Calculate the internal pressure of a tube based on flow rate

[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.

 

[russ_watters]

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?

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.

 

[PaulB]

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?

 

[Dullard]

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]

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.

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.

 

[PaulB]

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.

 

[PaulB]

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?

 

[Dullard]

what are your Length and Flowrate?

 

[PaulB]

what are your Length and Flowrate?

what are your Length and Flowrate?

 

[PaulB]

what are your Length and Flowrate?

Length is 0.3 m, flowrate is 8 mL/minute. How can I calculate the answer?

 

[Dullard]

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...).