Study on average Nusselt and Sherwood numbers in vertical plate channels with falling water film evaporation

In this paper, the effects of variable parameters on the average Nusselt and Sherwood numbers between moist air and liquid water film in vertical plate channels are investigated using an approach proposed by previous work. The validity of data is also investigated. Traditional correlations for the average Nusselt and Sherwood numbers are not comprehensive enough as they cannot indicate the effects of inlet parameters on heat and mass transfer process. In this research, correlations for the average Nusselt and Sherwood numbers are developed in terms of moist air inlet Reynolds number, ratio of water to moist air inlet mass flow rate, ratio of channel length to half channel width and moist air inlet dimensionless temperature. The definition of the moist air inlet dimensionless temperature takes into account the effects of moist air inlet dry-bulb and wet-bulb temperatures and water film inlet temperature. The correlations show that the moist air inlet dimensionless temperature has the greatest influence on the average Nusselt number compared with that of the other dimensionless parameters, but it has the lowest influence on the average Sherwood number. The results would be helpful to understand the heat and mass transfer behavior between moist air and liquid water film.