Question on non-condensables in ammonia

Hey all my question is whether or not air/non condensable can enter in your system on the high pressure side. I know it sounds like a "duh" question but I think I'm experiencing it.
We have a weld leaking just off our receiver, and I am wondering if this could be allowing air into the system. If the refrigerant changes state (read:volume) could this be swinging the pressures in the leak area enough to draw in air? Or is it due to some sort of venturi effect? Anybody able to take a stab at it?

Thanks

Not “duh” but YES, definitively!

Not exactly a ventury effect but because of the turbulence at the leak, eddy currents may produce which also create stagnant and low pressure regions around the leak that bring air in at the same time letting NH3 out.

Not just that, you can draw air and humidity in by two other phenomena not widely known to the average fridgie but well known by firemen which are counterflow diffusion and dispersion. These phenomena feed a fire fuel with oxygen (air) while every other combustion product gas is trying to escape out of the fire!

Both diffusion and dispersion explain the spreading of a fluid with high concentration of some compound to another with low concentration (like osmosis but without a membrane).

Because the random nature of these phenomena you cannot assert they will be present at every leak but they are more probable on larger leaks!

Interesting!
Is there somewhere that explains the counterflow diffusion and dispersion a bit more? Quick Google search came up empty. The way something at atmospheric pressure is able to get into a pressurized system like that is amazing. Thanks!

Maybe this is a question for chemical forums because they study these phenomena a lot for it affects chemical reactions.

You have to search for Fick’s law of diffusion, unfortunately there is no simple version:

http://en.wikipedia.org/wiki/Fick's_laws_of_diffusion.

Frick found out that the rate at which fluids mix depends on the square of the particles mean speed, and the viscocity of the fluids and size of the particles.

Smaller particles (like ammonia) and the higher the temperature (absolute) they diffuse faster.

For gaseous diffusion, the rate at which the gases diffuse vary inversely as the square root of their densities, irrespective of the fluid in which diffusion occurs.

Gas-liquid interfaces complicate these phenomena.

Dispersion: http://en.wikipedia.org/wiki/Dispersion_(chemistry) has to do to the way the fluids interact when mixed.

The basic mechanism of dispersion (gas liquid) is the formation of droplets that consists in drawing out liquid into a slender stream or filament that can be observed (for example) from a faucet of water using stroboscopic light (air water dispersion).

Quoting from Perry’s “Chemical Engineer Handbook” (mine is an old edition 1941! But Fick died in 1901):

“For example filaments of liquid are dragged out by the impingement of high velocity turbulent air or steam jets on the liquid surface. In this case a primary droplet is dragged away from the surface, carrying behind a filament that may be stretched out by the velocity and turbulence of the gas to a very fine thread before it collapses to droplets.”

This subject cannot be explained in simple terms!

It has been discussed in technical speculation in Forum look for very technical speculation.

I understand it can happen & find it nothing short of a miracle. But very theoretical & for practical purposes in refrigeration I don't think it serves a purpose.

Andy Pearson has been known to discuss it!

It goes to show that you have to have an open mind to things that may seem inpossible.

I think that this is impossible even theoretically. Diffusion can happen in the area where total pressure is equal or close to equal. However, when we have pressure of 150 psig inside and 0 psig outside of the system the air or moisture will not go into the refrigeration plant. Check for a leaks on low pressure side.

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Originally Posted by RANGER1

It has been discussed in technical speculation in Forum look for very technical speculation.

I understand it can happen & find it nothing short of a miracle. But very theoretical & for practical purposes in refrigeration I don't think it serves a purpose.

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If diffusion and dispersion weren’t important in refrigeration then absorption cooling wouldn’t exist!

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Andy Pearson has been known to discuss it!

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Sounds he’s a smart guy!

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It goes to show that you have to have an open mind to things that may seem inpossible.

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If counterflow diffusion where impossible then how do you explain a fire? What is the mechanism that feeds low temperature low pressure oxygen into a high temperature and higher pressure area!

In air conditioning it is known that humidity travels counterflow in air.

What makes water from a leaking heat exchanger fill the whole inner volume of a system that is not working.

If you ever experienced refrigerant migration, these mechanisms are the ones that feed the oil with refrigerant vapor, without pressure differentials.

What you should be questioning is not that it seldom happens but if it happens in amounts large enough to be a problem in the system. I think that this is rare but it does happen.

