**1. Introduction**

Thermal Energy Storage (TES) technology has gained increasing worldwide attention, because it, among others, has been regarded as an effective way to compensate for the intermittence of renewable sources [1,2]. Among various TES technologies, Latent Heat Thermal Energy Storage, (LHTES), utilising Phase Change Materials, (PCMs), is one of the most attractive forms, with a relatively high storage density and small temperature changes from storage to retrieval [3]. PCMs are substances with the property of heat absorption when they undergo a phase change from solid to liquid, liquid to gas, or vice versa [4–6]. These PCMs are widely applicable in a broad range of industrial areas. For instance, they can be encapsulated in building materials, e.g., gypsum plasterboard, cubicle, and wall board in order to enhance the thermal storage capacity [7,8]. PCMs are also considered to improve the frosting/defrosting operating performance of air source heat pumps [9]. Likewise, PCMs are frequently used in order to produce thermoregulated textiles, where they are generally entrapped in micro/nano-capsules to prevent leakage [10]. PCMs-assisted packaging is an innovative technology, which can plenarily control temperature-sensitive food products under different conditions [11]. In addition, PCMs also play an important

**Citation:** Ochman, A.; Chen, W.-Q.; Błasiak, P.; Pomorski, M.; Pietrowicz, S. The Use of Capsuled Paraffin Wax in Low-Temperature Thermal Energy Storage Applications: An Experimental and Numerical Investigation. *Energies* **2021**, *14*, 538. https://doi.org/10.3390/en14030538

Received: 21 December 2020 Accepted: 17 January 2021 Published: 21 January 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

role in a large number of fields, like temperature-adjustable greenhouses [12,13], waste heat recovery [14], and building air-conditioning [15]. High-temperature PCMs have attracted considerable interests over the past decade, which is extraordinarily promising in the concentrated solar thermal field and other high-temperature-required domains [16–18]. On the other hand, Amin et al. [19] considered a different temperature interval with a focus on low-temperature PCMs that are encapsulated in spheres.

PCMs can be generally classified into two types: organic and inorganic. Most inorganic PCMs are barely applicable to the TES system due to their toxicity, corrosivity, and supercooling properties. In contrast, organic PCMs are relatively safe, chemically inert and ecologically friendly [20]. Among diverse organic PCMs, paraffin wax is one of the most common materials, with several remarkable properties, e.g., high energy storage density, relatively low cost in commerce, and a small super-cooling trend. Paraffin wax (usually extracted from ozokerite, petroleum, natural gas, etc.) has a wide range of phase change temperatures and it has a general chemical formula C*n* H2*n*+2 (*n* ≥ 4, the higher the value of *n* the higher the melting temperature) [21]. Consequently, an ideal scheme seems to be to use capsuled paraffin wax as a storage material and proposals for such a method have already been tackled by groups of researchers [22,23].

Plenty of investigations on the mathematical models and numerical analyses with PCMs that are capsuled in different configurations have been performed and reported in the literature. Shamsundar and Sparrow [24] resolved the enthalpy equation using the finite difference approach and performed an analysis of the multidimensional transient solidification process with the change of density and an increasing shrinkage cavity. The authors noted that the highest impact of the density ratio and the Stefan number on the heat transfer occurred at almost the end of solidification. In a horizontal tube with unfixed solid PCMs inside, the thermal behaviours of the PCMs (heat flux densities, geometric shape, melting rates, etc.) were obtained by Bareiss and Beer [25] through neglecting the inertial force. The authors pointed out that the gravity of the solid PCMs and pressure forces in a thin liquid layer jointly formed a force balance. Bilir and Ilken [26] investigated PCMs capsuled in a spherical/cylindrical container employing the third kind of boundary condition. The authors derived correlations that utilise the Biot number, the Stefan number and the dimensionless surface temperature to present the dimensionless total solidification time of PCMs. Verma et al. [27] studied the mathematical models that are based on the first and second law of thermodynamics regarding the LHTES system with PCMs inside. The authors indicated that the model based on the first law of thermodynamics had been experimentally validated, and could be employed to model PCMs. However, the model based on the second law of thermodynamics required additional work related to its experimental verification. A numerical model regarding the solidification process of PCMs in a triplex tube with external and internal fins was proposed by Al-Abidi et al. [28]. The authors noted that factors, including the fin length, the fin thickness, and the numbers of fins, had a considerable impact on the heat transfer. However, the effect of the fin thickness was assessed to be less than that of the fin length. Similarly, Li et al. [29] explored the enhancement effect of aluminium oxide on phase change heat transfer in the triplex tube with fins. The conducted research revealed that an extra alumina contributed to a stronger conduction and the best discharging rate was determined in the case of *dp* = 40 nm. The entropy optimization method was applied in order to study the solidification behaviour of nanoparticle-enhanced PCMs in the LHTES system affected by a magnetic field by Shah et al. [30]. The authors indicated that the Lorentz force, caused by the Hartmann number, and buoyancy forces had positive and negative impacts on the solidification rate of nanoparticle-enhanced PCMs, respectively. Jourabian et al. [31] utilised the enthalpy-based Lattice Boltzmann method and double distribution function to explore the melting process of the ice within a semicircle enclosure. The authors noticed that the concentration of nanoparticles had a positive and an adverse effect on the thermal conductivity and the latent heat of PCMs, respectively, but a negligible impact on the average Nusselt number. A novel PCM-air tubular heat exchanger and the corresponding

analytical solution were proposed by Dubovsky et al. [32]. The authors successfully predicted the results of separate tubes and verified the applicability of the analytical solution to the practical heat exchangers. Darzi et al. [33] presented several simulations of the symmetric melting process between two cylinders in an eccentric and concentric position using N-eicosane as the PCM. The authors pointed out that the downward movement of the inner cylinder caused a significant increase in the melting rate due to the dominance of convective heat transfer in most areas of the PCM. Mahdaoui et al. [34] proposed a numerical model involving the natural convection phenomenon in the PCM-melted region around a horizontal cylinder. As a result of the conducted research, the authors assessed that regardless of the assumed boundary conditions, (constant temperature of the cylinder walls, constant heat flux), the melting of the PCM in the lower part was ineffective since the energy was transferred mainly by convection to the top of the cylinder. Regin et al. [35] focused on the cylindrical PCM-melting model integrated into the LHTES system, which was combined with a solar water heating collector. The conducted analyses indicated that the melting of PCMs was primarily dependent on the magnitude of the temperature range of the phase transformation, the Stefan number, and the capsule radius. Although these papers have successfully studied diverse mathematical and numerical PCM melting/solidification models employing different constraints. Additionally, it was considered various influencing factors and configurations, none of them pays attention to the changes in the internal structure of the PCMs during the phase change process. Furthermore, most of them only deal with the PCMs capsuled in horizontal cylinders and heat transfer is uniformly along the circumference of the circular cylinder. Accordingly, we have made an attempt to investigate the case of PCMs capsuled in the vertical position of a cylinder, which will undergo several heat-flow processes of the cross-flow of air with different velocities. We are highly expecting to test and compare the capabilities of the mixture of paraffin wax and water in different heat flux environments and to more explicitly describe the characteristic parameters of five-phase change regions of the mixed PCMs. In addition, a Scanning Electron Microscope (SEM) will be expedient in confirming the specific changes in the internal structure of the mixed PCMs during the phase transition.

The motivation to undertake the analyses carried out in the article is to design a container for storing/accumulating cold "energy" cooperating with the heat pump. The presented literature analysis shows that one of the most promising candidates that can be directly applied in the analysed device and its ranges of the temperature is the PCMcapsuled paraffin wax. This container unit filled with PCM has to operate with a system named a Flower Shape Oscillating Heat Pipe (FSOHP), which was described in detail by Czajkowski et al. in [36] and it has also been patented in [37] by Pietrowicz et al. Thus, an integral element in the innovative system for cooling mixed substances is a special exchanger that contains the PCM described and studied in this paper. The operational parameters of the exchanger have been defined and described by Ochman and Pietrowicz in [38], and have also been patented by Pietrowicz et al. [39]. What is important, due to the required technological process, PCMs are expected to store the "cold" energy in the range of 4 ◦C to 6 ◦C. The paraffin wax, due to its thermodynamic and functional properties, is a pertinent candidate for this novel system, as it was mentioned.

Thus, when preparing the design procedures that are dedicated for a storage tank, the authors of the article needed to have a complete, validated mathematical model of the thermal-flow processes occurring in the tested phase change material and to have knowledge of the impact of the operating conditions of the designed storage tank on the temperature change in the PCMs, depending on the total applied mass of the PCM. It was also important to determine the time that is needed for the phase changes and to compare them with different values of the supplied heat flux. The authors of the article also believe that the developed numerical procedures together with the conducted research will help in the future during the optimization process of the construction of a cold accumulator cooperating with a heat pump and a mixing/dissolver device.

