TY - JOUR
T1 - A rigorous approach for characterising the limiting optimal efficiency of working fluids in organic Rankine cycles
AU - González, Johan
AU - Llovell, Fèlix
AU - Garrido, José Matías
AU - Quinteros-Lama, Héctor
N1 - Publisher Copyright:
© 2022 Elsevier Ltd
PY - 2022/9/1
Y1 - 2022/9/1
N2 - Organic Rankine cycles (ORCs) are a standard and simple layout to convert thermal energy to mechanical energy and, subsequently, electrical energy. On the one hand, it is essential to select the proper working fluids. On the other hand, criteria to choose optimal operation conditions are also necessary. This contribution presents a rigorous and general approach based on the Helmholtz energy function to analyse the optimal performance of an organic Rankine cycle irrespective of the working fluid. The new approach is applied for the n-alkane series and a set of refrigerants using the perturbed-chain statistical association fluid theory (PC-SAFT) equation of state as a calculation tool. The study reveals that a dry global optimum cannot be achieved without partial condensation, and guidelines to avoid this fact are shown. Also, it is parametrically demonstrated that the optimum behaviour of an organic Rankine cycle is not directly connected to the isentropic behaviour of the fluids. However, it is proved that a slightly dry fluid is more suitable for a good performance than a very dry fluid, because the optimum range of expansion lies in a feasible range of temperature, avoiding problems with the limit of the solid phase.
AB - Organic Rankine cycles (ORCs) are a standard and simple layout to convert thermal energy to mechanical energy and, subsequently, electrical energy. On the one hand, it is essential to select the proper working fluids. On the other hand, criteria to choose optimal operation conditions are also necessary. This contribution presents a rigorous and general approach based on the Helmholtz energy function to analyse the optimal performance of an organic Rankine cycle irrespective of the working fluid. The new approach is applied for the n-alkane series and a set of refrigerants using the perturbed-chain statistical association fluid theory (PC-SAFT) equation of state as a calculation tool. The study reveals that a dry global optimum cannot be achieved without partial condensation, and guidelines to avoid this fact are shown. Also, it is parametrically demonstrated that the optimum behaviour of an organic Rankine cycle is not directly connected to the isentropic behaviour of the fluids. However, it is proved that a slightly dry fluid is more suitable for a good performance than a very dry fluid, because the optimum range of expansion lies in a feasible range of temperature, avoiding problems with the limit of the solid phase.
KW - Fluorocarbons
KW - Low-grade heat
KW - Organic Rankine cycles (ORCs)
KW - SAFT
KW - Working fluids
UR - http://www.scopus.com/inward/record.url?scp=85130399207&partnerID=8YFLogxK
U2 - 10.1016/j.energy.2022.124191
DO - 10.1016/j.energy.2022.124191
M3 - Article
AN - SCOPUS:85130399207
SN - 0360-5442
VL - 254
JO - Energy
JF - Energy
M1 - 124191
ER -