DIY Liquid Nitrogen
With the same frivolity as "Has anyone ever built a dalek", I wonder
if any of you have thought about making liquid nitrogen at home. I always liked cryogenics as a kid :-) Of course anything is possible - it's just a matter of cost! :-) M |
Markus Splenius wrote:
With the same frivolity as "Has anyone ever built a dalek", I wonder if any of you have thought about making liquid nitrogen at home. I always liked cryogenics as a kid :-) Of course anything is possible - it's just a matter of cost! :-) It's very, very difficult to do on any kind of DIY budget :-) However, the good news is it's very easy to buy, and quite cheap too. You'll need a reasonable sized dewar, maybe 20-25l, and an account with BOC. I pay ~£40 per fillup. -- Grunff |
Grunff wrote:
Markus Splenius wrote: With the same frivolity as "Has anyone ever built a dalek", I wonder if any of you have thought about making liquid nitrogen at home. I always liked cryogenics as a kid :-) Of course anything is possible - it's just a matter of cost! :-) It's very, very difficult to do on any kind of DIY budget :-) However, the good news is it's very easy to buy, and quite cheap too. You'll need a reasonable sized dewar, maybe 20-25l, and an account with BOC. I pay ~£40 per fillup. Or in a farming area, talk to the local AI man. (And no, I don't mean Artificial Intelligence.) -- Ian White Abingdon, England |
On Fri, 07 Jan 2005 15:42:35 +0000, Grunff wrote:
Markus Splenius wrote: With the same frivolity as "Has anyone ever built a dalek", I wonder if any of you have thought about making liquid nitrogen at home. I always liked cryogenics as a kid :-) Of course anything is possible - it's just a matter of cost! :-) It's very, very difficult to do on any kind of DIY budget :-) However, the good news is it's very easy to buy, and quite cheap too. You'll need a reasonable sized dewar, maybe 20-25l, and an account with BOC. I pay ~£40 per fillup. And what do you use it for Grunff? Surely not just for party tricks? :-) M. |
Markus Splenius wrote:
And what do you use it for Grunff? Surely not just for party tricks? :-) Sadly it is just for messing around. I have a nitrogen laser which I run off it sometimes, but that's about the most useful thing I do with it! What happened was I missed it too much after my time in the lab, so had to sort out a private supply. -- Grunff |
Grunff wrote:
Markus Splenius wrote: With the same frivolity as "Has anyone ever built a dalek", I wonder if any of you have thought about making liquid nitrogen at home. I always liked cryogenics as a kid :-) Of course anything is possible - it's just a matter of cost! :-) It's very, very difficult to do on any kind of DIY budget :-) However, the good news is it's very easy to buy, and quite cheap too. You'll need a reasonable sized dewar, maybe 20-25l, and an account with BOC. I pay ~?40 per fillup. What sort of requirements are there on getting an account? How much is a dewar? Hydrogen peroxide vacuum distillation to make HTP for rockets is annoying, and I was wondering if O2 might be more usable. (messing around in garage making rockets - eventual goal is a 4 stage orbital one with a kilo to orbit.) |
Ian Stirling wrote:
What sort of requirements are there on getting an account? This varies a lot depending on who you talk to. There is supposed to be a minimum annual spend, but I've never had this enforced. I buy 2-3 loads a year. How much is a dewar? New a 25l dewar is about £300, but you can get second hand ones for around £100. Hydrogen peroxide vacuum distillation to make HTP for rockets is annoying, and I was wondering if O2 might be more usable. Liquid O2 is a lot less readily available, but you can still get it if you try. (messing around in garage making rockets - eventual goal is a 4 stage orbital one with a kilo to orbit.) Excellent! -- Grunff |
"Markus Splenius" wrote in message
... On Fri, 07 Jan 2005 15:42:35 +0000, Grunff wrote: Markus Splenius wrote: With the same frivolity as "Has anyone ever built a dalek", I wonder if any of you have thought about making liquid nitrogen at home. I always liked cryogenics as a kid :-) Of course anything is possible - it's just a matter of cost! :-) It's very, very difficult to do on any kind of DIY budget :-) However, the good news is it's very easy to buy, and quite cheap too. You'll need a reasonable sized dewar, maybe 20-25l, and an account with BOC. I pay ~£40 per fillup. And what do you use it for Grunff? Surely not just for party tricks? :-) Ice cream, of course! I'm half-seriously thinking about doing it as a finale for one of our barbeques this summer. -- Richard Sampson mail me at richard at olifant d-ot co do-t uk |
