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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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Thanks for the response. Instead of the exhaust air coming into contact with the ambient air, it could be sent into a heat exchanger to cool ambient air. Doing it this way would allow you to use different gases to be heated, not just air depending on efficiency. The working fluid would then be recycled.
Bob Clark
Last edited by RGClark (2026-03-18 22:22:20)
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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For RGClark re new topic and potential educational value ...
I ran a quick search and found 7 pages of topics with posts that contain the word "thermodynamics". The list goes back to 2002 when the forum was starting.
I then ran a search for topics with the word "thermodynamics" in the title and there was only one. That one was a study of compression of air in a pipe.
Your topic here could be an opportunity for development and presentation of a series on how air conditioning works, with a focus on the specific gas behavior you've identified as of interest. It would help greatly if we could see pictures to help us understand the physics involved.
Modern AI systems can create pictures, but up to this point their ability to implement physics has been limited. If you have the time and energy, and if the quest is of interest, it might be interesting to see if illustrations of the physics of air conditioning can be created.
When I think of air conditioning, the image that comes to mind is of the traditional compressor with a motor driving a reciprocating piston pump. Gas coming from a location to be cooled is heated by compression, and then released into a system of radiators that allows thermal energy to flow to the ambient air. The gas that has released thermal energy is then fed back into the location to be cooled.
The system you are describing would appear to operate somewhat differently. It would be interesting to see if both systems could be shown in this topic, so that comparison might be possible.
(th)
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For RGClark re air conditioning...
Your idea for a new concept likely differences from traditional designs....
In the course of investigating traditional designs, I learned that the piston pump has been gone from the scene for some time, replaced by scroll pumps which are free of vibration and operate with direct current. Here is a snippet Google prepared to summarize the modern systems. I asked about Carrier in particular.
Carrier home air conditioners and heat pumps primarily use variable-speed scroll compressors and rotary compressors. These compressors circulate refrigerant and are often powered by Inverter technology for high efficiency, variable speeds, and quiet operation.
Key Pump and Compressor Types in Carrier Residential Units:
Scroll Compressors (Inverter-Driven): Used in top-tier Carrier Infinity and Performance series heat pumps and AC units for precise temperature control and high efficiency.
Rotary Compressors (Inverter-Driven): Used in high-wall and ductless mini-split systems for compact, efficient, and variable-speed operation.
Condensate Pumps (Condensing Pumps): Specific, separate pumps used for removing water buildup from the evaporator coil in condensate removal systems.
Two-Stage and Single-Stage Compressors: Used in Performance and Comfort series units respectively for reliable, standard, and enhanced cooling and heating.
These units utilize Puron® refrigerant (R-410A), or the updated Puron Advance™ (R-454B) in newer, environmentally friendly models.
From videos Google found, I get the impression home air conditioners use phase change from liquid to gas to capture thermal energy inside a volume to be cooled and phase change back to liquid to release that energy to the outside air.
(th)
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For RGClark ...
This post is an attempt to pursue the topic of high temperature cooling.
The ambient conditions on Venus will be challenging. kbd512 and others have invested some thought in this problem.
Your re-introduction of the topic of high temperature cooling is welcome in that context.
How ** simple ** an air conditioning system for Venus would be is a good question, but if humans (or even robotic systems) are to enjoy an extended life on the surface of Venus, mastery of high temperature cooling is a requirement.
Ideally, your investigation will reveal a way to keep the cabin of a Venus Rover cool enough for shirt sleeved humans.
As indicated earlier, kdb512 has already done some preliminary thinking about this interesting problem.
A small reactor would (presumably) be the power source for a Venus Rover, and the hot temperatures it achieves can be delivered to the ambient atmosphere of Venus, which is much more dense than Earth's atmosphere at sea level, and which therefore is better able to absorb thermal energy from the hot reactor. The challenge for designers is to deliver 20 Centigrade air to the crew while keeping the reactor itself cool. Power from the reactor can be realized as electricity, so electricity can be used as needed.
It's been a while since members of NewMars have tackled Venus challenges.