In the presented article, the thermal-flow processes occurring in the low-temperature PCM were experimentally tested and then numerically investigated. The experiments were carried out for fully turbulent flow (15,250 < Re < 52,750) and for three cylindrical modules filled with a PCM with fixed heights of 250 mm and with outer diameters of 15, 22, and 28 mm, respectively. For this purpose, a special set-up was designed and constructed, in which a wind tunnel is the main element. Additionally, special test procedures were developed and adapted. Subsequently, a mathematical model of thermal-flow processes existing in the phase change material, based on the enthalpy porosity method, was proposed and validated. Finally, the numerical calculations, during the transient processes, were carried out for various boundary conditions that are close to those expected during the real operation of the device.

The structure of the article consisted of the following elements: Section 2 describes the tested phase change material, with a description of the thermophysical properties and the analysis of the internal structure while using a SEM. The test stand, tested modules filled with PCM and measurement procedures are described in Section 3. Section 4 presents the mathematical model and numerical procedures, numerical domains with the applied boundary conditions and applied thermal properties. The experimental studies are detailed and discussed in Section 5. Additionally, this Section compares the results of the numerical studies with the experimental data and summarizes them by the relative error analysis. Section 6 concludes the work, where the most important results and observations from the conducted research are presented.

#### **2. Phase Change Material (PCM)**

#### *2.1. General Description of the PCM*

To meet the thermal requirements, i.e., the phase change temperature range and usability, the research was conducted on a commercial phase-change material, which was paraffin wax capsules in a melamine-formaldehyde membrane and water mixture, produced by the *MikroCaps* company [40]. Table 1 shows the selected thermophysical properties describing the tested PCM.

**Table 1.** The thermophysical properties of the Phase Change Material (PCM) used during the experiments [40].

#### *2.2. Analysis of the PCM's Internal Structure*

#### 2.2.1. Test Conditions and Testing Procedures

The purpose of the analysis described in this section was to observe whether and how the internal structure of the PCM changes at the characteristic temperature points. The structure of the material was studied while using a Scanning Electron Microscope (SEM). A *Prisma* E scanning electron microscope from Thermo Fisher Scientific was used for this purpose. A special table with a Peltier system was installed in the test chamber in order to regulate the sample temperature in the phase transition range, i.e., from 0 ◦C to 16 ◦C. Figure 1 shows the system with the studied sample along with the details of the test chamber.

(**a**) Test chamber with mounted the Peltier system and sample. (**b**) Prepared

**Figure 1.** Description of the Scanning Electron Microscope (SEM) chamber and the prepared sample.

> During the measurements, the focusing beam power was set from 20 to 25 kV. Those values were experimentally selected to ensure the right quality of contrast and sharpness of an image. It should be mentioned that the power of the selected high-energy electron beam allowed for the analysis of the sample without its visible degradation of the sample.

sample.

Efforts were made to keep the relative humidity value in the measuring chamber at 17 ÷ 42% in order to maintain the emulsion structure of the sample during the analyses of the PCM structure. Maintaining these parameters ensured that the evaporation of water from the material was minimized by achieving thermal conditions far from saturation conditions. Figure 2 presents the change in sample temperature and humidity during the experiment.

**Figure 2.** Temperature and relative humidity profiles maintained during measurement.

## 2.2.2. SEM Analysing

Figure 3 presents the results of the SEM's investigation of the PCM structure for selected temperature points that were defined at 0 ◦C, 5.5 ◦C, and 15 ◦C.

(**a**) 15 ◦C, 500×

(**d**) 5.5 ◦C, 3000×

(**e**) 0 ◦C, 3000×

(**c**) 5.5 ◦C, 2000×

(**f**) 0 ◦C, 6000×

**Figure 3.** Analysis of the PCM internal structure, made for different temperatures and magnifications obtained while using the SEM.

> Those temperatures have been selected, because the potential changes in the structure were expected. Thus, the temperature of 15 ◦C (Figure 3a,b) is significantly separated from the phase transition temperature, which was estimated at between 4 ◦C and 6 ◦C (Figure 3c,d). Because the analysed substance is an emulsion of two components-paraffin wax and water, analysis at 0 ◦C (Figure 3e,f) was also potentially considered, due to the phase change of the water.

> The investigation showed that the diameter of the analysed paraffin capsules is between 3 and 8 μm. This differs from the values declared by the manufacturer and described

in Table 1. Additionally, it was observed from Figure 3e,f, that, for 0 ◦C, the distances between microcapsules increase in comparison with other tested temperatures, which are a consequence of the presence of water in the form of ice and a higher value of the specific volume compared to other temperature tests. Generally, it can be concluded that, in the studied temperature ranges, no significant changes in the internal structure were noticed. This is an important fact that was used later during numerical simulations. The substance that is taken into account is homogeneous and the separation of components, i.e., sedimentation, is not later considered.

#### **3. Experimental Set-Up and Measuring Procedure**


**Table 2.** *Cont.*

**Table 2.** *Cont.*

**Author Contributions:** Writing—original draft preparation, L.F.-P. and P.G.-A.; writing—reviewing and editing, C.D.-P. and A.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the "Junta de Castilla y León", grant number VA294-P18.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data sharing not applicable.

**Acknowledgments:** L.F.-P. and P.G.-A. acknowledge predoctoral grants funded by the "Junta de Castilla y León" and the University of Valladolid, respectively.

**Conflicts of Interest:** The authors declare no conflict of interest.


**5. Techniques used to improve the quality control procedures during the extreme events.**

Quality of data during the extreme events such as strong cold fronts and hurricanes may de‐ crease resulting in a higher number of "true" outliers than that during the normal climate conditions. (28) carefully analyzed the sample examples of these extreme weather conditions to quantitatively demonstrate the causes of the outliers and then developed tools to reset the Type II error flags. The following discussion will elaborate on this technique.

#### **5.1. Relationship between interval of measurement and QA failures**

Fig. 1 shows the result for maximum temperature at Silver Lake Brighton, Utah. The IDW approach results in a large bias. The best fit line for IDW indicates the estimates are system‐ atically high by over 8 F (8.27); the slope is also greater than one (1.0684). When the best fit line for IDW estimates was forced through zero, the slope was 1.2152. On the other hand the estimates from the SRT indicate almost no bias as evidenced by the best-fit slope (0.9922).

For the minimum temperature estimates a similar result was found (Fig. 2). The slope of the best-fit line for the SRT indicates an unbiased (0.9931) while the slope for the IDW estimates indicates a large bias on the order of 20% (slope = 1.1933). The reader should note the SRT unbiased estimators are derived every 24 days (see ) and that applying the SRT only once

**Figure 2.** The results of estimating minimum temperature at Silver Lake Brighton, UT for both the IDW and the

**5. Techniques used to improve the quality control procedures during the**

Quality of data during the extreme events such as strong cold fronts and hurricanes may de‐ crease resulting in a higher number of "true" outliers than that during the normal climate conditions. (28) carefully analyzed the sample examples of these extreme weather conditions to quantitatively demonstrate the causes of the outliers and then developed tools to reset the

Type II error flags. The following discussion will elaborate on this technique.

for the entire period will degrade the results shown (7).

10 Practical Concepts of Quality Control

SRT methods.

**extreme events.**

Analyses were conducted to prepare artificial max and min temperature records (not the measurements, but the values identified as the max and min from the hourly time series) for different times-of-observation from available hourly time series of measurements. The ob‐ servation time for coop weather stations varies from site-to-site. Here we define the AM sta‐ tion, PM station, and nighttime station according to the time of observation (i.e. morning, afternoon-evening, and midnight respectively). The cooperative network has a higher num‐ ber of PM stations but AM measurements are also common; the Automated Weather Data Network uses a midnight to midnight observation period.

The daily precipitation accumulates the precipitation for the past 24 hours ending at the time of observation. The precipitation during the time interval may not match the precipi‐ tation from nearby neighboring stations due to event slicing, i.e. precipitation may occur both before and after a station's time of observation. Thus, a single storm can be sliced in‐ to two observation periods.

