Can somebody check my calculations?

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Maciek Szymanski
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Can somebody check my calculations?

Post by Maciek Szymanski »

This is not fusor related, but I hope that someone with the vacuum experience can help me. I was asked to calculate gas load for a spectrometer chamber. This is open system with a large slot pumped differentialy (the spectrometer needs better vacuum than the experimental chamber). The calculation is quite simple, but my result was questioned. I’ve asked three people to check it, but can’t get confirmation nor correction for two weeks. I think that for somebody with experience it is not more than 10 minutes. I would be thankful if someone can have a look on it.


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Roberto Ferrari
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Re: Can somebody check my calculations?

Post by Roberto Ferrari »

Maciek
Why the document is dated March 23th?
What is the spectrometer volume?
You say the system is differentially pumped but you don´t show were are the pumps located.
You jump from conductance to volumetric flow.
What is the throughput of the pump?
Where the H2 comes from?
Roberto
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Maciek Szymanski
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Re: Can somebody check my calculations?

Post by Maciek Szymanski »

Thank you for response.
  • The date is a mistake - I've rewriten the calculations in english to post it here, and written a wrong date.
  • The volume of the spectrometer is small compared to the experimental chamber and for the initial calculation do not matter in my opinion. The point of the calculation is first estimate of the spectrometer pumping system, so I'm assuming that the spectrometer pump keeps the pressure at the required level and the leak through the slit at the shown pressures defines the minimal throughput of the pump system.
  • There is the pV flow calculated between total conductance and the volumetric flow.
  • The pump system throughput is the point of calculation (theoretically it should equal the leak, in practice ofcourse it must be more).
  • The experimental chamber is filled with the hydrogen at 1e-4 hPa and 50°C.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland
Roberto Ferrari
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Re: Can somebody check my calculations?

Post by Roberto Ferrari »

Hi Maciek

I agree with your analysis until the last but one statement.
Seems there is a factor wrongly applied.
Are you writing 15.000 l/s? (sorry Americans, we both use the dot for the thousands and the comma for the decimals).
I got 1,59 l/s, the delta pressure is 10-3.
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Maciek Szymanski
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Re: Can somebody check my calculations?

Post by Maciek Szymanski »

The pV flow is:

q = C*(p1 - p2) = 15,9*(1e-4 - 1e-7) = 15,9*9,99e-5 =1,59e-3 hPa*l/s

Calculating volumetric flow at spectrometer chamber pressure p2:

q_v = q/p2 = (1,59e-3)/(1e-7) = 15900 l/s
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland
Roberto Ferrari
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Re: Can somebody check my calculations?

Post by Roberto Ferrari »

Hi Maciek

Sorry not being of more help.
Surely you could submit your doubt to physicsforums.com

Best
Roberto
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Maciek Szymanski
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Re: Can somebody check my calculations?

Post by Maciek Szymanski »

Thank you anyway! You made me recheck the calculations once again, that's good. Yesterday the vacuum equipment supplier has confirmed the result (indirectly, but a simple recalculation has proven the method).
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland
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