A study of flow boiling heat transfer with refrigerant mixtures

Abstract

Mixture effects are studied on horizontal flow boiling heat transfer with both azeotropic and non-azeotropic refrigerant mixtures. More than 2000 local heat transfer coefficients are obtained with the azeotropie R 12/R 152a mixture and compared against the previously measured data with the non-azeotropic R22/R114 mixture. In a convective evaporation region, small mass transfer resistance is found for mixtures. The variation of physical properties due to mixing is responsible for almost all of the heat transfer degradation. In a partial boiling region, however, severe degradation of heat transfer with mixtures, similar to that in nucleate pool boiling heat transfer with mixtures, is found. A suppression of nucleate boiling at lower qualities due to loss of wall superheat with mixtures is responsible for this degradation. An analysis is developed to predict a transition quality by using Hsu's onset of nucleate boiling theory. The prediction agreed well with observed transition qualities for both pure and mixed refrigerants. Correlations, based on the supposition of Chen and using only phase equilibrium data to consider mixture effects, are developed with mean deviations of 7.2 and 9.6% for pure and mixed refrigerants.