1993 Volume 10 Issue 3 Pages 437-444
The evaporation and condensation heat transfer and pressure drop characteristics for HFC-134a in a horizontal tube have been studied experimentally. During the courses of both the evaporation and condensation experiments,the saturation temperature of the refrigerant,refrigerant mass flux and oil concentration in the refrigerant were varied parametrically. A smooth tube and an inner finned tube respectively were used as the tube to be tested in the present study. In addition to the oil free experiments, other experiments were performed to investigate the effect of oil-refrigerant mixture on the heat transfer and pressure drop characteristics. The present evaporation and condensation heat transfer coefficients for HFC-134a without oil in the smooth tube were found to be about 25% higher than those for CFC-12 at similar mass fluxes. Furthermore,it was found that the pressure drop through the smooth tube for HFC-134a became about 10% larger than those for CFC-12 in evaporation experiments. In the oil-refrigerant mixture experiments,the results indicated that both evaporation and condensation heat transfer coefficients for HFC-134a were influenced by the oil concentration at the large mass fluxes.
