Heat Transfer to Freon near the Critical Pressure Flowing in Tubes (3rd Report, Post-Dryout Heat Transfer)

Studies of the post-dryout heat transfer were made based on the experimental data of the heat transfer to Freon 22 flowing upward in vertical, uniformly heated round tubes (9 and 13 mm ID) for a range of reduced pressure of 0.68 to 0.92, mass velocity of 400 to 1 600 kg/(m²·s) and heat flux of 12 to 70kW/m². The wall temperatures estimated by the use of a conventional, theoretical model agreed qualitatively with those measured, but not quantitatively. A nondimensional parameter Kn was introduced to a model for the post-dryout regime to take account of the thermodynamic nonequilibrium between the vapor and the liquid droplets. A correlation of Kn was obtained, and this correlation, used with the correlation for the heat transfer to the superheated vapor, was successful in predicting the wall temperature.