Modeling of oil retention in microchannel type evaporators and its effects on refrigerant heat transfer

This paper presents a new model for lubricant retention in microchannel type evaporators and shows a comparison between experimental and simulation results using refrigerants R134a and R410A and synthetic polyolester (POE) mixtures. Two different microchannel geometries were considered: a single and a double slab heat exchanger. The model predictions of the heat transfer capacities were within  ± 10% with respect to the experimental data. The pressure drops were estimated with an error that ranged from  ± 20% to  ± 50%. Oil retention was predicted both locally and for the entire heat exchanger. The negative effect of oil on the performance of heat exchangers differs with oil concentrations and most of the lubricant was retained in the superheated region of the evaporator and in the outlet header. The predicted oil retention volume was within  ± 60% and the simulation results suggested that the geometry details inside the headers have significant effects on the amount of oil retained.