An experimental investigation on convective boiling heat transfer of R-454B with lubricant oil of POE-32 or POE-68 mixture in a horizontal smooth tube

The effect of lubricant (POE-32 and POE-68) on convective boiling heat transfer is experimentally investigated inside a smooth horizontal copper tube having an outer diameter of 9.52 mm. R-32, R-454B, and R-410A are used as working fluids. The oil mass concentration ranges from 0% to 6%. For pure refrigerant, the heat transfer coefficient (HTC) of R-454B is about 4-5% higher than those of R-32 and R-410A. The presence of lubricant oil deteriorates the HTC and increases the pressure drop appreciably, and it becomes more pronounced with oil concentrations. The HTC increases with the increase in the heat flux, but there is no definite tendency regarding the effect of lubricants on HTC subject to heat flux. The deteriorations of HTC become more severe at high vapor quality with impairment of more than 40%. With a 3% oil concentration, the level-off for the HTC of the R-32/POE-32 mixture occurs at a vapor quality of 0.7 and is 0.8 for R-410A/POE-32, and R-454B/POE-32, respectively. For vapor quality ranges from 0.1 to 0.6 at the 3% oil concentration, the effect of the POE-68 oil on HTC is more pronounced than that POE-32 in the R-32/oil mixture. For the R-454B/oil mixture, the effect of lubricant on HTC is lessened. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study found that the presence of lubricant and increase in oil concentration significantly affect the heat transfer coefficient, which increases with heat flux. Lubricant may lead to deterioration of HTC, especially at high vapor qualities.