Comparison of dual-pressure organic Rankine cycle using zeotropic mixtures

The dual-evaporation organic Rankine cycle (DORC) using zeotropic mixtures can effectively reduce the irreversible loss both in the evaporator and condenser, and thus improve the net power output compared to the DORC using pure working fluid. This paper investigated the DORC using zeotropic mixtures for recovering lowgrade energy. The effects of different condensation temperatures (fixed dew point and fixed bubble point condensation temperature, optimized condensation temperature), temperature glide of zeotropic mixtures and cooling water temperature rise on the net power output of the DORC were investigated. The results indicate that the DORC using zeotropic mixtures under optimal mass fraction can improve the net power output by 6.4-16.6% compared to the DORC using pure working fluid. In selecting the zeotropic mixtures for the DORC, the maximum value of the temperature glide of the zeotropic mixtures under condensation pressure should be larger than the cooling medium temperature increase. The irreversible loss in the evaporator is the most among the four irreversible losses, followed by that in the condenser. However, the effect of irreversible loss in the condenser on the variation trend of the total irreversible loss is the most significant.