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psusi

How the heck do you pipe LOX?

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psusi    245

I liquefied a bunch of oxygen to fuel the rocket but I can't seem to pipe the damn stuff over to it!  I ran only 1000g/s and looped it back to pre-cool the pipes but that was taking forever.  I tried switching to just running supercoolant through the pipes at -220 for several cycles and it didn't seem to exchange much heat with the pipes.  I went back to LOX and 1000g packets still get up to -180 half way there.

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NurdRage    119

It's taking forever?

Your LOX condenser shouldn't be too far from your rocket. Like maybe one screen (two max).

But as long as the LOX coming back around the loop is less than the boiling temperature, that's enough. You don't necessarily need to wait for the pipe itself to get that cold. If the returning LOX is still less than -183C then just go with it. Crank up the volume to full 10kg/s and fire up the rocket.

What's the entry temperature? are you pumping out LOX already near -183C, or are you chilling it a bit further to say -200 before pumping it out?

If it's -210C then it should survive most loops directly unless they're really long, or you made them out of bad materials like regular pipe. 

 

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Gurgel    1482

Ceramic insulated pipes and make sure to put in 10kg/sec. Do not put in less, the pipes will warm it up too fast. Loop it back so nothing warms up when done. And do not pipe it over long distances, just as NurdRage says. I usually make that max half a screen or so.

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KittenIsAGeek    1459

There are several different methods.  One method is to pipe through radiant pipes in vacuum.  The pipes will quickly reach the temperature of the LOX and after repairing, you shouldn't have a problem.

Another method is to use insulated ceramic or, preferably, Insulation pipes.  You'll have some pipes break until the internal temperature reaches equilibrium. 

Either way, you also want, as @Gurgel stated, to loop your pipes back.  You can either empty back into the reservoir, or keep the LOX flowing in a circle -- both methods work -- but you do NOT want the LOX to stop in the pipe. 

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psusi    245

It is a screen or two away.  I have a ladder going up past the liquefaction room to a tower with jet suits to fly over to the rocket.  The LOX starts at -200... close to its freezing point, and goes through insulated igneous pipe half way there where I switched to insulated ceramic.  All but one pipe section is in vacuum.  At about that half way point it is already up to -183 where it would boil.  I even initially tried just letting it get to the rocket above its boiling point as long as it was only 1000g packets it should work but it seemed like the rocket refused to accept it and instead did damage to the pipe.

The temperature of the pipe hardly seems to want to change yet it keeps heating up the LOX.  I don't understand why the 10kg packets of -220 supercoolant didn't get it cooled down.  I think it may be better to use normal pipe so the SC can get it chilled, at least until it gets close enough to the rocket where it would be exposed to the hot exhaust.

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Gurgel    1482
2 minutes ago, KittenIsAGeek said:

Another method is to use insulated ceramic or, preferably, Insulation pipes.  You'll have some pipes break until the internal temperature reaches equilibrium. 

Never had any breakage, but I only use short pipes and cool the LOX down a bit more than needed.

2 minutes ago, psusi said:

At about that half way point it is already up to -183 where it would boil. 

You may be able to use radiant pipes then and loop them earlier initially to make them cool down fast.

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Idea of easily extending the length of cooled pipe: run the return line 2 tiles up or down from the outbound line. And gradually move a return bridge farther and farther away as the pipes cool down 

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Coolthulhu    1045

To sum up:

  • Short pipes
  • Loop back
  • Ensure all packets are 10kg/s. Note: automation-disabled pump usually outputs one 4kg packet after disabling - take care of that.
  • Overcool the LOX to just above solidification temperature. Make sure to do that before pumping.
  • Pipe as much as you can through true vacuum that never gets any gases/liquids/solid on it

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Neotuck    2220

Have you tried using metal pipes in a vacuum? They will get damaged at first but they cool quickly and the vacuum will provide perfect insulation

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Ixenzo    62

Speaking of radiant pipes in vacuum, every time I've tried it it would go as planned half the way and then get stuck on a single segment, breaking over and over. Once I switch to insulated pipes it works flawlessly.

