Very technical speculation

[RANGER1]

This question is out of my league!

If you have say an ammonia or any plant for that matter, plant running at possitive system pressure,with a leak.
Is it possible for air/water to enter that pressurized system in normal atmospheric conditions.


A very big name in refrigeration in UK claims that this is possible, but I don't have
the theory behind me to grasp it.
Any theories or scientific answers to this one?

[monkey spanners]

Bernoulli's theorum?

Not sure if it would work in an actual system to pull moisture in through a leak.

[mad fridgie]

Hi Ranger, MS is right.

Think of a venturi, much like on many of your dosing systems.

If you have hole (leak point) in your pipe, and sufficient "flow" a vacuum can be made at the surface of the hole, drawing in air.

[chillerman2006]

Is it possible for air/water to enter that pressurized system in normal atmospheric conditions.

Hi Ranger

When the unit is not running 'No' as the higher pressure will prevent the ingress of air/moisture

When the unit runs 'Yes' it is possible

The flow of refrigerant will draw into its flow the abient air/moisture

Think about how your turbo torch works, it has vents along the stem to draw into its path air (oxygen) to increase flame temperature

The mapp gas has a higher pressure than atmosphere, but it becomes the motive force to draw in the air as its flows to the tip...... same thing with a refrigeration system

R's chillerman

[chillerman2006]

Hi MF

done it again mate ..... time it takes me to word it right... you have replied 1st

R's chillerman

[hvacrmedic]

Hi Ranger

When the unit is not running 'No' as the higher pressure will prevent the ingress of air/moisture

When the unit runs 'Yes' it is possible

The flow of refrigerant will draw into its flow the abient air/moisture

Think about how your turbo torch works, it has vents along the stem to draw into its path air (oxygen) to increase flame temperature

The mapp gas has a higher pressure than atmosphere, but it becomes the motive force to draw in the air as its flows to the tip...... same thing with a refrigeration system

R's chillerman

The torch relies upon the venturi effect to draw in oxygen. There is no similarity between this and refrigerant flowing through a constant diameter pipe.

[paul_h]

Yep, carburetors need chokes/venturies to change air speed over the fuel jets. Take the chokes* out, no outside gas/liquid with enter the stream, constant diameter pipe shouldn't have anything enter. Pressure wins without venturi effect.

* By choke I don't mean the butterfly flap you use to start a cold engine, but the insert you put into the throttle body, ie on a 40mm dia weber, you put in a 32mm-36mm convex restriction tube, to speed up air to draw in the fuel from the fuel jets. Without the diameter change, it won't pull in anything from outside (ie the fuel)

[RANGER1]

Bernoulli's theorum?

Not sure if it would work in an actual system to pull moisture in through a leak.

I think this is what I was informed about but due to ignorance did"nt understand.
I checked it out on google & makes sense , but never heard of it.

Don't let any ping pong ball or any other type of ball near your fridge plants
especially if you suspect a leak!

I'm guessing that pressure behind leak & size of hole might be important?

A venturi would also be possible I guess under correct circumstances, velocity point of leak etc.

You learn something new eveyday, if your lucky.


Thanks for replies


Next question which may have been explained before.

If purging ammonia/air gas out of a liquid drain on ammonia condensor into bucket of water.

Water can be sucked up hose then bown out again if valve only cracked open.

So assuming ammonia readily absorbs the ammonia causing vacuum & siphoning effect until further pressure build up behind saturated water.

Does this seem like a fair explanation, or is bernoulli at work again or possibly something else?

[Grizzly]

Thanks for your original post Ranger.
As they say "I learned something today".

I had never made the connection between a leak and a venturi principle before.
Very interesting and very applicable to most of us.
Thanks Grizzly

[RANGER1]

Thanks for your original post Ranger.
As they say "I learned something today".

I had never made the connection between a leak and a venturi principle before.
Very interesting and very applicable to most of us.
Thanks Grizzly

Grizzly, might be worth having a look on the internet if you hav'nt already "Bernoulli's theorum"

[mad fridgie]

I think DesA is quite a specialist on this sort of thing, maybe he has drawing or vid of this in action

[chillerman2006]

The torch relies upon the venturi effect to draw in oxygen. There is no similarity between this and refrigerant flowing through a constant diameter pipe.

shame you could not explain how it works !

check the post above mine.... which says the same thing.... hmmm I wonder why that is

R's chillerman

[glenn1340]

Slightly off on a tangent here but I work on dessicant dryers typically down to -70c dew point and I`ve been told that moisture can by travel against a flow of air through a purge orifice to give a false indication on a hygrometer.
A bit like salmon swiming upstream. You could say it sounds a bit fishy but there you are.

[hvacrmedic]

shame you could not explain how it works !

check the post above mine.... which says the same thing.... hmmm I wonder why that is

R's chillerman

I can explain how it works, I simply didn't. Don't you have Google at your disposal, or Wikipedia?

[Peter_1]

The torch relies upon the venturi effect to draw in oxygen. There is no similarity between this and refrigerant flowing through a constant diameter pipe.

Bernoulli doesn't state that you need a venturi, you only need need a velocity increase

[chillerman2006]

I can explain how it works, I simply didn't.

