Condensation heat transfer and pressure drop characteristics of zeotropic mixtures of R134a/R245fa in plate heat exchangers

Abstract

Zeotropic mixtures have shown great potential to improve the system efficiency compared with the use of pure fluids as the working fluids. However, there is a lack of analysis of the heat transfer during the phase change of zeotropic mixtures in plate heat exchangers, which is a common heat transfer device used as the evaporator and condenser in these systems. This paper presents an experimental analysis of the flow condensation heat transfer and pressure drop characteristics of zeotropic mixtures in a plate heat exchanger. The objectives are to obtain prediction methods for the heat transfer coefficient and frictional pressure drop and to quantify the degradation of the heat transfer coefficient by using mixtures. Zeotropic mixtures of R134a/R245fa with five different quantitative compositions were experimentally tested with the bubble point temperatures of 30°C to 50°C and various mass fluxes. The experimental results indicate that condensation of the mixtures is governed by a shear-controlled process, similar to what happens with pure fluids. Moreover, the heat transfer degradation of the zeotropic mixture caused by the mixture effects increases with decreasing condensation temperature and mass flux. There is a 48% maximum decrease in the heat transfer coefficient for the mixture of R134a/R245fa with 0.431/0.569 in mass fraction. A modified Silver-Bell-Ghaly method provides a good prediction for the heat transfer data with a mean absolute percentage deviation of 12.2%. A pure-fluid correlation developed in a previous work by the authors enables a prediction with an 8.6% mean absolute percentage deviation for the pressure drop data.