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psusi    245
1 hour ago, caffeinated21 said:

If you can have nothing but vacuum between your LOX setup and rocket, why not just move the lox closer? Insulated pipes seem to offer a lot more resilience. 

The problem with insulated pipes is that they won't cool off themselves and stop warming the LOX.  I would think that sending full 10kg packets would just mean there was more TC and so it would heat up about as fast, but I guess that's ignored since the insulated pipes only use their own TC, and so doing that works.

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Neotuck    2220
41 minutes ago, psusi said:

The problem with insulated pipes is that they won't cool off themselves and stop warming the LOX.

Insulated pipes don't create heat

If the LOX warms up in the the pipes, then the pipes will cool down proportionately

unless there's some ONI physics at work here than I'm unaware of

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psusi    245
24 minutes ago, Neotuck said:

Insulated pipes don't create heat

If the LOX warms up in the the pipes, then the pipes will cool down proportionately

unless there's some ONI physics at work here than I'm unaware of

I let -220 supercoolant run for at least half a dozen cycles and the pipe temperature only changed by a few degrees.  It's insulated so it doesn't exchange heat very well with the contents, and it has 400kg of mass, so eventually it may cool down but it's going to take a long, long, long time.

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Neotuck    2220
22 minutes ago, psusi said:

I let -220 supercoolant run for at least half a dozen cycles and the pipe temperature only changed by a few degrees.  It's insulated so it doesn't exchange heat very well with the contents, and it has 400kg of mass, so eventually it may cool down but it's going to take a long, long, long time.

main reason I prefer radiant pipes in a vacuum is to allow them to exchange temp quickly and repair any damage done in the first cycle, rather than have insulated pipes break 50 or so cycles later when you're not expecting it 

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KittenIsAGeek    1459

There are two cases where insulated pipes don't work for LOX: 

  1. Material isn't an insulator.  For example, any material other than ceramic or Insulation will give you problems.  Insulated igneous, for example, has a thermal conductivity of 0.02.  Insulated sandstone has a TC of 0.029.  By comparison, insulated Ceramic has a TC of 0.006.  This means that insulated ceramic will transfer only 30% of the thermal energy that insulated igneous will.  This will have a substantial effect on how much the temperature of your LOX changes while it is in the pipe.
  2. The LOX isn't moving, or has to travel a large distance.

Lets take some examples.  First, assume you just built a ceramic pipe segment and the ceramic was at the temperature of your base: 24 C.  Lets also assume that your LOX is at -200 C, giving a decent split between gas and solid forms.  This is a temperature delta of 224 C.  This gives the ceramic pipe segment a positive energy difference of about 75 million DTU (will be relevant later).  Assuming that a single segment of pipe is 1m, and you're transferring 10kg/s of LOX through the pipe, a ceramic pipe can transfer only 1.344 watts/s to the LOX.  This will change the LOX temperature by 0.00014 C/s.  Which is perhaps nothing at all as long as the liquid keeps moving.  Running the same scenario with insulated igneous gives an energy difference of 89.6 million DTU and a transfer rate of 44.8 watts/s.  This can change the temperature of the LOX by 0.005 C/s. Again, not a lot, but you will start to see a slow change in the temperature of the LOX as it passes through the pipe.

If the LOX isn't flowing, on the other hand, the LOX in the igneous will warm up 35 times faster than LOX in a ceramic pipe.  This can be significant, because the igneous can transfer a total of almost 90 million DTU to the LOX, while ceramic can only potentially transfer 75 million.  10kg of LOX has a thermal capacity of 10100 DTU/C.  At 44.8 watts/s, your LOX will raise 1C every 225s.  Meanwhile you will not notice an obvious change in the igneous pipe temperature because it will take almost 9000 seconds to lose enough thermal energy to drop in temperature by 1 C.  In a ceramic pipe, on the other hand, your LOX will only increase by 1 C after 7515 seconds.

