How does the expansion turbine affect the air in an air-cycle cooling system?

In an air-cycle cooling system, the expansion turbine plays a crucial role in regulating the temperature and pressure of the air. When air passes through the expansion turbine, it undergoes a process of adiabatic expansion. This process involves a rapid decrease in pressure as the air is allowed to expand, which consequently leads to a decrease in temperature.

As the air expands, it does work on the surroundings, and since no heat is added to the system during this expansion (adiabatic process), the internal energy of the air reduces, resulting in a drop in temperature. Additionally, since the pressure drops as the air expands, this aspect also contributes to the cooling effect. Thus, the expansion turbine effectively decreases both the temperature and pressure of the air, making it a vital component in achieving the desired cooling in an aircraft's cabin atmosphere control system.

This correlation between the expansion turbine's action and the simultaneous decrease in temperature and pressure helps in efficiently cooling the air within the cabin, ensuring a comfortable environment for passengers.