Thermal Analysis and Cost Estimation of Stirling Cycle Engine

Stirling engine technologies have been applied to cogeneration systems mainly for residential applications. The performance of Stirling engines has been evaluated considering different operational conditions, which include the electrical and thermal production. Thermodynamic analysis of the Stirling engine’s performance has been conducted, using specially designed computing codes along with the thermal balance study of the technology. The performance of the unit has been evaluated considering different operational conditions, which include the electrical and thermal production, working fluid mean pressure or mass, components geometrical sizing. The thermal-economic evaluation represents an effective tool to optimize a power plant with this type of technology. This study presents a mathematical model that includes a set of equations able to describe and simulate the physical system, as well as a set of equations that define the cost of each plant component. The physical model attempts to simulate the real conditions of a micro-CHP unit based on an alpha type Stirling Engine, by taking into account the imperfect regeneration and the pumping losses. The cost expression for each component integrates thermodynamic and cost coefficients adjusted for this kind of technology and also taking into account real market data. The simulations were performed through a MatLab® code that assesses the thermodynamic efficiency, including heat transfer limitations and pumping losses throughout the system, and the purchase costs of the equipment. Results showed the Stirling engine performance depends on geometrical and physical parameters which optimization is required in order to obtain the best performance. Regenerator is one of the most important components of the Stirling engine. The maximum heat transferred to and from the regenerator matrix is higher than the energy transferred to the other two heat exchangers. Results demonstrated that the engine efficiency achieves a higher value when hydrogen is the working fluid. It is verified that cost estimation based on sizing and quality parameters has a good correlation with the capital investment costs of commercial models. The total capital costs are close to real commercial models for similar applications. Plus, the engine bulk and the heater are the most expensive components. Key-Words: CHP Applications, High-efficiency, Energy Conversion, Stirling Engines, Cost Estimation