Evacuated Canister and Flow Rate

Dylano

Hello everyone, I am currently in a mechanical engineering program, and I am on my first co-op work term. I have been assigned to make modifications to a PVC collection device involving flow rates, but I have not yet taken any courses relative to flow. I was hoping I could get some help and some explanations of the theory involved.

So I have a PVC canister, with a volume of 1 litre. The canister is evacuated to -26 inches of mercury. The canister is then attached to a series two of plastic tubes to restrict the air flow. The first tube has a inner diameter of 1.58 mm and a length of 60 cm. The second tube has an inner diameter of 0.0635 mm and has a variable length. Then the system is open to normal atmospheric pressure.

The goal of this apparatus is to collect samples of air over a 24-36 hour time period. I am looking for some way to model this so that I can perform calculations with different volumes/diameters of tube/etc. I am really unsure how to do this as the pressure inside the canister is changing, which would also affect the flow rate (I am assuming).

Thanks!