**A Study on the Application Possibility of the Vehicle Air Conditioning System Using Vortex Tube**

### **Younghyeon Kim 1, Seokyeon Im 2,\* and Jaeyoung Han 3,\***

Received: 9 August 2020; Accepted: 7 October 2020; Published: 8 October 2020

**Abstract:** Since refrigerants applied to vehicle air conditioning systems exacerbate global warming, many studies have been conducted to supplement them. However, most studies have attempted to maximize the efficiency and minimize the environmental impact of the refrigerant, and thus, an air conditioning system without refrigerant is required. The vortex tube is a temperature separation system capable of separating air at low and high temperatures using compressed air. When applied to an air conditioning system, it is possible to construct an eco-friendly system that does not use a refrigerant. In this paper, various temperature changes and characteristics of a vortex tube were identified and applied to an air conditioning system simulation device. Additionally, an air conditioning system simulation device using indirect heat exchange and direct heat exchange methods was constructed to test the low-temperature air flow rate (yc), according to the temperature and pressure. As a result of the experiment, the temperature of the indirect heat exchange method was found to be higher than the direct heat exchange method, but the direct heat exchange method had low flow resistance. As a result, the direct heat exchange method can easily control the temperature according to the pressure and the low-temperature air flow rate (yc). Therefore, it was judged that the direct heat exchange method is more feasible for use in air conditioning systems than the indirect heat exchange method.

**Keywords:** vortex generator; vortex tube; temperature separation; the low-temperature air flow ratio (yc), inlet pressure (Pi)

### **1. Introduction**

With rapid industrialization, the share of fossil fuels has increased significantly from the beginning of the industrial revolution to the present, and as means of transportation and efficient heating and cooling systems have been developed, more environmental pollution has been produced. Furthermore, the excessive use of refrigerant has caused environmental problems such as ozone layer destruction and global warming, and the ripple effects are accelerating. Accordingly, restrictions on the use of CFC (Chloro Fluoro Carbon)-based refrigerants have been strengthened, and R134a has been developed as an alternative. This refrigerant has been applied to facilities such as automobile air conditioning systems and household refrigerators. However, while R134a has an ozone depletion index of 0, its global warming index of 1430 is insufficient to compensate for environmental problems [1,2]. As an alternative to solve the problems associated with freon (CFC) used as a refrigerant in automobiles, research has been actively conducted, where one possible measure is the vortex tube [3].

The vortex tube was discovered by Ranque in 1928 and has since become widely promoted to the academic community by Hilsch [4,5]. Thereafter, modeling studies were conducted by Fulton, Stephan, Deissler and Permuter, Kassner, Upendra, and Gao et al. for energy separation, and models proposed by Fulton and Kassner have been widely accepted [6–11]. Hilsch et al. experimented to find nozzle diameters and low-temperature exit conditions for three cases of tube radii of 4.6 mm, 9.6 mm, and 17.6 mm. Westley et al. conducted a study on vortex tube dimensional conditions to find the ratio of the tube area of the low-temperature air outlet area to the tube area of the nozzle's total area to spray compressed air into the tube [12]. Hartnett and Eckert et al. measured the tube velocity, pressure, and temperature distribution through experiments and found that the vortex tube had a high wall temperature and a low central temperature [13]. Takanama et al. designed the shape of a vortex tube with high energy efficiency by researching the relationship between the temperature and velocity distribution of air flowing in the vortex internal production chamber and the dimensions of the tube, nozzle, and low-temperature outlet orifice [14]. Comassar and Stepan et al. presented a single-flow vortex tube to evaluate the energy separation performance and confirmed that the counter-flow vortex tube performance was higher than the single-flow vortex tube [15,16]. Frohlingsdorf et al. analyzed energy separation and flow in a Ranque–Hilsch vortex tube using CFX, shear stress, and axial symmetry models [17]. Smith Eiamsa-ard et al. performed a thermal separation simulation of a Ranque–Hilsch vortex tube in a finite volume approach using a standard turbulence model and a logarithmic stress model (ASM) [18]. Skye et al. compared the performance predicted by the CFD model with commercial vortex tube experimental data and confirmed the industrial applicability of vortex tubes [19].

Until recently, studies on the industrial use of vortex tubes are ongoing, and experimental analysis of vortex tube energy separation phenomena and comparative analysis through models are continuously being studied [20–23]. B.E. Mtopi Fotso et al., and others, showed modeling and thermal analysis of solar generators equipped with vortex tubes for hybrid vehicles, showing the application of vortex tubes to vehicles [24]. Additionally, Hitesh R. Thakare et al. performed a technical and economic evaluation of the vortex tube's industrial applications to show that the industrial use of vortex tubes is advantageous for shortening production cycles [25].

In this study, the vortex tube was found to be eco-friendly because it does not require a refrigerant; and because it is sufficiently applicable to air conditioning systems in the future automobile field, a study was conducted to integrate a vortex tube into a vehicle air conditioning system. The experiment was performed by dividing it into two parts: an indirect heat exchange method and a direct heat exchange method. In particular, among the factors affecting the energy separation of the vortex tube, the temperature is controlled by controlling the supply pressure (Pi), the nozzle area ratio (Sn), and the number of nozzle holes (Nh) of the vortex tube generator, and the low-temperature air flow rate (yc) is controlled using a throttle valve. We obtained the experimental data for the four basic and influential characteristics in the characteristic experiment, and based on this, analyzed the optimum temperature characteristics by installing them in heat exchangers of different shapes using the indirect and direct methods.

### **2. Experimental Approach**

### *2.1. Principle of Vortex Tube*

The vortex tube is an energy separation device that separates compressed air into hot and cold air samples without chemical reaction or combustion. The vortex tube has a simple structure, but the cause and phenomenon of energy separation are complicated. In general, Fulton's theory describing the domains of free vortex and forced vortex is accepted. According to the theory, compressed fluid forms a free vortex with high velocity at the tangential nozzle of the tube.

$$wr^2 = const.\tag{1}$$

At this time, as the flow proceeds toward the throttle valve, the free vortex is the result of friction between the fluid layers, and a forced vortex is formed in the center of the tube.

$$w = \text{const.}\tag{2}$$

Due to this change in flow type, momentum transfer occurs from the center of the tube to the wall, and the center of the vortex is cooled more than the outside. However, to achieve energy balance, heat is transferred to the inner layer; however, since the momentum transfer is greater than the transfer of heat, the outside air temperature rises as does the stagnant temperature, and air is discharged through the throttle valve as a high-temperature flow. At this time, the fluid inside drops to a lower temperature by losing momentum greater than the received thermal energy, and becomes a low-temperature flow with temperature lower than the inlet temperature; this air is discharged to the outside through the low-temperature outlet orifice. Figures 1 and 2 clearly show the phenomenon of this vortex tube [26]. What is shown in the vertical direction in Figure 1 is a visual representation of the force magnitude in the vortex tangent direction.

**Figure 1.** Cross-section of the vortex tube in the "free" and "forced" vortex flow.

**Figure 2.** Supposed flow pattern and energy flow in the counter flow type.

### *2.2. Setup of Feasibility Study*

In this study, the vortex tube device was applied to a vehicle air conditioning system. Therefore, through a basic experiment with an actual manufactured vortex tube, it was confirmed whether energy separation had been properly performed; also, the number of nozzle holes (Nh) of the vortex generator was changed according to the supply pressure (Pi) to change the temperature according to

the low-temperature airflow ratio (yc). Schematics of the basic experimental device and the actual experimental device are shown in Figures 3 and 4.

**Figure 3.** Schematic diagram of the vortex tube system.

The specifications of the vortex tube produced in the experiment are shown in Table 1. The air conditioning system to be applied to the experiment was divided into two types: an indirect heat exchange method and a direct heat exchange method.

Compressed air that has undergone energy separation through the vortex tube first controls the temperature through a low-temperature and high-temperature valve, and this air is moved into the chamber through an indirect heater core where heat exchange is performed using a direct air conditioning filter. The temperature is measured. The heater core of the indirect heat exchanger used in the experiment is shown in Figure 5; the air conditioning filter of the direct heat exchanger is shown in Figure 6.

**Figure 4.** Photograph of the experimental apparatus for the vortex tube.

**Figure 5.** Indirect type heater core.

**Figure 6.** Direct type air conditioning filter.

#### *2.3. Experimental Apparatus*

Figures 7 and 8 show the schematic and actual experimental device for the indirect heat exchanger. Figures 9 and 10 show a schematic of the direct heat exchange method and an actual experimental device. Configurations of the experimental device for the vortex tube can be largely divided into three types: a supply unit that supplies compressed air, a test unit that performs temperature separation experiments, and a control unit that controls the system. The supply section consists of an air compressor, air dryer, air surge tank, and pressure regulator, which supplies compressed air. The test section consists of a vortex tube and a throttle valve, thermocouple, pressure gauge, flow meter, etc., that can control the low-temperature air flow rate (yc). The control part is composed of a part that controls pressure and flow rate and a part that checks data from each temperature sensor. The air entering the inlets (shown in Figures 7 and 9) is hot and cold air separated through the vortex tube; this air is supplied to each inlet. Table 2 shows the specifications of the device used in the experiment.

The compressed air produced by the compressor enters the surge tank. After enough air is present in the surge tank, it passes through the filter and is supplied to the vortex tube inlet. This phenomenon is a process that is conducted to catch the pulsation of the air generated by the compressor, and the following method was used to reduce the experimental error. Then, the supplied air passes through the vortex generator, and the vortex is generated inside the experimental apparatus. The generated vortex induces an energy separation phenomenon in the tube structure, and air separates into hot air and cold air and is discharged. Each type of air is then heat exchanged through the heater core. The air that has undergone heat exchange and the outside air are mixed in the chamber; according to the flow of the air, the experiment was performed by dividing it into indirect and direct methods. If there was no difference of 0.1 ◦C for 100 s, the temperature was determined to be in a normal state, and the corresponding temperature was measured. In addition, the reliability of the experimental results was secured through repeated experiments.

**Figure 7.** Schematic diagram of the indirect heater core.

**Figure 8.** Photograph of an indirect experimental device with a heater core.

**Figure 9.** Schematic diagram of the direct air conditioning filter.

**Figure 10.** Photograph of the direct experimental device with air conditioning filter.

**Table 2.** Range and uncertainly of the equipment used in the experiment.

### **3. Results and Discussion**

### *3.1. Temperature Change According to Pressure and Generator Nozzle*

The temperature change according to the pressure in the vortex tube device and the number of nozzles of the generator was investigated. The nozzle area ratio of Sn = 0.142 was set using a commonly known standard. The nozzle area ratio is the standard of the vortex tube that is set to best separate high temperature air. In addition, since the vortex formed in the vortex tube varies depending on the inlet supply pressure, the experiment was performed between Pi = 0.5 kgf/cm2 and Pi = 5.0 kgf/cm2 at Pi = 0.5 kgf/cm2 intervals. For each experiment, the high-temperature air temperature difference ΔTh and the low-temperature air temperature difference ΔTc at low temperature air flow rate (yc) = 0.1~1.0 were measured. Results are shown in Figures 11–20.

