What is the main purpose of the secondary heat exchanger in an air-cycle system?

The main purpose of the secondary heat exchanger in an air-cycle system is to cool the air further. In an air-cycle cooling system, air passes through various stages, and the secondary heat exchanger plays a crucial role in enhancing the overall cooling efficiency. This component utilizes ambient air to remove additional heat from the primary compressed air, ensuring that the air reaching the cabin or engine is at a lower temperature.

By cooling the air further after it has already been cooled in the primary heat exchanger, the secondary heat exchanger improves the performance and comfort of the system—especially in warmer conditions or during high-demand operations. This additional cooling is critical for maintaining optimal operating temperatures and preventing overheating in the system.

The other options do not align with the primary function of the secondary heat exchanger. It does not provide lubrication, assist in compression, or introduce humidity into the air cycle. Instead, its main role is focused exclusively on cooling, which is essential for the efficiency and safety of the overall air-conditioning system.