secondary air fan

例句：

1. 1.The secondary air fan is designed to improve the efficiency of the exhaust system.
   次级空气风扇设计用来提高排气系统的效率。
2. 2.The secondary air fan helps to cool down the room quickly during hot weather.
   次级空气风扇在炎热天气中快速冷却房间。
3. 3.The secondary air fan has a small noise level, making it suitable for use in quiet environments.
   次级空气风扇噪音小，适合在安静的环境中使用。