Introduction: Homemade Liquid Nitrogen Generator

Did you ever think you could make liquid nitrogen in your own garage? This is an industrial process so how can an individual do this? Still doubt me? Intrigued? Read on.

As a lover of science I tried to think of a challenging project that was out of the ordinary. After going through the internet web and Youtube I realized that no one had made liquid nitrogen in his home. Yes, I did see some videos where some would use a Stirling Cooler from a cryorefrigerator and use this to condense nitrogen on the exterior of the cold-head. While one is making liquified gas, this is done using a prefabricated machine. I wanted to make the machine that liquefies the gas. Furthermore, a cryocooler has a very low production rate. You will only get about 500 - 1000ml per day. On the following pages I will walk you through the basics of how to build your own liquid nitrogen generator. Using easily obtained materials you can liquefy nitrogen or air. The unit cools to -320F in under 50 minutes. The production rate is about 350 cc/hr.

A full tutorial and plans are at http://homemadeliquidnitrogen.com This page goes over theory, thermodynamics and more detail on where to get components and how to build this. This Instructable serves as a general introduction to how this baby is put together.

I have just added a new web tutorial on how to make your own N2 gas from the air. I will add this as a new Instructable in the next few days. You can get a link for it at the end of this one.

I have also built a high-precision cryogenic digital LCD thermometer for this project, which you can buy for yourself. You can see how it compares with an Omega digital thermometer here.

Ok. The video above gives you a quick 3 minute overview of the project. At the end of this tutorial I briefly mention the PSA I made for making the pure N2 from the air for the generator. If you're ready for 320 degrees below zero we can begin...

Step 1: Overview

The liquefication generator has a few basic components. Starting in order:

1. Scrubber - This removes CO2 and H20 from the gas stream. Without this the water and CO2 would freeze and clog the tubing and valves

2. Filter - We need to remove any micro-particles that can clog our compressor valves

3. Compressor - This compresses the gas to high pressure. Two important factors are the pressure and flow rate. This project uses an oil-free scuba compressor delivers a pressure of 3500 psi at a flow rate of 3 SCFM (I jacked it up to 4 SCFM). It is possible to use a regular refrigerator compressor, but the production rate will be significantly reduced

4. Pre-cooler - This cools the hot, compressed gas before entering the cooling tower.

5. Regenerative cooling tower - Hot compressed gas flows through a counter-current system to cool the gas to cryogenic temperatures. Expanded, non-liquid gas returns to get recompressed.

6. Throttle - This is a needle-valve that enables a controlled expansion of the gas without losing the pressure behind it.

7. Baffle - This reduces the velocity of the expanded gas so it does not dissipate the cooled liquid into the gas-stream. It also provides a larger surface area for condensation.

7. Reservoir- This is the collection system that collects the gas. Heat exchange with the environment is minimal.

Above is a picture of an early version of the generator using a recycle can. Later you will see an improved version.

Step 2: Compressor Filter

You need to protect the compressor's valves and cylinders from debris and water. You can purchase an inexpensive vacuum filter from a distributer. I bought a Vaccon 10 um filter. The part number is VF500F.

Step 3: Compressor

This is the most expensive component. I used a RIX oil-free SA-3E. This delivers 3 SCFM @ 3500psi (230 ATM). I modified the motor and pulleys to deliver 4 SCFM. A higher flow gives you a faster cool-down and production rate. The high pressure allows you to have a larger temperature drop when you throttle the gas to a lower pressure. You can use a regular refrigerator compressor, but you will be waiting a long time to drop 400 degrees Fahrenheit from the ambient temperature to -320F if you only have 40 ATM of pressure.

My compressor allows me to get to -320F in 45 minutes. I am guessing that a standard compressor at 40 ATM will take 6 times longer, or 4 1/2 hours. Of course, if the flow rate is less then you have to add more time.

Step 4: The Scrubber

You can make this components out of PVC pipe. I used 4" PCV. You need to get the correct fittings to get to a pipe size that you can then attach to your compressor. The scrubber uses a material called zeolite, or molecular sieve. I specifically used 13x molecular sieve and added some 4A sieve material that had a color indicator added so I know when it has reached saturation. You determine the size of the scrubber based on your flow rate. If you want 3-4 SCFM then you need about 10-15lbs of the material and size the scrubber based on this.

