11.4 Air Conditioning Air & Vapour Cycle Machines Flashcards
What is the air cycle system also known as as
Air conditioning pack
What is the pressure and temperature of air that enters the ac from bleed air
30-40psi 150°C
What does a compressor do to air
Raises temperature and air pressure
What powers the air conditioning compressor
Air cycle machine turbine
What does a heat exchanger do in the AC system
Cools the air
How is moisture removed from air before being condensed
Water extractor duct
Where is water from the water extractors sent
Spray nozzles into ram air inlet to improve cooling efficiency in heat exchangers
What happens when ice builds up in the condenser or exit of the turbine
Bleed Air bypassed around heat exchangers and ACM (air cycle machine) to melt ice and free exit of system
What does the pack/flow control valve do
Regulates that bleed air from the pneumatic manifold into the air cycle AC system
Where is the switch for pack/flow valve located
Flight deck
How is the pack/flow valve powered
Electrically or pneumatically
If power to the pack/flow valve stops what happens
The valve is spring loaded so will automatically close
What happens to mass flow of AC when altitude increases
Mass flow decreases
What happens to volumetric flow as altitude increases
Remains constant
What is the difference between mass flow and volumetric flow
Mass flow is the weight of the aid volumetric is the volume of the air, volume remains constant but due to lower air pressure mass decreases
What happens to AC when an aircraft is not fully loaded
AC works at lower capacity to save energy (this works by pack valve partially closing, constricting air flow)
How does a heat exchanger work
Heat transfer between two fluids (eg air) cold outside Rama air cools hot bleed air. Has fin like tubes inside to achieve this
What is the Pack valve purpose
Control airflow into the cabin
How is the flow of ram air regulated in the heat exchanger
Modulating inlet and exit doors which modulate in flight to provide required cooling effect
What must happen to ram inlet doors when your on the ground
There is insufficient air passing through the ram inlet doors so a fan is used to induce adequate air flow to cool heat exchangers
Are water separations needed in flight
Not really as air is ver dry and very cold
What can a high cabin humidity lead to
Fog, water droplets, passenger discomfort and corrosion in the cabin
Simply, how does the water separator remove water from the air
Humid air from ACM emerges and is forced through a fibreglass sock that condenses and combines mist into water drops. Dry air passes through and the water collects on the sides of the separator and drains out the unit
How is the air from the ACM prevented from being too cold
Air is bypassed around the ACM and it then prevents air being too cold and forming ice on the exit or in the condenser
What air trim air valances
Used in some systems to mix conditioned air provide accurate temperature controlled air to the cabin and flight deck.
(Mix bleed and conditioned air)
What is the purpose of the mix chamber
Collect temperature controlled conditioned air from pack then distribute the warm/cool air to the flight compartments in the aircraft
Where is the RAM air inlet located
Underside of an aircraft often on wing to body fairing
How is the amount of air into the ram air inlet controlled
Using a modulating door controlled by actuators on the inlet
What does the ram air go after entering through the ram air inlet
To the primary and secondary heat exchangers
What is the purpose of ram air in the heat exchangers
To remove hear from bleed air in the heat exchangers
What is used to increase ram air recovery
Modulating vanes on the ram air exhaust
What provides flow of air across the heat exchangers
A ram air fan, runs off a common shaft with the ACM powered by the ACM turbine
What type of AC doesn’t doesn’t require bleed air
Vapour cycle machine air condition system
What type of AC doesn’t doesn’t require bleed air
Vapour cycle machine air condition system
How does a vapour cycle machine air conditioner system work
Transfers heat from inside the cabin to outside the cabin working on the principles of thermodynamics. Heat is transferred to refrigerant liquid which turns to vapour as it gains extra heat energy. Vapour then gets compressed making it even hotter. Heated vapour releases the gained heat to the outside air and returns to the cabin as a liquid, basically like a fridge.
What are the steps of refrigeration
Compression, condensation, receiver-dryer, expansion, evaporation, repeat
What refrigerant is commonly used
Tetrafluroethane (R134a) (Freon)
What is the boiling point of R134a refrigerant
-26°C
What refrigerant is no longer used due to ozone damage
Dichlorodiflouromethane (R12)
What is the reservoir of the vapour cycle system called
Receiver dryer, contains refrigerant and can replace any missing refrigerant
What does water in refrigerant do
Can create an acid that can damage components or can form ice and block flow of refrigerant around the system
How do you know if refrigerant is low in receiver dryer (reservoir)
There will be bubbles visible in the sight glass
What does the compressor do
Increases pressure and temperature of low pressure low temp air
