Thermodynamic analysis of a two-stage humidification–dehumidification system with reflux configuration

• Published in: Energy conversion and management 2019-10, Vol.197, p.111872, Article 111872
• Main Authors: Huang, Xin, Liu, Weihong, Yu, Xiangqian, Ke, Tingfen, Ling, Xiang, Li, Yang
• Format: Article
• Language: English
• Subjects: Air extraction/injection; Air temperature; Configurations; Dehumidification; Desalination; Energy efficiency; Flow rates; Heat; Humidification; Humidification–dehumidification; Injection; Mass flow rate; Power efficiency; Reflux configuration; Reflux ratio; Specific heat; Technology; Thermodynamic analysis; Thermodynamic models; Unity
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2019.111872

•Air temperatures at extraction/injection point equal only under certain conditions.•Effect of mass flow rate ratio in second stage on evaporation rate is negligible.•Energy efficiency peaks at pinch point heat capacity rate ratio of dehumidifier equal to unity.•A reflux configuration is introduced into system to improve the energy efficiency. Humidification–dehumidification technology is an innovative desalination technology which is promising for small-scale desalination applications. The relative low energy efficiency made the early system less competitive. Multi-stage humidification–dehumidification technology is one of the approaches that effectively improve the system energy efficiency. In this study, an air extraction/injection two-stage humidification–dehumidification system with reflux configuration is proposed. The reflux configuration is introduced into the two-stage system to improve the energy efficiency by eliminating the difference between the air temperatures at the extraction and injection points. A thermodynamic model is developed to investigate the system performance. It is found that the air temperatures at the extraction and injection points are only identical when the pinch point heat capacity rate ratio of first-stage dehumidifier less than unity and that of second-stage dehumidifier greater than unity. The influence of liquid-to-air mass flow rate ratio in the second stage on the energy efficiency of the system is negligible when the pinch point heat capacity rate ratio of first-stage and second-stage dehumidifier both greater than unity. The energy efficiency peaks when the pinch point heat capacity rate ratio of first-stage or second-stage dehumidifier equals unity. Additionally, the reflux configuration can improve the energy efficiency of two-stage system by 30%.