A Comparative Study on Flow Boiling Heat-Transfer Coefficient of R-134a and R-134a/R-290/R-600a Refrigerant Mixture

The flow boiling heat-transfer coefficients of R-134a and R-134a/R-290/R-600a zeotropic refrigerant mixture were experimentally measured in a smooth horizontal tube of a 9.52-mm diameter. The values were compared for similar working pressure, reduced pressure, and liquid entry saturation temperature. The tests were conducted under varied heat flux conditions for stratified flow patterns; the conditions are found in evaporators of refrigerators and deep freezers. The varied heat flux conditions were imposed on the test fluids using a coaxial counter-current heat exchanger test section. The heat-transfer coefficients of the R-134a/R-290/R-600a refrigerant mixture were found to be better than those of R-134a under the same pressure and reduced pressure. However, under the same liquid entry temperature, the values of R-134a were found to be higher at low vapor qualities and lower at higher vapor qualities.