**Figure 3.** Example time intervals for observations at Mitchell, NE (after 28).

The measurements of the maximum and the minimum temperature are the result of making discrete intervals on a continuous variable. The maximum or minimum temperature takes the maximum value or the minimum value of temperature during the specific time interval. Thus the maximum temperature or the minimum temperature is not necessarily the maxi‐ mum or minimum value of a diurnal cycle. Examples of the differences were obtained from three time intervals (see Fig 3) after28)). The hourly measurements of air temperature were retrieved from 1:00 March 11 to 17:00 March 13, 2002 at Mitchell, NE. The times of observa‐ tion are marked. Point *A* shows the minimum air temperature obtained for March 11 for AM stations, and *B* is the maximum temperature obtained for March 13 at the PM stations. The minimum temperature may carry over to the following interval for AM stations and the maximum temperature may carry over to the following interval for PM stations. We have therefore marked these as problematic in Table 4to note that the thermodynamic state of the atmosphere will be represented differently for AM and PM stations. Through analysis of the time series of AM, PM and midnight calculated from the high quality hourly data we find that measurements obtained at the PM station have a higher risk of QA failure when com‐ pared to neighboring AM stations. The difference in temperature at different observation times may reach 20 o F for temperature and several inches for precipitation. Therefore the QA failures may not be due to sensor problems but, to comparing data from stations where the sensors are employed differently. To avoid this problem AM stations can be compared to AM stations, PM stations to PM stations, etc. Note this problem will be solved if moderniza‐ tion of network provides hourly or sub-hourly data at most station sites.

precipitation events, in which only a single station received significant precipitation. Higher precipitation entries occurring in isolation are more likely to be identified as potential outli‐ ers. These problems were expected to be avoided by examining the precipitation over larger

Toward a Better Quality Control of Weather Data

http://dx.doi.org/10.5772/51632

13

No significant relationship is found between the topography and the fraction of flagged re‐ cords. Some clusters of stations with high flag frequency are located along the mountains; however, other mountainous stations do not show this pattern. Moreover, some locations with similar topography have different patterns. For the State of Colorado, a high fraction of flags occurs along the foothills of the Rocky Mountains where the mountains meet the high plains. A high fraction was also found along interstate highways 25 and 70 in east Colorado. These situations may come about because the weather stations were managed by different organizations or different sensors were employed at these stations. These differences lead to

**Figure 4.** Time series of Stratton and a neighboring station during 2002 droughts. a) The daily time series of Tmax for

Stratton and Stratton AWDN station (a058019). b) Hourly time series at Stratton AWDN station. (after 28).

intervals, e.g. summing consecutive days into event totals.

possible higher fraction of flagged records in some areas.

**5.3. 2002 drought events**

**Table 4.** Time interval and possible performance of three intervals of measurements.

#### **5.2. 1993 floods**

Quality control procedures were applied to the data for the 1993 Midwest floods over the Missouri River Basin and part of the upper Mississippi River Basin, where heavy rainfall and floods occurred (28). The spatial regression test performs well and flags 5~7 % of the data for most of the area at *f*=3. The spatial patterns of the fraction of the flagged records do not coincide with the spatial pattern of return period. For example, the southeast part of Ne‐ braska does not show a high fraction of flagged records although most stations have return periods of more than 1000 years. While, upper Wisconsin has a higher fraction of flagged records although the precipitation for this case has a lower return period in that area.

The analysis shows a significantly higher fraction of flagged records using AWDN stations in North Dakota than in other states. This demonstrates that the differences in daily precipi‐ tation obtained from stations with different times of observation contributed to the high fraction of QA failures. A high risk of failure would occur in such cases when the measure‐ ments of the current station and the reference station are obtained from PM stations and AM stations respectively. The situation worsens if the measurements at weather stations were obtained from different time intervals and the distribution of stations with different time-ofobservation is unfavorable. This would be the case for an isolated AM or PM station.

Among the 13 flags at Grand Forks, 9 flags may be due to the different times of observation or perhaps the size and spacing of clouds (28). Four other flags occurred during localized precipitation events, in which only a single station received significant precipitation. Higher precipitation entries occurring in isolation are more likely to be identified as potential outli‐ ers. These problems were expected to be avoided by examining the precipitation over larger intervals, e.g. summing consecutive days into event totals.

#### **5.3. 2002 drought events**

maximum temperature may carry over to the following interval for PM stations. We have therefore marked these as problematic in Table 4to note that the thermodynamic state of the atmosphere will be represented differently for AM and PM stations. Through analysis of the time series of AM, PM and midnight calculated from the high quality hourly data we find that measurements obtained at the PM station have a higher risk of QA failure when com‐ pared to neighboring AM stations. The difference in temperature at different observation

failures may not be due to sensor problems but, to comparing data from stations where the sensors are employed differently. To avoid this problem AM stations can be compared to AM stations, PM stations to PM stations, etc. Note this problem will be solved if moderniza‐

Time intervals (e.g.) ~7:00 ~ 17:00 ~midnight

Precipitation Good Good Good

records although the precipitation for this case has a lower return period in that area.

observation is unfavorable. This would be the case for an isolated AM or PM station.

Among the 13 flags at Grand Forks, 9 flags may be due to the different times of observation or perhaps the size and spacing of clouds (28). Four other flags occurred during localized

The analysis shows a significantly higher fraction of flagged records using AWDN stations in North Dakota than in other states. This demonstrates that the differences in daily precipi‐ tation obtained from stations with different times of observation contributed to the high fraction of QA failures. A high risk of failure would occur in such cases when the measure‐ ments of the current station and the reference station are obtained from PM stations and AM stations respectively. The situation worsens if the measurements at weather stations were obtained from different time intervals and the distribution of stations with different time-of-

Quality control procedures were applied to the data for the 1993 Midwest floods over the Missouri River Basin and part of the upper Mississippi River Basin, where heavy rainfall and floods occurred (28). The spatial regression test performs well and flags 5~7 % of the data for most of the area at *f*=3. The spatial patterns of the fraction of the flagged records do not coincide with the spatial pattern of return period. For example, the southeast part of Ne‐ braska does not show a high fraction of flagged records although most stations have return periods of more than 1000 years. While, upper Wisconsin has a higher fraction of flagged

tion of network provides hourly or sub-hourly data at most station sites.

Maximum temperature Problematic

**Table 4.** Time interval and possible performance of three intervals of measurements.

Minimum temperature Problematic

F for temperature and several inches for precipitation. Therefore the QA

**AM station PM station Nighttime station**

**(AWDN)**

times may reach 20 o

12 Practical Concepts of Quality Control

**5.2. 1993 floods**

No significant relationship is found between the topography and the fraction of flagged re‐ cords. Some clusters of stations with high flag frequency are located along the mountains; however, other mountainous stations do not show this pattern. Moreover, some locations with similar topography have different patterns. For the State of Colorado, a high fraction of flags occurs along the foothills of the Rocky Mountains where the mountains meet the high plains. A high fraction was also found along interstate highways 25 and 70 in east Colorado. These situations may come about because the weather stations were managed by different organizations or different sensors were employed at these stations. These differences lead to possible higher fraction of flagged records in some areas.

**Figure 4.** Time series of Stratton and a neighboring station during 2002 droughts. a) The daily time series of Tmax for Stratton and Stratton AWDN station (a058019). b) Hourly time series at Stratton AWDN station. (after 28).

Instrumental failures and abnormal events also lead to QA failures. Fig. 4 shows the time series of the Stratton Station in Color adooperated as part of the automated weather net‐ work. This station has nighttime (midnight) readings while all of the neighboring sites are AM or PM stations. Stratton thus has the most flagged records in the state (6): the highlight‐ ed records in Fig. 4 were flagged. We checked the hourly data time series to investigate the QA failure in the daily maximum temperature time series for the time period from April 20 to May 20, 2002. No value was found to support a Tmax of 88 for May 6 in the hourly time series, thus 88 o F appears to be an outlier. On May 7 a high of 85 o F is recorded for the PM station observation interval, in which the value of the afternoon of May 6 is recorded as the high on May 7. The 102 o F observation of May 8 at 6:00 AM appears to be an observation error caused by a spike in the instrument reading.    Daily weather maps and spatial pattern of flagged records for 1992 Andrew Hurricane events. (after 28).

The spatial patterns of flagged records are significant for both the spatial regression test of the cold front events and the tropical storm events. However, most of these flagged records are type I errors, thus we tested a simple pattern recognition tool to assist in reducing these flags.

 The flags in the spatial pattern figures are cumulative for the days indicated. The test shows that the spatial regression test explicitly marks the track of the tropical storm. Starting from the second land-fall of Hurricane Andrew at mid-south Louisiana, the weather stations along the route have flagged records. The wind field formed by Hurricane Andrew helps to define the influence zone of the hurricane on flags. Many stations without flags have daily precipitation of more than 2 inches as the hurricane passes, which confirms that the spa‐ tial regression test is performing reasonably well in the presence of high precipitation events.

#### **5.5. Cold front in 1990**

Flags for the cold front event during October, 1990 were examined. The maximum air tem‐ perature dropped by as much as 40 o F during the passage of the cold front. Spatial patterns of flags on October 6 coincide with the area traversed by the cold front and many stations were flagged in such states as North Dakota, South Dakota, Iowa, and Nebraska. On Octo‐ ber 7, the cold front moved to southeast regions beyond Nebraska and Iowa. Of course near‐ by stations on opposite sides of the cold front may experience different temperatures thus leading to flags. This may be further complicated when different times of observation are involved. The cold front continues moving and the area of high frequency of flags also moves with the front correspondingly.

