Heated Nitrogen backfill

Gray Wolf

A Posse ad Esse. From Possibility to realization.

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• Nov 5, 2017

• #21

WaterFarmFan said:

As for safety, I currently have a 25' copper coil, and from my reading these have a psi rating of >1000? Does this sound correct? If so, even if I raised my oil to temps, the psi would be in ~20 range and way below tolerances. If this is not enough heating surface area for my desired flow rate, I could then upgrade to a 50' stainless.

Click to expand...

Copper tubing is adequate in the pressure ranges you will be operating in. It actually has better heat transfer characteristics than stainless.

 

WaterFarmFan

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• Nov 6, 2017

• #22

Gray Wolf said:

Stainless overbraided PTFE should work.

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What kind of fitting would you recommend for 30 psi max? How much give does the PTFE have? Would a 3/8" barb connection work for a 6AN hose? It seems most lines and fittings (on Amazon or ebay) are geared towards automotive applications.

Also, how would you recommend connecting the copper coil to ptfe line?

Thanks!

 

WaterFarmFan

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• Nov 28, 2017

• #23

Well, I have been a bit busy, but finally got the new rig together for backfilling my vacuum oven with heated nitrogen. I will be testing this evening. I used -8AN hose with 3/8" stainless barb connections, and this allows a .5-1mm gap which ptfe tape easily seals tight. I also cut about a 10" of cooper off of the exit side to connect stainless hose sooner. I will be wrapping this up tight with additional foil and will allow heat to rise from the oil and keep the needle valve base and tee at ~200F. Here is the short list of components:

25' 3/8" copper wort chiller
10' -8AN stainless braided ptfe lined hose (used for race car fuel lines)
Swagelok Stainless Poppet Check Valve, Adjustable Pressure (3 to 50 psi)
Swagelok Stainless Integral Bonnet Needle Valve
Various 3/8" barb stainless NPT connectors
Stainless tee
Stainless ball valve (for fresh air)
Green PTFE Oxygen rated tape
Stainless hose clamps

Harvesting some terps from fresh flowers frozen in ln2 soon. First up will be some Chem 91 x I95 & Chem D x I95!!!

 

Gray Wolf

A Posse ad Esse. From Possibility to realization.

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• Nov 28, 2017

• #24

WaterFarmFan said:

What kind of fitting would you recommend for 30 psi max? How much give does the PTFE have? Would a 3/8" barb connection work for a 6AN hose? It seems most lines and fittings (on Amazon or ebay) are geared towards automotive applications.

Also, how would you recommend connecting the copper coil to ptfe line?

Thanks!

Click to expand...

Sorry to just notice this! I have all my hoses made up with swaged JIC or compression fittings, by someone like Associated Hose or Detroit Flex.

The assemblies are rated at over 3KSI.

 

WaterFarmFan

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• Nov 28, 2017

• #25

Gray Wolf said:

Sorry to just notice this! I have all my hoses made up with swaged JIC or compression fittings, by someone like Associated Hose or Detroit Flex.

The assemblies are rated at over 3KSI.

Click to expand...

Do you think that a plate style heat exchanger might work better than the coil for surface area?

 

Gray Wolf

A Posse ad Esse. From Possibility to realization.

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• Nov 29, 2017

• #26

WaterFarmFan said:

Do you think that a plate style heat exchanger might work better than the coil for surface area?

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If it has more surface area and is rated for at least 350 psi, it should work better.

 

WaterFarmFan

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• Nov 29, 2017

• #27

Thanks. I figured as much and ordered this 60 plate model earlier today:

https://www.amazon.com/B3-16A-Plate-Heat-Exchanger-Female/dp/B074PP2NKV

It is listed at 9 ft2 surface area which I have calculated as ~5x increase over my coil. The very irregular flow pattern within the plates should greatly increase contact between nitrogen molecules and heated walls versus the smooth bore of the coil. I plan to fill one side with oil and then submerge the entire heat exchanger just to the top in a pid controlled pot of oil. Once it has reached temp, it should maintain well.

 

WaterFarmFan

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• Nov 29, 2017

• #28

I ordered fittings to run a cross hose that will create a connection between the alternating sides, so the gas will pass through the exchanger twice before exiting, with hot oil only on the outside. Will have it in a few days.

 

WaterFarmFan

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• Dec 2, 2017

• #29

This looks to be a winner! Pressure tested great. Will put through the paces tomorrow. The heat exchanger that I bought direct from Duda had 1" male NPT threads, so i went with stainless 1" female to 3/8" female reducer and then stainless 3/8" male NPT with 3/8" barbs. All other components are the same, but I reduced the fresh air hose length. The heat exchanger with hot oil pot and pid controlled heating element are directly behind vacuum oven, but completely outside of my lab space for safety.

 

WaterFarmFan

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• Dec 5, 2017

• #30

Success! This setup worked fantastic. It took some experimenting, but I ended up setting the regulator to ~10psi with the needle valve open ~1/16 of a rotation. Not sure about the exact residence time, but it takes ~2 minutes to backfill my 0.9 cf vacuum oven or ~4 seconds per in Hg with the vacuum oven backfill valve wide open. I set my oil bath to 240F and based on my observation of temps in oven, nitrogen gas was exiting in 220-230F range. I will be lowering oil temp slightly for next run. The heat exchanger is completely submerged in oil with about 1/2" covering the top. I wrapped the pot in HD foil and created a "chimney" stack wrapping up the tee that let hot rise and keep the stainless valves at temperature.

 

WaterFarmFan

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• Dec 5, 2017

• #31

Thanks to all the people that contributed to this thread!!! Most helpful!!!

 

MEMED

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• Dec 6, 2017

• #32

Congrats! It looks great. I am enjoying watching your progress.

 

WaterFarmFan

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• Dec 6, 2017

• #33

Thanks Memed! I simply fucking love to experiment - it is like going to the gym for your mind! Over the course of an hour, I had to try 100+ different variations with slight tweaks. I started with much higher psi on my nitrogen regulator, but I found that my needle valve was not sensitive enough and even the slightest of turns would let the gas escape too fast. I tested exhaust temps with a thermocouple on the fresh air intake (with the vacuum oven valve closed), but the system behaves a bit differently when closed loop to my oven that has a vacuum. The vacuum "pulls" at the needle valve having an effect on psi in the exchanger. Solution was to lower the psi at the regulator and let the needle valve do its job, which is force nitrogen gas to stay in heat exchanger long enough to raise temperature of molecules.