1、Air Condition System And Pressurization SystemAir Condition System以B747-800为例747-8 engine bleed system747-8 engine bleed system wThe 747-8 airplane is powered by General Electric GENX-2B engines.The engine bleed systems supply air from the engine compressor.There are four identical engine bleed syst
2、ems per airplane with independent control and indication for each system 747-8 engine bleed system wThe system schematic(top)and component locations(bottom)in the 747-8 engine bleed system.747-8 engine bleed system wThe air temperature and air pressure are regulated before being delivered to airplan
3、e systems.The bleed air is used for CACTCS,engine anti-ice,wing anti-ice,the hydraulic air-driven pump,the leading-edge flap drive unit,the nitrogen generation system,aft cargo heat,total air temperature probe aspiration,and hydraulic reservoir pressurization.All four engine bleed systems are connec
4、ted by a common manifold.747-8 engine bleed systemwTechnological advancements enabled Boeing to make several improvements to the bleed system on the 747-8.These improvements include:747-8 engine bleed systemwNew digital bleedwThe system has no mechanical position switches and reduced use and consoli
5、dation of sensors.747-8 engine bleed systemwNo remote valve controllerswThe torque motor and solenoid are built into the valve design,allowing for easier troubleshooting and improved fault isolation.747-8 engine bleed systemwFewer servo/sense lines wThis increases system reliability.747-8 SUBFREEZIN
6、G PACK747-8 SUBFREEZING PACKwThe 747-8 air-conditioning pack has several key features that allow it to be classified as a true subfreezing pack,which will operate to temperatures below the freezing point of water at all altitudes(see fig.747-400 air-conditioning pack system).747-8 SUBFREEZING PACKw
7、While earlier air-conditioning packs can drive subfreezing during all conditions,there are limitations that need to be placed upon the system due to the operating environment and the technology implemented within the system.747-8 SUBFREEZING PACKwAs a result,below 25,000 feet(7,620 meters),where env
8、ironmental icing is a factor,the pack turbine discharge(i.e.,pack outlet)is limited to approximately 35 degrees F(1.67 degrees C)prior to mixing of recirculated air in the main distribution plenum.At cruise,where icing concerns are not a critical issue for operation,many packs do drive subfreezing a
9、s conditions warrant.Figure:747-8 air-conditioning pack wA diagram of the 747-8 air-conditioning pack system.747-8 SUBFREEZING PACKwThe 747-8 pack incorporates technology that enables it to function as a subfreezing conditioned air supply during all phases of operation,both on the ground and in flig
10、ht.Key factors that enable this technology to overcome environmental limitations include the use of:747-8 SUBFREEZING PACKwHigh-pressure water separation,which mitigates the buildup of ice within the air cycle machine(ACM).wIntegrated pack control features that mitigate ice formation within the air-
11、conditioning pack.747-8 SUBFREEZING PACKwA compact mixing section at the turbine outlet of the pack,which allows recirculated air from the airplane ambient environment to be mixed directly with pack outlet air prior to implementing outlet discharge temperature limitations.High-pressure water separat
12、ion.w The air-conditioning pack incorporates a water extraction loop within the pack to extract water and avoid ice formation at the ACM turbine outlet.This is accomplished by routing the air appropriately within the pack;water separation is accomplished within the pack itself as part of the air-con
13、ditioning process.High-pressure water separation.wAir that has been heated in the ACM compressor section is first cooled by the main heat exchanger.The air is then further cooled below its dew point as it travels through the condenser section.Within the condenser section,water droplets are formed,al
14、lowing water to be removed from the system.High-pressure water separation.wThe water extractor then removes the water particles from the high pressure in the ACM by creating a vortex,which forces the water to collect at the walls of the unit.The dried air then passes into the reheater,where the air
15、is again raised to the temperature of the air entering the water extraction loop before entering the ACM turbine inlet.High-pressure water separation.wThe water that is removed is then injected into the ram heat exchanger cooling air inlet by means of the water injectors to increase cooling efficien
16、cy of the ram air subsystem.This functionality is particularly critical for ground operations.Integrated pack control wThe pack temperature is modulated using the ram air door actuators(RADAs)and the temperature control valve(TCV).The RADAs modulate the ram air flow to regulate ACM compressor outlet
17、 temperature.Integrated pack control wThe TCV position controls the amount of hot air that bypasses the turbine,allowing it to adjust the ACM speed and subsequent pack discharge temperature downstream of the water extractor prior to flow injection into the ACM turbine section.Integrated pack control
18、 wThe ability to adjust this temperature in conjunction with the necessary components and controls to sense flow restrictions associated with ice buildup within the ACM enables the system to avoid and control ice formation within the condenser.In addition,the ability to control the temperature withi
19、n this stage of the ACM operation increases the efficiency and performance of the high-pressure water extraction process.Integrated pack control wThe components and technology provided within the ACM allow the unit to function as a cooling unit with increased capacity due to the use of a“defrost cyc
20、le,”as required to mitigate the presence of ice.This protects the pack against the damage that could be caused by ice buildup within the ACM.Because of this capability,the 747-8 pack can safely operate below freezing and provide increased cooling capacity during all operating conditions.Compact mixi
21、ng section.w The pack discharge air from the ACM turbine section is then sent to the compact mixer prior to distribution into the main airplane cabin area.The compact mixer ensures the efficient mixing of outside air delivered by the ACM with recirculated air from the main cabin zones.Compact mixing
