 2018.

Synthesis of Chemical Elements and Solid Structures in Atomic-Nuclear Reactions in Dense Gas-Metal Systems…

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[17] Ishkhanov BA, Kapitonov IM. Interaction of electromagnetic interaction with atomic

[18] Bethe H, Morisson P. Elementary Nuclear Theory. New York: John Willey & Sons, Inc;

[19] Mukhin KN. Experimental nuclear physics. Physics of Atomic Nucleus. Moscow:

[20] Didyk AY, Wiśniewski R. Properties of hydrogen and its isotopes under high pressure and technological applications. Dubna: JINR. 2013. pp. 320. ISBN: 978-5-9530-0358-2 [21] Sierk AJ. Mass-assimetric fission of light nuclei 1985. Macroscopic Model of Rotating

[22] Oppenheimer JR, Fillips M. Note for the transmission functions for deuteron. Physics

[24] Shilov VM. Sub-barrier fusion of spherical nuclei of medium atomic number. Nuclear

[25] Kálmán P, Keszthelyi T. Lattice effects in solid state internal conversion. Nuclear Physics.

[26] Bosch F, Faestermann T, Friese J, et al. Observation of bound-state β- decay of fully ionized 187Re: 187Re - 187Os Cosmochronometry Decay. Physical Review Letters. 1996;77(26):5190-

[27] Volkov V V, Cherepanov EA. Formation of nuclear molecules in cluster radioactivity. On interpretation of the cluster radioactivity mechanism. Physics of Particles and Nuclei

[28] Ishkhanov BS, Kapitonov IM, Tutyn IAM. LIBROKOM. 2009. http://nuclphys.sinp.msu.

[30] Mishinsky GV. Multinuclear reaction in condensed helium. Nuclear Physics. 2017;9(1):94- 105. RENSIT and Nuclear Physics, RENSIT. Atom in a strong magnetic field. Transforma-

[31] Wiśniewski R, Wilczyńska-Kitowska T, Didyk AY. Dubna oscillations phenomenon. In

[29] Bethe HA. Energy production in stars. Physics Review. 1939;55:434-456

tion of atoms into transatoms. 2017;9(2):147-160

[23] Tarakanov AV, Shilov VM, Schmidt R. Nuclear Physics. 1991;53(5):1285-1291

pp 20

1956. p. 356

nuclei. MSU. 1979:215

Energoatomiz-dat. 1983;1

Review. 1935;48(15):500-502

Physics. 2012;75(4):485-490

Letters. 2013;3(180):347-353

preparation for publication

ru/nuclsynt.html

5193

Nuclei. Physics Review. 1986:55(6):582-583

C79. 2009;031602(R):P.031602-1-031606-4

rays with maximum energy of 10MeV in condensed deuterium at a pressure of 2.2 kbar. Preprint P15-2018- 3. Dubna: JINR, RF, Particles and Nuclei, Letters 2018, in press. 2018. pp 20

[17] Ishkhanov BA, Kapitonov IM. Interaction of electromagnetic interaction with atomic nuclei. MSU. 1979:215

[5] Didyk AY, Wiśniewski R. Nuclear Reactions in deuterium-saturated palladium under irradiation by 10MeV γ quanta in dense molecular deuterium at 1.2kbar pressure.

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in

[6] Didyk AY, Wiśniewski R. Synthesis of micro particles in molecular hydrogen at 1 kbar pressure in nuclear reactions induced by braking γ rays of 10MeV threshold energy. The Chemical Composition and Structures at the Inner Surfaces of the Pressure Chamber

[7] Didyk AY, Wiśniewski R. Nuclear reactions in palladium saturated with deuterium and rhenium in dense deuterium gas under irradiation by γ quanta of continuous spectrum

[8] Didyk AY, Wiśniewski R. Results of radiation of aluminum and homogeneous alloy YMn2 by 23MeV energy γ quanta in the atmosphere of molecular deuterium at 2kbar

[9] Didyk AY, Wiśniewski R. Changes observed in the surfaces, bulk properties and chemical composition of vanadium and stainless steel specimens irradiated in dense gaseous deuterium by γ quanta of threshold energy 23 MeV. Preprint P15-2012-75, Dubna: JINR, RF,

[10] Didyk AY, Wiśniewski R. Results of radiation of complex system –Al-Y-Mn2- Al- Y-Mn2- Cu- SS by 23MeV energy γ quanta in the atmosphere of molecular deuterium at 2kbar

[11] Didyk AY, Wiśniewski R. Results of radiation of complex system Sn- Mo- Fe-Ni-Bi-Ta-Cu by 23MeV energy γ quanta in the atmosphere of molecular deuterium at 2kbar pressure.

[12] Didyk AY, Wiśniewski R, Wilczyńska-Kitowska T. The carbon-based structures synthetized through nuclear reaction in helium at 1.1kbar pressure under irradiation with braking γ rays of 10mev threshold energy. Europhysics Letters. 2015;109:22001-22006 [13] Didyk AY, Wiśniewski R. Synthesis of new structures and substances in dense gases H2, D2, and He under irradiation by braking 10MeV γ rays in Cu0.98 Be0.02 pressure chamber.

[14] Didyk AY, Wiśniewski R, Wilczyńska-Kitowska, T. Some physical properties of graphitelike object obtained by γ quanta irradiation with threshold energy of 10MeV of pure

[15] Didyk AY, Wiśniewski R. Synthesis of micro particles in molecular hydrogen at 1kbar pressure in nuclear reactions induced by braking γ rays of 10MeV threshold energy. The chemical composition and structures at the inner surfaces of the pressure chamber com-

[16] Didyk AY, Wiśniewski R, Myshinsky GW, Semin WA, Wilczyńska-Kitowska T. Synthesis of solid-state structures and chemical elements under irradiation by bremsstrahlung γ

ponents. P15-2014 – 2, pp. 40. Particles and Nuclei, Letters. 2015;12(7):1298-1317

gaseous he under pressure, in CuBe2 apparatus. JPSA. 2016;6(6):1-11

with boundary 23MeV energy. Preprint R15-2012-63, Dubna: JINR, 2012. pp. 21

Components. Preprint P15-2014-2, Dubna: JINR, RF, 2014. pp 41

pressure. Preprint P15-2013-41, Dubna, JINR, RF, 2013. pp 18

pressure. Preprint P15-2013-41, Dubna: JINR, RF, 2013. pp 19

Europhysics Letters. 2013;103:42002-42008

2012. pp 14

the Environment

72

To be published

JPSA. 2016;6(4):13-21

**Section 3**

**Nuclear Thermal Hydraulics**

## **Nuclear Thermal Hydraulics**

**Chapter 4**

**Provisional chapter**

**Dense Granular Flow as Heat Transfer Media: A New**

**Dense Granular Flow as Heat Transfer Media: A New**

High power target systems require reliable high-temperature heat transfer media. Dense granular flow materials have potential to work as heat transfer media, especially at high temperature. In this chapter, a brief review of dense granular and their heat transfer properties is introduced, including basic concepts of heat transfer, thermal behavior of these materials, and factors that affect this behavior. The implementation of these materials as targets is addressed, where two targets were designed, constructed, and tested based on the concept of dense granular flow. The results of the application of a hopper flow-type target in 2.5 MW accelerator-driven system (ADS) and a chute flow-type target

In nuclear area, an accelerator is always helpful to generate particles uncommon or indiscrete in the natural world. Target materials are exposed to certain projectiles; as a result, secondary

For most cases, the higher particle flux outcome is more helpful. To achieve this, the target systems are designed to stand high beam intensity. Most of beam power deposits in the target material. The kinetic energy of the beam converts into internal energy and increase the temperature of target. This process also leads to radiation damage of target material and even

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

DOI: 10.5772/intechopen.77276

**Type of High Power Target Design**

**Type of High Power Target Design**

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

in the material irradiation facility will be presented.

**Keywords:** dense granular flow, high power target, prototype facility

particles in the form of neutrons, photons, neutrino, and so on are generated.

Xuezhi Zhang and Lei Yang

Xuezhi Zhang and Lei Yang

**Abstract**

**1. Introduction**

target failure.

http://dx.doi.org/10.5772/intechopen.77276

### **Dense Granular Flow as Heat Transfer Media: A New Type of High Power Target Design Dense Granular Flow as Heat Transfer Media: A New Type of High Power Target Design**

DOI: 10.5772/intechopen.77276

Xuezhi Zhang and Lei Yang Xuezhi Zhang and Lei Yang

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.77276

### **Abstract**

High power target systems require reliable high-temperature heat transfer media. Dense granular flow materials have potential to work as heat transfer media, especially at high temperature. In this chapter, a brief review of dense granular and their heat transfer properties is introduced, including basic concepts of heat transfer, thermal behavior of these materials, and factors that affect this behavior. The implementation of these materials as targets is addressed, where two targets were designed, constructed, and tested based on the concept of dense granular flow. The results of the application of a hopper flow-type target in 2.5 MW accelerator-driven system (ADS) and a chute flow-type target in the material irradiation facility will be presented.

