酯類冷凍油與R-134a冷媒混合物於平滑管外之池沸騰熱傳研究

The study of pool boiling characteristics for R-134a and lubricant oil mixture

王孝哲(Xiao-Zhe Wang)

指導教授 ： 崔燕勇 ； 王啟川

國立交通大學/工學院/機械工程系所/碩士(2019年)

摘要

本計畫探討R-134a於平滑管外之沸騰熱傳性能，並添加可與冷媒完全互溶之冷凍潤滑油，而測試管為19.05mm，實驗控制的參數有熱通量10~90 kW/m2、飽和溫度10, 0, -6℃、冷凍潤滑油黏度68, 170 cSt，另外油重量比例以1%, 3%, 5%, 10%來探討冷凍油對於熱傳係數之影響。實驗顯示高黏度的POEA-170熱傳增益皆比POEA-68還高，而兩種混合物在油比例1%~5%皆有讓熱傳增益的可能性，其中在油比例3%飽和溫度-6℃可達到最高峰46%。而熱傳增益從5%開始下降，但仍然有最高26%的情況發生。當油比例提升到10%時，熱傳係數皆比純冷媒還差，但高黏度的POEA-170在低熱通量時的下降幅度僅有6%，而低黏度的POEA-68則下降了21%，但在高熱通量90 kW/m2時兩者又都一起下降了40%左右，可能在高熱通量時黏滯性對熱傳的增益影響低於油層阻擋熱傳的影響，從觀察視窗也可看出兩者的成核址密度也有明顯的差異。而每個油比例的熱傳增益最大值皆發生在-6℃，且黏度越高的冷媒有越高的熱傳增益，實驗也透過高速攝影機來分析氣泡大小與氣泡生成頻率，且兩者在油比例從1%提升到3%的氣泡生成時間最大有57%的提升，可能也是造成熱傳在3%最高的主因。

關鍵字

R-134a ； 酯類冷凍潤滑油 ； 池沸騰 ； 平滑管 ； 冷凍油黏度

並列摘要

In this study, the effects of lubricant on the nucleate pool boiling heat transfer of the R-134a refrigerant on the outside of smooth tubes are examined in detail. To examine the aforementioned effects, copper tubes with diameters of 19.05 mm is employed as test samples. Cartridge heaters, which is installed inside of the tubes, play as heat sources. Two lubricating oils of POEA-68 and POEA-170 are utilized as the testing lubricant. The influences are examined with the heat fluxes in the range from 10 kW/m2 to 90 kW/m2, and the weight ratio between the lubricant and the refrigerant ranging from 1% to 10% at the saturated temperatures of -6 °C, 0 °C, and 10 °C. A high-speed camera is also adopted for analyzing the boiling phenomena. For all cases in this study, it is found that the nucleate boiling heat transfer of the mixture between lubricant and refrigerant with the weight ratio in the range from 1% to 5% is better than that of the pure refrigerant, and the oil with higher viscosity (POEA-170) performs better than that of the lower viscosity (POEA-68). In specifically, maximum heat-transfer improvement of 46% compared to the pure refrigerant is achieved by the mixture of the POEV-170 and R-134a refrigerant with a mixed ratio of 3% and saturated temperature of -6 °C. The improvement is still achieved 26% at the 5% ratio; however, it decreases with the increase in the weight ratio greater than 5%. At the 10% ratio and low heat fluxes, the nucleate boiling performances are 6% and 21% worse than that of the pure refrigerant for mixtures of POEA-170 and POEA-68, respectively. At a heat flux of 90 kW/m2, the nucleate boiling performance is dropped to 40% for both of the mixtures. The time of the bubble generation is increased up to approximate 57% for the increase in the weight ratio from 1% to 3%.

並列關鍵字

R-134a ； Polyol Ester lubricant ； pool boiling ； smooth tube ； viscosity

參考文獻

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