Energy and exergy analyses of a cryogenic reverse Brayton cycle with waste heat recovery

In a typical reverse Brayton cycle (RBC), a great amount of compression heat is just wasted, for which there are two different temperature levels. The basic organic Rankine cycle (ORC) and the regenerative ORC with improvement were then applied to recover waste heat. Considering that the waste gas after ORC was reused, the total exergy efficiency was defined to evaluate different cycles. A simulation method was conducted to predict cycle performances and the coupling between RBC and ORC was clarified. The feasibility of replacing the after cooler with the evaporator was analysed. Compared with the typical RBC, a relative improvement of 18.2% was achieved for COP in the combined system and the cooling exergy efficiency was increased by 16.8%. The correspondence of the total exergy efficiency and the COP of whole system exited in different cycle layouts. Proper organisation of the RBC with ORC could promote the energy efficiency.