Liquid Nitrogen Generator - Overview----make money online

in today's video I'd like to talk about

my DIY with nitrogen generator this is a

project that I built in 2008 and showed

at Maker Faire 2010 where jeri ellsworth

made a video about it and I'll put a

link in the description but I actually

haven't talked about this in a video

myself so I dusted the parts off and

we'll try to make some liquid nitrogen

today the parts from left to right our

laptop to control the whole system

circuit board to control the cryocooler

along with a bench power supply and then

we have the cryo cooler itself sitting

on top of a stainless steel thermos in

front of a much larger thermos called a

do our with the Lindy sticker on it then

the black tank is a nitrogen gas storage

tank a black compressor pulled out of an

air conditioner next to that and then an

air dryer and nitrogen separator device

so let's start on the right side and

we'll talk about the nitrogen generation

system the purpose of the components

that you can see here is just to

generate a dry nitrogen gas source so

you could actually replace all of these

parts with just the cylinder of nitrogen

however there's quite an expansion ratio

to make one liter of liquid nitrogen it

takes approximately 700 litres of dry

nitrogen gas at atmospheric conditions

so if you tried to make this liquid

nitrogen generator by going down to the

welding store just getting tanks of

nitrogen you'd end up spending much more

for the nitrogen gas so anyway the

purpose of all this is to take air just

plane all the hemisphere air compress it

and filter it and dry it so that we have

a source of dry nitrogen so we start

here with this compressor and the reason

I didn't use my shop compressor is

because this system has to run day and

night and I didn't want the compressor

to be noisy running at night so these

compressors are super quiet this came

out of a small air conditioner or maybe

a refrigerator and the inlet is here so

it's just got a filter just a you know

filter out large dust particles and on

the high-pressure air which is wet and

then filled with oil as well from the

compressor comes out here and goes

through this setup so there's a pressure

release valve

since this compressor doesn't have it's

not easy to turn it on and off and so if

it's under pressure it doesn't like to

start so what I did is I had a

spring-loaded relief valve just to keep

the pressure

Austan going into this whole system they

probably a hundred psi or 120 or

something like that

the first stage is just to get out a lot

of water and oil mist here and then

there's a regulator to step it down to

something you know 80 80 psi or

something just to get a constant

pressure from there and then the semi

dry and semi wet 80 psi air goes into

this whole set up and even though it

looks complicated it's really just a

bunch of filters over and over again so

there's an oil coalescing filter and

then these I've actually packed with

carbon to try to get more of the oil

mist out and the cylinders in the back

are filled with silica gel to dry the

air so this was kind of a welding

project and you know I had some I

learned how to do an o-ring gland on the

mill and all that kind of stuff so a lot

of these projects just involve building

things to practice building things I'm

sure I could have bought a commercial

hair dryer for much a cheaper and

quicker but then you don't learn

anything the one thing I did learn is

that it's it doesn't actually get the

air very dry was just silica gel so to

get really really dry air you either

need a special drying membrane or a

cryogenic freezer which you need liquid

nitrogen for so that doesn't really work

that well anyway after going through

this convoluted path of filters we go

through an indicator glass so this has

silica gel with a indicator that turns

pink when it's exhausted and as you can

see it's completely pink now because

this thing has been sitting on the shelf

for a while

this would let me know if I needed to

open this up and recharge the silica gel

that's inside there and you can recharge

it just by putting it in the oven to

drive off the moisture and then you know

it acts like a moisture sponge

following this we go through the actual

nitrogen separation membrane and so this

is a really tricky part of the whole

system I probably spent as long on eBay

looking for a nitrogen separation

membrane as I did looking for the

cryocooler which is kind of the heart of

this whole system you can find these

industrially and they're actually quite

large I mean like you know a four foot

long bundle it's maybe six inches in

diameter meant for industrial use but

finding them small like this is tricky

and the way it works is that you know

80% nitrogen 20% oxygen air goes in at

high pressure on one side and as the air

molecules drift through the tubes the

oxygen tends to diffuse through the tube

whereas the nitrogen does not so by the

time you get to the other side the gas

that's coming out the end of the tubes

is nitrogen enriched and the stuff that

comes out the side of the tubes is

oxygen enriched and by playing with the

flow rate through this and the pressure

