Flow Boiling Heat Transfer and Pressure Drop Characteristics of a 45/55% by Weight Mixture of R321R125

Abstract

This study investigates the heat transfer and pressure drop characteristics of a 45/55% by weight mixture of R321R125. For mass fluxes above 150 x 103 Ibm/ft2_h (200 kglm2-s) and heat fluxes below 6400 Btu/ft2_h (20 kW/m2), the experimental Nusselt number is dependent on both heat flux and qUality. An increase in either of these qualities results in anincrease in the Nusselt number. For mass fluxes below 150 x 103 lbm/ft2-h (200 kglm2-s), the Nusselt number is independent of qUality. Pressure drop is dependent on heat flux and quality for the entire range of mass fluxes tested. The accuracy of several two-phase correlations in predicting the experimental data is examined. The Shah [1976] correlation underpredicts the experimental Nusselt number and this is attributed to an underestimation of the convective boiling contribution. The Jung and Radermacher [1989] correlation overpredicts the data. This is due, in part, to the absence of accurate surface tension data for the mixture. The Wattelet [1994] correlation predicts the experimental Nusselt number to within ??20%. The Sousa [1993] correlation predicts the experimental pressure drop to within ?? 10%. iiiAir Conditioning and Refrigeration Center Project 3