A Novel Desiccant-based Humidification-dehumidification System To Harvest Freshwater From The Atmospheric Air
Syed M. Zubair , محمد على محمود أحمد
كلية الهندسة-جامعة الملك فهد للبترول والمعادن · السعودية
Freshwater is transforming into a rare asset in numerous areas around the globe. In coastal zones, the moisture content held in the air is substantial. In such humid zones, harvesting water from the atmospheric air is promising to help secure reasonable amounts of freshwater. In a conventional HDH system, a constant feed of seawater is required to run the system. As a result of extracting freshwater from the saline water, it is rejected at higher salinity; thus, it cannot be recirculated as feed again. This study aims to develop a zero-brine discharge system that eliminates the continuous need for the supply of source and sink in the conventional method. Based on the fact that the earth’s atmosphere holds a vast amount of water, that can be considered a reliable freshwater resource. In this regard, this research will achieve the collecting of freshwater from the humid air by using a desiccant-based humidification-dehumidification (HDH) system coupled with moisture extractors.The setup of the proposed system configuration comprises two parts, a basic HDH system and desiccant-based moisture extractors. Due to freshwater extraction, the liquid desiccant leaves the HDH part at a higher concentration. It then enters the air dryer, diluted by absorbing water vapor from the ambient air. This diluted desiccant is directed to the HDH part to close the desiccant loop. Mathematical modeling of heat and mass transfer processes between the air and desiccant in the humidifier, dehumidifier, and moisture extractor is developed to predict the performance of the desalination system as well as the freshwater to be produced. Thermodynamic balancing is a powerful tool to minimize entropy generation in a thermal system. This tool improves the proposed system's performance by extracting the recirculated air. It is implemented for 0 - 22 and infinity extractions. An innovative model based on the particle-swarm minimization technique is used to reach the maximum possible number of extractions. Also, the feasibility of adding an extra number of moisture extractors is studied to enhance freshwater production from the humid air.This research investigates the performance of moisture extractors, dehumidifiers, and humidifiers before and after extraction. The optimized design using an artificial neural network is developed for possible mass production for such systems with the ultimate objectives of reducing energy consumption, increasing environmental protection, and improving performance with less operating and initial cost. The results indicate that the developed artificial neural network has high accuracy in predicting the performance and design parameters, demonstrating minimum accuracy of 98.3%, 96.4%, and 98.9% for zero, single, and double extractions, respectively. Then, an experimental study was conducted on a desiccant (Lithium Bromide) heated Open-Air humidification dehumidification cycle-based atmospheric water generator at the steady-state condition with brine recirculation designed, constructed, and operated in a controlled environment. The results show that the built system can produce distillate water of about 51 Liters per day.