Gerry Cox wrote:
>
> I need to cool an object to 4C below ambient. Ambient is in the range 20C to
> 30C. The object does not generate any heat of its own. Cooling does not have
> to be rapid.
snip
> So I am experimenting with the idea of using a compressed air supply, which
> is available near the device, to achieve the cooling.  To achieve
> temperature control, I could turn a pneumatic valve on and of at varying
> duty cycles monitoring the temperature with my PIC - low rate PWM. I suppose
> my real question is how do I design the expander and heat exchanger.  An air
> supply is available at up to 6 Bar with quite high flow rate. The
> temperature of the compressed air before expansion is close to the ambient.
> Ideas anyone?
>
> Thanks in anticipation,
> Gerry.

Well, you could try a vortex cooler... I don't know the name of the
maker, but we
use a small tube like device about 1 1/2 inches by 10 inches long for
the
cooling/heating system in an enviroment suit that the company I work for
sells.

You put in about 30-100 PSI to a fitting in about 1/3 the way down the
tube,
 and out of one end comes cold air, and out of the other
end comes hot air.  Don't know how cold it is, but it produces frost on
the
cold end if left running very long. We use them in other parts of our
plant
for cooling adheasive coated foam used in makeing another product.
 If you are interested, I will try to find out more about the thing and
where we get them from... maybe they would sell them in small amounts.


AG