Calculate the internal pressure of a tube based on flow rate

• I
• PaulB
In summary, the conversation discusses a pump of unknown flowrate pumping water through a tube of known length and diameter. The flowrate of water exiting the tube is also known, and the individual is seeking to calculate the internal pressure of the tubing at sea level elevation. However, with the limited information provided, it is not possible to accurately calculate the internal pressure. With additional assumptions and information, there are methods such as using a pipe/tubing pressure drop table or the Darcy-Weisbach equation that can provide a decent approximation of the internal pressure.
PaulB
TL;DR Summary
Calculate exit pressure from tube based on flowrate
I have pump of unknown flowrate pumping water through a tube of length L and diameter D. I know that the flowrate of water exiting the tube is X mL/min. I would like to know the internal pressure of the tubing, how can I calculate it? This all occurs at sea level elevation.

PaulB said:
I have pump of unknown flowrate pumping water through a tube of length L and diameter D. I know that the flowrate of water exiting the tube is X mL/min.
You said you don't know the flow rate and then that you do. Which is it? More to the point: do you have a complete picture of the system configuration? If not, exactly what do you know and not know?

PaulB said:
I would like to know the internal pressure of the tubing, how can I calculate it? This all occurs at sea level elevation.
Not with the information provided, no. It could even be zero.

russ_watters said:
You said you don't know the flow rate and then that you do. Which is it? More to the point: do you have a complete picture of the system configuration? If not, exactly what do you know and not know?
I know the flowrate of the water exiting the tubing. I don't have any knowledge of the florwrate of the water entering the tube. All I know is tube length, diameter, water density and atmospheric conditions. Is it possible to determine internal pressure from this?

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Given an elevation profile of the tube (and the info in the OP), there is enough information to calculate the pressure at any point in the tube. Temperature, surface roughness, and the precise properties of the water would have to be assumed.

Depending on the precision of the answer that you require, you might just be able to use a standard 'pipe/tubing pressure drop' table (for your tubing size) and add/subtract gravity head for elevation changes.

russ_watters
PaulB said:
I know the flowrate of the water exiting the tubing. I don't have any knowledge of the florwrate of the water entering the tube.
The flow rates into and out of the tube must be the same due to conservation of mass.
PaulB said:
All I know is tube length, diameter, water density and atmospheric conditions. Is it possible to determine internal pressure from this?
You said this all occurs at sea level - so it's completely horizontal? Do you know the hose material?

I agree with @Dullard that with a few assumptions you can calculate an answer but if it is accurate enough for your needs is another matter.

russ_watters said:
The flow rates into and out of the tube must be the same due to conservation of mass.

You said this all occurs at sea level - so it's completely horizontal? Do you know the hose material?

I agree with @Dullard that with a few assumptions you can calculate an answer but if it is accurate enough for your needs is another matter.

The tube is completely horizontal. Material is PVC, actual inner diameter is 1 mm. I am just looking for a decent approximation of internal pressure. How can I calculate?

what are your Length and Flowrate?

russ_watters
Dullard said:
what are your Length and Flowrate?
Dullard said:
what are your Length and Flowrate?

Dullard said:
what are your Length and Flowrate?
Length is 0.3 m, flowrate is 8 mL/minute. How can I calculate the answer?

I used Darcy-Weisbach:
The pressure at the inlet to your tube is approx 0.2 PSI (1450 Pa) higher than the outlet pressure. The pressure change across the length is linear (0.1 PSI at the midpoint...).

russ_watters

1. How is the internal pressure of a tube calculated?

The internal pressure of a tube can be calculated using the formula P = (4 * Q * µ) / (π * r^3), where P is the internal pressure, Q is the flow rate, µ is the dynamic viscosity, and r is the radius of the tube.

2. What is the relationship between flow rate and internal pressure?

The internal pressure of a tube is directly proportional to the flow rate. This means that as the flow rate increases, the internal pressure also increases.

3. What factors can affect the internal pressure of a tube?

The internal pressure of a tube can be affected by various factors such as the flow rate, viscosity of the fluid, and the radius of the tube. Additionally, changes in temperature and the presence of any obstructions in the tube can also impact the internal pressure.

4. How can the internal pressure of a tube be measured?

The internal pressure of a tube can be measured using a pressure gauge or a manometer. These instruments can provide accurate readings of the pressure inside the tube.

5. Can the internal pressure of a tube be controlled?

Yes, the internal pressure of a tube can be controlled by adjusting the flow rate, changing the viscosity of the fluid, or altering the radius of the tube. Additionally, using pressure regulators or valves can also help in controlling the internal pressure.

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