Thermo-Economic and Heat Transfer Optimization of Working-Fluid Mixtures in a Low-Temperature Organic Rankine Cycle System†
AbstractIn the present paper, we consider the employment of working-fluid mixtures in organic Rankine cycle (ORC) systems with respect to thermodynamic and heat-transfer performance, component sizing and capital costs. The selected working-fluid mixtures promise reduced exergy losses due to their non-isothermal phase-change behaviour, and thus improved cycle efficiencies and power outputs over their respective pure-fluid components. A multi-objective cost-power optimization of a specific low-temperature ORC system (operating with geothermal water at 98 °C) reveals that the use of working-fluid-mixtures does indeed show a thermodynamic improvement over the pure-fluids. At the same time, heat transfer and cost analyses, however, suggest that it also requires larger evaporators, condensers and expanders; thus, the resulting ORC systems are also associated with higher costs. In particular, 50% n-pentane + 50% n-hexane and 60% R-245fa + 40% R-227ea mixtures lead to the thermodynamically optimal cycles, whereas pure n-pentane and pure R-245fa have lower plant costs, both estimated as having ∼14% lower costs per unit power output compared to the thermodynamically optimal mixtures. These conclusions highlight the importance of using system cost minimization as a design objective for ORC plants. View Full-Text
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Oyewunmi, O.A.; Markides, C.N. Thermo-Economic and Heat Transfer Optimization of Working-Fluid Mixtures in a Low-Temperature Organic Rankine Cycle System. Energies 2016, 9, 448.
Oyewunmi OA, Markides CN. Thermo-Economic and Heat Transfer Optimization of Working-Fluid Mixtures in a Low-Temperature Organic Rankine Cycle System. Energies. 2016; 9(6):448.Chicago/Turabian Style
Oyewunmi, Oyeniyi A.; Markides, Christos N. 2016. "Thermo-Economic and Heat Transfer Optimization of Working-Fluid Mixtures in a Low-Temperature Organic Rankine Cycle System." Energies 9, no. 6: 448.
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