**Figure 11.** Temperature differences ΔTh and ΔTc according to inlet pressure (Pi) 0.5 kgf/cm2.

**Figure 12.** Temperature differences ΔTh and ΔTc according to inlet pressure (Pi) 1.0 kgf/cm2.

**Figure 13.** Temperature differences ΔTh and ΔTc according to inlet pressure (Pi) 1.5 kgf/cm2.

**Figure 14.** Temperature differences ΔTh and ΔTc according to inlet pressure (Pi) 2.0 kgf/cm2.

**Figure 15.** Temperature differences ΔTh and ΔTc according to inlet pressure (Pi) 2.5 kgf/cm2.

**Figure 16.** Temperature differences ΔTh and ΔTc according to inlet pressure (Pi) 3.0 kgf/cm2.

**Figure 17.** Temperature differences ΔTh and ΔTc according to inlet pressure (Pi) 3.5 kgf/cm2.

**Figure 18.** Temperature differences ΔTh and ΔTc according to inlet pressure (Pi) 4.0 kgf/cm2.

**Figure 19.** Temperature differences ΔTh and ΔTc according to inlet pressure (Pi) 4.5 kgf/cm2.

**Figure 20.** Temperature differences ΔTh and ΔTc according to inlet pressure (Pi) 5.0 kgf/cm2.

According to the experimental results, it was confirmed that ΔTh showed the highest high-temperature air from yc = 0.6 to 0.8 at high temperatures, and yc = 0.8 in the case of ΔTh, max as the pressure increased. In the case of low temperature, ΔTc showed the maximum low-temperature air from yc = 0.4 to 0.6, and in the case of ΔTc, max in the same case as the high temperature, yc = 0.5. As a result of these experiments, when the throttle valve on the high-temperature outlet is closed, yc increases and the flow cross-sectional area of the high-temperature outlet decreases. Therefore, the air at the high-temperature outlet flows back to the relatively low-temperature outlet, and the central flow becomes smooth. Additionally, when yc relatively decreases, the flow cross-sectional area of the high-temperature outlet becomes wider, and ΔTc tends to increase because the stagnation point in the vortex tube moves more toward the high-temperature outlet than it does when yc increases. It was judged that ΔTh and ΔTc increased because of active energy separation due to increases in momentum transfer between the central flow and the flow near the wall due to the change in yc. Through the experiments, it was found that ΔTh and ΔTc increased in a similar manner as the inlet pressure (Pi) flowing into the vortex tube increased. As the inlet pressure increased, the flow rate increased, and so the energy loss of the flow decreased, regardless of the number of nozzles, and the energy separation phenomenon became relatively large. This experiment trend showed similar tendencies of low-temperature outlet flow rate and entire pressure section, just as in Stephan [7]. Table 3 shows the ΔTh, max and ΔTc, max values of yc, and the number of nozzles depending on the pressure; in the case of Th, it can be seen that the number of nozzles varied from inlet pressure Pi = 0.5 to 2.0 kgf/cm2. However, after Pi = 2.0 kgf/cm2, it can be seen that the number of nozzles appears constant; in the case of Tc, the number of nozzles seems to change at Pi = 1.0 kgf/cm2. Overall, in the case of Th, the temperature was highest at yc = 0.8, and the nozzles were found to be efficient when they had seven holes. Tc was found to have its lowest temperature at yc = 0.5, and the number of nozzles was found to be efficient at seven.

**Table 3.** Th, max and Tc, max of yc and nozzle holes depending on the pressure.

### *3.2. Discharge Flow Rate and Temperature Di*ff*erence between* Δ*Th, max and* Δ*Tc, max According to Pressure*

As an initial experiment, we tried to determine the total flow rate according to the supply pressure. The table that summarizes the data according to the number of nozzles is shown in Figure 21.

**Figure 21.** Total discharge flow rate of intake air pressure by the number of nozzles.

The nozzle cross-section (Sn) of the generator was selected as a high-temperature type. As a result of experiments on low-temperature and high-temperature type nozzles, the temperature difference was found not to be large in the low-temperature region, but showed a difference of about 8 ◦C in the high-temperature region. This phenomenon is considered to be due to an increase in flow resistance because the cross-sectional area of the high-temperature nozzle has a smaller area ratio than that of the low-temperature nozzle. This can be seen in the nozzle cross-section experiment [27]. The purpose of this experiment was to determine the conditions for effective temperature separation characteristics with minimal flow. Like in the basic experiment, the supply pressure between Pi = 0.5 kgf/cm2 and Pi = 5.0 kgf/cm2 to the vortex generator was set at the interval of Pi = 0.5 kgf/cm2. In the experiment, it can be seen that the discharge flow rate increased proportionally as the inlet supply pressure increased, regardless of the number of generator nozzles. Under the same pressure condition, the number of nozzles tends to slightly increase as the size of the nozzle decreases, which means that when the generator's nozzle cross-section (Sn) is the same, as the number of generator nozzles decreases, the nozzle inner diameter (Dn) of the nozzle cross-section (Sn) increases. Therefore, it is considered that the total discharge flow rate increases because the flow resistance of compressed air, through which the supply pressure flows through the generator nozzle, decreases. From the experimental results, according to the number of nozzles and the supply pressure of the vortex generator, the maximum high-temperature air temperature difference (ΔTh, max) and the maximum low-temperature air temperature difference (ΔTc, max) under each condition are determined and shown in Figure 22.

**Figure 22.** Temperature difference ΔTh, max and ΔTc, max according to the number of nozzle holes.

As a result of the experiment, most high-temperature and low-temperature air temperature separation characteristics showed good efficiency under certain conditions in the case of the seven nozzles, but there was not a large difference in temperature. Furthermore, it can be seen that for the temperature separation characteristic, the maximum high-temperature air temperature difference (ΔTh, max) and the maximum low-temperature air temperature difference (ΔTc, max) changed significantly as the supply pressure increased. The high-temperature air of the seven nozzles with high efficiency changed from 7.99 ◦C when the maximum hot air temperature difference (ΔTh, max) Pi = 0.5 kgf/cm2 to 60.51 ◦C when Pi = 5.0 kgf/cm2, and showed a temperature difference of 52.52 ◦C. The low temperature air varied from −5.57 ◦C when the maximum low temperature air temperature difference (ΔTc,max) Pi = 0.5 kgf/cm2 to −36.33 ◦C when Pi = 5.0 kgf/cm2, and showed a temperature difference of 30.76 ◦C. The result of this experiment provides information for the application of a vehicle air conditioning system. Current air conditioning systems for vehicles have values of Pi = 2.5 kgf/cm2 to Pi = 5.0 kgf/cm2, where the temperature change is constant in a vehicle with an air conditioning system using a refrigerant. Based on the experimental results, it is considered that controlling the flow

rate and temperature values required for heating and cooling by checking the discharge flow rate and the temperature difference between the hot and cold parts is a key point.

### *3.3. Temperature Control of Indirect Heat Exchange Method According to Pressure*

To measure the temperature of the indirect heat exchanger, between Pi = 0.5 kgf/cm2 and Pi = 5.0 kgf/cm2 and Pi = kgf/cm2 were set based on the number of nozzles of the vortex generator, which was the most efficient in the basic experiment. In the high-temperature type device, the experiment was conducted at a section yc = 0.6 to 0.8 at a point where the efficiency of the low-temperature air flow rate (yc) was good; the experiment was conducted at yc = 0.4 to 0.6 for a section of low-temperature type. Figure 23 shows these results graphically. As in the basic experiment, it can be seen that the vortex tube increases in efficiency with increasing pressure. In the experiment, the value of Taoc ( ◦C) is the point at which the temperature of both the vortex tube cold and hot outlets passes through the heater core. Additionally, the value of ΔTac ( ◦C) was expressed by measuring the temperature of the flow flowing into the front and rear ends of the chamber surrounding the heater core. In the case of Taoc ( ◦C), the temperature was measured by comparing the low-temperature air flow rate (yc) of the flow. In the low-temperature region, the temperature difference of Taoc ( ◦C) was not large, but it was 21.84 ◦C when Pi = 0.5 kgf/cm2 at yc = 0.6, where the efficiency was best in proportion to the discharge flow rate, and when Pi = 5.0 kgf/cm2. The temperature difference changed to 9.87 ◦C and showed a maximum temperature difference of 11.97 ◦C. The value of ΔTac ( ◦C) was also measured using the low-temperature airflow ratio (yc), and the temperature difference was similar to Taoc ( ◦C). The value of ΔTac ( ◦C) showed values of −0.03 ◦C when Pi = 0.5 kgf/cm2 at yc = 0.6, and −11.92 ◦C when Pi = 5.0 kgf/cm2, resulting in a maximum temperature difference of 11.95 ◦C. Through this, the low-temperature measurement of the indirect heat exchange method according to the pressure, yc = 0.5 was excellent in the basic experiment, but when heat exchange was performed, the resulting value of yc = 0.6, which indicates a relatively large discharge flow rate due to flow rate resistance, was the best.

**Figure 23.** Indirect heat exchange method of ΔTaoc and ΔTac according to pressure.

As can be seen in Figure 24, the temperature difference was higher in the high-temperature region than in the low-temperature region. At yc = 0.8, the highest temperature of Taoc ( ◦C), when Pi = 0.5 kgf/cm2, was 23.00 ◦C; when Pi = 5.0 kgf/cm2, this value changed to 38.79 ◦C, showing a maximum temperature difference of 15.79 ◦C. The value of ΔTac ( ◦C) was measured through the low-temperature airflow ratio (yc), and the temperature difference had a result somewhat similar to that for Taoc ( ◦C). At yc = 0.8, Pi = 0.5 kgf/cm2 showed a difference of 0.02 ◦C, and Pi = 5.0 kgf/cm2 showed a difference of 15.95 ◦C; the pressure difference resulted in a maximum temperature difference of 15.93 ◦C. However, in the high-temperature region of the indirect heat exchange method, it was confirmed that, unlike in the case at low temperature, the influence of pressure was large. In the case of yc = 0.8, it can be seen that the discharge flow rate is low and the temperature change is small until the pressure becomes Pi = 3.0 kgf/cm2; the pressure changes significantly after Pi = 3.0 kgf/cm2. Through these experiments, it is thought that the reaction rate of the heat exchanger will be higher than between yc = 0.7 and 0.8 in the indirect heat exchange method when yc = 0.6, which has a constant temperature change and a large discharge flow rate. Therefore, as a result of confirming the temperature difference according to the low-temperature air flow rate (yc) through an indirect heat exchange method that changes according to the pressure, it was determined that a value of yc = 0.6 is suitable for regions of both low temperature and high temperature.