Your initiative provides at least a chance of a renewed glance at the problem.
We now have thinking tools available to help. I saw a demonstration last night of CoPilot taking on a complex data processing challenge under the leadership of a ** very ** experienced IT professional. The result was (to me for sure) stunning.
It is possible that CoPilot might perform as well under your leadership.
One detail that may be of interest in the Venus case ... the atmosphere is so dense, buoyancy is sufficient to permit "flight" as a realistic option.
Per Google:
The average surface temperature of Venus is approximately 465 degrees Centigrade (870 degrees Fahrenheit)
This extreme heat is caused by a massive greenhouse effect, driven by a thick, carbon dioxide atmosphere that traps solar heat. Surface temperatures are consistent across the planet, day or night, and are high enough to melt lead.NASA (.gov)
Key Surface Temperature Facts:
Celsius: ~ 465
NASA Science (.gov)
Fahrenheit: ~ 870
NASA (.gov)
Kelvin: ~ 737
.
Wikipedia
Why it's hot: The atmosphere is 90+ times denser than Earth's, creating intense pressure along with the heat-trapping effect.This constant, intense heat makes the surface of Venus the hottest in our solar system, even hotter than Mercury, which is closer to the sun.
NASA Science (.gov)
The critical temperature for this study is the temperature achieved by a Small Nuclear Reactor. It is the flow of heat from the reactor to the atmosphere that provides any power that might be achieved.
it should be noted that few materials can withstand operating at these temperatures, but in his earlier investigations, kbd512 found some candidates.
(th)
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This post offers a glimpse of the temperatures that might be available from small nuclear reactors ..
Per Google:
Small nuclear reactors, specifically Small Modular Reactors (SMRs) and advanced microreactors, are designed to operate across a broad temperature range depending on their coolant type, with upper limits generally falling between 500°C and 950°C for high-temperature designs. While traditional water-cooled SMRs operate at lower temperatures (around 300°C), advanced Generation IV SMRs can reach temperatures exceeding 1000°C in specialized, Very High Temperature Reactor (VHTR) designs.
GRS gGmbH
Upper Temperature Ranges by Reactor Type:High-Temperature Gas-Cooled Reactors (HTGR): These typically use helium as a coolant and reach outlet temperatures between 500°C and 950°C. The HTR-PM in China, for example, operates with an outlet temperature of roughly 750°C.
ANSTO
Molten Salt Reactors (MSR): These designs use liquid fuel or coolant and can operate at high temperatures, with some concepts tested to be stable up to 1,400°C, though typical operating temperatures are designed around 700°C–800°C.World Nuclear Association
Liquid Metal-Cooled Fast Reactors (LFR/SFR): These reactors use sodium or lead as coolant and commonly operate in the range of 500°C to 800°C.World Nuclear Association
Very High Temperature Reactors (VHTR): Designed specifically for high-temperature process heat, these reactors target outlet temperatures of 700°C–950°C, with future goals to reach above 1000°C.Gen IV International Forum
Water-Cooled SMRs: These are scaled-down versions of conventional reactors (like NuScale or BWRX-300) and operate at lower temperatures, typically around 300°C–320°C.ANSTO
Applications of High-Temperature Heat:The upper temperature range allows small reactors to move beyond electricity generation into industrial applications, such as hydrogen production (requiring 700°C–950°C), steel manufacturing, and chemical processing.
ScienceDirect.com
The greater the gap between the high temperature and the ambient temperature of the surroundings, the better.
(th)
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post 1 is the distance that the flow rate of heat get absorbed by the walls
Post 2 is what happens with not flow movement
post 3 for heat exchanger is about the flow of the heat through the fins of the unit with respect to the direction of flow through the collector and what you do with that flow.
The exchanger usually has a second to get a differential temperature to occur such that it is similar to the heat pump in that the first exchanger blows into the house for heating or cooling while the second exchanger on the outside is blowing towards the outside. what changes is the direct of fluid flow from 1 to 2 in say clockwise direction but for the opposite means the flow is counter clockwise, Which means you have heat in one direction and the other is cooling.
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