differential you can sort of decide how

much nitrogen purity you want so slower

flow rates mean that the oxygen has more

time to escape and then you can pick off

a higher quality nitrogen stream out the

end and as you can see to control the

flow rate I have this you know needle

valve with a flow meter there just to

check exactly how much it's going

through it and this was a source of

constant difficulty with this system

because I had to adjust the needle valve

quite quite regularly so after all that

the stream of about 80 psi almost all

nitrogen and hopefully pretty dry comes

out here and goes into the tank for

storage so this this part is just a

buffer this tank probably could have

been quite a bit smaller but it made the

job easier so I could adjust the flow

rate up and down and I'd have a big

buffer of nitrogen here so I don't have

to worry too much and then the idea is

that the vessel in which the liquid

nitrogen is being created you know ie

the nitrogen is being condensed into a

liquid you want there to be a slight

positive pressure of nitrogen gas in

there so if there's a slight leak it

doesn't pull in atmospheric air we'll

talk about this later but basically that

it's controlled by a pressure valve and

this is set to something very low like

maybe half a PSI above MC

and this is connected to the vessel in

which the liquid nitro the quit faction

is happening and then there's a valve

here that adds nitrogen gas to the tank

so basically when it's fallen below a

half a PSI or something the valve opens

and sends nitrogen into the tank and

then when it gets up to 1/2 PSI it shuts

off so this whole thing is really just a

dry nitrogen gas regulating system the

heart of the whole system is this

Stirling cycle cryocooler basically it's

just a refrigerator that's designed to

pump heat across a very high temperature

differential so I'll take this out in a

minute you'll see that the tip of this

device can get down to you know 75

degrees Kelvin and the rejection

temperature can be about room

temperature even a little bit above

normally I'd have this thing positioned

onto the large Dewar so that as the

liquid nitrogen is created on the tip of

this because it's so cold

it'll just drip down and fill up this

large Dewar for today's demo I'm going

to use the smaller thermos the

cryocooler is driven by this electronics

board this was part of a superconducting

RF filter so this was a piece of

equipment designed to be installed in

cell phone base stations and the RF

filter is superconducting and so you

have to get it down to liquid nitrogen

temperatures to use a high high

temperature superconductor so the whole

thing was marketed as this device that

you could install in your cell phone

tower and it included all the self

monitoring it was completely

self-contained didn't require water

cooling or anything in this case I've

replaced the fins and the fan that used

to be on this for air cooling with the

tubes that are going to my water chiller

so now it's a water cooled device I'm

using a benchtop power supply to power

it since this is a telco piece of

equipment it uses like a 27 or 28 volt

standard so I'm giving it you know about

28 volts there just about a little under

and it's currently idling so it's only

drawing you know 40 milliamps there's

thing when I turn it on via computer

control we'll see it starts drawing

quite a bit more

this particular cryocooler is rated at

140 watts continuous input power and I

think you get about seven to ten watts

of pumping of power being pumped from 77

Kelvin up to room temperature however

you can overdrive it and so since I have

the control software installed on my

computer we're talking to the circuit

board over a serial link I can download

new firmware parameters to it and get

the power up to maybe about a hundred

sixty hundred sixty-five watts and it

seems more than happy to run at that

power level as well especially with the

water cooling this Stirling cycle

cryocooler works on the principle that

if you compress a gas it gets warm if

you expand the gas it gets cold so what

it does is it moves GATT working gas

which is helium in this case down to the

tip of the device where it expands it so

the tip gets cold and then it moves that

chunk of gas back up to here and

compresses it so it gets warm so that we

can see the water cooling lines here are

where the heat is rejected and the tip

here is where it gets cold and it's

called Stirling cycle because it has two

Pistons inside here one piston moves the

gas back and forth the displacer so when

the displacer is down at the tip here

there's no gas or there's very little

gas here it's all contained here and

when the displacer moves back up the gas

is forced back to here then there's

another piston up here which is driven

by these coils it's basically a linear

motor and when that piston moves it

changes the pressure depending you know

where the gas is so it's relatively or

it's it's being compressed here and

expanded here so we get heat pumped when

I had the cryocooler installed in large

Dewar I added this large heatsink with a

copper sort of a heat bar there and had

this screwed to the end of the cryo

