Mathematical Modeling of Desiccant-Based Atmospheric Water Generation Authors

Abstract

Challenges of population growth, rapid urbanization, climate change, depletion of local water supplies, and rising demand from agriculture, industry, and the energy sectors are all contributing to water scarcity and the lack of access to clean water. The UN reported that in 2021, over 45% of the world population would suffer from accessing safely managed sanitation facilities, and over 25% would live in water-stress areas. Under the current trend, by 2030, the world would be faced with a 40% water deficit, forcing governments, companies, and research scientists, to find a solution to the critical problem of water scarcity. Over the years, seawater desalination has been considered the most viable solution, but it has a large eco-logical footprint, and high energy consumption and only a few countries can afford it. Recently, significant efforts have been devoted to harvesting water from clouds, fog, or water vapor in the atmosphere, particularly in dry regions. Harvesting atmospheric water by solar regeneration desiccants is a promising water source due to its low energy cost and low impact on the environment. However, the actual published results of the amount of water generated are still insignificant. This paper attempts to predict and improve the behavior of water absorption and desorption by the Calcium Chloride (CaCl2) desiccant by developing a mathematical model coupled with an empirical formula, including a phase change mass conservation equation, a momentum conservation equation, and an energy equation. The mathematical and empirical models were combined and solved numerically using the MATLAB® PDE solver pdepe; Results were compared to experimental investigations conducted at Effat University Lab in Jeddah. The comparison in the cases of absorption and desorption shows good agreement between simulations and experiments in terms of water content, average temperature, relative humidity, and solution depth. It was found that using an air pump boosts the absorption in deep containers, however, the use of a thin layer is still more effective. The mean absolute error (MAE) of the model was found to be 3.13% and 7.32% for absorption and desorption, respectively. The results of this research highlight the potential and promise of desiccant-based atmospheric water generation as a viable solution to water scarcity, and help achieve UN Sustainable Development Goal 6, “Ensure availability and sustainable management of water and sanitation for all."