Tony Bryer wrote:
I remember going to a Royal Institution (?) science lecture whilst at school and the lecturer put a sausage in a flask of liquid gas. When he took it out it was of course supercold: he dropped it and it shattered into fragments. Ever since I've wondered what those fragments would be when thawed out: a sort of mince? I'm not asking you to repeat the experiment g Small, squishy lumps of sausage meat. One great thing you can use it for is freezing herbs. I haven't done this in years (been too busy with house project), but the quick freezing really preserves the flavour. -- Grunff |
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Andrew Chesters wrote:
Grunff wrote: Ian Stirling wrote: What sort of requirements are there on getting an account? This varies a lot depending on who you talk to. There is supposed to be a minimum annual spend, but I've never had this enforced. I buy 2-3 loads a year. Thanks. How much is a dewar? New a 25l dewar is about ?300, but you can get second hand ones for around ?100. Hydrogen peroxide vacuum distillation to make HTP for rockets is annoying, and I was wondering if O2 might be more usable. Liquid O2 is a lot less readily available, but you can still get it if you try. HTP H2O2 is even less available. IIRC, 70-90% may be available if you're willing to buy a train load, but otherwise you've pretty much got to distill it yourself. (messing around in garage making rockets - eventual goal is a 4 stage orbital one with a kilo to orbit.) Excellent! Agree with the "Excellent"; but I somehow hope I live up-range from Ian!! Well, I can always get you on reentry :) Actually, the stage weights are fairly modest, somewhere around 5Kg, 25Kg, 125Kg, 625Kg (fueled), so on launch it's well under a ton. And the first stage is meant to come back on a parasail. The second stage, which bits may reenter intact of, has a dry weight of only 25Kg. I was initially considering a launch from around John-o-groats (sp?) over the pole. |
On Fri, 07 Jan 2005 15:42:35 +0000, Grunff wrote:
Markus Splenius wrote: With the same frivolity as "Has anyone ever built a dalek", I wonder if any of you have thought about making liquid nitrogen at home. I always liked cryogenics as a kid :-) Of course anything is possible - it's just a matter of cost! :-) It's very, very difficult to do on any kind of DIY budget :-) I would think you would need at least a scuba bottle compressor. You then need a longish length of very very small gauge metal tube (probably less than 0.5mm ID). This you coil so it fits into a very very small thermos flask. The output of the scuba receiver (already cooled to ambient) compressed at about 200 bar goes into the fine tube the air escaping from the open end of the is cool this pre-cools the compressed air coming down the fine tube until the stuff coming out is so cold it's liquid. I've done this at college with a 200 bar bottle of nitrogen as the source. This made about a thimble full in 5 minutes. The flask part being the size of a thimble so it might only work on that scale. 8-( I expect there are some nasty gotchas like having to get rid of all the water and CO2 from the air before compression? 8-( -- Ed Sirett - Property maintainer and registered gas fitter. The FAQ for uk.diy is at www.diyfaq.org.uk Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html |
"Ian Stirling" wrote in message ... Grunff wrote: Markus Splenius wrote: With the same frivolity as "Has anyone ever built a dalek", I wonder if any of you have thought about making liquid nitrogen at home. Hydrogen peroxide vacuum distillation to make HTP for rockets is annoying, and I was wondering if O2 might be more usable. (messing around in garage making rockets - eventual goal is a 4 stage orbital one with a kilo to orbit.) Why 4 stage ? I've always thought the helium weather balloon (also from BOC) then a single stage (fired in the correct direction and not through the balloon aka "the difficult bit") was the most elegant approach. (this is about to go sooooo OT) |
On Fri, 07 Jan 2005 15:42:35 +0000, Grunff wrote:
