Chapter 8 - Aircraft Environmental Systems Flashcards
What are the two reasons for temperature control?
Maintain a suitable cabin temperature
Cools the heat released from cabin equipment and the occupants of the cabin
Humidity control helps to remove what?
Remove excess moisture from the cabin
To prevent low humidity
What can moisture cause?
It can cause misting of transparencies
It can cause malfunction of electronics
High humidity retards the body cooling which leads to rapid exhaustion
Ventilation control helps to prevent what?
CO2 rising above safe levels
Prevent the accumulation of unpleasant odours
Purity control helps to do what?
Maintain life sustaining composition of air
Ensure no other gases are introduced
Ensure fumes and dust particles are removed
What makes a basic air conditioning system?
Hot air
Cold air
Mixing unit
Controls
What can ice formation cause?
Loss of lift, increase in drag, a shift in the position of the C of G which may cause the aircraft to become unstable, restriction of the flying controls, failure of pressure systems.
What are the four factors that need to be controlled in cabin air con?
Temperature
Humidity
Purity
Ventilation
What are the three methods of ice protection?
Thermal
Fluids
Mechanical
How does mechanical de icing work?
From using the de icing boot. (Inflated with air which the. Creates ridges which then dislodges ice and then deflates again)
What are the ground de icing methods?
Soft broom brushing
Thermal
Fluid
What’s used for rain protection?
Screen wiper system
What are the maintenance checks for the screen wiper system?
Examine condition of the blade
Check range of movement
Check for correct pushed position
Examine condition of screen wash pipes effects
Check tension of wiper arm loading device
How is cooling achieved?
By using a basic vapour compression cycle.
How can boiling points of liquids be changed?
By increasing or decreasing the pressure acting on the liquid
High pressure =
Low pressure =
High boiling points
Low boiling point
What happens in heat transfer?
Heat flows from the hot object to the colder object until the temperature of the objects are equal.
Why must the process of heat transfer be reversed?
In order to cool an object below its normal temperature
What does the refrigeration system require to provide a cooling effect?
An input of energy
When gases are expanded and compressed what happens to their temperature?
Expanded = cool Compressed = hot
What happens to the gas when it goes into the compressor?
It turns into liquid
What does the expansion valve cause?
Causes the substance n the pipes to decrease in pressure. Causing the boiling point to also decrease.
What is a refrigerant?
Is the substance used in the refrigeration pipes. It must be a substance which is easily converted from a vapour to a liquid and vice a versa. The most common refrigerants are the chlorofluorocarbons or freon.
What does a compressor do?
It sucks the vapour into the cylinder on the up stroke and forces it out, under pressure, on the down stroke.
Within the condenser coil what two effects take place?
The refrigerant changes to a liquid.
The refrigerant gives off the heat gained in the compression process.
What happens in the expansion valve?
The refrigerant pressure reduces as it passes through the expansion valve.
Within the evaporator what two effects take place?
The refrigerant changes to a vapour.
The expanding refrigerant vapour cools and absorbs heat energy from the area near the evaporator.
What are the 4 stages of refrigeration?
Compressing
Condensing
Expanding
Evaporating
What 3 things change a refrigerants state?
The condenser (V to L) The evaporator (L to V) Transfer of latent heat
What is latent heat?
The energy required to change the state of a substance
What does latent mean?
Hidden
How do you break or form bonds between particles?
Break (energy added)
Form (energy removed)
Heat energy is removed from the refrigerant at 2 points, what 2 points?
Compressor
Condenser
At what two points is heat energy absorbed by refrigerant?
Expansion valve
Evaporator
What are the two types of heat absorption?
Latent heat absorption
Sensible heat absorption
What’s the difference between latent heat and sensible heat?
Latent heat changes the state not the temperature and sensible heat only changes the temperature
