Issue with Liquid Hydrogen

[Nedix]

Hello all,

I have a problem with liquid hydrogen distribution and I can't seem to pin it down. I've built the small O2H2 maker this time, I usually build the big one with the buffer tanks inside the chambers. With the small one, at least for the liquid hydrogen I always get cracked pipes randomly when I fuel the rockets or when it is simply recirculating. I've tried even building the pipes out of insulation, and I had to do it at least on the right hand side; I assumed it is because there are still traces of polluted oxygen and perhaps there is a heat exchange between the pipes and the surroundings. All the other pipes are ceramic.

Liquid oxygen works perfectly fine, no cracked pipes with or without the buffer tank.

Has anyone encounter this?

[Yoma_Nosme]

Some advices.

Use more bridges if you like they don't heat up...so no cold loss in them...if you use pipe-bridge-pipe and so on you half the amount of possible breaks...but it's not perfect either

Radiant pipes get cold faster so you have some breaking but when they reach equilibrium temp you've made it.

Cool the hydrogen more...the colder it is when you pump it the more overhead you have till it warms up and change from liquid to gas.

Start with 1000g at first till your radiant pipes reach equilibrium then open the valve to full capacity. 1000g packets won't break your pipes.

Edit.  Radiant pipes have to be in vacuum for them to work best so they don't leak cold to the gas around 

[Nedix]

Radiant or insulated? I either misunderstand what you are saying or ...

I will try to limit the output and see the result. Thanks.

[nakomaru]

If you used insulated insulation pipes, the only reason is because you are sending boiling hydrogen in. The obvious location I see it boiling is inside your liquid reservoir in exchange with the insulated tile below.

You can build the reservoir on top of mesh or airflow tiles in a vacuum to perfectly insulate your reservoir.

[suxkar]

Building a reservoir for the supercoolant right before the piping goes inside the hydrogen chamber will help you equalize the temperature, otherwise you might end up with solid hydrogen since the liquid phase has a very limited range. As nakomaru said, reservoirs need to be built on top of mesh/airflow tiles otherwise the content will exchange heat with the tile as if it was debris. Even insulated tiles will incur in such exchange, which cannot be allowed with liquid hydrogen since, again, it stays liquid only in a 5 degree range.
Mesh/airflow tiles are perfect insulation because they transfer heat as if they were made of the medium they contain, which means that if they are in vacuum they do not exchange heat, but, in your case, since you have gas wondering (see next paragraph) around, they would still allow it.
The main problem you are experiencing is I believe the fact that part of your setup does not have space exposure. Any leak in the pipes resuls in hydrogen/oxygen evaporating and remaining in non space exposed tiles, facilitating heat exchange. The amount is very tiny and still decreases over time, but very slowly (it's an annoying situation with environments that are part space and part not). Normally the heat exchange would be negligible but in the case of liquid hydrogen the huge temperature differential will still cause damage.
So unless you wait for any gas to dissipate from the right side area and avoid any further incident, or just build everything with insulation, the problem will keep on coming back, it's a circle: gas causes pipes to break, more gas is leaked, which exchanges heat with the environment and causes more pipes to break and so on.
Another solution, which I you personally suggest, is to just move everything to a location that is entirely exposed to space and start again.

[TheMule]

Quote

Radiant or insulated?

 

Radiant. Lead or gold possibly. They have the lowest SHC.

The idea is that initially hydrogen exchanges heat with the pipe itself, cooling them down. Eventually it evaporates and breaks the pipe.

So, you need:
1) to pre cool the pipes with supercoolant, or

2) limit the amount of heat hydrogen needs to cool down the pipes (using low SHC materials) and/or

3) increase the capacity of hydrogen to receive it w/o evaporating (use lower temp) and/or

4) reduce the amount of piping segments (using bridges)

@Nedix is suggesting 2), 3) and 4). 

Ceramic doesn't work too well because it transfers small amounts of heat but it has also a lot of heat to tranfer because of high SHC,

 

Still radiant pipe is limited to vacuumed areas strictly. You need ceramic / insulation for the silos.