It's very, very difficult to do on any kind of DIY budget :-) No, many people have built LN2 refrigerators. It's hard to do it efficiently, but refrigeration to this temperature isn't much harder than making your own gas turbine. Don't forget that Ohnes liquified helium in 1911 and discovered superconductivity almost immediately afterwards. Nitrogen was back in the 1880's. Now how much technology did any lab have back then that you can't reproduce in a half-decent modern home workshop ? -- Smert' spamionam |
On Fri, 07 Jan 2005 16:42:15 +0000, Grunff wrote:
New a 25l dewar is about £300, but you can get second hand ones for around £100. Even more fun - damaged Dewars are free and the TIG welding course is about £200. If it's not aluminium and the damage is minor, you might just be able to silver solder it. |
"Andy Dingley" wrote in message ... On Fri, 07 Jan 2005 15:42:35 +0000, Grunff wrote: It's very, very difficult to do on any kind of DIY budget :-) No, many people have built LN2 refrigerators. It's hard to do it efficiently, but refrigeration to this temperature isn't much harder than making your own gas turbine. Don't forget that Ohnes liquified helium in 1911 and discovered superconductivity almost immediately afterwards. Nitrogen was back in the 1880's. Now how much technology did any lab have back then that you can't reproduce in a half-decent modern home workshop ? Well the availability of whatever ore the Curies purified radium from is presumably a little harder to get now :-) |
"Ian Stirling" wrote in message ... Andrew Chesters wrote: Grunff wrote: Ian Stirling wrote: What sort of requirements are there on getting an account? This varies a lot depending on who you talk to. There is supposed to be a minimum annual spend, but I've never had this enforced. I buy 2-3 loads a year. Thanks. How much is a dewar? New a 25l dewar is about ?300, but you can get second hand ones for around ?100. Hydrogen peroxide vacuum distillation to make HTP for rockets is annoying, and I was wondering if O2 might be more usable. Liquid O2 is a lot less readily available, but you can still get it if you try. HTP H2O2 is even less available. IIRC, 70-90% may be available if you're willing to buy a train load, but otherwise you've pretty much got to distill it yourself. (messing around in garage making rockets - eventual goal is a 4 stage orbital one with a kilo to orbit.) Excellent! Agree with the "Excellent"; but I somehow hope I live up-range from Ian!! Well, I can always get you on reentry :) Actually, the stage weights are fairly modest, somewhere around 5Kg, 25Kg, 125Kg, 625Kg (fueled), so on launch it's well under a ton. And the first stage is meant to come back on a parasail. The second stage, which bits may reenter intact of, has a dry weight of only 25Kg. I was initially considering a launch from around John-o-groats (sp?) over the pole. That'll cost you in orbital velocity: you won't pick up anything from the earth's rotation in that direction. I assume you've done the calculations :-). I've been down to the ESA launch site at Kourou, French Guiana, and it's there for a good reason, unobstructed launch path east over the atlantic and only 5 degrees north. You'd better talk to the folks in the Orkneys, they're due north of John O'Groats! Andy. |
andrewpreece wrote:
"Ian Stirling" wrote in message ... Andrew Chesters wrote: Grunff wrote: Ian Stirling wrote: What sort of requirements are there on getting an account? This varies a lot depending on who you talk to. There is supposed to be a minimum annual spend, but I've never had this enforced. I buy 2-3 loads a year. Thanks. How much is a dewar? New a 25l dewar is about ?300, but you can get second hand ones for around ?100. Hydrogen peroxide vacuum distillation to make HTP for rockets is annoying, and I was wondering if O2 might be more usable. Liquid O2 is a lot less readily available, but you can still get it if you try. snip I was initially considering a launch from around John-o-groats (sp?) over the pole. That'll cost you in orbital velocity: you won't pick up anything from the earth's rotation in that direction. I assume you've done the calculations :-). I've been down to the ESA launch site at Kourou, French Guiana, and it's there for a good reason, unobstructed launch path east over the atlantic and only 5 degrees north. You'd better talk to the folks in the Orkneys, they're due north of John O'Groats! Not quite due north. I'm budgeting for a very, very large contingancy delta-v, around a kilometer a second, just in case. Part of the design is to be able to cope with unexpected stage underperformance, or the flame going out. Fuel is cheap. |
"Mike" wrote
