Cryogenic Vessel Design Tips
Cryogenic Vessel Design Tips
(OP)
Hi All
I'm designing an LNG vessel as an onboard fuel supply for natural gas powered trucks.
First prototype is performing ok but there is plenty of room for improvement. Mainly excessive heat inleak throught the feedthroughs and inner vessel supports.
Incidentally it's insulated with 3M glass microspheres + 10 micron vacuum. This seems to be performing well but MLI seems to be the way to go.
Any tips or pointers toward books or papers on the subject would be appreciated.
Cheers
elbrownos
I'm designing an LNG vessel as an onboard fuel supply for natural gas powered trucks.
First prototype is performing ok but there is plenty of room for improvement. Mainly excessive heat inleak throught the feedthroughs and inner vessel supports.
Incidentally it's insulated with 3M glass microspheres + 10 micron vacuum. This seems to be performing well but MLI seems to be the way to go.
Any tips or pointers toward books or papers on the subject would be appreciated.
Cheers
elbrownos





RE: Cryogenic Vessel Design Tips
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Bottom line, the design of inner vessel supports can be done using basic principals, such as by calculating the thermal conductivity through supports assuming the inner surface is at low temperature, the outer surface is at ambient temperature, and there is a thermal gradient between with no other heat transfer (such as convective heat transfer) off the sides of the support. Note that the thermal conductivity of most materials varies considerably depending on temperature, so I would suggest getting real properties data for thermal conductivity for the supports you use from NIST.
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More later if you're interested......
RE: Cryogenic Vessel Design Tips
That's the problem I'm finding - nobody wants to give away their secrets.
The book looks good, I've just ordered it.
The tank is around 27" OD so there isn't enough room in the vacuum space to do anything complicated.
Mind if I ask what your experience in this is?
RE: Cryogenic Vessel Design Tips
RE: Cryogenic Vessel Design Tips
RE: Cryogenic Vessel Design Tips
If MLI isn't used, perlite is the next best material. The only issue with Perlite is that as the vessel shrinks and expands (which it generally does to some degree, not to mention some motion caused by this being on a truck) the perlite will crush and end up as a powder at the bottom of the annular space leaving a hole at the top. This also effectively becomes 'concrete' which will damage piping in the annular space.
For a tank like this, MLI is the only reasonable material to use.
RE: Cryogenic Vessel Design Tips
My problem with MLI is that all information about its application is proprietary.
http://www
RE: Cryogenic Vessel Design Tips
RE: Cryogenic Vessel Design Tips
For me they are great because I can concentrate on the vessel design without worrying about how to wrap MLI. Down the road I will squeeze that extra bit of performance by exploring MLI.
I have a vacuum gauge on the prototype vessel so if there was a degradation of vacuum I would know about it.
RE: Cryogenic Vessel Design Tips
RE: Cryogenic Vessel Design Tips
RE: Cryogenic Vessel Design Tips
They also reference some testing done and a patent. I'd be interested in seeing what testing they've done. I don't see anything on their web site.
After giving it some thought, I could see how spheres might provide a bit more 'flow' inside the annular space due to their spherical nature when compared to perlite which is relatively jagged and tends to create 'shear stresses' between particles when they need to flow, or move about, in the annular space. Most of your large, cryogenic tanks today use perlite. Those that don't use MLI, mostly on hydrogen and always on helium tanks. I've not heard of microspheres being used in general industry. It's obviously very new but probably also limited to aerospace at the moment.
One other thing you might consider to reduce heat leak if you really need to do so would be to add a shield which can reduce heat leak by a factor of 10.
RE: Cryogenic Vessel Design Tips
What pump out port are you using? Have you verified it can handle significant amounts of vibration? We've found many off the shelf units leak under vibration and have designed our own for use in portable equipment. I've also seen pump out ports with pipe thread on the vacuum side for the thermocouple gage tube. Those pipe threads are also prone to leakage.
RE: Cryogenic Vessel Design Tips
I couldn't get it below 80 microns warm so clearly there was water vapour which is now frozen. I thought this might be an issue with the microspheres as they were sitting around in our store for a few months unsealed.
I'm using a Cryocomp V1000 port as found on Chart LNG tanks, with a 1/8" NPT side port for the vacuum gauge.
The microspheres do flow quite easily, especially when excited by a pneumatic vibrator. They also turn to smoke so you need a sealed system for handling them.
When you say shield, do you mean a vapour cooled shield?
It looks very effective but perhaps not feasible for a small tank.
Barron's arrived and looks very useful.
There's a list of reports linked at the bottom of that webpage.
Have you got any experience with getters?
RE: Cryogenic Vessel Design Tips
RE: Cryogenic Vessel Design Tips
Regarding shield, yes a shield that uses the LNG taken out of the tank, be it gasseous or liquid. It would be expensive to integrate into the design I know, so that's the trade off.
Regarding getters, I'm not that familiar with the various types. As Compositpro mentions, the inner vessel will do a great job pulling any water out.
One other tip is to heat the inner and outer vessels when pulling a vacuum, preferably around 150 to 200 F to help get the water molecules out.
RE: Cryogenic Vessel Design Tips
Are there problems with corrosion when the gases leak out?
Aerogel beads might work.
RE: Cryogenic Vessel Design Tips
Due to the small size of the vessel (approx 1" vacuum space) there is no room to do anything intricate.
RE: Cryogenic Vessel Design Tips
The boiloff is around 5% per day, corresponding to around 20 watts of heat inleak.
What's a good target, 1 or 2% per day?
Level measurement is another challenge. Capacitance gauges seem to be popular but thermally I can't think of a good way to install one.
RE: Cryogenic Vessel Design Tips
You might want to see what liquid cylinder manufacturers use for a level sensor. Basically, it's a spring loaded float. Here's a web site for example:
http://