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In the book Modern Engineering for Design of Liquid Propellant Rocket Engines, the following excerpt appear in chapter 9 - Interconnecting Components and Mounts:

The liquid-oxygen lines were not insulated since the chill-down recirculation flow rates and subcooling requirements were acceptable without insulation.

What is meant by chill-down recirculation flow rates and why does it influence the insulation of the LOx line?

Is this a unique case or a universal case for all launch vehicle using LOx?

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  • $\begingroup$ In the first stage of the Saturn V, the LOX tank was above the kerosene tank. The LOX lines leading through the kerosene tank were isolated to avoid solid kerosene and too many gas bubbles within the LOX. Heat transfer from air to LOX plumbing is lower than from liquid kerosene. $\endgroup$ – Uwe Nov 22 '18 at 11:01
  • $\begingroup$ When LOX in the tank is chilled down and subcooled, the LOX in the plumbing should be subcooled too. Recirculation is needed to equalize temperatures of LOX and tank structure as wells plumbing material. $\endgroup$ – Uwe Nov 22 '18 at 12:35
  • $\begingroup$ @Uwe so subcooling is cooling LOx below its boiling point correct? Is it required in all Cryo rockets? And what is recirculated between what?- a little bit elaboration on the "recirculation" will be appreciated $\endgroup$ – karthikeyan Nov 22 '18 at 13:09
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    $\begingroup$ Yes, subcooling is cooling LOx below its boiling point to increase density and to load more LOX mass into the same tank volume. LOX is recirculated within the tank and its plumbing to equalize temperatures. $\endgroup$ – Uwe Nov 22 '18 at 15:40
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Vacuum-jacketed lines were used for both LOX and LH2 plumbing in the aft boattail of the Space Shuttle Orbiter.

See also Insulation used in the plumbing line of the actual rockets

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My guess is that you don't have to insulate the lines, because the rate at which you charge and discharge your tanks is high enough that you won't gain enough heat to vaporize your Lox.

If your mass flow rate was really low,maybe you would have to consider the heat loss while in transit from tank to injector.

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    $\begingroup$ Is it lose heat or gain heat?! Also, what is chill down recirculation? $\endgroup$ – karthikeyan Nov 22 '18 at 6:02
  • $\begingroup$ @karthikeyan I had it backwards, its too late into the night! Yeah it should gain heat from the surroundings as it moves through the fill lines. I'm not sure about the recirculation bit. What page is the quotation you have on in your book? $\endgroup$ – WhisperingShiba Nov 22 '18 at 6:07
  • $\begingroup$ Page 311 in chapter 9, section 9.1 $\endgroup$ – karthikeyan Nov 22 '18 at 6:13
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    $\begingroup$ @karthikeyan I'm not 100% sure about this chill-down recirculation flow rate thing, but you can pump Lox and Lh2 into the pipes to cool them down, then vent the tank and pipes, then fill again to make sure as little heat is gained as possible during fill. Huzel & Huang suggest only insulating H2 lines, not your Lox lines, as its easy to sub-cool LOx compared to LH2. In short: Insulate your H2 lines not your Ox lines $\endgroup$ – WhisperingShiba Nov 22 '18 at 22:38

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