Thermolytic osmotic heat engine for low-grade heat harvesting: Thermodynamic investigation and potential application exploration. (1st February 2020)

• Record Type: Journal Article
• Authors: Tong, Xin; Liu, Su; Yan, Junchen; Broesicke, Osvaldo A.; Chen, Yongsheng; Crittenden, John
• Is Part Of: Applied energy. Volume 259(2020)
• Publication Date: 2020-02-01
• Subjects: Osmotic heat engine -- Waste heat -- Solar thermal energy -- Energy efficiency -- Exergy efficiency; Power (Mechanics) -- Periodicals; Energy conservation -- Periodicals; Energy conversion -- Periodicals; 621.042
• DOI: 10.1016/j.apenergy.2019.114192
• Languages: English
• ISSNs: 0306-2619

Abstract

Graphical abstract: Highlights: Both energy and exergy efficiency are calculated for thermolytic osmotic heat engine. The osmotic heat engine efficiencies are higher at lower operating temperatures. Energy return on investment is high when industrial waste heat is the energy source. Solar thermal powered-osmotic heat engine has a lower energy return on investment. Abstract: The osmotic heat engine is a promising technology for harvesting low-grade heat from different heat sources. However, a better understanding of the system performance, thermodynamic efficiencies, and suitable application circumstances (type of heat sources, system energy generation capacity, etc.) is needed before the transition can be made from conceptual design to practice. Firstly, the energy efficiency ( ƞth ) and exergy efficiency ( ƞX ) of a thermolytic osmotic heat engine (NH4 HCO3 solution as the working fluid) were investigated in this study. It was found that the osmotic heat engine performs better when the operating temperature (heat source temperature) is lower (323 K). Additionally, a higher draw solution concentration and a lower feed solution concentration can increase both ƞX and ƞth . Subsequently, the energy return on investment with either low-grade industrial waste heat or solar thermal energy acting as the heat source was calculated. It was found that different energy return on investment values can be obtained with different heat sources. The results show that when industrial waste heat is used as the heat source, a much higher energy return on investment value (approximately 55) can be obtained. This finding indicates that it is suitable to generate electricity from industrial waste heat using the osmotic heat engine. When solar thermal energy is used as the heat source the energy return on investment value is 1.3–2.2 because there is a large amount of embodied energy in the flat-plate solar collector. This study represents a step forward towards the practical application of the osmotic heat engine.