臺灣大學: 機械工程學研究所陳瑤明周珀丞Chou, Po-ChengPo-ChengChou2013-04-012018-06-282013-04-012018-06-282010http://ntur.lib.ntu.edu.tw//handle/246246/256271相變化熱傳應用於微流道具高均溫性與低工質需求等優點，能有效提高其散熱效率；多孔表面結構提供大量成核址和連通孔洞更能提升微流道熱傳性能。本研究於1平方英吋銅表面以樹枝狀銅粉燒結多孔微流道蒸發器，以R-134a為工質，在流量範圍133~417ml/min、飽和壓力800kpa下進行熱傳實驗。探討不同孔徑分布對多孔微流道之熱傳、壓降、壓力不穩定性的影響，並與平板流道進行比較。 實驗結果顯示平板微流道蒸發器的熱傳係數在乾度小於0.4前，屬於核沸騰機制；實驗所得熱傳係數代入Cooper池沸騰經驗式之總平均誤差為8.2%，而乾度於0.4以上，屬強制對流沸騰為主。臨界熱通量隨流量上升而增加，可達127.9W/cm2。而壓降則隨流量與熱通量上升而增加，帶入考慮表面張力與黏度之分離流壓降經驗式總平均誤差約17%。壓降震盪顯示平板微流道具有不穩定性，其震盪幅度在接近起始沸騰時最大，流量效應影響不大。 多孔性結構微流道蒸發器熱傳係數在低熱通量時就達到峰值，隨熱通量與乾度上升而下降，隨質量流率上升而增加，與平板流道乾度於0.4以上趨勢相近。探討不同參數的實驗發現，孔徑分布直接影響熱傳性能，而具雙孔徑分布結構更能有效提升。最佳多孔微流道熱傳係數較平板微流道提升10倍；臨界熱通量並與平板差異不大；壓降較平板微流道平均增加20%；而最大壓降振幅較平板微流道下降47%，顯示其散熱應用上與流動穩定方面極具潛力。Phase-change heat transfer provides advantages such as good temperature uniformity, less coolant flow rates requirement and high cooling efficiency. Porous media surface possesses a lot of nucleate sites and the connected pores which can enhance heat transfer coefficient. In present study, the flow boiling experiments were conducted with porous microchannels evaporators sintered with copper dendritic powder on 1 square inch copper substrates. Working fluid R-134a was used at volume flow rate from 133~417ml/min and the saturated pressure of 800kpa. The purpose of this research is to investigate heat transfer characteristics, pressure drop, pressure instability, heat transfer enhanced in different pore distributions and to compare with plane microchannels evaporators. The results of the plane microchannels evaporator showed the heat mechanism was dominated by the nucleation boiling before quality 0.4. The experiment data were substituted into the Cooper’s pool boiling correlation, the mean average error was 8.2%. On the other hand, when the quality was over 0.4, the heat mechanism was dominated by the forced convection boiling. Critical heat flux (CHF) increased with increasing volume flow rate and reached to 127.9W/cm2. The pressure drop increases with increasing heat flux and volume flow rate. The experiment results also substituted into the correlation considered surface tension and viscosity, and the average error was 17%. Pressure drop oscillation suggested the presence of instability inside the plane microchannels. The maximum amplitude of oscillation was found to be near the onset of nucleation and independent of volume flow rate. The experiment results showed that the heat transfer coefficient of porous microchannels reached the peak value at low quality, than decreased with increasing quality and increased with increasing volume flow rate. The trend is almost the same with plane microchannels when the quality is over 0.4. The investigation of different parameters indicated that pore distribution affects the heat transfer characteristic directly. The heat transfer coefficient can be enhanced with dual- pore distribution structure. The best performance were achieved by the porous microchannels and the heat transfer coefficient enhanced about 10 times larger than the plane microchannels. Pressure drop and the maximum pressure instability amplitude of porous structure channel was 20% higher and 47% lower than plane channel near the onset of nucleation respectively. To conclude the results of the study, the porous microchannels evaporator is highly potential for the industrial cooling applications and flow stability.3677958 bytesapplication/pdfen-US微流道沸騰熱傳增強多孔性結構孔徑分布microchannelboiling heat transfer enhancementporous structurepore distributionthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/256271/1/ntu-99-R97522311-1.pdf