- #1

mallorn

- 1

- 0

## Homework Statement

Hi everyone,

I'm trying to calculate the flow rate of air in straight tubing that is 30cm long and has a diameter of .1875 in and has an outlet into a 100 mL vial which is vented to the atmosphere. The starting of the system pressure is 20 psi and the ending psi is 14.6, since it's in equilibrium with the atmosphere. The end goal of the problem is to see how long it takes to completely flush the vial with air three times. To do that, I'd need the volumetric flow rate of the air in the tubing.

## Homework Equations

and## The Attempt at a Solution

I was using the flow rate calculator from pipeflowcalculations.com but got a result (.002 cubic meters/sec, which is 120,000 mL/min) that I wanted to confirm using manual calculations.

However, I've been running into some problems that I wanted to consult with you guys:

I was thinking to calculate it using the Darcy-Weisenbach equation V=sqrt(2g*Pressure Drop/density* (length/diameter)*darcy friction factor. Would it be ok to ignore the friction factor in this case since the length is so small?

Another option would be to use the definition of pressure as density*head*gravity and the equation as follows:

V= Square root (2*g*h)

Pressure/g*density= h

But when I try to solve it the units don't match up, even when I convert them all to SI.

What do you all think is the best approach and is my train of thought correct? Thank you very much!