cooler and my thinking was that well I

want to make sure that this thing is

interfaced temp temperature wise with

the gas that's in the door I'm not sure

it made a huge difference or not but I'm

not going to use this today what I'm

going to do instead of setting the whole

system up is just put this into the

thermos this is a vacuum flask with a

nice large opening on the top I'm just

going to put this on here and run it and

what will happen is the tip will get

really cold

old and the thermos will keep the air

from forming too much ice on here and

eventually the entire system will get

cold enough to start liquefying nitrogen

out of the air since I'm not going to

use the nitrogen filter we're also going

to be liquefying oxygen out of the air

so the result will have its liquid air

basically okay I'm going to send the

command to start the cooldown sequence

and you can see that we're drawing power

now and I'm going to zoom in here so you

can see ice crystals starting to form

the way the system works is it has to

ramp up power very slowly if it went to

full power right away the piston inside

here were actually hit its limits if the

tip isn't cold because the gas pressure

is still relatively high there we're

currently running at about sixty watts

input power and originally the device

had temperature sensors on the cold end

of the prior cooler and it would use

this information to figure out how much

power it could pump in without breaking

the cryocooler as I mentioned it can't

go to full power right away when the

device is warm so unfortunately the

temperature sensors broke they're very

difficult to remove and I had them off

and then they were working and then they

grow up anyway so I've replaced the

temperature sensors with fixed resistors

and now I just edit the power settings

manually the cryocooler has this passive

spring-loaded counterbalance on the back

since inside the cryocooler there's a

piston that's moving up and forth the

whole thing would shake wildly if it

didn't have a counterbalance so there's

a spring-loaded set of weights up here

really just washers and the weights are

set up you can even see they marked at

sixty point five Hertz to absorb that

frequency being generated by the piston

inside so I thought I'd play with the

camera shutter so we can see what this

thing looks like sort of going in and

out of phase with the cameras sync rate

oK we've only been running for about 20

minutes here we've got the power cranked

up to 150 watts input power and we're

looking down into the do our there and

what you're seeing dripping off is the

liquid air so it's covered in snow

that's the tip of the cryocooler that's

very cold but you'll see every once in a

while a drop comes off and that's a

mixture of liquid oxygen and liquid

nitrogen and it's hitting the bottom of

the flask and hopefully being collected

so let me zoom out here and you can see

kind of the whole setup right now

there's no filtering going on so it's

going to get very snowy in there because

the air has a lot of water in it and

it's currently just pulling in

atmospheric air through these open ports

here's an information screen from the

control software showing the current

state of the board as you can see it's

running it right about 150 watts and the

cryocooler itself requires 15 volts RMS

at about 10 amps but the measurement

system is pretty cool even shows the

phase angle and the RMS total current

you know including the imaginary part

the PWM drive is running pretty close to

a hundred percent you can actually

squeeze a little bit more out of it by

increasing the input voltage and so the

software compensates for the total you

know rail voltage that's generated from

the input and will actually back the PWM

duty cycle down as you give it more

input voltage up to a point okay it's

been about an hour and so I lifted the

cryocooler out of the Dewar and you can

see before the tip has time to warm up

there's still liquid air dripping off

the tip and falling down into the Dewar

which is pretty cool so I'm going to

pour the liquid air out into a Styrofoam

cup so that we can get a look at it

and verify that it's actually air I'm

going to dip this green LED into the

liquid nitrogen to show that the cold

temperatures change the physical nature

of the semiconductor

as you can see it went out but as it

warms up you'll see that it starts off

orange and as it warms up it'll turn

back to green slowly to show that this

is a mix of liquid nitrogen and liquid

oxygen I'm going to put a very strong

neodymium magnet near the surface of the

liquid

and since option is paramagnetic it's

actually going to leap out of the

Styrofoam container and pull up to the

magnet see that so I'll let the magnet

boil off everything that's stuck to it

and we'll just I'm not actually touching

the liquid I'm still a few millimeters

above the surface you'll see it shoot up

the magnet like that the oxygen content

is not that high because it's you can

tell that the color of the liquid is not

that blue if this were 50% or higher

liquid oxygen you would definitely see a

blue tint to the liquid okay see you

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