Enhanced Boiling Heat Transfer in Sintered Microchannels with Porous Media
Date Issued
2007
Date
2007
Author(s)
Huang, Chun-Yu
DOI
zh-TW
Abstract
Microchannel evaporator has the advantages of compactness, minimal coolant usage, high heat transfer coefficient, and high critical heat flux. Most of recent researches emphasize heat transfer mechanism, flow instability, and pressure drop analysis but not too much focuses on heat transfer enhancement in microchannel evaporator. For the purpose of enhancing boiling heat transfer in microchannel evaporator, this research takes advantage of porous media with more nucleation sites and larger inner areas to produce microchannels.
This study manufacture microchannels with porosity range between 41% and 66% by adjusting the sintered temperature and we use dendritic copper powders in average particle size of 30μm. The hydraulic diameter’s range of these porous microchannels is 292μm to 327μm. The working fluid used is refrigerant R-134a, operating pressure is 800 kpa, and volume flow rate ranges from 100 ml/min to 166 ml/min.
The result reveals that heat transfer coefficient of solid microchannel evaporator is primarily affected by heat flux、quality and volume flow rate. As quality and heat flux increase, the heat transfer coefficient will rise up first and then go down. The peak value will happen earlier as long as flow rate higher and the overall boiling heat transfer capacity of solid microchannel evaporator is better in higher volume flow rate. The same trend can be observed in porous microchannel evaporator. Furthermore, with the increase of the porosity, the peak value will be shown up earlier. In the aspects of boiling heat transfer enhancement, the porous microchannel evaporator with the highest porosity of 66% performs best in heat transfer enhancement and the heat transfer enhancement ratios are 1 to 5 times, comparing with solid microchannel evaporator. As far as CHF is concerned, porous microchannel evapoator have the same tendency of solid microchannel evaporator. CHF will go higher as volume flow rate increases. CHF can reach a value of 93W/cm2 to 143W/cm2 and it is enhanced 5% to 23%.
With the same of characteristics between solid and porous microchannel evaporator, that pressure drop rises with the increase of volume flow rate and heat flux, the latter’s pressure drop will rise up around 30% to 260% as porosity increases. When the volume flow rate is 166ml/min, the highest pressure drop happens to porous microchannel evaporator with porosity of 66% and it is 30kpa.
Subjects
微流道
沸騰熱傳增強
多孔性結構
microchannel
Enhanced boiling
porous media
Type
thesis
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