> > I don't have any experience with this either, but I'd guess that you
> > could braze some of that wrap-around fin material onto the tubes
before
> > pushing them through. Imagine a bunch of 1" long fins oriented
radially
> > from the tubes--that would add a lot of surface area for contact with
> > the foam.
> >
> > One other thing to think about: Ice. Maybe the airplane is just
> > sitting on the ramp and it is raining/freezing: That carbon matrix
will
> > hold a brick of frozen water that might add a lot of weight. Will
> > expanding ice break up the foam?
> >
> > The idea is interesting and I hope somebody pursues it, but it
probably
> > won't be me. Experimental airplane, one-off engine setup--I don't >
> think I
> > want to add another variable to the mix. But it would make for some
> > interesting car-top wind tunnel testing. Paul, have you still got the
> > rig? Anybody know where to get some of this carbon foam and what it >
> costs?
> >
> > Mark Waldron
> >
> > Liquid cooling systems function by several steps. The heat is >
> transferred from the
> > engine metal to the fluid coolant. The effectiveness of that transfer
> > is controlled
> > by a coef., the area of contact and the speed of the coolant flowing
> > over the
> > metal surface. The higher the speed of the coolant the better. The >
> coolant is then
> > piped to the heat exchanger and the process is reversed. Heat is >
> transfered from
> > the coolant to the tubes also controlled by a coef. , the contact
> area > of the tubes
> > and the speed the coolant flows over the metal.
> >
> > In this carbon design that has not changed. The tubes are best shaped
> > as a wide
> > thin oval to maximize the area of contact between coolant and metal.
> > Therefore you
> > still need the same number of tubes. Then the heat must be
> transferred > out of the
> > metal tubes to the air fins. In this case it is a porous carbon foam.
> > If the coefficient
> > of the transfer is not as good as a brazed aluminum joint there will
> > be no
> > advantage. As Bill Schertz pointed out this is a series of point >
> contacts.
> > Obviously not as good as a brazed large area joint.
> >
> > Perhaps I am not putting this very well. Perhaps Bill Schertz will >
> explain it better.
> > Frankly I kind doubt this porous carbon foam idea has any real >
> advantage when it comes to liquid cooled engine "radiators".
> > Paul Lamar
>
> Paul,
> You explained it well. Heat flow is like current flow in a series
> electric circuit. There is a thermal "resistance", defined by the heat
> transfer coefficient, at each material interface. It is going to take a
> lot of R&D money to conquer the corrosion problems between carbon foam
> and metal core tubes. My guess is, that we will not see wide use of
> the carbon foam in a radiator until it can be mated to a high thermal
> conductivity plastic core. I agree with Mark; we have enough
> relatively untested variables to work with already. I vote to let the
> automotive industry develop an all plastic and carbon radiator that
> weighs less than a pound. Then we can test one in an airplane.
>
> Aubrey Thompson
>
> Paul, and Group,
> If you read the linked paper near the start of the thread it appears
> that they have already made radiators. The radiators produced using
> a realitively conventional approach using a wide flat sided tube in
direct
> contact, (built up), and a tube pushed through a modified block of the
> material. Both styles performed better than the same size aluminum fin
> radiators. The results were noteable, better than 10%. That is a BIG
> difference, so I have to guess that the cost or the toughness isn't as
> good or someone would be manufacturing them already!
> Bill Jepson

Eliminate those corosion problems with carbon fiber tubes stuck in carbon
foam ?
http://tinyurl.com/2xolsx
jofarr, soddy tn

jofar,
Carbon fiber has nowhere near the heat transfer. The resin is a
pretty good insulator.
Bill Jepson
PS The heat transfer might be helped by a fairly "dry" matrix, but then
you risk leaks!
WRJ


The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://www.rotaryeng.net
Copyright 1998-2007 All world wide rights reserved.