[Gurgel]

I have never had any problems with insulated ceramic pipes and liquid Hydrogen. The trick is to make it cold enough. It should at least be 2C or so below vaporization as it always will heat up a bit, depending on pipe length. That does require more precise regulation than with Oxygen though.

[psusi]

7 hours ago, nakomaru said:

If you used insulated insulation pipes, the only reason is because you are sending boiling hydrogen in. The obvious location I see it boiling is inside your liquid reservoir in exchange with the insulated tile below.

You can build the reservoir on top of mesh or airflow tiles in a vacuum to perfectly insulate your reservoir.

He isn't storing the hydrogen in a reservoir.

4 hours ago, Gurgel said:

I have never had any problems with insulated ceramic pipes and liquid Hydrogen. The trick is to make it cold enough. It should at least be 2C or so below vaporization as it always will heat up a bit, depending on pipe length. That does require more precise regulation than with Oxygen though.

The trick is keeping the pipe short enough, so either only pump the hydrogen a very short distance, or replace half the pipe segments with bridges.  I want to say the distance is around 50 or 60 pipe segments at which the hydrogen will boil.

[Gurgel]

14 hours ago, psusi said:

The trick is keeping the pipe short enough, so either only pump the hydrogen a very short distance, or replace half the pipe segments with bridges.  I want to say the distance is around 50 or 60 pipe segments at which the hydrogen will boil.

Yes. The problem is that you can cool liquid Hydrogen only a few C below its vaporization point.

[Nedix]

I've built the hydrogen maker in another spot where it was complete vacuum and I even used a ton of bridges but the problem is still there: I can't transport max liquid hydrogen in the pipes, they eventually break. I even cooled the liquid hydrogen to -260 deg and still the same. I gave up and limited the flow to 1kg/s it seems this is the only way.

 

PS: the liquid oxygen is working absolutely fine with a 10kg/s flow

[beowulf2010]

Once the pipes come to temperature, the issue will go away. So, the best thing to do is use radiant pipes in a vacuum so that they come down to temperature quickly allowing you to move up from 1kg/s flow much sooner. 

Insulated pipes give you the most problems due to the mass and "insulated" property. 

[Nedix]

Thanks for the tip, I started to gradually replace the pipes with radiant in vacuum. They immediately become damaged but in a couple of ticks they reach the cooled temperature and they pretty much stay there.

Just a side question - I'd like to avoid living this - will replacing the pipes with radiant in the path of the rockets' exhaust will cause burst damage (via heating the liquid hydrogen)?

[psusi]

1 hour ago, beowulf2010 said:

Once the pipes come to temperature, the issue will go away.

If they are insulated, they will never come to temperature.  Well, maybe if you give it 1,000 cycles.  On the other hand, being insulated they exchange rather little heat with the contents.  Radiant pipes also can't be used near the rocket or the exhaust will get them very hot, very quickly.

[beowulf2010]

1 hour ago, psusi said:

If they are insulated, they will never come to temperature.  Well, maybe if you give it 1,000 cycles. 

Which is why he was having the breakage issues. 

It's easy enough to avoid the rocket heat column with the piping to fill the tanks so I don't see the issue with using radiant in a vacuum walled off from the actual silo with short filling branches that are controlled by valves so that they're empty when not being used. 

[psusi]

4 hours ago, beowulf2010 said:

It's easy enough to avoid the rocket heat column with the piping to fill the tanks so I don't see the issue with using radiant in a vacuum walled off from the actual silo with short filling branches that are controlled by valves so that they're empty when not being used. 

You mean just let the section of pipe close to the rocket get hot when it launches and lands, and then use a valve to limit the flow when you start filling to cool down the pipe again, every time you launch?  That seems annoying.  I'll just stick with insulated pipes and not worry about it since it seems to work just fine.

[beowulf2010]

2 hours ago, psusi said:

You mean just let the section of pipe close to the rocket get hot when it launches and lands, and then use a valve to limit the flow when you start filling to cool down the pipe again, every time you launch?  That seems annoying.  I'll just stick with insulated pipes and not worry about it since it seems to work just fine.

No, I mean have a full recirculation loop outside the hot area with shutoffs leading to feeder lines as short as possible made from either normal or radiant pipes and bridges. 

