4.3. Loop heat pipe design

The experiments' goal was to determine the influence of various dependencies such as kind of wick structure, kind of working fluid, and amount of working fluid on LHP cooling efficiency. Therefore, special experimental LHP was designed with aluminum block mounted on the evaporator part to fix insulated gate bipolar transistor (IGBT). All parts of LHP (evaporator,

Figure 13. Porous sintered wick structures: a—Copper, b—Nickel.

Figure 14. LHP model: 1—compensation chamber; 2—rubber seal; 3—evaporator; 4—vapor line; 5—condenser; 6 filling valve; 7—liquid line.

4.4. Determination of loop heat pipe cooling efficiency

Porosity (%) 67–70 Outer/inner diameter (mm) 26/8

Table 6. Main design parameters of the LHP.

150–350 W.

Determination of the LHP cooling efficiency was performed on the experimental measuring unit, which is shown in Figure 15. Fixed IGBT on the evaporator of LHP was loaded by electric power. Produced heat by IGBT on the evaporator of LHP was removed by working fluid to the condenser of LHP. The condenser of LHP was made as tube heat exchanger and the cooling circle of heat exchanger was regulated by the thermostat at constant temperature 20C. The gist of the LHP cooling efficiency determination is on measuring IGBT temperature with gradually increasing loaded heat by IGBT in steps 50 W from 100 W till the IGBT reaches permissible temperature 100C. The temperature of the IGBT was measured by thermocouple inserted under IGBT. For better heat transport, thermal conductive paste was applied on the connection between

At first, measurements of influence of the working fluid amount on LHP cooling efficiency were performed. Four amounts 40, 50, 60, 80% of total LHP volume in LHP with working fluid water were investigated. In Figure 16, the influence of working fluid amount in dependencies on LHP cooling efficiency with working fluid water depending on loaded heat is shown. It is seen that the LHP with working fluid volume is 60% and the best operating LHP is in range of

Next, the measurement of influence of wick structures on LHP ability to remove heat from IGBT was performed. The measurement was performed on LHP with the working fluid of water and amount of 60% total LHP volume. In Figure 17, the results of the influence of the wick structure on LHP cooling efficiency depending on loaded heat are shown. Two wick

IGBT and aluminum block and between aluminum block and the evaporator.

Evaporator Compensation chamber

Outer/inner diameter (mm) 28/26 Charge mass

Saddle Vapor line

Sintered copper powder Liquid line

Outer/inner diameter (mm) 26/8 Condenser

Total length (mm) 130 Outer/inner diameter (mm) 35/33 Active length (mm) 86 Length (mm) 110

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http://dx.doi.org/10.5772/intechopen.71763

Material Copper Distilled water 60%

Size (length/high/wide) 118/89/40 Length (mm) 670 Material Alumina Outer/inner diameter (mm) 6/4

Number of vapor grooves 6 Length (mm) 820 Porosity (%) 52–55 Outer/inner diameter (mm) 6/4

Sintered nickel powder Length (mm) 420 Number of vapor grooves 6 Outer/ inner diameter (mm) 6/4

compensation chamber, vapor and liquid line) were made from copper pipes. As a working fluid, distilled water and acetone were used. Inside the evaporator, wick structure made by sintering metal powder was inserted. To avoid heat loss (it is also called heat leak) into the compensation chamber, a brass flange with rubber seal was inserted between the evaporator and the compensation chamber. In Figure 15, the model of LHP design is shown, and the main parameters of LHP design are given in Table 6.

Figure 15. Schema of measuring unit: 1—PC; 2—data logger; 3—IGBT; 4—electric power supply; 5—thermocouple; 6 thermostat.


Table 6. Main design parameters of the LHP.

compensation chamber, vapor and liquid line) were made from copper pipes. As a working fluid, distilled water and acetone were used. Inside the evaporator, wick structure made by sintering metal powder was inserted. To avoid heat loss (it is also called heat leak) into the compensation chamber, a brass flange with rubber seal was inserted between the evaporator and the compensation chamber. In Figure 15, the model of LHP design is shown, and the main

Figure 15. Schema of measuring unit: 1—PC; 2—data logger; 3—IGBT; 4—electric power supply; 5—thermocouple; 6—

Figure 14. LHP model: 1—compensation chamber; 2—rubber seal; 3—evaporator; 4—vapor line; 5—condenser; 6—

parameters of LHP design are given in Table 6.

filling valve; 7—liquid line.

156 Porosity - Process, Technologies and Applications

thermostat.
