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Hydrogen leakage rates

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browniebob

browniebob

Military
Feb 23, 2005
8
Hello All,

I'm faced with the following issue: I have some batterys in a box and these batterys release Hydrogen gas. I want to know, given the cracks and other tiny imperfections in the metal box's construction, how much Hydrogen will exit the box. In essence, if I know the generation rate (something very low) and approximate the imperfections by a set of 6 1mm holes (one per surface) then how do I calcualte the partial pressure of Hydrogen? As a side question, if I released some known amount of H gas, then would it almost immediately equlibriate in the chamber (its about 12"x12"x24"); how does one get a "time constant" for a diffusion like this?

BB
 
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As you mentioned you know the hydrogen mass release rate. Now calculate the differential pressure of hydrogen that will give the same mass flow rate through the 6 1mm holes. This is the equilibrium pressure that will be in the box at steady state because then the mass flow rate from the box to the atmosphere will equal the rate of hydrogen mass generated inside the box.

To calculate the time to reach that equilibrium is more comlex you have to solve the instantanius pressure rise and flow out of the box differential equations. Since the pressure will be quite small you can use the ideal gas law p*v=ro*R*T to calculate the incremental rise in the pressure inside the box due to incremental addition of hydrogen gas and at the same time the incremental flow from the box to the atmosphere due to the incremental rise in the pressure inside the box. This will form a differential equation that you can solve to reach the time to equilibrium.
 
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This makes sense, yes. So if the :
rate of generation > rate of leakage

then that condition will persist until the > becomes =.
How do I calculate the leakage rate then, as a function of partial pressure (or rather, the pp difference inside-outside)? (Sorry, Im an EE, no background in this fluids stuff)
 
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