The Jet Powered-Beer Cooler

Aircraft Environmental Control System (ECS) Pressurisation and Air conditioning System PAC

Jet Powered Beer Cooler Aircraft Air Conditioning Enviromental Control System ECS Aircraft ECS 737 747 757 777 A319 A320 Tornado Cold Air Unit Air Cycle Machine Aircraft ECS Air Cycle Machine Compressor Aircraft ECS Air Cycle Machine Turbine Aircraft ECS Heat Exchanger Blower Aircraft Auxiliary Power Unit BAC1-11 737

Here is using a re-created aircraft air conditioning system to chill beer! A gas turbine auxiliary power unit is used to provide a feed of pressurized hot air in to a system of heat exchangers and expansion turbine unit. The system is a simplified version of what is routinely fitted to most jet air liners and military aircraft too.

System Diagram: Hot pressurised air  (180 degrees C and 38 PSI) is provided by a gas turbine engine. The gas turbine engine features an over-size compressor and is able to provide an air feed by bleeding it off before the combustion process. The engine an APU (Auxiliary Power Unit) normally resides in the rear of a commercial aircraft and is run on the ground for this purpose and to provide electrical power. The APU is also used to start the aircraft engines, during this phase the bleed air supply to the air-conditioning is temporarily shut off and diverted to the engines in order to drive the starters. In flight the main engines provide the bleed air to operate the air conditioning and pressurise the cabin. Also in flight ram-air cooling cools the heat exchnagers.

Bleed air from the APU first enters a heat exchanger that cools it using atmospheric air that is blown through it with an electric fan. The heat exchanger is in tandem with a second unit and receives the cooling air from it. The cooled air then enters a small centrifugal compressor unit that raises the pressure further. Due to this additional compression the air again becomes hot and is cooled in the second heat exchanger that is receiving cooling air from the fan. The re-cooled air now enters a radial inflow turbine unit that is driving the centrifugal compressor. The air expands in the turbine and the temperature drops to around freezing point and is exhausted to atmosphere in a cold state. Significant “mechanical work” takes place in the turbine that is required to drive the compressor and so the air looses it’s energy that was in the form of heat and pressure. The special unit that incorporates the compressor and expansion turbine is known as a “Cold Air Unit” CAU or “Air Cycle Machine” ACM.

The air exiting the system was originally drawn in to the gas turbine and heated by it’s compressor, the air now emerges colder than it went in! Water vapour contained in the atmosphere condenses out in he expanding exhaust and forms fog.

The cooling system:  Two automotive inter-cooler units are used as heat exchangers to carry the pressurised air from the APU. A 500W 28V DC fan blows air through the inter-coolers. High pressure automotive silicone hoses feed the air to and from the CAU.

The mysterious unit known as a CAU. When you sit in a plane you are breathing air that has passed through one of these. This one is fitted to  Tornado fighter jet and was part of the cockpit and avionics cooling system.

The CAU consists of a centrifugal compressor connected to a radial inflow turbine. It is constructed a bit like an automotive turbo-charger but is NOT a turbo charger and cannot be used as one -  it will not withstand the temperature! This high speed turbo-machine uses ball race bearings that are lubricated by an integral reservoir. Lubricating oil (synthetic oil similar to turbine oil) is stored within the unit and flows to the bearings by means of a wick.

Unlike a turbo-charger, the hottest part is the compressor, the turbine exhaust is cold air.

Centrifugal compressor unit housed in a stainless steel volute casing.

Expansion turbine unit housed in a low temperature aluminium housing.

DC motor driven blower unit with high speed axial fan. The heat exchangers would benefit from two of these.

Aircraft ECS Heat Exchanger Connections

Automotive silicone hoses fitted with V-clamp flange type adapters.

Aircraft ECS Pre Cooler Intercooler Heat Exchangers

Two automotive inter-coolers used as heat exchangers, the higher pressure cooler receives cooling air first. Large surface area heat exchangers are used with generous size hoses to minimize pressure losses.

Garrett  GTCP-85 model auxiliary power unit. An air bleed is taken from the unit via a ball valve to control the mass flow. Air at this point is very hot around 180 degrees c. The gas turbine consists of a double sided centrifugal compressor supplying a second single compressor and is driven by a single radial inflow turbine. A single can type combustor is fitted to this model gas turbine. The two stage compressor system is lightly loaded and is able to cope with the changing air bleed demands without surging. This typical Garrett arrangement is more docile that a heavier loaded single stage APU configuration.The APU also drives an AC Generator, the generator supplies a transformer rectifier unit (TRU) that in turn supplies the blower fan motor.

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