Dr Lucas Lovis

Atmospheric water generators produce liquid water from humidity in the air. Hence, this technology provides a pathway to alleviate water scarcity. In contrast to conventional day-night monocyclic systems, multicyclic atmospheric water generators conduct multiple sorption and desorption cycles per day. The specific water production for multicyclic desiccant based atmospheric water generators primarily depends on the water sorption and desorption rates of the desiccant, as opposed to the uptake capacity. The mechanisms governing the equilibrium uptake capacity of desiccants and the interparticle diffusion rate of water vapour are well known, however, the mechanisms governing the intraparticle diffusion and sorption rate of water vapour within desiccants are not well summarised. In this review, methods for the enhancement of the intraparticle water vapour diffusion and macroscopic sorption rate are identified, including the effects of pore microstructure, surface hydrophilicity, and composites. Additionally, desiccants with the highest potential specific water production and lowest potential specific energy consumption are identified. To date, the polyamide 6-LiCl nanofibrous membrane demonstrates the highest ideal specific water production of 230 L.kg-1.day-1. The ideal specific energy consumption is similar between the investigated desiccants and primarily depends on the latent heat of sorption. Furthermore, the suitability of various empirical kinetic models for the investigated desiccants is discussed. The variable order model provides a better fit to sorption and desorption kinetic data than the commonly used linear driving force model.

Water scarcity is a significant issue in developing countries and remote locations, however, atmospheric water vapour is a widely available and yet underutilised water reservoir. Desiccant coated heat exchangers are a potential sorption reactor for multicyclic atmospheric water generation due to the enhanced heat and mass transfer to the desiccant. This study utilised a transient one-dimensional mathematical model for a plate-fin desiccant coated heat exchanger and adapted the model for atmospheric water generation. From this, a heat and mass transfer analysis and parametric study were conducted to determine the effect of the operational and geometric parameters on the specific water production and specific energy consumption. The heat and mass transfer analysis found that the coating at the inlet and outlet regions of the channels were underutilised. The parametric study found that the adsorption and desorption cycle times should be optimised independently, the primary air velocity should be high during adsorption and low during desorption, and secondary channel cooling during adsorption did not significantly improve performance. The highest specific water production and the lowest specific energy consumption recorded in this study were 5.8 L kg-1 day-1 and 7.7 MJ L-1 respectively. The recorded specific water production values were higher than most desiccant based atmospheric water generators in the literature. However, the performance was significantly reduced at higher ambient temperatures.