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From: "Eric Ruttan" <ericruttan@chartermi.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-725015@logan.com>
Subject: Re: [FlyRotary] Re: Heating the Fuel
Date: Fri, 11 Feb 2005 12:04:42 -0500

All right I will bottom post.  I feel so cheap...

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

A heat pipe is a closed system under negative pressure using a medium that
cannot be "cracked" by heating.  RV fuel tanks are open and vented and
heated fuel will expel parts of itself permanently.

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

As the fuel is heated the parts with the lowest vapor pressure will vaporize
first.  These may vent or condense, if the tank is cool enough.  These may
also chemically separate and the fuel with remixed condensate might not be
what we started with.

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

Fuel is a heterogeneous mixture that will separate into its parts as it is
heated.  Even fuel left open to the air will do this without heating over
time.  Diesel (Jet whatever, kerosene, et. al.) are much more homogeneous
and much less likely to separate.

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

Eric