**Figure 24.** Indirect heat exchange method of ΔTh according to pressure.

### *3.4. Temperature Control of Direct Heat Exchange Method According to Pressure*

To evaluate the temperature difference with the indirect heat exchange method using the vortex tube, the supply pressure between Pi = 0.5 kgf/cm2 and Pi = 5.0 kgf/cm2 was the same as that in the basic experiment using seven nozzles for the vortex generator under the same test conditions. The inlet pressure was set at Pi = 0.5 kgf/cm2 intervals. Furthermore, as the direct heat exchange method has a larger discharge flow rate than that of the indirect heat exchange method, experiments were conducted at yc = 0.3 to 0.8 for both the low-temperature type and the high-temperature type by increasing the section of the low-temperature air flow rate (yc). To make a difference from the indirect heat exchange method, a heater core that does heat exchange was not used. Figures 25 and 26 are the results of experiments conducted in a direct manner in which compressed air, which has undergone temperature separation, enters the chamber directly and is discharged through an air conditioning filter. Through the experiments, the value yc = 0.6, which indicates the best efficiency at the exit of the low-temperature region, led to a value of Tco ( ◦C) = 21.76 ◦C when Pi = 0.5 kgf/cm2; this changed to 9.87 ◦C when Pi = 5.0 kgf/cm2, resulting in a maximum of 11.89 ◦C ΔTah ( ◦C). Through this direct heat exchange method, the low-temperature airflow ratio (yc) did not change between the indirect and direct heat exchange methods. As a result of an experiment that involved adding yc = 0.3, 0.7, and 0.8 of Tco ( ◦C) in the direct heat exchange method, it was confirmed that the efficiency decreased as the pressure increased because the flow rate was insufficient in the low-temperature region, similar to the cases of yc = 0.6, 0.7. It was confirmed that Tho ( ◦C) produces a high-temperature region and has a resulting value similar to that of the indirect heat exchange method and similar to the value of the low-temperature region. The efficiency at Tho ( ◦C) was the best at yc = 0.6; when Pi = 0.5 kgf/cm2, it was 22.97 ◦C. Additionally, when Pi = 5.0 kgf/cm2, it changed to 34.66 ◦C and showed a maximum temperature difference of 11.63 ◦C. Comparing the two areas, when the ratio of the discharge flow rate became high (yc = 0.3 to 0.4), it showed a trend similar to that in the basic experiment. This is because the supply pressure increases as the discharge flow rate increases in the high-temperature region, thereby increasing the flow rate discharged to the high-temperature outlet stage. Therefore, heat loss in the high-temperature chamber decreased, and the amount of temperature change decreased.

**Figure 25.** Direct heat exchange method of ΔTco according to pressure.

**Figure 26.** Direct heat exchange method of ΔTho according to pressure.

### **4. Conclusions**

Using a vortex tube, a basic experiment was conducted to investigate the temperature separation phenomenon according to the number of nozzles of the generator according to the supply pressure (Pi) and the low-temperature air flow rate (yc). In basic temperature difference experiments, the following conclusions were obtained using indirect and direct methods with a heater core that can be applied to a vehicle air conditioning system.

1. When the supply pressure between Pi = 0.5 kgf/cm2 and Pi = 5.0 kgf/cm2, the maximum high-temperature air temperature difference (ΔTh, max) appeared at yc = 0.8, and the maximum low-temperature air temperature difference (ΔTc, max) appeared at yc = 0.5.

2. Using 4, 5, 6, 7, and 8 nozzles in the vortex tube generator, the maximum high-temperature air temperature difference (ΔTh, max) and the maximum low-temperature air temperature difference (ΔTc, max) appeared for the maximum number of seven nozzles of the vortex tube generator.

3. The total discharge flow rate was tested by setting the supply pressure between Pi = 0.5 kgf/cm2 and Pi = 5.0 kgf/cm2 at intervals of Pi = kgf/cm2 at the nozzle area ratio Sn = 0.142 (high temperature type). The discharge flow rate tended to increase in proportion to the pressure increase; and, as the number of nozzles of the generator decreased, the nozzle inner diameter (Dn) increased, resulting in four nozzles having the highest discharge flow rate.

4. In the indirect heat exchange method, efficiency was best at yc = 0.8 in the high-temperature region, and at yc = 0.5 in the low-temperature region.

5. According to the results of temperature measurement in the indirect heat exchange method, Taoc ( ◦C) changed from 21.84 ◦C to 9.87 ◦C when the pressure was between Pi = 0.5 kgf/cm2 and Pi = 5.0 kgf/cm2 in the low-temperature region at yc = 0.6 and in the high-temperature region at yc = 0.8. Taoh ( ◦C) showed a maximum change of 15.79 ◦C, from 23.00 ◦C to 38.79 ◦C.

6. In the direct heat exchange method, the flow rate was slower than in the indirect heat exchange method, so the discharge flow rate was large; the area of the low-temperature air flow rate (yc) was measured at yc = 0.3~0.8. Excellent results were obtained in the two regions at yc = 0.6. Unlike in the indirect method, yc = 0.6 was excellent at high temperature, and seems to have been affected by the discharge flow rate.

7. According to the temperature measurement results using the direct heat exchange method, when yc = 0.6 and between Pi = 0.5 kgf/cm2 and Pi = 5.0 kgf/cm2, Tco ( ◦C) changed from 21.76 ◦C to 9.87 ◦C and its maximum difference was 11.89 ◦C. Additionally, Tho ( ◦C) showed a maximum change of 11.63 ◦C from 22.97 ◦C to 34.66 ◦C.

To conclude this study, the temperature difference between the indirect heat exchange method and the direct heat exchange method showed a maximum value of about 4 ◦C in the high-temperature region; the temperature difference in the low-temperature region was insignificant. Although the indirect heat exchange method looks slightly better when comparing the time to reach normal temperature, the indirect heat exchange method takes about four times longer than the direct heat exchange method, and the direct heat exchange method seems to have an excellent reaction speed. This is because the use of an indirect heat exchange type heater core induces flow velocity resistance, and the heat exchange of the heater core is performed only with air. However, when applied to an air conditioning system, the indirect heat exchange method, using external air or internal air, can implement a filter to reduce foreign substances; however, in the direct method, compressed air can be filtered only through the air conditioning filter. It is thought that it may be necessary to solve this problem. Therefore, for a vehicle air conditioning system, a direct heat exchange method with low reaction speed and low flow resistance can be used and, in the case of low-temperature airflow ratio (yc), a value of yc = 0.6, with high efficiency in both the low temperature and high-temperature regions, will subsequently be used in the air conditioning system of an eco-friendly vehicle. It is judged that this system can be applied and used effectively.

**Author Contributions:** All authors contributed to this research in collaboration. Y.K. have an experiment, S.I. proposed the conceptualization, and J.H. provided substantial help with the paper schedule and implemented the proposed vehicle air conditioning system using vortex tube. All authors have read and agreed to the published version of the manuscript.

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

**Acknowledgments:** This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (no. NRF-2019R1G1A1100739).

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

### **Nomenclature**

### **Subscript**

### **References**

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**Abstract**

The gold standard for measuring telomere length is technically challenging, which limits its use in large population studies. Numerous bioinformatics tools have recently been developed to estimate telomere length using high-throughput sequencing data. This allows for scaling up telomere length estimates in large datasets. Telomere length depends substantially on genetics, and many genetic studies have looked at this relationship, which provides an opportunity to predict telomere length from genotyping data. However, in part because environment also significantly affects telomere length, the accuracy of telomere length predictions and estimates made from genomic data remains uncertain. In this chapter, we will summarize currently available bioinformatics tools for predicting or measuring telomere length from genomics datasets, and we will discuss each method's limitations and advantages.

**Keywords:** DNA sequencing, genomics, genetics, population sciences, bioinformatics

### **1. Introduction**

Telomere length, as a biomarker of aging and genome integrity, has frequently been used in aging and health research. Telomere length in blood leukocytes or peripheral blood mononuclear cells (PBMCs) reflects the progressive shortening of telomeres in hematopoietic stem and progenitor cells (HSPCs) and correlates with telomere length in other tissues [1]. Among leukocyte types, naïve T-cells and B-cells have the longest telomeres, whereas NK- and memory T-cells have shorter telomeres within the same individual [2]. However, consistent with blood telomere length as a representative marker for telomere attrition in other tissues, telomere length in all cell types shows an inverse correlation with participant age. Many age related diseases are associated with diminished telomere length in leukocytes or PBMCs, including cardiovascular disease [3] and cancer [4]. Accurate and accessible telomere length techniques are increasingly needed in population studies to evaluate the biological aging process and genome maintenance, and may represent a target for the development of strategies for early detection and prevention of disease.

The gold standard measurement of telomere length is by Terminal Restriction Fragment (TRF) analysis. This approach involves frequent-cutting restriction enzymes that do not recognize the telomeric repeats, followed by Southern

hybridization [5]. The entire process of TRF can take up to one week, making it infeasible to apply on a large population scale. Flow cytometry-based fluorescent in situ hybridization (flow-FISH) is frequently used in clinical settings for patient diagnoses of telomere related disease [6]. An advantage of this approach is that it allows for determination of telomere length for specific cell population, but it requires expertise in flow cytometry and still labor intensive. Currently, the monochrome multiplex–quantitative polymerase chain reaction (MM–qPCR) is widely used in population-based studies because it is less labor intensive and relevantly fast in the turnaround time [7]. However, even this approach requires careful attention to details that may affect the results of the analysis and places demands on sample processing that may not be compatible with population studies [8].

Recently, genomics datasets have been produced from many large population cohorts, enabling new approaches to estimating telomere length through bioinformatics tools. These approaches afford an opportunity to estimate telomere length in large-scale population datasets. In this chapter, we summarize currently available tools for predicting or measuring telomere length from genomics datasets, and we will discuss each method's limitations and advantages.


