Study of the relative humidity effects on the water condensation performance of adsorption-based atmospheric water harvesting using passive radiative condensers

Abstract

Adsorption-based atmospheric water harvesting (ABAWH) and passive radiative condensers are two examples of dew water collection. The application of passive radiative condensers to ABAWH has recently been demonstrated. However, ABAWH prefers high relative humidity (RH) for higher water uptake by adsorbents, while radiative condensers favor low RH for higher radiative cooling power, so there exists a desired RH for the water harvesting system under different conditions. However, this has not been previously studied. Therefore, we pioneer the development of a numerical model to obtain the desired RH for the water harvesting system and determine optimum operating parameters for maximum water production under different conditions. The adsorption isotherms are fit based on experimental results, and the effect of RH on radiative cooling power is mathematically predicted via cloud-cover fraction. Based on the numerical results, the desired RH ranges from 20 % to 29 % for 200 g MIL-101-Cr (HF) under certain conditions. Compared to other factors, the radiative condensation emitter and climate have a greater influence on the water condensation rate. Overall, this work provides guidelines on the design and setting of in-situ large-scale applications of ABAWH systems using passive radiative condensers for the greatest decentralized freshwater condensation performance under specific weather conditions.