What is the purpose of a heat exchanger?

The purpose of a heat exchanger is primarily to reduce the temperature of bleed air. In aviation systems, bleed air is extracted from the engine's compressor section for various uses, including cabin pressurization and engine start assistance. However, this bleed air can be very hot, and it's essential to manage its temperature to ensure that it can be safely used within the aircraft’s environmental control systems without causing damage or inefficiency.

By utilizing a heat exchanger, the hot bleed air can transfer its thermal energy to another fluid, which can be cooler—often air from outside the aircraft or an internal system—thus lowering its temperature before it enters the cabin or other systems. This process helps maintain a comfortable environment for passengers and crew and supports other aircraft systems that rely on bleed air.

The other options relate to different functions that do not align with the main role of a heat exchanger. Eliminating moisture addresses humidity control rather than temperature management, pumping air focuses more on airflow rather than cooling, and increasing engine efficiency pertains to weight and thrust management, which is outside the scope of what a heat exchanger is designed to do.