| Well the availability of whatever ore the Curies purified radium | from is presumably a little harder to get now :-) And can you imagine the expression on a buyer's face when you answered "no, there's no asbestos in the house, but we did do some radiology experiments in the scullery" Owain |
On Fri, 7 Jan 2005 20:49:46 -0000, "Mike" wrote:
Well the availability of whatever ore the Curies purified radium from is presumably a little harder to get now :-) No idea - the usual "ores" for the back-bedroom Teller-wannabees these days are that old favourite, thorium from caravan gas mantles, or else americium from smoke detectors. The Curies went through _tons_ of pitchblende. We just don't have the space to do it these days. -- Smert' spamionam |
No idea - the usual "ores" for the back-bedroom Teller-wannabees these days are that old favourite, thorium from caravan gas mantles, I think most, maybe all, don't have it anymore. Damn them and their ways to constantly foil my evil plans!!! Sam |
"Ian Stirling" wrote in message ... andrewpreece wrote: "Ian Stirling" wrote in message ... Andrew Chesters wrote: Grunff wrote: Ian Stirling wrote: What sort of requirements are there on getting an account? This varies a lot depending on who you talk to. There is supposed to be a minimum annual spend, but I've never had this enforced. I buy 2-3 loads a year. Thanks. How much is a dewar? New a 25l dewar is about ?300, but you can get second hand ones for around ?100. Hydrogen peroxide vacuum distillation to make HTP for rockets is annoying, and I was wondering if O2 might be more usable. Liquid O2 is a lot less readily available, but you can still get it if you try. snip I was initially considering a launch from around John-o-groats (sp?) over the pole. That'll cost you in orbital velocity: you won't pick up anything from the earth's rotation in that direction. I assume you've done the calculations :-). I've been down to the ESA launch site at Kourou, French Guiana, and it's there for a good reason, unobstructed launch path east over the atlantic and only 5 degrees north. You'd better talk to the folks in the Orkneys, they're due north of John O'Groats! Not quite due north. I'm budgeting for a very, very large contingancy delta-v, around a kilometer a second, just in case. Part of the design is to be able to cope with unexpected stage underperformance, or the flame going out. Fuel is cheap. Fascinating: I thought at first you were making it up! AFAIK noone has done anything like this, the X-prize contestants aren't anywhere near orbital velocity and the performance needed in terms of fuel goes up as the square of the velocity, and you reckon you've a km/sec delta-v as contingency! I am all admiration Sir! I've seen other rocket groups' websites ( one group is called MARS ) but none are quite as ambitious. The amount of human effort needed to achieve the kind of performance you specify is considerable. Any chance of a technical overview or is it all under wraps? Andy. |
"andrewpreece" wrote in message ... ! AFAIK noone has done anything like this, the X-prize contestants aren't anywhere near orbital velocity Aren't they ? I thought the prize had been won. Don't they actually have to achieve orbit to win ? |
Mike wrote:
Aren't they ? I thought the prize had been won. Don't they actually have to achieve orbit to win ? No just a specific height, 100km IIRC, their trajectory was something like this ... ^ / \ | | | | | | | | / | / \ -/ \- Wouldn't "orbital velocity" vary depending on the height you wished to orbit at? Perhaps someone was thinking of "escape velocity" which is about 26,000mph |
"Andy Burns" wrote in message ... Mike wrote: Aren't they ? I thought the prize had been won. Don't they actually have to achieve orbit to win ? No just a specific height, 100km IIRC, their trajectory was something like this ... ^ / \ | | | | | | | | / | / \ -/ \- Wouldn't "orbital velocity" vary depending on the height you wished to orbit at? Whay does the shuttle and Spacelab need ? That sounds a good start. Perhaps someone was thinking of "escape velocity" which is about 26,000mph So this Virgin "spaceplane" they're building won't even get you near a proper orbit then ? Does it reach the point where you feel weightless (other than when it goes into a controlled dive) ? |
Andy Dingley wrote:
Don't forget that Ohnes liquified helium in 1911 and discovered superconductivity almost immediately afterwards. Nitrogen was back in the 1880's. Now how much technology did any lab have back then that you can't reproduce in a half-decent modern home workshop ? This is a fair point, but it would be quite a bit of work none the less. Got any diagrams etc. of homebuilt kit? -- Grunff |