**2.2 General conditions**

*Vascular Biology - Selection of Mechanisms and Clinical Applications*

where the primary closure of the wounds, the cure by secondary intention or the skin grafts were in the lower steps of this ladder and the flaps in the higher [4, 5]. With the improvement in optical tools, it became easier to perform the vascular

anastomoses that allowed free flap transfer and to set up skilled teams. As the tissue transfers became more dynamic and the microsurgery success rates rose, the benefits became more and more evident [5]. It was proven that the transfer of healthy tissues to the hand or head and neck allowed surgeons to achieve faster and better recoveries in areas of high functional demand, also with much more aesthetically acceptable results and lower morbidity. The same happened to breast surgery, where reconstructions with a natural shape and adequate volume could be achieved; the scars were hidden in the distance, and there was no need to use prosthesis. In lower limb osteomyelitis, free muscle flaps became the alternative to amputation. In addition, the advent of perforator flaps, mainly due to the contributions of Song and Koshima [5], thanks to whom it was not necessary to take the underlying muscle to transfer a fasciocutaneous flap, made it possible to further minimise the morbidity of these microsurgical interventions. Finally, a revision of the reconstructive ladder was proposed, the simplicity of the reconstruction would prevail, but pursuing the best aesthetic and functional results. So, a switch to a reconstructive elevator was made. In this way, microsurgical reconstructions became the first-line option for many patients and the technique was extended to a multitude of

Multiple aspects regarding the environment in the operating room and the position are particularly important in microsurgery. It is imperative to have enough field to allow an easy movement. This aspect, which is less substantial in *macro-*surgery, becomes absolutely fundamental in microsurgery. Mention it at the beginning, does

A two-team approach is usually chosen in reconstructive microsurgery, one will raise the flap and the other will set the recipient site where this is going to be transplanted [7]. Therefore, all the time spent planning disposition is properly invested. This is true both for placing the patient in the proper position, and for the surgeon to adopt a comfortable and durable posture. Since the surgery will be prolonged, we must meticulously paddle all bony prominences of the patient and the areas at risk of neurovascular compression. It must be encouraged to take all the necessary anaesthesia monitoring measures at the beginning, just to avoid emergencies or interruptions during delicate stages of surgery. It is also sensible to foresee how the

The comfort of the surgeon is a must when it comes the time to perform the microvascular anastomosis, primarily regarding the back, scapular and muscular groups. The sutures used usually size about 75–100 μm and the vessel lumen just a few millimetres; therefore, any tremor will greatly hinder the precision and success of the anastomoses. We cannot afford mistakes at any point of the microvascular anastomosis. The surgeon must be perpendicular disposition to the vessels and seated in a self-regulating chair that allows a self-sufficient height adjust. He or she should also be with the feet on a flat surface, the arms supported on a cloth and the hands on some comfortable place of the field to work only with the intrinsic

**204**

muscles of the hand [1].

centres [5, 6].

**2.1 Ergonomy**

**2. Basic principles in microsurgery**

nothing but tries to emphasise its relevance.

microscope will be arranged in the room.

After having invested enough time planning the operating room configuration, it is time to choose the vessels in the recipient area, since those of the flap are already determined and are assumed to be healthy because of their undamaged origin. It is essential to emphasise that the dissection must be very scrupulous, some groups advocate applying tension to the tissues around the vessel, without any direct pulling or forceps grasping on it, as not to generate any intimal traumas that may cause a thrombotic source [8, 9]. Any injury to the intima of the vessel, unnoticed or not, will expose the subendothelial collagen of the lumen, leading to a thrombotic focus. There are situations where it is impossible not to manipulate the vessel, as it happens in cervical dissections for oncological reasons; in these cases, a high incidence of thrombosis in the recipient vein has been demonstrated [6].

We must choose healthy vessels, without excessive fibrotic or irradiated tissue around them, this will allow us to perform a clean dissection, achieving a blood-less field. If blood accumulates in the field, we should spare no expense in abundantly rinse the area and review haemostasis. Blood has a red light refraction that deteriorates the sight with usual optical tools and releases procoagulant factors inducing vascular thrombosis [10, 11]. In limbs with previous surgeries or trauma, in case of doubt, we must carry out explorations such as angiography or Doppler, to check the availability of adequate vessels [12–15]. We should recruit as much vessel length as necessary to prevent any tension in the anastomosis, since the use of vein grafts, although may be needed, should be avoided due to its higher incidence of complications.

Before sectioning the donor artery to which we are going to transfer our flap, we must ensure that it has a good flow, we should ideally evince pulse [8]. Once sectioned, it will only be valid if we observe the exit of an abundant spurt of pulsatile blood. On the other hand, the vein that receives the blood from the flap in the recipient area must have at least the diameter that the vein of the flap has; otherwise, a bottleneck will form and prevent a good return and a venous congestion may develop in the flap.

Once the vessels in the receiving area are all set, we proceed to review the haemostasis and the perfusion of our previously dissected flap, then we release and transfer it [8, 10]. We should section the artery first and then the vein, as to avoid any congestion. Then we have to adapt the flap in the recipient area, since after anastomosis the flap will become edematised and its fixation in some deep spaces will be complex. This fixation is a mandatory prior step in all free flaps but in those in which the anastomosis lies in a deeper plane. In the head and neck reconstruction, small and intricate spaces make it advisable to do the fixation at first; but in breast reconstruction, we can only secure it with a gauze before microvascular anastomosis [6].

When performing the anastomosis, we prefer to adjust each vessel end in a simple microvascular clamp, tension-less approximate both ends and perform the microvascular anastomosis sparing as much proximal dissection as possible between the vessels of the flap pedicle and between the ones of the recipient area. On the other hand, we can place the anastomosis vessels end in a double microvascular clamp and approximate them [16]. The anastomosis should be placed on a rubber contrast and this over a wet gauze to avoid pooling and elevate the anastomosis from the surrounding field, full of thrombogenic debris [10] (**Figures 1** and **2**).

It is characteristic of the lumen of vessels to show a diameter smaller than that seen before severing them. This phenomenon is known as vasospasm. To mitigate it, we must perform a mechanical dilatation of the vessel lumen with specific dilator forceps and with agents such as lidocaine 1–2% or papaverine 3%, the latter being our preference [8–11]. Another dilatation technique is to abundantly rinse lumen with heparinised serum (200–300 IU/ml) [11–17]. It is key to remove the adventitia next to the anastomosis; we usually remove 2–3 mm with cutting technique, by pulling the adventitia over the lumen of the vessel and making a section parallel to the light. Aggressive adventitectomies leave the proximity of the anastamosis lacking *vasa vasorum*; this can cause ischemia in the vessel wall and, secondary to this, a failure or a pseudoaneurysm. On the other hand, the adventitia is highly thrombogenic, its entry with a knot into the lumen can be disastrous [18]. No technique completely removes the adventitia, but the sharp dissection seems more respectful with the intima [19]. Before carrying out the anastomosis, we must ensure that there are no intimal lesions in the lumen of the vessel, venous valves or branches, that may cause turbulence or resistance to flow in the vicinity of anastomosis [8].

There is debate about which anastomoses to perform first, whether arterial or venous. If there is no limitation for the position of a vessel deeper than another, as happens in breast reconstruction where the internal mammary vein usually has a more medial position, we can choose any one of them [6, 8]. Many groups choose to start with the arterial anastomosis to minimise isquemia time, taking into account that they do not usually experience added venous congestion. We usually start with the venous anastomosis to avoid any congestion within the flap that can cause a thrombus in its internal circuit. At the time of removing the clamps, once the anastomosis is completed, it is clearly preferable to remove the venous one first.

#### **Figure 1.**

*General overview of a microvascular anastomosis. Artery microvascular anastomosis is performed in a blood-less field after vein anastomosis (in a second plane), in a higher position over a rubber medium contrast and wet gauzes. A protected 5F Redon is usually placed under the anastomosis. Dissection of the vessels in each side of the anastomosis is limited, only simple vascular clamps are employed; this eases the one-side-up technique (see below). In this figure, the first two stitches of the triangulation technique are depicted.*

**207**

**2.3 Team**

*anastomosis.*

**Figure 2.**

The use of microsurgical techniques is not limited to reference centres with a high availability of resources, although their routine use is almost exclusive of these. This is due to the disposability of a microsurgical team with several surgeons

*Examples of the limited pedicle dissection before anastomosis. In the upper picture, we can see a free epigastric flap for an axillary free lymph node transfer. Marked with a star, we see the donor posterior circumflex humeral artery; below it, the inferior epigastric artery of the free flap is shown with both veins at each side. In the lower picture, we see the free flap before the transfer. Marked with a thunder, we see the inferior epigastric pedicle severed before its entrance in the abdominal rectus muscle; the inferior epigastirc vein is marked with a heart, it has been cut near its mouth in the circumflex iliac vein and laid prepared for the lymphovenous*

In this kind of surgery, each mistake has its consequences. So, if we perform these interventions with a very scarce and inexperienced team, these day-long surgeries can be translated into fatigue, nerve-wrecking and inaccuracies. This

trained in microvascular anastomosis and free flaps management.

*Basic Principles in Microvascular Anastomosis and Free Tissue Transfer*

*DOI: http://dx.doi.org/10.5772/intechopen.91917*

*Basic Principles in Microvascular Anastomosis and Free Tissue Transfer DOI: http://dx.doi.org/10.5772/intechopen.91917*

#### **Figure 2.**

*Vascular Biology - Selection of Mechanisms and Clinical Applications*

(**Figures 1** and **2**).

of anastomosis [8].

the microvascular anastomosis sparing as much proximal dissection as possible between the vessels of the flap pedicle and between the ones of the recipient area. On the other hand, we can place the anastomosis vessels end in a double microvascular clamp and approximate them [16]. The anastomosis should be placed on a rubber contrast and this over a wet gauze to avoid pooling and elevate the anastomosis from the surrounding field, full of thrombogenic debris [10]

It is characteristic of the lumen of vessels to show a diameter smaller than that seen before severing them. This phenomenon is known as vasospasm. To mitigate it, we must perform a mechanical dilatation of the vessel lumen with specific dilator forceps and with agents such as lidocaine 1–2% or papaverine 3%, the latter being our preference [8–11]. Another dilatation technique is to abundantly rinse lumen with heparinised serum (200–300 IU/ml) [11–17]. It is key to remove the adventitia next to the anastomosis; we usually remove 2–3 mm with cutting technique, by pulling the adventitia over the lumen of the vessel and making a section parallel to the light. Aggressive adventitectomies leave the proximity of the anastamosis lacking *vasa vasorum*; this can cause ischemia in the vessel wall and, secondary to this, a failure or a pseudoaneurysm. On the other hand, the adventitia is highly thrombogenic, its entry with a knot into the lumen can be disastrous [18]. No technique completely removes the adventitia, but the sharp dissection seems more respectful with the intima [19]. Before carrying out the anastomosis, we must ensure that there are no intimal lesions in the lumen of the vessel, venous valves or branches, that may cause turbulence or resistance to flow in the vicinity

There is debate about which anastomoses to perform first, whether arterial or venous. If there is no limitation for the position of a vessel deeper than another, as happens in breast reconstruction where the internal mammary vein usually has a more medial position, we can choose any one of them [6, 8]. Many groups choose to start with the arterial anastomosis to minimise isquemia time, taking into account that they do not usually experience added venous congestion. We usually start with the venous anastomosis to avoid any congestion within the flap that can cause a thrombus in its internal circuit. At the time of removing the clamps, once the anastomosis is completed, it is clearly preferable to remove the venous one first.