A similar phenomenon can be found in the test of the precipitation and the minimum tem‐ perature. A spatial regression test of any of these three variables can roughly mark the movements of the cold front events. The identified movements of the cold fronts and associ‐ ated flagging of "good records" may lead to more manual work to examine the records.

Instrumental failures and abnormal events also lead to QA failures. Fig. 4 shows the time series of the Stratton Station in Color adooperated as part of the automated weather net‐ work. This station has nighttime (midnight) readings while all of the neighboring sites are AM or PM stations. Stratton thus has the most flagged records in the state (6): the highlight‐ ed records in Fig. 4 were flagged. We checked the hourly data time series to investigate the QA failure in the daily maximum temperature time series for the time period from April 20 to May 20, 2002. No value was found to support a Tmax of 88 for May 6 in the hourly time

station observation interval, in which the value of the afternoon of May 6 is recorded as the

17 is supported by the hourly observation time series (see Fig. 4 (b)) and is apparently asso‐

In Fig. 5 the evolution of the spatial pattern of flagged records from August 25 to August 28, 1992 during Hurricane Andrew and the corresponding daily weather maps shows a heavy pat‐ tern of flagging.. The flags in the spatial pattern figures are cumulative for the days indicated. The test shows that the spatial regression test explicitly marks the track of the tropical storm. Starting from the second land-fall of Hurricane Andrew at mid-south Louisiana, the weather stations along the route have flagged records. The wind field formed by Hurricane Andrew helps to define the influence zone of the hurricane on flags. Many stations without flags have daily precipitation of more than 2 inches as the hurricane passes, which confirms that the spa‐ tial regression test is performing reasonably well in the presence of high precipitation events.

Flags for the cold front event during October, 1990 were examined. The maximum air tem‐

of flags on October 6 coincide with the area traversed by the cold front and many stations were flagged in such states as North Dakota, South Dakota, Iowa, and Nebraska. On Octo‐ ber 7, the cold front moved to southeast regions beyond Nebraska and Iowa. Of course near‐ by stations on opposite sides of the cold front may experience different temperatures thus leading to flags. This may be further complicated when different times of observation are involved. The cold front continues moving and the area of high frequency of flags also

A similar phenomenon can be found in the test of the precipitation and the minimum tem‐ perature. A spatial regression test of any of these three variables can roughly mark the movements of the cold front events. The identified movements of the cold fronts and associ‐ ated flagging of "good records" may lead to more manual work to examine the records. Simple pattern recognition tools have been developed to identify the spatial patterns of

F observation of May 8 at 6:00 AM appears to be an observation

F during the passage of the cold front. Spatial patterns

F is recorded for the PM

F at 8:00 AM May

F appears to be an outlier. On May 7 a high of 85 o

error caused by a spike in the instrument reading. The observation of 93 o

ciated with a down burst from a decaying thunderstorm.

series, thus 88 o

high on May 7. The 102 o

14 Practical Concepts of Quality Control

**5.4. 1992 Andrew Hurricane**

**5.5. Cold front in 1990**

perature dropped by as much as 40 o

moves with the front correspondingly.

these flags and reset these flags automatically (see Fig. 6).

**Figure 5.** Daily weather maps and spatial pattern of flagged records for 1992 Andrew Hurricane events. (after 28).

The spatial patterns of flagged records are significant for both the spatial regression test of the cold front events and the tropical storm events. However, most of these flagged records are type I errors, thus we tested a simple pattern recognition tool to assist in reducing these flags. Differences still exist between the distribution patterns of the flagged records for the cold front event and the tropical storm events due to the characteristics of cold front events and tropical storm events. These differences are:

**•** Cold fronts have wide influence zones where the passages of the cold fronts are wider and the large areas immediately behind the cold front may have a significant flagged frac‐ tion of weather stations. The influence zones of the tropical storms are smaller where only the stations along the storm route and the neighboring stations have flags.

**5.6. Resetting the flags for cold front events and hurricanes**

standard deviation of the temperature change can be calculated as:

Some measurements during the cold front and the hurricane were valid but flagged as outliers due to the effect of QC tests during times of large temperature changes caused by the cold front passages and the heavy precipitation occurring in hurricanes. A simple spatial scheme was de‐ veloped to recognize regions where flags have been set due to Type I errors. The stations along the cold front may experience the mixed population where some stations have been affected by the cold fronts and others have not. A complex pattern recognition method can be applied to identify the influence zone of the cold fronts through the temperature changes (e.g. using some methods described in Jain et al, 2000). In our work, we use the simple rule to reset the flag given that significant temperature changes occur when the cold front passes. The mean and the

> 1 1 *<sup>n</sup>*

<sup>1</sup> \* \*

change at the*i* th station for the current day, *n* is the number of neighboring stations, and *σΔ<sup>T</sup>* is the standard deviation of the temperature change for the current day. A second round test

where*ΔT* is the difference between maximum/minimum air temperature for the current day and the last day. The cutoff value *f'* takes a value of 3.0. The test results with this refinement for Tmax are shown in Fig. 7 for Oct. 7, 1990. The results obtained using the refinements de‐ scribed in this section were labeled "modified SRT" and the results using the original SRT were labeled "original SRT" in Fig. 7 and 8. Of the 291 flags originally noted only 41 flags

For the heavy precipitation events, we compare the amount of precipitation at neighboring stations to see whether heavy precipitation occurred. We use a similar approach as for tem‐ perature to check the number of neighboring stations that have significant precipitation,

( ) *i threshold*

*i T T n* <sup>=</sup>

( ) <sup>2</sup> 0

*T* is the mean temperature change of the reference stations, *ΔTi*

' ' D - £D £D + *Tf T Tf*

s

remain after the reset phase. The daily temperature drops more than 20 o

*n T i i i*

=

*n*

sD

is applied to records that were flagged in the first round:

where the flags were reset and the largest drop is 55 o

z

where *<sup>Δ</sup>*¯

*i*

*TT TT*

 s

F.

= ³ *count p p* (10)

D= D å (7)

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http://dx.doi.org/10.5772/51632

17

= D D -D D å (8)

D D *T T* (9)

is the temperature

F at most stations

**•** Cold fronts exert influences on both the air temperature and precipitation. The temper‐ ature differences between the regions immediately ahead of the cold fronts and regions behind can reach 10~20 o C. The precipitation events caused by the cold fronts may be significant, depending on the moisture in the atmosphere during the passage. The trop‐ ical storms generally produce a significant amount of precipitation. A few inches of rainfall in 24 hours is very common along the track because the tropical storms general‐ ly carry a large amount of moisture.

**Figure 6.** Spatial patterns of flagged records for cold front events and related fronts. The temperature map is the in‐ terpolated maximum temperature difference between October 6 and October 7, 1990. The color front is on October 7, and the black one is on October 6. The flags are the QA failures on that day.

#### **5.6. Resetting the flags for cold front events and hurricanes**

tion of weather stations. The influence zones of the tropical storms are smaller where only

**•** Cold fronts exert influences on both the air temperature and precipitation. The temper‐ ature differences between the regions immediately ahead of the cold fronts and regions

significant, depending on the moisture in the atmosphere during the passage. The trop‐ ical storms generally produce a significant amount of precipitation. A few inches of rainfall in 24 hours is very common along the track because the tropical storms general‐

**Figure 6.** Spatial patterns of flagged records for cold front events and related fronts. The temperature map is the in‐ terpolated maximum temperature difference between October 6 and October 7, 1990. The color front is on October

7, and the black one is on October 6. The flags are the QA failures on that day.

C. The precipitation events caused by the cold fronts may be

the stations along the storm route and the neighboring stations have flags.

behind can reach 10~20 o

16 Practical Concepts of Quality Control

ly carry a large amount of moisture.