Mike wrote:
Whay does the shuttle and Spacelab need ? That sounds a good start. Apparently the ISS is currently 349km high and whizzing over Egypt http://science.nasa.gov/temp/StationLoc.html Some nice formulae for calulating orbital speeds for a given altitude http://www.aerospaceweb.org/question...ft/q0164.shtml for 300km it would be 17000mph So this Virgin "spaceplane" they're building won't even get you near a proper orbit then ? Does it reach the point where you feel weightless (other than when it goes into a controlled dive) ? From what I heard the Virgin/SpaceShipTwo will go higher than the SpaceShipOne, and you will get several minutes of weighlessness for your $200,000 |
In article ,
Grunff writes: Andy Dingley wrote: Don't forget that Ohnes liquified helium in 1911 and discovered superconductivity almost immediately afterwards. Nitrogen was back in the 1880's. Now how much technology did any lab have back then that you can't reproduce in a half-decent modern home workshop ? This is a fair point, but it would be quite a bit of work none the less. Got any diagrams etc. of homebuilt kit? ISTR it can be done with a compressor and pair of concentric copper pipes. These are coiled up and inserted into a thermos or dewer. Air is pumped down the central one which has an expansion jet on the end which cools the air. The cool air is recovered back up the outside one which further cools the air coming down the central one, until eventually the air gets cold enough to start liquifying when it leaves the expansion jet. At least, this is my recollection of one way of doing it from O-level physics. There appear to be some details missing from this, like where the heat gets dumped. Probably, the compressed air is cooled back down to room temperature before it enters the coil to be further cooled by the returning air. (It is not necessary to send the same air round and round the system.) Obviously, starting with air, you end up with liquified air rather than nitrogen. The boiling points of nitrogen, oxygen and argon are near enough you'll get them all ISTR. This subject came up a few months back, as I was considering trying to do this with a compressor from a freezer. I did google around thinking there was probably a secret society of low temperature hobbists out there doing this, but came up with nothing, so if there is, they are very secret. I couldn't even find a description of the process above which I recall from my O-level physics lessons. -- Andrew Gabriel |
"Markus Splenius" wrote in message
However, the good news is it's very easy to buy, and quite cheap too. You'll need a reasonable sized dewar, maybe 20-25l, and an account with BOC. I pay ~£40 per fillup. And what do you use it for Grunff? Surely not just for party tricks? It was to give him the reputation of a hard man but his wife found him rather cold so she broke it off. Apparently they all give him the cold shoulder these days. So be careful! -- Posted via Mailgate.ORG Server - http://www.Mailgate.ORG |
andrewpreece wrote:
"Ian Stirling" wrote in message snip I'm budgeting for a very, very large contingancy delta-v, around a kilometer a second, just in case. Part of the design is to be able to cope with unexpected stage underperformance, or the flame going out. Fuel is cheap. Fascinating: I thought at first you were making it up! AFAIK noone has done anything like this, the X-prize contestants aren't anywhere near orbital velocity and the performance needed in terms of fuel goes up as the square of the velocity, and you reckon you've a km/sec delta-v as contingency! I am all admiration Sir! I've seen other rocket groups' websites ( one group is called MARS ) but none are quite as ambitious. The amount of human effort needed to achieve the kind of performance you specify is considerable. Any chance of a technical overview or is it all under wraps? At the moment I'm working on ancillery systems, guidance and stuff, and working out best ways of making cheap small regeneratively cooled rocket engines. In a way, it's not very ambitious. Some groups are going for things like single stage or 2 stage to orbit. This means that you almost have to go to extreme lengths to reduce the weight of the vehicle, and are very highly penalised by small size due to having to push through the atmosphere. (adding