Experimental study on optimum performance of two-stage air-heated bubble-column humidification–dehumidification system

Abstract

An experimental investigation of a small-scale air-heated humidification–dehumidification (HDH) desalination system with bubble- column humidification and dehumidification units was conducted. The study addressed the performance of the multistage air-heated  bubble-column HDH system, which has limited coverage in the literature, by operating two bubble-column humidifiers in series for the  air humidification process with air reheating. The effect of operating parameters such as airflow rate, air temperature, and saline water  levels in both humidifiers on the performance metrics of the system were investigated. The product distillate rate, energy consumption,  gain output ratio (GOR), and specific energy consumption (SEC) are the main indicators of performance for the proposed desalination  system. Response surface methodology (RSM) was applied to the current system using the design of experiment (DoE) for the prediction  of variables that greatly affect productivity and energy input. The airflow rate, air temperature, and water level of the second humidifier have a favourable effect on the distillate rate and GOR of the system. In contrast, the effect of the water level inside the first humidifier is  insignificant. Furthermore, the RSM optimization approach was used to obtain the optimum distillate productivity. An optimized distillate  rate of 0.45 L/h and a GOR of 0.4 are achieved at 1.5 SCFM (standard cubic feet per minute) of airflow rate, and 6.5 cm of water level in the  second humidifier with 140°C air inlet temperature. The numerical optimization reveals the optimal operating parameters, that correspond to maximum distillate production of 0.3 L/h with minimum input energy of 0.71 kW, to be 139°C air temperature, 1.13 SCFM of  airflow rate, 6.5 cm and 3 cm water levels of second and first humidifier, respectively.