Now lets look at the thermal capacities.  Insulated pipes have 400kg of material and carry 10kg/s of liquid.  Even if the thermal capacities of LOX and your pipe were identical, this gives the pipe 40 times the energy difference per degree C simply because of the mass.  If all things were equal, your LOX would raise by 40C every time your pipe drops by 1C until equilibrium is reached.  In actuality, insulated Ceramic pipes have 33 times more thermal energy per degree C while insulated igneous pipes have 39.6 times more.  Since there's a temperature delta of 224 C, there's millions of available DTU that can be transferred into the LOX, provided there is time to do so. 

If your pipe's building materials are 100 C instead of 24 C, this increases the total available energy that can be transferred to the LOX and may make it appear that your LOX is being heated by the pipe without appearing to change the pipe's temperature.  For the purposes of this document I'm ignoring the maximum and minimum transfer rates that are calculated by the thermal deltas.  For example, if your ceramic pipe segment is at -100 C, it is highly unlikely that the LOX temperature will be affected, as the transfer rate will be too low and will round down to zero -- even if the liquid isn't circulating.

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KittenIsAGeek    1459
18 minutes ago, caffeinated21 said:

I’m sure your math adds up but I can tell you in-game the temps change faster then you predict. 

I agree.  For example, I'm fairly certain that a single pipe segment isn't 1m of area for the purposes of thermal transfer.  There are also hidden factors based on how the energy is being transferred, and there are min/max qualifiers for transfer. 

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Yoma_Nosme    480

In case nobody has mentioned, pipe bridges(connected with pipe,ofc)!

On the same length they have only 50% of the pipe so to say...meaning you get them down to temperature faster...

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SkunkMaster    226

The most easy way to pump lox / lh2 is by pumping it at 1kg/s or less.

Make sure it never backs up, with a backloop or overflow output.

 

You can use any kind of pipe with this kinda plumbing. 

 

Second solution is using insulated insulation pipes.

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psusi    245
6 hours ago, SkunkMaster said:

The most easy way to pump lox / lh2 is by pumping it at 1kg/s or less.

Nope; I said that was the first thing I tried and it heated to boiling before reaching the rocket and wouldn't even enter the rocket.  Using the full 10 kg packets is working.

7 hours ago, Yoma_Nosme said:

In case nobody has mentioned, pipe bridges(connected with pipe,ofc)!

On the same length they have only 50% of the pipe so to say...meaning you get them down to temperature faster...

Yep; I've been adding more bridges, especially close to the rocket for this reason.

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SkunkMaster    226
2 minutes ago, psusi said:

Nope; I said that was the first thing I tried and it heated to boiling before reaching the rocket and wouldn't even enter the rocket.  Using the full 10 kg packets is working.

1kg, not 1.5kg, or so. it HAS to be 1kg at most.. it wont break the pipes ;) 100% guaranteed.

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psusi    245
11 minutes ago, SkunkMaster said:

1kg, not 1.5kg, or so. it HAS to be 1kg at most.. it wont break the pipes ;) 100% guaranteed.

Yes, 1kg does not break the pipes, but the LOX heats up much faster and like I said, won't enter the rocket once it's over -180.

 

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SkunkMaster    226
Just now, psusi said:

Yes, 1kg does not break the pipes, but the LOX heats up much faster and like I said, won't enter the rocket once it's over -180.

 

I've never had problems with lox entering the rocket, no matter the temp. - That might've been changed, but eh, i doubt it ? 

 

You're certain it's not just hitting the limit or something ? 

 

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psusi    245

I've since noticed that while the rocket launches fine while entombed by falling regolith, the fuel tanks won't load, so maybe that is what was going on.  Either way, 10 kg works and is much faster ;)

 

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