Analytical model for thermal efficiency of organic Rankine cycles, considering superheating, heat recovery, pump and expander efficiencies

Abstract

This article proposes a new analytical model that calculates the thermal efficiency of subcritical Organic Rankine Cycles (ORCs) and integrates the main cycle components and parameters in a single analytical solution accounting the effect of turbine and pump isentropic efficiencies, heat recuperation, superheating, fluid type, and hot and cold reservoir temperatures. Previous analytical models for ORCs covered neither heat recuperation, nor pump isentropic efficiency, which are important features for improving the cycle thermal efficiency. The analytical solution was compared with numerical solutions of ORCs for 22 fluids, and the model showed highly accurate for wet and isentropic fluids. The highest percentage divergences were verified for both dry fluids of heavier molecular weight and evaporation temperatures close to the fluid́s critical temperature. The model can be applied to most fluids and for the main operation conditions of ORC applications.