Correlations for the mass transfer coefficient in desiccant matrices when using linear driving force and pseudo-gas-side-controlled models

Abstract

Following a previous research on the simplified simulation of desiccant matrices with the linear driving force and the pseudo-gas-side-controlled models, correlations for predicting the mass transfer coefficient values are investigated. The study is centred on the behaviour of an element of a cell of a compact desiccant matrix and the reference data are provided by the results of a detailed numerical model. The response of the solid desiccant to a step change in the airflow state is simulated, for both adsorption and desorption processes, until the desiccant achieves equilibrium with the airflow.The previous research has shown that, when adopting just one of the two simplified models with a constant mass transfer coefficient for the whole range considered of the desiccant wall thicknesses, the accuracy of the results becomes questionable. The linear driving force model is suitable when the mass transfer resistance on the solid side is high, while the pseudo-gas-side-controlled model performs well for cases with low mass transfer resistance.Useful correlations for estimating the mass transfer coefficient for the processes of both adsorption and desorption as a function of the desiccant wall thickness are now investigated. The correlations are tested and it is found that, when using the linear driving force model in desorption cases, a correction of the correlation accounting for the operating conditions is required in order to obtain acceptably accurate results with the proposed methodology.