Sensitivity analysis of operating conditions of a Stirling cycle via a process simulation approach

Global energy demand drives the search for efficient and sustainable technologies. In this context, the study of thermodynamic cycles, such as the Stirling cycle, is essential. Although the ideal Stirling cycle matches Carnot efficiency, irreversible losses in real systems limit its performance. This study investigates the efficiency of Stirling cycles operating with inert fluids using a process simulation approach, employing the Aspen Plus software, as shown in the diagram, which includes a heat exchanger for heating the cycle fluid, coupled to a Gibbs reactor for fuel combustion, an expansion operation, another heat exchanger for cooling the cycle fluid, and a compression operation. A Stirling cycle with air (inert fluid) in steady state was simulated in Aspen Plus, employing the Peng-Robinson equation and ethanol as fuel for the heating stage. Through sensitivity analyses, the cycle efficiency was evaluated by varying the fuel flow rate (1 to 15 kg/h), compressor pressure (20 to 200 bar), and cooler temperature (0 to 75 °C), while maintaining an air flow rate of 1 kg/h in the cycle. The results indicate the influence of operating conditions on cycle efficiency. For different fuel flow rates, a point of maximum efficiency was observed at intermediate compressor pressures (approximately 65 bar), decreasing at higher pressures. Efficiency also showed higher values ​​for higher fuel flow rates and lower cooler outlet temperatures. Under the analyzed conditions, the maximum efficiency achieved was approximately 23%. With the results obtained, it was possible to perform preliminary simulations that will enable process optimization, including analyses of alternative substances for both the cycle and the fuel, as well as economic and environmental assessments.