**Keywords:** dense granular flow, high power target, prototype facility

### **1. Introduction**

In nuclear area, an accelerator is always helpful to generate particles uncommon or indiscrete in the natural world. Target materials are exposed to certain projectiles; as a result, secondary particles in the form of neutrons, photons, neutrino, and so on are generated.

For most cases, the higher particle flux outcome is more helpful. To achieve this, the target systems are designed to stand high beam intensity. Most of beam power deposits in the target material. The kinetic energy of the beam converts into internal energy and increase the temperature of target. This process also leads to radiation damage of target material and even target failure.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Lots of effort has been made to achieve high power target. But not until the 1990s, a specific megawatt target never came up. As examples, Weapons Neutron Research project in Los Alamos Neutron Science Center achieved 70 kW target with tungsten material, while Rutherford Appleton Laboratory reached 160 kW using 800 MeV protons and tungsten with tantalum cladding [1].

heat from one surface to another through void following the Stephan-Boltzmann law, which indicates the radiation heat transfer rate is proportional to the cubic of temperature. Hence, if radiation happens effectively in the media, heat transfer can be more efficient at high

Dense Granular Flow as Heat Transfer Media: A New Type of High Power Target Design

http://dx.doi.org/10.5772/intechopen.77276

79

At high temperature, thermodynamics principles allow fluid's thermal energy transfers more efficiently. But most practical heat transfer media failed under such temperature: Liquid water transforms to supercritical state over 385°C [7, 8]; steam reacts with common structural materials over 900°C [9], and about one-third of the zircaloy in the core create a sizable hydrogen bubble from the Zr-steam interactions [10]; liquid sodium or lithium, Na-K alloy, and mercury are all vaporized under 900°C; lead-bismuth eutectic, liquid lead's corrosion-erosion effect grows significant at 480–550°C [11, 12]. What's more, for nuclear usage, liquid metal loop needs multiple conditioning systems, which makes the system complicated and expensive, such as International Fusion Materials Irradiation Facility (IFMIF) [13] and eXperimental Accelerator-Driven System (XT-ADS) device [14]. Gases seem to be another good choice, which has been testified in high-temperature gas-cooled reactors. But they have to be pressur-

Granular material is a promising solution. Granular material is composed of discrete solid particles and gaseous environment where the particles immerse. Such material has been used for heating since ancient Rome by Lucretius [16]. Modern research can be trace back to Maxwell's era and got broad attentions in the twentieth century due to popularization of bed reactors [17]. Nowadays, granular heat exchanger has been widely used in many industrial areas. They perform effective heating or cooling in so many industrial processes that indicate granular materials are realistic to be a promising heat transfer media. Packed bed and powder jet solution had been came up by research groups to solve the high power density removal issues of target [18, 19]. Pebble bed fusion reactors and fission first wall breeding layers also adopt granular material using the unique advantages in the high-temperature heat transfer [20–23]. Flow of granular state enhances heat transport process, leading to better heat transfer performance and more realistic feasibility, especially for extreme internal heat source such as

Its potential of heat transfer usage stems from flowability and thermal properties, which has been widely studied and practiced. The flowability allows granular materials to convey long distance by multiple methods. But granular materials' flowability is quite different from fluids'. Although granular dynamics uses many hydrodynamics concepts, granular dynamics behaves quite different from fluid. Some of granular materials' unique properties are critically

When granular materials flow out from a vessel under the action of gravity, the mass flow rate M is approximately independent of the head of material head H, just as an hourglass does. The most important research of this phenomenon was successively recorded by Beverloo et al., Aldin and Gunn, and Nedderman [24–28]. This phenomenon requires that the granular material must be not too smooth and small, while the bulk has a height not less than twice

orifice diameter. A quantitative result of this flow gives a relationship of [28].

temperature.

ized due to their low volume heat capacity [15].

spallation reaction, compared to present solutions.

helpful to be heat transfer media.

**2.2. Characteristic of granular flow**

As mentioned above, cooling is essential to the high power target. Conventional cooling channels take too much space inside the target body and gradually get close to the limit. The MarkIII target of Swiss Spallation Neutron Source project in Paul Scherrer Institute (PSI) reaches 1.2 MW beam power based on such concept. Some projects adopt rotating target to even and lower the power density within the target body, such as European Spallation Source and China Spallation Neutron Source [1–4].

For solid target, radiation material damage also causes swelling and creep, which might damage the cooling channel and cause cooling deterioration, as the displacement per atom (DPA) increases. One way to bypass the damage is using liquid metal as target material. Meanwhile, the flow of liquid metal removes the power deposit and dumps the heat in the heat exchanger. These properties make liquid metal target a promising solution of high power target. In PSI, MEGAwatt PIlot Experiment (MEGAPIE) achieved 0.8 MW with lead bismuth eutectic (LBE). Spallation Neutron Source in US and Japan Spallation Neutron Source also achieved 1.4 and 1 MW beam power with mercury [1].

Here we are going to present a third option of target cooling, which is based on the dense granular flow [5]. Granular system makes solid materials flow like fluid and perform heat removing. Meanwhile, the candidate target materials are more various, which give better feasibility depending on the purpose of the facility.

## **2. Heat transfer media and heat transfer in granular material**

### **2.1. Conventional heat transfer media**

The continuous research of the thermal properties of materials is explained both by practical needs and fundamental science. Heat removal is always a crucial issue for energy conversion in the energy industry owing to increased levels of power requirement and energy efficiency. The search for materials that transfer heat well under high temperature and energy flux has covered all the industry area and never ends, and it is especially essential for design of the next generation of reactors and neutron facilities.

A medium's transfer heat ability follows three basic heat transfer ways, conduction, radiation, and convection. Conduction dominates solids' heat transfer behavior, while convection makes fluids absorb heat from a source and dump heat to a sink very efficiently. In field of nuclear energy, water is still the most important heat transfer material for cost and reliability reasons, while liquid metal such as sodium and gases such as helium take the rest portion. These fluid heat transfer media are capable of removing 102 –105 W/m2 K from surface of power component and reaching up to the order of ~106 W/m2 K while boiling [6]. At high temperature, some particular situations differ because of radiation. Radiation transfers heat from one surface to another through void following the Stephan-Boltzmann law, which indicates the radiation heat transfer rate is proportional to the cubic of temperature. Hence, if radiation happens effectively in the media, heat transfer can be more efficient at high temperature.

At high temperature, thermodynamics principles allow fluid's thermal energy transfers more efficiently. But most practical heat transfer media failed under such temperature: Liquid water transforms to supercritical state over 385°C [7, 8]; steam reacts with common structural materials over 900°C [9], and about one-third of the zircaloy in the core create a sizable hydrogen bubble from the Zr-steam interactions [10]; liquid sodium or lithium, Na-K alloy, and mercury are all vaporized under 900°C; lead-bismuth eutectic, liquid lead's corrosion-erosion effect grows significant at 480–550°C [11, 12]. What's more, for nuclear usage, liquid metal loop needs multiple conditioning systems, which makes the system complicated and expensive, such as International Fusion Materials Irradiation Facility (IFMIF) [13] and eXperimental Accelerator-Driven System (XT-ADS) device [14]. Gases seem to be another good choice, which has been testified in high-temperature gas-cooled reactors. But they have to be pressurized due to their low volume heat capacity [15].