Zeolite is a naturally occurring, finely porous material. By fine I mean the holes are only angstroms in size. Molecular sieve is man-made, but the structure is the same. CO2 and water enter and bind within the pores, letting the other gases, like O2 and N2, to pass through. The color-indicator will change from light blue to gray when the material can not adsorb any more water. One regenerates the material by heating to 350F, driving off the CO2 and water.

Now, back to the device. I cut a disc of 200 micron screening. This holds the 10 lbs of material in place so it does not get sucked into the compressor, but still allows for air-flow. I glued this material between the 4-to-2 inch reducer and the coupler fitting. We need to filter smaller material, so I took 11 MERV air-conditional filter material and cut it into a large circular disc. This should filter 1-3um particles. If you can get a 12 MERV this is better. I fashioned a circular ring of stainless steel that I got at a hardware store and fixed the filter material on top of the 200um screening. Then, poured in 10 lbs of 13x and 4A sieve. I then made another filter disc out of the air-conditioning material and fixed it on the top with a stainless steel ring. This keeps the material clean. You don't want particles clogging the sieve's pores.

The top of the scrubber needs three inputs. One is to allow for fresh gas input. The other connects to the regenerated gas. This is gas from the cooling tower that did not liquefy. The gas is already cool, free of CO2 and water, and in my case is 98.5% nitrogen. I don't want to waste this gas to the atmosphere so I reuse it, reducing the amount of fresh N2 that I need to make. This is why it is called regenerated gas because it comes from the original gas I fed into the tower. The third input allows any excess gas to vent out.

The only other connection is at the bottom where you connect the scrubber to the compressor. I placed a 10um vacuum water trap between the scrubber and the compressor. This will remove particles that can fowl up the compressor, and also serve as a check that no water gets into the cylinders. I also used this spot as a place to insert a gas-analysis meter that I made to monitor the purity of the N2.

You will need to buy a pipe/tube bender to make the coils and rings. I've shown a picture of one above. Mine is meant to bend 1/4" tubing/rod.

Step 5: Pre-cooler

The compressed gas leaving the compressor is hot. You want to remove this heat using an ice bath. The pre-cooler is sized to fit into a large bucket.

Basically, the precooler is a long coil of tubing. I used 20 feet of 1/4" 304 seamless stainless steel with a 0.035" wall thickness. Again, one could go to 0.027" wall, but this got too thin for me. I did not want a wall rupture at 3500 PSI. I go through the engineering calculations for verifying the integrity of the tubing at the tutorial site.

I added 0.016" thick aluminum fins which increased dT/dt even further by allowing better heat transfer. I carefully drilled a hole 1/64" smaller than the tubing. I then cut the square and snapped the fin in place. I can then submerse the cooler in an ice bath or expose it to sub-freezing outdoor temperatures when available.

Step 6: Regenerative Cooling Tower

This is the part that will take the most work. My final tower uses a large concrete cardboard form container that is 50 inches high and 24 inches in diameter. However, I had good success with an earlier version that used a 36 gallon plastic recycle can. The compressed gas goes into the tower through a long helical coil and re-expands through a needle valve at the end into the reservoir. The cold gas that did not liquefy returns through Teflon tubing around this coil. This cold gas cools the steel tubing further. This process repeats until the steel tubing is cold enough to liquefy the gas.

I used 305 stainless steel 1/4" tubing with a 0.035" wall thickness. There are many places that sell this near you. If you are going to do this with a standard refrigerator compressor than you can use copper tubing. Just make sure it is rated for the pressure from the compressor. Now the PTFE (Teflon) tubing is critical. It is one of the few materials that is flexible and can withstand cryogenic temperatures. I used plastic tubing in the beginning, but it would eventually crack.

My tower uses 80 feet of tubing. You can do this with 40-60 feet, but this increases the cool-down time. Again, everything is about tradeoffs. You need to insert the steel coil into the Teflon tubing. You want the Teflon tubing diameter to be a little bigger than the coil. Mine was 1" corrugated tubing which allows it to be flexible. This wraps over the 1/4" stainless tubing.

