Simultaneous heat and mass transfer in wetted-wall columns.

Experiments were carried out on a wetted-wall column and data for simultaneous heat and mass transfer (air-water system) was analysed according to existing theories. Provision of a gas sampling probe made it possible to follow the condition of the gas as it travelled in the column. It was thus possible to calculate the heat and mass transfer coefficients at different sections within the wetted-wall column. Entrance effects were found to be considerable, resulting in a significant variation of the transfer coefficients along the column. However, the overall coefficients (based on the measurement of the conditions at inlet and exit of the column only) agree very closely with those values averaged for the whole column. As saturation is approached, the magnitude of the transfer coefficients fall and the condition curve becomes asymptotic to the saturation curve. Application of the boundary layer theory for the prediction of heat and mass transfer rates, was able to explain qualitatively the process of heat and mass transfer along the column. The predicted rates from the boundary layer theory are some 30% lower than the experimental values which suggests the existence of eddies in the gas film, resulting in higher rates of heat and mass transfer than theory predicts