Thermodynamic and thermoeconomic analysis and optimization of a novel dual-loop power/refrigeration cycle

Abstract

Exploration of the ejector refrigeration cycle (ERC) in the combination with well-known power cycles to produce cooling output as well as power output is highlighted in recent decades. Since organic Rankine cycle (ORC) is practically usable than other power cycles, a combination of the ORC/ERC in a novel form is presented. Power and refrigeration sub-cycles are combined by a common condenser in separate loops to form dual-loop power/refrigeration cycle. The exhaust of the turbine is mixed with the outlet flow of the ejector, and then the mixed flow is fed into the condenser. Thermodynamic and thermoeconomic analysis of the proposed cycle are carried out with different working fluids (i.e., isobutane, isobutene, butene, cis-2-butene, n-butane, R236fa, and R245fa) showing that among all working fluids isobutane is the best one from thermodynamic, thermoeconomic, and environmental viewpoints. The results of exergy analysis showed that among all components generator accounts for the biggest exergy destruction rate followed by the heater for all selected working fluids. In addition, multi-objective optimization of the proposed cycle is carried out by considering of generator pressure, heater pressure, evaporator temperature, and condenser temperature as decision variables, using the genetic algorithm (GA). The results of the optimization demonstrated that the proposed cycle performs in an optimum state based on the selected objective functions when generator pressure, heater pressure, evaporator temperature, and condenser temperature work at 3 MPa, 1 MPa, 280 K, and 299.8 K, respectively, as isobutane is used. In this case, the optimum net output power, cooling output, thermal efficiency, exergy efficiency, total SUCP (sum unit cost of the product) of the system are calculated 15.22 kW, 61.99 kW, 39.02%, 25.09%, and 86.04 $/GJ, respectively. To better understand the effect of various parameters on system performance, a comprehensive parametric study of some key parameters on performance criteria is carried out. It is shown that the net output power, exergy efficiency, and total SUCP of the system can be optimized based on the generator pressure. In addition, the total SUCP of the system can be minimized by evaporator temperature, too. Also, it is shown that higher cooling output, net output power, thermal efficiency, and exergy efficiency can be obtained at lower heater pressures as well as condenser temperatures. Moreover, at higher generator pressures and evaporator temperatures, a higher cooling output and thermal efficiency can also result.