Some measurements during the cold front and the hurricane were valid but flagged as outliers due to the effect of QC tests during times of large temperature changes caused by the cold front passages and the heavy precipitation occurring in hurricanes. A simple spatial scheme was de‐ veloped to recognize regions where flags have been set due to Type I errors. The stations along the cold front may experience the mixed population where some stations have been affected by the cold fronts and others have not. A complex pattern recognition method can be applied to identify the influence zone of the cold fronts through the temperature changes (e.g. using some methods described in Jain et al, 2000). In our work, we use the simple rule to reset the flag given that significant temperature changes occur when the cold front passes. The mean and the standard deviation of the temperature change can be calculated as:

$$\overline{\Delta T} = \frac{1}{n} \sum\_{l=1}^{n} \Delta T\_l \tag{7}$$

$$\left| \sigma\_{\Delta T} \right|^2 = \frac{1}{n} \sum\_{l=0}^{n} \left( \Delta T\_l \, \text{\*} \, \Delta T\_l \right) - \overline{\Delta T} \, \text{\*} \, \overline{\Delta T} \tag{8}$$

where *<sup>Δ</sup>*¯ *T* is the mean temperature change of the reference stations, *ΔTi* is the temperature change at the*i* th station for the current day, *n* is the number of neighboring stations, and *σΔ<sup>T</sup>* is the standard deviation of the temperature change for the current day. A second round test is applied to records that were flagged in the first round:

$$
\overline{\Delta T} - f' \sigma\_{\Lambda \overline{I}} \le \Delta T \le \overline{\Delta T} + f' \sigma\_{\Lambda \overline{I}} \tag{9}
$$

where*ΔT* is the difference between maximum/minimum air temperature for the current day and the last day. The cutoff value *f'* takes a value of 3.0. The test results with this refinement for Tmax are shown in Fig. 7 for Oct. 7, 1990. The results obtained using the refinements de‐ scribed in this section were labeled "modified SRT" and the results using the original SRT were labeled "original SRT" in Fig. 7 and 8. Of the 291 flags originally noted only 41 flags remain after the reset phase. The daily temperature drops more than 20 o F at most stations where the flags were reset and the largest drop is 55 o F.

For the heavy precipitation events, we compare the amount of precipitation at neighboring stations to see whether heavy precipitation occurred. We use a similar approach as for tem‐ perature to check the number of neighboring stations that have significant precipitation,

$$
\zeta = \text{count}(p\_i \ge p\_{\text{threshold}}) \tag{10}
$$

where the *p <sup>i</sup>* is the daily precipitation amount at a neighboring station, and *p threshold* is a threshold beyond which we recognize that a significant precipitation event has occurred at the neighboring station, e.g. 1 in. When *ζ* ≥2and*p phigh* , we reset the flag. Here *p* is the precip‐ itation amount of the current station, and *p high* is the upper threshold beyond which the threshold will flag the measurement. Fig.8 shows maps of flags after the reset process. Of the 78 flags originally noted only 41 flags remain after the reset phase. Most of the remain‐ ing flags are due to the precipitation being higher than the upper threshold.

Flags for the Andrew 1992 hurricane. The flags are the cumulative flags starting from Aug. 20 to Aug. 29, 1992. The flags by the modified SRT method overlay the flags by the

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19

**6. Multiple interval methods based on measurements from reference**

based on the empirical statistical distributions underlying the observations.

precipitation and is inefficient in identifying the outliers.

sults in fewer Type I errors than the other methods.

One QC approach involved developing threshold quantification methods to identify a sub‐ set of data consisting of potential outliers in the precipitation observations with the aim of reducing the manual checking workload. This QC method for precipitation was developed

The search for precipitation quality control (QC) methods has proven difficult. The high spatial and temporal variability associated with precipitation data causes high uncertainty and edge creep when regression-based approaches are applied. Precipitation frequency dis‐ tributions are generally skewed rather than normally distributed. The commonly assumed normal distribution in QC methods is not a good representation of the actual distribution of

The SRTmethod is able to identify many of the errant data values but the rate of finding er‐ rant values to that of making type I errors is conservatively 1:6. This is not acceptable be‐ cause it would take excessive manpower to check all the flagged values that are generated in a nationwide network. For example, the number of precipitation observations from the co‐ operative network in a typical day is 4000. Using an error rate of 2% and considering the type I error rate indicates that several hundred values may be flagged, requiring substantial

(29) found the use of a single gamma distribution fit to all precipitation data was ineffective. A second test, the multiple intervals gamma distribution (MIGD) method, was introduced. It assumed that meteorological conditions that produce a certain range in average precipita‐ tion at surrounding stations will produce a predictable range at the target station. The MIGD method sorts data into bins according to the average of precipitation at neighboring stations; then, for the events in a specific bin, an associated gamma distribution is derived by fit to the same events at the target station. The new gamma distributions can then be used to establish the threshold for QC according to the user-selected probability of exceed‐ ance. We also employed the *Q* test for precipitation (20) using a metric based on compari‐ sons with neighboring stations. The performance of the three approaches was evaluated by assessing the fraction of "known" errors that can be identified in a seeded error dataset(18). The single gamma distribution and *Q*-test approach were found to be relatively efficient at identifying extreme precipitation values as potential outliers. However, the MIGD method outperforms the other two QC methods. This method identifies more seeded errors and re‐

original SRT method.

**stations for precipitation.**

personnel resources for assessment.

**Figure 7.** All points shown were flagged by the original SRT method while the red points were those that are flagged by the modified SRT method for maximum daily Temperature. Blue symbols are those that are reset by the modified SRT method.

**Figure 8.** This is the reset of flags for the Andrew 1992 hurricane. The flags are the cumulative flags starting from Aug. 20 to Aug. 29, 1992. The flags by the modified SRT method overlay the flags by the original SRT method.

Flags for the Andrew 1992 hurricane. The flags are the cumulative flags starting from Aug. 20 to Aug. 29, 1992. The flags by the modified SRT method overlay the flags by the original SRT method.

where the *p <sup>i</sup>*

18 Practical Concepts of Quality Control

the modified SRT method.

is the daily precipitation amount at a neighboring station, and *p threshold* is a

threshold beyond which we recognize that a significant precipitation event has occurred at the neighboring station, e.g. 1 in. When *ζ* ≥2and*p phigh* , we reset the flag. Here *p* is the precip‐ itation amount of the current station, and *p high* is the upper threshold beyond which the threshold will flag the measurement. Fig.8 shows maps of flags after the reset process. Of the 78 flags originally noted only 41 flags remain after the reset phase. Most of the remain‐

**Figure 7.** All points shown were flagged by the original SRT method while the red points were those that are flagged by the modified SRT method for maximum daily Temperature. Blue symbols are those that are reset by

**Figure 8.** This is the reset of flags for the Andrew 1992 hurricane. The flags are the cumulative flags starting from Aug.

20 to Aug. 29, 1992. The flags by the modified SRT method overlay the flags by the original SRT method.

ing flags are due to the precipitation being higher than the upper threshold.


*2.1. Technical Approach*

A collection of machine tools available at OMAX, CBA, and other facilities were selected for the project. One of the early tasks was to define a reference part that was suitable to be machined and/or fabricated with all the selected machine tools. A decision was made to use one the flexures investigated at NASA/JPL as a key component of prototype microsplines for asteroid grippers developed under the Asteroid Redirect Mission [5,6]. As shown in Figure 1, the flexure consists of 11 full-length and 2 half-length spring-like elements. The length and width of the flexure elements were 36.3 mm and 0.5 mm, respectively. The separation between each element was 0.76 mm. The aspect ratio (length/width) was therefore 72.6. The widths of the element and gap between them are 0.51 mm and 0.76 mm, respectively. The aspect ratios of the length-to-width and length-to-thickness were 71.5 and 47.7. The above are the dimensions of the full-scale flexure. Small-scale flexures with 0.5, 0.4, and 0.33 were also machined using several tools. The flexure is extremely delicate and flexible. It took only very weak side force exerted onto the flexure element during machining to deflect them permanently. During the course of machining, strengthening tabs were used to support the delicate elements (Figure 1a). Figure 1b shows the tool path with several color coded curves: green—traverse without cutting, magenta—lead in and out, and blue—cut at quality five level. The tool path shown in Figure 1b included two steps: (1) machine the flexure with the tabs in place and (2) remove the tabs. Figure 1c shows the final part with the tabs removed.

(**c**) Finish Flexure

**Figure 1.** DXF of flexure selected as the reference part for the MicroCutting Project.

The flexure, machined or fabricated from materials that were most suitable for the individual tools, were then inspected qualitatively and quantitatively to compare the performances of these machine tools.

#### *2.2. Micro Abrasive Waterjet Technology*

The AWJ is amenable to micromachining as the diameter of the AWJ can potentially reduce to micro scales [7]. The μAWJ technology was developed and commercialized under the support of an SBIR Phase II/IIB grant. Several novel processes were developed and incorporated into the MicroMAX for meso-micro machining of 2D and 3D parts. The main focus was to downsize the AWJ nozzle capable of meso-micro machining. As such, several challenges were present as the three-phase, supersonic slurry flow inside the nozzle transitions from a gravity-dominated flow to a microfluidic flow. Novel processes and apparatus were developed to enable μAWJ technology for industrial applications [4].

At present, the 7/15 nozzle with an orifice and a mixing tube ID of 0.007" (0.18 mm) and 0.015" (0.38 mm) is the smallest production nozzle whereas the 5/10 nozzle is currently used for special applications. Garnet with 240 mesh can be readily used with these nozzles. For garnets finer than 240 mesh, a proprietary process was developed to enhance their flowability. Success in developing the AWJ technology led to the culmination in the release of the MicroMAX as a new product debuted in 2013. It has a position accuracy and repeatability of 15 μm and 5 μm, respectively. A MicroMAX

version II with the incorporation of a Rotary Axis for machining axisymmetric features was released for production in 2016.

