![airliner - What exactly are those openings in the bellies of many jetliners? - Aviation Stack Exchange airliner - What exactly are those openings in the bellies of many jetliners? - Aviation Stack Exchange](https://i.stack.imgur.com/mJHRy.jpg)
airliner - What exactly are those openings in the bellies of many jetliners? - Aviation Stack Exchange
The PACK 1 ram air inlet door is seen closing after the APU bleed air was selected to the off position. | By A320 Systems | Facebook
Fahad Naim - (B787)✓The ground cooling valve lets air go through the ram air circuit and across the heat exchanger. - This air cools the nitrogen generation system (NGS) air when the
Aviation-knowledge - features hot windscreen demisters and a fresh air blower for use on the ground when there is no ram air. The heater muff or exhaust muff is a close fitting
![File:Air intakes of RAM air for environmental control systems of Boeing 747-8I.jpg - Wikimedia Commons File:Air intakes of RAM air for environmental control systems of Boeing 747-8I.jpg - Wikimedia Commons](https://upload.wikimedia.org/wikipedia/commons/1/1f/Air_intakes_of_RAM_air_for_environmental_control_systems_of_Boeing_747-8I.jpg)
File:Air intakes of RAM air for environmental control systems of Boeing 747-8I.jpg - Wikimedia Commons
![Entropy | Free Full-Text | Cooling Ability/Capacity and Exergy Penalty Analysis of Each Heat Sink of Modern Supersonic Aircraft Entropy | Free Full-Text | Cooling Ability/Capacity and Exergy Penalty Analysis of Each Heat Sink of Modern Supersonic Aircraft](https://www.mdpi.com/entropy/entropy-21-00223/article_deploy/html/images/entropy-21-00223-g001.png)