Session: 11-13-01 Fundamentals and Applications of Evaporation, Boiling and Condensation

Paper Number: 73182

Start Time: Wednesday, 10:25 AM

73182 - Experimental Investigation on the Effect of Condenser Length on the Heat Transfer Performance of an ω-Shaped Cryogenic Axially Grooved Heat Pipe 

The Ω-shaped axially grooved heat pipes have been extensively used in the thermal control systems of aerospace projects due to their powerful heat transfer capability, excellent temperature uniformity, long transmission distance, lack of moving parts and stable operation in micro-gravity environments. In order to optimize the coupling between the heat pipe and the cold source and to study the influence of different condenser length on the performance of the heat pipe, a set of Ω-shaped axially grooved heat pipe filled with nitrogen as the working fluid with a gas reservoir working at room temperature was designed based on the heat transport demand in space cryogenic environment. The total length of the heat pipe is 575 mm，the outer diameter is 15 mm, and the volume of gas reservoir is 300 ml. The experimental system consists of an Ω-shaped axially grooved heat pipe, a vacuum insulation system, a cryogenic refrigeration system, a temperature measurement system, a heating system and a nitrogen filling system. The supercritical startup performance of the heat pipe in the liquid nitrogen temperature zone and the heat transfer performance under different heat fluxes of the condensation section are tested. The length of evaporation section of the heat pipe is set to be 80 mm in all tests, and the lengths of the condenser section are 77 mm, 52 mm, 31 mm, 10 mm, respectively. The heat transfer resistance of the heat pipe under different working conditions are analyzed. The experimental results reveal that the heat pipe with gas reservoir starts up rapidly as soon as the condensation section is cooled below the critical temperature of liquid nitrogen. The heat pipe has a high degree of temperature uniformity. When the liquid filling rate of the heat pipe is 100%, for a given operating temperature and the same heat load, with the decrease in the condenser length, the condenser heat flux increases, the heat transfer resistance of the heat pipe increases, and the maximum heat transfer capacity will decrease. It is postulated that this phenomenon is caused by the decrease of capillary pressure due to the increase of the contact angle between the working fluid and the wick surface. For a given operating temperature with the same length of the condensation section, the heat transfer resistance of the heat pipe will decrease as the heat load increases. This heat pipe can work properly with the condenser length of only 10 mm, whose  heat transfer resistance is 0.12K/W when the heat load is 20 W. When the length of condenser section is 77 mm, the heat transfer resistance is only 0.08 K/W when the heat load is 20 W . The Different length of condenser results in different heat exchange areas. Therefore, a greater degree of supercooling is required to dissipate the same heat load with a larger heat flux. This results in a lower temperature of the condenser, which in turn increases the total thermal resistance of the heat pipe. Therefore, different length of the condenser section has an important impact on the heat transfer performance of the heat pipe.

Presenting Author: Yongyan Li Shanghai Institute of Technical Physics Chinese Academy of Sciences

Authors:

Yongyan Li Shanghai Institute of Technical Physics Chinese Academy of Sciences
Nanxi Li Shanghai Institute of Technical Physics Chinese Academy of Sciences
Deping Dong Shanghai Institute of Technical Physics Chinese Academy of Sciences