Characterising the heat and mass transfer coefficients for a crossflow interaction of air and water

An experimental study was performed in order to characterise the heat and mass transfer processes, where an air stream passes through a sheet of falling water in a crossflow configuration. To achieve this, the hydrodynamics of a vertical liquid sheet in a ducted gaseous crossflow were studied. Four distinct flow regimes were identified (a stable sheet, a broken sheet, a flapping sheet and a lifted sheet) and mapped using Reynolds and Weber numbers. Subsequently, the Buckingham π theorem and a least squares analyses were employed leading to the proposal of two new dimensionless numbers referred to as the Prandtl Number of Evaporation and the Schmidt Number of Evaporation. These describe the heat and mass transfer in low temperature evaporation processes with crossflow interaction. Using these dimensionless numbers, empirical correlations for Sherwood and Nusselt numbers for the identified flow regimes were experimentally determined. These correlations were in a good agreement with their corresponding experimental values. It was found that flapping sheets have the strongest heat and mass transfer intensities whereas the weakest intensities were seen for the “stable” sheets.