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

Abstract

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 qc, and derived an empirical correlation. In this study, we have calculated the heat transfer coefficient of the condensate film hf with the Nusselt equation and evaluated the condensation heat transfer coefficient hc from qc and the measured temperature distributions. We also compared hc with hc correlations based on the heat and mass transfer analogy and the diffusion layer model. Results from both correlations agreed relatively well with the hc data, but the correlations underestimated hc for high hc near the inlet with a thin thermal boundary layer and overestimated hc for low hc.

Prediction Method of Condensation Heat Transfer from Steam-Air Mixture for CFD Application

“…7 and σ = ±36 % in Fig. 8 were close to σ = ±30 % and σ = ±34 % [15], respectively, where the correlations were applied between the bulk and the condensation surface. Figs.…”

“…(11) and ( 12) by Liao and Vierow [14] were similar, and they were smaller than the measured hc,exp for z = 50 mm near the test section inlet, and were larger than hc,exp for the downstream region in Nos. 8 and 9 with small qc [15]. The average of hc,cal by Liao and Vierow [14] was 9.5 % larger than that by Araki et al [13], and was 1.2 % smaller than the average of hc,exp.…”

“…In the previous study [15], hf = 6.3-22.2 kW/m 2 K and hconv = 0.007-0.037 kW/m 2 K for hc = 0.060-4.5 kW/m 2 K, hence effects of hf and hconv on hc could not be neglected.…”

“…We compared the measured hc with the correlations based on the analogy between heat and mass transfer by Araki et al [13] and based on the diffusion layer model by Liao and Vierow [14]. From these comparisons, good agreement was confirmed between the measured hc and correlations [15]. One technical issue however remained: the prediction method of hc from physical quantities in the computational cell next to the condensation surface.…”

“…hc,exp was obtained by using Eq. (2) [15] and was defined between the bulk and condensation surface. hc,cal/hc,exp was small for small z like z = 0.09 m, and in the figure it is not shown for z = 0.05 m. In the turbulent boundary layer, changes of Tg and Xs were relatively small (see Fig.…”