## *2.3. Machine Tools and Participants*

The participants in the Microcutting Project included MIT/CBA (www.cba.mit.edu), OMAX (www.omax.com), Formlabs (www.formlabs.com), Datron (www.datron.com/), (Moog Inc. (http: //www.moog.com/), and BMF Precision Technology Co, Ltd. (http://bmftec.com/). Machine tools available at the facilities of the participants and used in the project included CBA Digital Fabrication Facility (http://cba.mit.edu/tools/index.html) Beam Dynamics Model LMC10000 CO2 laser system— 1.2 m × 1.2 m cutting area, 30.5 m vertical travel, 500 w (1550 W peak), 25 μm overall accuracy, 51 m/min max cutting speed (91 m/min traverse speed) Sodick SL400G Wire EDM—X, Y, Z Axis travel, 400 × 300 × 250 mm; wire diameter range: 0.051 to 0.30 mm.

Zund G-3 L-2500—Repeatability ± 0.03 mm, position accuracy ± 0.1 mm/m, working area 1800 mm × 2500 mm, high speed router 3.6 kW 50,000 rpm.

FabLight 3000 Fiber Laser—3 kW laser, working area of 6.35 m × 1.27 m and tubes of diameter 12.7 mm to 5.1 mm. Capable of cutting steel, stainless steel, spring steel, aluminum, copper, brass, titanium. Repeatability of 15 μm, accuracy of ± 20 μm/m.

Oxford Solid State Micromachining Laser—532 nm diode-pumped solid-state laser, 150 mm X-Y travel, 50 mm Z travel, 1 micron resolution. It has spot size of approximately 20 microns. The laser outputs approximately 6W of power at 10 kHz and can quickly cut through materials typically up to 0.5 mm thick. It's used for fine cutting, ablation, engraving, and marking

OMAX 5555 JetMachining Center at CBA—X-Y Travel 1.4 × 1.4 m, Tilt-A-Jet, MAXJET 5i Nozzle (10/21), 7/15 Mini MAXJET 5 Nozzle, Precision Optical Locator, pneumatic drill OMAX Corporation MicroMAX—A MicroMAX equipped with a Tilt-A-Jet (TAJ), a Rotary Axis (RA), and a Precision Optical Locator (POL) is available at the OMAX facility (https://www.omax.com/omax-waterjet/micromax). For meso-micro machining, the 7/15 and 5/10 nozzles have been used routinely for cutting demo parts and conducting in-house R&D. The nozzles were driven by an EnduroMAX 40 hp crankshaft pump (Model 4060V) with pressures up to 410 MPa. For these small nozzles, an excess flow control valve was installed to drain a part of the water through the high-pressure pump. At pressures below about 70 MPa, the Bernoulli vacuum was too weak to entrain all the abrasive into the mixing chamber. Vacuum Assist accessory was used to remove the excessive abrasive to mitigate clogging of the nozzle.

AWJ machining was controlled by an IntelliMAX Software Suite featuring an extensive tool set to streamline production. The Suite is based on a precision cutting model in which each engineering material is assigned with a machineability index according to its properties derived from the results of extensive cutting tests. The intuitive Suite that is easy to use consists of a PC-based CAD-LAYOUT and CAM-MAKE. A set of steel slats spaced 25 mm apart is installed inside each JetMachining Center to support the workpiece. A 10 cm thick polyurethane honeycomb placed on top of the slats is often used to provide a firm support to workpieces made from thin materials. Since the AWJ exerts very low force onto the workpiece, it can be secured by relatively simple fixtures such as carpenter clamps. A number of options is available to secure the workpiece depending on the setup. For small parts, thin tabs are incorporated into the tool path to prevent losing it into the tank below. Machining is carried out by setting a standoff distance of 0.76 mm between the tip of the nozzle to the top surface of the workpiece. The tool offset is set to on half of the exit diameter of the AWJ. Depending on the thickness of the workpiece and the required edge quality of cut from Q1 for raw cut to Q5 for precision cut, the cutting speed is set intelligently by MAKE according to the machineability index. The cutting speed also varies according to the shape and curvature of the tool path. For example, the traverse of the nozzle speeds up in straight segments and slows down during corner passing to maintain the same kerf width.

Formlabs-Form 2 Printer—Build Volume: 145 ×145 ×175 mm, Layer Thickness: 25, 50, 100 microns, Laser Spot Size: 140 μm, Laser Power: 250 mW, Wavelength: 405 nm (violet), automated resin system, self-heating resin tank, auto-generated supports. Machine size: 350 mm (L) Ã—330 mm (W) Ã—520 mm (H). *JMMP* **2020**, *4*, 19

Moog, Inc. —These parts were made from metal powders, an aluminum alloy and stainless steel, using laser powder bed fusion. The equipment included:

They were then trimmed to correct thickness with a φ0.25-mm wire EDM (Mistsubishi MV2400S) for 30 min approximately.

Boston Micro Fabrication (BMF) Material Technology Inc.—Digital Lighting Processing (DLP), similar to Stereolithography Appearance (SLA), was used to fabricate the flexures (https://web.archive. org/web/20140221025534/, https://thre3d.com/how-it-works/light-photopolymerization/digital-lightprocessing-dlp). It is a 3D printing process working with photopolymers. In DLP, a 3D model is constructed and 'sliced' through software. Once the sliced images are received by the printer, curable liquid, e.g. monomer or pre-cured resin, is exposed to a pattern of UV-light, in order to selectively solidify a cross-section of the designed parts. The cured cross-section is then lowered below the surface level of the liquid, allowing the liquid to backfill for curing and bonding of subsequent cross-sections. The process is repeated until all the slices of the 3D model and hence the printing parts are completed. The liquid is then drained from the vat, followed by demolding and post-curing of the parts. The nanoArch Micro Scale 3D Printing System InP140 (https://bmftec.com/) nanoArch®is the first commercialized high resolution, multimaterial 3D micro-fabrication equipment based on PμLSE (Projection Micro Litho Stereo Exposure) technology, which is designed for scientific R&D of functional composite materials.

Datron-Neo Milling Machine (https://www.datron-neo.com/us/datron-neo-simple-milling/ overview/). Masking tapes and super glue were used to secure the workpiece onto the substrate.


**6. Conclusions**

The following conclusions can be drawn from this study:

**Author Contributions:** Conceptualization, M.W. and J.F.; methodology and investigation, M.W., G.S., P.D., N.G. and P.T., writing—original draft preparation, M.W.; visualization, M.W.; supervision, J.F. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data supporting findings of this study is contained within this article.

**Acknowledgments:** The publication cost of this paper was covered with funds provided by the Polish National Agency for Academic Exchange (NAWA): "MATBUD'2023—Developing international scientific cooperation in the field of building materials engineering" BPI/WTP/2021/1/00002, MATBUD'2023.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.


**2.2. Squirting cucumber (***Ecballium elaterium* **(L.) A. Rich.) fruit juice**

2105.74 μg of chlorophyll/g fresh tissue, respectively, for the treatment with a magnetic field

**Figure 2.** The effect of a magnetic field strength of 150 mT applied to potato tubers for different periods (a. 0 h, b. 24 h, c.

48 30.75 d 40.25 d 1327.69 e 72 29.25 d 42.45 d 1321.12 e

48 21.25 b 88.27 a 2000.27 ab 72 17.00 a 90.78 a 2105.74 a

48 26.25 c 77.27 b 1558.34 d 72 20.50 b 78.00 b 1789.46 c

**Table 3.** The effect of different magnetic field strengths applied to potato tubers for different periods of time on the day

**sprouts Plant height (cm) Total chlorophyll content (μg**

**chlorophyll/g fresh tissue)**

**Day of emergence of**

0—control 0 39.50 e 25.56 e 1127.46 g 75 24 31.25 d 39.00 d 1214.56 f

150 24 26.00 c 80.35 b 1927.36 b

300 24 31.00 d 75.76 c 1500.48 d

Each value is the mean of five replications. All experiments were repeated two times. Values within a column followed by different letters are significantly different at the 0.01 level.

of emergence of sprouts, plant height, and total chlorophyll content in cv. "Marabel".

strength of 150 mT for 72 h (**Table 3** and **Figure 2**).

48 h and d. 72 h) on plant development in cv. "Marabel".

**Treatment period (h)**

**Magnetic field strength (mT)**

90 Advances in Seed Biology

Squirting cucumber (*Ecballium elaterium* (L.) A. Rich.), which is commonly found in Turkey, is an important medicinal plant [29]. It contains different compounds such as α-elaterin (cucurbitacin E), β-elaterin (cucurbitacin B), elatericine A [30], and elatericine B (cucurbitacin I) in different plant organs [31]. It also contains sterols, phenolic compounds, vitamins, flavonoids, alkaloids, resin, starch, amino acids, and fatty acids [31]. *In vitro* regeneration was affected significantly by squirting cucumber fruit juice [32]. It was also reported that squirting cucumber fruit juice stimulated rapid germination and seedling growth in rapeseed [33].

