Article ID: 19-10DC_OA
Adsorption/desorption rate of vapor to adsorbent on an adsorption heat exchanger is one of the important characteristics in order to design and improve the performance of adsorption chillers and dehumidifying/humidifying desiccant systems effectively. In the present study, for a silica gel thin film adsorbent coated on an aluminum plate in a cross-fin tube heat exchanger, measurement of equilibrium adsorption of water vapor by TGA and measurement of adsorption/desorption rate by gravimetric method under different flow velocities of moist air were performed. The equilibrium adsorption was formulated with function of relative humidity. In addition, the overall mass transfer resistance related to both the mass diffusion in the film and the mass transfer in the boundary layer on the film was investigated. It was clarified that the influence of the resistance on the reaction rate appeared only at the beginning of reaction, and the resistance decreased with the increase of the velocity, especially in adsorption. Furthermore, the resistance in desorption was less than half in adsorption. Consequently, the resistance in the boundary layer was a negligible quantity for desorption when the flow rate was above 0.1 m ･s-1. Finally, correlations were proposed to predict these resistances.
