Abstract
The potential use of many common hydrofluorocarbons and hydrocarbons as well as new hydrofluoroolefins, i.e. R1234yf and R1234ze(E) working fluids for a combined organic Rankine cycle and vapor compression refrigeration (ORC-VCR) system activated by low-grade thermal energy is evaluated. The basic ORC operates between 80 and 40 degrees C typical for low-grade thermal energy power plants while the basic VCR cycle operates between 5 and 40 degrees C. The system performance is characterized by the overall system coefficient of performance (COPS) and the total mass flow rate of the working fluid for each kW cooling capacity ((m)over dot(total)). The effects of different working parameters such as the evaporator, condenser, and boiler temperatures on the system performance are examined. The results illustrate that the maximum COPS values are attained using the highest boiling candidates with overhanging T-s diagram, i.e. R245fa and R600, while R600 has the lowest m_ total under the considered operating conditions. Among the proposed candidates, R600 is the best candidate for the ORC-VCR system from the perspectives of environmental issues and system performance. Nevertheless, its flammability should attract enough attention. The maximum COPS using R600 is found to reach up to 0.718 at a condenser temperature of 30 degrees C and the basic values for the remaining parameters. (C) 2016 Production and hosting by Elsevier B.V. on behalf of Cairo University.