### **2.2. Characteristic of granular flow**

Lots of effort has been made to achieve high power target. But not until the 1990s, a specific megawatt target never came up. As examples, Weapons Neutron Research project in Los Alamos Neutron Science Center achieved 70 kW target with tungsten material, while Rutherford Appleton Laboratory reached 160 kW using 800 MeV protons and tungsten with

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in

As mentioned above, cooling is essential to the high power target. Conventional cooling channels take too much space inside the target body and gradually get close to the limit. The MarkIII target of Swiss Spallation Neutron Source project in Paul Scherrer Institute (PSI) reaches 1.2 MW beam power based on such concept. Some projects adopt rotating target to even and lower the power density within the target body, such as European Spallation Source

For solid target, radiation material damage also causes swelling and creep, which might damage the cooling channel and cause cooling deterioration, as the displacement per atom (DPA) increases. One way to bypass the damage is using liquid metal as target material. Meanwhile, the flow of liquid metal removes the power deposit and dumps the heat in the heat exchanger. These properties make liquid metal target a promising solution of high power target. In PSI, MEGAwatt PIlot Experiment (MEGAPIE) achieved 0.8 MW with lead bismuth eutectic (LBE). Spallation Neutron Source in US and Japan Spallation Neutron Source also achieved 1.4 and

Here we are going to present a third option of target cooling, which is based on the dense granular flow [5]. Granular system makes solid materials flow like fluid and perform heat removing. Meanwhile, the candidate target materials are more various, which give better fea-

The continuous research of the thermal properties of materials is explained both by practical needs and fundamental science. Heat removal is always a crucial issue for energy conversion in the energy industry owing to increased levels of power requirement and energy efficiency. The search for materials that transfer heat well under high temperature and energy flux has covered all the industry area and never ends, and it is especially essential for design of the

A medium's transfer heat ability follows three basic heat transfer ways, conduction, radiation, and convection. Conduction dominates solids' heat transfer behavior, while convection makes fluids absorb heat from a source and dump heat to a sink very efficiently. In field of nuclear energy, water is still the most important heat transfer material for cost and reliability reasons, while liquid metal such as sodium and gases such as helium take the rest

high temperature, some particular situations differ because of radiation. Radiation transfers

–105

W/m2

W/m2

K while boiling [6]. At

K from sur-

**2. Heat transfer media and heat transfer in granular material**

portion. These fluid heat transfer media are capable of removing 102

face of power component and reaching up to the order of ~106

tantalum cladding [1].

the Environment

78

and China Spallation Neutron Source [1–4].

1 MW beam power with mercury [1].

**2.1. Conventional heat transfer media**

sibility depending on the purpose of the facility.

next generation of reactors and neutron facilities.

Granular material is a promising solution. Granular material is composed of discrete solid particles and gaseous environment where the particles immerse. Such material has been used for heating since ancient Rome by Lucretius [16]. Modern research can be trace back to Maxwell's era and got broad attentions in the twentieth century due to popularization of bed reactors [17]. Nowadays, granular heat exchanger has been widely used in many industrial areas. They perform effective heating or cooling in so many industrial processes that indicate granular materials are realistic to be a promising heat transfer media. Packed bed and powder jet solution had been came up by research groups to solve the high power density removal issues of target [18, 19]. Pebble bed fusion reactors and fission first wall breeding layers also adopt granular material using the unique advantages in the high-temperature heat transfer [20–23]. Flow of granular state enhances heat transport process, leading to better heat transfer performance and more realistic feasibility, especially for extreme internal heat source such as spallation reaction, compared to present solutions.

Its potential of heat transfer usage stems from flowability and thermal properties, which has been widely studied and practiced. The flowability allows granular materials to convey long distance by multiple methods. But granular materials' flowability is quite different from fluids'. Although granular dynamics uses many hydrodynamics concepts, granular dynamics behaves quite different from fluid. Some of granular materials' unique properties are critically helpful to be heat transfer media.

When granular materials flow out from a vessel under the action of gravity, the mass flow rate M is approximately independent of the head of material head H, just as an hourglass does. The most important research of this phenomenon was successively recorded by Beverloo et al., Aldin and Gunn, and Nedderman [24–28]. This phenomenon requires that the granular material must be not too smooth and small, while the bulk has a height not less than twice orifice diameter. A quantitative result of this flow gives a relationship of [28].

$$
\dot{m} = 0.58 \,\rho\_s \sqrt{g} \left( D - 1.4 \, d\_\rho \right)^{2.5} F(\theta\_{\omega'} \beta) \tag{1}
$$

As Yagi and Kunii reviewed, heat transfer in granular media happens in all three ways and their coupled effects [38]. Most concerned mechanisms of heat transfer in granular

Dense Granular Flow as Heat Transfer Media: A New Type of High Power Target Design

http://dx.doi.org/10.5772/intechopen.77276

The first stage was observed by several early researchers, depicted as a sharp temperature drop at the wall [36, 39, 40]. In this stage, the maximum heat transfer is at the order of ~103

In vacuum, the solid dominates the heat transfer rate, proved by the coefficient of bronze and glass, which are 30 and 5 W/m2 K, respectively. This result agrees well with the contact heat transfer analysis, and we will discuss this effect in the effective thermal conductivity of granular material in later section. In contrast, the gas phase decides the heat transfer in atmosphere,

almost 1 [42–45], which means only little solid contact at the wall leads to a minor heat trans-

Although most researches did not evaluate the specific limit of heat transfer rate, they did observe effect of various factors. Most of them have relationship with the second stage.

K [35, 41]. It is believed that the porosity near the wall reaches

K for granules' diameter at the order of millimeter in air. Such order is determined by different researchers and methods [39, 41]. When the pressure drops to 0.1 Pa, the wall heat transfer coefficient decreases to the order of ~10 W/m2 K. Most significant heat transfer coefficient drop happens when pressure changes from ~1 kPa to 1 Pa, leading to the change of one

W/

81

media are listed in **Table 1**.

m2

and a half order.

reaching the order of ~103

W/m2

fer mechanism only significant in vacuum.

**Table 1.** Mechanism of heat transfer in granular media.

where m, ρs , D, dp, θ, and β represent mass flow rate, particle material density, orifice diameter, particle diameter, wall angle, and an angle related to friction of the material [29]. This result implies the flow rate could be controlled by local valve.

As the immerging depth increase, the normal pressure of most fluids increases linearly and is proportional to the depth. But the normal pressure of granular system gradually reaches a constant. Different from fluids, inside the granular system and between the granules and the container walls, friction exists. The upward friction force exerted by the wall neutralizes the weight of grains. An important quantitative explanation given by Janssen is in accord with the experimental stress result [30].

Other granular properties also have special effects, which stem from the friction, dissipation, and size effect of granules. These effects lead to phenomenons in granular flow, such as the jamming and dilatancy properties prevent flow channel collapse [31]; while dissipation property prevents long-range disturbance propagation [32].

### **2.3. Thermal properties of granular flow**

Granular materials' thermal properties are decided by the components which make the effective properties vary largely. As high-temperature heat transfer media, high-melting-point metal alloy, ceramics, and other materials with good heat conductivity can be the solid particle candidate. There are relatively few gases performing heat transfer effectively, among which helium is representative. The large number of material combination makes granular media satisfy varieties of actual needs. For instance, the heat transfer media in traditional nuclear reactor need to minimize the neutron absorption and maximize the neutron moderation, while the heat transfer media had better to be the spallation material in a spallation target which needs high spallation neutron production.

Some effective thermophysical properties such as critical temperature, density, and specific heat can be estimated using simple calculations based on the properties of the initial components. But quantities such as heat transfer coefficient and effective heat conductivity are far more complicated than those. The following subsections will review critical thermal properties to get a better view of granular heat transfer media's potential.

The mainstream viewpoint of heat transfer between granular material and a panel has two stages: heat transfers from the wall surface to the first granular layer next to the wall, and heat diffuses from the first layer to the inside of granular material [33–36]. Sullivan and Sabersky [36] adopted concepts of fluid heat transfer such as Peclet and Nusselt number dealing with this process. An analytical result of temperature distribution can be derived from principles of heat transfer. This work was further extended by Spelt et al. [36, 37].

### *2.3.1. Mechanisms*

For both two stages, whatever discrete model or continuous model is applied, one should realize that the structure of granular material leads to more heat transfer mechanisms. As Yagi and Kunii reviewed, heat transfer in granular media happens in all three ways and their coupled effects [38]. Most concerned mechanisms of heat transfer in granular media are listed in **Table 1**.

*m*̇ = 0.58 *ρs* √

the experimental stress result [30].

**2.3. Thermal properties of granular flow**

result implies the flow rate could be controlled by local valve.

erty prevents long-range disturbance propagation [32].

target which needs high spallation neutron production.

ties to get a better view of granular heat transfer media's potential.

of heat transfer. This work was further extended by Spelt et al. [36, 37].

where m, ρs

the Environment

80

*2.3.1. Mechanisms*

\_\_

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in

*g* (*D* − 1.4 *dp*)

eter, particle diameter, wall angle, and an angle related to friction of the material [29]. This

As the immerging depth increase, the normal pressure of most fluids increases linearly and is proportional to the depth. But the normal pressure of granular system gradually reaches a constant. Different from fluids, inside the granular system and between the granules and the container walls, friction exists. The upward friction force exerted by the wall neutralizes the weight of grains. An important quantitative explanation given by Janssen is in accord with

Other granular properties also have special effects, which stem from the friction, dissipation, and size effect of granules. These effects lead to phenomenons in granular flow, such as the jamming and dilatancy properties prevent flow channel collapse [31]; while dissipation prop-

Granular materials' thermal properties are decided by the components which make the effective properties vary largely. As high-temperature heat transfer media, high-melting-point metal alloy, ceramics, and other materials with good heat conductivity can be the solid particle candidate. There are relatively few gases performing heat transfer effectively, among which helium is representative. The large number of material combination makes granular media satisfy varieties of actual needs. For instance, the heat transfer media in traditional nuclear reactor need to minimize the neutron absorption and maximize the neutron moderation, while the heat transfer media had better to be the spallation material in a spallation

Some effective thermophysical properties such as critical temperature, density, and specific heat can be estimated using simple calculations based on the properties of the initial components. But quantities such as heat transfer coefficient and effective heat conductivity are far more complicated than those. The following subsections will review critical thermal proper-

The mainstream viewpoint of heat transfer between granular material and a panel has two stages: heat transfers from the wall surface to the first granular layer next to the wall, and heat diffuses from the first layer to the inside of granular material [33–36]. Sullivan and Sabersky [36] adopted concepts of fluid heat transfer such as Peclet and Nusselt number dealing with this process. An analytical result of temperature distribution can be derived from principles

For both two stages, whatever discrete model or continuous model is applied, one should realize that the structure of granular material leads to more heat transfer mechanisms.

