Condensation Heat Transfer for Downward Flows of Steam-Air Mixture in a Circular Pipe

抄録

In our previous study, we measured the radial and axial temperature distributions of steam-air mixture in a vertical circular pipe (diameter, 49.5 mm; cooling height, 610 mm) and the cooling water in the annulus gap (8.5 mm) outside the pipe, and the temperature gradients in the pipe wall (thickness, 5.5 mm) between the steam-air mixture and cooling water. From the temperatures, we evaluated condensation heat fluxes q_c, and derived an empirical correlation. In this study, we have calculated the heat transfer coefficient of the condensate film h_f with the Nusselt equation and evaluated the condensation heat transfer coefficient h_c from q_c and the measured temperature distributions. We also compared h_c with h_c correlations based on the heat and mass transfer analogy and the diffusion layer model. Results from both correlations agreed relatively well with the h_c data, but the correlations underestimated h_c for high h_c near the inlet with a thin thermal boundary layer and overestimated h_c for low h_c.