What is Air Conditioning Pack and Air Cooling System (ACM) Aircraft ? - اسأل الطيار ask pilot


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الثلاثاء، 7 يوليو 2020

What is Air Conditioning Pack and Air Cooling System (ACM) Aircraft ?

What is Air Conditioning Pack and Air Cooling System (ACM) Aircraft ?

**Aircraft Environmental System PACKS- (Pressurization Air Conditioning Kits)
Most jetliners are equipped with "p-a-c-k-s" which stands for Pressurization Air Conditioning Kits". The air conditioning (A/C) packs are usually located at the lower wing/fuselage root fairing beneath the fuselage.
To control cabin temperature the cooled air from ACM is simply mixed with hot bleed air. Two or more temperature mixing valves are used for this purpose.
In large aircraft, the whole environmental heating/cooling system is bundled together, including ACM, bleed heat source, and mixing valves. This package is commonly referred to as a “PACK”. Normally two are installed for capacity and redundancy.
In most modern aircraft, comfort is controlled via automatic temperature control systems tied to cabin air temperature sensors. Manual control of the temperature mixing valves is usually available to back up the automatic system.
The pack allows bleed air to be cooled for conditioning the flight and passenger compartment. The air conditioning system is based on an Air Cycle Machine (ACM) cooling device, which is mostly used in turbine-powered aircraft. The air cycle system is often called the air conditioning package or Pack.

Usually, Air conditioning packs are located left and right wing to body area near the main landing gear of an airplane. Packs remove the excessive heat from bleed air entering to packs from aircraft bleed air system and supplies air to the cabin at a desired temperature.
**Air Cycle Machine (ACM)
An ACM comprising a compressor and a turbine mounted on the same shaft. Air Cycle Machines, high-pressure bleed air from the engines is first passed through a compressor, further squeezing the already hot gas. It is then routed through a heat exchanger or two to remove heat. The now cooler but still highly compressed air then passes through an expansion chamber into a larger chamber. The combined effects of driving the turbine and expanding into a larger chamber dramatically cools the air (usually down close freezing; water traps are critical in the system to prevent freeze-up).

The expansion turbine is connected by shaft to the ACM’s compressor, so expanding air works to compress the upstream bleed air similar to the way a turbine engine or a piston engine turbocharger works. This cycle may be repeated several times, with the end result that system air temperature is cooled far below ambient temperature.
For more information, please refer sources given below.

Excerpted and adapted from The Turbine Pilot's Flight Manual - 3rd Edition (ASA, 2012)

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