Experimental study of surface effect on flow boiling heat transfer in horizontal smooth tubes

In the present study the experiments on flow boiling heat transfer in two horizontal smooth copper tubes are carried out with pure refrigerants HFC134a, HCFC123, HCFC22, CFC114 and CFC12 using water-heated double-tube type test sections. One test tube is of 8.4 mm inside diameter, and the other is of 7.9 mm inside diameter. For both tubes the surface roughness is measured and the surface micro-geometry is observed with SEM. From the experimental results, the surface effect on flow boiling heat transfer is clarified and a correlation for the heat transfer coefficient is proposed in consideration of the surface effect. This correlation equation agrees well with the experimental data from different sources.