The present study examines the influence of polyolester lubricant oil (POEA-68 and POEA-170) with R-134a on the nucleate pool boiling performance for a horizontal smooth tube. The heat flux ranges from 10 kW/m² to 90 kW/m² and the lubricant mass fraction varied from 1% to 10% at a saturation temperature of 10 °C, 0 °C and, -6 °C, respectively. The experimental results show that the heat transfer coefficient (HTC) of the pure refrigerant is increased with an increase in saturation temperature. But the presence of lubricant oil alters the HTC considerably. The addition of 3% POEA-68 lubricant shows the highest 29.3% HTC enhancement relative to pure refrigerant at a supplied heat flux of 70 kW/m² and at a saturation temperature of 0 °C. Whereas for R-134a/POEA-170 lubricant mixture at 3% of mass fraction, the highest enhancement in HTC was around 26% at a supplied heat flux of 70 kW/m² and -6 °C saturation temperature. The bubble size is reduced and the bubble density is increased appreciably with the addition of POE oil. It was observed that the HTC of lubricant-refrigerant mixtures differs appreciably with the variation of lubricant oi mass fraction ($\omega$). The HTC first decreases at a very low mass fraction ($\omega$ ≤ 1%), followed by an appreciable increase in the range of 1% ≤ $\omega$ ≤ 3%, and finally reveals a continuous decline for the higher mass fraction. The dramatic decrease in HTC for lubricant-refrigerant mixture is associated with mass transfer resistance and a significant increase in surface tension.

本研究研究了带有R-134a的多元醇酯润滑油（POEA-68和POEA-170）对水平光滑管的核池沸腾性能的影响。在饱和温度分别为10°C，0°C和-6°C时，热通量从10 kW / m ²到90 kW / m ²，润滑剂质量分数从1％到10％变化。实验结果表明，纯制冷剂的传热系数（HTC）随着饱和温度的升高而增加。但是润滑油的存在极大地改变了HTC。相对于纯制冷剂，在提供的70 kW / m ^2的热通量下，添加3％POEA-68润滑剂显示出最高的HTC增强29.3％且饱和温度为0°C。对于质量分数为3％的R-134a / POEA-170润滑剂混合物，在提供的70 kW / m ^2的热通量和-6°C的饱和温度下，HTC的最高增强约为26％。加入POE油后，气泡尺寸减小，气泡密度明显增加。观察到，润滑剂-制冷剂混合物的HTC随润滑剂或质量分数的变化而显着不同（$\omega$）。HTC首先以非常低的质量分数下降（$\omega$ ≤1％），然后在1％≤范围内显着增加$\omega$≤3％，并最终显示出较高质量分数的连续下降。润滑剂-制冷剂混合物的HTC急剧下降与传质阻力和表面张力显着增加有关。