Air cooling cycle of works on the reverse Brayton or Joule cycle. Air is compressed and then the heat is removed; this air is then expanded to a lower temperature than before it was compressed. Heat can then be extracted to provide useful cooling with return air to the initial state (see Fig. 2.14). The work is taken from the air by expanding due to the expansion turbine, which removes energy, as shown in the movement of the blade round of expansion of the air. This work can be usefully employed to run other devices, such as generators, fans.
Often it is used for supply compressor as shown. Sometimes, compressor, called " boot compressor operates from extender, letting the two stages of compression. Increased pressure on the hot side of further elevates the temperature and makes the air cycle system produce more useable heat (at high temperature). Cold air after turbines can be used as a refrigerant or directly in an open system, as shown or indirectly through С‚РµРїР»РѕРѕР±РјРµРЅРЅРёРє in a closed system.
Efficiency of such systems limited, largely determined by the efficiency of compression and expansion, as well as those heat exchangers are employed.
Initially, slow-speed reciprocating compressors and expanders are used. The low efficiency and reliability of such equipment were the main factors replacement of such systems with vapour compression equipment. However, the development of rotary compressors and expanders (e.g.. car turbo-chargers), and this has significantly improved the isentropic efficiency and reliability of air cycle. Turbojet technology together with the development of aviation bearings and ceramic components provide further increase in efficiency.
The main application of this cycle air conditioning and pressurization of the aircraft. The turbine is used for the compression and expansion of the queue at a very high speed to obtain the required differential pressure and, consequently, are noisy. The COP is lower than with other systems..