Liquid Nitrogen Piping
Liquid Nitrogen Piping
(OP)
I have no experience with cryogenic piping, but need to quickly design a 50' liquid N2 run that will feed an environmental chamber for low temperature product testing. The line will be valved off for weeks at a time when this low temperature test is not taking place.
My question is this - what design provisions should I make to handle the rapid cooldown of the pipeline when the valve is opened, and the resulting pressure spike from the flashing liquid? Are relief valves enough?
---KenRad
My question is this - what design provisions should I make to handle the rapid cooldown of the pipeline when the valve is opened, and the resulting pressure spike from the flashing liquid? Are relief valves enough?
---KenRad





RE: Liquid Nitrogen Piping
"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.
http://www.youtube.com/watch?v=hpiIWMWWVco
"Being GREEN isn't easy." Kermit
http://virtualpipeline.spaces.live.com
RE: Liquid Nitrogen Piping
You probably want to fence it or otherwise restrict personnel access. ... but beware of confined space/ inert atmosphere hazards too.
Speaking of which, that hazard also exists for whatever boils off in/on/around the environmental chamber. Could you possibly use CO2 instead of N2?
I'd use flange guards to limit collateral damage from flange leaks, which are inevitable, given the transients.
Are you sure you can't afford/get mechanical refrigeration equipment? I ask because I have used CO2 for cooling a small environmental chamber, and quickly tired of lugging bottles around. Even with big dewars, handling all the evaporative refrigerant is a cost.
Or maybe you have a central LN2 supply, and just want to tap off a bit once in a while. If your outfit is that big, your safety/ environmental guys will want to be in on your project from the beginning, and they will have a _lot_ to say about your piping design.
Mike Halloran
Pembroke Pines, FL, USA
RE: Liquid Nitrogen Piping
When opening a valve to this line, you won't build up pressure, so pressure spikes aren't an issue. As the liquid flashes on the hot surface, any excess pressure just pushes the liquid back toward the source so you typically get a pulsing effect. You'll hear the flow rise and fall as some liquid goes in, flashes off, and flow temporarily stops or reverses.
To size thermal relief valves, assume the line is full of liquid (100% vapor fraction), the valves are shut, and you have a heat leak of at least 0.25 Btu/ft2-s. This is a nominal heat leak value, so I'd suggest doubling to provide a factor of safety.
RE: Liquid Nitrogen Piping
iainuts - Thanks; I hadn't even thought of the fact that the pressure buildup from flashing will just push the liquid back into the storage vessel when the valve is opened. So relief sizing would be only based on the flashing of liquid trapped between shut valves.
So after the line is cooled down, the rate of flashing will be reduced to what occurs from ambient heat gain through the insulation. To ensure that my process user is only getting liquid, I suppose that I will need some kind of vapor vent near the point of use. Any recommendations on manufacturers of these?
---KenRad
RE: Liquid Nitrogen Piping
Old guy story- I have seen rupture of a several mile long pipeline when purged with liquid N with the end open,
due to overpressure by rapid vaporization. Liquid CO2 pipeline is a whole different story.
RE: Liquid Nitrogen Piping
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You might also contact ACME Cryogenics, Technifab or Cryolab. Note these companies may not advertise these things on their web site but you can ask and at least get some leads. I'm sure there are others.
http://www.acmecryo.com/
http://www.technifab.com/
http://www.cryofab.com/
RE: Liquid Nitrogen Piping