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The liquid nitrogen heat exchanger for the butane flood line.
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well... ive no experiance, and i certainly have nothing running....
but since noone else is comenting... ill tell you that the obivious way to move nitrogen about from dewar to dewar atleast, is to simply thread a dip tube in, and pump nitrogen gas from a compressed cylinder such that the nitrogen fluid is forced out.
regarding the heat exchangers... you might look up lytron. they make all sorts of cryogenic heat exchangers for all sorts of equipment. biggest issue i recall reading about is moisture fouling in these sorts of heat exchangers.
any moisture will clog small orifices, and can lead to poor flow rate or even explosions in extreme cases. i read about a million dollar NMR exploding in some canadian university when moisture blocked some sort of helium expansion valve.
but since noone else is comenting... ill tell you that the obivious way to move nitrogen about from dewar to dewar atleast, is to simply thread a dip tube in, and pump nitrogen gas from a compressed cylinder such that the nitrogen fluid is forced out.
regarding the heat exchangers... you might look up lytron. they make all sorts of cryogenic heat exchangers for all sorts of equipment. biggest issue i recall reading about is moisture fouling in these sorts of heat exchangers.
any moisture will clog small orifices, and can lead to poor flow rate or even explosions in extreme cases. i read about a million dollar NMR exploding in some canadian university when moisture blocked some sort of helium expansion valve.
Our reverse flow exchanger is en-route, so any day now.
No need to pump liquid N2. If you get a liquid Dewar with a dip tube, and a 250 psi pressure relief to atmosphere, you have both a limited amount of vapor (without heat) and a 250 psi pressure head to force the liquid N2 up the dip tube and through a heat exchanger.
If you need loads of vapor, you would use the liquid and a vaporizer to convert the liquid to a gas at your flow rates.
The best alloy for cryogenic application is 300 series austenitic stainless, and the 3/8" tubing and fittings that we are experimenting with has an ASME rated burst above 3,000 psi psi, which means actual burst is above 9,000 psi.
Here is a good link on Parker tubing and fittings, with charts and explanations:
http://www.parker.com/literature/Instrumentation%20Products%20Division%20Europe/CTS%20TECH%20GUIDE%20BOOK.pdf
The biggest bugaboos that we've found thus far, is that butane gets thicker as the temperature drops and water content can turn to slush in the lines, elevating the heat exchanger pressure.
The limitation on that side of the heat exchanger is the high pressure shut off on the pumps, so should never reach more than
those limits.
Pressure can be relieved some by using larger diameter tubing and more time, but there are practical limits.
Water must be drained regularly and kept low to operate at around -30C, so that needs to be added to the start up ritual, as does the regular replacement of an over sized filter drier after the recovery pump.
My latest design for WolfWurx, relocates the 1/2" X 9" filter drier to a position after the heat exchanger, but installs a water trap between it and the heat exchanger. It should catch most of the condensed liquid before it reaches the drier/filter.
It and the counterflow heat exchanger are scheduled to go on WolfWurx's original automated Mk VA, supplied to a willing friend at material and outside labor cost, which he affectionately named "Beta Bitch." She is returning from two seasons of So Or beta testing and for both the VA2 and the latest VA3 upgrades to beta test. It will include thermocouples at the injection port and drier to more precisely keep track of temperatures.
You can also get larger tank valves. WolfWurx is currently using Manchester 100# tanks with 3/4" valves and fittings, instead of the standard 1/4", which offers even more relief.
Skunk Pharm Research's experiments chilling the tank directly using a liquid N2 coil wrapped around an insulated tank, quickly turned the contents of our tank to jello, thus our high hopes move to a counter flow heat exchanger.
Cooling after recovery is another issue, and while WolfWurx is currently using a three coil hybrid heat exchanger, suitable with either DI/alcohol or N2/alcohol, if you were using only liquid N2, you could use counter flow heat exchangers there as well, and greatly reduce the bulk of the system.
While we are discussing liquid N2 as a refrigerant, it only reduces the surface area and time needed to drop the temperature to close to 30F. With a larger heat exchanger, you could use process chillers.
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Good job!
We put liquid N2 on Joe's Mk IVB, using a counter flow heat exchanger donated by Permaculture, which works well too.
Nice thread. I'm looking at fitting up the counter flow N2 coil as well. i actually purchased the coil GW linked awhile back.
GW, what did you use to connect fittings to the coil? I looks like the inner tube is 1/2" and I could use a standard compression fitting. I guess I need to cut off the garden hose fitting and find a compression fitting for that side as well?
Thanks,
GH
GW, what did you use to connect fittings to the coil? I looks like the inner tube is 1/2" and I could use a standard compression fitting. I guess I need to cut off the garden hose fitting and find a compression fitting for that side as well?
Thanks,
GH
I picked up metric to 1/2 inch compression fittings from Swagelok
Chonkski
Member
I'm interested ??