a percent to the dry mass of a 1 or 2 stage vehicle can often be the difference between having a payload, and not being able to reach orbit empty. If you're willing to go with more stages, then in some ways things get easier. You throw away empty tanks along the way, which means that you don't have to have one big very light tank. You reduce the total mass you have to take to orbit, as the size of rocket engine on the upper stages is smaller, hence lighter, so you don't have to worry so much about the takeoff engines weight, or make it so that it can be throttled down so far, and in some cases can eliminate the need for the engine to be restartable. All of this is good, as it makes the hard bits (rocket engine, ...) a little easier, and means that instead of needing Aluminium-Lithium tanks, you can go with not very good steel or fiberglass, can use screwfix 2.99 full-bore ball valves instead of machining something exotic and light, ... Yes, it may use 25 times more fuel than a 'good' rocket, but fuel is cheap. (I'm aiming for a cost for the whole thing of only 10K ) This is for around a kilo to LEO. For much more, this approach starts to break down, and you need to go to appropriate high technology in some parts in order to keep costs down. It doesn't make sense to (for example) make a much larger rocket out of simple to construct steel, if the overall cost is lower with better harder to weld steel. |
Or in a farming area, talk to the local AI man. (And no, I don't mean Artificial Intelligence.) I thought most of that was on these news groups g Dave -- Some people use windows, others have a life. |
Dave Stanton wrote:
Or in a farming area, talk to the local AI man. (And no, I don't mean Artificial Intelligence.) I thought most of that was on these news groups g One of the best things about this ng is that it has plenty of the real stuff (and this time I *do* mean Intelligence) -- Ian White Abingdon, England |
"Andy Burns" wrote in message ... Mike wrote: Whay does the shuttle and Spacelab need ? That sounds a good start. Apparently the ISS is currently 349km high and whizzing over Egypt http://science.nasa.gov/temp/StationLoc.html Some nice formulae for calulating orbital speeds for a given altitude http://www.aerospaceweb.org/question...ft/q0164.shtml for 300km it would be 17000mph So this Virgin "spaceplane" they're building won't even get you near a proper orbit then ? Does it reach the point where you feel weightless (other than when it goes into a controlled dive) ? From what I heard the Virgin/SpaceShipTwo will go higher than the SpaceShipOne, and you will get several minutes of weighlessness for your $200,000 Is that real weightlessness or the same as you can get in one of those Russian transport planes for $5k ? |
"Andrew Gabriel" wrote in message ... In article , Grunff writes: Andy Dingley wrote: Don't forget that Ohnes liquified helium in 1911 and discovered superconductivity almost immediately afterwards. Nitrogen was back in the 1880's. Now how much technology did any lab have back then that you can't reproduce in a half-decent modern home workshop ? This is a fair point, but it would be quite a bit of work none the less. Got any diagrams etc. of homebuilt kit? ISTR it can be done with a compressor and pair of concentric copper pipes. These are coiled up and inserted into a thermos or dewer. Air is pumped down the central one which has an expansion jet on the end which cools the air. The cool air is recovered back up the outside one which further cools the air coming down the central one, until eventually the air gets cold enough to start liquifying when it leaves the expansion jet. At least, this is my recollection of one way of doing it from O-level physics. There appear to be some details missing from this, like where the heat gets dumped. Probably, the compressed air is cooled back down to room temperature before it enters the coil to be further cooled by the returning air. (It is not necessary to send the same air round and round the system.) Obviously, starting with air, you end up with liquified air rather than nitrogen. The boiling points of nitrogen, oxygen and argon are near enough you'll get them all ISTR. This subject came up a few months back, as I was considering trying to do this with a compressor from a freezer. I did google around thinking there was probably a secret society of low temperature hobbists out there doing this, but came up with nothing, so if there is, they are very secret. I couldn't even find a description of the process above which I recall from my O-level physics lessons. Don't shout this too loud or we'll have Prescott's mob doing part whatever's next "Licencing and control of home research laboratories" Yes, Mr BCO, this is where we attach the brain to the lightning rod. Can I have yours ? |
