Non-Isothermal Kinetic Model of Water Vapor Adsorption on a Desiccant Bed for Harvesting Water from Atmospheric Air

Desiccants are used in the process industry for the drying of technical gases. An emerging application is fresh water production from the water vapor of atmospheric air using adsorbents in a day-night cycle. Water adsorption is performed at night and desorption using solar heat during the daytime. In this paper, a non-isothermal kinetic model of a packed bed of desiccant pellets is developed to determine possible uptake improvements by elucidating the complex mass- and heat-transfer interdependent resistances. Shallow beds thinner than 1 cm are required to handle bed diffusion and thermal conduction effects. Options for improvements regarding intragranular water vapor diffusion are limited. The adsorption process quickly becomes convection- and radiation-limited by the strong exothermicity of water adsorption. Steep parts in the water adsorption isotherm enhance the thermal effects. Water vapor supply by air convection is another factor limiting water uptake in real-world applications. The use of adsorbent particle beds is problematic for water-from-air production applications.

Automated summary

This paper developed a non-isothermal kinetic model to study the production of fresh water from atmospheric water vapor using desiccant pellets in a day-night cycle. The study found that factors like bed thickness and water vapor diffusion have impacts on the absorption efficiency.