What is the primary purpose of the heat exchanger in the bleed air system?

• A. To increase the bleed air pressure.
• B. To humidify the cabin air.
• C. To initially reduce the temperature of the bleed air.
• D. To filter contaminants from the bleed air.

Answer: (C)

Bleed air from the engine is extremely hot. The heat exchanger uses cooling air (ram air) to remove heat from that bleed air, bringing its temperature down to a level suitable for the air conditioning packs and cabin conditioning. This cooling happens early in the environmental control process, making it the first step in tempering the bleed air. It isn’t intended to raise pressure, humidify, or filter—those functions are handled by other systems. So the primary purpose is to initially reduce the temperature of the bleed air.