Error analysis of ORC performance calculation based on the Helmholtz equation with different binary interaction parameters of mixture

Abstract

Mixtures have been widely researched for organic Rankine cycle (ORC) application in various heat sources. In this contribution, the calculation errors of cycle performance are analyzed by investigating the property uncertainty of mixtures, based on the Helmholtz equation with three groups of binary interaction parameters (BIPs), namely newly fitted BIPs, estimated BIPs and BIPs = 1. Nine mixtures are selected for the ORC and six cycle parameters are determined under different molar fractions of mixtures and operating temperatures. When the results of fitted BIPs are considered as the basis of comparison, the relative errors of estimated BIPs and BIPs = 1 vary greatly with the molar fraction of mixture, but change little with the cycle temperature. Deviations of pumping work are always the largest among the considered parameters. For HFC/HFC mixtures, cycle parameters except pumping work have average absolute relative deviations (AARDs) less than 5%. However, for HFC/HC and HFO/HC mixtures, BIPs = 1 has an AARD of pumping work larger than 20%. The AARD of pumping work for the estimated BIPs is around 10%. In the future performance evaluation of alternative mixture with few or no experimental data, the above analysis is helpful for choosing appropriate BIPs and estimating the errors of cycle parameters.