The heat transfer characteristics of refrigerant-oil mixture flow boiling inside circular tubes filled with metal foam were experimentally investigated. The metal foams are 5 ppi / 95% porosity and 10 ppi / 95% porosity copper foams. The experimental conditions include saturation pressure of 995 kPa

mass flux from 10 to 30 kg/(m2.s)

heat flux from 3.1 to 9.3 kW/m2

inlet vapor quality from 0.175 to 0.775

and oil concentration from 0% to 5%. The experimental results show that: metal foam enhances the flow boiling heat transfer coefficient of refrigerant by a maximum of 185% at oil free conditions

while the enhancement effect of metal foam is weaken at oil presence conditions; the flow boiling heat transfer coefficient for the circular tube filled with high ppi metal foam is higher than that for the tube filled with low ppi ones. A new correlation of heat transfer coefficient for refrigerant-oil mixture flow boiling inside circular tubes filled with metal foam is developed based on the flow pattern

and it can agree with 98% of the experimental data within a deviation of ±30%.