>
>The problem with boiling the fuel is that most of = it will=20 then escape out
>the vent before it can re-condense. I'm = sure=20 this will more than offset
>any fuel gains from drag-free=20 cooling. Even moderately raising the temp
>(and vapor = pressure)=20 will probably cause excessive evaporative loss of the =
>fuel. We=20 have to face the fact the fuel is not an acceptable coolant for =
>this=20 application. That's OK, there is still Evans or water and the = rest=20
>of the wing surface to be=20 used.
>

         = Look up=20 "heat pipe" using=20 Google.

         The = returned=20 vapor will quickly condense in the cool tank. The
only way it will = not=20 condense is if the tank, and it's entire contents,
reach the = boiling point=20 of the fuel.

         = Until the=20 entire tank and the fuel in it warm up to the boiling
point, all = of the=20 vapor will condense on the walls and on the surface of
the fuel in = the=20 tank. As long as most of the vapors are condensing, the
fuel = properties=20 will not = change.

         This=20 is why you need to monitor the fuel tank temperature if you
are = planning=20 to use the fuel as coolant. If you dump too much heat into the =
tank, it=20 will become warm enough to vaporize the fuel. You probably would =
not want=20 the tank to become much hotter than, say, 140 F, I would = guess.

Bill Dube

Good reference on the heat pipe Bill. The 140 Deg = figure is=20 about what my seat of the pants guess was. I figured 120 = as a safe=20 margin. If my instrumentation and methodology was good = during my=20 test (must repeat it to be sure) then there is a = possibility "fuel=20 cooling" will be useful.

The basic numbers so far:

I got 2 degrees of oil cooling with something like 20 - 30 = GPH of=20 fuel flow through heat exchanger.

Temperature rise in the tank was on the order of .1 degrees = (lets=20 say it was .2 for sake of argument)

We need about 40 degrees of oil cooling, about 20 times what I = got in the=20 experiment. Also means we need 20x the fuel flow or about 500 = GPH (8 1/3=20 GPM).

Assuming this means a temp rise in the tank of 20 x .2 = or 4=20 degrees, that implies that there is a huge margin of safety = here. =20 And this was only using one of the two tanks. If it was = required, I'd be=20 happy to utilize both tanks.

I will be the first to admit that this sounds too good to be = true. =20 I must repeat the experiment to verify the basic numbers.

Tracy