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To GW Johnson:
A known principle of de Laval rocket nozzles is as the exhaust proceeds down to the exit it cools as it expands. I wondered if this could be used for an air conditioning principle.
GW, living in Texas I’m sure you’re aware of that yearly process of putting in the heavy window air conditioners in Summer and taking out those same heavy window air conditioners in Winter. That’s onerous enough for young fit males to do, but imagine how bad it is older people or single moms who have to call over their beefy neighbor to do it for them every year.
So I had been thinking alternative lightweight means to do it. I wanted to see if using that principle of de Laval nozzles could do it. So the idea is heat the air then allow it to expand out the de Laval nozzle to cool. The equations are complicated so I put it through an AI program.
I originally asked what would be the temperature needed in the heating chamber and the nozzle expansion ratio. It gave me a temperature of 810 K. That was rather a high temperature for a consumer home device, so I asked it to try it at 450 K. This is a temperature reached by home ovens so I consider it more feasible:
Query: Modify problem slightly: exit temp at 285 K, heating chamber at 450K, what’s the nozzle ratio still under non-ideal.
https://chatgpt.com/s/t_69b9623459a8819 … fe34b44dd6
I was supersized to see the nozzle expansion ratio wasn’t anything especially great at ca. 1.6 to 1.8. I had been concerned it would be too high and we would get the dangerous phenomenon of flow separation. But ca. 1.6 to 1.8 should be in the safe range.
So GW, are these AI generated results valid?
Bob Clark
Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):
“Anything worth doing is worth doing for a billion dollars.”
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The lowered static temperatures obtained in the supersonic expansion of a De Laval nozzle are intimately associated with the supersonic speed. As soon as the stream slows down by any means whatsoever, it rewarms. If dead still, it is at its stagnation temperature. Unlike pressure, you ALWAYS recover the full stagnation temperature, no matter what. Ttot = Tstatic * (1 + const * Mach^2) where constant = (gamma - 1)/2, and for air, gamma = 1.4 is usually a very good model.
I ran into that many years ago with ingested cooling air for the electronics in a towed decoy. Once we started looking at supersonic speeds, the cooling air started getting hot. You may capture it at high speed relative to the decoy, but you must slow it down very slow relative to the decoy in order to use it for anything at all.
The missile seeker guys also ran into this decades ago, missiles being mostly supersonic, even by the early 1950's.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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