Converting mbar liters/s to grams per year

[NoNickName]

I've got a mass spectrometer, measuring helium leakages from a known volume as a multiple of mbar l/s, e.g. 10e-5 mbar l/s is the leakage capable of changing the pressure by 0.01mbar in 0.1 liter of volume in a time of 100seconds.
This is normal for all mass spectrometers.

How this can be converted into grams/year as required per EN378-2?

Thanks anybody

[chemi-cool]

Try here. Who knows........

http://www.onlineconversion.com



Chemi

[The Viking]

So,
You got a pressure differential / volume / time.

And you want to get a weight differential / time.

Sorry M8, can't se how it can be done, its a bit like comparing apples and pears to me. Completely different units...


You could obviously calculate the volume lost per /time unit and multiply this with the specific weight of your chosen gas...
Just a thought.

[Brian_UK]

Doubt if you have a set of weighing scales suitable but..

What is the weight of the helium at the start of the test and at the end ?

Would these numbers help in the calculation?

edit: I think my comments above are foolish having now read the article linked below. I also think that you are using a machine that is not designed to give you the answers that you want. (I could be wrong of course)

http://www.fda.gov/ora/Inspect_ref/itg/itg20.html

[NoNickName]

The viking: I'm not comparing apples to pears: pV = nRT, and as such a variation of pressure corresponds, everything else unchanged, to a variation in moles of gas.

For Brian: I can't weigh the helium, because I'm just testing a leakage of few parts per million of helium gas into a controlled chamber. But you are right: I just would like to resolve the scale into something human readable, also because the EN378 gives me a max leakage rate as grams/years and not in ppm or mbar l/s

[Peter_1]

I can't answer your question but are you sure EN378 asks for gr/years?
I can be wrong but I think EN378 asks for a leakage in %/year of the total gas charge in the system and there's also a specification about the accuracy of the leak checker which is in gr/years.

[Paulajayne]

From EN378

". Maximum leakage rates

Refrigerant leaks shall be identified and repaired as soon as practicable by a competent person and the system shall only be put into service again when all leaks have been repaired and a competent person has inspected the installation. All measures, in accordance with the best available techniques, have to be taken in order to reduce the relative loss of refrigerant below a maximum of 5%."

[US Iceman]

All measures, in accordance with the best available techniques, have to be taken in order to reduce the relative loss of refrigerant below a maximum of 5%."

That's interesting... 5% of what?

The total refrigerant charge I would assume, but is there a rate at which the 5% is based on, or is it simply 5% of the total charge at any one time?

[The Viking]

The viking: I'm not comparing apples to pears: pV = nRT, and as such a variation of pressure corresponds, everything else unchanged, to a variation in moles of gas.

OK,
But to me, the formula given as mBar/l/s does not contain any weight reference...
And you are asking for g/yr, which to me do contain a weight reference.
Thus it will not be a simple formula and thus the second part of my previous post:

You could obviously calculate the volume lost per /time unit and multiply this with the specific weight of your chosen gas...
Just a thought.

[Peter_1]

That's interesting... 5% of what?

The total refrigerant charge I would assume, but is there a rate at which the 5% is based on, or is it simply 5% of the total charge at any one time?

No, it's 5% of the initial charge which can be found in the logbook.

[US Iceman]

Thanks Peter. That makes sense.

[NoNickName]

Thanks all.
For The Viking: the weight is grams of the selected refrigerant. In my case is grams of helium, which by chance is much lighter and molecularly smaller. So the helium leakage must be then be converted to refrigerant leakage by means of respective molecular radius.

Peter: thanks for your input. Very much appreciated, so it looks like it really doesn't matter what it is the leak rate of a newly bought component?

[Peter_1]

No it doesn't matter, as long as you stay below 5% of the initial charge.
Are you testing the compressors in vacuum or under pressure? At Copeland and Bitzer, they're testing the compressors under vacuum and the mass spectrometer is at the outlet of the vacuumpump.

[NoNickName]

I'm pressurizing the compressor with helium and test it in a chamber.

[Peter_1]

So completely different as they do it at Copeland or Bitzer.
They need much less gas to test and they can install their spectrometer on a safe place.
They also heat the windings with a controlled DC current to speed up the vacuum process while heating the varnish.

[NoNickName]

So completely different as they do it at Copeland or Bitzer.
They need much less gas to test and they can install their spectrometer on a safe place.
They also heat the windings with a controlled DC current to speed up the vacuum process while heating the varnish.

I see but how do they test the compressor for leakages without pressurizing the compressor?

[Peter_1]

They put the compressor under vacuum with vacuum hoses coming through a platform.

Above the compressor test stand hangs some sort of a shelter/hood in steel of +/- 1 to 2 mm thick.
At the underside, there's a gasket.

On this hood, there's a connection with a helium hose.

They lower electrically this hood over the compressor housing and the gasket seals by his own weight on the flat platform where the compressor is standing on.

As the housing is closed, they inject some helium in this housing and start at the vacuumpump the helium measurement which enters the compressor via eventual leaks.

They know the amount of standard leaks through the
gaskets (every gasket leaks a certain amount helium they told me) and the leakchecker records this preset value and gives a printout of an eventual leak.

While this leakcheck is performing, they make ready another compressor on a second platform and on a tirth they disconnect an already tested compressor.

There's a roller chain behind these test stands which delivers the compressors.

I don't remember if the helium is exhausted by a fan before they lift up the hood.

I think Daikin Europe here nearby is doing it the same way.

Does this make sense Alles.?

[NoNickName]

Yeah, well it's not much different from what we do.