# Fluid flow rate calculation

Summary:
Fluid dynamics and flow rate calculation from outside tank to inside tank!
I am trying to calculate the flow rate of O2 from a known volume 25 in^3. The cylinder will fill up to a maximum pressure of 140 psi in 11.26 seconds. Any help to determine the flow rate will be appreciated. Do I use Bernoulli equation to find the flow rate?

Baluncore
Welcome to PF.
I think you must specify the dimensions of the path the O2 will flow to escape from the volume.

The tubing length is about 35 ft with an ID of 1/16”

berkeman
Mentor
Summary:: Flow rate calculation from a known volume. Time to fill the cylinder of 25 in^3 and max pressure

I am trying to calculate the flow rate of O2 from a known volume 25 in^3. The cylinder will fill up to a maximum pressure of 140 psi in 11.26 seconds. Any help to determine the flow rate will be appreciated. Do I use Bernoulli equation to find the flow rate?
The O2 is flowing from where to where? Into or out of the ##25 in^3## volume? If into, what is the pressure available from the source?

The O2 is flowing from where to where? Into or out of the ##25 in^3## volume? If into, what is the pressure available from the source?

Pressure source is from a tank outside the building. Pressure on that tank is 150 psi. So o2 flows from that tank and into 25 in^3 volume. Tubing ID is 1/16”

berkeman
Mentor
The cylinder will fill up to a maximum pressure of 140 psi in 11.26 seconds.
Pressure source is from a tank outside the building. Pressure on that tank is 150 psi.
The tubing length is about 35 ft with an ID of 1/16”

So there is only a 10psi drop in flowing from the outside tank through all that tiny tubing and the final valve into the smaller tank? Or is there a booster pump involved? Have you tried this yet?

So there is only a 10psi drop in flowing from the outside tank through all that tiny tubing and the final valve into the smaller tank? Or is there a booster pump involved? Have you tried this yet?
Ok. Just found out that part of that line will be 1/4" ID on 20' length.

I am trying to calculate the flow rate of O2 that flows from a tank outside a building to a known volume 25 in^3 inside the building. The pipe length from outside source to inside source is 70 ft at .25” ID and 1 ft at 1/16” ID. Outside source is at 150 psi. The cylinder inside will fill up to a maximum pressure of 140 psi in 11.26 seconds. Any help in determining the flow rate will be appreciated. Do I use Bernoulli equation to find the flow rate?

[Mentor Note -- two threads on the same question merged]

Last edited by a moderator:
Baluncore
This appears to be a duplication of a previous thread.

The flow rate will change as the gas flows between the two volumes.
Why specify the flow ?
How do you want to specify the flow ?
Will it be by volume/second if the gas was at a standard atmospheric pressure ?

• berkeman
Chestermiller
Mentor
What is in the piping and receiver before filling begins (pressure?)?

Is there a valve between the source and the inlet piping? If so, how restrictive is this valve?

You realize that the volume of the piping is much greater than the volume you are filling, right?

jrmichler
Mentor
You know the volume of the inside cylinder. You know the initial and final pressures in the inside cylinder. You know the filling time to four decimal places. That is sufficient information to calculate the average flow rate.

You know the volume of the inside cylinder. You know the initial and final pressures in the inside cylinder. You know the filling time to four decimal places. That is sufficient information to calculate the average flow rate.
Yes. So is it as simple as applying Bernoulli principles? Can I also use Reynolds equation assuming the flow is turbulent?

Is this not done simply by dividing the volume of the 25 inch3 by 11.26 seconds?

• 256bits
256bits
Gold Member
Is this not done simply by dividing the volume of the 25 inch3 by 11.26 seconds?
It will give you the average volumetric flow rate, but not the amount of mass of o2 in the second tank.
Unless we assume that the temperature of the gas in the 25 inch3 volume does not rise and it is an isothermal process with heat flow out of that small tank.
Or we could wait until the temperature stabilizes, re-measure the pressure, and use the ideal gas law to determine the mass of O2 in the small container.
See http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node17.html section 2.3.3