*General overview of a microvascular anastomosis. Artery microvascular anastomosis is performed in a blood-less field after vein anastomosis (in a second plane), in a higher position over a rubber medium contrast and wet gauzes. A protected 5F Redon is usually placed under the anastomosis. Dissection of the vessels in each side of the anastomosis is limited, only simple vascular clamps are employed; this eases the one-side-up technique (see below). In this figure, the first two stitches of the triangulation technique are depicted.*

**206**

**Figure 1.**

*Examples of the limited pedicle dissection before anastomosis. In the upper picture, we can see a free epigastric flap for an axillary free lymph node transfer. Marked with a star, we see the donor posterior circumflex humeral artery; below it, the inferior epigastric artery of the free flap is shown with both veins at each side. In the lower picture, we see the free flap before the transfer. Marked with a thunder, we see the inferior epigastric pedicle severed before its entrance in the abdominal rectus muscle; the inferior epigastirc vein is marked with a heart, it has been cut near its mouth in the circumflex iliac vein and laid prepared for the lymphovenous anastomosis.*

#### **2.3 Team**

The use of microsurgical techniques is not limited to reference centres with a high availability of resources, although their routine use is almost exclusive of these. This is due to the disposability of a microsurgical team with several surgeons trained in microvascular anastomosis and free flaps management.

In this kind of surgery, each mistake has its consequences. So, if we perform these interventions with a very scarce and inexperienced team, these day-long surgeries can be translated into fatigue, nerve-wrecking and inaccuracies. This

ultimately will generate failures in the microvascular anastomosis and problems in the perfusion of the flap. Therefore, having a team that allows pauses and relays, without stopping the procedure, is a fundamental element. Likewise, this second fresh team will overcome emergencies (more frequent in the first 48–72 h) or can replace a tired first team. It seems sensible to have at least four microsurgeons, two assistants and two experienced scrub nurses [20].

A microsurgical team must function as a unit that critically analyses its results, seeking rates of failure lower than 5% in free flaps. Errors and the morbidity of the interventions must be analysed, minimising both. This constant improvement is hard to achieve if several microsurgeons are not available.

### **3. Microsurgical tools and instruments**

#### **3.1 Tools**

Microsurgery results from adapting the visual inaccuracy of our naked eye, to the fine movements of our hands. Here is where magnification arises. This can be done by two optical tools: the microscope and the magnifying loupe. In both, good lighting is essential [21, 22].

Surgical microscopes occupy a large space in the operating room but allow a magnification of up to 40× with greater illumination. In addition, they have pedals to control zoom and focus with the feet. Smaller magnification of 6–12× is usually used for the preparation of the vessels, and then it is increased up to 20× before the microanastomosis. In addition, the microscope gives us a wide range of field and provides the same vision to the surgeon and the assistant, enhancing the collaboration between them [21].

On the other hand, loupes are very cost-effective and easily transportable visual systems. The most common magnification employed in microsurgery is between 2.5× and 4.5×. In skilled hands, microscope has not proved to be superior *versus* loupes in achieving high success rates in free tissue transfers [23].

There are two types of magnifying loupes, on the one hand the compound or Galilean loupes and on the other hand the prismatic. The former consist of two lenses in line, and offer less weight and cost, although their magnification (2.5×) and depth of field are lower. The latter use a prism inside to reach a longer path of light through the lenses, which allows greater magnification and field depth, although they can be darker, heavier, more expensive and fragile [22].

#### **3.2 Basic microsurgery instruments kit**

The microsurgical instruments have evolved from ophthalmology or jewellery material to extremely specific and precise tools [7]. The basic kit is not made up of too much surgical material. This material should ideally be antireflective and cylindrical to allow its sliding from the index to the middle fingers and facilitate the passage of the needle through the tissues using only the intrinsic musculature. The size of the material should be about 16 cm to facilitate its support in the first hand commissure. In the case of working in very small fields, as in the case of hand surgery, smaller material, about 8 cm, with flat surface may be useful. Nowadays the self-locking material has lost interest, the mere requisite is just to offer little resistance when grasping to preclude any fatigue of the thenar eminence with prolonged use [24].

The basic kit consists of two scissors, a needle holder and a jeweller forceps. One of the scissors should be curved and round tipped, to be useful to dissect.

**209**

*Basic Principles in Microvascular Anastomosis and Free Tissue Transfer*

Other pair should be straight and pointed to perform the adventitectomy and to cut sutures. These pointed scissors should not be used for tissue dissection, because of the possible vessel trauma that they would generate. The jeweller forceps must have a precise closure, with enough contact between surfaces at the tip, just to handle

Other instruments that can also be useful are an aspiration system, an irrigation system and a bipolar forceps identical to jeweller forceps but protected. Our preference is to prepare a fixed suction system in the corner of the field, and to avoid introducing traditional aspirators directly over the vessels. Usually we fix a 5F Redon drain in a corner of the field or under the rubber contrast and we keep it connected to soft aspiration, in such way that it rests distant from the area of the anastomosis but does not allow pooling. We also avoid the contact of celluloses or cotton gauzes

directly with the lumen of the vessel due to their thrombogenic properties.

For the lumen irrigation, we use a heparin solution with 200–250 IU/ml [11]. Washing the lumen of the vessel directly can hydrodissect the vessel wall, exposing the subintimal collagen. Therefore, we introduce a blunt-tipped lacrimal cannula into the lumen of the vessel before anastomosis to perform a gentle wash [17]. Likewise, we usually do an irrigation of the flap through the artery with 20 or 30 ml of heparin solution, prior to the transfer; this checks the correct flow in the vascular

This delicate material requires little but precise care. First of all, we should avoid falls during surgery or washing, as the tips of the material can be damaged. If this happens, the closure of the material would not be perfect and its functionality would be noticeably reduced. It is also necessary to avoid the tips of the material to be oriented towards the sides in the store box, since movements with the box closed

The material should preferably be washed by the scrub nurse or the surgeon himself, who is familiar with it and will be more careful with its handling. A final wash should be done with distilled water and dried with an air gun to prevent rust

During surgery, the material must always be clean and moist, so that the sutures do not adhere to its surface. Dirty material and damaged tips will cause problems

The most common sutures elected are the 9-0 on a 100-μm needle and the 10-0 on a 75-μm needle. Because of the ease of knotting and the low tissue reaction, the most used material in sutures is nylon. Some authors prefer polypropylene due to a

There is no stipulated standard on how to perform a microvascular anastomosis,

the choice of the specific technique is operator-dependent. However, there are certain issues that we must avoid: a narrowing of the vascular lumen, an irregular distribution of the diameters of the vessels that would generate folds and irregularities, an excessive suture material inside the vascular lumen, and above anything else transmural sutures that bite the posterior wall closing the vascular lumen [24].

with the suture technique at key moments of the intervention.

lower tissue reaction, but its knots may be less reliable.

**4. Microsurgery techniques**

*DOI: http://dx.doi.org/10.5772/intechopen.91917*

fine sutures of 75 or 100 μm.

circuit of the flap.

formation.

**3.4 Sutures**

**3.3 Instruments care**

could also damage the tips inadvertently.

*Basic Principles in Microvascular Anastomosis and Free Tissue Transfer DOI: http://dx.doi.org/10.5772/intechopen.91917*

Other pair should be straight and pointed to perform the adventitectomy and to cut sutures. These pointed scissors should not be used for tissue dissection, because of the possible vessel trauma that they would generate. The jeweller forceps must have a precise closure, with enough contact between surfaces at the tip, just to handle fine sutures of 75 or 100 μm.

Other instruments that can also be useful are an aspiration system, an irrigation system and a bipolar forceps identical to jeweller forceps but protected. Our preference is to prepare a fixed suction system in the corner of the field, and to avoid introducing traditional aspirators directly over the vessels. Usually we fix a 5F Redon drain in a corner of the field or under the rubber contrast and we keep it connected to soft aspiration, in such way that it rests distant from the area of the anastomosis but does not allow pooling. We also avoid the contact of celluloses or cotton gauzes directly with the lumen of the vessel due to their thrombogenic properties.

For the lumen irrigation, we use a heparin solution with 200–250 IU/ml [11]. Washing the lumen of the vessel directly can hydrodissect the vessel wall, exposing the subintimal collagen. Therefore, we introduce a blunt-tipped lacrimal cannula into the lumen of the vessel before anastomosis to perform a gentle wash [17]. Likewise, we usually do an irrigation of the flap through the artery with 20 or 30 ml of heparin solution, prior to the transfer; this checks the correct flow in the vascular circuit of the flap.

#### **3.3 Instruments care**

*Vascular Biology - Selection of Mechanisms and Clinical Applications*

assistants and two experienced scrub nurses [20].

**3. Microsurgical tools and instruments**

**3.1 Tools**

lighting is essential [21, 22].

tion between them [21].

