Experimental Study of an Improved Capillary Pumped Looped System for Electronics Cooling
Yi- Hsiang Hung
|摘要:||本論文主要是改善毛細泵迴路系統在電子冷卻上之實驗研究，使用一溝槽外形的銅塊放置在蒸發器內部，其截面積尺寸為 ，並且此溝槽是由5個平行的矩形的通道構成用以提供蒸發器內的蒸氣流往蒸氣線，其每一個通道的尺寸為長 和寬為 、高為 ，並且在溝槽的上方和一多孔性材質緊密接觸，其尺寸為 且平均孔隙平徑為 。冷凝器是由水冷式的雙套管來達到冷卻的目地。另外，選用直徑為 光滑的鐵氟龍管來當作蒸氣線和液態線並且選用去離子水來當作實驗的工作流體，而在改善CPL系統的部份，我們將利用純棉的薄紗布去覆蓋在溝槽通道的側面和底面，用以增加蒸發器的蒸發面積。實驗的目的探討在不同輸入功率、冷凝器的冷卻溫度、工作流體的填充量、蒸發器和冷凝器之間的高度差及覆蓋在溝槽表面的紗布對熱傳性能的影響。在實驗參數的範圍上，加熱功率從5到260 W、冷卻溫度從20到40度、流體填充量從50 到75% 及蒸發器和冷凝器的高度差從0到10公分，此實驗的操作中止是以蒸發器的平均溫度到達80度為限。
An experiment is carried out in the present study to investigate an improved design of a CPL (Capillary Pumped Loop) system for electronic cooling. The evaporator of the CPL system is modeled by a grooved square copper plate of size glued onto another heated rectangular copper plate of the same size. The grooved copper plate contains five parallel rectangular open channels for the vapor generated in the evaporator to flow into a vapor transport line. Each channel is characterized by 30 mm in length, 2.4 mm in width, and 3 mm in height. A porous wick made from open-cell blowing foam of polyvinyl alcohol with a mean pore radius of 21μm and having a size of is placed on the grooved copper plate. The condenser is made of a double-pipe heat exchanger with liquid water flowing in the outer pipe. Besides, smooth teflon tubes of inside diameter 4.5 mm are chosen for the vapor and liquid transport lines. The deionized water is selected as the working fluid. Moreover, a thin cotton gauze layer of 150μm in thickness is covered on the side and bottom walls of the grooved channels to provide more surface area for liquid vaporization. Tests are conducted for the liquid inventory varied from 50% to 75%, cooling water temperature in the condenser from 20℃ to 40℃, condenser-evaporator relative height from 0 to 10 cm. The test is terminated when the mean evaporator temperature exceeds 80℃. In the study how the liquid inventory, cooling water temperature in the condenser, relative height between the condenser and evaporator, and cotton gauze layer covering affect the CPL performance is investigated in detail. The experimental results show that the liquid inventory significantly affects the heat transfer performance of the system. An optimal liquid inventory exists at which the maximum power input to the evaporator is the highest and the minimum thermal resistance of the CPL is the lowest. The CPL heat transfer capability is only slightly affected by the cooling water temperature in the condenser. But the evaporator temperature is noticeably higher for a higher cooling water temperature in the condenser. An increase in the relative height between the condenser and evaporator results in a significant improvement in the CPL performance. Besides, for a larger relative condenser-evaporator height the influences of the liquid inventory on the performance of the CPL are milder. Covering a thin cotton gauze layer on the side and bottom surfaces of the grooved channels can substantially improve the heat transfer performance of the CPL system under certain conditions. For other conditions the improvement is comparatively smaller. Finally, empirical correlations for the Qe,max and Rth,min are proposed for the CPL with and without cotton gauze covering for thermal design of CPU cooling. For all cases tested in the present CPL system the highest Qe,max is 255W.
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