Performance analysis of a multi-stage humidification–dehumidification desalination system with different salinity levels

Humidification–dehumidification (HDH) technology is an innovative desalination technology that is inexpensive and reliable for small-scale applications. With the development of research, increasing scholars are beginning to adopt a closed-water cycle configuration to improve the HDH system efficiency. The resulting problems of salt accumulation and salinity regulation have not yet been effectively addressed. This paper presents a thermodynamic analysis of a closed-water multi-stage HDH desalination system with different salinity levels. The increase in salinity results in a decrease in the water productivity (~0.75% per 1% increase in the salinity) and maximum energy efficiency (in an average of 11.44% for 20% salinity). It is suggested that the salinity level in the system should be kept below 15% to prevent the maximum energy efficiency of the system lower than that of the open-water system. Additionally, the parameter referred to as the pinch point heat capacity rate ratio is introduced to assess the system performance with different salinity levels. The energy efficiency is maximised when the pinch point heat capacity rate ratio of the 1st-stage dehumidifier is equal to unity at any salinity level. Meanwhile, the effect of salinity on energy efficiency can be judged as an enhanced or diminished role based on whether the pinch point heat capacity rate ratio of the 1st-stage dehumidifier is less or greater than unity.