In Stationeers almost every substance can be gaseous, liquid or solid. Which one it is at the moment depends only on pressure and temperature. If you know the limits, you can store gases compactly as liquids and cool by evaporation – and you avoid pipe damage that seems to come out of nowhere.
Three limits per substance
Every substance has three important values in the game data:
- Freezing point: below it, it becomes solid.
- Minimum pressure for liquid: below it, it cannot be liquid, however cold.
- Critical temperature: above it, there is no liquid any more, however high the pressure.
In between runs the vapour pressure curve: if the pressure is above the vapour pressure at the current temperature, the substance condenses; if it is below, it evaporates.
| Substance | Freezing point | Minimum pressure for liquid | liquid up to | Heat of vaporisation |
|---|---|---|---|---|
| Oxygen | 56.4 K | 6.3 kPa | 162.3 K | 800 J/mol |
| Nitrogen | 40.0 K | 6.3 kPa | 190.0 K | 500 J/mol |
| Carbon Dioxide | 217.8 K | 517 kPa | 266.3 K | 600 J/mol |
| Methane | 81.5 K | 6.3 kPa | 195.0 K | 1,000 J/mol |
| Hydrogen | 15.2 K | 6.3 kPa | 70.1 K | 200 J/mol |
| Pollutant | 173.3 K | 1,800 kPa | 433.9 K | 2,000 J/mol |
| Nitrous Oxide | 251.4 K | 800 kPa | 430.6 K | 4,000 J/mol |
| Water / Steam | 273.15 K | 6.3 kPa | 643.7 K | 8,000 J/mol |
Helium never changes phase in the game. At 100 kPa water boils at about 384 K in the game, not at 373 K. Carbon dioxide, pollutant and nitrous oxide cannot be liquid at 100 kPa at all – their minimum pressure is higher.
Where this surprises you in pipes
A gas pipe tolerates at most 2 % liquid; more damages it. Three cases come up in practice:
- Pollutant under pressure: from 1,800 kPa pollutant can turn liquid even at room temperature. A waste line into which you press pollutant then collects liquid.
- Nitrous oxide: from 800 kPa and below 430.6 K – so at room temperature as well – it can condense.
- Carbon dioxide outdoors: on Mars the outside air drops to about −50 °C (223 K) at night. An uninsulated line with carbon dioxide under high pressure can then get into the liquid range – that becomes possible from 517 kPa.
Liquid lines face the opposite: if the temperature drops below the freezing point, the liquid solidifies into chunks of ice that end up in the world. Water freezes at 273.15 K, polluted water already at 276.15 K.
And in an empty liquid line part of the liquid evaporates at once until the vapour pressure is reached. You can lead that gas away with a Purge Valve.
Using phase changes
Compact storage. Liquid takes up far less room than gas. Liquid nitrous oxide needs 0.026 litres per mole, carbon dioxide and pollutant 0.04 litres each. At 100 kPa and 20 °C one mole of gas would need about 24 litres instead.
Cooling by evaporation. When evaporating, a substance needs its heat of vaporisation; when condensing, it releases it again. Every refrigerator relies on that: a refrigerant is compressed and condenses where the heat should go; then it is expanded through a valve and evaporates where cooling is wanted. Nitrous oxide brings a lot of heat of vaporisation at 4,000 J per mole and can be kept liquid at room temperature. Keep in mind, though: it is an oxidiser.
There are dedicated parts for this:
| Part | Setting | how it works according to the game code |
|---|---|---|
| Condensation Chamber | chamber pressure, 0–6,000 kPa | Input fills the 400-litre chamber up to this pressure; condensate drains into the liquid line at up to 10 L per tick |
| Evaporation Chamber | minimum pressure, 0–6,000 kPa | fills up to 10 % (40 L) with liquid; gas only leaves above the set value |
| Condensation Valve | no effect | moves liquid from a gas pipe into a liquid line, up to 10 L per tick, unpowered |
| Expansion Valve | no effect | pushes liquid from a liquid line into a gas pipe, up to 10 L per tick, unpowered |
On both chambers Input2 is not a second gas input but a heat exchange port: the gas network on it only exchanges heat with the chamber; its gas does not flow in. On the condensation chamber that is where the cooling loop goes, on the evaporation chamber a warm loop that supplies the heat of vaporisation. Below 101.325 kPa in that network the exchange drops. With Open = 1 both chambers dump their contents into the surroundings.
You open and close the two valves on the valve itself (On). A gas pipe may hold at most 2 % liquid – so behind an expansion valve the liquid really has to be able to evaporate.
A calculation: evaporating one litre of water
One litre of water is 1 / 0.018 ≈ 55.6 mol. At 72 J per mole and kelvin it needs about 4,000 J per kelvin.
- Heating from 20 °C to 384 K: 4,000 · (384 − 293.15) ≈ 363,000 J
- Evaporating: 55.6 · 8,000 ≈ 445,000 J
Together about 808 kJ. A 2 kW wall heater would need almost seven minutes for that. The other way round, condensing steam releases the same heat again – so a condenser needs strong cooling.
Where next
- Heat exchangers and heat transport: pipe to pipe, gas to liquid – moving heat between loops
- Tanks and gas storage: sizes, insulation, safe filling – storing liquid safely
- Pipes and lines: gas, liquid, insulated – limits of gas and liquid pipes
- All phase diagrams: Gases