What is not rare is that fluid flows produce all sorts of induced currents and low pressure zones like in a ventury or an eductor and these eddies may bring in air into the system.

Like you I try to keep an open mind and never say never!

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Originally Posted by Segei

I think that this is impossible even theoretically. Diffusion can happen in the area where total pressure is equal or close to equal. However, when we have pressure of 150 psig inside and 0 psig outside of the system the air or moisture will not go into the refrigeration plant. Check for a leaks on low pressure side.

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The larger the pressure drop the MORE PROBABLE this effect is because these eddies get more energy!

For your statement to be even close to truth all leaks need to happen trhough ventury shaped openings so that no reverse eddies (in the opening) are formed!

If you can't at least keep an open mind, maybe there is no point in arguing with you.

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Originally Posted by aramis

The larger the pressure drop the MORE PROBABLE this effect is because these eddies get more energy!

For your statement to be even close to truth all leaks need to happen trhough ventury shaped openings so that no reverse eddies (in the opening) are formed!

If you can't at least keep an open mind, maybe there is no point in arguing with you.

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Eddies created by kinetic energy of fluid or gas. However, I'm doubt that this energy will overcome 150 psig pressure difference. Actually, nobody ask you to argue with me.:D

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Originally Posted by aramis

If diffusion and dispersion weren’t important in refrigeration then absorption cooling wouldn’t exist!



Sounds he’s a smart guy!





If counterflow diffusion where impossible then how do you explain a fire? What is the mechanism that feeds low temperature low pressure oxygen into a high temperature and higher pressure area!

In air conditioning it is known that humidity travels counterflow in air.

What makes water from a leaking heat exchanger fill the whole inner volume of a system that is not working.

If you ever experienced refrigerant migration, these mechanisms are the ones that feed the oil with refrigerant vapor, without pressure differentials.

What you should be questioning is not that it seldom happens but if it happens in amounts large enough to be a problem in the system. I think that this is rare but it does happen.

What is not rare is that fluid flows produce all sorts of induced currents and low pressure zones like in a ventury or an eductor and these eddies may bring in air into the system.

Like you I try to keep an open mind and never say never!

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No doubt Andy is a smart guy.

I was only refering to air going into a system when gas was pissing out.

I'd love to hear from anyone who purged air out of a positive pressure system that had it because of an outward leak, possible but highly unlikely!

Hey guys.

I've had situations on at least three ammonia refrigeration plants (that run positive pressure) which seem to accumulate non condensibles.

There does not seem to be a common thread between them as to why it happens.

1). I have seen it happen on a +25kpa plant which has been maintained well, with minimal opening of system (and reasonable purging of any works).*

2). I have seen a truck load of non condensibles appear almost out of the blue (and quite quickly) on a different positive pressure pant that barely had any significant works at all. On said plant I have seen the purger accrue significant purge hours & characteristic round medium sized bubbles in tattler bucket.*

3). I have also seen it happen on a +200kpa plant which requires quite regular purging.

I have done a small amount of research into the issue, questions have been raised about the possibility of the ammonia breaking down & becomming Nitrogen + Hydrogen (in their gaseous forms), however information that I have found relating to breakdown of ammonia due to temperature suggests that it only happens in the order of 450 - 500°C (unlikely temperatures for a standard two stage system).

Another possibility is that some sort of electrolytic action causes the ammonia to break down.

Perhaps others have experienced something similar - or maybe the systems that I'm talking about have other reasons a to why it's happening. Either way, for the time being, I just accept that it "seems" to happen and I watch for the tell tale signs & purge accordingly.

Mr Saurus.

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Originally Posted by HVACRsaurus

Hey guys.

I've had situations on at least three ammonia refrigeration plants (that run positive pressure) which seem to accumulate non condensibles.

There does not seem to be a common thread between them as to why it happens.

1). I have seen it happen on a +25kpa plant which has been maintained well, with minimal opening of system (and reasonable purging of any works).*

2). I have seen a truck load of non condensibles appear almost out of the blue (and quite quickly) on a different positive pressure pant that barely had any significant works at all. On said plant I have seen the purger accrue significant purge hours & characteristic round medium sized bubbles in tattler bucket.*

3). I have also seen it happen on a +200kpa plant which requires quite regular purging.

I have done a small amount of research into the issue, questions have been raised about the possibility of the ammonia breaking down & becomming Nitrogen + Hydrogen (in their gaseous forms), however information that I have found relating to breakdown of ammonia due to temperature suggests that it only happens in the order of 450 - 500°C (unlikely temperatures for a standard two stage system).