[nakomaru]

It's been stated, but to clarify, only insulated pipes made of insulation will never break or transfer any heat, unless you pump boiling hydrogen through. Ceramic will easily transfer heat and boil hydrogen, unless it stays moving and is well enough below boiling.

[Nedix]

That's the thing that puzzles me. Even if I cool the liquid hydrogen around -255-257 degrees and continuously circulate it through the pipes it still warms up and breaks the pipes if it's more than 1kg/s packets.

[KittenIsAGeek]

I don't know what your insulated pipes are made of, but the only two materials I've used successfully for piping liquid hydrogen is ceramic and Insulation.  However, with large temperature differentials, ceramic will still exchange heat energy with your hydrogen, warming it slightly.

The only method for piping it that has worked consistently for me is to use a recirculating pipe.  When the tank is full, the pump shuts off and the excess liquid hydrogen flows back into storage.  Any hydrogen that sits in pipes will evaporate, breaking the pipe, so it needs to flow back into storage where it can be re-cooled to temperature.

 

[nakomaru]

6 hours ago, Nedix said:

Even if I cool the liquid hydrogen around -255-257 degrees and continuously circulate it through the pipes it still warms up and breaks the pipes

It can happen in normal play with ceramic even when recirculating, especially because pumps can send 2kg packets when starting or stopping, which have much less thermal capacity and heat up faster. You can use a shutoff in your LH2 room to guarantee 10kg packets go through, and set your tank to a multiple of 10kg.

[psusi]

9 hours ago, beowulf2010 said:

No, I mean have a full recirculation loop outside the hot area with shutoffs leading to feeder lines as short as possible made from either normal or radiant pipes and bridges. 

If the "feeder lines" as you call them are made out of radiant pipes as well, then why even treat them as separate from the main line?  In other words, that sounds exactly like what I was saying in that you have radiant pipes that get hot at launch and have to be cooled again with a restricted flow, except for the part that you say to keep the full flow going until you get close to the heat, then restrict it, instead of just keeping the whole thing restricted.  I don't see what you gain by doing that.

9 hours ago, nakomaru said:

It's been stated, but to clarify, only insulated pipes made of insulation will never break or transfer any heat, unless you pump boiling hydrogen through. Ceramic will easily transfer heat and boil hydrogen, unless it stays moving and is well enough below boiling.

Yes, it needs to stay moving in ceramic pipes, but even then, it can only move through around 50 pipe segments before it boils.

7 hours ago, Nedix said:

That's the thing that puzzles me. Even if I cool the liquid hydrogen around -255-257 degrees and continuously circulate it through the pipes it still warms up and breaks the pipes if it's more than 1kg/s packets.

Are you using the full 10 kg or somewhere between?  With the full 10 kg, it will heat up more slowly and should be able to make it through about 50 segments of ceramic insulated pipe.

1 hour ago, nakomaru said:

It can happen in normal play with ceramic even when recirculating, especially because pumps can send 2kg packets when starting or stopping, which have much less thermal capacity and heat up faster. You can use a shutoff in your LH2 room to guarantee 10kg packets go through, and set your tank to a multiple of 10kg.

I used a power shutoff to kill the pump and it never produced a < 10kg packet.

[nakomaru]

2 hours ago, psusi said:

I used a power shutoff to kill the pump and it never produced a < 10kg packet.

You can guarantee it with a liquid shutoff, or you can not pay attention. The choice is yours.

[Nedix]

There could be another thing. I never had a major surplus of liquid hydrogen in the production chamber. I did have enough to load the loop but not too much buffer so I'm thinking that even if the initial batch gets out at -255 and gets recirculated, starting with the fourth ('ish) the hydrogen is not that cool anymore. I'm waiting now to produce more and then do some other runs.

The current production loop looks something like this (with the hydrogen on the right hand side):

[Nitroturtle]

I would suggest crossing your bunker walls using bridges.  Even in insulated pipe, you'll get some heat transfer from the wall which is typically very hot.  Using a bridge to cross the wall eliminates this issue.

[Nedix]

I thought of that but surprisingly that's not where I lose chill. The biggest loss happens between the 1st and 2nd H2 line in the area of the left rocket. I will have to move all the bridges one square down so I can make room for a cross bridge.