Experimental analysis and modeling of lubricant effects in microchannel evaporators working with low GWP refrigerants

In any vapor compression system, lubricant is needed to guarantee safe and reliable compressor operation. Indeed, most compressor mechanical failures are generally due to improper oil management, such as, lack of proper lubrication inside the compressor. Since in the usual operating condition of the system a small portion of oil circulates with the refrigerant through the system components, it can be retained inside the heat exchangers leading to oil missing from the compressor. In present article, the lubricant retention characteristics of two microchannel type evaporators for residential air conditioning systems and the oil detrimental effects on evaporator capacity and refrigerant-side pressure drop were investigated. The working fluids used in this study were R410A, as reference refrigerant, and low global warming potential refrigerants R32, R1234yf, and R454B, a new low global warming potential mixture candidate to replace R410A, whereas the lubricant was VG 32 Polyolester oil. The effects of oil mass fractions and degree of superheat were experimentally investigated considering working conditions typically found in air conditioning systems. Finally, the experimental results of the present article provided data that were used to develop and validate a semi-empirical model for microchannel evaporator simulation able to account for the oil presence. The developed model was summarized in the current article and the results were compared with the experimental ones in term of oil retention, capacity, and refrigerant-side pressure drop.