**3.2 Basic microsurgery instruments kit**

hard to achieve if several microsurgeons are not available.

ultimately will generate failures in the microvascular anastomosis and problems in the perfusion of the flap. Therefore, having a team that allows pauses and relays, without stopping the procedure, is a fundamental element. Likewise, this second fresh team will overcome emergencies (more frequent in the first 48–72 h) or can replace a tired first team. It seems sensible to have at least four microsurgeons, two

A microsurgical team must function as a unit that critically analyses its results, seeking rates of failure lower than 5% in free flaps. Errors and the morbidity of the interventions must be analysed, minimising both. This constant improvement is

Microsurgery results from adapting the visual inaccuracy of our naked eye, to the fine movements of our hands. Here is where magnification arises. This can be done by two optical tools: the microscope and the magnifying loupe. In both, good

Surgical microscopes occupy a large space in the operating room but allow a magnification of up to 40× with greater illumination. In addition, they have pedals to control zoom and focus with the feet. Smaller magnification of 6–12× is usually used for the preparation of the vessels, and then it is increased up to 20× before the microanastomosis. In addition, the microscope gives us a wide range of field and provides the same vision to the surgeon and the assistant, enhancing the collabora-

On the other hand, loupes are very cost-effective and easily transportable visual systems. The most common magnification employed in microsurgery is between 2.5× and 4.5×. In skilled hands, microscope has not proved to be superior *versus*

There are two types of magnifying loupes, on the one hand the compound or Galilean loupes and on the other hand the prismatic. The former consist of two lenses in line, and offer less weight and cost, although their magnification (2.5×) and depth of field are lower. The latter use a prism inside to reach a longer path of light through the lenses, which allows greater magnification and field depth,

The microsurgical instruments have evolved from ophthalmology or jewellery material to extremely specific and precise tools [7]. The basic kit is not made up of too much surgical material. This material should ideally be antireflective and cylindrical to allow its sliding from the index to the middle fingers and facilitate the passage of the needle through the tissues using only the intrinsic musculature. The size of the material should be about 16 cm to facilitate its support in the first hand commissure. In the case of working in very small fields, as in the case of hand surgery, smaller material, about 8 cm, with flat surface may be useful. Nowadays the self-locking material has lost interest, the mere requisite is just to offer little resistance when grasping to preclude any fatigue of the thenar eminence with

The basic kit consists of two scissors, a needle holder and a jeweller forceps. One of the scissors should be curved and round tipped, to be useful to dissect.

loupes in achieving high success rates in free tissue transfers [23].

although they can be darker, heavier, more expensive and fragile [22].

**208**

prolonged use [24].

This delicate material requires little but precise care. First of all, we should avoid falls during surgery or washing, as the tips of the material can be damaged. If this happens, the closure of the material would not be perfect and its functionality would be noticeably reduced. It is also necessary to avoid the tips of the material to be oriented towards the sides in the store box, since movements with the box closed could also damage the tips inadvertently.

The material should preferably be washed by the scrub nurse or the surgeon himself, who is familiar with it and will be more careful with its handling. A final wash should be done with distilled water and dried with an air gun to prevent rust formation.

During surgery, the material must always be clean and moist, so that the sutures do not adhere to its surface. Dirty material and damaged tips will cause problems with the suture technique at key moments of the intervention.

#### **3.4 Sutures**

The most common sutures elected are the 9-0 on a 100-μm needle and the 10-0 on a 75-μm needle. Because of the ease of knotting and the low tissue reaction, the most used material in sutures is nylon. Some authors prefer polypropylene due to a lower tissue reaction, but its knots may be less reliable.

#### **4. Microsurgery techniques**

There is no stipulated standard on how to perform a microvascular anastomosis, the choice of the specific technique is operator-dependent. However, there are certain issues that we must avoid: a narrowing of the vascular lumen, an irregular distribution of the diameters of the vessels that would generate folds and irregularities, an excessive suture material inside the vascular lumen, and above anything else transmural sutures that bite the posterior wall closing the vascular lumen [24].


**Abstract**

In this chapter, three-dimensional microstrip antennas operating in the dominant TM10 mode of the L1 band at 1.57542 GHz are presented, which either provide uniform phase response and stable phase center, or wide angular beam coverage. A Finite-Difference Time-domain scheme has been developed and used to elucidate the interplay between the proposed antennas and several ground plane configurations. Experimental results are presented and compared to simulations to illustrate the impact of several 3-D geometries on the phase response, phase center, half power beam width, gain, and polarization purity. We report for the first-time novel threedimensional microstrip antenna topologies for precise surveying applications by fostering a nearly uniform phase response when the 3D structure is bent by angles ranging from 15° to 30° **without significantly compromising the gain and polarization performance** of the equivalent flat patch antenna. The proposed antennas exhibit half-power-beamwidths up to 40 and 80% greater than the equivalent flat structure that can be realized if positioned downward and upward respectively, for bend angles above 45° accompanied with a variety of spatial coverage patterns to suit applications involving highly dynamic platforms.

**Keywords:** three-dimensional (3D) microstrip antennas, global positioning system, low-elevation pattern coverage, GPS tracking of sounding rockets and unmanned aerial vehicles, GPS aerospace applications


1. Introduction

Size-shrinkage as a main trend of the electronics development has already brought not only cutoff frequency but also energy consumption increase. In addition, a current leakage of the fieldeffect transistor (FET) has also increased. The leakage current consists of a current from the drain to the source (Isd) due to overlapping of the p-n transition regions in the contacts and a tunneling current from the gate to the channel (Ig). Moreover, in the FET size-shrinkage, the Ig part becomes more important; for example, at 130 nm technology, it takes less than 5% of whole leakage, at 90 nm, it takes 40%, and at 65 nm, it takes 90%, respectively [1]. To decrease the Isd, SOI substrates and vertical orientations of the FET are used. This effectively decreases the width of the cross section for the Isd. Note that this accompanies the two-dimensional character of the FET channel. To diminish the Ig, high-k dielectrics are used as the gate insulators. This increases the capacity between the gate and the channel and decreases the pinch-off voltage or energy of

© 2017 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.

the tunneling carriers. Another way is to use quantum well for the FET channel, for example, InSb layer [2]. This also diminishes gate voltage because the band inversion is not required. As a result, the cut-off frequency can be increased up to 300 GHz. One can see that two-dimensional systems of carriers (2DSC) are inherent to the modern nanoFET.

In this chapter, an application of the 2DSC in a FET gate is considered for further leakage reducing.

### 2. Resonant tunneling of carriers

Tunneling has been revealed by Esaki [3] and studied mainly in semiconductor diodes since 1958. Several years before, Shriffer had proposed size-quantization of the carriers in semiconductor films [4] that was observed by Tsui in InAs tunneling diode [5]. Then Esaki [6] and Kazarinov and Suris [7] proposed carriers resonant tunneling (CRT) in semiconductor heterostructures. In 1974, this effect was observed [6]. On the base CRT, a resonant-tunneling diode (RTD) [8] and resonant-tunneling transistor (RTT) [9] are realized as highest-frequency solid-state devices up to date. Carriers tunneling is well-known to play a negative role in modern c CMOS transistors made on the base technology of 45 nm or less. However, the instances of the RTD and RTT give us a hope that a proper application of the CRT can improve the situation in the FET. To clarify this, let us consider the CRT in detail.

Usually, the CRT is observed in a double-barrier heterostructure, the conduction band profile of which is shown in Figure 1. In a thin layer of a narrow band gap semiconductors, the localized states are forming and called subband states or levels. The ground subband state has energy Ez0. As a result, the barriers transparency has sharp peaks up to 1 in its energy dependency when the incident-electron energy along z direction Ez approaches to Ez0 and, what is more important to this chapter, it decreases down to Tz ¼ 10�4 at intermediate energy [6].

To calculate current-voltage characteristics, one can consider model of sequential tunneling [10]. In this model, tunneling of the electron can be described as sequential quantum transition perturbed by tunnel Hamiltonian T [11]. In first term of the perturbation theory, one can expect to find the probability of the transition as follows:

$$\mathcal{W}\_{\vec{\eta}} = \frac{2\pi}{\hbar} |\Psi\_i| T |\Psi\_f|^2 \delta(E\_f - E\_i) \tag{1}$$

where ћ is Planck constant, Ψi,f are electron wave functions, Ei,f are energy of initial and final states. Since the potential is in the one z direction, the electron wave functions are as follows:

$$
\Psi\_{i,f} = \chi\_{i,f}(\mathbf{z}) \exp\left(\frac{i}{\hbar} \left[p\_{xi,f}\mathbf{x} + p\_{yi,f}y\right]\right) \tag{2}
$$

Then the matrix element of T is as follows:

$$
\Psi\_i|T|\Psi\_f = T\_{\sharp}\delta(p\_{x\sharp} - p\_{xi})\delta(p\_{y\sharp} - p\_{yi})\tag{3}
$$

Figure 1. Energy profile of the conduction band bottom of the two barrier heterostructure.

the tunneling carriers. Another way is to use quantum well for the FET channel, for example, InSb layer [2]. This also diminishes gate voltage because the band inversion is not required. As a result, the cut-off frequency can be increased up to 300 GHz. One can see that two-dimensional

In this chapter, an application of the 2DSC in a FET gate is considered for further leakage

Tunneling has been revealed by Esaki [3] and studied mainly in semiconductor diodes since 1958. Several years before, Shriffer had proposed size-quantization of the carriers in semiconductor films [4] that was observed by Tsui in InAs tunneling diode [5]. Then Esaki [6] and Kazarinov and Suris [7] proposed carriers resonant tunneling (CRT) in semiconductor heterostructures. In 1974, this effect was observed [6]. On the base CRT, a resonant-tunneling diode (RTD) [8] and resonant-tunneling transistor (RTT) [9] are realized as highest-frequency solid-state devices up to date. Carriers tunneling is well-known to play a negative role in modern c CMOS transistors made on the base technology of 45 nm or less. However, the instances of the RTD and RTT give us a hope that a proper application of the CRT can improve the situation in the FET. To clarify

Usually, the CRT is observed in a double-barrier heterostructure, the conduction band profile of which is shown in Figure 1. In a thin layer of a narrow band gap semiconductors, the localized states are forming and called subband states or levels. The ground subband state has energy Ez0. As a result, the barriers transparency has sharp peaks up to 1 in its energy dependency when the incident-electron energy along z direction Ez approaches to Ez0 and, what is more important to

To calculate current-voltage characteristics, one can consider model of sequential tunneling [10]. In this model, tunneling of the electron can be described as sequential quantum transition perturbed by tunnel Hamiltonian T [11]. In first term of the perturbation theory,

ℏ jΨijTjΨf j

where ћ is Planck constant, Ψi,f are electron wave functions, Ei,f are energy of initial and final states. Since the potential is in the one z direction, the electron wave functions are as follows:

i

2

ℏ ½pxi,f x þ pyi,f y�

ΨijTjΨf ¼ Tif δðpxf � pxiÞδðpyf � pyiÞ ð3Þ

δðEf � EiÞ ð1Þ

ð2Þ

this chapter, it decreases down to Tz ¼ 10�4 at intermediate energy [6].

one can expect to find the probability of the transition as follows:

Wif ¼ 2π

Ψi,f ¼ χi,fðzÞexp

systems of carriers (2DSC) are inherent to the modern nanoFET.

28 Different Types of Field-Effect Transistors - Theory and Applications

2. Resonant tunneling of carriers

this, let us consider the CRT in detail.

