The basic reverse-Joule air cycle is often modified by placing a counter-flow heat exchanger between the air entering the compressor and the air entering the expander, known as a recuperator or regenerator (see below).
Click on icon to down schematic of air cycle system with recuperation.
Click on icon to down load pressure-enthalpy diagram of air cycle system with recuperation.
Recuperation increases the compressor discharge temperature, and therefore the scope for heat recovery, and reduces the temperature of the cooled air leaving the expander, without increasing the pressure ratio. The result is an increase in refrigeration duty, although the higher temperature of air in the compressor causes an increase in compressor power consumption. However, the overall effect of recuperation is usually an increase in Coefficient of Performance (COP) or energy efficiency. 
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