Effect of oil on two-phase pressure drop of refrigerant flow boiling inside circular tubes filled with metal foam

Two-phase pressure drop characteristics of refrigerant-oil mixture in circular tubes filled with metal foam were experimentally investigated. Experimental conditions cover nominal oil concentrations from 0% to 5%, metal foam structures of 5 PPI and 10 PPI, vapor qualities from 0.2 to 0.8, and mass fluxes from 30 to 90 kg/m2s. The test results show that the pressure drop increases with the increase of oil concentration, mass flux or vapor quality. The presence of oil increases pressure drop by a maximum of 25% and 50% for 5 PPI and 10 PPI metal foams, respectively. The enhancement effect of oil for high PPI metal foam is more evident than that for low PPI metal foam. A correlation for predicting the two-phase pressure drop of refrigerant-oil mixture in circular metal-foam tubes was developed, and it agrees with 90% of the experimental data within a deviation of ±20%.