singel09
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Are Fuel Tanks Heated?

Sun Feb 20, 2005 8:18 pm

Aviation Kerosine has a lot of specs that the oil companies need to adhere to. One of them is the freezing point of -47 degrees Celcius (-53 degrees Fahrenheit).

Once the planes are up there, outside air temperature are measured of -60 degrees Celcius (-76 degrees Fahrenheit). So my question is then, are fuel tanks in whatever way heated of protected by any means to allow the kerosine get below 47 degrees Celcius (-53 degrees Fahrenheit).

Thanks for any input !

MAuse
 
cheekie747girl
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RE: Are Fuel Tanks Heated?

Sun Feb 20, 2005 8:57 pm

Fuel tanks themselves are not heated (on larger aircraft), but the fuel is heated when it passes through various heat-exchangers in the engine. Fuel temp is monitored by the crew, and often the freezing of minute droplets of water suspended in the fuel is more of a problem than fuel freezing itself-hence regular 'water drains' of fuel tanks. Also, on larger aircraft, a large engine bleed air duct runs alongside the front of the wing tanks, inside the leading edges, and this gets quite hot. Also, on the 747 the centre wing tank sits adjacent to the air-conditioning packs which get pretty hot too.

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musang
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RE: Are Fuel Tanks Heated?

Sun Feb 20, 2005 9:22 pm

Another concept is hydraulic fluid heat exchangers located in the fuel tanks. Dual purpose - cools hyd. fluid while warming fuel. Don't have any manuals to hand, but I believe its fairly widespread.

Regards - Musang
 
Santhosh
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RE: Are Fuel Tanks Heated?

Sun Feb 20, 2005 9:29 pm

What type of hear exchangers are used in aircraft to heat up the fuel?

George
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air2gxs
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RE: Are Fuel Tanks Heated?

Sun Feb 20, 2005 10:11 pm

George,

There are different types depending on manufacturer. The in tank hydraulic fluid coolers/fuel heaters are immersion type (obviously). The engines can have air/fuel heat exchangers or oil/fuel heat exchangers.
 
Santhosh
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RE: Are Fuel Tanks Heated?

Mon Feb 21, 2005 1:11 am

George- Thanx for the infro.

Regards
George
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pilotaydin
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RE: Are Fuel Tanks Heated?

Mon Feb 21, 2005 4:21 am

I believe United Airlines has a procedure where they test the specific fuel onboard the a/c for that day, when it is due over the pole, and they uplink the exact freezing point of the fuel to the flight crew after testing, so that they can take the necessary precautions while over the pole....

anyone have a more detailed break down, i'd like to learn more!
The only time there is too much fuel onboard, is when you're on fire!
 
dl757md
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RE: Are Fuel Tanks Heated?

Mon Feb 21, 2005 5:14 am

While it's not heating in the traditional sense, airflow over the wings causes friction which heats the tanks a certain amount. I believe there is a procedure to increase Mach number in the event of a fuel temp warning. Can any pilots confirm this?

Dl757Md
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Starlionblue
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RE: Are Fuel Tanks Heated?

Mon Feb 21, 2005 6:10 am

"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
SlamClick
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RE: Are Fuel Tanks Heated?

Mon Feb 21, 2005 7:04 am

Quoting Dl757md (reply 7):
I believe there is a procedure to increase Mach number in the event of a fuel temp warning. Can any pilots confirm this?


True! It was the procedure on a couple of planes that I flew. Ram rise apparently applies to fuel also. I've only had low fuel temp a couple of times, usually after a long time at high altitude.

Transferring fuel can help as well, if that is possible in your type.

Problem with the hydraulics warming the fuel is that at cruise the hydraulics are not getting much of a workout and the hydraulic fluid temperature itself is not going to be all that high.
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BALandorLivery
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RE: Are Fuel Tanks Heated?

Mon Feb 21, 2005 10:31 am

Fuel is heated because in solution with the fuel there is always some water. At the extremely cold temperatures during cruise the water can crystalise and the crystals block the filters or disrupt fuel flow to the engines in some way.

Heating the fuel melts any ice crystals so that there are no problems.

Regds.
 
airplay
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RE: Are Fuel Tanks Heated?

