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View Full Version : Nitrous oxide (N2O) as low-stage refrigerant



DaBit
28-08-2003, 02:45 PM
For us hobbyists it is hard to obtain refrigerants, and typical low stage refrigerants useable below the -60C / -75F mark, such as R23 or R508b, is really impossible.

Viable alternatives are R170 (ethane) and R1150 (ethylene).

Another possible alternative from thermodynamic point of view is nitrous oxide (N2O), which can possibly be obtained though automotive tuning shops by us hobbyists.

Some properties:

- Melting point : -91 C / -132F
- Boiling point (1.013 bar) : -88.5 C / -126F
- Critical temperature : 36.4 C / 97F
- Latent heat of vaporization (1.013 bar at boiling point) : 376.14 kJ/kg
- DOT Hazard class : Non-flammable Gas
- Toxicity: None Established
- good compatibility with copper, fair compatibility with carbon steel

Gas decomposition under pressure might happen above 300C / 570F, but we don't get there.

At 15 bar (~225psi) condensing pressure, condesning temperature is ~ -33C / -27F, which is doable with R507 or R404a in the high stage.

I don't have much data on this gas, but would it be suitable as 'The Alternative When Everything Else Fails'? Would it be compatible with POE oil?

Wat would be the discharge temperature when evaporating at -85C and condensing at -35C, with heat exchange between suction and liquid lines?

Prof Sporlan
28-08-2003, 05:53 PM
DaBit, you really do enjoy exploring the obscure topics of refrigeration theory and practice... :)

One would think nitrous oxide (R-744A) would have similar thermodynamic characteristics to carbon dioxide (R-744). Both possess the same molecular weight, and both have similar critical temperatures and pressures.

The triple point temperature of nitous oxide (-90.8C) is well below that of CO2 (-56.6C), which should be a bonus. Less chance of forming "dry ice" in the evaporator, or whatever one calls solid nitrous oxide. :)

One would think using nitrous oxide as a refrigerant is doable, but the Prof can't remember anyone doing so. It might be that CO2 is simply cheaper, and works as well or better than nitrous oxide.

DaBit
28-08-2003, 06:58 PM
Originally posted by Prof Sporlan
DaBit, you really do enjoy exploring the obscure topics of refrigeration theory and practice... :)

That's more fun than installing the same model AC for the 1000st time :D

(And as a hobbyist you simply have to, since the refrigeration business is not exactly hobbyist-friendly. When does Sporlan start making 1/32 ton valves which I can buy in a normal store? :) )


One would think nitrous oxide (R-744A) would have similar thermodynamic characteristics to carbon dioxide (R-744). Both possess the same molecular weight, and both have similar critical temperatures and pressures.

Just curious: Are these factors the main determinants of the thermodynamic properties of a fluid?


The triple point temperature of nitrous oxide (-90.8C) is well below that of CO2 (-56.6C), which should be a bonus. Less chance of forming "dry ice" in the evaporator, or whatever one calls solid nitrous oxide. :)

'Dry ice' at -90C is indeed a limiting factor,
but it is low enough to keep me satisfied for a few days. :D


One would think using nitrous oxide as a refrigerant is doable, but the Prof can't remember anyone doing so.

And neither does google dig up any links to nitrous oxide as a refrigerant.


It might be that CO2 is simply cheaper, and works as well or better than nitrous oxide.

For temperatures above -56C CO2 probably is more suitable. And CO2 is very cheap...

The main question is: would it be just as 'safe' as, for example, ethane? I don't want to accidentally blow the roof from the house due to some unforeseen reaction.

And I also wonder what the discharge temp would be with nitrous oxide, and whether or not it is compatible with POE oil.

I know that it is used in those cardridges you must put in those homemade whipped cream devices, so it cannot be as expensive and hard to obtain as ethane, R23 or R508b.

Argus
28-08-2003, 07:00 PM
I concur with the Professor....But there's more.

One reason why Nitrous Oxide is a non starter as a refrigerant that you may consider is related to the reason why the STEK regulations make it equally impossible for you to opbtain HFC's in the Netherlands. STEK (amongst other things) is part of the Dutch Kyoto compliance mechanisms aggregated in the EC's basket approach.

Nitrous Oxide is a recognised Kyoto greenhouse gas and as such is prescribed in the EC equally with HFC's. 'Frivolous' uses in sporting activities will, no doubt, be banned.