Another possibility is that some sort of electrolytic action causes the ammonia to break down.

Perhaps others have experienced something similar - or maybe the systems that I'm talking about have other reasons a to why it's happening. Either way, for the time being, I just accept that it "seems" to happen and I watch for the tell tale signs & purge accordingly.

Mr Saurus.

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Did these plants had the leaks on high side?
I see explanation that non condensibles came from oil or ammonia.
Let's have a look at eddies. Kinetic energy of liquid or gas movement create counter-flows. To push air into the system, this energy of counter-flows should be transformed to pressure. It is impossible to create 150 psig pressure from kinetic energy of the gas. Look at centrifugal compressors. They transform kinetic energy of the gas to the pressure. Do you know any air one stage centrifugal compressor that can create pressure of 150 psig? This is just impossible.

Good! You understand half the process.

The main stream produces eddies that bring in air.

Now diffusion and dispersion come into play to get this air into the main stream without having to raise the pressure.

Tough this pressure raise is not as high as you think because by Dalton’s Law of Partial Pressures, you have the partial pressure of air in ammonia working on your side.

Not to mention chemical attraction between ammonia and polar molecules like water vapor and gaseous oxygen that also favors the intake of contaminants in the main stream.

Dispersion works thanks to Brownian Motion, this in itself is enough to explain some contaminat intake.

Not just diffusion, this is turbulent diffusion, which is very efficient in rapidly decreasing concentration of contaminants and released into the system.

You can observe this turbulent diffusion with smoke, generally you smell the smoke even if you are far away the main smoke plume this is turbulent diffusion at work. Even upstream!

As I said before it is not a question whether this happens, the big doubt is if it happens in large amounts. Tough a leak may go undetected for long time especially if you don’t keep track of refrigerant mass charged in the system.

Now if you want proof, there are now studies on this subject in any serious level, so for the moment it’s just a matter of keeping an open mind … or not!

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Originally Posted by RANGER1

No doubt Andy is a smart guy.

I was only refering to air going into a system when gas was pissing out.

I'd love to hear from anyone who purged air out of a positive pressure system that had it because of an outward leak, possible but highly unlikely!

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If Andy reads this post I hope he can contribute with his opinion.

Unless your system works in vacuum (which I doubt) almost all systems contaminants have found their way into a positive pressure system.

The problem is to discard how many of these were affected because of bad practices.

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Originally Posted by HVACRsaurus

Hey guys.

I've had situations on at least three ammonia refrigeration plants (that run positive pressure) which seem to accumulate non condensibles…

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All I can tell you is to minimize this problem you have to:
- Get rid of all possible leaks
- Review your operational procedures constantly.
- Keep strict records on procedures and refrigerant and oil use.
Even recording and reviewing these tapes may help you pinpoint where the problem is.

If you can, make analysis of the products you are using. Sometimes contaminants may come from unexpected sources.

As for the breakdown of ammonia, the temperatures and pressures you measure are average values.

Brownian Motion theory explains that a very small percentage of the molecules may be experimenting a number of collisions far above the average and molecules may dissociate. But they should turn back into ammonia unless they find a contaminant first.

So keeping contaminants in the system low is a priority.

I hope you solve this problem!

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Originally Posted by aramis

Good! You understand half the process.

The main stream produces eddies that bring in air.

Now diffusion and dispersion come into play to get this air into the main stream without having to raise the pressure.

Tough this pressure raise is not as high as you think because by Dalton’s Law of Partial Pressures, you have the partial pressure of air in ammonia working on your side.

Not to mention chemical attraction between ammonia and polar molecules like water vapor and gaseous oxygen that also favors the intake of contaminants in the main stream.

Dispersion works thanks to Brownian Motion, this in itself is enough to explain some contaminat intake.

Not just diffusion, this is turbulent diffusion, which is very efficient in rapidly decreasing concentration of contaminants and released into the system.

You can observe this turbulent diffusion with smoke, generally you smell the smoke even if you are far away the main smoke plume this is turbulent diffusion at work. Even upstream!

As I said before it is not a question whether this happens, the big doubt is if it happens in large amounts. Tough a leak may go undetected for long time especially if you don’t keep track of refrigerant mass charged in the system.

Now if you want proof, there are now studies on this subject in any serious level, so for the moment it’s just a matter of keeping an open mind … or not!

