The impact of thermodynamic balancing on the performance of a humidification dehumidification desalination system

Abstract

The humidification-dehumidification (HDH) desalination is a favorable option for small scale and off-grid applications. Its main disadvantage is the low thermal efficiency compared with other thermal desalination techniques. This study demonstrates the importance of using the thermodynamic balancing concept in enhancing the thermal efficiency of HDH systems. An experimental HDH setup has been built to produce 276 kg of pure water per day (peak capacity) costing 0.033 $/L. The physical understanding of the balancing concept is clarified by representing the experimental results on the temperature enthalpy diagram. The enthalpy pinch model can be solved numerically, analytically, or pseudo-analytically to estimate the performance at the balanced conditions (upper limit of performance). Moreover, a novel parameter, dimensionless enthalpy pinch (Ψ¯) is proposed to be a measure of the thermal efficiency and a size index. The theoretical model has been validated against the experimental results with a maximum error of 6%. It can be concluded that adjusting the operating conditions to balance the system thermodynamically can improve economic performance by about 40%. Moreover, theoretically, the parametric study shows that the dehumidifier Ψ¯ is more dominating on the gain output ratio (GOR) than the humidifier Ψ¯. Also, at a fixed Ψ¯, the maximum (Tmax) and minimum (Tmin) temperature influences the GOR significantly only at a low enthalpy pinch value (Ψ¯ < 20%) where decreasing Tmax or increasing Tmin has a positive effect on the GOR.