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Heat transfer in gases

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This was my testing setup. Corner chambers had 500 kg of hydrogen per tile to provide sufficient thermal mass in gas form, edge chambers had 2 kg of oxygen per tile. The insulated walls are made of abyssalite, normal walls are granite to allow thermal transfer. In both experiments the temperature difference was 200 C, i.e. the cold part was at -100 C and the hot part was at +100 C.


In first experiment, the oxygen was hot and the hydrogen was cold, drawing heat from the hot oxygen chambers.









In second experiment, the oxygen was cold and the hydrogen was hot, sending heat to the cold oxygen chambers.







My conclusion from these experiments is that in gases, heat transfers readily upwards, i.e. a hot gas tile below and cold gas tile above exchange heat very fast, while the opposite is rather slow. Horizontal heat transfer is somewhere in between these. The behavior mimics real world but misses mass transfer (wind and turbulence), it just consists of heat exchange between gas tiles.

Heating is best done from below, cooling is best done from above. That's actually good for both bristle blossom and pincha pepper farms as both plants are oriented exactly in the favorable way. The horizontal transfer is, however, in my opinion a bit too slow for a gas. Here's how heat is coming out of a localised heat source:


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Some time ago I claimed that the gas exchange heat more readily with a wall than with adjacent gas tile. So I went and made some tests about it.

Here's what I got when I used standard oxygen concentrations (2 kg/tile) along granite walls:


On first glance it appears as if it confirms my claim - the gas temperature does not spread that far along the wall, so clearly the wall is "sucking" the heat. But there's a catch. There's just 2 kg of oxygen in a tile, while the wall has 200 kg reported mass of granite. If I increase amount of oxygen per tile so that both the wall and the gas have about the same heat capacity per tile (155 kg of oxygen per tile), here's what happens:


So my conclusion is that the phenomenon is actually correct. The wall has great heat capacity and it maintains the thermal gradient high, that's why it cools the gas down more readily than adjacent gas tile.


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7 minutes ago, Executive_Lurker said:

Quick question (hopefully) is the whole "heat transfer is faster between tiles on gas than it is gas on gas" thing scientifically accurate? Is that how it would work IRL?

P.s. thanks for all the cool experiments. Love checking them out. Thanks for making the game better

Well, yes and no.  In RL, there would be convection, which ONI does not model.  The gas would heat up at the tiles then float upwards.  (Hot gas expands and becomes less dense)  Then, it would cool and start to sink.  Eventually, you'll get small circle (or several) flow of air that transports the heat from the bottom to the top and thoroughly mixes the air throughout the room.  Without convection, it could take a while for the heat within a gas to equalize throughout it.  This is why air pockets are good for insulation.  Limit the convection and heat has a hard time moving through the gas.


What ONI is doing here is just favoring heat moving to the tiles above it.  Which is why there's this 'beam' affect in the pictures.  The game does have some kind of gas movement built within it, however.  You'll notice that lighter gases tend to go up and to the left while heavier gases tend to sink down and to the right corner.  This kind-of creates a flow of air throughout the base, but it's marginal at best.


As for the heat transfer part of your question.  Solids, in general, at least metals, will tend to shed or gain heat rapidly regardless of medium they're touching.  So yes, a fluid to solid will generally transfer heat quickly.  Solids, being solid, are efficient  at transporting heat (photons) through their structure because they're orderly.  A fluid is a disordered structure and is much slower at moving heat throughout it, but this disorder typically makes them great soaks for heat.

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