An experimental study and empirical correlations to describe the effect of lubricant oil on the nucleate boiling heat transfer performance for R-1234ze and R-134a

In the present work, nucleate boiling heat transfer characteristics of R-134a and R-1234ze refrigerants subject to the influence of lubricant oil on a plate surface were experimentally examined. Eight types of lubricants, including POEA68, POEA120, POEA170, POEB68, POEB120, POEB170, POEC170, and POED 150, were used for investigations; the experiments were carried out at saturated temperatures of 0 °C and 10 °C, respectively. The oil concentrations range from 0% to 10% and heat fluxes vary from 10 kW/m2 to 70 kW/m2. The test results for pure refrigerants are in line with the existing data and correlations. With the presence of lubricant, the heat transfer coefficient may be slightly higher or lower than those of pure refrigerants, depending on the lubricant and operating pressure. However, all the heat transfer coefficients deteriorate appreciably as compared to the pure refrigerants when the oil concentration exceeds 5%. A correlation is developed that is capable of describing the influence of lubricant oil. The proposed correlation not only can predict the influence of the lubricants of this study but also can extend to predict existing data with a good accuracy.