Isn't that the idea behind triple evacuation,don't know if the moisture actually sticks to the nitrogen

 

If you mean to ask if Nitrogen chemically bonds to H2O by co-valency, then no, it does not.

What happens with moisture in the atmosphere is that water molecules can fit between molecules of Nitrogen, Oxygen, and the few rare gasses that make up the air we breathe. When that air is cold, there is little space between the Nitrogen and Oxygen, so the atmosphere can hold very little moisture as there is not enough room between the air molecules. When the atmosphere is warm, it can hold a lot of moisture, because the molecules of Nitrogen and Oxygen have more distance between them, essentially "making room" for more moisture.

The dry Nitrogen we use has already had its moisture removed, but it is also warm from the van or from absorbing heat from the roof or the sun. So, we have a ready-made absorbing medium for moisture: plenty of room between the Nitrogen molecules because of the temperature, and little or no resident moisture already taking up the spaces.

When the Nitrogen is introduced into the system, the moisture easily finds spaces to take up, seeking osmotic equilibrium until the moisture is equally distributed throughout the gas.

Then, when we depressurize the system, the moisture is carried out with the departing Nitrogen.

But "clinging?" No, just finding a space for the departing ride.

 

alot of good info. thanks! i have been through a 4 year program with ACCA and we were taught this stuff in class. my man just argues with my knowledge

 

At any given temperature and pressure the number of gas molecules per liter is the same irregardless of the composition of the gas. At standard temperature and pressure that number is called a Mole. It has nothing to do with how big they are. Gas molecules have random movement (Brownian motion) and are evenly distributed at equilibrium. This is something all gas mixtures achieve over time even with no mechanical mixing. They do not "pack" as in a solid or liquid.

Nitrogen is cheap and easy to supply free of contaminants (like water). It's also inert which means it won't react with seals, solvents or anything else the line. It's not posionous obviously since it makes up about 80% of the atmosphere so venting it isn't an issue. And one of it's best qualities, it doesn't blow up!

When you release the nitrogen from the tank it cools down signifcantly. It's not warm from the truck. Two things drive water from liquid to gas. One you can increase the temperature which will increase it's partial pressure. Two, you can lower the pressure. That's why water boils at a lower temperature at high altitude. Note the trade off though. If you evacuate a line the temperature of the remaining gas in the line drops.

 

At any given temperature and pressure the number of gas molecules per liter is the same irregardless of the composition of the gas. At standard temperature and pressure that number is called a Mole. It has nothing to do with how big they are. Gas molecules have random movement (Brownian motion) and are evenly distributed at equilibrium. This is something all gas mixtures achieve over time even with no mechanical mixing. They do not "pack" as in a solid or liquid.

After several minutes of contemplation, I am not certain how this post finds relevance in this question. The temperature of any gas partially determines the spacial distance between gas molecules at any given moment, Brownian motion aside. It is the density of any gas, determined by temperature and pressure, that either allows or nearly eliminates the possibility of said gas taking on moisture.

Introducing the dry gas at room temperature allows it to take on moisture, thus acting as a medium for the removal of moisture in the system.

 

Well I am no physicist or chemist; but I used dry nitrogen for years because of the belief that it worked. When I was introduced to the practice I was told the nitrogen reduced the surface tension of the water molecules and decreased the attraction of one water molecule to another making moisture removal easier.

Use your search engine to browse for “surface tension” and you can undoubtedly find more information than you care to read.

You will have to decide for yourself whether or not that is the reason that nitrogen works . I don't know I only know from experience that the nitrogen helps in the removal of moisture.

Forty some odd years ago we did the triple evacuation with virgin refrigerant, before we switched to nitrogen. I was told at that time that either would reduce the surface tension of the moisture.

 

To answer the original question, no water does not bond to nitrogen.

There's really no magic or complex explanation required. The most effective way to turn liquid water into vapor is by pulling a vacuum. Nitrogen mixes with water vapor as predicted by the ideal gas law:

pV=nRT

Vapor pressure is driven by temperature and pressure. It really doesn't matter what the molecular weight of the gas above the liquid is. Helium would be no more (or less) effective than nitrogen but a lot more expensive.

Osmotic equilibrium applies only to movement between liquids not to a state change from liquid to gas.

Reduced surface tension would increase surface area and increase vapor pressure but the difference between air (~80% nitrogen), pure nitrogen or just about any other gas you could use would be minimal. To really have any measurable effect on surface tension you have to dissolve something (a surfactant) in the water. But dissolving anything in water raises it's boiling point making it harder to drive into a gas.

I don't know how to fix an air conditioner but I do have a degree in chemistry.

 

I don't know how to fix an air conditioner but I do have a degree in chemistry.

