*Manuscript Click here to download Manuscript: Vapour power cycles with isothermal expansion RevisedClick 10 hereno figs.docx to view linked References 1 2 3 4 Review of low-temperature vapour power cycle engines with quasi- 5 isothermal expansion 6 7 8 Opubo N. Igobo, Philip A. Davies 9 10 Sustainable Environment Research Group, School of Engineering and Applied Science, Aston University, 11 Birmingham, B4 7ET, UK email:
[email protected] 12 13 14 15 Abstract 16 17 External combustion heat cycle engines convert thermal energy into useful work. Thermal energy 18 resources include solar, geothermal, bioenergy, and waste heat. To harness these and maximize work 19 output, there has been a renaissance of interest in the investigation of vapour power cycles for quasi- 20 isothermal (near constant temperature) instead of adiabatic expansion. Quasi-isothermal expansion 21 has the advantage of bringing the cycle efficiency closer to the ideal Carnot efficiency, but it requires 22 heat to be transferred to the working fluid as it expands. This paper reviews various low-temperature 23 vapour power cycle heat engines with quasi-isothermal expansion, including the methods employed to 24 realize the heat transfer. The heat engines take the form of the Rankine cycle with continuous heat 25 addition during the expansion process, or the Stirling cycle with a condensable vapour as working 26 fluid. Compared to more standard Stirling engines using gas, the specific work output is higher. 27 28 Cryogenic heat engines based on the Rankine cycle have also been enhanced with quasi-isothermal 29 expansion. Liquid flooded expansion and expander surface heating are the two main heat transfer 30 methods employed.