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eltech
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Gas Detection

10/29/2025 4:13 PM

If you have a sealed tank (vessel) that occasionally creates hydrogen gas, and you want a hydrogen detector to pick up the readings as quickly as possible through a 4-meter sampling line on top of the tank, will a 1/2'' or 1''$ line react quicker?
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Rixter
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#1

Re: gas detection

10/29/2025 5:08 PM

For a given amount of hydrogen, the gradient of the concentration will be greater for the 1/2" line than the 1" line. Fick's law states that the rate of diffusion is proportional to this gradient (or change of concentration per length of pipe).

https://en.wikipedia.org/wiki/Fick%27s_laws_of_diffusion
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Rixter
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#2
In reply to #1

Re: gas detection

10/29/2025 8:59 PM

Sorry, #1 is not correct...

If you have a sealed tank (vessel) that occasionally creates hydrogen gas, and you want a hydrogen detector to pick up the readings as quickly as possible through a 4-meter sampling line on top of the tank, will a 1/2'' or 1''$ line react quicker?

Using Fick's Law:

where Rate is the diffusion rate of gas through a pipe, D is a constant depending on gases present, A is the cross-sectional area of the pipe, ΔC is the difference in concentration between ends of the pipe, and L is the length of the pipe.

The diffusion rate is proportional to A, the cross-sectional area, so the 1" pipe would provide a quicker response.

gas diffusion through a pipe radius
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Deefburger
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#3
In reply to #2

Re: gas detection

10/30/2025 11:19 PM

Translation: The bigger cross section will give you faster results every time.

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Deefburger
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#4

Re: Gas Detection

10/30/2025 11:23 PM

Point the line up. That'll help too with Hydrogen. If you were looking for a heavy gas like tungsten hexafloride, you would point the line down.

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Rixter
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#5
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Re: Gas Detection

10/31/2025 8:17 AM

Actually, if you want fast results, you would want to evacuate the air, if possible. The rate of diffusion is highly dependent on whatever gas might also be present.
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SolarEagle
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#6

Re: Gas Detection

10/31/2025 10:36 AM

I think the hydrogen gas would rise to the top filling the smaller tube faster than the larger tube, but I don't think it would matter, the hydrogen would seek out the top no matter the size of the tube...

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powermeter
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#7

Re: Gas Detection

11/02/2025 9:41 PM

The detector's response speed depends primarily on how long it takes for "fresh" sample gas to reach the detector sensor from the top of the tank. This is affected by two main factors: the gas flow rate in the tubing and the volume inside the tubing.

So my answer is: using a 1-inch tubing will result in a faster response than using a 1/2-inch tubing.
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