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Vessel Sizing Question

Vessel Sizing Question

Vessel Sizing Question

(OP)
I would appreciate any help I could get on a problem I am having at work. Thanks in advance!

I have a system that I am designing a test chamber for. We have a customer requirement that states the maximum rate of pressure change the system needs to be able to be subjected to during testing is 0.01 psi/sec and I have a pump that I know has a minimum pumping speed of 100 l/min to a maxiumum of 400 l/min. How would I size the interior volume of my chamber to know that I am capable of achieving the pressure change requirement? Thanks!

RE: Vessel Sizing Question

If you start with air at pressure of, say 14.51 psia in a 5 liter soft plastic bottle, you would have a volume of air in that 5 liter bottle at 14.50 psia. Now you increase the pressure in the soft plastic bottle to 14.51 psia and the bottle expands in size, so the bottle would now have a volume of 5 x 14.51 = 14.50 x V2 or V2 = 5 x 14.51/14.50 liters = 1.00069 x 5 liters = 5.0034 liters

From that experiment you can infer that, if you did that in 1 second, it would be a change of air volume of 5.0034 - 5 liters = 0.0034 liters in that 1 second.

Problem is that 0.0034 l/s air flow will only change the pressure by 0.01 psi, if the bottle is about 5 liters in size. If the bottle is a different size, say bigger than 5 liters, then that flow rate won't change the pressure by that much. Do the problem again, but instead of using 5 liters, use the volume of the container that you have to fill. You will find that you will need 2 x the flow rate to change the pressure by the same 0.01 psi/s, if your container has a 10 Liter volume.

Neglecting air compressibility of course, which you can do at low pressures like that example.

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RE: Vessel Sizing Question

The question is, if it air or liquid you're pressurising with?

The pressure rise is very low, 0.6 psi /min. If it's air, what pressure is your "pump" flow at?

If it's liquid system without any air gap, you would need a huge volume at 100l/sec to make this sort of pressure rise.

Give us a but more info and you might get a more specific response. It's all very vague at the moment.

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Also: There's usually a good reason why everyone does it that way

RE: Vessel Sizing Question

(OP)
Thanks for the responses. Here is a little more info that I should have included. Our system will be placecd inside of an aluminum chamber (which is what I am trying to size). Then we will be using a vacuum pump that has a pumping rate of 100 l/min - 400 l/min to pull a vacuum, the medium is air. Our requirements state we should be able to control pressure at any rate in the range of +/- .01 psi/sec over the range of 11.7-17.7 psi.

RE: Vessel Sizing Question

So you're pulling the air from AROUND the vessel that is inside an aluminum container?
Is your pump pulling 100 liter/min or 400 liter/min?
How is that rate controlled?

RE: Vessel Sizing Question

(OP)
According to our lab tech. Plan is to have the vacuum pump not controlled, but instead running at full speed. They will control the system leak rate with a proportional valve vented to the atmosphere. Yes, we are pulling the air from around our system inside of a sealed chamber.

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