Constructal design and optimization of a direct contact humidification–dehumidification desalination unit

• Published in: Desalination Vol. 293; pp. 69 - 77
• Main Authors: Mehrgoo, Morteza, Amidpour, Majid
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.05.2012; Elsevier
• Subjects: air; air flow; algorithms; Applied sciences; cold; Constructal theory; Desalination; Direct contact; Drinking water and swimming-pool water. Desalination; energy; Exact sciences and technology; freshwater; heat; Humidification–dehumidification; multipliers; Pollution; recycling; water temperature; Water treatment and pollution; Humidification–dehumidification; Direct contact; Desalination; Constructal theory; System architecture; Energy consumption; Dehumidification; Humidification-dehumidification; Modeling; Hot water; Optimization; Design; Air flow; Genetic algorithm; Production; Humidification; Recycling
• ISSN: 0011-9164; 1873-4464
• DOI: 10.1016/j.desal.2012.02.025

This study shows that the main design features of a direct contact humidification–dehumidification (HD) desalination process can be determined based on the method of the constructal design. A direct contact HD unit has three main sections: the humidifier, the dehumidifier and the heat source. To analyze and optimize such unit, two flow models for air circulation are considered: natural and forced circulations. The objective is increasing the water production rate over the volume occupied by the plant. The parameters considered in this work are the air flow rate, tube diameters ratio, temperatures and flow rates of inlet saline and fresh water. The Lagrangian multipliers and genetic algorithm (GA) methods are used to optimize the production rate subject to global constraint (fixed volume). The constructal design developed in this paper explains the influences of the inlet cold and hot water temperatures and air flow rate on the basic design parameters of HD system architecture. It shows that the optimal configuration of HD system is consequently temperature dependent. Finally, the analysis shows that if the humidifier inlet water temperature is high, recycling of the humidifier outlet water results in about 15–25% reduction in the specific thermal energy consumption. ► A direct contact humidification–dehumidification desalination unit is modeled and analyzed. ► The constructal theory is incorporated with mathematical modeling to optimize the proposed unit. ► The Genetic Algorithm and Lagrange multiplier methods are used to optimize the fresh water production rate. ► All design parameters change in proportion with the water inlet temperatures of the dehumidifier and humidifier. ► The water to air mass flow rate ratio (saline and fresh water) significantly affects on the main design parameters. ► Recycling ratio is found as an effective way for declining the energy consumption of unit.