Mature squirting cucumber fruits were collected from their natural growing areas around Ankara. Fruit juice was extracted and then filtered in order to remove the bigger parts. The fruit juice was subject to sterile filtration and kept in the refrigerator at −20°C.

In a study conducted for overcoming dormancy in cv. "Marabel" potato tubers using squirting cucumber mature fruit juice, tubers at 40–60 g in weight were rinsed for 6 h at 180 rpm in bottles containing water with different concentrations of mature squirting cucumber fruit juice (0-control, 200, 400, 800, and 1600 μl/L). Then, the tubers were planted in pots. Ten pots were used for each concentration, and one tuber was put in each pot. A pot was considered an experimental unit. The study used two parallel treatments according to the Completely Randomized Design concept. Data were statistically analyzed by Duncan's multiple range test using IBM SPSS Statistics 22 software. Values presented in percentages were subjected to arcsine (√*X*) transformation before statistical analysis [19].

Results clearly showed that squirting cucumber fruit juice had a significant role in overcoming dormancy in potato tubers. The best result was recorded at a concentration of 800 μl/L of fruit juice as 16.25 days. That meant that the sprouts of tubers treated with 800 μl/L of fruit juice emerged above the ground 16.25 days after planting. In contrast, in the control treatment where no fruit juice was used, sprouts emerged above ground later than the other treatments. From the results of the study, it could be concluded that squirting cucumber fruit juice stimulated sprout development by overcoming dormancy in potato tubers (**Table 4**).

In **Figure 3**, plant development was recorded for tubers treated with different concentrations of squirting cucumber fruit juice at the end of the 45th day. For a concentration of 800 μl/L of fruit juice, the plants grew better than any of the others. Squirting cucumber fruit juice at a concentration of 800 μl/L encouraged plants to develop faster and with more energy by overcoming dormancy in tubers. At this concentration, plants had more branches and leaves.

#### **2.3. Sodium hypochlorite solutions**

Sodium hypochlorite (NaOCl) has been most widely used for surface sterilization. NaOCl is highly effective against all kinds of bacteria, fungi, and viruses [34, 35]. Moreover, NaOCl has strong oxidizing properties that make it highly reactive with amino acids [36, 37], nucleic acids [38], amines, and amides [39, 40].

The most important treatment prior to culture initiation is perhaps surface-sterilization of the explant. Since *in vitro* conditions provide bacteria and fungi with an optimal growth

Each value is the mean of five replications. All experiments were repeated two times. Values within a column followed by different letters are significantly different at the 0.01 level.

**Table 4.** The effect of different concentrations of squirting cucumber fruit juice on the day of emergence of sprouts in potato cv. "Marabel".

**Figure 3.** Plant development at the 45th day for potato tubers of the cv. "Marabel" treated with different concentrations of squirting cucumber fruit juice.

environment, unsuccessful sterilization hinders the progress of tissue culture studies. On the one hand, sterilization of the tissue aims to eliminate all microorganisms that can easily grow *in vitro* conditions; on the other hand, it should guarantee the explant's viability and regeneration capacity, which are known to be affected by the concentration, treatment period [41], and temperature of the disinfectant [42].

NaOCl can also be used for overcoming dormancy [43–45] by decomposing germination inhibitors [46], scarifying the seed coat [42, 47], and increasing α-amylase activity [48].

In the study conducted by Telci et al. [49], sodium hypochlorite (NaOCl) solution was successfully used to overcome dormancy in the seeds of *Lathyrus chrysanthus* Boiss., which is used as an ornamental plant with its big, colorful flowers. In the study, *L. chrysanthus* Boiss. seeds of an ecotype (Diyarbakir) from southeast Turkey were treated with a 3.75% NaOCl solution at three different temperatures (25, 35, and 45°C) for 15 min with continuous stirring. This was followed by rinsing three times with sterile water. Seeds were then germinated on a basal medium containing Murashige and Skoog's (MS) mineral salts and vitamins [50], 3% sucrose, and 0.7% agar in Magenta vessels (15 × 15 cm). The pH of the medium was adjusted to 5.8 prior to autoclaving. For seed germination, cultures were incubated at 15±1°C in the dark for 5 days. Then, all cultures were transferred to a growth chamber for incubation at 25±1°C under cool white fluorescent light (27 μmol m−2 s−1) with a 16-h light/8-h dark photoperiod. Seed germination and seedling growth percentages were recorded after 5 and 14 days following culture initiation, whereas seedling height and root length, seedling fresh and dry weights, chlorophyll a, chlorophyll b, and total chlorophyll contents were noted 28 days after culture initiation. The chlorophyll contents were determined in the leaves of seedlings according to the protocol of Curtis and Shetty [21]. All statistical analyses were performed using SPSS for Windows software. Three replicates were tested. Petri dishes (100 × 10 mm) were considered the units of replication, and there were 30 seeds per replication. All experiments were repeated twice. One-way Analysis of Variance (ANOVA) was used to test the effect of the 3.75% NaOCl solution at different temperatures. Duncan's multiple range test was used for comparing the means. Data given in percentages were subjected to arcsine (√*X*) transformation before statistical analysis [19].

The lowest values were recorded in a 3.75% NaOCl solution at a 45°C temperature. Low results at 45°C could be attributed to the fact that the activity of NaOCl increases [51], and it penetrates more easily through the seed coat [52]. The highest results in all characteristics examined were obtained from a 3.75% NaOCl solution at 35°C. Seed germination and seedling growth percentages decreased to 67.76 and 53.53% at 45°C, while they were 88.74 and 77.74% in a 3.75% NaOCl solution at 35°C. Seedling height and root length were 6.77 and 9.26 cm in a 3.75% NaOCl solution at 35°C temperature (**Table 5** and **Figure 4**). These findings were parallel to those of Hsiao and Hans [53], Hsiao and Quick [54], and Yildiz and Er [42] who reported that disinfectants at high concentrations and high temperatures affected seed germination and seedling growth negatively.

The highest seedling fresh and dry weights and tissue water content were recorded when seeds were treated with a 3.75% NaOCl solution at 35°C for 15 min (**Table 5**). The fresh weight

environment, unsuccessful sterilization hinders the progress of tissue culture studies. On the one hand, sterilization of the tissue aims to eliminate all microorganisms that can easily grow *in vitro* conditions; on the other hand, it should guarantee the explant's viability and regeneration capacity, which are known to be affected by the concentration, treatment period

**Figure 3.** Plant development at the 45th day for potato tubers of the cv. "Marabel" treated with different concentrations

**Table 4.** The effect of different concentrations of squirting cucumber fruit juice on the day of emergence of sprouts in

**Concentration of squirting cucumber fruit juice (μl/L) Day of emergence of sprouts**

0—control 31.50 c 200 23.00 bc 400 22.00 bc 800 16.25 a 1600 20.00 b

potato cv. "Marabel".

92 Advances in Seed Biology

Each value is the mean of five replications. All experiments were repeated two times. Values within a column followed by different letters are significantly different at the 0.01 level.

NaOCl can also be used for overcoming dormancy [43–45] by decomposing germination

In the study conducted by Telci et al. [49], sodium hypochlorite (NaOCl) solution was successfully used to overcome dormancy in the seeds of *Lathyrus chrysanthus* Boiss., which is used as an ornamental plant with its big, colorful flowers. In the study, *L. chrysanthus* Boiss. seeds of an ecotype (Diyarbakir) from southeast Turkey were treated with a 3.75% NaOCl solution at three different temperatures (25, 35, and 45°C) for 15 min with continuous stirring. This was followed by rinsing three times with sterile water. Seeds were then germinated on a basal medium containing Murashige and Skoog's (MS) mineral salts and vitamins [50], 3%

inhibitors [46], scarifying the seed coat [42, 47], and increasing α-amylase activity [48].

[41], and temperature of the disinfectant [42].

of squirting cucumber fruit juice.

Values in a column followed by different letters are significantly different at the 0.01 level in germination percentage, root length, seedling fresh, and dry weights and chlorophyll a content, while significantly different at the 0.05 level in seedling growth, seedling height, chlorophyll b, and total chlorophyll contents. 1 Seedling growth means seedlings developed out of the total germinated seeds.

**Table 5.** The effects of a 3.75% NaOCl solution at different temperatures on *in vitro* seed germination, seedling growth, seedling height, root length, seedling fresh and dry weights, chlorophyll a, chlorophyll b, and total chlorophyll contents in the leaves of *L. chrysanthus* Boiss. seedlings.

