TITLE:
A Loop Thermosyphon Type Cooling System for High Heat Flux
AUTHORS:
Jiwon Yeo, Seiya Yamashita, Mizuki Hayashida, Shigeru Koyama
KEYWORDS:
Cooling, Boiling, Loop Thermosyphon, Grobal Warming Potential, Thermal Resistance
JOURNAL NAME:
Journal of Electronics Cooling and Thermal Control,
Vol.4 No.4,
December
31,
2014
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/cm2, 106 W/cm2,
104 W/cm2 and 60 W/cm2, 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 (cm2·K)/W
around the effective heat flux of 100 W/cm2. 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/cm2 in effective heat flux. However,
it increases drastically due to the appearance of dry-patch if the effective
heat flux exceeds 116 W/cm2. On the other hand, in cases of
copper-plated and finned surfaces, the dry-patch does not appear up to 150 W/cm2 in effective heat flux, and the boiling thermal resistances of those surfaces
keep 0.1 (cm2·K)/W.