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Peter_1
03-02-2009, 09:48 AM
I wondered how fast water evaporates at very high vacuum levels so that we could visualize a vacuum process in our refrigeration systems better.

A client tied a bottle of water with duct tape behind the window of a huge deep vacuum machine and pulled it vacuum.
It evaporates first and i finally freezes and the splashes freezes against the window.

I think this is a unique movie.

I posted this movie (33MB) on http://rapidshare.com/files/190366409/MOV01357.MPG

nicolacozma
03-02-2009, 10:45 AM
Very impressive and also didactic. I will use it for trainings.
Thanks Frank

Quality
03-02-2009, 11:07 AM
I am sure that I have read some where that the freezing point of water actualy rises above 0 degrees C at high vacuum levels. I will have to have another look. But as for the video its great

Argus
03-02-2009, 11:25 AM
.



Removing water in quantity from a system under a high vacuum requires heat as well as low pressure. In fact it's largely governed on the ambient temperature at the machine as well as the prevailing pressure in the system.

Too high a vacuum depresses the boiling point and ice can be the result. Removal in that condition uses sublimation and the removal rate is very slow.

It's worth looking at the tables used in absorption systems which will provide the boiling point at the ambient temperatures.

There is a technique for removing large amounts of moisture from chillers, typically after a tube burst, and it's not a quick process and certainly not just throwing a vacuum pump on and leaving it.


.

nike123
03-02-2009, 11:32 AM
I am sure that I have read some where that the freezing point of water actualy rises above 0 degrees C at high vacuum levels. I will have to have another look. But as for the video its great

http://www.its.caltech.edu/~atomic/snowcrystals/ice/h2ophase.gif
http://www.lsbu.ac.uk/water/phase.html

Thermatech
03-02-2009, 11:46 AM
Is this not the reason why we encourage engineers to use triple evacuation method with OFN purge between & then double check that no moisture is left with vacume pressure rise test ?

If any liquid water left in the refrigeration tubes becomes ice during vac then it should melt & become vapor during the pressure rise test & make reduced vac reading.

Problem is very few engineers seem to bother with this procedure.

Quality
03-02-2009, 11:50 AM
http://www.its.caltech.edu/~atomic/snowcrystals/ice/h2ophase.gif
http://www.lsbu.ac.uk/water/phase.html
Good diagrams they are Nike 123:)

Peter_1
03-02-2009, 01:00 PM
Is this not the reason why we encourage engineers to use triple evacuation method with OFN purge between & then double check that no moisture is left with vacume pressure rise test ?

If any liquid water left in the refrigeration tubes becomes ice during vac then it should melt & become vapor during the pressure rise test & make reduced vac reading.

Problem is very few engineers seem to bother with this procedure.
Agree 100% with you

icemakerman
05-02-2009, 09:11 AM
I am sure that I have read some where that the freezing point of water actualy rises above 0 degrees C at high vacuum levels. I will have to have another look. But as for the video its great
dont know where u might have read this but i was under the impression that if the pressure is lowered so is the boiling/freezing temp...same as refrigerants...thus vacuum applied to the sealed system causes water to evaporate at same ambient ...is this not basic knowledge taught to 1st years

Quality
05-02-2009, 01:42 PM
obviously I must be thick

paul_h
05-02-2009, 02:29 PM
The worst thing is trying to evac a freezer after a low side leak, while trying to keep everything in the freezer cold so the owner doesn't lose stock.
It doesn't work :(

I got blockages in the system after trying that. In the end I had to reclaim, and heat up the evap with a turbo torch while evacuating the second time.

taz24
05-02-2009, 02:47 PM
dont know where u might have read this but i was under the impression that if the pressure is lowered so is the boiling/freezing temp...same as refrigerants...thus vacuum applied to the sealed system causes water to evaporate at same ambient ...is this not basic knowledge taught to 1st years


Icemakerman I think you will find that Quality is quite right.
Vacuum does strange things to water and it does make it freeze at about 1 degC not 0 degC.

Cheers taz.

nike123
05-02-2009, 03:35 PM
Icemakerman I think you will find that Quality is quite right.
Vacuum does strange things to water and it does make it freeze at about 1 degC not 0 degC.

Cheers taz.


Where is that on diagrams wich I posted?:confused:
I see rise only until 0.0098C at 4,58 Torr (triple point) and then fall again below 0.

