Steady-state post-critical heat flux heat transfer to a refrigerant

Abstract

Heat transfer in the post-critical heat flux (CHF) regime was studied experimentally under steady-state conditions producing low superheat temperature of the heated surface. Experiments were performed with the vertical flow of refrigerant-12 in a tube with inside diameter of 7.75 mm over the mass flux range of 182 to 808 kg/sq m s at a pressure of 1 MPa. Liquid heating produced the low wall-superheat in the post-CHF region at steady state, which is typical of heat exchanger operation. Superheated vapor measured at the test section exit in most tests ensured that the entire post-CHF region was included. Heat transfer results were compared to predictions from nine post-CHF correlations and models. The potential for thermodynamic nonequilibrium diminishes and direct wall-drop heat transfer is enhanced when wall-superheat is low. These two phenomena were considered in the comparisons, and the best predictions of independent data for two fluids, refrigerant-12 and water, were obtained from a single correlation that included both phenomena explicitly. 15 refs.