Newsgroup sci.engr.chem 17462

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On Sat, 16 Nov 96 15:08:22 GMT, charliew@hal-pc.org (charliew) wrote:
>I'm not certain about fuel tank heaters, but it is most 
>likely that there are none.  Jet fuel has a freeze point 
>specification that is approximately -51 deg F, meaning that 
>this stuff doesn't need to be heated, because it will not 
>freeze at normal altitudes.
Actually, the fuel has to be heated because in fact normal outside air
temp is often -40 deg C  to -60 deg C at 30,000 to 40-000+ feet and
prolonged flight at these altitudes will coagulate and/or  freeze jet
fuel (kerosene). I've seen planes with both electrical and pneumatic
(compressed  i.e. hot engine bleed air) that heat both the fuel in the
tanks as well as in fuel lines on the way to the engines to melt ice
crystals.
Another reason to keep the fuel heated is this. After a prolonged high
altitude flight, fuel cooled to the outside air temps would keep the
aircraft skin chilled to the same temp on descent into moist air (all
air at low altitudes being moist to some extent). The result would be
a build up of ice on the wings, minor in drier air, very serious in
precipitation. Also after landing, moisture will condense and freeze
to the wing surface surprisingly quick (even if it's warm outside) .
It will take a while for the fuel temp to increase, possibly causing
delays for satisfactory/permanent ice removal..
WW

On Sat, 16 Nov 1996 14:14:06 +0000, kangaroo 
wrote:
>Say. how could the tank be almost empty if they still had a way to go to 
>their destination?
Well, this could be a prime flaming opportunity.... (bad pun)
It's standard to have a number of seperate isolated fuel tanks and
systems in just about any type of aircraft. I've seen as many as 8.
One reason is safety, if one of your fuel systems malfunctions, or has
contaminated fuel then you have redundancy with the other systems.
Another reason is to facilitate fuel distribution, mainly once
airborne. I don't know about 747 fuel systems but I imagine the center
fuel tank was low because the overall weight of the aircraft needed to
be distributed away from the fuselage. The maximum fuselage loading is
often a limiting factor even when the aircraft is well under it's
overall maximum takeoff weight. 
WW

Mark S. Bilk wrote:
> Thus, contrary to the "Fume Theory", an empty tank would be
> no more likely to explode than a half-full one.  The tank's
> being empty would *not* constitute a hazardous condition.
Please remember that minutes prior to the explosion, the pilots did have
some fuel flow warning lights come up. That much was made public.
I do not know what actions the pilots took as a result of these alarms.
However, lets assume for a minute that a fuel pump in an essentially
empty tank was accidentally running and that such pump normally uses the
fuel to cool itself. (Please note the word "assume"). If the fuel pump
was running in an empty tank, it might explain that the "plane" was not
getting as much fuel as it was expecting to be getting since one of its
pumps was not delivering fuel. Such pump might overheat because of lack
of coolant and eventually cause a fire/explosion/spark.
I do not know if that 747-100's FDR was sophisticated enough to record
which fuel pumps were running and when they were running. I do know that
the FDR was rather old and primitive compared to newer units.
I also know that they were not able to recover that fuel pump (or were
they?).
Since the NTSB has not yet announced the probable cause of the crash, I
tend to give credence to this theory since so many of its details are
missing (area where crucial evidence is missing).
They were able to detect traces of explosives that were left on a seat
weeks before, but were unable to find the pump in that tank.

Hi,
Does anyone in ChemE land have any experience with mechanical
foambreakers? Are they efficient? Do they work at all? Are they worth the
huge monetary outlay?
Thanks
Doug Nutter

Without the proper fuel/air mixture even an open flame will not 
cause the explosion.  In a closed fuel system (ie. fuel injecton 
system) there is no available entry port for the necessary oxygen to 
support an explosion.
As a kid living on a West Texas ranch 30 years ago, we would often fill 
55 gal. drums with 5 gal. of gasoline and add oxygen from a welding 
cylinder.  The drums were ignited with Potassium Permanganate and 
glycerin.  Very foolish!  However, I learned in my early attempts that 
atmospheric oxygen (21.96%) would not explode the drums.  After several 
attempts, I decided that a little oxygen might improve the reaction.  The 
resulting explosion could be heard in town 3 miles away and the initial 
fireball at ground level was white (as in blinding).  A secondary 
fireball would occur about 100-200 feet higher up and would be bright 
orange. The secondary fireball would occur as a result of the top of 
the barrel "dragging" fuel vapor behind it as it shot upwards.  
Apparently, the oxygen was used up in the initial blast and the secondary 
flame would burn orange rather than white.
(Note:  I was well away and in a creek bed. The drum completely 
disintegrated with large pieces of shrapnel going about 100 yds.  Only 
the bottom of the drum would be left.  Don't try this!)
Kerosene has a higher flash point than gasoline and also burns with an 
orange flame.  I believe the witnesses to the TWA 800 flight saw a WHITE 
fireball.  Explosions producing white light are caused by high explosives 
- not fuel.  PETN (as in Primacord) is a good example. Nitro-Carbo 
Nitrate (fertilizer/diesel) is low tech and burns with a dull orange.  I 
have never seen a flame produced with dynamite - even on the darkest 
night. I am not familiar with the flame color of the other explosives.
Any ideas on this?