You may care to search in the EC web sites for the European Climate Change Programme (ECCP) that lays out the EC's policy on Greenhouse gases and deals with future uses of all the substances.
________
Honda NSR150SP/RR (http://www.honda-wiki.org/wiki/Honda_NSR150SP/RR)

DaBit
28-08-2003, 11:03 PM
Originally posted by Argus
[B]One reason why Nitrous Oxide is a non starter as a refrigerant that you may consider is related to the reason why the STEK regulations make it equally impossible for you to opbtain HFC's in the Netherlands. STEK (amongst other things) is part of the Dutch Kyoto compliance mechanisms aggregated in the EC's basket approach.

Please don't get me started on STEK. I am willing to get my license, and I am even willing to administer the small amount of refrigerant I use (I do not vent, I already recover). But I am not willing to accept a job at a STEK-licensed company only to be able to buy and use refrigerant. Especially not when the same refrigerant (R134a this time) is found in air horn canisters (ttp://www.icecoldcomputing.com/images/page_images/pc3_refrigerant_source.jpg), ready to be blown into the air. That's 300g, or almost 1lb per canister. More than my yearly refrigerant usage.

They simply give me no possibility to do it legal. And it took me half an hour to get someone on the phone who even remotely knew what he was talking about.

So what I do is this: I let a STEK-licensed professional leak-proof the system (which is more a formality since I already did that myself), and I have him grossly overcharge the thing. Then, at home, I recover the refrigerant using an empty bottle and a small hermetic compressor, and charge the right amount, having some left to play.

It seems to me that this is legal. But I am just mad that, for example, I can build and launch rockets if I want to (and solid rocket engine fuel doesn't release nitrogen fumes, ahum), but not use tiny amounts of refrigerant for my own pleasure.


Nitrous Oxide is a recognised Kyoto greenhouse gas and as such is prescribed in the EC equally with HFC's. 'Frivolous' uses in sporting activities will, no doubt, be banned.

It was, and is, used as a propellant, and I have never read any article about a future ban on nitrous oxide for this purpose.

Personally I don't care whether it is a greenhouse gas or not. If I have to drive 150km/100 miles to get ethane, I am destroying the environment much more than when I run out to the local store and get some nitrous oxide. Hell, if I fart, I already release more greenhouse gas (methane) than what I need to get the system going.


You may care to search in the EC web sites for the European Climate Change Programme (ECCP) that lays out the EC's policy on Greenhouse gases and deals with future uses of all the substances.

I will. Might be good for a good laugh with the current inconsistent policy.

Edit: Sorry, please do not understand this as a personal attack. I am just ranting.

ghg
19-04-2004, 02:18 PM
As prof Sporlan notes nitrous should have (and does) have
similar thermodynamics to CO2.. The big killer is..

Nitrous Oxide is a strong oxidizer (they use it for extra O2
in racing cars). What happens to strong oxidizers in oil?

ka-boom.

numerous stories of tech's pressure testing an HVAC system
with O2 instead of N2.. sometimes they get 5 mins before
the compressor oil lights off. Results are like a mortar round hit.
Nitrous may last 10 mins.. or last until the compressor is started...

--ghg

DaBit
19-04-2004, 02:55 PM
Nitrous Oxide is a strong oxidizer (they use it for extra O2
in racing cars). What happens to strong oxidizers in oil?

ka-boom.

Nope, nitrous oxide itself is not an oxidizer. Even better, it is almost inert (and that's why it is used extensively in the medical and food processing business). BUT: at high temperatures the nitrous decomposes into N2 and O2, releasing 33% (by volume) of oxygen and 66% nitrogen. We are talking about 600 degrees centigrade without catalyst and at atmospheric pressure. When metallic particles are available (which act as a catalyst) and when under pressure, this temperature becomes lower (300-400 deg.C).

Now, in a racing car the 33% oxygen itself is not that special in a racing engine, though it is a nice extra. The cooling effect produced by the vaporizing nitrous allows more fuel/air to be sucked into the cylinder, which is what produces the bulk of the horsepower gain. See it as a 'super-intercooler'.


Results are like a mortar round hit.
Nitrous may last 10 mins.. or last until the compressor is started...

OK, assume we have a system charged with nitrous, equipped with a high pressure break plate or something. Now, due to some reasons, the nitrous starts decomposing. Then we have AT MOST a 33% oxygen level; hardly more than compressed air. And even 33% is optimistic since then all nitrous must decompose.

