What Is the Stirling Cycle?
The full name of the Stirling cycle is "the ideal cycle of the Stirling hot air engine", also known as the "ideal cycle of the piston hot air engine", commonly known as the "hot gas cycle". A closed-type generalized Carnot cycle that uses the heat recovery under constant volume and is the most perfect in thermodynamic theory. It was named after British engineer Robert Stirling (1790 ~ 1878) first proposed in 1816. The Stirling cycle is a reversible cycle consisting of two constant volume heat absorption processes and two constant temperature expansion processes, and the heat released by the constant volume heat release process is exactly absorbed by the constant volume heat absorption process. The heat engine absorbs heat from a high-temperature heat source during expansion at a constant temperature ( T 1), and releases heat to a low-temperature heat source during compression at a constant temperature ( T 2). [1]
- The ideal thermodynamic cycle of a hot gas engine (that is, a Stirling engine) is composed of four reversible processes: isothermal heat absorption, isothermal heat release, isothermal heat release, and isothermal heat absorption:
- (1) The low-temperature and low-temperature working medium receives the piston's constant temperature compression process while radiating heat to the external cold source;
- (2) During the process of constant volume heating of the cryogenic working medium under constant volume conditions, the pressure and temperature are increased accordingly;
- (3) While the high-pressure and high-temperature working medium absorbs heat from the external heat source, it promotes the constant-temperature expansion process of the piston for external work;
- (4) The process of constant volume heat release from the high-temperature working fluid to the regenerator under constant volume conditions, the pressure and temperature are reduced accordingly and returned to the initial state, thereby completing a closed cycle. The two isothermal processes absorb heat from a high-temperature heat source and release heat to a low-temperature heat source, while the heat of the two isovolumetric processes is the internal heat recovery of the cycle, that is, the isovolumic heat absorption process just absorbs the heat released by the isovolumic heat release . The cycle is therefore a reversible cycle between a high-temperature heat source and a low-temperature heat source. Its p- diagram and Ts diagram are shown in the drawings.
- Stirling cycle
- The main advantage of the Stirling cycle is that under the ideal conditions of extreme heat recovery (that is, the heat released during the constant volume heat release process is exactly equal to the heat required for the constant volume heating process), the cycle thermal efficiency can be equal to Carnot within the same temperature limit. Thermal efficiency of the cycle. However, because the surface of some equipment (such as heaters) has always been required to work at the maximum temperature of the cycle, the maximum temperature of the cycle is directly limited by the heat resistance of the metal, and there is irreversible loss such as friction, so the Sterling is further improved. There are still some difficulties with the actual thermal efficiency of the cycle. When this cycle is reversed, it can become the refrigeration cycle or heat pump cycle with the highest coefficient of performance. [2]
- In 1816, the Scottish R. Stirling (Robert Stirling) applied for a patent for hot air reciprocating "external combustion engine" working according to this cycle, called Stirling
- How it works (3 photos)