, D, dp, θ, and β represent mass flow rate, particle material density, orifice diam-

2.5 *F*(*θω*, *β*) (1)

The first stage was observed by several early researchers, depicted as a sharp temperature drop at the wall [36, 39, 40]. In this stage, the maximum heat transfer is at the order of ~103 W/ m2 K for granules' diameter at the order of millimeter in air. Such order is determined by different researchers and methods [39, 41]. When the pressure drops to 0.1 Pa, the wall heat transfer coefficient decreases to the order of ~10 W/m2 K. Most significant heat transfer coefficient drop happens when pressure changes from ~1 kPa to 1 Pa, leading to the change of one and a half order.

In vacuum, the solid dominates the heat transfer rate, proved by the coefficient of bronze and glass, which are 30 and 5 W/m2 K, respectively. This result agrees well with the contact heat transfer analysis, and we will discuss this effect in the effective thermal conductivity of granular material in later section. In contrast, the gas phase decides the heat transfer in atmosphere, reaching the order of ~103 W/m2 K [35, 41]. It is believed that the porosity near the wall reaches almost 1 [42–45], which means only little solid contact at the wall leads to a minor heat transfer mechanism only significant in vacuum.

Although most researches did not evaluate the specific limit of heat transfer rate, they did observe effect of various factors. Most of them have relationship with the second stage.

**Table 1.** Mechanism of heat transfer in granular media.

In this stage the heat transport can be considered as heat diffusion in a continuous media with effective properties of granular material. The complexity of heat transfer mechanism makes multiple parameters dependence.

### *2.3.2. Effect of material constituent*

Granular material component combination is the most principle factor of heat transfer properties. In the past century, a number of various granules' heat transfer properties have been studied. A collection of experimental data is shown in **Table 2**. It shows gas phase plays a decisive role in granular materials' heat transfer property, while the solid particle geometry plays a role as important as its inherent properties. Large surface-volume ratio makes the temperature of fluid and solid phase nearly uniform [46, 47].

In energy area, most heat transfer is performed under pressure. Pressurization enhanced heat transfer in two aspects: increase boiling temperature and volume heat capacity. Highmelting-point solid granules need none of these improvements and hence may significantly reduce engineering difficulty, risk and cost. The pressure concept in granular system also has two aspects: the gas pressure and particle compress pressure.

Early stage of ETC of granular material focuses on experimental determination. Back to 1926, Aberdeen and Laby studied effective thermal conductivity (ETC) of monox powder when immersed in air, in carbon dioxide, and in hydrogen at various pressures has been determined. They found a linear relation between the conductivity of the powder and the logarithm of the pressure of the gas in which it is immersed. The result fits in

$$k = \frac{k\_\gamma}{2} \log\_{10} \frac{p}{W} \tag{2}$$

the effect of radiation [38]. As Botterill published in 1989, the radiation is proportional to T3

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**Table 2.** Some experimental result of effective heat transfer coefficient (ETC) [39, 49, 50].

σ, and the character length represented by Dp; hence a radiation term of ETC falls in the

form of

,

where k is effective heat transfer coefficient and kf is fluid heat transfer coefficient and *n* is a constant for each specific gas [48].

### *2.3.3. Effect of temperature*

Microscope heat transfer mechanism decides most condensed matters' thermal conductivity deteriorates as temperature increases while gases are contrary. In a granular material, solid phase has more significant heat conductivity than gas phase. On the other hand, the packed solid particle structure is point contact for most cases; hence, the gas voids play an important role in the effective heat conduct which increases as temperature rises. Radiation also significantly improves effective heat conductivity of granular material under high temperature. Solid surfaces and voids allow radiation to perform efficient heat transfer, while such mechanism does not exist in bulk solid or pure gas.

Yagi and Kunii [38] determined ETC for several materials, in the temperature range of 100–800°C. The result shows an accelerated increase of ETC as the temperature increases. Most materials' ETC doubled or tripled for the test range. They proposed a model considering

In this stage the heat transport can be considered as heat diffusion in a continuous media with effective properties of granular material. The complexity of heat transfer mechanism

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in

Granular material component combination is the most principle factor of heat transfer properties. In the past century, a number of various granules' heat transfer properties have been studied. A collection of experimental data is shown in **Table 2**. It shows gas phase plays a decisive role in granular materials' heat transfer property, while the solid particle geometry plays a role as important as its inherent properties. Large surface-volume ratio makes the

In energy area, most heat transfer is performed under pressure. Pressurization enhanced heat transfer in two aspects: increase boiling temperature and volume heat capacity. Highmelting-point solid granules need none of these improvements and hence may significantly reduce engineering difficulty, risk and cost. The pressure concept in granular system also has

Early stage of ETC of granular material focuses on experimental determination. Back to 1926, Aberdeen and Laby studied effective thermal conductivity (ETC) of monox powder when immersed in air, in carbon dioxide, and in hydrogen at various pressures has been determined. They found a linear relation between the conductivity of the powder and the loga-

> 2 log10 *p*\_\_

Microscope heat transfer mechanism decides most condensed matters' thermal conductivity deteriorates as temperature increases while gases are contrary. In a granular material, solid phase has more significant heat conductivity than gas phase. On the other hand, the packed solid particle structure is point contact for most cases; hence, the gas voids play an important role in the effective heat conduct which increases as temperature rises. Radiation also significantly improves effective heat conductivity of granular material under high temperature. Solid surfaces and voids allow radiation to perform efficient heat transfer, while such mecha-

Yagi and Kunii [38] determined ETC for several materials, in the temperature range of 100–800°C. The result shows an accelerated increase of ETC as the temperature increases. Most materials' ETC doubled or tripled for the test range. They proposed a model considering

*n* (2)

is fluid heat transfer coefficient and *n* is a

makes multiple parameters dependence.

temperature of fluid and solid phase nearly uniform [46, 47].

two aspects: the gas pressure and particle compress pressure.

*k* = *kf* \_\_

nism does not exist in bulk solid or pure gas.

constant for each specific gas [48].

*2.3.3. Effect of temperature*

where k is effective heat transfer coefficient and kf

rithm of the pressure of the gas in which it is immersed. The result fits in

*2.3.2. Effect of material constituent*

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**Table 2.** Some experimental result of effective heat transfer coefficient (ETC) [39, 49, 50].

the effect of radiation [38]. As Botterill published in 1989, the radiation is proportional to T3 , σ, and the character length represented by Dp; hence a radiation term of ETC falls in the form of

$$k\_r = 4\sigma \chi D\_p T^3 \tag{3}$$

in which *β* = *l*

*k* = *kf*

*p* /*Dp* , *γ* = *l s* /*Dp* , = *l v* /*Dp*

Zehner and Schlunder's model:

\_\_\_\_ 1 − *ε*)

(1 + *k* \_\_*r kf*) + *kf* √

tact term which applies for various material properties.

(1 − 1 √

*2.3.6. Total heat transfer coefficient*

heat resistance as follows [35]:

averaged value:

theory is given by

\_\_1

*α* = \_\_1

*αETC* = 2 √

*α* = *αw*

The total heat transfer depends on time, hence given by.

\_\_\_\_\_ 1 1 + √ \_\_ \_\_*π* 2 √ \_\_ *τ*

. hrs, hrv, lp, ls

tion and shows the particle size effect. The result fits temperature effect well [38].

