AirConditioning Flashcards
what are the main functinos of the aircon system? (6)
- temperature control
- pressurize cabin (altitude of 8,000 ft minimum)
- cool avionics bay in flight
- ventilation of cabin for comfort
- arrest of particles (ozone, hygiene)
- emergency oxygen supply during low level flight
what are five requirements to keep in mind while designing the airconditioning system
- comfort
- maintenence
- initial cost
- energy consumption
- payload range
why is temerature important to transistors?
if it is to hot atoms diffuse causing irriversible damage
-cold can double lifetime
who regulates air flow in the cabin
FAR or JAR
what are the types of things that the FAR (or JAR) regulates?
- amount of air per time for cabin, crew, and cockpit
- max flow rate by a person
- circulation time (20x per minute) -> every 3 min get completely new air (60% outside air and 40% re ventilated)
- air quality
what percentage haemoglobin does your body need and at what altitude (and by regualtion is this)
90% is normally sufficient and this is at 10,000 ft. regulations say 8000ft to be safe
what are some main sources of heat flows to account for in the cabin
sun radiation
passengers
inflight entertainment
electric devices
draw the major components to demonstrate system functionality
see pic.
include:
- aircon packs
- bleed air (engines)
- mixing chamber
- trim air
- air distributino ducts
- air outlets
- hepa particle arrestors
- air outflow valve
draw the detail view of the air generation units
see pic.
include:
- primary heat exchanger
- compressor
- main heat exchanger
- reheater (mostly as a passby)
- turbine (extreme cooling here)
- condenser (some air directly from reheater)
- out
- ram air inlet
- ram air outlet
- HP water extractor
- temperature control valve
how is air in duct between mixer and agu have problems? how is this remedied?
ice accretion
periodically apply warm air (at energy at cooling cost)
what is a design driver for the aircon system?
power (kW) needed for cooling
what other system does the aircon system drive
pneumatic and bleed air
how is the mixer temp controlled?
- temp sensor in mixer tells pack controller and the pack provides the necessary air temp.
- necessary air temp leaving mixer is lowest cooling demand
how is pack temp controled
- ram air inlet adjusted
- trim air added (temp control valve)
how is each zone temp controlled
-temp sensor on some deu’s in cabin
-tells zone controller (know desired temp from indication)
-adjusts amount of trim air added to each zone (initial temp from mixing is lowest cooling demand
-
what are sources of noise from the aircon system
- mixing chamber
- air outlets
- elbows in pipes
- flow restrictors (orifice plates)
- trim air into distribution ducts
- recirculation fans
- pipe branch
which is easier to cancel out, low or high frequency noise?
high frequency noise -> want more holes in orifice plates
-mixing chamber wil produce low frequency noise
what are the goals of air outlets
even air distributino
-low noise levels
how are cabin air outlets designed?
- internal flow moving devices
- raising surface
how does the airflow promote hygene?
- 2d
- air from passenger to down (cross only below seats
- gentle flow (.25m/s
describe the humidity of air comfort and in the cabin. how is humidity regulated
air outside: 3% in flight
- in cabin depends on passenger density (5-15%)
- no health regs, just not as comfortable (60% is max comfort)
- regulation:
- no addition (PAX are only humidity source)
- using 40% mixed air is good for maintaining humidity
what are some requirements of the thermal insulation?
- keep heat out
- fire resistant
- reduce noise at all frequencies
- no temperature gradient
- easy to install
- lightweight
- not store humidity
what is ozone, where
what to do
toxic
high altitudes and latitudes
ozone converters
what air is ventilated directly out vs recirculated
direct out: -galleys
- lavatories
- avionics
- cargo
what are the three methods of filters used for partical intercept
direct interception: particles too big to go through
inertial impaction: molecules get stuck instead of following tortuous path of airflow
diffusional imtereption: small particles take a more moing path through and will get stuck
how efficient are the particle filters?
recirc air always has less than “fresh air”
what are the ways in which the aircon system affects the cabin comfort
AIRCONDITIONING: -temperature, pressure, flow velocity (air) -ozone, carbon, smells, (particles) -pressure SYSTEM: -available space -noise levels
what are the valves (and controllers) involved in pressure monitoring
normal ops:
- cabin pressure controller (CPC) which serves to monitor pressures and communicate and actuate valves
- outflow valves
emergency:
- negative pressure valve (between cargo and deck)
- safety valves (if pressure greater than critical value it will allow air out of the fuselage)
explain the control of the outflow valves
there are two cabin pressure controllers which each connect to a electronic actuator on both outflow valves. There is also a mechanical linkage to a third motor on each valve for manual operation
how are the negative pressure relief valve and the safety valves operated?
They are mechanical -> no electronic control
what are normal operation ranges for the ducts temperatures -> when are these extended and how
8 - 50 deg C
extended during pullup and pull down from 2 to 70 deg C
summarize the temperature control of the system
each zone temp is set by pilot in cockpit. This tone controller detects each zone temp and will send signals to adjust trim air valve to specific zones or change mixing chamber temp if needed via changing the pack outlet temp. The pack outlet temp can be controlled via the ram air inlet and the temp control bypass valve
how are the volume flows of each pipe determined and what is physically changed in the system to change them.
measured: place box with equal pressure to outside at duct outlet. Get volume flow by differential pressure over a orifice after the flow has been allowed to go (because measuring pressure is difficult due to turbulence)
change orifices in distribution pipes to adjust volume flows.
what test means are used for flow optimization in the cabin?
soap bubbles with helium are circulated in the cabin and long exposure photos are taken and this is turned into a gradient field with software.
