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paulw1283
17-05-2006, 03:17 AM
I need a source of cold air for an application I'm designing. What's the easiest and simplest way to achieve this?

I cannot use freeze spray since tetraflouroethene is heavier than air and can displace air in the lungs.

I cannot use any gas that depletes the ozone layer.

I cannot use any gas that is toxic or have any harm to humans.

The temperature of the gas coming out of the tank (or canister) must be colder than -10 F

The gas must be able to be stored in a tank/canister in liquid form for a significant amount of time without must leaking and has no pressure problems as long as the ambient temperature is not too hot.

Any gas that satisfy all those requirements? Thanks a bunch.

Peter_1
17-05-2006, 06:07 AM
Nitrogen will be the only one.

NoNickName
17-05-2006, 07:09 AM
Propane is also ok, as long as you are not smoking.

Johnny Rod
17-05-2006, 09:43 AM
Carbon dioxide? I use it in the lab to get down to below -20C.

Anything that isn't air will have some consequence - even nitrogen could be regarded as hazardous because it will suffocate you. Depends what you can or can't get away with.

Peter_1
17-05-2006, 02:57 PM
Indeed Johnny Rod, CO2 is also usable.

The MG Pony
17-05-2006, 11:09 PM
Why not have a small phase change unit cooling a tube and push a low flow of air through it?

paulw1283
17-05-2006, 11:37 PM
Why not have a small phase change unit cooling a tube and push a low flow of air through it?

How fast do you think that can lower the temperature of the air to below 0 F? I hope it can be done in seconds.

paulw1283
17-05-2006, 11:38 PM
Indeed Johnny Rod, CO2 is also usable.

That's what I thought first.

Then I did some research on CO2 and it turns out CO2 is toxic in high concentrations. Or am I wrong?

Dan
17-05-2006, 11:39 PM
I cannot use any gas that is toxic or have any harm to humans.

All gases that do not include oxygen can suffocate or otherwise be harmful to humans. I think if you explained your need a little better that you would get considerably better answers. My first question is how large a space is it that you wish to cool, and for how long? Vortex tubes come to mind. :)

But you can cool significant quantities of air by passing it over a sealed unit as MG Pony suggests. Again, to what end and how much?

The MG Pony
17-05-2006, 11:49 PM
ya and it would chill the air very fast in small quantities, and fare as safe goes no gass is safe other then good ol air.

paulw1283
19-05-2006, 12:18 AM
I don't need much air, just a continuous light breeze, like when you spray a bottle of perfume

How fast can the air be cooled with such a tube design? I prefer the temperature to be around or below 0 F. Is that possible?

I can probably have a mechanism that sprays liquid CO2 or tetrafluroethene to the outside of the tube but I really am not sure if I can get the air inside the tube cold enough, fast enough.

What material should the tube be made with? thanks

Dan
19-05-2006, 01:09 AM
Sounds like sizing is an issue. Is this to be a portable device? I understand that you have an idea that you choose to keep proprietary. I further think that your idea is doable. I feel like I am playing one of those hand held computer games that asks you 20 questions and then successfully tells you what object or thing you are thinking of.

Since this is a mysterious experiment at this point... and if you are moving a small mass of air, as you imply, I would begin with the smallest diameter-and-length combination of copper tubing that you can find readily and that you can coil into the size that you consider acceptable for your purposes, that you can blow air through. But that implies a blower. Do a search for Hilsch or Vortex Tube.

Without knowing how, what, or why you are experimenting with such a device I doubt that I can really help you other than to say, "Yes, it can be done." :)

Peter_1
19-05-2006, 06:35 AM
I don't need much air, just a continuous light breeze, like when you spray a bottle of perfume

How fast can the air be cooled with such a tube design? I prefer the temperature to be around or below 0 F. Is that possible?



If you need only these small amounts, use then a vortex tube.
It converts compressed air in a flow at the left of 60C to 80C (140F tot 175F) and on the right side air at 0C to -15C (32F to 5F) without any other source then compressed air.
Is that what you're looking for?

See attached picture I just made where I hold one in my hand with and without a muffler.

The MG Pony
19-05-2006, 07:44 AM
2 feet of copper in copper tube the outer jacket refrigerated and the inner tube is where the air is blowen through, this will come out plenty cold at a steady light breeze

Dan
20-05-2006, 04:25 PM
Peter, why am I not surprised that you made a Vortex tube? Lol!

paulw1283
21-05-2006, 02:37 AM
Thanks for all the help guys, really appreciate it.

One more thing though.

Whether I use the vortex tube or a "coil cooling" method via refrigerant, a source of compressed air is needed.

As to the vortex tube, is there a relationship between the PSI of the air and the amount of cooling it can achieve? Does higher pressure compressed air equates to cooler air possible? Or is this something dependent on the design of the tube?

Thanks

Peter_1
21-05-2006, 09:05 AM
Read once this http://www.exair.com/vortextube/vt_page.htm?source=google&group=vortextube

It depends on the orifice you insert in the vortex and the pressure.

paulw1283
27-05-2006, 03:59 PM
So a high pressure is needed for cold air. But that'll make the nozzle pressure and flow rate high right?

Peter_1
27-05-2006, 04:15 PM
So a high pressure is needed for cold air. But that'll make the nozzle pressure and flow rate high right?
This is relative: what is a high air pressure, a high nozzle pressure an a high flow rate?
You have to test this.

Making cold air will cost energy, unless you use the energy stored in a liquid refrigerant.

paulw1283
30-05-2006, 08:01 PM
Thanks. Can they (vortex tubes) be made pretty cheaply if mass produced? I only need a tiny unit with a very small flow, and with an input pressure of about 100psig.

I really hope the price per unit can be very low.

Do you know if they can be under $3 per unit?

Peter_1
30-05-2006, 10:23 PM
You still haven't given an answer what capacity you need and for what purpose you will need it.

Peter_1
30-05-2006, 10:25 PM
Or use Peltier elements

paulw1283
31-05-2006, 02:44 PM
I emailed Exair and they have a model that inputs 100 PSIG air at 2 SCFM and outputs 0.6 SCFM of -40C air, which is great.

But I think even 0.6 is more than I need. Even 0.15 SCFM is enough for me. So what do you think?

Mass produced, they shouldn't be that expensive right?

Peter_1
31-05-2006, 04:43 PM
How many pieces you're thinking on and what's the purpose of the unit?
3 $ seems extremely low, it must be made in a CNC machining center. These machines costs a lot to operate.
3 , let's take 1 $ material, 2 $ labour, so all the handling and machining must be done in less then 1 minute. Forget it.

Given an output of -40C doesn't say anything...is that flow enough to cool your object (is it for CPU cooling)

You seems afraid to give answers on our questions.:confused:

The MG Pony
31-05-2006, 09:44 PM
. < With the lack of comprehensive information thats all I can realy think of to say.