Exergetic analysis of the humidification-dehumidificationdesalination cycle involving variation in top temperature

Abstract

• Effects of the top temperature variation on the HDH cycles is presented. • CAOW cycles involving zero or single air and water extractions were analysed. • Gain-out put ratio and exergetic efficiency parameters were studied in detail. • For extraction cycles, peak GOR corresponds to maximum exergetic efficiency point. Saline water desalination is attaining a prime focus to meet the challenges of water scarcity in the developing countries. Solar energy could be effectively utilized for desalinating the saline/sea water. In this respect, humidification dehumidification (HDH) cycle could prove as a promising solar driven desalination technology. In this paper, exergy analysis of single extraction air heated and water heated HDH desalination cycles are examined in detail. The top temperature and extraction rate parameters are considered crucial for any typical single extraction HDH cycle. Analysis of the effects of varying top cyclic temperature keeping fixed extraction/injection rate of 70% water/air stream is carried out. The top temperature is varied between 60 °C−80 °C range. For the air heated air extraction cycle, total exergy destroyed is higher at lower top temperatures, resulting in lower exergetic efficiency. A similar trend is also followed by the air heated water extraction cycle for the top temperatures ranging up to 70 °C. The total exergy destroyed registered an increase above 70 °C because of the significant rise in exergy destruction for the heater component. In the water heated cycle with water/air extraction, exergy destroyed decreases at lower top temperatures, thereby yielding higher exergetic efficiencies. For each HDH cycle configuration, correlation between the gain output ratio (GOR) and exergetic efficiency is additionally obtained. The results revealed that at the given top temperature, sub-component effectiveness, mass flow rate ratio and bottom temperature parameters, the GOR increases with the exergetic efficiency of the cycle.