On Mon, 03 Feb 2003 05:33:35 +0000, Ian Woollard <[EMAIL PROTECTED]> wrote:
>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 I'd rather take my thermal stress across outside air than across my vehicle skin, any day. :-) >>It's easier to keep the vehicle cool if none of it gets hot in the >>first place. >> >Trivially true, but that's not an option. With the caveat that the vehicle will get warm no matter what you do, I don't agree. You have a bunch of heat building up where the vehicle hits the air. There are a few things you can do with it. You can use the shock wave to take most of the heating in the air in front of the vehicle, and only heat the vehicle with air that's already dumped most of its heat into the shock wave. Then most of your heat transfer into the vehicle is radiative. Or you can absorb the heat in some kind of heat sink, and radiate it away after entry. That's what the tiles do, though the Shuttle's design also uses some shock standoff to keep rates down. Or you can dump the heat into some kind of sacrificial medium, and throw it away as it heats up. This describes ablatives and film cooling. For film cooling, I don't see the benefit of letting the incoming air heat the skin, and then cooling the skin. Why not just cool the incoming air? -R _______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
