pressurization system in aircraft

Pressurization System In Aircraft - There are two types of air conditioners commonly used in airplanes. Air cycle air conditioning is used in most turbine powered aircraft. The exhaust air from the engine, or APU, uses pressurized air in the cooling process. Vapor cycle air conditioning systems are often used in commercial aircraft. This function is the same in houses and cars. Note that some turbine-powered aircraft use vapor cycle air conditioning.

Air cycle air cooler The air cycle air cooler prepares the bleed air from the engine to pressurize the cabin. to maintain a comfortable headroom at heights and on the ground; The temperature and volume of the air must be controlled. The air circulation system is called the air conditioning package or package. Commonly found in the lower fuselage or tail section of turbine-powered aircraft. [Figure 1]

Pressurization System In Aircraft

Figure 1. Boeing 737 air circulation system. The photo was taken of the air conditioners below the air conditioners on each side of the plane.

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At high system operating temperatures, the bleed air is too hot for home use without cooling, even though it has a cool temperature. It is released into the air circulation system and passes through the heat exchanger system. Ram air cools the bleed air. This cool bleed air enters the blower. There, The air is compressed before flowing through a second heat exchanger where it is recooled by ram air. The exhaust air is driven through an expansion turbine and returned to the air cycler for further cooling. The water is then removed and mixed with the bypass air for final temperature adjustment. It is sent to the cabinet through the air distribution system.

By examining the operation of each component in the air circulation process; A better understanding of how air is adjusted for room service will be developed. See Figure 2, which describes the air conditioning system of the Boeing 737 air conditioner.

Pneumatic System Supply An air circulation air conditioner supplies air through the aircraft's pneumatic system. Again, The lung system is supplied from the exhaust air hoses on each engine pressurization unit or from the APU pneumatic supply. An external source of air pressure can be connected while the aircraft is on the ground. In normal flight operations, air pressure (pneumatic manifold) is controlled by valves, Bleed air of the engine is provided through the use of regulators and hoses. Air conditioning packages such as antifreeze and hydraulic pressure systems are also provided along with other critical air conditioning systems.

Component Operating Package The package valve is a valve that controls the bleed air from the manifold to the air cycle air conditioning system. Controlled from the air conditioning switch in the cockpit. Many pocket valves are electrically controlled and pneumatically operated. Also known as supply shutoff valve; The package valve opens and closes and supplies the air conditioning system with a volume of warm air in a regulated air cycle. [Figure 3] When overheating or other abnormal conditions require turning off the air conditioner. A signal to close is sent to the valve.

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Figure 3. This diagram of the packet valve is open, Shows the complexity of the valve that closes and adjusts. It is operated manually from the cockpit and automatically responds to the constraints of the supply and air circulation system.

Bleed Air BypassA means that some compressed air supplied to the system's air circulation air conditioning system is available on all aircraft. This warm air must be mixed with the cold air produced by the air circulation system so that the air reaching the interior remains at a comfortable temperature. to meet the vehicle's temperature control requirements; It controls intake air and cooling air simultaneously. It can be controlled manually with the cabin temperature selector in manual mode. Other air circulation systems include a temperature control valve, It can refer to a valve that controls the flow of air around an air circulation cooling system, such as an air pressure control valve or similar.

Primary Heat Exchanger Generally, The hot air prepared to pass through the air cycle passes through a heat exchanger in the first stage. Similar to a radiator in a car. Controlled ram air flow reduces the temperature of the air in the system and circulates through the exchanger. [Figure 4] When the plane is on the ground, A fan draws air through the ram air duct, which can be used for heat exchange when the aircraft is parked. Ram flaps are adjusted to increase or decrease ram air flow to the wing depending on the flapping position of the wing in flight. During slow flight, When the folds are expanded, The doors open. At high speed, the flaps retract and the doors move to the closed position, reducing ram air to the exhaust. A similar function is performed by a valve on a small plane. [Figure 5]

Figure 4. The primary and secondary heat exchangers in an air circulation air conditioning system are of the same construction. As the ram air passes over variable coils and fins, both cool the air.

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Figure 5. The ram air gate controls the air flow in the primary and secondary heat exchangers.

Cooling Turbine Unit or Secondary Heat Exchanger with Air Circulation The heart of an air conditioning system is the cooling turbine unit, also known as an air circulation machine (ACM). It consists of a compressor driven by a turbine on a common shaft. System air flows from the primary heat exchanger to the ACM compressor side. As the air is compressed, the temperature increases. It is then sent to a secondary heat exchanger similar to the primary heat exchanger in the RAM duct. At high temperatures, the compressed air of the ACM readily transfers heat energy to the ram air. cooling system Air flow from the series system and pressure from the ACM compressor are still discharged from the secondary heat exchanger. It leads to the turbine side of the ACM. The steep blade angle of an ACM turbine extracts more energy from the wind as it passes through and drives the turbine. Once exceeded, it allows air to expand in the ACM outlet, cooling it further. The combined loss of energy from the atmosphere first drives the turbine and then the expansion at the turbine outlet cools the air temperature of the system. [Figure 6]

Figure 6. Air cycle machine cut diagram The main housing supports a single shaft connecting the compressor and turbine. Oil lubricates and cools the shaft bearings.

Water Separation Cold air from an air conditioner does not hold the same amount of water as it does when heated. A water separator is used to remove water from the saturated air before it is sent to the cabin. The index works with non-moving parts. Misty air is drawn from the ACM and encapsulated into larger droplets through a fiberglass sock. The internal structure of the seal allows air and water to circulate. Water collects on the sides of the seal and exits the chamber as it air dries. Blocking process includes bypass valve. [Figure 7]

Aircraft Air Conditioning Systems

Figure 7. A water separator draws the air/water mixture from the ACM expansion turbine and removes the water. Centrifugal force sends water to the walls of the collector exiting the chamber.

As mentioned, the air leaving the ACM turbine is expanded and cooled. It will be very cold. This freezes the water in the water separator, restricting or blocking air flow. A temperature sensor in the separator controls a coolant bypass valve designed to maintain air in the separator chamber above freezing temperatures. The valve is a temperature control valve. 35° valve; It is distinguished by other names similar to the opposite IC solution. When opened, it passes hot air around the ACM. Air is separated from the water upstream and forced into an expansion tube where the air is heated enough to prevent freezing. Therefore, The coolant bypass valve controls the temperature of the ACM exhaust air as it passes through the water separator so it is not cooled. This valve is shown in Figure 1 and illustrated with the system in Figure 2.

All air circulation air conditioners use an air circulation machine with at least a ram air heat exchanger and an expansion turbine to remove heat energy from the air, but there are differences. A different example of the system described above can be found on the McDonnell Douglas DC-10. Compressed blood air exits the pneumatic manifold.

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