Experimental adjustment of the turbulent Schmidt number to model the evaporation rate of swimming pools in CFD programmes

Abstract

Water evaporation rate is among the most significant parameters to design and select air conditioning systems in buildings with indoor swimming pools. Experimental correlations are today widely used to estimate water evaporation rate, although discrepancies of up to 80% among existing correlations have been shown. An alternative to these empirical methods is the calculation of evaporation rate through computer fluid dynamics techniques. One of the most significant parameters to solve the mass transfer at the air-water interface in these models is the value of the turbulent Schmidt number. Although this value depends on air and water conditions (i.e., temperatures, velocities, and vapour pressure, among others), commercial computer fluid dynamics programmes set a fixed value by default. This study presents a new value through an experimental adjustment. A total of 40 experimental tests have been performed in a wind tunnel under typical conditions in indoor swimming pools. Afterwards, the adjustment was validated with data from 145 experimental tests reported in the scientific literature. The mean relative error in the evaporation rate using the turbulent Schmidt number was 7%, as against 25% using the value by default. The maximum error was reduced from 35% to 15% in forced convection regime.