Energy and exergy analysis of a combined system: cascade organic Rankine cycle and cascade refrigeration cycle

In this paper, a new combined system is proposed for recovering thermal energy at medium temperature using a cascade organic Rankine cycle to feed a cascade refrigeration cycle. Energy and exergy analysis is applied to the combined system to determine its performance using different working fluids under the same operating conditions taking into account the effect of some operating parameters and the selection of organic fluids on cycle performance. The pair of organic fluid (Toluene/R245fa) used for the cascade organic Rankine cycle and the pairs (R717/R744, R717/R23, R134a/R23) used for the cascade refrigeration cycles. The results show that the combined system function with the couple (R717/R23) for cascade refrigeration cycle gives better exergy efficiency 50.03% compared to other couples, 49.57% for the couple (R717/R744), and 48.01% for the couple (R134a/R23). The thermodynamic evaluation shows that the operating temperatures, such as the cascade organic Rankine cycle evaporation temperature and the cascade refrigeration cycle evaporation temperature influence the performance of the combined system.