⎧ ⎪ ⎨ ⎪ ⎩

\_\_\_\_\_ 2 1 − *kf* \_\_ *ks B*

⎡

(1 − *kf* \_\_ *ks* )*B* \_\_\_\_\_\_\_\_

2 ⋅ ln *k*\_\_\_*s kf B* − \_\_\_ *B* + 1

Dense Granular Flow as Heat Transfer Media: A New Type of High Power Target Design

(1 − *kf* \_\_ *ks B*)

⎢ ⎣

in which B is a deformation factor. This model represents a significant improvement of con-

Schlunder gave explanation of the combination of wall heat transfer and ETC as a serial of

Because the heat diffusive process inside the granules varies as time changes, total heat transfer coefficient also depends on time. Most measured total heat transfer coefficient is time

> *t* ∫ 0 *t*

In three situations, (1) t goes to 0, (2) bed heat capacity is infinity, and (3) the bed is under perfect mixing, αETC reaches a maximum and hence derives the maximum heat transfer coefficient, i.e., the wall heat transfer coefficient. A typical time dependence of αETC based on Fourier

> \_\_\_\_\_\_\_ (*ck*) \_\_\_\_\_\_\_*bed* √ \_\_\_

, where *τ* = *αw*

Through the experiments of various components' combination, Ernst showed α decreases as time increases, which is less significant for lower pressure and larger granules [39]. Such

2 \_\_\_\_\_\_ (*ck*)*bed*

*α* = \_\_\_1 *αw* + \_\_\_\_ 1 *αETC*

\_\_\_\_ 1 − *ε* , and lv

ficient of solid to solid, void to void, effective length of centers, thermal conduction, and fluid film at the contact point. They considered effect of fluid flow using Ranz fluid mixing equa-

represent radiation heat transfer coef-

http://dx.doi.org/10.5772/intechopen.77276

2 − \_\_\_\_\_ *B* − 1 1 − *kf* \_\_ *ks B*

*at d t*′ (8)

*t* (9)

*t* (10)

⎤

⎥ ⎦ + \_\_\_\_ 1 *kf* \_\_ *kr* + *kf* \_\_ *ks*

⎫ ⎪ ⎬ ⎪ ⎭

(6)

85

(7)

where σ is Stefan-Boltzmann coefficient and χ is coefficient depending on the specific model. A comparative research of various radiation models and experimental results was also given by Botterill [49].

In a word, unlike traditional heat transfer material, granular material could perform better under high temperature; as previous study of gas cooling reactor, heat conductivity of graphite pebble bed exceeds pure graphite for temperature higher than 1400°C [2]. Further experimental results were reported in [38, 49, 50].

### *2.3.4. Effect of gas motion*

As is well known, forced convection enhanced heat transfer properties. Packed bed is motionless granules with gas flows through. Researches of these systems explain the motion effect of gas phase, which also implies the same effect in granular flow.

Bunnell et al. studied a wall-heated packed bed with different superficial gas velocity, measured the inner temperature distribution, and calculated ETC through these results. They found effective thermal conductivity dependence on mass velocity of the gas, and the gas phase and solid phase temperatures are nearly uniform [51].

Solid particle motion enhanced cold and hot particles mixing, hence increasing the heat transfer rate. A lot of research about packed bed also showed that only fluid flow rate increase also leads to enhancement of ETC [46, 50, 52–55].

### *2.3.5. Models of ETC*

To get a quick evaluation of granular materials, researchers had come up with various models, from simple to complex. Three most important models are as follows:

Maxwell (1881):

$$k = k\_s \left[ \frac{2\varepsilon \left| k\_s + (3 - 2\varepsilon) \right| k\_s}{\left( 3 - \varepsilon \right) k\_s + \varepsilon \left| k\_s \right|} \right] \tag{4}$$

This model is probably the earliest method for granular ETC evaluation. It represents a series model that considers the system as a parallel-serial thermal resistance system [53] which got its popularity in the early age.

Yagi and Kunii [38]:

$$k = k\_s \frac{\rho\_l \rho\_v}{\rho\_s \left(\frac{k\_s}{k\_s}\right) + \frac{1}{\frac{1}{\Psi} + \left(D\_p h\_v/k\_s\right)}} + \varepsilon \beta D\_p h\_{rv}/k\_s\tag{5}$$

in which *β* = *l p* /*Dp* , *γ* = *l s* /*Dp* , = *l v* /*Dp* . hrs, hrv, lp, ls , and lv represent radiation heat transfer coefficient of solid to solid, void to void, effective length of centers, thermal conduction, and fluid film at the contact point. They considered effect of fluid flow using Ranz fluid mixing equation and shows the particle size effect. The result fits temperature effect well [38].

Zehner and Schlunder's model:

*kr* = 4 *Dp T*3 (3)

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in

where σ is Stefan-Boltzmann coefficient and χ is coefficient depending on the specific model. A comparative research of various radiation models and experimental results was also given

In a word, unlike traditional heat transfer material, granular material could perform better under high temperature; as previous study of gas cooling reactor, heat conductivity of graphite pebble bed exceeds pure graphite for temperature higher than 1400°C [2]. Further experi-

As is well known, forced convection enhanced heat transfer properties. Packed bed is motionless granules with gas flows through. Researches of these systems explain the motion effect of

Bunnell et al. studied a wall-heated packed bed with different superficial gas velocity, measured the inner temperature distribution, and calculated ETC through these results. They found effective thermal conductivity dependence on mass velocity of the gas, and the gas

Solid particle motion enhanced cold and hot particles mixing, hence increasing the heat transfer rate. A lot of research about packed bed also showed that only fluid flow rate increase also

To get a quick evaluation of granular materials, researchers had come up with various mod-

2*ε kg* + (3 − 2*ε*) *k* \_\_\_\_\_\_\_\_\_\_\_*s*

This model is probably the earliest method for granular ETC evaluation. It represents a series model that considers the system as a parallel-serial thermal resistance system [53] which got

*β*(1 − *ε*) \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

) + \_\_\_\_\_\_\_\_\_\_ 1 \_\_1 + (*Dp hrs*/*kg*) + *Dp hrv* /*kg*

)

(5)

(3 − *ε*) *kg* + *ε ks* ] (4)

els, from simple to complex. Three most important models are as follows:

(

*γ*( *kg* \_\_ *ks*

by Botterill [49].

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84

*2.3.4. Effect of gas motion*

*2.3.5. Models of ETC*

Maxwell (1881):

mental results were reported in [38, 49, 50].

leads to enhancement of ETC [46, 50, 52–55].

*k* = *kg*[

its popularity in the early age.

*k* = *kg*

Yagi and Kunii [38]:

gas phase, which also implies the same effect in granular flow.

phase and solid phase temperatures are nearly uniform [51].

$$k = k\_{\uparrow}^{\prime}(1 - 1\sqrt{1 - \varepsilon})\left(1 + \frac{k\_{\uparrow}}{k\_{\uparrow}}\right) + k\_{\uparrow}\sqrt{1 - \varepsilon} \left\{ \frac{2}{1 - \frac{k\_{\uparrow}}{k\_{\downarrow}}B} \left[ \frac{\left(1 - \frac{k\_{\uparrow}}{k\_{\downarrow}}\right)B}{\left(1 - \frac{k\_{\uparrow}}{k\_{\downarrow}}B\right)}, \cdot \ln\frac{k\_{\downarrow}}{k\_{\uparrow}B} - \frac{B + 1}{2} - \frac{B - 1}{1 - \frac{k\_{\uparrow}}{k\_{\downarrow}}B} \right] + \frac{1}{\frac{k\_{\uparrow}}{k\_{\downarrow}} + \frac{k\_{\uparrow}}{k\_{\downarrow}}} \right\} \tag{6}$$

in which B is a deformation factor. This model represents a significant improvement of contact term which applies for various material properties.

### *2.3.6. Total heat transfer coefficient*

Schlunder gave explanation of the combination of wall heat transfer and ETC as a serial of heat resistance as follows [35]:

$$\frac{1}{a} = \frac{1}{a\_v} + \frac{1}{a\_{\rm rrc}} \tag{7}$$

Because the heat diffusive process inside the granules varies as time changes, total heat transfer coefficient also depends on time. Most measured total heat transfer coefficient is time averaged value:

$$
\alpha = \frac{1}{t} \int\_0^t a\_i \, dt'\tag{8}
$$

In three situations, (1) t goes to 0, (2) bed heat capacity is infinity, and (3) the bed is under perfect mixing, αETC reaches a maximum and hence derives the maximum heat transfer coefficient, i.e., the wall heat transfer coefficient. A typical time dependence of αETC based on Fourier theory is given by

$$\alpha\_{ETC} = \frac{2\sqrt{(\rho ck)\_{val}}}{\sqrt{\pi t}} \tag{9}$$

The total heat transfer depends on time, hence given by.

$$a = a\_w \frac{1}{1 + \frac{\sqrt{\pi}}{2} \sqrt{\tau}} \quad \text{where} \quad \tau = \frac{a\_v^2}{\left(\rho ck\right)\_{bd}} t \tag{10}$$

Through the experiments of various components' combination, Ernst showed α decreases as time increases, which is less significant for lower pressure and larger granules [39]. Such

time-dependent phenomenon has been observed by other researches [36, 56]. The total heat transfer coefficient fell in the range of 50–200 W/m2 ·K which is also a typical range of most facility situation [57].