22、 section.wConsequently,rather than controlling the pack discharge temperature downstream of the turbine directly,the compact mixer outlet temperature is controlled according to the following schedule,which is strictly based on altitude:Compact mixing section.wFrom 0 to 25,000 feet(0 to 7,620 meters)
23、,control the minimum outlet temperature to 37 degrees F(3 degrees C).Compact mixing section.wFrom 25,000 to 30,000 feet(7,620 to 9,144 meters),control the minimum outlet temperature linearly from 37 degrees F(3 degrees C)at 25,000 feet(7,620 meters)to 29 degrees F(2 degrees C)at 30,000 feet(9,144 me
24、ters).Compact mixing section.wAbove 30,000 feet(9,144 meters),control the minimum outlet temperature to 29 degrees F(2 degrees C).Compact mixing section.wn this way,the compact mixer allows the turbine discharge temperature to float well below freezing to directly address the air-conditioning load i
25、mposed by the recirculated air from the main cabin zones and allows the pack to provide more of its available capacity as a result.Compact mixing section.w For example,during hot-day ground conditions with very warm recirculated air injection,the pack has the capacity to drive cold,as necessary,to m
26、aintain a temperature above 37 degrees F(3 degrees C)at the discharge downstream of the compact mixer section.Pressurization SystemAIRBUS A380 wSafety is Airbus prime concern and Airbus will never compromise on this aspect,which is the foundation of its business.This applies to the A380 in the same
27、way as to all its other products,be it during the development phase as in production and subsequently during the service life.This also applies to the particular component referred to in the report Cabin pressurization wCabin pressurization is used to create a safe and comfortable environment for ai
28、rcraft passengers and crew flying at high altitude by pumping conditioned air into the cabin.This air is usually bled off from the engines at the compressor stage.Cabin pressurizationwThe air is then cooled,humidified,mixed with recirculated air if necessary and distributed to the cabin by one or mo
29、reenvironmental control systems.The cabin pressure is regulated by the outflow valve.Need for cabin pressurizationwPressurization becomes necessary at altitudes above 12,500 feet(3,800 m)to 14,000 feet(4,300 m)above sea level to protect crew and passengers from the risk of a number of physiological
30、problems caused by the low outside air pressure above that altitude;it also serves to generally increase passenger comfort.HypoxiawThe lower partial pressure of oxygen at altitude reduces the alveolar oxygen tension in the lungs and subsequently in the brain,leading to sluggish thinking,dimmed visio
31、n,loss of consciousness,and ultimately death.In some individuals,particularly those with heart or lung disease,symptoms may begin as low as 5,000 feet(1,500 m),although most passengers can tolerate altitudes of 8,000 feet(2,400 m)without ill effect.HypoxiawAt this altitude,there is about 25%less oxy
32、gen than there is at sea level.Hypoxia may be addressed by the administration of supplemental oxygen,either through an oxygen mask or through a nasal cannula.Without pressurization,sufficient oxygen can be delivered up to an altitude of about 40,000 feet(12,000 m).HypoxiawThat is because a human bei
33、ng that is used to living at sea level needs about 0.20 bar partial oxygen pressure to function normally and that pressure can be maintained up to about 40,000 feet(12,000 m)by increasing themole fraction of oxygen in the air that is being breathed.HypoxiawAt 40,000 feet(12,000 m)the ambient air pre
34、ssure falls to about 0.2 bar and to maintain a minimum partial pressure of oxygen of 0.2 bar requires breathing 100%oxygen using a oxygen mask.Emergency oxygen supply masks in the passenger compartment of airliners do not need to be pressure-demand masks because most flights stay below 40,000 feet(1
35、2,000 m).HypoxiawAbove that altitude the partial pressure of oxygen will fall below 0.2 bar even at 100%oxygen and some degree of cabin pressurisation or rapid descent is essential to avoid the risk of hypoxia.Altitude sicknesswHyperventilation,the bodys most common response to hypoxia,does help to
36、partially restore the partial pressure of oxygen in the blood,but it also causes carbon dioxide(CO2)to out-gas,raising the blood pH and inducing alkalosis.Altitude sicknesswPassengers may experience fatigue,nausea,headaches,sleeplessness,and(on extended flights)even pulmonary oedema.These are the sa
37、me symptoms that mountain climbers experience,but the limited duration of powered flight makes the development of pulmonary oedema unlikely.Altitude sicknesswAltitude sickness may be controlled by a full pressure suit with helmet and faceplate,which completely envelopes the body in a pressurized env
38、ironment;this is clearly impractical for commercial passengers.Decompression sicknessw The low local partial pressure of gases,principally nitrogen(N2)but including all other gases,may cause dissolved gases in the bloodstream to precipitate out,resulting in gas embolism or bubbles in the bloodstream
39、.Decompression sicknessw The mechanism is the same as for compressed-air divers on ascent from depth.Symptoms may include the early symptoms of the bendstiredness,forgetfulness,headache,stroke,thrombosis,and subcutaneous itchingbut rarely the full symptoms of the bends.Decompression sickness may als
40、o be controlled by a full-pressure suit as for altitude sickness.Barotraumaw As the aircraft climbs or descends,passengers may experience discomfort or acute pain as gases trapped within their bodies expand or contract.The most common problems occur with air trapped in the middle ear(aerotitus)or pa
41、ranasal sinuses by a blocked Eustachian tube or sinuses.Barotraumaw Pain may also be experienced in the gastrointestinal tract or even the teeth(barodontalgia).Usually these are not severe enough to cause actual trauma but can result in soreness in the ear that persists after the flight and can exacerbate or precipitate pre-existing medical conditions,such as pneumothorax.BarotraumawPressurization of the cargo hold is also required to prevent damage to pressure sensitive goods that might leak,expand,burst or be crushed on re-pressurization.