Hi hvacrmedic

You take the time to comment, but provide no explanation..... can you not spare us more of your time and help with the theory/conclusion more

Bernoulli doesn't state that you need a venturi, you only need need a velocity increase

Hi Peter

they both need the presence of a motive force/flow, neither principles would work with a static gas/liquid

the venturi effect requires flow

the Bernoulli's theorem requires flow

or do they ?

R's chillerman

[chillerman2006]

Hi All

thinking about this further Bernoulli's theorem, is based upon a constant diameter tube for gas/fluid flow

where in a system would we get a leak from a constant diameter tube ..... ?

leaks occur at joints where there is a point (however small) that the constant diameter changes

there will be either an increase or decrease in diameter, which would make the cause of moisture/air

ingress as closely related to a venturi effect as Bernoulli's theorem

theory/thought anyone ???

R's chillerman

[Peter_1]

This question is out of my league!

If you have say an ammonia or any plant for that matter, plant running at possitive system pressure,with a leak.
Is it possible for air/water to enter that pressurized system in normal atmospheric conditions.


A very big name in refrigeration in UK claims that this is possible, but I don't have
the theory behind me to grasp it.
Any theories or scientific answers to this one?

I think it's only possible in a system with a pressure inside the system almost equal to atmospheric pressure (so in the LP line) and the hole in a certain, 'right' place in the system at a velocity high enough to create a very local underpressure.
Or a hole in a the reduction of the flow.
Anyway, if inside pressure is high enough, then Bernouilli will not provoke such a large underpressure that a local vacuum will occur.
It's possible but this is for me more a theoretical possibility then a practical one.
And it's not because a big company is telling this that this is also a true statement. I've seen and experience experience enough to mark this last statement as very true.

[chillerman2006]

I think it's only possible in a system with a pressure inside the system almost equal to atmospheric pressure (so in the LP line) and the hole in a certain, 'right' place in the system at a velocity high enough to create a very local underpressure.
Or a hole in a the reduction of the flow.
Anyway, if inside pressure is high enough, then Bernouilli will not provoke such a large underpressure that a local vacuum will occur.
It's possible but this is for me more a theoretical possibility then a practical one.
And it's not because a big company is telling this that this is also a true statement. I've seen and experience experience enough to mark this last statement as very true.

Hi Peter

I know your experience/knowledge far exceed mine, so I direct this question at yourself for an accurate answer. At the point of a joint, elbow (increased turbulence) or straight connection, there will be to some point, a lower pressure at the edges of the flow, due to increased velocity, for example a lip where two tubes join.. the liquid/vapour at this point will be drawn into the flow by motive force yes/no ? ...... If so and there is a leak at this point, will this not draw in ambient air/moisture ? The theory seems to say yes but as you said above, is this just theory or practical/fact ?

Anyone else who can explain this for us, also please do

R's chillerman

[Peter_1]

I agree Chillerman with your last post but creating a negative pressure to counteract completely (and a little bit more) the static pressure existing inside the system will need extremely high speeds. I will post once an exerise I give in my PPL lessons to explain the lift effect on a wing.
I also agree that you have a small reduction in every joint.
But I agree with MF, DesA is THE man to bring the light to all of us.

[chillerman2006]

Hi Peter

thanks for response/document... certainly a very interesting post by Ranger, on the verge/edge of my knowledge/understanding.... will be very interesting to hear what DesA has to say on the subject,
if he does see this thread

R's chillerman

[mad fridgie]

......................................

[NH3LVR]

I have thought about the idea of a leak on the low side drawing in air before. I think it would be theoretically possible, but unlikely.
But then us old NH3 guys like a little air. Keeps the head pressure up in the winter.

But just for fun let me share one with you.
I was working on three R-502 blast freezers in the middle of Nowhere, Alaska. These were old Bohn units that I had seen before. They were long past the end of their expected life.
I did some work on them and started them up. At first all went fine as I was chilling the boxes. As the load dropped off I began to experience erratic feeding from the TX valve. Adjustments did no good. After working on this over a period of a few days I was unable to sort it out.
One coil had easily accessible TX valves. There were three coils in each evaporator and the suctions tied together in a common header. Each suction had a 1/4" tubed brazed into it for the equalizing line with a tee and Schrader valve to attach my gauges.
I restarted and slowly turned the feed down on one TX valve. With a gauge attached to two coils I noticed that the pressure on the one which was feeding less was lower than the other.
Feeling I was about to be a hero or a fool I un-brazed one of the connections. The 1/4" tube was curved inside the pipe facing into the gas flow. I repaired the three on that coil, started up and adjusted the TX valves. All was fine.
If I would have been adventuresome I would have turned the tubes facing away from the gas stream and saw what happened.
Was my theory correct? Maybe. But they worked well and I seemed to have solved the problem.
Let me know what you guys think.

[RANGER1]

Slightly off on a tangent here but I work on dessicant dryers typically down to -70c dew point and I`ve been told that moisture can by travel against a flow of air through a purge orifice to give a false indication on a hygrometer.
A bit like salmon swiming upstream. You could say it sounds a bit fishy but there you are.

This may be another theory other than venturi & Bernoulli's theorum.

Vapour pressure is another possible theory behind air or other gases entering a fridge system in our case.

I think this is what the UK guru was on about "in theory" of course.

[Magoo]

Hi Ranger1
different approach, when venting ammonia to a bucket of water, the way the water is or can be sucked up the hose always annoyed me. So can see how a small leak could suck air and moisture into a positive pressure system. The attraction of water to ammonia.