## **3. Implementation of granular flow target**

With the concept of dense granular flow cooling, the target can be designed according to different demands. Two different types of granular flow target have been developed for China Initiative Accelerator-Driven System (CIADS) project and China material irradiation facility project. For both designs helium was selected as the cover gas, concerning its high thermal conductivity and safety. In principle, pressure was set lower than 1 atm to prevent leakage and help target-beam line coupling. For each case, gas pressure was variable parameter. The difference of the two targets includes structure, target material, beam energy, spectrum, and so on.

By the end of 2017, two prototype facilities were constructed and tested with electrical heating, up to about 300°C. The beam coupling experiments are planned to be performed later, depending on the progress of radiation shielding hall.

**Figure 1.** Schematic diagram of CIADS.

Dense Granular Flow as Heat Transfer Media: A New Type of High Power Target Design

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**Figure 2.** Electron beam coupling test facility.

### **3.1. ADS target**

For CIADS, the target needs to prove high neutron yield inside a subcritical reactor core. To replenish the neutrons in a subcritical power reactor, the target-beam power is very high. The primary design chose proton beam of 500 MeV @ 5 mA and beam power of 2.5 MW.

Meanwhile, the space for the target installation is very limited to lower the neutron leakage and increase the effective neutron multiplication factor (keff) of the reactor. Usually the installation space is in vacancy of several removed fuel components. In CIADS, the diameter of the target tube needs to be under 30 cm. To fit this space, a thin and long vertical tube was applied as target tube. The dense granular flow went downward within. The beam line installed coaxially in the target tube sent protons deep into the target granules and reacted at the same level of the core center. **Figure 1** shows a schematic view of CIADS, which adopts a loop target section.

Tungsten was selected as the target material. Minor iron was added to optimize the mechanical properties. The alloy was made into 1 mm sphere. Tungsten generates abundant neutrons in spallation reaction which is widely adopted in neutron resources. With the basic idea of dense granular flow, the tungsten also plays a role as coolant. Considering the beam heat load and material's temperature endurance, the circulation mass flow is required about 200 kg/s. Compared to the fluidized dilute granular flow developed in the Rutherford Appleton Laboratory, we believed that the dense flow is more stable and lowers the requirement of gas system, for this specific case.

To sustain the operation, the system also included conveying, cooling, conditioning, monitoring, cleaning, and other affiliate systems. To lift the spheres back into the target, a chain conveyor is employed. The spheres inside flow vertically under gravity. When the spheres Dense Granular Flow as Heat Transfer Media: A New Type of High Power Target Design http://dx.doi.org/10.5772/intechopen.77276 87

**Figure 1.** Schematic diagram of CIADS.

time-dependent phenomenon has been observed by other researches [36, 56]. The total heat

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in

With the concept of dense granular flow cooling, the target can be designed according to different demands. Two different types of granular flow target have been developed for China Initiative Accelerator-Driven System (CIADS) project and China material irradiation facility project. For both designs helium was selected as the cover gas, concerning its high thermal conductivity and safety. In principle, pressure was set lower than 1 atm to prevent leakage and help target-beam line coupling. For each case, gas pressure was variable parameter. The difference of the two targets includes structure, target material, beam

By the end of 2017, two prototype facilities were constructed and tested with electrical heating, up to about 300°C. The beam coupling experiments are planned to be performed later,

For CIADS, the target needs to prove high neutron yield inside a subcritical reactor core. To replenish the neutrons in a subcritical power reactor, the target-beam power is very high. The

Meanwhile, the space for the target installation is very limited to lower the neutron leakage and increase the effective neutron multiplication factor (keff) of the reactor. Usually the installation space is in vacancy of several removed fuel components. In CIADS, the diameter of the target tube needs to be under 30 cm. To fit this space, a thin and long vertical tube was applied as target tube. The dense granular flow went downward within. The beam line installed coaxially in the target tube sent protons deep into the target granules and reacted at the same level of the core center. **Figure 1** shows a schematic view of CIADS, which adopts a

Tungsten was selected as the target material. Minor iron was added to optimize the mechanical properties. The alloy was made into 1 mm sphere. Tungsten generates abundant neutrons in spallation reaction which is widely adopted in neutron resources. With the basic idea of dense granular flow, the tungsten also plays a role as coolant. Considering the beam heat load and material's temperature endurance, the circulation mass flow is required about 200 kg/s. Compared to the fluidized dilute granular flow developed in the Rutherford Appleton Laboratory, we believed that the dense flow is more stable and lowers the requirement of gas

To sustain the operation, the system also included conveying, cooling, conditioning, monitoring, cleaning, and other affiliate systems. To lift the spheres back into the target, a chain conveyor is employed. The spheres inside flow vertically under gravity. When the spheres

primary design chose proton beam of 500 MeV @ 5 mA and beam power of 2.5 MW.

·K which is also a typical range of most

transfer coefficient fell in the range of 50–200 W/m2

**3. Implementation of granular flow target**

depending on the progress of radiation shielding hall.

facility situation [57].

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86

energy, spectrum, and so on.

**3.1. ADS target**

loop target section.

system, for this specific case.

flow to the bottom of the loop, the elevator lifts them back to the top, and the spheres reenter into the target. The elevator actively supplies the energy to sustain the circulation; hence the reliability and feasibility should be carefully considered. Other confines came from the ADS application, such as airtight and compact. Due to the grain size and density, pneumatic system does not fit the system well. Both conventional mechanical conveyer and a new developed magnetic conveyer are chosen as potential candidate. The heat of spheres will be removed in a panel heat exchanger. Through the steel shell of the heat transfer panel, the heat is transferred to the counter water flow. The width of parallel flow channel formed by the panels is large enough to avoid arching and clogging. **Figure 2** shows an electron beam coupling test facility constructed in 2015. Without conditioning and some other minor systems, the facility is simplified to test the circulation and heat loading effect. As shown in **Figure 3**, the coupling section is about 1:5 to the full scale.

The full-scale testing was setup later in 2017, as shown in **Figure 4**. The model facilities were put into practice as a preliminary design verification by Institute of Modern Physics, Lanzhou. Other than the components of previous system, sieving and cover gas systems were installed. Conveying system was updated to a magnet conveyer, and heat exchange test was elevated to about 250°C.

### **3.2. Target for material irradiation facility**

Material irradiation facility also requires intensive neutron source to test material tolerance of radiation damage. The China material irradiation facility aims at a small-scale and low-cost facility. To maximize the radiation effect, the facility design took the advantage of forward neutrons. The system adopted deuterium beam of 20 MeV@5 mA and beryllium as the target material. Due to 20 MeV deuterium only has a very low penetration at the order of millimeter; there is hardly effective neutrons leak out, with the previous configuration. Hence, a new structure based on chute flow was adopted.

**Figure 4.** Prototype facility and heating test.

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**Figure 5.** Simulation of beam heat load.

**Figure 3.** Profile of coupling section.

Dense Granular Flow as Heat Transfer Media: A New Type of High Power Target Design http://dx.doi.org/10.5772/intechopen.77276 89

**Figure 4.** Prototype facility and heating test.

flow to the bottom of the loop, the elevator lifts them back to the top, and the spheres reenter into the target. The elevator actively supplies the energy to sustain the circulation; hence the reliability and feasibility should be carefully considered. Other confines came from the ADS application, such as airtight and compact. Due to the grain size and density, pneumatic system does not fit the system well. Both conventional mechanical conveyer and a new developed magnetic conveyer are chosen as potential candidate. The heat of spheres will be removed in a panel heat exchanger. Through the steel shell of the heat transfer panel, the heat is transferred to the counter water flow. The width of parallel flow channel formed by the panels is large enough to avoid arching and clogging. **Figure 2** shows an electron beam coupling test facility constructed in 2015. Without conditioning and some other minor systems, the facility is simplified to test the circulation and heat loading effect. As shown in **Figure 3**, the coupling

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in

The full-scale testing was setup later in 2017, as shown in **Figure 4**. The model facilities were put into practice as a preliminary design verification by Institute of Modern Physics, Lanzhou. Other than the components of previous system, sieving and cover gas systems were installed. Conveying system was updated to a magnet conveyer, and heat exchange test was elevated

Material irradiation facility also requires intensive neutron source to test material tolerance of radiation damage. The China material irradiation facility aims at a small-scale and low-cost facility. To maximize the radiation effect, the facility design took the advantage of forward neutrons. The system adopted deuterium beam of 20 MeV@5 mA and beryllium as the target material. Due to 20 MeV deuterium only has a very low penetration at the order of millimeter; there is hardly effective neutrons leak out, with the previous configuration. Hence, a new

section is about 1:5 to the full scale.