The ends of the tubing need high-pressure, stainless steel fittings and adapters. I got mine from Swagelok, but there are other companies that sell similar parts.

You then insert the coil into the garbage can or container. Industrial manufacturers fill the container with perlite and create a vacuum to prevent heat from entering from the environment. I filled my container with alumina silica high-temperature wool. This is normally used to insulate furnaces to contain the heat. Well, guess what? It also contains the heat of the outside from getting to our coils. You need to loosely fill the container with the material so it stays fluffy. Air is also an excellent insulator.

The pictures above show me using the 36 gallon recycle container. At the end of this tutorial you will see the concrete form container which houses a bigger run of coil. The stainless steel tubing is surrounded by the Teflon tubing. This, in turn, is wrapped with polypropylene foam to further decrease heat penetration.

Step 7: Throttle

The gas expands using a needle valve as mentioned earlier. One controls the pressure by finely tuning the orifice opening with a large lever/knob. I made a large lever because the standard knob handle is too small for fine control. Furthermore, as the temperature drops one finds difficulty turning the knob because it gets frozen in position. A large lever makes this fact mute.

I extended the stem so it would reach the outside. I insulated the connection to the stem with Teflon to reduce any heat transfer through the stem from the outside.

Step 8: Baffle

The expanded gas distal to the needle valve moves at a high velocity. This can agitate the liquefied gas in the reservoir and blow it back out into the gas stream. You need to slow the gas down to allow the droplets to collect and drop into the container. Until I figured out this simple step I was never collecting a lot of liquid.

Making this is very easy. I used a fitting and attached it to 1/4" copper refrigerator tubing. I drilled a few holes with a 1/8" drill bit on the other end and fixed some copper abrasive scrubbing sponge that I got at a food store. Make sure the copper wool (abrasive scrubber) does not come off. The other pictures show how this part relates to the needle valve and reservoir.

Step 9: Reservoir

The reservoir holds the collected liquefied gas, whether that is N2 or air. A simple stainless steel vacuum bottle, or a thermos as many of you would know it, serves this purpose very nicely. Such a simple solution that eluded me for some time. The trick is to fashion an adapter that allows you to contain the expanding gas and direct it to the regeneration Teflon tubing that surrounds the high pressure stainless steel tubing. The details, along with all the other methods I tried, can be found at my extensive tutorial at http://homemadeliquidnitrogen.com

Basically, the baffle connects to the output of the needle valve. The inflow to the valve connects to a tube fitting on the end of the high pressure tubing. A Teflon cylinder surrounds this and just fits over the orifice of the thermos. Small screws keep this fixed so the pressure of the expanding gas does not push it off. A small tube of Teflon goes from the bottom of the thermos to the outside through an insulated jacket to allow the liquefied gas to escape. A small plug keeps the liquid contained until you are ready to drain the system.

In addition to these connections, there is a small opening for a RTD probe for monitoring the temperature. I am currently using a unit I bought, which is seen in the video at the beginning of this Instructable. I have developed a low-cost LCD cryogenic thermometer that is accurate to 0.1F. I plan on posting this as a new Instructable in the near future.

Step 10: Summary

This project allows an individual to do what only commercial industry has done in the past. You can generate your own liquid air or nitrogen with a high production rate. The cool-down period depends on your compressor, length of regeneration tubing and how well you can insulate your system. In the past, making liquid nitrogen in your garage seemed impossible. Not any more.

Good luck and stay cool.

Step 11: Making Pure N2 for Liquefication

I have gotten a lot of comments suggesting that I am making liquid air, which contains O2, and not liquid N2. I made a pressure swing adsorper that removes the O2 from the air, leaving 98.5% pure N2. If I used a second stage I could get 99.999% pure N2. I feed this N2 into the liquid nitrogen generator. I am putting out about 30 L/min of 98.5% N2.

I have just finished writing a web tutorial on this subject which you can find here. This can also be used for having a pure source of N2 in your garage. I use it for filling my tires. I will write this as its own Instructable in the next few days.

You can click on the this link to see a video I made, showing my PSA device.

Comments

author
MrB21 made it!(author)2017-07-11

can i use 300psi air compressor

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pmk222 made it!(author)2016-02-10

what would be a minimum pressure rating you would recommend? i have a higher volume fan but is only rated somewhere between 1 and 5 psi

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Andrew_F made it!(author)2017-07-10

Like 1000 psi

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jts4 made it!(author)2015-10-12

Could this make liquid hydrogen?

