2 replies to this topic

[procengsas]

Hello,

I would like to find out why chlorine cylinders tend to freeze during transfer. Just a curious question.

Thanks

[Art Montemayor]

Procengas:

Basically, chlorine liquid will evaporate and cool when gas is drawn out of a cylinder. Chlorine cylinders do not store the chlorine as a gas. The substance exists as a SATURATED LIQUID within the cylinder – exactly as CO2, Freon, ammonia, LPG, etc. etc.

It is only the uneducated layman that calls the substance in the cylinder a "gas". We engineers know (or should know) the big difference. You will note that all the refrigerants exhibit this same characteristic. Chlorine is also a "refrigerant" of sorts. It can be classed as a refrigerant because of its relative critical point of 290 oF and 1159 psia – which means that it can exist as a liquid a temperatures below 290 oF (with corresponding lower pressures).

If you draw off the saturated gas from a cylinder of liquid chlorine, you are adiabatically expanding the contents and thereby causing an adiabatic, thermodynamic expansion where the enthalpy is kept constant. The result is a dramatic lowering of the temperature in the remaining liquid. This is exactly what happens in all mechanical refrigeration processes – where Freon, butane, propane, ammonia, etc. are used as the refrigerant fluid.

The process is definitely NOT an example of the Joule-Thomson Effect.

[pawan]

Art is right as usual.
In case of many gases as already mentioned by Art, they are generally in liquid form
based on their critical points.

So when they expand, as explained by Art, there is a drop in temperature & hence frosting.
Also this is not freezing of chlorine, there is frosting on the cylinder due to cooling of surrounding air
to its freezing level.