Flow boiling pressure drop and heat transfer at high mass fluxes for R514a in a single microchannel

Abstract

This paper presents pioneer experimental data about flow boiling heat transfer coefficient and pressure drop for R514a, which is a new environmentally friendly HFO refrigerant substitute for the HCFC R123. Data was collected in a single 1.1 mm internal diameter microchannel with high mass velocity conditions, ranging from 1500 to 7000 kg/m2s, allowing measurements of very high heat transfer coefficients, above 50 kW/m2K. In addition, saturation temperatures up to 92 °C were tested, which has an important application in evaporators of organic Rankine cycles. Comparisons were made between the experimental results of R514a and R123. R514a showed a general trend of a higher heat transfer coefficient and pressure drop (up to 20% higher) relative to R123. Frictional pressure drop literature correlations could predict the R514a data with a mean absolute error below 20% and heat transfer coefficient correlations with mean absolute error below 25%.