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PeterI13 made it!(author)2016-01-16

In theory, yes. However, you would have to provide the unit with a gas mixture containing pure hydrogen. That seems like an added cost and danger factor that I wouldn't want to deal with. This system is relatively safe because the gases involved are inert under usual conditions, and the only comparable risk to a hydrogen explosion during liquid nitrogen production is a pressure buildup from boiling nitrogen.

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Amp1098 made it!(author)2016-03-11

Ignoring the danger, an electrolysis device could provide the machine with pure hydrogen. Also you can liquify the oxygen.

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Andrew_F made it!(author)2017-07-10

I would recommend not liquifying hydrogen if you don't have a good method of separating the hydrogen and oxygen, that will be a lethal combination and you could, quite literally, blow up your entire house. It would be utterly destructive sending shrapnel down the block.

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cryophile made it!(author)2016-03-11

Can you adapt it to liquify NO2?

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Andrew_F made it!(author)2017-07-10

You need to first get a good NO2 source. The reason this works so well is because the air is mostly N2 and O2. NO2 would condense out at a much higher temperature. Condensing point for N2: -320F -|- O2: -297F -|- NO2: -127F

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nicko0 made it!(author)2014-12-28

i use liquid oxygen for scientific glass blowing. would you help design one for liquid oxygen/

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Cooper18 made it!(author)2016-03-25

If I understand what's going on in this process just use the "exhaust gas" from the PSA instead of the N2

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Andrew_F made it!(author)2017-07-10

The gas has some N2 contamination but liquid oxygen will boil off first and can be captured and recondensed if necessary.

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AhmadD36 made it!(author)2017-01-16

Do you turn nitrogen gas to liquid when pressed 230 atm?

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NathanB186 made it!(author)2017-02-10

When N2 is above -147 C (that is the case here), it does not liquefy no matter the pressure. This is the critical temperature.

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Andrew_F made it!(author)2017-07-10

And it is capable of reaching that temperature.

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imsmooth made it!(author)2017-01-17

The N2 is compress and cooled. Without the cooling there is no pressure you can achieve to get liquid N2. I compress between 3000-3400 psi so that's close to 205-230 atm as you stated. The expanding gas at the needle valve (throttle) drops the temperature and this cooler gas chills the compressed, unexpanded gas further. Eventually, the gas gets cold enough to liquefy. This is all explained in great detail at the website tutorial I mention in this instructable.

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AhmadD36 made it!(author)2017-01-18

The gas cools itself?

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Andrew_F made it!(author)2017-07-10

No, the gas cools when it has a change of state through the flash valve in the diagram. It cools in the same way that a refrigerator does.

author
Randomlycrazy1 made it!(author)2017-04-30

It is relying on the ideal gas law where p1v1/T=p2v2/T.

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helzcurrah made it!(author)2015-02-11

Hi there,

I work as an engineer for one of the companies that makes Liquid nitrogen. I just want to point out there are some very serious risks with this type of equipment which even the professional companies sometimes fall foul of. My professional advice would be "don't try this without proper chemical engineering training", but since I know you already are, here are some safety tips to consider:

* Never store liquid nitrogen or operate this equipment in an enclosed area, always ensure sufficient ventilation. Nitrogen is an asphyxiate with no smell. The only way to protect yourself is to operate outdoors AND wear a gas composition monitor to warn you if oxygen levels in the air fall below 19.5%

* Make sure the equipment is thermally isolated well as it reaches extremely cold temperatures and you may burn yourself if you touch it. Frostbite may also occur if you spill any cold product on yourself. Always wear full length clothes and insulated gloves.

* If there is any possibility of liquid nitrogen being trapped in a part of the equipment (due to closed valves or ice blockage), fit pressure relief devices. When the liquid warms and expands, it can cause an explosion if there is no escape path.

* Distillation columns take in a lot of hydrocarbons and nitrous oxide with the air. These components build up in the distillation still, and can cause an explosion when they react with the liquid oxygen in the still. Ensure you purge the liquid often enough to remove these contaminants.

