So for awhile now we have been needing a more manageable LN2 solution. Our large 180L tanks just don't cut it for portability so we decided to build this smaller guy. Now we're able to fill this guy off our larger tanks and basically take it anywhere! ROCK ON! Also makes for easy testing of cooling systems since its easier to move and able to fit into smaller spaces. We built almost everything you see with the exception ofcourse being the actual vacuum tank. The tank is a simple vacuum jacketed 50L system with a NW-50 on top. The tank was of course cleaned up and refinished as I do with all old equipment I purchase. Everything else is brand new and/or custom. I built the custom cover on the bottom. It serves several purposes. It's a load bearing system on the inside made up of several crossing straps that terminate at load bearing welded D rings around the perimeter. This gives us additional securing options when traveling. The cover is also made of a tough cross weaved vinyl with an inner padding so the tank can be banged around a bit and wont be damaged. There is also a matching dolly so the tank can be moved around easily when full. Lastly, we had custom decals printed so everything matched and so everything was a little tougher when exposed to the cold from drips and condensate.
For the withdraw system, we're currently using a pressure reinforced NW-50 ring and a custom machined cap to interface with the tank. I designed in both a gas and liquid withdraw system as well as two separate pressure reliefs, gauge, and pressure building circuit similar to full sized vessels. Currently we have engineered the pressure vessel with a FoS of 3.0 but we're still making a few adjustments and tweaking the design. As you can tell, everything was done with Swagelok which is great, but as most of you know is SUPER expensive. Its funny. This all started when we decided we didn't want to pay $1000+ for a LN2 withdraw system made with crappy parts from the plumbing aisle of your local hardware store (Seriously, go look at the commercial offerings). We therefore resolved to instead build it ourselves out of higher grade materials. Ultimately though, with all the additions, and design changes it ended up costing way more haha. There's your text book example of scope creep for the day! All in all, I'm still very happy. The only thing that we still nervously chuckle at is the fact that we intentionally designed in valves not rated for cryogenic use... Yes yes, I know... This was decided because it was just a quick simple build, and the tank has a really short duty cycle. The valves so far are holding up really well. We're keeping our eyes on them though lol. To Cristen the new "fun" tank (as we're calling it), we chilled some celebratory adult beverages. Cheers!
WARNING Please be smart with LN2! Cryogenic burns are no laughing matter. Beyond the visible hazards are the invisible ones. Liquid nitrogen has about a 1:695 expansion ratio! Oxygen depleted atmospheres are a very real threat when dealing with large quantities of LN2. You are generally safe yourself with small tanks but do also consider mans best friend closer to the ground! Ventilation is a must! Most people that survive in larger accidents, claim to have felt like nothing was wrong just before passing out. They felt they were breathing just fine! If you use larger tanks. Do yourself a favor. Install an oxygen monitoring system. Yes they are expensive... We use both a wall mounted unit and disposable personal versions. What price do you put on your life? Just be smart. Use gear rated for cryogenic use! Ventilation! Pressure reliefs + backups on all tanks (Never completely seal a LN2 tank)! Proper signage and O2 monitors if work space warrants it. This is a VERY brief overview. Go do your research and check out the MSDS on LN2 before having fun yourself.
More pictures in a directly following post...
- Extremely rough concepts on the "think bench" using spare parts in stock just to brainstorm.
- Initial CAD concepts of what we played with on the "think bench".
- Close up of NW-50 port before refinishing.
- Top of tank after media blasting exterior.
- Another view of tank after media blasting.
- View of side vacuum port after media blasting tank exterior.
- Tank getting its new paint job.
- Initial non matching snowflake decal.
- Initial school bus yellow decal.
- Partial CAD view. I removed all the valves and other Swagelok for a clear view of the custom machined NW50 blank.
- Transparent view to reveal the over pressure ring.
- Sectional view of the primary parts.
- Exploded view of the primary parts.
- First test fit of new copper vaporizer. This just goes to show that copper work is possible if you have enough patience. In addition to very slowly coiling this around a form, I made use of a technique developed by brass instrument makers. For the critical bends, water was frozen into the lines before bending to discourage crimping. I wish I had worked the initial loop a little more at the top but overall I am very satisfied with the results. Outside of a few small scale tests to determine maximum bend radius both frozen and unfrozen, this was a first attempt success.
- Partially compete. Still lots of Swagelok to design in and purchase... $$$
- Partially compete. Still lots of Swagelok to design in and purchase... $$$
- Custom made decals designed to match the yellow webbing in the case. The standard decals just looked terrible and nothing matched so I decided to go back to the drawing board. All decals were built from scratch using Adobe Illustrator (Vector art compatibility) for printing by the local sign shop.
- Ratcheting strap that feeds through the loops under the D rings as additional option for securing the tank while transporting.
- Heavy duty welded D rings around the perimeter of the case. Can be used as tie downs, for lifting, etc.
- Custom load bearing case built out of an inner crisscross webbing system with a free floating outer vinyl shell for abrasion resistance.