Analysis of a combined power and ejector-refrigeration cycle using low temperature heat

This paper presents the thermodynamic study of a thermal system which combines an organic Rankine cycle (ORC) and an ejector refrigeration cycle. The performance of different working fluids (R123, R141b, R245fa, R600a, R601a) is investigated using classical (1st and 2nd law) and finite-size thermodynamics for a case for which the power to refrigeration ratio is 10. At first the pressure at the turbine inlet is fixed and the heat source temperature, the evaporation temperature, the cooling water temperature and the expansion ratio of the turbine are varied one at a time. Their effect on the thermal efficiency, the total exergy destruction, the total thermal conductance and the entrainment ratio of the ejector is calculated and analyzed. Further results are then obtained by varying either the inlet pressure of the pump (or, equivalently, the evaporation temperature) or the inlet pressure of the turbine. They show that these variables can be optimized to get a minimum total thermal conductance. R141b has the lowest optimum pressure and smallest total thermal conductance for both these optimum conditions. On the other hand, R601a has the highest thermal efficiency and lowest total exergy destruction in both optimum cases.