Effect of working-fluid mixtures on organic Rankine cycle system performance : heat transfer and cost analysis

Loading...
Thumbnail Image

Date

Authors

Oyewunmi, O.A.
Markides, C.N.

Journal Title

Journal ISSN

Volume Title

Publisher

International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics

Abstract

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.
A thermodynamic limitation of single-component working fluids in organic Rankine cycles (ORCs) is the large exergy destruction (and, consequently, useful power loss) associated with evaporation and condensation. Due to their non-isothermal phase-change behaviour, non-azeotropic working-fluid mixtures have shown reduced exergy losses, leading to improved cycle efficiencies and power outputs. These benefits are exclusively observed from a thermodynamic perspective. The present paper considers the effects of selecting such working-fluid mixtures on heat transfer performance, component sizing and system costs compared with those of pure fluids; a mixture of n-pentane and n-hexane is selected. While the fluid-mixture cycles do indeed allow higher efficiencies and the generation of higher power outputs, they require larger evaporators, condensers and expanders; thus, the resulting ORC systems are more expensive than those based on the pure fluids. While a working-fluid mixture (60% n-pentane + 40% n-hexane) leads to the thermodynamically optimal cycle, a pure n-pentane ORC system has reduced costs of 37% per unit power output over the thermodynamic optimum.

Description

Keywords

Organic Rankine cycles, Working-fluid mixtures, Benefits, Thermodynamic

Sustainable Development Goals

Citation

Oyewunmi, OA & Markides CN 2015, 'Effect of working-fluid mixtures on organic Rankine cycle system performance : heat transfer and cost analysis', Paper presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 20-23 July 2015.