# Homework Help: Volumetric flow rate of bubble out of the straw

1. Dec 6, 2015

### Charles CL

1. The problem statement, all variables and given/known data
Imagine that you are blowing air through a straw in a cup of water and the root of the straw was connected through a rectangular box with empty base and every side of the rectangular box was cut into "teeth" shape. Bubbles will come out from the teeth of the rectangular box after the straw with certain volumetric flow rate. I couldn't find an idea of how to get the volumteric flow rate of it which related the area of the straw, the area of the triangular teeth and other parameters with the volumetric flow rate of the bubbles.

teeth shape --> vvvvvvvv
Please refer to the attached picture for your reference of how it looks like.

2. The attempt at a solution
May i know how to calculate volumetric flow rate of the bubble out of the teeth of the rectangular box that connected to the straw?

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2. Dec 6, 2015

### Leon666

Volumetric flow rate is the linear velocity times the area...
V*A

If you have the straws's area and the flow rate at the straw, you can calculate the linear velocity of the fluid...

That's a very simplified approach, but at the level of information given I think that it should be enough

3. Dec 6, 2015

### Charles CL

Dear Leon666,

I need to find the volumetric flow rate (m^3/s),Q of the gas bubble come out from the triangular teeth.
Total area,A for the teeth is 0.0016m^2, velocity,v = unknown (m/s).
I wonder is there any formula can be used to calculate the velocity of the bubble, so that i can put it into the equation Q=v*A to get the volumetric flow rate?

Meanwhile, i found an equation for 'Orifice' Openings,
Q = Cd*A*[(2*delta P)/air density]^n
Discharge coefficient, Cd = 0.61,
Discharge Area, A = 0.0016m^2,
Pressure difference, delta P = 200 Pa,
Air density = 1.2 kg/m^3,
flow exponent, n = 0.5 (assumed flow in turbulent)

Therefore, Q = 0.0178 m^3/s
(I wonder this equation is applicable for my case or not?)

Last edited: Dec 6, 2015