Molecular property methods for assessing efficiency of organic Rankine cycles

• Published in: Energy (Oxford) 2018-01, Vol.142, p.108-120
• Main Authors: Lukawski, Maciej Z., DiPippo, Ronald, Tester, Jefferson W.
• Format: Article
• Language: English
• Subjects: Climate change; Computational fluid dynamics; Computer aided molecular design (CAMD); Critical temperature; Efficiency; Equations of state; Flammability; Global warming; Heat; Heat recovery; Ideal gas; Low global warming potential (GWP); Mathematical models; Molecular group contribution method; Molecular properties; Molecular structure; Organic Rankine cycle (ORC); Rankine cycle; Robustness (mathematics); Specific heat; Temperature; Thermodynamic properties; Thermodynamics; Working fluid screening; Working fluids
• ISSN: 0360-5442; 1873-6785
• DOI: 10.1016/j.energy.2017.09.140

This paper presents a robust method for assessing the efficiency of organic Rankine cycle (ORC) plants based on the molecular structures of the working fluids employed. The developed methodology uses molecular group contribution methods and does not require equations of state or extensive experimental data. The maximum utilization efficiency ɳu* of an ORC plant was correlated with two thermodynamic properties of the working fluid, namely, its critical temperature Tc and reduced ideal gas heat capacity Cp0/R. The developed correlations predict ɳu* with an average error of 0.9–1.5 percentage points. The optimum ORC heat source temperature Ths* can be predicted with an average error of 3.5 °C to 6.6 °C. The developed methodology was validated using a numerical model of an optimized ORC. It was then used to estimate ɳu* and Ths* of 92 working fluids with low global warming potentials (GWP100  0.1 kg/m3). Lastly, best candidate next-generation, low-GWP working fluids were selected for a more detailed examination. •ORC efficiency was predicted based on molecular structures of working fluids.•ORC efficiency is strongly correlated with working fluid properties: Cp0/R and Tc.•Cp0/R and Tc were evaluated using molecular group contribution methods.•ORC efficiency was assessed for 92 working fluids with low global warming potential.