Pierce Nichols wrote:

At 05:33 AM 2/3/2003 +0000, Ian Woollard wrote:

Randall Clague wrote:

I could be wrong, but I think of it as a flash evaporator on nuclear
steroids.  Dump the water out the back.  It will boil, and then
disassociate, and then blow away, taking a bunch of heat with it.
If you do that you've used the latent heat of vapourisation in cooling the hot air near to the body, rather than in cooling the body; which I don't think is as good, since the cooled air may not be in contact with the vehicle, but I could certainly be wrong also.


Actually, it will cool the boundary layer. Since all of the heat transfer mechanisms that transfer heat to the body operate through the boundary layer, that is more or less equivalent to cooling the body.
True, but any of the cooling from the latent heat of vapourisation that doesn't cool the boundary layer is wasted, and some is very likely to be wasted; latent heat of vapourisation is a very significant fraction of the cooling. Also the boundary layer probably can't go below the boiling point of water in practice; and the steam itself will help keep it close to that anyway.

Atleast if you cool the body you know the cooling is used to cool the boundary layer via conduction.

Anyway, the only way to know for sure is to try it. It may not matter much in fact; or it may matter some but be difficult to do.

        -p


Mars or Bust!
www.marssociety.com

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