*If you are running this in your garage (I know I told you not to), don't enter before you take an atmosphere reading. Make sure oxygen is between 19.5 and 22%.

* Make sure all the pipework and vessel is constructed from clean, oxygen-safe metal. During startup, the unit will produce liquid oxygen before it starts to produce liquid nitrogen. High concentration oxygen reacts with any organic contamination, and even metal can become a fuel source for a fire. Carbon steel is not an appropriate material, stainless steel, aluminium or monel is better. Definitely do not use rubber pipes, seals or oil based lubricants!

* There is a chance the atmosphere around the equipment will be oxygen rich, so take care to eliminate all sources of ignition, such as electrical switches, flames, static on your clothes, sparking tools and anything that gets very hot.

author
Andrew_F made it!(author)2017-07-10

This is a link to get the gas monitor.

https://www.pksafety.com/bw-clip-2-year-single-gas...

Whenever you feel woozy, stop. Using a candle is NOT an indicator of air quality. Too MUCH oxygen can be lethal as well. The majority of suffocation deaths happen when the worker is unaccompanied. Use the buddy system to prevent a Fatality.

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AlyssonR2 made it!(author)2017-04-30

Excellent points!

Having seen the results of a LOX leak on tarmac - it is NOT a good thing to have hanging around!

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acoleman3 made it!(author)2015-06-08

wow, glad to see someone who's actually "in the know" providing safety tips and not some armchair "expert" like i've seen in the comment section of a lot of 'ibles that had any hazards to them.

author
gith made it!(author)2015-06-08

Helzcurrah

You know us so well, Thanks for the safety tips they may safe someone from great difficulty. You know like death.. all joking aside thanks for pointing out some of the dangers that can be encounterd with this.

author
studleylee made it!(author)2015-06-07

Great instructable!!!

@ helzcurrah Looking forward to seeing you do some instructables on related topics. I think adding a timed fresh air inlet fan to the "garage" to cycle out the undesirable product might be good. I Might be making one of these systems soon.

author
tilak.conrad made it!(author)2017-04-30

So glad instructables.com sent this out again. Really great instructable imsmooth - congratulations and thanks very much.

Question if I may;

I'd like to make a few kilo's of Dry Ice regularly - would there be a way to do this - presumably I'd have to create sufficient CO2 - is there a way better than vinegar/baking soda to make large quantities of CO2? Could this then be fed in to a modified version of your solution to make Dry Ice.

Apologies in advance if this is a stupid question - best regards and TIA for any advice & guidence you or others can provide

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sifu-dianji made it!(author)2017-05-11

could use a CO2 extingiusher, then you wouldn't need to use this.

be sure to check H+S, and do a risk assesment. I don't know the dangers of this, so be thorough before you try this.

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davea0511 made it!(author)2017-04-30

Wow. Interested in just an n2 generator, feed into fridge so food will last longer.

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imcp1024 made it!(author)2017-04-30

today's frost free fridges would not take kindly to that. better off cleaning condensor fins.

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davea0511 made it!(author)2017-04-30

My point is that you remove O2 from the fridge the food then doesn't oxidize, which is the #1 facilitator of food spoilage (why food keeps longer with plastic wrap).

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Elfinberry made it!(author)2017-05-01

My only concern with replacing all of the air in the fridge with N2 comes from displacing the O2. Breathing N2 will only kill you because you aren't breathing O2. You would want to take that into account in case someone went to reach for the item in the back and passed out.

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EvanE21 made it!(author)2017-04-30

How would a nitrogen flush affect the frost free aspect of the fridge? You'd even still need it -- water is still coming off the food, plus you're cycling air in each time you open it. I'm curious what you envision the problem being.

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imcp1024 made it!(author)2017-04-30

I had only imagined they intended to use the liquid nitrogen to cool the interior of the fridge. This would interfere with the defrost cycle. I didn't think of prolonging food life after decades of only getting as much produce as I need.

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CraigH23 made it!(author)2017-05-01

Excellent project. I had searched for something like this years ago, but assumed it was too dangerous, now reading this I still think that.

