Optimization of Two-Stage Modified Air Heated HDH Desalination Systems

The present study compares HDH systems with different numbers of heaters as well as open air and closed air configurations. An open air cycle with a single heater and a single humidification process is considered the baseline. It is compared to modified HDH systems with multiple heaters and humidification processes. The current study also compares open air and closed air modified air heated HDH systems with two-stage humidification. The analytical solution for these HDH systems is computed using EES. Results indicate that the modified HDH system shows significantly enhanced gained output ratio (GOR). However, when comparing open air and closed air modified air heated HDH systems, the closed air system has a higher GOR (= 2.1) than the open air system. The present study includes a parametric analysis to identify the influencing factors to get the optimal operating conditions. The parametric study indicates that system performance is greatly affected by the mass flow rates of air and water, heater-1, and heater-3. Hence, these parameters are chosen as design variables for the optimization study. The optimization process analyzes the effect of varying these variables simultaneously and identifying their optimum values for peak system performance. The study considered optimum placement of heaters within the system to keep the total heat input unchanged. A 7-level Box–Behnken design of experiment method is created using ‘SAS JMP,’ which generated 16,807 operating points and is analyzed using EES software. A mathematical model to establish a relationship between GOR and operating conditions is developed using neural networks. Finally, a genetic algorithm optimization is performed in MATLAB to identify optimum operating conditions. At optimum values, the system produces the highest GOR of 3.68. An exergy and economic analyses of these HDH systems are also performed to assess the cost of the system using the economic model.