In the air cycle machine, bleed air from the gas turbine engine changes which of these attributes?

• A. Increase pressure, decrease temperature, decrease velocity
• B. Decrease pressure, decrease temperature, increase velocity
• C. Decrease pressure, increase temperature, increase velocity
• D. Increase pressure, increase temperature, decrease velocity

Answer: (B)

In an air cycle machine, bleed air from the engine is expanded in the turbine stage, which cools it. This expansion lowers the air’s static pressure and its temperature. As the air expands, some of its enthalpy is converted into kinetic energy, so the velocity exits higher than it entered. So the bleed air leaves with lower pressure, lower temperature, but higher velocity.