**3.2. Target for material irradiation facility**

structure based on chute flow was adopted.

**Figure 3.** Profile of coupling section.

to about 250°C.

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**Figure 5.** Simulation of beam heat load.

To demonstrate the heat load effect of this chute flow target, this progress is simulated by our GPU code [58]. **Figure 5** showed one of the simulation results of heat deposition in a chute flow. The result showed the 20 MeV beam particles only penetrate several millimeters into the flow. According to the design and simulation, mass flow at about 2–3 m/s is sufficient to remove the heat. The parameters of feeding rate, chute slope, beam spot position, and flow channel width system could be well adjusted to required reaction region. After its first test, target section of the facility in **Figure 2** was replaced by a slope chute. **Figure 6** showed the test loop facility and targets applied in the system. An acrylic chute was chosen to observe the flow status, and a stainless steel chute was installed for beam coupling effect of the facility. The experimental result is showed lower right.

The target design is first tested on remodeled small-scale circulation loop for ADS target in 2015. The facility is also radiated by electron beam. Temperature of the flow increased slightly,

Dense Granular Flow as Heat Transfer Media: A New Type of High Power Target Design

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which showed that the system heat removal is workable.

**Figure 8.** Static granular target.

**Figure 7.** Prototype of material irradiation facility target and heating.

**Figure 6.** Electron beam coupling of chute flow target.

Dense Granular Flow as Heat Transfer Media: A New Type of High Power Target Design http://dx.doi.org/10.5772/intechopen.77276 91

**Figure 7.** Prototype of material irradiation facility target and heating.

**Figure 8.** Static granular target.

To demonstrate the heat load effect of this chute flow target, this progress is simulated by our GPU code [58]. **Figure 5** showed one of the simulation results of heat deposition in a chute flow. The result showed the 20 MeV beam particles only penetrate several millimeters into the flow. According to the design and simulation, mass flow at about 2–3 m/s is sufficient to remove the heat. The parameters of feeding rate, chute slope, beam spot position, and flow channel width system could be well adjusted to required reaction region. After its first test, target section of the facility in **Figure 2** was replaced by a slope chute. **Figure 6** showed the test loop facility and targets applied in the system. An acrylic chute was chosen to observe the flow status, and a stainless steel chute was installed for beam coupling effect of the facility.

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in

The experimental result is showed lower right.

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**Figure 6.** Electron beam coupling of chute flow target.

The target design is first tested on remodeled small-scale circulation loop for ADS target in 2015. The facility is also radiated by electron beam. Temperature of the flow increased slightly, which showed that the system heat removal is workable.

Later in 2017, a full-scale prototype facility finished its major construction, as shown in **Figure 7**. Due to the radiation hazards, instead of actual beam, system used laser and electric heating to test temperature endurance and heat removal effect. 30 kW electric heating offered major overall heating power, while laser provided a high power density up to 3 MW/cm2 . Granular flow reached an average temperature more than 300°C and maximum temperature more than 500°C. High-temperature testing was performed over 200 h, among which the longest continuous run lasts more than 100 h.

**Author details**

**References**

Xuezhi Zhang and Lei Yang\*

2014;**761**:58-68

& Sons, Inc; 2011. pp. xi-xii

John Wiley & Sons, Inc.; 2011. pp. 305-308

[4] Bauer Go

\*Address all correspondence to<EMAIL_ADDRESS>
Journal of Nuclear Materials. 2010;**398**(1-3):19-27

Institute of Modern Physics of the Chinese Academy of Sciences, Lanzhou, China

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Energy Encyclopedia. John Wiley & Sons, Inc.; 2011. pp. 353-364

Design Activity: Final report. ENEA, Frascati, Italy: Dipt. Energia; 1997

flow target. SCIENCE CHINA Technological Sciences. 2015;**58**(10):1705-1711 [6] Incropera F. Fundamentals of Heat and Mass Transfer. John Wiley & Sons; 2011

OECD. Towards reliable high power spallation target design. 2003. pp. 81-93

To test the neutron performance of this target material, a static granular target as shown in **Figure 8** was installed in the beamline of a 20 MeV linear accelerator. The neutron yield data is tested through proton beam and the same 1 mm beryllium in static vacuum chamber. Five stacks of activated foils are located around the chamber. The measurement of the foils deduced a total neutron flux of 2.14×1013/cm2 ·mA·s.

## **4. Conclusion**

The unique property of dense granular flow makes it possible to transfer heat effectively at high temperature. The major mechanism and factors of granular were reviewed. Using the granular material as heat transfer media and target material, two different configurations came up depending on the application. The prototype testing facilities were constructed. More designs and applications based on the granular heat transfer media are to be developed hopefully.

## **Acknowledgements**

The major work mentioned above is achieved by the staff members from spallation target department and advance nuclear material department of Institute of Modern Physics of the CAS.

## **Notation**

### **Author details**

Later in 2017, a full-scale prototype facility finished its major construction, as shown in **Figure 7**. Due to the radiation hazards, instead of actual beam, system used laser and electric heating to test temperature endurance and heat removal effect. 30 kW electric heating offered major

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in

flow reached an average temperature more than 300°C and maximum temperature more than 500°C. High-temperature testing was performed over 200 h, among which the longest con-

To test the neutron performance of this target material, a static granular target as shown in **Figure 8** was installed in the beamline of a 20 MeV linear accelerator. The neutron yield data is tested through proton beam and the same 1 mm beryllium in static vacuum chamber. Five stacks of activated foils are located around the chamber. The measurement of the foils

·mA·s.

The unique property of dense granular flow makes it possible to transfer heat effectively at high temperature. The major mechanism and factors of granular were reviewed. Using the granular material as heat transfer media and target material, two different configurations came up depending on the application. The prototype testing facilities were constructed. More designs and applications based on the granular heat transfer media are to be developed

The major work mentioned above is achieved by the staff members from spallation target department and advance nuclear material department of Institute of Modern Physics of the

. Granular

overall heating power, while laser provided a high power density up to 3 MW/cm2

tinuous run lasts more than 100 h.

**4. Conclusion**

the Environment

92

hopefully.

CAS.

**Notation**

**Acknowledgements**

deduced a total neutron flux of 2.14×1013/cm2

k effective thermal conductivity

kg gas phase thermal conductivity

ks solid phase thermal conductivity

Dp particle diameter

ε void fraction/porosity

Xuezhi Zhang and Lei Yang\*

\*Address all correspondence to<EMAIL_ADDRESS>
Institute of Modern Physics of the Chinese Academy of Sciences, Lanzhou, China

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**Chapter 5**

Provisional chapter

**Bubble Dynamics in a Narrow Rectangular Channel**

DOI: 10.5772/intechopen.74608

It is very important to study the bubble dynamics in order to understand the physical process of boiling heat transfer in a narrow channel. Experimental and theoretical studies on bubble dynamics in a narrow rectangular channel are proposed. The cross section of the narrow rectangular channel is 2 mm 8 mm. A high speed digital camera is applied to capture bubble behaviors from the narrow side and wide side of the narrow rectangular channel. Bubble growth rate, bubble departure diameter, bubble interface parameter and others are obtained according to the observation. A force balance analysis on a growing bubble is proposed to predict the bubble departure diameter and sliding bubble velocity, and the predicted results agree with the experimental data. Thus, the mechanism of bubble departure, slide and lift-off behavior in a narrow rectangular channel can be

Thermal hydraulics and safety analysis are important in nuclear reactor design and operation. There have been active investigations on nuclear thermal hydraulics and safety analysis in different core fuel elements. The rod bundles with grid spacers and plate-type fuel elements are frequently encountered at the aspect of developing new type nuclear reactor. The coolant channels of the plate-type fuel element are composed of some typical narrow rectangular channels, and the flow and heat transfer in a narrow rectangular channel is also widely employed in the compact evaporators and heat exchangers. So it is important to perform the

During the last decades, there were a lot of investigations focusing on two-phase flow and boiling heat transfer in narrow rectangular channels in published literatures [1–14]. The results

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

thermal hydraulic study of boiling heat transfer in the narrow rectangular channels.

Bubble Dynamics in a Narrow Rectangular Channel

Xu Jianjun, Xie Tianzhou, Chen Bingde and Bao Wei

Xu Jianjun, Xie Tianzhou, Chen Bingde and Bao Wei

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.74608

explained by the analysis of forces.

