Modeling and optimizing the atmospheric water harvesting System: Application of PAN-PDMS polymeric membrane

Potable water scarcity is an increasingly demanding global issue and the extraction of potable water from the humidity of ambient air can be a solution to this problem. In this research combination of membranes, vacuum pump and vapor compression refrigeration (VCR) system is proposed as a water harvesting system. Polymeric membranes Polydimethylsiloxane (PDMS) and polyacrylonitrile (PAN), helped to separate water vapor from air by increasing the partial pressure of water vapor on the permeate side due to the separation process. The water vapor permeability has been assumed constant even with change in the pressure difference on two sides of the membrane in many research studies. However, this research uses its own developed relations obtained based on experimental results for variable pressure difference on both sides of membranes. As this proposed membrane system provides the air with near saturated water vapor conditions, thus, VCR system requires lower cooling capacity and lower electricity consumption for the condensation process. This proposed water harvesting system is modeled in energy and economic aspects for the first time and is optimized in this research by applying multi-objective Genetic Algorithm (GA) technique. The water production rate and the total annual cost rate were considered as two objective functions. Also, five design variables are selected after considering their effects on the objective functions. The optimization procedure performed for four different climate zones of Iran. Optimization results for the second zone showed 3.56 L per hour water production rate with about 29 % lower energy consumption in comparison with that for typical condensation process of water vapor in the same atmospheric air. The improved values for water vapor removal efficiency, water production cost, and the energy consumption were 63.6 %, 0.31 $ per liter, and 1714 $\text{kJ}$ per liter respectively.