Gas absorption with first order chemical reaction in a laminar falling film over a reacting solid wall

In the present work, a general case of gas absorption with first order irreversible chemical reaction in a liquid film, for laminar flow over a solid wall, has been analyzed theoretically. First order chemical reaction between the diffused solute and the wall is also considered. Laplace transform followed by power series method has been applied to solve the governing equations. Thereafter, the obtained analytical solution of the developed general model has been successfully verified by an explicit numerical scheme. The general model has also been reduced to six simplified cases, tackled by previous workers and an excellent agreement in the solutions is observed. Moreover, the results are validated by the experimental data available in the literature. The obtained concentration profiles in both the phases have been used to find the absorption rates and enhancement factor. Further, the effect of various parameters on concentration profile of solute, enhancement factor and eigen-values have been analyzed. Existence of positive eigen-values for the counter-current absorption is also described which was not pointed out by any of the previous researchers. It is concluded that in a co-current system, for Hatta number greater than 7 approximately, the variation in enhancement factor follows a linear trend on a log–log plot and that there is no effect of rate constants for higher values of Hatta number. It is further shown that the reaction at solid wall has appreciable effect on the absorption rate.