Then the matrix element of T is as follows:

reducing.

where Tif ¼ χijTjχf . As one can see from Eqs. (1) and (3), the tunneling electrons save its energy and planar components of the momentum. Since the electron effective mass is equal on both sides of the barrier, the tunneling electron also saves Ez energy. To calculate current, one should sum transition probabilities timed on electron charge from given equation:

$$I = \sum\_{i,f} \varepsilon \mathcal{W}\_{\circ}(f\_i - f\_f) \tag{4}$$

where fi,f, Fermi-Dirac distribution functions of electrons in initial and final states. Let us suppose that Tif is a constant, then Tif ¼ τ�1 , where τ is a tunneling rate of the electrons. According to Eqs. (1) and (3), one can get the following:

$$I = \frac{e}{\pi} \sum\_{i \in \mathcal{E} \cup \{\mathcal{E}\_0\}} (f\_i - f\_f) = \frac{e}{\pi} (N\_i(\mathcal{E}\_{\mathfrak{z}0}) - N\_f(\mathcal{E}\_{\mathfrak{z}0})) \tag{5}$$

where i(Ez0) and f(Ez0) are the initial and final states which have the same energy Ez0 of motion in z direction; Ni(Ez0) and Nf(Ez0) are the number of electrons populating the initial and final states. Using low-temperature limit that is kT << EF and kT << Ez1�Ez0 and also supposing final states as empty that is Nf(Ez0) ¼ 0 as usual, one can calculate Ni(Ez0) as a number of filled states on a Fermi-hemisphere intersection disk taking at a momentum pz0 in the phase space (see gray disc in Figure 2) where Ez0 ¼ (pz0) 2 /2m\* and m\* is an electron effective mass. Thus, the tunnel current can be found as follows:

$$I = \frac{e(p\_F^2 - p\_{z0}^2)S}{(2\pi\tau\hbar^2)} = e\mathfrak{g}\_{2D}\mathcal{S}(E\_{Fe} - E\_{z0})/\tau\tag{6}$$

where e is an electron charge, pF is a Fermi momentum of electrons, g2D is a density of twodimensional states of electrons, and S is a sample area.

Let us suppose the emitter grounded, i. e., μfe ¼ const, then the voltage dependence of Ez0(V) determines the I-V curve. If the barriers width D is greater than the quantum well (QW) width d, then Ez0(V) can be found from linear Stark effect:

$$E\_{z0}(V) = E\_{z0}(0) - eV/\alpha \tag{7}$$

where α is a leverage factor, i.e., α ¼ D/(d1 þ d2). Since usually Ez0(0) > μfe, there is a threshold voltage Vth higher than a resonant current I that has appeared when Ez0(Vth) ¼ μfe. Then combining Eqs. (6) and (7), one can get the following expression for the current I:

$$I = e^2 \mathcal{g}\_{2D} \mathcal{S} (V - V\_{th}) / \alpha \pi \tag{8}$$

Eq. (8) is justified when μfe > Ez0(V) > Ece. At the current peak voltage Vp, the subband energy Ez0 approaches to Ece, i.e., Ez0(Vp) ¼ Ece, and after that the resonant current drops down to zero.

As a result, the I-V curve of the RTD is shown in Figure 3 as solid line. It is worth noting that Eq. (8) describes only resonant part of the current. Nonresonant current usually is monotonic

Figure 2. Momentum space of the emitter and states available for resonant tunneling.

on a Fermi-hemisphere intersection disk taking at a momentum pz0 in the phase space (see

where e is an electron charge, pF is a Fermi momentum of electrons, g2D is a density of two-

Let us suppose the emitter grounded, i. e., μfe ¼ const, then the voltage dependence of Ez0(V) determines the I-V curve. If the barriers width D is greater than the quantum well (QW) width

where α is a leverage factor, i.e., α ¼ D/(d1 þ d2). Since usually Ez0(0) > μfe, there is a threshold voltage Vth higher than a resonant current I that has appeared when Ez0(Vth) ¼ μfe. Then

Eq. (8) is justified when μfe > Ez0(V) > Ece. At the current peak voltage Vp, the subband energy Ez0 approaches to Ece, i.e., Ez0(Vp) ¼ Ece, and after that the resonant current drops down to

As a result, the I-V curve of the RTD is shown in Figure 3 as solid line. It is worth noting that Eq. (8) describes only resonant part of the current. Nonresonant current usually is monotonic

combining Eqs. (6) and (7), one can get the following expression for the current I:

I ¼ e 2

Figure 2. Momentum space of the emitter and states available for resonant tunneling.

/2m\* and m\* is an electron effective mass. Thus, the

ð2πτℏ2Þ ¼ eg2DSðEFe � Ez0Þ=τ ð6Þ

Ez0ðVÞ ¼ Ez0ð0Þ � eV=α ð7Þ

g2DS Vð Þ � Vth =ατ ð8Þ

2

F � p2 z0ÞS

I ¼ eðp2

dimensional states of electrons, and S is a sample area.

d, then Ez0(V) can be found from linear Stark effect:

gray disc in Figure 2) where Ez0 ¼ (pz0)

30 Different Types of Field-Effect Transistors - Theory and Applications

tunnel current can be found as follows:

zero.

Figure 3. Current-voltage characteristics of RTD with a single quantum well between barriers (solid line) and a double quantum wells (dashed line).

function of the voltage and includes scattering tunneling and tunneling across all barriers. This provides nonzero current at any nonzero voltage. Thus, one can see that two-dimensional state in the QW produces the resonant tunneling in a finite resonant voltage range from Vth to Vp and depresses the resonant tunneling at other voltages. This resonant voltage range can be further shrunk if another QW will be used (see Figure 4). In this case, the resonant tunneling is possible only at resonant voltage Vp1 when E01(Vp1) ¼ E02(Vp1). This decreases significantly the width of the current peak in the I-V curve (see Figure 3 dashed line).

Thus, the application of 2DSCs could significantly decrease the carriers tunneling in a wide range of the applied voltage. This means there is a new way to decrease carriers tunneling between a

Figure 4. Energy profile of the conduction band bottom of the heterostructure with two quantum wells.

gate and a channel that is application 2DSCs in them. Semiconductor heterostructures with two 2DSCs separated by a tunnel barrier have been studied and demonstrated their properties [11].


Preface

Chapter 9 **Integrated Management of Helicoverpa armigera in Soybean**

Yaghoub Fathipour and Amin Sedaratian

**Cropping Systems 231**

**VI** Contents

This book provides an overview of the pest resistance soybeans. The authors contributed 9 chapters in which they attempt to review recent research on soybean resistance to Hemipter‐ an pests and, in the light of various challenges to manage Hemipteran pests, propose strat‐ egies for successful and sustainable use of host plant resistance (HPR) in soybean against these pests.

The chapters also aim to present some focal issues related to weed management in soybean growing areas, which include weed potential to cause severe damage and yield losses by weeds, the evolution of resistant weeds in GR soybean monoculture, the soybean manage‐ ment characterization in the main producing countries and discussions about the benefits of IWM use as an accurate control measure. A set of information for researchers and experts on weed management service area is presented, reporting clearly and objectively the major im‐ pacts of the current management used, as well as the outlook for soybean farming.

This book will be useful for soybean researchers and other academic staff and will provide its readers with valuable insight into the last developments in the field.

> **Hany A. El-Shemy, Professor** Cairo University, EGYPT

**Chapter 1**

**Nutritional Requirements of Soybean Cyst Nematodes**

Soybeans [*Glycine max*] are the second largest cash crop in US Agriculture, but the soybean yield is compromised by infections from *Heterodera glycines*, also known as Soybean Cyst Nematodes [SCN]. SCN are the most devastating pathogen or plant disease soybean farmers confront. This obligate pathogen requires nutrients from the plant to complete its life cycle. To date, SCN nutritional requirements are not clearly defined. Growth media supporting SCN still contain soy products. Understanding the SCN nutritional requirements and how host plants meet those requirements should lead to the control of SCN infestations. The nutritional requirements of SCN are reviewed in this chapter and those requirements are compared to those of other nematodes. Carbohydrates, vitamins, amino acids, lipids, and other nutritional

The survival of parasitic nematodes requires adequate nutrition. These essential nutrients are at least partially supplied by the host. But, availability of nutrients may not alone be sufficient for survival and reproduction. The parasite must also be able to establish a feeding site. Both the establishment of the feeding site and the presence of adequate nutrients for the soybean

Nematodes have differing mouth part structures which are adapted to their food source [1]. In the case of plant-parasitic nematodes, a stylet [analogous to a hypodermic needle], is used to puncture plant cells and a pump mechanism located in the nematode esophagus allows for exchange of fluids between the nematode and plant [1]. Most studies of the economically important root-knot and cyst-forming plant-parasitic nematodes have focused on what fluids are secreted by the nematode and how this facilitates establishment of a feeding site [2-4].

> © 2013 Goheen et al.; licensee InTech. This is an open access article 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.

© 2013 Goheen et al.; licensee InTech. This is a paper 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.

Steven C. Goheen, James A. Campbell and

Additional information is available at the end of the chapter

Patricia Donald

**1. Introduction**

http://dx.doi.org/10.5772/54247

requirements are discussed.

**1.1. Feeding site establishment**

cyst nematode [SCN] are discussed below.


Adaptation Strategies for Climate Variability in the High Rainfall Zone of India, Assam

*Pallab Kumar Sarma, Nikhilesh Baruah, Rupam Borah, Rupshree Borah, Arunjyoti Sonowal, Rekhashree Kalita, Prasanta Neog, Prabal Saikia and Nipen Gogoi*


*3.3. Fermentation*

The fungus *Penicillum* sp. N-5 was cultured in one hundred 1000 mL Erlenmeyer flasks at 25 ◦C for 30 days; these contained autoclaved rice solid-substrate medium composed of 50 g rice and 50 mL 3‰ saline water.

#### *3.4. Extraction and Purification*

After incubation, the mycelia and solid rice medium were extracted four times with EtOAc, and 75 g of residue was obtained. Next, the residue was separated by a gradient of petroleum ether/EtOAc from 9:1 to 0:10 (*v*/*v*) on silica gel CC and divided into six fractions (Fr.1–Fr.6). Fr. 2 (10 g) was separated to Sephadex LH-20 (methanol) to yield three sub-fractions (SFrs. 2.1–2.3). SFrs.2.3 (1.2 g) was applied to silica gel CC (DCM/MeOH *v*/*v*, 100:1) and further purified by reversed-phase (RP) high performance liquid chromatography (HPLC; 90–10% MeCN/H2O for 25 min) to obtain compounds **1** (5 mg) and **3** (7 mg). Fr. 3 (16 g) was also separated to Sephadex LH-20 (methanol) to yield four sub-fractions (SFrs. 3.1–3.4). SFrs.3.1 (1.6 g) was separated to silica gel CC (DCM/MeOH *v*/*v*, 80:1) and further purified by reversed-phase (RP) high performance liquid chromatography (HPLC; 75–25% MeCN/H2O for 22 min) to yield compounds **2** (11 mg) and **15** (6 mg).

