Either will work, though LN2 has more BTU’s/lb heat of vaporization, so it comes down to price per BTU.
file:///C:/Users/ejdla/AppData/Local/Temp/R&T_2006_-Cryogenic_Food_Freezing_Overview-_Lang.pdf
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PS: I prefer LN2 among other reasons, because it isn’t a greenhouse gas. It’s mostly what our atmosphere is at around 78%.
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I use ln2 regularly to chill my solvent tank. It’s cheaper than dry ice. You can throttle the liquid flow so it won’t chill your solvent too much. I run the vent hose out of the booth so it’s not as loud, which seems to help
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How are you guys getting the LN2 into the heat exchangers? Coils, etc…
With a hose
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My hose from the LN2 is outfitted with a brass sintered disk. Just swap that out? Go straight from tank to coil? How do you vent the gas?
I would remove that filter and attach it to the coil/jacket/heatX and vent out the other side. I wouldn’t let it close off inside whatever it is filling. Let it hiss out the other end, unless you have a prv in place.
Any kind of special PRV on the end? Whats people using? What about a valve slightly open?
150 psi prv. And it’s not on the end.
And it’s a swagelok needle valve, not a quarter turn ball valve. The tank should have an outlet at the top and bottom of the jacket
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Has anyone used LN2 in a tube style heat exchanger? What would be the setup for something like that?
Thx guys
I have used them, it works well.
I actually coiled some 1/2" 304SS tubing in about a 10" diameter coil and put JIC compression fittings on both ends. It easily stretched and retracted for attaching to the Dewar liquid valve, which allowed me to use it as the throttle, rather that provide my own valve that will operate reliably at those temperatures.
Thermal extraction was accomodated by the coil spring action and no polymers were used to fail at low temperatures.
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I know Im being a pain, but if anyone can post pics that would be awesome!
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I use an orifice or a throttling valve on the discharge end of the heat exchanger and use the Dewar valve for on and off .
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Ummm, I don’t seem to have a close up of one in action, but here is a picture of a system in assembly before plumbing.
. The LPG goes through the center tube and the LN2 the outer shell. On and off is controlled with the Dewar liquid valve and flow by an orifice or cracked valve on the discharge end.
Most valves are not operable after a few moments exposure to LN2, so plan to set it quick or use an orifice.
The connection between the Dewar and the HEX was a 10" coil of 1/2" 304SS tubing.
The discharge is directed through a hose into a muffle box, because it is loud.
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those coils are very nice!
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Latent heat of vaporization for CO2= 574 Kj/Kg (247 BTU/lb)
Latent heat of vaporization for N2 = 199 Kj/Kg (86 BTU/lb)
1 Liter liquid CO2= 2.24 lbs (1.02 Kg)
1 Liter liquid N2= 1.78 lbs (.81 Kg)
Ahoy @Graywolf ! Good to see you over here man. You probably don’t recognize my screen name, but we have met in person a couple of times and chatted on ICMag. I was up there in Portland for Dr. Melamede’s (sp?) lecture 5-6 years ago.
Anyways, I know specific latent heat of vaporization can be situation dependent but I have always thought, based on the above data found on engineeringtoolbox, that it’s actually CO2 that has the significantly higher (almost 3X) heat of vaporization and is also slightly more dense in the liquid phase, adding to the advantage.
Also, due to its triple point, liquid CO2 must be metered into the heat exchanger under pressure (75 PSIA) in order to actually have a phase change from liquid to vapor occur and not dry ice formation.
Both pressurized vessel cooling jackets and dry ice formation (blockage) have caused serious problems for operators attempting to harness the latent heat of vaporization of CO2.
Using LN2 doesn’t require a pressurized jacket nor does it have the possibility of blockage due to dry ice formation. It does however requires close monitoring of the process like you mentioned in order to make sure you don’t get things too cold which may get difficult as cooling loads change and pressure/liquid level in the dewar changes.
LN2 only has about 1/3 the latent heat of vap. as CO2 and is also less dense in the liquid phase so unless you can get a super deal on LN2, I would think CO2 is usually the most efficient option.
This is why I vastly prefer to used coils immersed in DI/alcohol slurry over liquid injected heat exchangers.
Using dry ice has an additional advantage IMO because sublimation at 1 atm occurs at -78.5C versus the vaporization of the liquid at 5.1atm (75PSIA) with occurs at -56.7C so you get things a little colder if that’s desired.
@thedabbincabin I would suggest that you go with a coil in DI/alcohol slurry for your Corken. That’s what I use for mine and it works great.
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I just spent some quality time researching and you are right about C02 having a higher latent heat than LN2. It appears Air Products left out a decimal point. When I convert kj/(kg K) to BTU/(lb F), 856 btu/lb becomes 85.9 btu/lb.
https://sms.asu.edu/sites/default/files/safetygram-7_ln2.pdf
LN2 does have a higher specific heat at 1.04 Kj/(Kg K) versus 0.839 for CO2, and starts out at -195C versus -78C so a Latent heat of vaporization comparison is not the complete picture or apples and apples.
We’ve successfully used both coils submerged in CO2 dry ice/alcohol slurries, and LN2 counter flow heat exchangers for chilling injections, and CO2 dry ice/alcohol slurries for chilling pump discharge, as well as a counterflow exchanger chilled by a -15C Merlin 150 chiller.
I don’t recommend LN2 through a counterflow exchanger for cooling the pump discharge, but it does an excellent job chilling the LPG injection, albeit noisy.
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