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

Abstract

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.

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

“…However, there are very few published databases for temperature distributions. In our previous study [8], we therefore measured radial and axial temperature distributions of the steam-air mixture in a simple vertical circular pipe (diameter, 49.5 mm) and the cooling water in the annulus gap outside the pipe, and the temperature gradients in the pipe wall between the mixture and cooling water to provide a database, which can be used to validate the prediction capability for temperature distributions of the steam and non-condensable gas mixture in the thermal boundary layer in CFD models. We evaluated condensation heat fluxes from the measured temperatures and derived an experimental correlation for heat fluxes, but we did not obtain condensation heat transfer coefficients.…”

“…In our previous study [8], we measured the radial temperature distribution of the steam-air mixture in a simple vertical circular pipe in quasi-steady states to provide a database validating computation capability of a CFD code. The apparatus consisted of a steam supply system, an air supply system, a simple mixing tee for steam and air, an inlet section (the ratio of the length L to the diameter d, L/d = 10) to the test section, a test section, an exhaust pipe, and a cooling water system to feed low-temperature water into the cooling annulus in the test section.…”

“…Table 1 lists the main experimental conditions for eleven cases [8]. Our interest was temperature distributions in the thermal boundary layer and the experimental conditions did not simulate thermal-hydraulic features such as velocities and temperatures in CV during LOCA conditions.…”

“…Nuz /Nu∞ = 1+C/(z/d), C = 0.8{1+70000/Reg 3/2 } for 3000 < Reg < 500000 (7) In Eqs. ( 2)-( 7), the values of qave, Reg, Tb, Tw and Γ were taken from our previous study [8].…”

“…In our previous study [8], the dimensionless temperature was defined for the difference between the center and wall surface temperatures (Tc -Tw) because we did not obtain the liquid film surface temperature Tf. This time, we obtained Tf from Eq.…”