Peter_1
06-02-2009, 06:00 AM
It is 24C in the vacuum chamber.
Peter

THE WOMBAT
06-02-2009, 11:04 AM
We had a large centrif split and If you want to vac out a split chiller fast,, use more than one vac pump. But we also had 4 x 3Kw blow heaters and put up plastic sheeting up to encase the whole chiller in an ambient of 40*c. This reduced the vac out time by half.
Higher ambient temps always speed up moisture removal. You wont remove water if the piping enviroment is below -0*c

Quality
06-02-2009, 04:38 PM
It is 24C in the vacuum chamber.
Peter
Amazing Really

Peter_1
06-02-2009, 07:54 PM
I will ask once he's doing the test again and continues it's vacuum while the water is frozen.
Wonder if you see any change in the ice level.
This machine can go really, realy deep in vacuum.
Last stage is a diffusion pump http://en.wikipedia.org/wiki/Diffusion_pump and in the newer versions, they use turbomolecular pumps http://en.wikipedia.org/wiki/Turbomolecular_pump (price +/- 25,000 /pump and +/- 6 to 10 pumps /chamber)

K.R.Iyer
06-02-2009, 08:04 PM
Peter_1,
Very impressive video. Thanks for this effort. I am just wondering what would be the size of vacuum pump used here and what vacuum level it was maintaining inside the chamber - considering the relative ease with which the water was boiled and frozen.

Peter_1
06-02-2009, 08:19 PM
See http://www.refrigeration-engineer.com/forums/showthread.php?t=5660 and http://www.refrigeration-engineer.com/forums/showthread.php?t=5203
I can stand in the chamber.
They reach a vacuum in the range of 10^-8 Pa

K.R.Iyer
06-02-2009, 08:30 PM
Is this not the reason why we encourage engineers to use triple evacuation method with OFN purge between & then double check that no moisture is left with vacume pressure rise test ?

If any liquid water left in the refrigeration tubes becomes ice during vac then it should melt & become vapor during the pressure rise test & make reduced vac reading.

Problem is very few engineers seem to bother with this procedure.

Thermatech,
I do triple evacuation in my service jobs - but my understanding is that the triple evacuation is done to get the residual moisture out of compressor oil!
With the smaller capacity (regularly well maintained) vacuum pumps that we use in the field , I wonder if we can freeze water inside the system - to be frank it is a struggle reaching 500Microns!
By the way, 100 - 200LPM pumps are generally used in India for field system vacuumising. By any chance, do contractors use bigger pumps in UK or other places?

WINJA
08-02-2009, 06:44 AM
The worst thing is trying to evac a freezer after a low side leak, while trying to keep everything in the freezer cold so the owner doesn't lose stock.
It doesn't work :(

I got blockages in the system after trying that. In the end I had to reclaim, and heat up the evap with a turbo torch while evacuating the second time.
Really ? because i had the same issue and with a few drier changes and put it on defrost a few extra times while putting heat on the txv and it was sorted

nike123
08-02-2009, 08:07 AM
Really ? because i had the same issue and with a few drier changes and put it on defrost a few extra times while putting heat on the txv and it was sorted

And how is that better way off doing things then Paul is done at domestic freezer. For every filter replacement, I suppose that you need to reclaim refrigerant, braze new filter under nitrogen and evacuate and recharge new refrigerant. If you do it like that few times, how much do you think it will cost the owner of that freezer to do things in that way. Or you work for banans?;)

nike123
08-02-2009, 08:20 AM
Amazing Really

When lowering chamber pressure, water evaporates and takes heat from surrounding water (there is not possible to change in state of the matter without heat is taken from surrounding) because in that chamber all heat from surrounding is gone with vacuumed air. That is why water freezes and that is why in chamber is no more 24C when water start to freeze.
So it is not 24C water temperature when it starts to freeze and nothing amazing is happening except physics laws at act.

Peter_1
08-02-2009, 08:23 AM
.... For every filter replacement, I suppose that you need to reclaim refrigerant, braze new filter under nitrogen and evacuate and recharge new refrigerant. If you do it like that few times, how much do you think it will cost the owner of that freezer to do things in that way. Or you work for banans?:eek:

You only need to pump it down to the receiver, you don't need to reclaim it. Pumping down takes only the time to walk to your van for a new dryer.
I don't need to breeze new filters because they're all fitted with euro-couplings.
I even fitted for the same problem 3 dryers in line - after evacuating first as much as possible - and came back the other day to replace once again the 3 dryers for 1 final dryer.

There's also something like expensive labor hours. Evacuating water takes much more time then removing it with a dryer. Practice has shown that you never can remove water with a vacuum pump in a reasonable time. I had a thread some time ago with a broken PHE and we had buckets of water in the system.
But there's nothing wrong with Paul's method.
I always heat up the coil while evacuating, especially in a freezer because the moisture will stay there.