Keywords: narrow channel, bubble dynamics, force balance

Abstract

1. Introduction

### **Bubble Dynamics in a Narrow Rectangular Channel** Bubble Dynamics in a Narrow Rectangular Channel

DOI: 10.5772/intechopen.74608

Xu Jianjun, Xie Tianzhou, Chen Bingde and Bao Wei Xu Jianjun, Xie Tianzhou, Chen Bingde and Bao Wei

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.74608

### Abstract

[47] Aberdeen J, Laby T. Conduction of heat through powders and its dependence on the pressure and conductivity of the gaseous phase. Proceedings of the Royal Society of London Series a-Containing Papers of a Mathematical and Physical Character. 1926;**113**:459-447

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[50] Gelperin J, Kagan A. Study of heat transfer in gas flow in tubes packed with granular

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pp. 547-552

It is very important to study the bubble dynamics in order to understand the physical process of boiling heat transfer in a narrow channel. Experimental and theoretical studies on bubble dynamics in a narrow rectangular channel are proposed. The cross section of the narrow rectangular channel is 2 mm 8 mm. A high speed digital camera is applied to capture bubble behaviors from the narrow side and wide side of the narrow rectangular channel. Bubble growth rate, bubble departure diameter, bubble interface parameter and others are obtained according to the observation. A force balance analysis on a growing bubble is proposed to predict the bubble departure diameter and sliding bubble velocity, and the predicted results agree with the experimental data. Thus, the mechanism of bubble departure, slide and lift-off behavior in a narrow rectangular channel can be explained by the analysis of forces.

Keywords: narrow channel, bubble dynamics, force balance

### 1. Introduction

Thermal hydraulics and safety analysis are important in nuclear reactor design and operation. There have been active investigations on nuclear thermal hydraulics and safety analysis in different core fuel elements. The rod bundles with grid spacers and plate-type fuel elements are frequently encountered at the aspect of developing new type nuclear reactor. The coolant channels of the plate-type fuel element are composed of some typical narrow rectangular channels, and the flow and heat transfer in a narrow rectangular channel is also widely employed in the compact evaporators and heat exchangers. So it is important to perform the thermal hydraulic study of boiling heat transfer in the narrow rectangular channels.

During the last decades, there were a lot of investigations focusing on two-phase flow and boiling heat transfer in narrow rectangular channels in published literatures [1–14]. The results

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

show that two-phase flow and boiling heat transfer in a narrow channel is a very complex physical process. Some researchers think that boiling heat transfer in a narrow channel are different from that in an ordinary sized channel and the boiling heat transfer mechanism in a narrow rectangular channel is not fully understood.

In order to understand the physical process of boiling heat transfer in a narrow channel, and it is important to study the bubble growth, departure and lift-off behavior by using the visualized technology. Over the last half century, a lot of studies of bubble dynamics have been conducted, and this kind of study is significant to understand the boiling heat transfer mechanism. It is the fundamental for understanding and predicting the boiling heat transfer correctly. However, most of these studies have been focused on observation of bubble behaviors in an ordinary sized channel. In our previous work, bubble characteristics in narrow rectangular channel were visually studied, and the results showed that the bubbles departing from the nucleation sites always slid along the heating wall [15]. Some researchers presented the importance of the sliding bubble to enhance heat transfer in nucleate boiling [16–20], the results showed that turbulence caused by sliding bubbles could be an important mechanism in enhancing heat transfer. The effect of sliding bubbles on boiling heat transfer in a narrow channel will be more important than that in an ordinary sized channel because of the smaller cross section size.

side of the rectangular channel. The observation windows were made of optical quartz glass. The width of the narrow rectangular channel is 8 mm and height is 2 mm. The same experimental apparatus was described to investigate the bubble dynamics in the previous study of

Bubble Dynamics in a Narrow Rectangular Channel http://dx.doi.org/10.5772/intechopen.74608 99

In the present work, the experiment pressure was atmospheric pressure. The range of the liquid subcooling of the inlet of the test section was 10–40C. The range of mass flux was 129– 706 kg/m2 s. Temperatures at the wall, inlet, and outlet of the test section were registered by 1 mm diameter T-type thermocouples, which were calibrated and a uncertainty of 0.5C for all thermocouples. The uncertainty in the heat supplied to the test section was less than 0.9%. The heat loss of the test section was estimated to within 7% of the total of the heating power in the present study. Flow rate was measured by a venturimeter and the uncertainty was less than

the authors [13].

Figure 1. Schematic diagram of test section.

Figure 2. Definition of bubble equivalent diameter.

It is known that the analysis of forces acting on a single bubble is a promising approach to sufficiently understand the mechanism of bubble motion. Levy [21] first proposed a model for the prediction of bubble departure diameter based on the balance of forces, including the buoyancy, surface tension force and drag force. Klausner et al. [22] built the models of force balance to predict the bubble departure diameter and lift-off diameter, and there have been active investigations on the analysis of forces balance [14, 23–25], and these researches implies that bubble interface parameters were required as the input parameters in order to solve this model, including the bubble inclination angle, upstream contact angle, downstream contact angle and bubble contact diameter. It is also important to develop the wall heat flux partitioning model and the interfacial area transport equation for using computational fluid dynamics (CFD) code.

These studies in the above literatures have not provided an adequately detailed understanding of boiling heat transfer in a narrow rectangular channel. The present study showed bubble growth, departure, sliding and lift-off behaviors in a narrow rectangular channel, and the mechanism of bubble departure and lift-off from the heating wall was discussed based on the analysis of forces acting on the bubble.

### 2. Experimental facilities and measuring system

Figure 1 shows a schematic of the test section of the narrow rectangular channel. The cross section of the narrow rectangular channel was 2 8 mm2 , which was fabricated in an optical quartz glass. Both the wide side and the gap side of the optical quartz glass were polished to improve the transparency. Bubble behavior was visually observed from the wide side and gap

Figure 1. Schematic diagram of test section.

show that two-phase flow and boiling heat transfer in a narrow channel is a very complex physical process. Some researchers think that boiling heat transfer in a narrow channel are different from that in an ordinary sized channel and the boiling heat transfer mechanism in a

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in

In order to understand the physical process of boiling heat transfer in a narrow channel, and it is important to study the bubble growth, departure and lift-off behavior by using the visualized technology. Over the last half century, a lot of studies of bubble dynamics have been conducted, and this kind of study is significant to understand the boiling heat transfer mechanism. It is the fundamental for understanding and predicting the boiling heat transfer correctly. However, most of these studies have been focused on observation of bubble behaviors in an ordinary sized channel. In our previous work, bubble characteristics in narrow rectangular channel were visually studied, and the results showed that the bubbles departing from the nucleation sites always slid along the heating wall [15]. Some researchers presented the importance of the sliding bubble to enhance heat transfer in nucleate boiling [16–20], the results showed that turbulence caused by sliding bubbles could be an important mechanism in enhancing heat transfer. The effect of sliding bubbles on boiling heat transfer in a narrow channel will be more important than that in an ordinary sized channel because of the smaller

It is known that the analysis of forces acting on a single bubble is a promising approach to sufficiently understand the mechanism of bubble motion. Levy [21] first proposed a model for the prediction of bubble departure diameter based on the balance of forces, including the buoyancy, surface tension force and drag force. Klausner et al. [22] built the models of force balance to predict the bubble departure diameter and lift-off diameter, and there have been active investigations on the analysis of forces balance [14, 23–25], and these researches implies that bubble interface parameters were required as the input parameters in order to solve this model, including the bubble inclination angle, upstream contact angle, downstream contact angle and bubble contact diameter. It is also important to develop the wall heat flux partitioning model and the interfacial area transport equation for using computational fluid

These studies in the above literatures have not provided an adequately detailed understanding of boiling heat transfer in a narrow rectangular channel. The present study showed bubble growth, departure, sliding and lift-off behaviors in a narrow rectangular channel, and the mechanism of bubble departure and lift-off from the heating wall was discussed based on the

Figure 1 shows a schematic of the test section of the narrow rectangular channel. The cross

quartz glass. Both the wide side and the gap side of the optical quartz glass were polished to improve the transparency. Bubble behavior was visually observed from the wide side and gap

, which was fabricated in an optical

narrow rectangular channel is not fully understood.

cross section size.

the Environment

98

dynamics (CFD) code.

analysis of forces acting on the bubble.

2. Experimental facilities and measuring system

section of the narrow rectangular channel was 2 8 mm2

side of the rectangular channel. The observation windows were made of optical quartz glass. The width of the narrow rectangular channel is 8 mm and height is 2 mm. The same experimental apparatus was described to investigate the bubble dynamics in the previous study of the authors [13].