Abstract:

Calculation of the effective charge of refrigerants in a refrigeration system depends on the separation characteristics of refrigerants in the oil-refrigerant mixture. In the present study, the mass fraction variation with time for the refrigerants in the oil-refrigerant mixture is experimentally measured, and a mathematical model is developed to predict the mass fraction variation. In the experiment investigation, an experiment rig was built based on the principle that the refrigerant will separate from the solution when the external pressure drops, and the real-time variation of the mass fraction of R410A separating from POE68 lubricant is obtained by measuring the refractive index of the solution. It is found that the liquid refrigerant almost simultaneously evaporates to separates from the mixture as the pressure sharply decreases; the mass fraction variation of refrigerants firstly rapidly decreases, then slowly decreases, and finally stabilizes; with the increase of pressure drop, the maximum separation rate of refrigerant is increased by up to 16.4% per second, and the stabilization time of the mass fraction for the refrigerants is maximally decreased to 4 s. In the model developing, a refrigerant separation model is developed to predict the mass fraction changes of refrigerant with time based on the one-dimensional mass diffusion principle. The results show that the average absolute error between the experimental data and predicted data is less than 5% and the average relative error is less than 25%.

Key words: binary mixture, separation, experiments, dynamic modeling, vapor-liquid equilibria

摘要：

制冷系统中的有效充注量的计算依赖于制冷剂在润滑油中的动态析出特性。本文的目的是通过实验研究制冷剂在润滑油中析出时质量分数随时间变化的特性，并建立预测制冷剂质量分数动态变化的数学模型。实验方面，采用了外压骤降时制冷剂会析出的原理，搭建了动态溶析实验台，通过测量溶液折射率得到了R410A制冷剂在POE68润滑油中析出时质量分数的实时变化。实验结果表明，随着压力的骤降，制冷剂几乎同步析出，质量分数呈现急速下降、缓慢下降并最后稳定的动态变化趋势；随着压降幅度的增大，制冷剂最大析出速率增大，质量分数每秒最大下降16.4%，制冷剂质量分数稳定的时间变短，最短仅有4 s。建模方面，基于一维质量扩散原理，开发了能够预测制冷剂质量分数随时间变化的析出模型。模型结果表明，质量分数预测值与实验数据的平均绝对误差小于5%，平均相对误差小于25%。

关键词: 二元混合物, 析出, 实验, 动态建模, 汽液平衡