兩相冷卻系統之微蒸發器研究

本研究利用單相熱交換器的微流道設計，與廠商合作開發出泵浦，將熱交換器配合泵浦修改，使其成為一體化設計的薄型水泵，製作出較薄的取熱端，成為小型冷卻系統。與市售的系統比較，本研究製作的水泵在性能不變的情形下，可降低系統重量83 %，減少單相冷卻系統的耗能66 %。另進行兩相的研究，藉由可視化的觀察以及熱傳實驗，了解蒸發器內部的現象。直線流道與山型紋流道熱交換器，在兩相實驗中，壓降隨著乾度與流量的增加而增加，此現象符合傳統的兩相理論。兩相熱傳研究方面，山型紋流道的熱傳係數隨著乾度與流量的增加而增加，直線流道則是相反，熱傳係數隨著乾度增加而減少。從可視化觀察中，山型紋流道在實驗中，因為表面張力的作用，使上下流道的夾角聚集液體，當乾度增加時，流道底面仍保有液體蒸發，流道不會乾涸。直線流道觀察到乾涸現象，計算乾涸的時間與面積。在加熱量60 W時，53 %的時間流道內沒有液體，平均乾涸的面積有26 %。以乾涸面積與時間乘積為乾涸比例，發現乾涸比例與加熱量呈現線性關係。加熱量越高，乾涸的時間與面積均上升。山型紋蒸發器不易乾涸且熱傳係數較高，同時所需的泵動力低於單相狀態，更適用於兩相冷卻系統。

關鍵字

小型冷卻系統；微流道；山型紋；兩相蒸發器

並列摘要

This study incorporated the author’s previously published micro heat exchanger, which size of channel is hundreds of micron. A newly designed micro pump was combined with micro-channel heat exchanger to develop a high-performance, mini size liquid cooling system. In comparing to commercial product, thin pump in this study reduced weight of system about 83 % and power consumption of that about 66 %. Attributed to its high heat transfer coefficient, evaporating cooling involving the use of micro heat exchanger is considered a possible thermal management solution for cooling of high heat flux electronic devices. The desire to develop high-performance micro heat exchanger operating in the evaporation regime provides a major motivation for the present work. Flow boiling heat transfer in a micro heat exchanger with straight and chevron flow passages were tested in the present study. The boiling flow pattern was also observed for further understanding of the heat transfer mechanisms. The test results show that the heat transfer coefficient increased with increasing flow rate in both chevron and straight flow passages micro heat exchangers. But the effect of heat flux on the heat transfer coefficient in the straight passages heat exchanger is in adverse to that in the chevron passages heat exchanger. The heat transfer coefficient increased with increasing heat flux in the chevron passages heat exchanger but decreased in the straight passages heat exchanger. The flow visualization through transparent cover heat exchangers shows that partial dryout happened in the straight passages heat exchanger at the lowest heating rate condition. This caused a poor heat transfer area and significantly degraded the overall heat transfer performance. The partial dryout area ratio and time fraction increased with increasing heat flux and therefore the heat transfer coefficients decreased with increasing heating rate. For flow boiling in chevron passages heat exchanger, liquid film was dragged at the intersection corner between the upper and lower plate chevron passages by the surface tension force and supplement liquid flowed back into the heating surface from other chevron passages. No partial dryout was observed and therefore, the heat transfer performance test results followed the trend of conventional correlations. The chevron passages heat exchanger can be used in two phase cooling system.

並列關鍵字

Mini-liquid cooling system ； Micro heat exchanger ； Flow boiling ； Flow visualization ； Chevron flow passage

參考文獻

王啟川，2007，熱交換設計，五南圖書出版公司，台北。

Agostini, B., Fabbri, M., Park, J.E., Wojtan, L., Thome, J.R., and Michel, B., 2007, ”State of the Art of High Heat Flux Cooling Technologies,” Heat Transfer Engineering, Vol. 28, No. 4,pp. 258-281.

Agostini, B., and Bontemps, A., 2005, ”Vertical Flow Boiling of Refrigerant R134a in Small Channels,” International Journal of Heat and Fluid Flow, Vol. 26, pp. 296-306.

Asadi, M., Xie, G., and Sunden, B., 2014, ”A Review of Heat Transfer and Pressure drop characteristic of Single and Two-Phase microchannels,” International Journal of Heat and Mass Transfer, Vol. 79, pp. 34-53.

Cho, E. S., Koo, J. M., Jiang, L., Prasher, R. S., Kim, M. S., Santiago, J. G., Kenny, T. W., and Goodson, K. E., 2003, ”Experimental Study on Two-Phase Heat Transfer in Microchannel Heat Sinks with Hotspots, “ Proceedings 19th IEEE SEMI-THERM Symposium.

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兩相冷卻系統之微蒸發器研究

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