Measurement and correlation of frictional two-phase pressure drop of R410A/POE oil mixture flow boiling in a 7 mm straight micro-fin tube

Two-phase frictional pressure drop characteristics of R410A/POE oil mixture flow boiling inside a straight micro-fin tube with the outside diameter of 7.0 mm were investigated experimentally. Experimental parameters include the evaporation temperature of 5 °C, the mass flux from 200 to 400 kg/(m² s), the heat flux from 7.56 to 15.12 kW/m², the inlet vapor quality from 0.2 to 0.7, and nominal oil concentration from 0% to 5%. The test results show that frictional pressure drop of R410A/POE oil mixture increases with the mass flux, the presence of oil enhances two-phase frictional pressure drop, and the effect of oil on frictional pressure drop is more evident at higher vapor qualities where the local oil concentrations are higher. New correlations to predict the local frictional pressure drop of R410A/POE oil mixture flow boiling inside the straight micro-fin tube are developed based on local properties of refrigerant–oil mixture, and the measured local frictional pressure drop is well correlated with the empirical correlations proposed by the authors.