EFFECT OF WORKING-FLUID MIXTURES ON ORGANIC RANKINE CYCLE SYSTEMS: HEAT TRANSFER AND COST ANALYSIS
File(s)
Accepted version
Author(s)
Oyewunmi, OA
Markides, CN
Type
Conference Paper
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.
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.
Date Issued
2015-12-31
Date Acceptance
2015-06-01
Citation
Proceedings of the 3rd International Seminar on ORC Power Systems, 2015
ISBN
978-2-9600059-2-9
Publisher
University of Liège and Ghent University
Journal / Book Title
Proceedings of the 3rd International Seminar on ORC Power Systems
Source
3RD International Seminar on ORC Power Systems
Publication Status
Published
Start Date
2015-10-12
Finish Date
2015-10-14
Coverage Spatial
Brussels, Belgium