Operation optimisation of the unsaturated rapid cycling adsorbent bed for effective moisture enrichment: Coupled heat-mass transfer and dynamic adsorption modelling

Abstract

The unsaturated rapid cycle (USRC) is a potential method for effective water harvesting. The operation mode of USRC, although significant for improving water collection, is seldom investigated for lack of quantitative methods. In this study, we defined adsorption unsaturation Ψ and desorption saturation Φ to characterise the USRC. Subsequently, we constructed performance indices, the effective moisture enrichment rate (EMER) and time-averaged dewpoint increase (TADI) to evaluate the moisture enrichment. The optimisation process was simplified based on the heat-mass transfer analysis. We conducted a case study under summer conditions in Chongqing, a typical city in the hot-summer and cold-winter climate zone. The optimal operation mode of an aluminium fumarate-packed adsorbent bed was verified by the experiments within a relative deviation of 8%, which demonstrates the effectiveness of the optimisation approach. The results show that an operation mode with Φ equal to 32% and Ψ equal to 82% leads to a maximum EMER of the USRC, with an improvement of 4–5 times compared to the nearly saturated rapid cycle. In addition, this case study suggests that a higher desorption temperature, higher adsorbent porosity, and more humid ambient air were conducive to improving the EMER of the USRC.