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Tycho
23-05-2008, 11:48 PM
We've been having a discussion at work, as we have installed (made for ourselves) a ***** cleaning unit.

the unit is sucking gas from the top of bottles or tanks, and certain people clain that if we leave the unit running at -30 water will follow the ***** gas and exhaust the filters and then make it's way to the tank of now "clean" *****.

In the beginning we ran the unit like this and sent a sample to be analyzed and got the answer back that it was cleaner than what the Official ***** cleaning company could do...

Now we have installed a suction pressure regulator on the unit... but my question is, does water in the system freeze into the liquid and then evaporate along with the liquid and follow the gas out into the system?

nike123
24-05-2008, 04:21 AM
Now we have installed a suction pressure regulator on the unit... but my question is, does water in the system freeze into the liquid and then evaporate along with the liquid and follow the gas out into the system?



Frozen water could not be liquid. It is solid!

At -30C water is frozen and solid. It, however, could be sublimed in to water vapor at these temperatures at certain low pressure (38 Pa) and then follow the gas out into system.
http://en.wikipedia.org/wiki/Triple_point

Tycho
24-05-2008, 08:31 PM
Frozen water could not be liquid. It is solid!

At -30C water is frozen and solid. It, however, could be sublimed in to water vapor at these temperatures at certain low pressure (38 Pa) and then follow the gas out into system.
http://en.wikipedia.org/wiki/Triple_point

Interesting read thanks :D

And I meant that the water would freeze when the ***** liquid dropped below freezing point :D

US Iceman
25-05-2008, 01:57 AM
I think you have two issues Tycho. One is the water will freeze out of the refrigerant into a solid when the refrigerant is below freezing. This is how a "cold trap" works. The trap is cooled by a very cold moisture of some fluid. I have used glycol and dry ice.

The moisture pulled back through the cold trap freezes onto the inside surface of the trap.

If you remove the trap and let it warm up, the ice melts and can then be drained.

The other point is what nike123 suggested. This is essentially what happens when you pull a deep vacuum when evacuating a system.

TXiceman
27-05-2008, 12:42 AM
You have to look at the vapor pressure of water and see if it will go to vapor state at pressures above the 32 dF freeze point.

The water will stay in a liquid state for your higher pressure refrigerants as the 32 dF saturation pressure is above the vapor point for the water.

If you have ever gotten water in to a ***** system and operated an expasion device below 32 dF, it will ice in the expansion valve and create control problems.

The problem with just distilling off the refrigerant is you should still check it for purity due to acids and other contaminants.

Ken

Tycho
27-05-2008, 06:45 PM
What we do is take gas from the top of bottles with contaminated ***** and pull it through 2 x 8 danfoss filterdriers and then through the compressor and through another 2 x 8 filterdriers...

we have sent in ***** samples for analysis from some batches we did with low suction pressure, and the result we got back was better than what the main ***** supplier in Norway could manage.

Later it became a discussion that if the suction pressure was below 0 celcius then the ice would "insert spaced out explanation here" and evaporate and follow the ***** gas and we'd get a greater amount of contamination in the filters.



but now I see as quoted from the wikipedia article linked above that it needs to be at "0.01 C and a partial vapour pressure ca. 6.1173 millibars" for the water to be at the triple point...


so in my eyes this is a non issue...