I read an old book on electric cars from the 1960s. One design, used lead acid batteries, and liquid nitrogen. The N2 was circulated through copper pipe which at room temperature makes a good conductor of electricity to the motor, but cryo cooled it's resistance dropped much further. N2 was also cooling the motors for the same reason. At the point where the gas was released it was at a high enough pressure to run a turbine electrically coupled to the motor or battery. Basically, N2 was the fuel, the batteries were short term storage.

That started my interest in cryo gas production, but I think I'll leave it to the experts now. Liquid oxygen could be disastrous around petrol vehicles, nitrogen dangerous in the cabin.

Thanks, very interesting.

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motivated333 made it!(author)2017-05-01

Awesome write up. You are trending...

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AhmadD36 made it!(author)2017-01-14

What is the gas used for cooling up to 320 degrees below zero, and what is the pressure before and after the compressor
Please explain how to make the cooling circuit video

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imsmooth made it!(author)2017-01-14

Air. You should read the full explanation at www.homemadeliquidnitrogen.com

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AhmadD36 made it!(author)2017-01-15

Now it became clear idea
It is by nitrogen pressure
And not reduce temperature

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AlyssonR2 made it!(author)2017-04-30

AhmadD36:

It is the expansion of cold gas that drops the temperature of the nitrogen enough to liquify part of it.

Whatever doesn't liquify is cold enough to cool the next nitrogen in the cooling coil.

You can see the effect by discharging a CO2 fire extinguisher - the horn gets cold as the gas expands - and even solififies into dry ice.

author
imsmooth made it!(author)2017-04-30

Alysson

I'm just curious I've received a lot of comments today how did you find this instructable? was it featured somewhere ?

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AlyssonR2 made it!(author)2017-05-01

What davea0511 said - it was a featured 'ible today (yesterday, now).

author
AhmadD36 made it!(author)2017-01-14

I do not speak English language

I just want a detailed explanation of the cooling method and what is the necessary pressure to become liquid nitrogen


I own a heat exchanger and used the Freon r22 I have become the temperature -37 Celsius degree and I need -170 / -180 Celsius heat
What are the required supplies
Thank you

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DougM95 made it!(author)2017-04-30

Do you think you would get better heat transfer from your precooler if you soldered the aluminum fins to the tubing rather than having a mechanical (press fit) attachment? That way, you could have less tubing length, or keep the length and get more efficient cooling?

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imsmooth made it!(author)2017-04-30

Interesting. I might try it and see if there is a significant difference. I would have to use a solder gun and not a torch. If I used a MAPP torch the temperature might change the properties of the steel tubing, reducing its failure pressure rating and risk a pipe rupture. Solder, though, may not stick to the smooth stainless steel surface. I'll post my findings if I do it.

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ghouck made it!(author)2017-04-30

Perhaps you could use thermally-conductive 2-part epoxy like is used to cement heatsinks on computer components. Might get expensive though.

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JohnD212 made it!(author)2017-04-30

Not sure what a pressure swing adsor(b?)er is. If you are either blowing off the somewhat purer O2 into the air, or separating it as liq O2, be aware of its dangers. It is very reactive, and can cause fires and explosions.

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AdrianH67 made it!(author)2017-04-30

Pressure swing systems work by pumping a mix of gases in at high pressure. One gas, at elevated pressure, has a strong attraction to the inside of the tube, but the other gas flows right through. After a while, you start running the mix through a second parallel tube, and let the first tube depressurize. Once the pressure drops, the adsorbed gas separates from the adsorbent and vents away. Switching back and forth, you can collect the non-adsorbing gas in pretty high purity with no hazardous side products (and using only simple and affordable equipment).

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davea0511 made it!(author)2017-04-30

Coolguy is right. Putdown snobbish behavior is not welcome here.

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AdrianH67 made it!(author)2017-04-30

No, applepear is right. It would be very stupid to try running the Haber-Bosch process at home. Once you consider the amount of energy input, temperature, and pressure required, plus the low conversion rate per pass, you'd be about ten times as likely to kill yourself in a 3000 psi hydrogen explosion than you would be to produce any quantifiable amount of ammonia. He wasn't slinging insults, he was being pragmatic about the idea.

author
NoelA11 made it!(author)2017-04-30

using a sealed helium gas cooling circuit would increase production. better thermal characteristics than air without the water issues that comes with pressurizing air.

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