Doctor Love
kiwifarms.net
- Joined
- Nov 12, 2023
Surface area, conduction rate, gas composition all have an effect. What's the actual composition? High CO2 means you can use copper wool if needed, with less baffling.
Actually, now that you say it with aggressive baffling - have you tried aerofoiled, or perforated or like, needle-like baffling? Obviously not crossing the middle, but a combination of strong and soft to "spread and dampen" the flow as much as possible.
CO2, H2O and N2 seem to be the main components, so it's going to cool at the speed of its contact surface area until somewhere between 30C, 375C and whatever nitrogen is (high pressure but low af temperature) - it's the same reason why superheated steam is used in turbines, because it is extremely efficient at transferring energy.
You're right in that silver is a good baffle, but copper and weird shit, like diamond, is right at the top. You're dealing with ~1-2g of gases, total, and all of it has a low specific heat - I checked the tables and paraffin wax, coated in a full layer of metal like copper or silver with a high surface area, would work as a perfect heat sink. Wax has a huge "Specific Heat Capacity" - that is, it takes a lot of energy for it to heat up - napkin math says that you'd heat up a layer of wax adding up to a few grams at a rate of 1/500th the gases cooling. So if it's CO2 going from 800K down to 300K, then you're heating up the equivalent mass of wax by 1 degree.
Wax is hardly a super material, but that's the basis of a three-layer system "Break, transfer, sink" rather than just "break, transfer" - since the wax remains at such a low temperature, it cools the transfer metal too - meaning you don't have the transfer rate slowing down until long past the supercriticality window.
Edit: Woops, that was the molar rate, that's because wax has a super long chain length. It's still workable, but only a rate of 1/3 or so that of the gas. 100G of wax would still probably not melt, and it still absorbs heat 3 times as "well" as aluminium, but it's not as super impressive as I made it out to be.
Actually if you're available to be a guinea pig, @SHIGGSHOGG
Aluminium foil has an incredibly high heat transfer rate, and I can verify that it spreads out heat quickly enough that you would have trouble melting wax with a 2000W heat gun at max temperature, from less than an inch away.
If you have a candle, and some aluminium foil, you could test it with practically no overhead - just cut a hole down the middle of a candle, cover the inside in a generous layer of aluminium foil and then blast it with a blowtorch so that it's nice and melted against the foil. Then mount it to the end of a rifle, and shoot down it.
Wrap the outside in duct tape and some kind of support, and you're good to go - it's wax, so it's soft enough that it won't obstruct the barrel if it starts melting - aluminium suppressors melt so easily because they heat up readily. Wax would make a cheap solid heat sink, and if you really mix the foil in there, the heat might not even melt the wax - it would diffuse throughout it, so much
Different chemicals express changes in energy, as a change in temperature, at different rates. For most gases, it's ~1 or 2 and for PLA itself, it's 1.5 - while for paraffin, it's 2.5. Aluminium is 0.8, and silver is 0.25 - so do NOT use silver. Bad idea.
This means that for each unit of energy change, a certain amount is expressed as heat and thus, a phase change. Silver heats up ten times as much as wax - so if you had a pound of wax, the same energy to bring that wax up by 50C would bring the silver up by 500C. As the temperature rises, it slows this process down - and as the temperature difference rises, it increases the speed. So the silver would quickly take all of that heat from the gas (roughly 1 per gram) but it would spread it around the metal, increasing the temperature of the metal so much that the heat exchange rate slows down dramatically. You would want an additional heat sink, so that the silver stays at a high temperature but can still conduct that heat into something which isn't going to heat up as quickly.
Water would also work - but for you, the most likely candidate would be 3D Printed plastic, with a generous layering of aluminium foil. The goal is to use the foil as a intermediary, so the more of it that is in contact with the plastic heat-sink, the better.
Per unit volume, aluminium, silver or copper foil or plating on a heat sink material is best - organic materials have a much higher heat capacity than metals, so you could use 3D Printed plastic instead of wax if that's better. The goal is to make sure that the gases themselves contact the thin layer of metal, and that metal is in contact with the plastic directly - so that it transfers the heat across the gradient, which is kept strong by the high contact surface area, higher mass, and higher heat capacity. That way, the rate of heat transfer doesn't dramatically slow down when the metal heats up, and you can save some money.
The difference sounds minor, but the goal is to take heat away from the gas - so you'll want something on the other side of that silver, conducting heat away from it, as quickly as the gases can convect heat onto it. More silver would work, but then you're battling with silver's temperature rise - the longer the surface stays hot, the less heat it will take from the gases.
This means that for each unit of energy change, a certain amount is expressed as heat and thus, a phase change. Silver heats up ten times as much as wax - so if you had a pound of wax, the same energy to bring that wax up by 50C would bring the silver up by 500C. As the temperature rises, it slows this process down - and as the temperature difference rises, it increases the speed. So the silver would quickly take all of that heat from the gas (roughly 1 per gram) but it would spread it around the metal, increasing the temperature of the metal so much that the heat exchange rate slows down dramatically. You would want an additional heat sink, so that the silver stays at a high temperature but can still conduct that heat into something which isn't going to heat up as quickly.
Water would also work - but for you, the most likely candidate would be 3D Printed plastic, with a generous layering of aluminium foil. The goal is to use the foil as a intermediary, so the more of it that is in contact with the plastic heat-sink, the better.
Per unit volume, aluminium, silver or copper foil or plating on a heat sink material is best - organic materials have a much higher heat capacity than metals, so you could use 3D Printed plastic instead of wax if that's better. The goal is to make sure that the gases themselves contact the thin layer of metal, and that metal is in contact with the plastic directly - so that it transfers the heat across the gradient, which is kept strong by the high contact surface area, higher mass, and higher heat capacity. That way, the rate of heat transfer doesn't dramatically slow down when the metal heats up, and you can save some money.
The difference sounds minor, but the goal is to take heat away from the gas - so you'll want something on the other side of that silver, conducting heat away from it, as quickly as the gases can convect heat onto it. More silver would work, but then you're battling with silver's temperature rise - the longer the surface stays hot, the less heat it will take from the gases.
Now that I have the idea, I would definitely like to see it tested - 3D Printers can also be used, either with or without the wax. The wax is cheaper and a better heat sink and, if you have a flat enough surface, you can just melt some wax onto some foil, then sandwich it in an extremely thin layer, then cut the foil into disks, load it into a pipe and test it out. But, it would warp pretty quickly if there's no support - just nowhere near as quickly as you would expect, because wax tanks heat changes.
3D printed plastic can also work as a heat sink, and you can probably get the foil to adhere with a blowtorch or a heatgun without melting it - you have more control over the contact surface area and shape, and it would support itself better. The overall best would be an aluminium/silver plated metal structure which you can fill with plastic, wax or water, but that's not a "today" kind of thing.
Stats-wise, the best is actually silver-plated lithium sponge, but that's absolutely not something I'm willing to fuck around with, lithium would explode if the silver was scratched off.
Aluminium foil, diamond-dust polishing crystals - the steps are, as you said, break-up and transfer the heat, but then with an extra heat sink after that. Diamond powder also has an absurdly high heat transfer rate, and would probably be the best per unit of surface area - and you can actually mix them in and paint them on, then use an organic heat sink to disperse the heat.
So those are my two suggestions, either aluminium foil adhered onto a 3D-Printed can, or 3D Printed, sprayed down with a fine layer of diamond dust. If the cost of PLA is a factor, use a combo of that and some wax - DM me if you want me to design something more specific.
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