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Making the case for cascaded organic Rankine cycles for waste-heat recovery

White, M. ORCID: 0000-0002-7744-1993, Read, M. G. ORCID: 0000-0002-7753-2457 and Sayma, A. I. ORCID: 0000-0003-2315-0004 (2020). Making the case for cascaded organic Rankine cycles for waste-heat recovery. Energy, 211, 118912.. doi: 10.1016/j.energy.2020.118912

Abstract

The design of single-stage organic Rankine cycle (ORC) systems can be challenging owing to large volumetric expansion ratios and sub-atmospheric condensation pressures. Cascaded systems could lead to more efficient expansion processes, higher condensation pressures, whilst introducing the possibility of two-phase expansion to enhance performance. The aim of this paper is to compare single-stage ORC systems to a novel two-phase cascaded system that combines a two-phase expansion topping cycle and a single-phase bottoming cycle for waste-heat recovery applications. Thermodynamic cycle models are integrated with variable efficiency expander models and discretised heat-exchanger sizing models, and single- and multi-objective optimisation studies are completed for three heat-source temperatures (473, 523 and 573 K). The results indicate the relative performance improvement of cascaded systems increases as the heat-source temperature and relative heat-sink size increase, and could increase power output and first-law thermal efficiency by up to 11.1% and 9.5% respectively. The multi-objective optimisation reveals that for a fixed total heat-transfer area the cascaded systems produce approximately 3.6% and 10.5% more power than the single-stage systems for the 523 and 573 K cases respectively with a heat-sink mass-flow rate of 1 kg/s. This increases to 11.7% and 14.5% for heat-sink mass-flow rate of 4 kg/s.

Publication Type: Article
Publisher Keywords: organic Rankine cycle; ORC; cascaded; waste-heat recovery; optimisation; expander modelling
Subjects: Q Science > QC Physics
T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments: School of Mathematics, Computer Science & Engineering > Engineering > Mechanical Engineering & Aeronautics
Date Deposited: 29 Sep 2020 13:35
URI: https://openaccess.city.ac.uk/id/eprint/24962
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