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Low temperature Stirling engines pressurised with real gas effects

Sala, Fernando, Invernizzi, Costante M.
Energy 2014 v.75 pp. 225-236
engines, gases, pressure, simulation models, temperature
With the aim of improving the performance of Stirling engines for applications with relatively low maximum temperatures (150 °C–300 °C), working fluids that have noticeable real gas effects have been considered.The simulation model developed for the preliminary analysis of Stirling engines takes into account the losses of mechanical power and the efficiency of the regenerator with two adimensional coefficients, on the basis of experimental data available in literature. Comparisons between the working fluids were made having fixed the value of these two parameters. The results from this simplified analysis can be taken into consideration when evaluating the potential of these Stirling engines with real gas. They revealed that an engine cycle with a maximum pressure 3–4 times greater than the critical pressure and using a fluid with a critical temperature close to the minimum temperature of the engine cycle, gives an increase in power about 2.5 times greater than the case with ideal gas and an increase in cycle efficiency of around 50 percent. Such a result means that the use of fluid mixtures as the working fluids now becomes interesting, since the critical point of mixtures can be gradually adapted to meet design requirements.