aircycle

An air cycle is a thermodynamic cycle that uses air as its working fluid. It is a type of heat engine, meaning it converts thermal energy into mechanical work. Air cycles are fundamental to the operation of many refrigeration and power generation systems. The most common examples include the Brayton cycle and the reversed Brayton cycle.

The Brayton cycle is the basis for gas turbine engines, commonly found in aircraft and power plants. It consists of four main processes: isentropic compression of air, isobaric heat addition, isentropic expansion of the hot gases, and isobaric heat rejection. In a simple gas turbine, this expansion drives a turbine, which can then perform work, such as generating electricity or propelling an aircraft.

The reversed Brayton cycle, also known as the Joule cycle or the cold air standard Brayton cycle, is used for refrigeration. In this variant, the expansion process occurs at lower temperatures, absorbing heat from the space to be cooled. The compressed air is then cooled before expansion. This cycle is employed in some cryogenic applications and air conditioning systems where a refrigerant other than air is not desired or practical.

While air is a convenient and readily available working fluid, air cycles are generally less efficient than cycles using other working fluids like steam, especially at lower temperatures. However, their simplicity, reliability, and ability to operate at high temperatures make them suitable for specific applications. The efficiency of an air cycle is primarily influenced by the pressure ratio during compression and expansion.