Heat-Source-Constrained Optimization of an Organic Rankine Cycle Driven by a Finite Sensible Solar-HTF Source: Working-Fluid and Power-Efficiency Trade-offs

Ali Al Badri

doi:10.71229/e3n55n06

Authors

Ali Mohyee Abdollah Albadri Hakim Sabzevari University, Iran

DOI:

https://doi.org/10.71229/e3n55n06

Keywords:

Organic Rankine cycle; , solar thermal energy;, heat-source matching; , working-fluid selection; , reduced evaporation pressure; , pinch-point constraint; , thermodynamic optimization; , low-GWP refrigerants

Abstract

A steady-state subcritical organic Rankine cycle (ORC) coupled to a finite sensible solar heat-transfer-fluid (HTF) source was evaluated to distinguish useful net-power optima from thermal-efficiency limits. Five fluids were screened at nine heat-source temperatures (100–180°C) and 25 reduced evaporation pressures (Pr=0.20–0.80), with a common source heat-capacity rate of 1 kW K−1. Re-execution of the candidate-level Python model yielded 755 feasible and 370 rejected states among 1,125 candidates; all rejected primary-grid states failed the 10 K hot-end evaporator approach (32.9% rejection). At 150°C, R1234ze(E) delivered the highest primary-domain net power, 10.325 kW at Pr=0.80. A separately examined Pr=0.10–0.90 extension increased its power to 10.683 kW at the Pr=0.90 upper bound, which is not an unconstrained optimum. Its Pr=0.10 state was infeasible because evaporation pressure was below condensation pressure. The extended n-pentane power maximum occurred at an interior Pr=0.1304 and 8.200 kW. At 180°C, isobutane reached 17.149 kW at the extended upper bound Pr=0.90. For several fluids, maximizing efficiency alone approached zero-throughput pinch limits; the resulting limiting efficiency ratios are not realizable finite-output operating states. Reproducible code, the 1,125-state dataset, an analytical pinch unit test and mesh-refinement checks are provided. Property-path verification and limited R245fa cycle comparisons do not independently validate the thermophysical formulation or actual source-side heat transfer. All power figures are thermodynamic comparisons for the normalized source under the stated steady-state assumptions, not predictions of a specified solar plant.

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