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Here in Falcon 1 user guide, in table 2-1 in page 8, heated Helium is mentioned as used for tank pressurisation. What will be the temperature of such He and why is heated He used?

Location in the linked article for reference.

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    Sorry Karthik, didn't notice you were asking about the first reference to it, added an image to avoid confusion. – Magic Octopus Urn Sep 17 '18 at 17:34
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    If you haven't already read all of the answers to questions like Why does the Falcon 9 require a helium pressurization system? and How does tank pressurization work? and Why Use Helium? and Why do pressure-fed systems have to be pressurized with helium or nitrogen? this might be a good time. To "why is heated He used?" isn't the answer just that that's what generates the pressure? – uhoh Sep 17 '18 at 18:10
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    @uhoh I take the question to mean "why heated helium." – Wayne Conrad Sep 17 '18 at 18:53
  • It probably has something to do with adiabatic cooling. This one of the gas laws: https://en.wikipedia.org/wiki/Gas_laws#Gay-Lussac's_law When volume is constant, if pressure drops then temperature will drop too. If it drops too far, the cooling is so extreme that it can crack the metal tank. Therefore some kind of heating system is necessary to keep the temperature more or less constant. Kinda ironic that way. – DrZ214 Sep 17 '18 at 18:55
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    @WayneConrad as do I. Isn't the heating the helium what causes the helium to become pressurized, "the heating" being the thing that actually "generates the pressure?" A tank of liquid helium at its 1 bar boiling point will have a slow boil-off rate, nothing close to enough to help the tons per second of propellants out of the tank. Isn't the heating of the helium the thing that does the propellant-helping? – uhoh Sep 17 '18 at 19:05
  • @uhoh Oh, it's liquid He? I guess I should have known that, but I didn't (until just now). – Wayne Conrad Sep 17 '18 at 19:07
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    @WayneConrad I don't know for sure either way. But it's pretty cold - cold enough to freeze oxygen in the F9. The tanks are so small in the F9 that it's hard to imagine they can do so much displacement if not starting out as a liquid. Either way, heating is used to add pressurization. – uhoh Sep 17 '18 at 19:15
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    If gaseous helium is stored in a high pressure tank, its temperature will drop a lot during expansion. To compensate the temperature drop and to get more volume per mass, the helium is heated after expansion. – Uwe Sep 17 '18 at 22:21
  • @uhoh I guess adding a lot of He to a rigid container too can increase the pressure. – karthikeyan Sep 17 '18 at 22:46
  • @Uwe you mean by Joule Thompson effect. what is the inversion temperature for He? Would it heat up or cool upon expansion? Also, what is the source of hearing if it's going to cool? – karthikeyan Sep 17 '18 at 22:50
  • @MagicOctopusUrn thanks for making my question easier to understand! – karthikeyan Sep 17 '18 at 22:51
  • On page 9 of the Falcon 1's user's guide, it says the helium is stored in composite over-wrapped inconel tanks, so it is presumably stored as a high pressure gas. – Philip Ngai Sep 01 '23 at 02:15

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