Mon Feb 21, 2005 12:52 pm

Quoting BALandorLivery (reply 10):

Fuel is heated because in solution with the fuel there is always some water.


That is one reason. But not the whole story.

Jet fuel is made from several compounds each of which have their own freezing point. So the fuel doesn't freeze all at once. Wax crystals are the first to form. (paraffins are one form of wax found in Jet fuel)

These wax crystals are the nasty things that make it hard to pump through a fuel injector or filter. The fuel however is still pretty "pumpable" through the lower pressure sections of the fuel delivery system.

Also, if I'm not mistaken, the MD-90 sort of heats the fuel in the tanks. It pumps fuel to the oil cooler and returns the "heated" fuel to the tanks.

Just goes to show you...there's always an exception!

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wbmech
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RE: Are Fuel Tanks Heated?

Mon Feb 21, 2005 2:48 pm

Problem with the hydraulics warming the fuel is that at cruise the hydraulics are not getting much of a workout and the hydraulic fluid temperature itself is not going to be all that high


I tend to think the opposite is true. At cruise the hydraulic pumps are still putting out 3000 psi. The pressure still has to go somewhere, therefore instead of building excess pressure it is released through bypass valves. Without the fluid circulating throughout the entire system it gets cooled through the heat exchangers in the fuel tanks. On the ground with hydraulic pumps on and no actuators being used, the lines get very hot. At cruise it is the same principle with not many hydraulic actuators being used.
 
dl757md
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RE: Are Fuel Tanks Heated?

Mon Feb 21, 2005 3:09 pm

Quoting Wbmech (reply 12):
At cruise the hydraulic pumps are still putting out 3000 psi. The pressure still has to go somewhere, therefore instead of building excess pressure it is released through bypass valves.


Absolutely untrue! The pumps are feathered. As long as system pressure is about 3000psi then the pumps have no output other than case drain which is a very small amount and at about 80 psi. Only when there is a demand on the system and a corresponding pressure drop do the pumps output pressure/volume.

Dl757Md
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FredT
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RE: Are Fuel Tanks Heated?

Mon Feb 21, 2005 5:10 pm

There are also aircraft which have oil coolers in the fuel. Pretty much the same thing, only different…  Big grin

In fast jet world, fuel can be used as a coolant, being routed to wherever you need to cool things off. In order to keep the fuel temperature down (there’s a lot of power used, meaning lots of excess heat generated, in a very compact airframe) you can then spray the return fuel on the walls of the air ducts. A rather neat high-powered heat exchanger fan, that fuel-to-noise converter in the back end.

Yes, having fuel lines going to remote parts of the airframe causes a whole new batch of problems in itself. Many of the common coolants aren’t much more pleasant to deal with though.

Cheers,
Fred
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B747FE
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RE: Are Fuel Tanks Heated?

Tue Feb 22, 2005 12:27 am

Quoting Pilotaydin (reply 6):
so that they can take the necessary precautions while over the pole....


In the B747, before departure for a transpolar flight the procedure is to check the type of remaining fuel on board.
Jet A fuel (freezing point -40°C) in the tanks should be pumped to the CWT and reserve #2 and #3 tanks in order to be used during climb or initial cruise stage.

Besides the hydraulic fluid heat exchangers, we have the fuel heater and the fuel-oil cooler.
The fuel heater is an air-fuel heat exchanger.
The fuel entering the fuel pump passes through the fuel heater; however, the fuel is heated only when 15th-stage, bleed air passes through the heater air tubes. This system is controlled in manual or automatic mode, always OFF during take off, approach and landing.
Fuel-Oil Cooler receives metered fuel from fuel control unit which, after absorbing heat transferred to it from engine oil, continues to the fuel manifold.
It primary function is not to warm the fuel, but to cool the oil.

Regards,
B747FE.
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HAWK21M
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RE: Are Fuel Tanks Heated?

Tue Feb 22, 2005 2:10 am

Quoting Musang (reply 2):
Another concept is hydraulic fluid heat exchangers located in the fuel tanks. Dual purpose - cools hyd. fluid while warming fuel. Don't have any manuals to hand, but I believe its fairly widespread


Its that way on the B737.
regds
MEL
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