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It looks like you are theoretical guy. A lot of "smart" words and little proof. All your examples including fire, smoke and etc. happen in the areas with relatively equal pressure. This is the reason we have turbulence, flow, counter flow and etc. However, no explanation how counter pressure greater than 150 psig was created.
Regarding ammonia leaks. I work with ammonia refrigeration plants for 35 years. If you shut off ventilation, you can smell any small leak. This is not a *****.

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Originally Posted by Segei

It looks like you are theoretical guy

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Well, no. But I have imagination and desire to learn more than I know!

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A lot of "smart" words and little proof.

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Better than common words and no proof either!

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All your examples including fire, smoke and etc. happen in the areas with relatively equal pressure.

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If there is a temperature gradient in a fire of a given volume there is also a pressure gradient. This is common sense and a direct application of the ideal gas law.

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This is the reason we have turbulence, flow, counter flow and etc.

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Inside a 150 psi you have more turbulence and counter flow this is why you call it “turbulent flow”!

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However, no explanation how counter pressure greater than 150 psig was created.

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I explained, but you can’t understand it.

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Regarding ammonia leaks. I work with ammonia refrigeration plants for 35 years. If you shut off ventilation, you can smell any small leak. This is not a *****.

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And I hope you never have to leave that plant. Keep up the good work!

Eddie currents can provide areas of very low pressure, the prime example is cavitation.
Personally i do not think diffussion directly would be a major in the short term as indicated in the examples.
I do think it does come down to low pressure areas being produced.
Very interesting.

I have had on occassions when bleeding a section of ammonia pressure pipe into water that it starts to suck the water out of bucket, bleedin'annoying. Possibly the same effect happens with a high pressure leak.
magoo

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Originally Posted by mad fridgie

Eddie currents can provide areas of very low pressure, the prime example is cavitation.
Personally i do not think diffussion directly would be a major in the short term as indicated in the examples.
I do think it does come down to low pressure areas being produced.
Very interesting.

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You are right about low pressure. Vacuum can be from 0 bar(atmospheric pressure) to 1 bar(absolute vacuum). How to create 10 bars pressure not vacuum?

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Originally Posted by Segei

You are right about low pressure. Vacuum can be from 0 bar(atmospheric pressure) to 1 bar(absolute vacuum). How to create 10 bars pressure not vacuum?

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Best example I can give is the prop on a submarine, csvition is still produced at well over 100meters (10barg)
As you know water will boil below 1barg "cavitation" this how eddie current can produce very low pressures.

Never thought about this before. Is the pressure inside a flame indeed higher than the pressure of the air around it ?

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Originally Posted by mad fridgie

Best example I can give is the prop on a submarine, csvition is still produced at well over 100meters (10barg)
As you know water will boil below 1barg "cavitation" this how eddie current can produce very low pressures.

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Injector works the same way.http://en.wikipedia.org/wiki/Eductor-jet_pump High pressured liquid or gas create high speed and low pressure. Probably, this happen when we have leak. Ammonia leak create high speed and suck air and this mixture will go away from the leak, but not in opposite direction.

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Originally Posted by mad fridgie

Eddie currents can provide areas of very low pressure, the prime example is cavitation.
Personally i do not think diffussion directly would be a major in the short term as indicated in the examples.
I do think it does come down to low pressure areas being produced.
Very interesting.

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You opened a new point of discussion here and it is if leaks should be renamed to “sucks” for they may well be sucking now and then. And I admit it is a possibility.

If you allow diffusion though, leaks retain their name and take in gases that are not inside the system (not in large quantities but for long periods of time).

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Originally Posted by Magoo

I have had on occassions when bleeding a section of ammonia pressure pipe into water that it starts to suck the water out of bucket, bleedin'annoying. Possibly the same effect happens with a high pressure leak.
magoo

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Great example Magoo! You made me remember a vent valve that was soldered 1cm inside the line, it would suck your finger in if you opened it! The more velocity in the mains the more it would suck.

The problem is that leaks are much smaller than valve openings but the velocities of the refrigerant in the leak are low so I think this gives opportunity to diffuse gases in the opposite direction of the flow just like moisture does in air conditioning ducts.

But leaks in schraeder valves (or with obstacles like solder in the main line) may well be sucking part of the time!

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Originally Posted by mad fridgie

Best example I can give is the prop on a submarine, csvition is still produced at well over 100meters (10barg)
As you know water will boil below 1barg "cavitation" this how eddie current can produce very low pressures.

