Investigation of Heat Transfer on Microchannel Evaporator
Date Issued
2007
Date
2007
Author(s)
Chiu, Yi-Shan
DOI
zh-TW
Abstract
Microchannles provide a large heat transfer surface area per unit flow volume. Phase change in microchannel evaporator makes it desirable for three reasons：(1) high critical heat flux (2) high heat transfer coefficient (3) low coolant flow rate. Therefore, they are well suited for high heat flux removal and high temperature uniformity cooling applications.
Present research successfully established a reliable microchannel evaporator experimental system to investigate heat transfer behavior in microchannels and enhance heat transfer performance by sintered porous structure. The working liquid used is refrigerant R-134a, operating pressure is 8 bar, and mass flux ranges from 222 to 464kg/m2s. The microchannel evaporator was fabricated from oxygen-free copper, and top platform was cut to form 62 parallel rectangular 225μm×660μm microchannels. The top platform of porous microchannel evaporator was sintered to form 62 parallel rectangular 210μm×660μm microchannels. The thickness of porous surface structure is 96μm, and the porosity is 54%. The average particle size is 30μm.
The results reveal that flow boiling pressure drop is primarily affected by mass velocity and heat flux, which increases with increasing mass velocity and heat flux. The predictability of separated flow model is much better than homogeneous equilibrium model on flow boiling pressure drop in microchannel, and the lowest MAE is 10.6%. Flow boiling in microchannel can be classified either as boiling-dominated region or convection-dominated region. In boiling-dominated region, the heat transfer coefficient increases with increasing heat flux. In convection-dominated region, the heat transfer coefficient decreases with decreasing vapor quality. These two region are separated by the peak value of heat transfer coefficient, and this separation will change if mass velocity differs. The heat transfer data closely match with some previous correlations, and the lowest MAE is 13.6%. The critical heat flux is primarily affected by mass velocity, which increases with increasing mass velocity. The CHF data also closely match with some previous correlations, and the lowest MAE is 2.6%.
As for heat transfer enhancement, in the same volume flow rate 167 ml/min, the heat transfer coefficient and CHF of porous microchannel evaporator is enhanced by 2-3.8 times and 19-23% respectively.
Subjects
微流道
沸騰熱傳
多孔性結構
熱傳增強
microchannel
flow boiling
porous
sintered
Type
thesis
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