**Figure 4.** *In vitro* seedling growth from *L. chrysanthus* Boiss. seeds treated with a 3.75% NaOCl solution at temperatures of (a) 25°C, (b) 35°C and (c) 45°C for 15 min.

increase could be attributed to cell enlargement [55]. The increase in dry weight was due to cell division and new material synthesis [56]. Higher results in seedlings grown were from seeds treated with 3.75% NaOCl solution at 35°C for 15 min and could be caused by higher tissue water content as reported that *in vitro* explant growth and plantlet establishment have been affected significantly by tissue water content [57].

In the study, the highest chlorophyll a, chlorophyll b, and total chlorophyll contents were seen with a 3.75% NaOCl solution at 35°C temperature (**Table 5**).

#### **2.4. Gamma radiation**

Gamma rays have an ionizing radiation effect on plant growth and development by inducing cytological, biochemical, physiological, and morphological changes in cells and tissues by producing free radicals in cells [58–60]. Higher doses of gamma radiation have been reported to be inhibitory [61, 62], whereas lower doses are stimulatory. Low doses of gamma rays have been reported to increase seed germination and plant growth, cell proliferation, germination, cell growth, enzyme activity, stress resistance, and crop yields [63–69]. Stimulation of plant growth at low gamma radiation doses is known as hormesis [70]. The hormesis phenomenon is described as a stimulating effect on any factor in the growth of an organism [71].

In the study conducted by Beyaz et al. [72], the effects of gamma radiation on overcoming dormancy in seeds of *L. chrysanthus* Boiss. under *in vitro* conditions were examined. In the study, *L. chrysanthus* Boiss., seeds of an ecotype "Diyarbakir" were first irradiated with different doses (0-control, 50, 100, 150, 200, and 250 Gy) of 60Co γ rays at 0.8 kGy h−1 at the Sarayköy Nuclear Research and Training Center of the Turkish Atomic Energy Authority at Sarayköy, Ankara. Seeds were surface-sterilized with a 3.75% NaOCl solution at 35°C temperature for 15 min. as reported by Telci et al. [49]. The seeds were then placed between filter papers in Petri dishes each containing 6 ml of distilled water. The Petri dishes were incubated for 7 days at 15±1°C in the dark for seed germination. The pre-germinated seeds were then transferred to Magenta vessels (12 × 12 cm) containing a basal medium of Murashige and Skoog's (MS) mineral salts and vitamins [50], 3% sucrose, and 0.7% agar 14 days after the study initiation. The pH of the medium was adjusted to 5.8 prior to autoclaving. Then, all cultures were transferred to a growth chamber for incubation at 25±1°C under cool white fluorescent light (27 μmol m−2 s−1) with a 16-h light/8-h dark photoperiod. The seed germination percentage was determined at the end of the 7th day, while seedling growth percentage, seedling height, and root length were recorded 14 days after culture initiation [20]. All statistical analyses were performed using SPSS for Windows software. Three replicates were tested, and there were 30 seeds per replication. All experiments were repeated twice. One-way Analysis of Variance (ANOVA) was used to test the effect of different doses of gamma radiation on seed germination and seedling growth. Duncan's multiple range test was used for comparison of the means. Data given in percentages were subjected to arcsine (√*X*) transformation before statistical analysis [19].

The stimulatory effect of low gamma doses was observed in the study at a radiation dose of 150 Gy. The best results in seed germination percentage at the end of the 7th day and in seedling growth percentage, seedling height, and root length at the end of the 14th day were observed at a dose of 150 Gy of gamma radiation (**Table 6** and **Figure 5**). In doses over 150 Gy, the inhibitory effect of gamma radiation was seen. Seed germination percentage was 62.4% at a gamma radiation dose of 150 Gy, while it was 14.3% for a gamma radiation dose of 250 Gy (**Table 6**). The highest seedling growth percentage, seedling height, and root length were again recorded for a 150 Gy gamma radiation dose as 75.7%, 1.2 cm, and 2.9 cm, respectively.

increase could be attributed to cell enlargement [55]. The increase in dry weight was due to cell division and new material synthesis [56]. Higher results in seedlings grown were from seeds treated with 3.75% NaOCl solution at 35°C for 15 min and could be caused by higher tissue water content as reported that *in vitro* explant growth and plantlet establishment have

**Figure 4.** *In vitro* seedling growth from *L. chrysanthus* Boiss. seeds treated with a 3.75% NaOCl solution at temperatures

In the study, the highest chlorophyll a, chlorophyll b, and total chlorophyll contents were seen

Gamma rays have an ionizing radiation effect on plant growth and development by inducing cytological, biochemical, physiological, and morphological changes in cells and tissues by producing free radicals in cells [58–60]. Higher doses of gamma radiation have been reported to be inhibitory [61, 62], whereas lower doses are stimulatory. Low doses of gamma rays have been reported to increase seed germination and plant growth, cell proliferation, germination, cell growth, enzyme activity, stress resistance, and crop yields [63–69]. Stimulation of plant growth at low gamma radiation doses is known as hormesis [70]. The hormesis phenomenon

In the study conducted by Beyaz et al. [72], the effects of gamma radiation on overcoming dormancy in seeds of *L. chrysanthus* Boiss. under *in vitro* conditions were examined. In the study, *L. chrysanthus* Boiss., seeds of an ecotype "Diyarbakir" were first irradiated with different

is described as a stimulating effect on any factor in the growth of an organism [71].

been affected significantly by tissue water content [57].

**2.4. Gamma radiation**

of (a) 25°C, (b) 35°C and (c) 45°C for 15 min.

94 Advances in Seed Biology

with a 3.75% NaOCl solution at 35°C temperature (**Table 5**).

Values in a column followed by the different letters are significantly different at the 0.01 level. 1 Seedling growth percentage means seedlings developed out of the total seed number.

**Table 6.** Effects of different gamma doses on *in vitro* seed germination, seedling growth, seedling height, and root length in *L. chrysanthus* Boiss.

**Figure 5.** *In vitro* seed germination and seedling growth in *L. chrysanthus* Boiss. seeds irradiated with (a) 0, (b) 50, (c) 100, (d) 150, (e) 200, and (f) 250 Gy gamma doses (white vertical bar = 1 cm).

The root length obtained from seeds irradiated with 150 Gy of gamma radiation was significantly increased by 63.2% from 1.8 cm in the control treatment (0 Gy) to 2.9 cm, which has been confirmed by Melki and Marouani [73].


**Acknowledgements**

The authors would like to thank the staff and leaders at the school who have worked and are still working with us in the project "Value lift and the edifying mission of education". Their willingness to enter into challenging philosophical dialogs, and to contribute to the research and pedagogical development work, is pivotal to this article. Moreover, we would like to thank the University of Southeastern Norway, who has given us time to work on the project and write up the research. Moreover, our institution has provided the funding needed for this article to be published. Finally, we would like to thank Mia Vukovis in IntechOpen, and academic editor María Jose Hernandez-Serrano from the University of Salamanca, Spain, for the invitation to contribute to this important book.

### **Author details**

Eirik Hæreid Marcussen, Michael Weiss and Guro Hansen Helskog\* University of South Eastern Norway, Drammen, Norway

\*Address all correspondence to<EMAIL_ADDRESS>
© 2021 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.

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*DOI: http://dx.doi.org/10.5772/intechopen.96198*

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*How Philosophizing the Dialogos Way Can Promote Education for Sustainable Development DOI: http://dx.doi.org/10.5772/intechopen.96198*


**3. Design of Secured Cloud Storage Mechanism**

The architecture of a secure cloud TRA is explained in **Figure 2**. Movable equipment and the remote systems are connected to the mobile machinist and wireless access point. These are connected to either an entry point or satellite via the base station. The mobile user's request and response are delivered to cloud banking through the presently available SSL VPN with an additional layer of protection from ECC. **Figure 2** Architecture of secure TRA [1].

Central processors that are linked to the mobile network receive the mobile users' requests as well as send details such as user IDs and user location to banking database storage. The projected security theory enhances the level of protection that currently supports mobile banking and facilitates the realization of P2P networks.

The following are the objectives of the proposed framework:

• Assuring information security and privacy protection of entire mobile/remote user's activities in the cloud. ECC-based SSL VPN.

**Figure 2.** *Architecture of secure TRA.*

• ECC encryption helps to provide less bandwidth, computing power, and memory for creating customized security for data packets.


**Author details**

Julio Emmanuel González-Pérez, Nelly Ramírez-Corona and Aurelio López-Malo\* Department of Chemical, Food, and Environmental Engineering, Universidad de las Américas Puebla, Ex Hacienda Santa Catarina Mártir, Puebla, Mexico

\*Address all correspondence to<EMAIL_ADDRESS>
© 2022 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.

*Modeling of Drying Kinetics of Fresh and Osmodehydrated Apples during Convective Drying DOI: http://dx.doi.org/10.5772/intechopen.105162*