Peter_1
08-02-2009, 08:24 AM
When lowering chamber pressure, water evaporates and takes heat from surrounding water because in that chamber all heat from surrounding is gone with vacuumed air. That is why water freezes and that is why in chamber is no more 24C when water start to freeze.
So it is not 24C water temperature when it starts to freeze and nothing amazing is happening except physics laws at act.
Chamber is kept at 24C with +/- 20 kW of heaters.;)

Peter_1
08-02-2009, 08:26 AM
Chamber is kept at 24C with +/- 20 kW of heaters.;)

I personally think that due to the plastic, isolating bottle, heat can't be transfered fast enough while it is removed. Vacuum process is going so fast and heating can't follow fast enough.

nike123
08-02-2009, 08:41 AM
You only need to pump it down to the receiver, you don't need to reclaim it. Pumping down takes only the time to walk to your van for a new dryer.
I don't need to breeze new filters because they're all fitted with euro-couplings.
I even fitted for the same problem 3 dryers in line - after evacuating first as much as possible - and came back the other day to replace once again the 3 dryers for 1 final dryer.

There's also something like expensive labor hours. Evacuating water takes much more time then removing it with a dryer. Practice has shown that you never can remove water with a vacuum pump in a reasonable time. I had a thread some time ago with a broken PHE and we had buckets of water in the system.
But there's nothing wrong with Paul's method.
I always heat up the coil while evacuating, especially in a freezer because the moisture will stay there.

I agree with you when systems are big, not hermetical sealed and have receivers etc....
That is not what I (and Paul, if I got it correctly) was talking about.
When I work on hermetically sealed system I leave it like that. I was talking about small domestic hermetical sealed systems :

And how is that better way off doing things then Paul is done at domestic freezer.

It appears that we are talking here about "pears and apples".

nike123
08-02-2009, 08:47 AM
I personally think that due to the plastic, isolating bottle, heat can't be transfered fast enough while it is removed. Vacuum process is going so fast and heating can't follow fast enough.

I am sure that water doesn't freeze at 24C at any vacuum level. Here is case of higher heat removal (by change of state) than heat gain (from surrounding) in water which rapidly evaporate.
Also, in that high vacuum, there is not much matter to transfer heat by conduction and only significant heat could be transferred by IR radiation. Dont forget, vacuum is best isolator.

Peter_1
08-02-2009, 08:52 AM
And how is that better way off doing things then Paul is done at domestic freezer. ..)
Apples with pears?
Paul never said that this job was on a domestic freezer.
Winja didn't reply to Paul's message about a domestic freezer nor cooler I suppose. (TXV in his message)
And who's repairing a leak on a domestic freezer anyway?

Peter_1
08-02-2009, 08:55 AM
Here is case of higher heat removal (by change of state) than heat gain (from surrounding) in water which rapidly evaporate.
...
You're saying the same in other words

nike123
08-02-2009, 09:09 AM
Apples with pears?

Local adage (i taught it is more broader term) used when somebody compares two un-comparable things.


Paul never said that this job was on a domestic freezer.

By his description of his work I assumed that he talks about domestic fridge. And we all know how assuming could end up.:o


Winja didn't reply to Paul's message about a domestic freezer nor cooler I suppose. (TXV in his message)

More assuming.:D


And who's repairing a leak on a domestic freezer anyway?

I, sometimes do! Although, to my friends and relatives, mostly for "few" beers and supper. It cost them much more then if they will pay me by money and they are still happy.:D

nike123
08-02-2009, 09:18 AM
You're saying the same in other words

I saying it in a way I see it.
I am not contradicting you.

paul_h
08-02-2009, 12:12 PM
relax people.
I don't always work on domestics, in fact I try not too* :D

But I wouldn't be worried in the owner losing stock or keeping the freezer cold if it was a domestic would I? ;) . It was a very small commercial unit.

It was a small freezer room in a fishing shop, so lots of frozen fish that needed to be kept cold, but a very small condensing unit, no reciever etc. So uneconomical to repair using drier changes and multiple visits as you couldn't pump down, you'd need to do full reclaims and recharges.

edit: *Domestic a/c, yes I work on that, domestic refrig however, I avoid. Too hard when no one stocks parts in this side of the country. Big pain when you have too may customers desperate to get their fridge running and you can't get parts for a week or more. So I avoid domestic refrig, but I don't mind domestic a/c or commercial refrig.

WINJA
09-02-2009, 05:25 AM
And how is that better way off doing things then Paul is done at domestic freezer. For every filter replacement, I suppose that you need to reclaim refrigerant, braze new filter under nitrogen and evacuate and recharge new refrigerant. If you do it like that few times, how much do you think it will cost the owner of that freezer to do things in that way. Or you work for banans?;)
I didnt think he was working on a domestic as he said 'owner doesnt lose stock' and I dont know anyone who calls their food in their freezer at home stock , stock is more a retail or comercial term , my mistake

nike123
09-02-2009, 08:31 AM
I didnt think he was working on a domestic as he said 'owner doesnt lose stock' and I dont know anyone who calls their food in their freezer at home stock , stock is more a retail or comercial term , my mistake

Sorry, I was assuming, and acted upon that assumption.
If I sounded as preacher, i apologize, it was not my intention.