Experimental analysis and modeling of lubricant effects in microchannel evaporators working with low global warming potential refrigerants

Abstract

In any vapor compression system, lubricant is needed to guarantee compressor safe and reliable operation. Indeed, most compressor mechanical failures are generally due to improper oil management, i.e. 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 paper, the lubricant retention characteristics of two microchannel type evaporators for residential air conditioning systems and the oil detrimental effects on Downloaded by [Athabasca University] at 17:37 20 June 2016 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2 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 (LGWP) refrigerants R32, R1234yf, and R454B, a new LGWP mixture candidate to replace R410A, whereas the lubricant was VG 32 POE oil. The effects of oil mass fractions (OMF) and degree of superheat were experimentally investigated considering working conditions typically found in air conditioning systems. Finally, the experimental results of the present paper 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 present paper and its results were compared with the experimental ones in term of oil retention, capacity and refrigerant-side pressure drop.