Measurements of Temperature Distributions and Condensation Heat Fluxes for Downward Flows of Steam-Air Mixture in a Circular Pipe

Three quantities were measured to provide a database for validation of computations with a CFD (computational fluid dynamics) code. The quantities were the radial temperature distributions of steam-air mixture in a vertical circular pipe (diameter, 49.5 mm), the temperature gradients in the pipe wall (thickness, 5.5 mm) and the radial temperature distributions of the cooling water in the annulus gap (8.25 mm) outside the pipe. From these temperature distributions, three kinds of condensation heat fluxes were obtained from the enthalpy decreasing rate of the steam-air mixture based on the assumption of saturated conditions, the temperature gradient in the pipe wall, and the enthalpy increasing rate of the cooling water. These three heat fluxes were different especially in the downstream region, where the heat flux was low, so that the average of the three heat fluxes was used to evaluate factors affecting the condensation heat transfer. This average was expressed by a function of the steam density difference between the main flow of the mixture and the mixture on the wall surface, the average steam velocity and the thermal boundary layer thickness. The suction effect due to condensation was also discussed.