"Huge" wrote in message ... "Mike" writes: "andrewpreece" wrote in message ... ! AFAIK noone has done anything like this, the X-prize contestants aren't anywhere near orbital velocity Aren't they ? I thought the prize had been won. Don't they actually have to achieve orbit to win ? No. Yes. No. Is there a prize for real orbit then ? |
Ed Sirett wrote:
On Fri, 07 Jan 2005 15:42:35 +0000, Grunff wrote: Markus Splenius wrote: With the same frivolity as "Has anyone ever built a dalek", I wonder if any of you have thought about making liquid nitrogen at home. I always liked cryogenics as a kid :-) Of course anything is possible - it's just a matter of cost! :-) It's very, very difficult to do on any kind of DIY budget :-) I would think you would need at least a scuba bottle compressor. You then need a longish length of very very small gauge metal tube (probably less than 0.5mm ID). This you coil so it fits into a very very small thermos flask. The output of the scuba receiver (already cooled to ambient) compressed at about 200 bar goes into the fine tube the air escaping from the open end of the is cool this pre-cools the compressed air coming down the fine tube until the stuff coming out is so cold it's liquid. I've done this at college with a 200 bar bottle of nitrogen as the source. This made about a thimble full in 5 minutes. The flask part being the size of a thimble so it might only work on that scale. 8-( I expect there are some nasty gotchas like having to get rid of all the water and CO2 from the air before compression? 8-( Not really, any water in LN2 freezes so cold it sublimates away. CO2 freezes solid and in some situations can by seen as a frost on the walls of the Dewar or rolling around on the bottom as nodules. Peter -- Add my middle initial to email me. It has become attached to a country |
On Sat, 08 Jan 2005 01:45:11 +0000, Andrew Gabriel wrote:
In article , Grunff writes: Andy Dingley wrote: Don't forget that Ohnes liquified helium in 1911 and discovered superconductivity almost immediately afterwards. Nitrogen was back in the 1880's. Now how much technology did any lab have back then that you can't reproduce in a half-decent modern home workshop ? This is a fair point, but it would be quite a bit of work none the less. Got any diagrams etc. of homebuilt kit? ISTR it can be done with a compressor and pair of concentric copper pipes. These are coiled up and inserted into a thermos or dewer. Air is pumped down the central one which has an expansion jet on the end which cools the air. The cool air is recovered back up the outside one which further cools the air coming down the central one, until eventually the air gets cold enough to start liquifying when it leaves the expansion jet. At least, this is my recollection of one way of doing it from O-level physics. There appear to be some details missing from this, like where the heat gets dumped. Probably, the compressed air is cooled back down to room temperature before it enters the coil to be further cooled by the returning air. (It is not necessary to send the same air round and round the system.) Obviously, starting with air, you end up with liquified air rather than nitrogen. The boiling points of nitrogen, oxygen and argon are near enough you'll get them all ISTR. This subject came up a few months back, as I was considering trying to do this with a compressor from a freezer. I did google around thinking there was probably a secret society of low temperature hobbists out there doing this, but came up with nothing, so if there is, they are very secret. I couldn't even find a description of the process above which I recall from my O-level physics lessons. I don't know if you saw my post. I'm fairly sure you'll need 200bar for the air. The heat given off compressing air to that amount is huge. And needs to be removed before the compressed air enter the low temp part. I'm fairly sure the fridge kit is only good for a few bar output. -- Ed Sirett - Property maintainer and registered gas fitter. The FAQ for uk.diy is at www.diyfaq.org.uk Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html |
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