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Bill & Jim, first and most important, we are all in agreement that this is
not worth doing. However, you made a couple of assumptions that are not
quiet accurate. First, the pumps from Tracy will return 40 gal/hr to the
tank (not 15 - I know, I monitor it in flight). Second, there will be a
much higher rise in the fuel temp. Because the fuel would be going so
slowly through the heat exchanger I would EXPECT it to reach the temperature
of the incoming coolant, or about a 100 deg rise. This will not cause "the
mother of all vapor locks" becuase it will be headed back to the tank where
it will quickly be cooled. How quickly? Quickly enough that the temp of
the fuel on its way to the engine will be no warmer than ambient. It
matters not the volume of fuel in the tank (other than contact area). I
expect it to be the temp of the fuel going TO the engine to be at ambient -
and adding no additional risk of vapor lock.
But, the coolant will still only drop about 3 deg, which is not enough to
make it worth it.
Dave Leonard
>
> <... For a 10 degree rise in gasoline temperature you would get a
> 630/12000 = 0.0525 deg F drop in coolant temperature ...>
>
> OTOH, you'd soon heat your fuel to very near the coolant temp and have
> the mother of all vapor locks.
> If that's what you're looking for ... Jim S.
>
> William wrote:
>
> > Dave,
> > If you burn 10 g/hr, and are returning 15 g/hr to the tanks, that is
> > 15*6 = 90 #/hr of gasoline, with a specific heat of ~.7Btu/#, that
> > means you can transfer 90* 0.7 = 63 Btu/hr/degF rise in gasoline
> > temperature. Your coolant flow is probably about 25 gallons/minute, =
> > 25*60 = 1500 gallons/hour = ~1500*8 = 12000 #/hour. For a 10 degree
> > rise in gasoline temperature you would get a 630/12000 = 0.0525 deg F
> > drop in coolant temperature. Doesn't seem worth it.
> >
> > * note: I used rounded figures for densities and flow rates and heat
> > capacities. The fact remains that the flow mismatch makes this not do
> > much.
> > Bill Schertz
> > KIS Cruiser # 4045
> >
> > ----- Original Message -----
> > *From:* DaveLeonard <mailto:daveleonard@cox.net>
> > *To:* Rotary motors in aircraft <mailto:flyrotary@lancaironline.net>
> > *Sent:* Sunday, February 06, 2005 11:46 PM
> > *Subject:* [FlyRotary] Heating the Fuel
> >
> > In anticipation of the new turbo, I am considering ways to improve
> > coolant cooling. Besides the obvious more air, more ducting, more
> > radiator; I have been again toying with the idea of a heat
> > exchanger. This time coolant to fuel. The plan would be to use a
> > typical oil/water exchanger but use fuel instead of oil. I would
> > use the fuel on the way back to the tank, and the coolant after it
> > has already been cooled by the radiator. The fuel would then go
> > back to the nice metal tank of the RV.
> >
> > I am looking for input on the implications of heating the fuel. I
> > expect it would reach max temps of about 190 (usually a
> > little cooler) but quickly cool once in the tank. Can the fuel
> > tolerate that temp without vaporizing? It will probably expand in
> > the tank but I don't expect that will occur faster than it is used
> > up. I have no guess as to what temp will become steady state for
> > the fuel pumped out of the tank. My guess is that it will not be
> > much warmer than normal, but a slight increase in temp may help
> > with vaporization.
> >
> > The last question is how much will it cool the coolant. My hope
> > is about 10 deg but I doubt it will be quite that much. I know
> > others have considered using the fuel to cool (Tracy) and I would
> > appreciate your thoughts.
> >
> > Dave Leonard
> >
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
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