**3.6 Air expansion refrigeration systems**

There is a temperature rise when air is compressed. Thus, the temperature drops when the air is allowed to do work while expanding and is obtained by sensible heat only, which is the basis of the air liquefaction process. The main application for the expansion refrigeration system cycle is in the pressurization of aircraft and air

#### **Figure 3.**

*Vapor absorption refrigeration systems.*

**Figure 4.** *Steam jet refrigeration system.*

**Figure 5.** *Air or gas expansion refrigeration systems.*

conditioning. Also, the turbines used compression and expansion turns at very high speeds to achieve the actual pressure ratios, and as a result, it is noisy. Likewise, the coefficient of performance is lower compare to other refrigeration systems. The normal cycle uses the expansion of the air to drive the first stage of compression, so retrieve some of the input energy (**Figure 5**) [17].