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Of course you can have cavitation with large pressures all you need are large obstacles, like a propeller or a valve just opening.

Not just that high velocity with a sudden change of direction (or contraction) can also cause it.

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Originally Posted by Yuri B.

Never thought about this before. Is the pressure inside a flame indeed higher than the pressure of the air around it ?

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:off topic:

The very first expansion of a flame is caused by a pressure difference due to the heating of the gases, until it reaches a stable size.

The pressure difference still exists (because there still is a small temperature difference) but is much smaller and they are considered (for simplicity) to behave as constant pressure.

I Have a NH3 booster comp. that had a leaky shaft seal. Before the seal was replaced when this machine was on line the system had a lot of air entering it. After much discusion with refrigeration experts and chasing down air leaks it seems that a lot of the air was entering through the shaft seal. When the seal was replaced the air infiltration almost stopped. I am not sure about air being pulled into the comp.through the seal but it does seem likely after reading the preceding posts. C.D.

editing due to repeat of the same information sorry for mistake

Hi CD,
generally low stage boosters in negitve range have shaft seal areas at positve oil pressure, oil sealing and feeding seal compartment. Once stopped and idle they can possibly leak to atmosphere at positve pressure internally

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Originally Posted by Magoo

Hi CD,
generally low stage boosters in negitve range have shaft seal areas at positve oil pressure, oil sealing and feeding seal compartment. Once stopped and idle they can possibly leak to atmosphere at positve pressure internally

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It depends of manufacturer.I know that Frick compressors have positive pressure, but Micom compressors have negative pressure during operation.

Ammonia circuits: I have seen lots of positive (suction) pressure plants draw air...The most common point for it to happen is immediately downstream of the expansion device. The momentum change from inlet to outlet of the expansion device is huge and the downstream 2-phase is still pretty dense.

Normal Design discharge pipe sizing often gives velocities around 200 to 225 ft/sec. Thats about 18% of the Sonic Velocity. Various ordinary conditions, like lots of condensing capacity such that all the flow is going through one condenser, will more than double that velocity.....Now an ordinary elbow will have a pressure profile that can be readily measured. Compound that by introducing hot gas to a big coil with 100 Psig Pressure Difference available and you will have shock waves....And the refraction of standing shock waves will readily reduce pressures into a vacuum at every turn and every strainer. They are not pressures you can see on a conventional gauge and if the leak is a penetration in a rigid member you would expect it to leak outward during normal positive pressure conditions....But we all have stories of gaskets and O-Rings permitting leaks in one direction but sealing in the opposite....

As for Dissociation of the gas: It wants to happen at pretty high temperatures....Well above those encountered in a refrigeration circuit. There are a few local spots where it might occur: like ball bearings and the low pressure end of an unloaded crew compressor....The presence of oxygen and water both contribute to reducing the temperature required to promote dissociation. There is a lot of activity and study currently being applied to using ammonia as the base for hydrogen fuel cells and therefore to develop catalysts and techniques that will make an "ammonia cracker" portable and practical for a vehicle.

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Originally Posted by sterl

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Thanks for your valuable input sterl.

But pressure inside the system is still positive at the outlet of the expansion valve.

So in your opinion what is the mechanism that draws air in through a leak?

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Originally Posted by leewd

Hey all my question is whether or not air/non condensable can enter in your system on the high pressure side. I know it sounds like a "duh" question but I think I'm experiencing it.
We have a weld leaking just off our receiver, and I am wondering if this could be allowing air into the system. If the refrigerant changes state (read:volume) could this be swinging the pressures in the leak area enough to draw in air? Or is it due to some sort of venturi effect? Anybody able to take a stab at it?

Thanks

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I just read through the whole post and I'm just going to say that we have to agree to disagree, because I don't think non condensables can enter the system through a gas leak.

however, if you have a water cooled condenser, I would look at that for a leak, because ammonia systems can draw water through a leak, even with the pressure difference of the HP side to the water side.

Also a thing to consider is that of all the pollution that enters the system, you can only remove the gasses, the water or other contaminants will stay in the system.

A simple water test could show if it's water entering the system or "air"

your NH3 supplier should have a test kit with a test tube of glass, fill it up with liquid ammonia and let it boil off, what you are left with will be contaminants, and you can calculate the %

I think when you have 9% of water in the NH3, the system still runs "fine" but you loose 90% of the heat transfer in the evaps... Don't take my word for it on these numbers, because it's all from memory