How Does a Pressurized Tank Empty Over Time Through a Hole?

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Main Question or Discussion Point

I having difficulty wrapping my head around a concept that I wish to solve. I have a 10L tank of compressed air at 100psi. When an outlet hole of cross-sectional area of 0.115 in^2 is opened, I wish to develop a curve of pressure vs. time from t=0 until pressure drops to atmospheric. Many things can be neglected in this situation, such as friction etc., since I would like a general curve to compare with experimental data. I am unsure of how to apply fluid dynamics to a vessel that empties simply due to its own pressure difference through an area.

Temperature can be assumed to be constant at 25C as well.
 

Answers and Replies

Henryk
Gold Member
251
97
You can find engineering formula in places such as valve manufacturers, pneumatic handbooks, etc. Here is an example http://www.theleeco.com/engineering/engineering.cfm#lohm-laws-working-with-gases

You have to be aware that you will need two regimes for your problem: initially the inside pressure is greater than 1.9 x atmospheric and you need a sonic formula. At lower pressures subsonic equations will do.
 
3
0
Doesn't
You can find engineering formula in places such as valve manufacturers, pneumatic handbooks, etc. Here is an example http://www.theleeco.com/engineering/engineering.cfm#lohm-laws-working-with-gases

You have to be aware that you will need two regimes for your problem: initially the inside pressure is greater than 1.9 x atmospheric and you need a sonic formula. At lower pressures subsonic equations will do.
100psi relative is 114psi absolute, which is nearly eight times greater than atmospheric. Are you aware of any ways that this could be done to give a rugh estimate? After all I will be testing this and ultimately have the real data to compare this to.
 
Henryk
Gold Member
251
97
Follow the link. You will find a number of pages with relevant information. Lee valve company uses LOHMS concept. Find how to calculate LOHM for a give size orifice and then the flow rate as a function of pressure.
 

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