The danger is mainly (IMHO, that is) that a chain reaction decomposes the condensible nitrous into noncondensibles, raising pressure too much. In that case, the break plate should act and release the charge. Preferrably the break plate should be connected to a dip tube which dips into the oil, and end into a sandbox. Then, when things fail, the oil is dumped into the sandbox and extinguished.

I'm not using nitrous since I also considered the dangers to be too high. But it could work and be reasonably safe.

ghg
21-04-2004, 05:33 AM
nitrous and oil.
A southern Indiana Welding Supply converted a refrigerated storage
tank from CO2 service to nitrous service. They basically used nitrous
vapor to purge out the CO2, and cooled down the tank (-10 F or so)
and began loading nitrous liquid. CO2 often contains small
amounts of residual oil, depending on it's source. They
forgot to clean out the oil. The oil self ignited and the tank
exploded, killing people over a 300 feet away.
--ghg

cbfull
03-08-2007, 03:17 AM
Hell, if I fart, I already release more greenhouse gas (methane) than what I need to get the system going.


Not a well known fact but humans are unique in that we don't fart methane, we produce hydrogen gas. Methane is produced during the digestion of cellulose, and we don't have the enzyme required for that.

Also, why the concern over N2O being a greenhouse gas? I can't imagine N2O being a bigger contributor to the greenhouse effect than CO2. It's generally accepted that molecules containing carbon atoms are the major contributors. The atmosphere is already composed of nitrogen and oxygen so I don't see how a different atomic configuration could be worse than CO2 or methane.

US Iceman
03-08-2007, 04:04 AM
This topic of methane being a worse greenhouse gas is something I'm interested in. Some of the videos I've seen seem to make methane out to be a substantial problem, more so the hydrates if I remember correctly.

Any comments?

cbfull
03-08-2007, 05:50 AM
Methane is produced as a waste product by many, many organisms, including bacteria. Methane hydrate is basically methane dissolved in water under great pressure. It's the same as a salt like magnesium sulfate (epsom salts) that can hold on to 7 molecules of water for every one molecule of actual magnesium sulfate. You can usually find somewhere on the package the actual contents, "Magnesium sulfate heptahydrate".

In the case of methane hydrate, it can be disturbed where it hides in deep water and then violently bubble to the top (like shaking a 2-liter). Also rising water temperatures from global warming cause it to be released. There is apparently a tremendous amount of this form of methane, and no one knows just how much or how much disturbance it would take to release it.

That's all I can tell you.

The MG Pony
03-08-2007, 09:51 AM
*Grones*

Tell me, does Nitroglycerin sound like a good car coolant? Didn't think so, same thing trying to use NO2 as a refrigerant, oxidizer*Oil*compression*Heat=Hyper velocity metal.

Lowrider
04-08-2007, 12:00 AM
N20, or laughing gas as it's also called, is not suited for refrigeration as stated in the previous posts.

Futhermore STEK is still in use in Holland but when working with gasses under pressure even a well educated person without the right diploma's is liable by law! PED, although not completly active now, in the future will apply for your situation. The risks involved with working with gasses under pressure are not to be understated! That's why I had to get STEK, not just for save handling of refrigerants, but also to show I know how to make a proper joint in a system that's working under pressure!

I do agree the law is a bit to heavy in some points, asprecially in Holland, but we have to be aware of the dangers involved and protect people against themselve and others and the environment against them!!!!

ghg
11-08-2007, 07:18 PM
other posters are correct in that nitrous is
an oxidizer. When it hits oil under pressure,
it may 'do nothing' for awhile, but then
suddenly start a fire and/or explode. I know of
a welding supply that converted a CO2 liquid
tank to nitrous service (CO2 and N2O have
virtually same pressure/temp curve), but
he forgot to clean out the puddle of oil that
years of CO2 had drawn into the tank.

The tank was filled with a few tons of liquid N2O.
The resulting explosion blew out the manway
which hit and killed a person several hundred feet
away..

There exist special oils for vacuum pump
service in oxygen, but that is under vacuum, not
under pressure in a compressor.

CO2 has almost the same pressures as N2O,
so probably easier to use that
--ghg

The MG Pony
11-08-2007, 08:09 PM
O2 is a nightmare to figure out how to compres on the cheap, Hydrogen is simple after scrubing it of moisture and free O2, A good quality Minerol oil will work!

