2022 Volume 36 Issue 2 Pages 255-265
Wall functions are generally used in a numerical simulation of turbulent flows with computational fluid dynamics (CFD) codes. The logarithmic law is widely adopted for the wall functions, but its validity has not been confirmed for dimensionless profiles of temperature and steam mass fraction in condensation fields due to lack of data. In this study, we evaluated dimensionless profiles of temperature and steam mass fraction in flows of saturated steam and air mixtures in a vertical pipe with the diameter of 49.5 mm. The local Nusselt number Nuy and Sherwood number Shy (which were proposed in our previous study) were used for defining the dimensionless temperature T+ and steam mass fraction Ys+, respectively, because physical properties in computation cells in contact with the condensation surface are generally used in a CFD analysis. The T+ and Ys+ values obtained from the measured temperature profiles were smaller than the existing logarithmic law due to condensation in the turbulent boundary layer (i.e. mist generation), and correlations for T+ and Ys+ were obtained by using the least square method. The standard deviation of the correlations were 3.8 % and 0.75 ℃ for the steam mass fraction of Xs = 0.05-0.63 and the mixture temperature of Tg = 63-97 ℃, respectively.
