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#276 2025-04-05 17:04:25
- GW Johnson
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- From: McGregor, Texas USA
- Registered: 2011-12-04
- Posts: 5,909
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Re: Google Meet Collaboration - Meetings Plus Followup Discussion
I do not know what that heating system might really look like. I have yet to even bound the heat transfer problem, which will be the "long pole in the tent".
You have to understand, heat transfer, especially via gaseous media, is about the slowest physical process that we know. The proof of that thesis is the vast difference in time it takes 32 F air to kill you, versus 32 F water. And that transfer process is termed "convection", not "conduction". Conduction occurs within solid media that are in intimate contact.
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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#277 2025-04-05 18:06:06
- kbd512
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- Registered: 2015-01-02
- Posts: 8,086
Re: Google Meet Collaboration - Meetings Plus Followup Discussion
GW,
My opinion is that we will use induced turbulent flow to do a better job of transferring the heat into the Hydrogen. Maybe we don't even need a porous graphite core as such, for a flow rate of only 1 to 2kg/s, and a hollow channel wall cylinder design will work better. If we need more channel wall surface area for super heating or extended residence time in the engine, then we can use our large 100:1 expansion ratio nozzle as part of our heat exchange surface area. This will keep the engine as light as possible.
I won't pretend to know what the optimal approach is, so I'm not ruling out any particular approach unless it results in impractical component sizes, performance requirements, or costs. The major parts of the propulsion system have to be transportable to orbit in a Starship, or they're not very practical. As far as materials are concerned, we have the materials of the NERVA Program (Graphite structure with Zirconium Carbide cladding) which are known to work, as well as newer materials (Hafnium Carbide cladding) known to work even better.
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#278 2025-04-06 07:44:57
- tahanson43206
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- Registered: 2018-04-27
- Posts: 20,896
Re: Google Meet Collaboration - Meetings Plus Followup Discussion
The weekly Google Meeting is on track.
If all goes well, the waiting room will open at midnight UTC - 8 PM New Hampshire - 7 PM Houston
GW Johnson will be away on this occasion.
The waiting room is open at 23:58:23 UTC
https://www.reddit.com/r/rocketry/comme … ?rdt=38794
https://beyondnerva.wordpress.com/nucle … derations/
https://www.intechopen.com/chapters/81555
https://kb.osu.edu/server/api/core/bits … 9a/content
Post meeting report:
This was a ** really ** productive meeting! At this point, we appear to have the optical collection system stable, and the nozzle assembly appears to be approaching stable. The heating chamber is now receiving all the attention.
The links shown above in this post were provided by kbd512 as we proceeded. We also called up documents provided earlier by GW Johnson.
A key finding from the meeting is that the NERVA rocket used some method (we do not yet understand) to provide a long dwell time for hydrogen traveling through the body of the reactor that allowed the hydrogen to absorb the thermal energy that was present when the hydrogen passed through the throat and out into the expansion bell.
The External Heating chamber is going to have to perform a similar slowing function. At this point we don't understand how best to do that, but the team members are fully engaged, and we may have an answer next week.
(th)
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#279 2025-04-06 20:12:24
- kbd512
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- Registered: 2015-01-02
- Posts: 8,086
Re: Google Meet Collaboration - Meetings Plus Followup Discussion
tahanson43206,
Edits:
Non-Uniform Heating Impact on Specific Impulse in Nuclear Thermal Propulsion Engines
Nuclear Reactors - Spacecraft Propulsion, Research Reactors, and Reactor Analysis Topics
Mechanical properties of molded graphite-modulus and strength
Scientists successful in 3D printing complex graphite parts with 97% purity
In our meeting, I asked about the idea that a very large / high expansion ratio "channel wall nozzle", 3D printed in Carbon / Graphite, with an enormous amount of internal surface area and volume for heating of the Hydrogen propellant, could provide sufficient residence time to allow the Hydrogen propellant to achieve 3,000K:
An incredible variety of internal heat transfer tube configurations are possible, if they prove beneficial:
NERVA Fuel Element Diagram:AS.1943-5525.0000313/asset/c5aeca43-a962-4e4e-aea6-9cef2e00fad5/assets/images/large/figure2.jpg)
Proposed NVTR Fuel Element Diagram:
Last edited by kbd512 (2025-04-06 21:29:56)
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