Do you have info on ways to compress oxygen? I was thinking of using a stainless steel diaphram pump as the volumes I'd be dealing with will be a meer 2CFM or less!

HallsEngineer
17-08-2007, 08:50 AM
science direct.com has a paper on the theory
but it'll cost ya

The MG Pony
17-08-2007, 10:41 AM
science direct.com has a paper on the theory
but it'll cost ya

Oh that I'd wager indeed.

HallsEngineer
18-08-2007, 07:15 AM
I asked the people in the know at our place and yes it has been use sucessfully. But it is not used because of health and safety. I f a small amount of this stuff gets out it could kill you. very toxic and a great anestetic, you just fall asleep and never wake up!

The MG Pony
18-08-2007, 07:16 PM
I'm going on with O2, I think the thread has concluded on the NO2.

O2 compression is tricky, and you risk blowing up in flamage and if you don't you'll be well oxygenated! and alert, the H2 is an asphyxient providing you can keep it low enough!

HallsEngineer
19-08-2007, 08:32 AM
O2 compression how high do you need to go? there are oil free compressors. No oil less chance of explosion although metal can burn in pure O2

The MG Pony
19-08-2007, 10:13 AM
Max of 100 psi, standered tank grade carbon steel for storage vessel, alternitevaly I'll use 60 PSI Max with 316 SS.

Hydrogen I'll be using cleaned propane tank 120# @ 100psi, vast majority of the )2 will simply be dumped to atmospher at a remote vent should there be to much generated.

US Iceman
19-08-2007, 04:28 PM
I see a lot of comments about using various gases and materials in this thread. I would like to know how someone has arrived at a conclusion of using certain materials at certain pressures for specific gases.

This is beginning to look like backyard mechanics using trial and error methods to attempt a questionable project.

I would highly recommend anyone from attempting to "try" anything using other gases, unless they are a well qualified engineer.:(

And when I say engineer I do not mean someone who has tools.:o

NH3LVR
19-08-2007, 05:52 PM
I am afraid I kind of have to go with US Iceman on this one.
Technical speculations are fun. However we have to remember the possible results.
O2 is common and available. It is also very dangerous outside it proscribed uses. A few miles from where I sit there was a O2 tanker that overturned. Cars in the vicinity of the cloud caught fire spontaneously.
As to H2 I have had some experience with this. Please be aware that a discharge can and will ignite on its own, probably due to static electricity.
If you want to go REALLY cold you can expand Helium. This is common in High Tech Applications. Another Refrigerant that is available, although expensive is called Polycold.

The MG Pony
19-08-2007, 11:44 PM
Actualy allot of this with the H2 and O2 is well refined, it is a matter of resources availible.

These systems have been built for years, larger the tank lower pressur you can store it at and have enough, O2 is a waste product to me, but one of the guys wantes to use it for his welding, I never designed the system to store any quantity of it, main cell pressure is 20 psi and by the time it is out of the scrubber dryer system it is about 15 psi through to the compressor it is O2 free dry H2. O2 is harder to deal with due to obvious reasons.

The hydrogen system is hermetic and totaly O2 free, it goes through a catylyst that converts ANY free O2 back into water, so by the time it see's the compressor there is no O2 at all.

The O2 is only going to be gas state, if the tank where to rupture there would not be enough to do much, I am very well aware of the properties as I been making H2 gens for long time now, I normaly blow off the O2 continuously only keeping the cell at 20psi.

I did not feel any more detail was needed as all I need is info on O2 compressors, and H2 scrubers.

HallsEngineer
25-08-2007, 02:21 PM
I would not go near O2 or H2 plants anyway thanks though for the concern :rolleyes:. but yes i have seen them and the level of protection around them is very high in UK anyway.

PoodleHeadMikey
04-09-2007, 02:12 PM
Which would react violently with oil.

Since you are esperimenting; can you maybe use something other trhan oil as a lubricant?

PHM
--------

The MG Pony
06-09-2007, 04:14 AM
I would not go near O2 or H2 plants anyway thanks though for the concern :rolleyes:. but yes i have seen them and the level of protection around them is very high in UK anyway.

Last mini system I made a friend in the military asked me if I was making some thing to dispose of nerve gas, I didn't get the joke, but he explained it was more secure and tight then the plants that distroy the stuff!

Going boom has a tendancy to wreck ones day!