In-tube evaporation and condensation of HFC-134a and CFC-12 with various lubricant mixtures

Mandates currently in place by the Environmental Protection Agency require use of new environmentally acceptable refrigerants by 1996. Implementation of these new refrigerants by refrigeration and air-conditioning manufactures requires design data for the various components of these systems. This study focused on obtaining design data for evaporators and condensers of vapor compression systems. Specifically, a new environmentally acceptable refrigerant HFC-134a, which is targeted as a replacement for refrigerant CFC-12, was tested in an instrumented evaporator and condenser and their performance measured.;Heat transfer coefficients and pressure drops were measured during evaporation and condensation of HFC-134a and CFC-12 in smooth and micro-fin tubes. Two different diameter smooth tubes and micro-fin tubes were tested: 9.52-mm outside diameter tubes and 12.7-mm outside diameter tubes. Micro-fin tubes are characterized by the numerous small fins that spiral down the inner surface of the tube. The micro-fin tubes used in this study had 60 fins with a spiral angle of 17;The experimental data showed a significant increase in the performance of HFC-134a in the micro-fin tube as compared to the smooth tube. Specifically, evaporation heat transfer coefficients were increased by 50% to 100% with only a 10% to 30% increase in evaporation pressure drop, while condensation heat transfer coefficients were increased by 100% to 200% with a 40% to 100% increase in condensation pressure drop. Similar results were obtained for pure CFC-12 in the micro-fin tube.;The effects of lubricant concentration (...