Dimensionless Model of Frost Roughness on Cold Flat Plate Under Forced Convection

Laboratory experiments were conducted to generate empirical dimensionless correlations for estimating surface roughness of frost formed on a cold flat plate under forced convection. Environmental variables, including wall temperature T-s , air velocity V-air , relative humidity RH , and air temperature T-air , were considered when generating the correlations. The test conditions were chosen to simulate the environmental conditions experienced by cold-soaked fuel frost formation on the upper surface of airplane wings. Experimental conditions included wall temperatures from - 20 to - 5 & DEG; C , freestream temperatures from 8 to 16 & DEG; C , relative humidities from 60 to 91%, and air velocities from 0.5 to 2.5 m.s(-1) . The root-mean-square height, skewness, and equivalent sand-grain roughness height of frost were correlated as functions of the Reynolds number, absolute humidity, and dimensionless temperatures. The comparison between the correlation of frost equivalent sand-grain roughness height in this study and a previous model revealed the importance of test surface geometry on frost roughness formation.