Key parameter influence mechanism and optimal working fluid screening correlation for trans-critical organic Rankine cycle with open type heat sources

Abstract

Trans-critical organic Rankine cycles (ORC) are promising for low to medium temperature heat recovery. To achieve a better cycle performance, the screening of optimal working fluids is quite significant. The optimal working fluids vary with the heat sources, working conditions and performance criterion, and it is difficult to build a general optimal working fluid screening criterion for the trans-critical ORC. Finding the relationship between the working fluid thermodynamic properties and the cycle performance is an effective way to establish general method for optimal working fluid screening. This paper provides theoretical analysis of how the key working fluid thermodynamic properties influence on the cycle performance under a wide temperature range of open type heat sources using various working fluids. Especially the influence of ‘uniformity of cp’ on the heat source utilization is originally analysed. In addition, a relatively general quantitative correlation for selecting the optimal working fluid for trans-critical ORC with heat source temperatures from 150 to 350 °C is presented.