Discover How to Measure Flowrate Through Varying Tube Diameters

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In summary, the conversation discusses a setup with a source of air pressure, a tube for the air to flow through, a connector, and a flowmeter. The goal is to use the flowmeter readings to determine the diameter of the tube. To achieve this, a calibration curve is proposed using tubes of known diameter and reading the flowrate. However, changing the tube diameter does not affect the flowrate read by the flowmeter, possibly due to the smaller diameter connector. The setup is described and a solution is suggested using the concept of total conductance. The conversation also recommends referring to a resource on experimental design for further understanding.
  • #1
oceanspiral20
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I have a setup where there is a source of air pressure, a tube through which the air flows, a connector through which air flows, and a flow meter which reads the flowrate of the air at the end.
The final goal is to use the readings from the flowmeter to determine the diameter of the tube through which the air is flowing (the diameter will be the unknown).

So, to get there, I wanted to create a calibration curve to relate diameter of the tube (the eventual unknown) to the flowrate (our measured variable) by using tubes of known diameter and reading the flowrate for each known diameter. So, the pressure at the air source is a constant and the flowrate would be read for each different diameter tube. From here, I would ideally have a calibration curve which I could use to determine diameter of the tube based on a flowrate.

However, by changing out the diameter of the tube through which air is flowing, I'm not getting any change in the readout of the flowrate from the flowmeter.

I'm wondering if the reason is the connector which connects the tube to the flowmeter. The connector shrinks to a much smaller diameter than the tube - is this effectively a limiting factor? I'm wondering if, for each diameter tube, since the connector is a much smaller diameter than the tube, the flowrate read by the flowmeter is the same (because input pressure is the same, output diameter is the same, and maybe what happens in the middle - whether it flows through a large diameter tube or a small diameter tube - doesn't matter)?

So, if my description is confusing, the setup (direction of air flow left to right) looks like this:
air source at a constant pressure -> constant diameter connector -> Variable diameter tubes (from 2-10 mm) -> constant tapered Connector which shrinks to 1 mm diameter -> Flowmeter

Do I need to find a way to use the flowmeter to measure directly at the end of the tube rather than through a smaller connector? Or is there something else I'm missing here?

Thanks!
 
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  • #2
oceanspiral20 said:
I have a setup where there is a source of air pressure, a tube through which the air flows, a connector through which air flows, and a flow meter which reads the flowrate of the air at the end.
The final goal is to use the readings from the flowmeter to determine the diameter of the tube through which the air is flowing (the diameter will be the unknown).

So, to get there, I wanted to create a calibration curve to relate diameter of the tube (the eventual unknown) to the flowrate (our measured variable) by using tubes of known diameter and reading the flowrate for each known diameter. So, the pressure at the air source is a constant and the flowrate would be read for each different diameter tube. From here, I would ideally have a calibration curve which I could use to determine diameter of the tube based on a flowrate.

However, by changing out the diameter of the tube through which air is flowing, I'm not getting any change in the readout of the flowrate from the flowmeter.

I'm wondering if the reason is the connector which connects the tube to the flowmeter. The connector shrinks to a much smaller diameter than the tube - is this effectively a limiting factor? I'm wondering if, for each diameter tube, since the connector is a much smaller diameter than the tube, the flowrate read by the flowmeter is the same (because input pressure is the same, output diameter is the same, and maybe what happens in the middle - whether it flows through a large diameter tube or a small diameter tube - doesn't matter)?

So, if my description is confusing, the setup (direction of air flow left to right) looks like this:
air source at a constant pressure -> constant diameter connector -> Variable diameter tubes (from 2-10 mm) -> constant tapered Connector which shrinks to 1 mm diameter -> Flowmeter

Do I need to find a way to use the flowmeter to measure directly at the end of the tube rather than through a smaller connector? Or is there something else I'm missing here?

Thanks!

See p. 15 of this: https://indico.cern.ch/event/286275/contribution/149/material/slides/0.pdf or a book on basic experimental desing (e.g. Moore, Davis and Coplan, "Building Scientific Apparatus")

The total conductance of tubes in series are calculated like you would for resistances in parallel.

1/C_series = 1/C_1 + 1/C_2 + 1/C_3 + ...

Having a very small conductance tube on your flowmeter is going to be the limiting conductance of your system = 1/C_system = approx. 1/C_smallest
 

1. How do you measure flowrate through varying tube diameters?

The most common method is to use a flowmeter, which measures the volume or mass flowrate of a fluid passing through a specific point in the tube. Other methods include using pressure drop measurements or calculating flowrate based on the tube's dimensions and fluid properties.

2. What factors affect flowrate through varying tube diameters?

The main factors that affect flowrate are the tube diameter, fluid viscosity, fluid density, and the pressure difference between the two ends of the tube. Other factors such as tube roughness, temperature, and the presence of any obstructions can also impact flowrate.

3. Can flowrate be accurately measured through tubes with varying diameters?

Yes, modern flowmeters are designed to accurately measure flowrate through tubes with varying diameters. However, the accuracy may vary depending on the type of flowmeter and the conditions of the fluid and tube.

4. How does the tube diameter affect flowrate?

The tube diameter has a significant impact on flowrate as it determines the amount of space available for the fluid to flow through. A larger diameter allows for a higher flowrate, while a smaller diameter restricts flow and can result in a lower flowrate.

5. Are there any challenges in measuring flowrate through varying tube diameters?

Yes, there can be challenges in accurately measuring flowrate through varying tube diameters. Some common challenges include changes in fluid properties, such as viscosity, as well as changes in flow velocity and turbulence within the tube. Proper calibration and selection of the appropriate flowmeter can help overcome these challenges.

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