Liquid Nitrogen Vaporizer Design
Liquid Nitrogen Vaporizer Design
(OP)
Hello,
Does anyone have experience on designing vaporizers for cryogenic applications?
I'll be using fin tubes, on the input I have liquid nitrogen at -196°C and on the output I want gaseous nitrogen somewhere between 10 to 20°C.
The mass flow is known as it is pumped by a cryogenic pump, and the pressure on the output side is going to range from 0 to 220 bar as it is used for cylinder filling.
One thing to remember is the formation of ice on it, prejudicing the heat exchange, is there any rule of thumb to deal with that?
Thank you a lot for any inputs.
Does anyone have experience on designing vaporizers for cryogenic applications?
I'll be using fin tubes, on the input I have liquid nitrogen at -196°C and on the output I want gaseous nitrogen somewhere between 10 to 20°C.
The mass flow is known as it is pumped by a cryogenic pump, and the pressure on the output side is going to range from 0 to 220 bar as it is used for cylinder filling.
One thing to remember is the formation of ice on it, prejudicing the heat exchange, is there any rule of thumb to deal with that?
Thank you a lot for any inputs.





RE: Liquid Nitrogen Vaporizer Design
RE: Liquid Nitrogen Vaporizer Design
The oversizing is a bit of an art, but there are general rules that work well.
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P.E. Metallurgy, Plymouth Tube
RE: Liquid Nitrogen Vaporizer Design
Thank you a lot for the answers. I am aware this is a fairly standard product and we even got a few on our plant, I also hame some drawings of them on certain models, my goal is improving my understanding about the subject, so I'm more interested in learning rather than getting one.
If someone could help on that I'd aprecciate.
RE: Liquid Nitrogen Vaporizer Design
Their main advantage is that they are using essentially "free energy" for vaporisation, with little to no operating costs. You may need to remove ice manually if in a persistently cold region, but with your outlet temperature requirements, I suspect not.
Speaking of which, an outlet temperature of 10 to 20 degC is unlikely to happen unless you are in a very warm climate, or have an additional heater downstream of the vaporiser,. You are relying on ambient weather for your heat input - if the weather outside is 5degC, then your outlet temperature can't be above this. You can have a good approach temperature, but with the ice growth it will eventually widen over time. It's why you would typically aim for a specific approach temperature after a given period of time. A brochure would normally have a model, its nominal capacity for a given fluid, which is based on a run time, fixed weather conditions and an approximate approach temperature.
For cylinder filling though, you don't really want a warm gas outlet though as the cylinder may get too hot...
RE: Liquid Nitrogen Vaporizer Design
Thank you a lot for your inputs, I agree with everything you said. Btw, in the region I live the mean temperature is around 25C throughout the entire year :)
What I thought was using some proportion between the length of the tubes and their nominal capacity, and stabilish a relation to use on new projects, say I need to double the nominal capacity I'd simply double the length, some like a reverse engineering situation. What do you think?
Also, considering a simple model (ignoring ice formation), I could only calculate the energy flow required to vaporize and heat all the liquid nitrogen, and then calculate the equivalent length using basic heat transfer theory and apply some design factors to take into account the simplifications, do you think it is suitable?
RE: Liquid Nitrogen Vaporizer Design
RE: Liquid Nitrogen Vaporizer Design
RE: Liquid Nitrogen Vaporizer Design
There used to a guide published by Air Products that gave a general sizing method. I would assume that other bulk gas suppliers have similar references.
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P.E. Metallurgy, Plymouth Tube
RE: Liquid Nitrogen Vaporizer Design
RE: Liquid Nitrogen Vaporizer Design
RE: Liquid Nitrogen Vaporizer Design
In theory it is possible, but the size of the ambient vaporiser to do that would be monstrous. I've read about ambient vaporisers with insulation around a stainless steel liner to achieve this, but all it is doing is adding an additional layer of resistance. Icing is not a bad thing on an ambient, it just shows that the unit is working! With cylinder filling, it is intermittent use typically depending on the size of the buffer vessel. The reciprocating pump would run for a fixed period time, say 10 - 15 minutes, then shut off for 10 minutes or so while the gas in the buffer is being used. In a place where it is averages 25 degC ambient temperature, with this sort of operation any ice formation that does occur would just melt off quickly. The fouling would be more like fresh fluffy snow, rather than hard ice. As long as they have drainage under the vaporiser, there shouldn't be any concerns over small amounts of icing.
RE: Liquid Nitrogen Vaporizer Design
Ours often ice ~40% of the way if we go to full flow on a nice hot humid day. They are sized for that.
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P.E. Metallurgy, Plymouth Tube
RE: Liquid Nitrogen Vaporizer Design
RE: Liquid Nitrogen Vaporizer Design
RE: Liquid Nitrogen Vaporizer Design
RE: Liquid Nitrogen Vaporizer Design