Performance analysis of low temperature organic Rankine cycle with zeotropic refrigerant by Figure of Merit (FOM)

•A correction factor to transform the zeotropic fluid properties in a form of FOM was created.•An empirical correlation to estimate cycle efficiency from the FOM was developed for zeotropic mixtures.•The cycle efficiency could be evaluated from the η-FOM curve.

This paper proposed a dimensionless term, the “Figure of Merit” (FOM), to investigate the thermal performance of a low temperature, organic Rankine cycle using six zeotropic mixtures (R245fa/R152a, R245fa/R227ea, R245fa/R236ea, R245ca/R152a, R245ca/R227ea and R245ca/R236ea) as working fluids. An empirical correlation was developed to estimate the cycle efficiency from the FOM for all working fluids at condensing temperatures of 25–40 °C and evaporating temperatures of 80–130 °C. The model results fit very well with both the experimental data and that from other researchers.