I don't have a degree in chemistry, but I was taught that osmotic equilibrium applies equally to the distribution of a vapor as well as a liquid. This leads me to believe that leaving the Nitrogen in the system for a time allows for the water that is already in vapor form to be equally distributed throughout the gas.

Now, replacing the damp atmospheric air with a dry gas at room temperature would no doubt allow for more liquid water to become a vapor, since the rate of evaporation of water is dependent on the moisture in the air that surrounds it.

Or, in this case, the dry Nitrogen.

 

Different refrigerants have different levels of solubility of water. I have no information on some of the newer ones but R22 has a huge lead on all but R21
As a comparison R12 at 100 degf is 165 ppm by weight while R22 is 1800ppm. The worst on the list is R114. Very little affinity for water.
The practise used to be put R22 in the system and wait a bit then blow it out and evacuate. The term triple evacuation was just that. Pressurize-evacuate three times. Of course like today there are some that just blow and go.
Nitro will never do anything close to R22 as far as removing water.

 

AND, In reality, Nitrogen is NOT an inert gas.

Although it is often refered to as one.

 

Wow, this thread is getting deep... hope I remember half of this info someday when I might need it.

I've always kind of been under the impression the triple evac was for the older school days when guys didn't use micron gauges, so this was a way to kind of "over kill" and make sure a good vac was pulled.

I know it's certainly not a bad thing to do even with a micron gauge.

I'm guessing the odds are moisture isn't a huge problem to remove in 99% of system when we are talking about just humid air in the lines. A broken line at the bottom of a defrosted freezer however would be a major problem. But if you've got that problem you'd be doing everything short of blowing cotton balls through the lines to get it out lol

To spin this on a similar note. For those systems that have been run and there's still refrigerant in the lines (trapped in oil etc), does the N2 help assist the refrigerant out like it does with moisture?

 

Not really.

Although it does mix with the R22.
The nitrogen won't get under the oil to mix with the R22, on an old system.

 

Since it has been many years since I have been in a chemistry classroom, those who have been there more recently might enjoy this article:

http://pubs.acs.org/doi/abs/10.1021/jp962442w

I have been wrong before, and I no doubt will be again, but I am always trying to apply what I have learned.

 

Ok Ok.... I quit!
Now I wish I had gone to college for just this very reason! I loved chemistry..... but no,... I had to go Navy.....

 

What, too late for you to take advantage of the GI Bill?

Hey, I knew one of the very few Navy guys that had all three Navy experiences: underwater, on the water, and above the water. When I met him, he was in his 70's (a few years ago) and he was a Commander.

 

So what if we introduced a chemical like say ammonia to attach itself to the water? Would the removal of the ammonia take the water with it, or would it increase the boiling point of the water, thus, dropping the water off on its way out??

 

Probably eat through the copper before you got it out.

 

I think you are right. We'd need something that was not going to actively corrode copper, and if it left a residue behind, said residue would have to be basically inert in the system.

 

Not sure what you're suggesting. Introduce ammonia vapor to the system? An ammonia water solution would indeed have a lower boiling point (one of the few things that does) but even with a high pressure you'd be hard pressed to force any of it into solution. Even if you could it wouldn't do you much good. The vapor pressure of the ammonia is much lower than water so when you evacuate it's going to be driven off before you get much water to evaporate. Then you're back to having "pure" water again. The ammonia and water separate as gases so I'm not sure what you mean by "attach itself to the water".

You'd have to recapture all of the ammonia which would be a pain. Just dealing with the stuff is a pain and as beenthere pointed out it reacts with copper. In chemistry sometimes they use an acetone rinse to dry equipment but I don't think you want to be pumping acetone into system. It's nasty stuff too. I'm pretty sure if there were a magic bullet someone would have figured it out by now.

 

Not sure what you're suggesting. Introduce ammonia vapor to the system? An ammonia water solution would indeed have a lower boiling point (one of the few things that does) but even with a high pressure you'd be hard pressed to force any of it into solution. Even if you could it wouldn't do you much good. The vapor pressure of the ammonia is much lower than water so when you evacuate it's going to be driven off before you get much water to evaporate. Then you're back to having "pure" water again. The ammonia and water separate as gases so I'm not sure what you mean by "attach itself to the water".

You'd have to recapture all of the ammonia which would be a pain. Just dealing with the stuff is a pain and as beenthere pointed out it reacts with copper. In chemistry sometimes they use an acetone rinse to dry equipment but I don't think you want to be pumping acetone into system. It's nasty stuff too. I'm pretty sure if there were a magic bullet someone would have figured it out by now.

True.

There is very little under the sun that is "new." If a safe, easy, and speedy substance was found to get water out of a system, there would be a new multi-millionaire.

 

And now your standing there with a fishbowl on your head!

 

It push the moisture and over stuff out of the system to put in in a simplely.

Thanks for the information "Alden_Sloe" your saying the same stuff my wife ( a Chem Eng) says