Hemiacetalmeroterpenoid A (**1**): white powder, m.p. 122.8–124.1 ◦C; [*α*] 25 D -52 (*c* 0.02, MeOH), UV (MeOH) λmax (log *ε*): 206 (2.52) (Figure S33); ECD (MeOH) λmax (Δ*ε*): 240 (+5.47), 301 (−1.14), 362 (+0.61); 1H (600 MHz, CD3OD) and 13C NMR (150 MHz, CD3OD) data, see Table 1; HR-ESI-MS: *m*/*z* 459.23709 [M+H]+ (calcd. for C26H35O7, 459.23773).

Hemiacetalmeroterpenoid B (**2**): white powder, m.p. 106.9–108.4 ◦C; [*α*] 25 D −56 (*c* 0.02, MeOH), UV (MeOH) λmax (log *ε*): 205 (2.83), 238 (1.36) (Figure S34); ECD (MeOH) λmax (Δ*ε*): 206 (−11.92), 248 (+3.38), 311 (−1.19); 1H (600 MHz, CD3OD) and 13C NMR (150 MHz, CD3OD) data, see Table 1; HR-ESI-MS: *m*/*z* 445.25772 [M+H]+ (calcd. for C26H37O6, 445.25847).

Hemiacetalmeroterpenoid C (**3**): white powder, m.p. 100.8–102.6 ◦C; [*α*] 25 D −66 (*c* 0.02, MeOH), UV (MeOH) λmax (log *ε*): 205 (2.51), 260 (1.78) (Figure S35); ECD (MeOH) λmax (Δ*ε*): 206 (−18.31), 240 (+12.72), 310 (−2.18); 1H (600 MHz, CD3OD) and 13C NMR (150 MHz, CD3OD) data, see Table 1; HR-ESI-MS: *m*/*z* 509.25015 [M+Na]+ (calcd. for C28H38O7Na, 509.25097).

Astellolide J (**14**): yellow powder, m.p. 202.9–204.5 ◦C; [*α*] 25 D +16 (*c* 0.02, MeOH), UV (MeOH) λmax (log *ε*): 216 (3.15) (Figure S36); ECD (MeOH) λmax (Δ*ε*): 203 (−1.82), 225 (+3.27); 1H (400 MHz, CD3OD) and 13C NMR (100 MHz, CD3OD) data; HR-ESI-MS: *m*/*z* 305.13565 [M+Na]+ (calcd. for C15H22O5Na, 305.13594).

Astellolide Q (**15**): yellow powder, m.p. 160.1–162.2 ◦C; [*α*] 25 D +12 (*c* 0.02, MeOH), UV (MeOH) λmax (log *ε*): 218 (3.62) (Figure S37); ECD (MeOH) λmax (Δ*ε*): 232 (+5.19); 1H (400 MHz, CD3OD) and 13C NMR (100 MHz, CD3OD) data, see Table 2; HR-ESI-MS: *m*/*z* 347.14578 [M+Na]+ (calcd. for C17H24O6Na, 347.14578).


**3.2 Assessment of GLOF using remote sensing data and GIS**

Rugged mountain conditions make it difficult to investigate the glacial lakes for the whole region. However, the end moraine and the lakes in the blocked river valleys (e.g., Khurdopin glacial lake) were investigated with physical visits. However, the area's calculations and the causes of surging were made through remote sensing data and GIS

**109**

*Risks of Glaciers Lakes Outburst Flood along China Pakistan Economic Corridor*

**) Ice reserve (km3**

Swat 233 223.55 12.221 255 15.86 2 Chitral 542 1903.67 258.817 187 9.36 1 Gilgit 585 968.1 83.345 614 39.17 8 Hunza 1050 4677.34 808.794 110 3.21 1 Shigar 194 2240.08 581.27 54 1.09 0 Shyok 372 3547.84 891.8 66 2.68 6 Indus 1098 688 46.38 574 26.06 15 Shingo 172 36.91 1.009 238 11.59 5 Astore 588 607.03 47.931 126 5.52 9 Jhelum 384 148.18 6.943 196 11.78 5

**Glaciers Glacial lakes**

**) No. Area (km2**

**) Potential danger**

techniques. The Landsat satellite images for May and June 2017 were downloaded from the website; http://earthexplorer.usgs.gov/ to explore the formation of newly developed lakes due to river blockage caused by the surging of Khurdopin glacier. The formation of the newly developed lakes was identified from the visual interpretation of the images in the ArcGIS tool, whereas Temporal Geodetic mass balance is employed to compute the vertical changes in glaciers by using remote sensing data of that region. The potential GLOF lakes were identified base on the following criteria

*Summary of glaciers, glaciers lakes, and potentially dangerous lakes in CPEC region [31].*

The rise in water level in glacial lakes, which creates the condition to breach the lake. The lakes form on the glacial surface, which produces the combined effect with a

The valley lake also becomes the potential GLOF lake due to short distance from

A lake several times breaches and damages the downstream. These types of lakes

The physical conditions of the surrounding of the lake also play a vital role to

There is still no standard to identify the potential glacial lakes. The above men-

Remote sensing and field investigations are two basic methodologies used to assess the GLOF events (**Table 2**) and their credible effects. The number of glacial lakes, their areas, and geodetic mass balance for surging glaciers have been estimated through remote sensing techniques; whereas, field investigations help to assess the severity of the GLOF event. Moreover, the possible disaster from the potential hazard lake can be investigated through field investigations in terms of

Pakistan Snow and Ice Hydrology Project (PSIHP) of WAPDA in collaboration with a Canadian University studied the Khurdopin glacier for precipitation input. They also did field visit of Batura glacier and Passu lake through the collaboration of Joint Venture of National Science Foundation of China, under the umbrella of the institute of international Rivers and Eco-security, Yunnan University,

mother glaciers tongue and the size of lake also plays an important role.

tion criteria and condition decide the potential dangerous glacial lakes.

barrier strength, discharge conditions, and depth of the lake.

*DOI: http://dx.doi.org/10.5772/intechopen.93459*

**no. Area (km2**

**River basins**

**Table 1.**

and physical conditions [24]:

filled again and breach again.

group of lakes. It became potentially dangerous lakes.

identify the potential dangerous glacial lake.

**3.3 Field investigations for GLOF events**

*Risks of Glaciers Lakes Outburst Flood along China Pakistan Economic Corridor DOI: http://dx.doi.org/10.5772/intechopen.93459*

#### **Table 1.**

*Glaciers and the Polar Environment*

April, respectively [30].

**Figure 1.**

**3. Materials and methods**

*Study area of China Pakistan economic corridor.*

**3.1 Glaciers along CPEC route**

as major lakes, which contribute 62% of the total lakes. These major lakes form 93% of the lake area of the basin. New glacial lakes also formed due to glaciers thinning and retreating of this region. These lakes are categorized according to risk, 52 glacial lakes identified in this region. Passu lake has experienced historical GLOF events, which lie in the Hunza River basin [6]. The location of Passu lake is 38 km away and directed to the East-West of Passu glacier in the HKH region (**Figure 1**). The climate of Hunza is moderate, which have minimum and maximum temperature of 16 and 35.9°C, respectively. The annual average rainfall in this region is 136.2 mm with a minimum (2.1 mm) and maximum (283.2 mm) in November and

The CPEC route passes through the Hunza River basin which is a glaciated region of Gilgit Baltistan. The route starts from China to Pakistan through the Sost border which lies in the Hunza River basin. Approximately, 28% of the Hunza basin area is covered by glaciers, and Passu, Batura, and Ghulkin are some known glaciers that exist along the CPEC route (**Table 1**), which have an established history of GLOF events. The Karakoram Highway and other roads in Shimshal and the Nagar River basins have been damaged many times because of GLOF events from the glaciers.

Rugged mountain conditions make it difficult to investigate the glacial lakes for the whole region. However, the end moraine and the lakes in the blocked river valleys (e.g., Khurdopin glacial lake) were investigated with physical visits. However, the area's calculations and the causes of surging were made through remote sensing data and GIS

**3.2 Assessment of GLOF using remote sensing data and GIS**

**108**

*Summary of glaciers, glaciers lakes, and potentially dangerous lakes in CPEC region [31].*

techniques. The Landsat satellite images for May and June 2017 were downloaded from the website; http://earthexplorer.usgs.gov/ to explore the formation of newly developed lakes due to river blockage caused by the surging of Khurdopin glacier. The formation of the newly developed lakes was identified from the visual interpretation of the images in the ArcGIS tool, whereas Temporal Geodetic mass balance is employed to compute the vertical changes in glaciers by using remote sensing data of that region. The potential GLOF lakes were identified base on the following criteria and physical conditions [24]:

The rise in water level in glacial lakes, which creates the condition to breach the lake. The lakes form on the glacial surface, which produces the combined effect with a group of lakes. It became potentially dangerous lakes.

The valley lake also becomes the potential GLOF lake due to short distance from mother glaciers tongue and the size of lake also plays an important role.

A lake several times breaches and damages the downstream. These types of lakes filled again and breach again.

The physical conditions of the surrounding of the lake also play a vital role to identify the potential dangerous glacial lake.

There is still no standard to identify the potential glacial lakes. The above mention criteria and condition decide the potential dangerous glacial lakes.

#### **3.3 Field investigations for GLOF events**

Remote sensing and field investigations are two basic methodologies used to assess the GLOF events (**Table 2**) and their credible effects. The number of glacial lakes, their areas, and geodetic mass balance for surging glaciers have been estimated through remote sensing techniques; whereas, field investigations help to assess the severity of the GLOF event. Moreover, the possible disaster from the potential hazard lake can be investigated through field investigations in terms of barrier strength, discharge conditions, and depth of the lake.

Pakistan Snow and Ice Hydrology Project (PSIHP) of WAPDA in collaboration with a Canadian University studied the Khurdopin glacier for precipitation input. They also did field visit of Batura glacier and Passu lake through the collaboration of Joint Venture of National Science Foundation of China, under the umbrella of the institute of international Rivers and Eco-security, Yunnan University,

#### **Table 2.**

*History of major GLOF events in CPEC region.*

Kunming, China, and ICIMOD. The remote sensing and field observations analysis of Khurdopin glacier provides up to date evidence about glacier surge and its possible impacts on the downstream populations because of the newly developed lake.