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You have a good head Dave, your analysis is right on.
To amplify why vapor lock is not an issue here (assuming we
get adequate "tank cooling"), my plan was to cool the oil which gets to a
much higher temp than the coolant. I never got around to finding out
the boiling point of gasoline (anyone here know?) but it was my HOPE that it
would boil which would vastly increase the heat absorbed from the oil.
When the gasoline "steam" returned to the tank, it would immediately cool and
condense to it's liquid state, even if the tank was almost empty.
Possible flaw is that some components of gasoline might be more volatile
than others, remain in vapor state and escape from the tank vent.
Tracy (still dreaming of drag free cooling)
----- Original Message -----
Sent: Thursday, February 10, 2005 1:13
AM
Subject: [FlyRotary] Re: Heating the
Fuel
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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>>
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