Visualization of water adsorption/desorption phenomena in silica-gel particle by microfocus X-ray transmission imaging

Abstract

An adsorption heat pump system may make effective use of low-quality waste heat, but the system’s inadequate performance remains a critical issue. Improvements in efficiency and an understanding of the fundamental phenomena of water adsorption and desorption in a silica-gel particle are essential. X-ray transmission imaging was used to observe water adsorption/desorption phenomena in 3.7-mm-diameter silica-gel particles. Although previous studies did not conduct observations inside of the silica-gel particles, we were able to visualize the change in water distribution in silica-gel particles during adsorption and desorption using X-ray transmission imaging. When the silica-gel particles were cooled or heated, the adsorption or desorption proceeded gradually from the outer edge to the center, until the final equilibrium state of uniform water distribution was visible. A quantitative measurement of the water adsorbed in the silica-gel particles indicates that it took 20 min and 10 min to achieve adsorption and desorption equilibrium, respectively, in the silica-gel particle. In the silica-gel packed bed, all silica-gel particles desorbed at the same speed, but the adsorption slowed as the distance from the connection port increased.