Experimental analysis of quasi-local non-equilibrium boiling heat transfer with the refrigerants R1234ze(E) and R1234yf in a gasketed plate heat exchanger

Abstract

This paper experimentally analyzes the non-equilibrium boiling of R1234yf and R1234ze(E) utilizing quasi-local measurements in a plate heat exchanger. The corresponding mechanisms of the targeted processes were identified, and the influence of crucial parameters on the heat transfer performance was explored. Guidelines with respect to the selection of heat transfer correlations for the boiling heat transfer with inlet subcooling are provided. A database containing 270 quasi-local experimental data points was established and used to evaluate the predictive performance of the previous heat transfer models. In addition, new prediction methods are proposed for the subcooled boiling, saturated two-phase, superheating, and preheating regions, respectively. The local measurements are collected at various boiling pressures (0.9 MPa to 1.3 MPa), refrigerant mass fluxes (9 kg∙m^-2∙s^-1 to 15.6 kg∙m^-2∙s^-1), inlet subcooling degrees (8.1 K to 31 K), and heat fluxes (0.4 kW∙m^-2 to 44.1 kW∙m^-2). The results suggest that during high mass flux and moderate inlet subcooling and conditions, more than 23 % of the evaporator's heat transfer area constitutes subcooled boiling. The new prediction methods provide fair predictability, with a deviation of 15 % for the subcooled boiling correlation, 18 % for the two-phase correlation, 16 % for the superheating correlation, and 18 % for the preheating correlation, respectively. The accuracies of the new models are improved by more than 6 %-points compared to the existing prediction methods.