A Loop Thermosyphon Type Cooling System for High Heat Flux

Abstract

With rapid development of the semiconductor technology, more efficient cooling systems for electronic devices are needed. In this situation, in the present study, a loop thermosyphon type cooling system, which is composed mainly of a heating block, an evaporator and an air-cooled condenser, is investigated experimentally in order to evaluate the cooling performance. At first, it is examined that the optimum volume filling rate of this cooling system is approximately 40%. Next, four kinds of working fluids, R1234ze(E), R1234ze(Z), R134a and ethanol, are tested using a blasted heat transfer surface of the evaporator. In cases of R1234ze(E), R1234ze(Z), R134a and ethanol, the effective heat flux, at which the heating block surface temperature reaches 70° C , is 116 W/cm 2 , 106 W/cm 2 , 104 W/cm 2 and 60 W/cm 2 , respectively. This result indicates that R1234ze(E) is the most suitable for the present cooling system. The minimum boiling thermal resistance of R1234ze(E) is 0.05 (cm 2 · K)/W around the effective heat flux of 100 W/cm 2 . Finally, four kinds of heat transfer surfaces of the evaporator, smooth, blasted, copper-plated and finned surfaces, are tested using R1234ze(E) as working fluid. The boiling thermal resistance of the blasted surface is the smallest among tested heat transfer surfaces up to 116 W/cm 2 in effective heat flux. However, it increases drastically due to the appearance of dry-patch if the effective heat flux exceeds 116 W/cm 2 . On the other hand, in cases of copper-plated and finned surfaces, the dry-patch does not appear up to 150 W/cm 2 in effective heat flux, and the boiling thermal resistances of those surfaces keep 0.1 (cm 2 · K)/W.