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Session: Session 1: Working fluids
Session starts: Monday 12 October, 11:00
Presentation starts: 11:40
Room: 1A Europe

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Oyeniyi Oyewunmi (Imperial College London)
Christos Markides (Imperial College London)

Abstract:
The present paper considers the employment of working-fluid mixtures in organic Rankine cycle (ORC) systems with respect to heat transfer performance, component sizing and costs, using two sets of fluid mixtures: n-pentane + n-hexane and R-245fa + R-227ea. Due to their non-isothermal phase-change behaviour, these zeotropic working-fluid mixtures promise reduced exergy losses, and thus improved cycle efficiencies and power outputs over their respective pure-fluid components. Although the fluid-mixture cycles do indeed show a thermodynamic improvement over the pure-fluid cycles, the heat transfer and cost analyses reveal that they require larger evaporators, condensers and expanders; thus, the resulting ORC systems are also associated with higher costs, leading to possible compromises. In particular, 70 mol% n-pentane + 30 mol% n-hexane and equimolar R-245fa + R-227ea mixtures lead to the thermodynamically optimal cycles, whereas pure n-pentane and pure R-227ea have lower costs amounting to 14% and 5% per unit power output over the thermodynamically optimal mixtures, respectively.