I Calculate the internal pressure of a tube based on flow rate

AI Thread Summary
To calculate the internal pressure of a tube with known exit flow rate, length, diameter, and material, the Darcy-Weisbach equation can be applied. The flow rates into and out of the tube must be equal due to conservation of mass, and the system is assumed to be horizontal at sea level. Given the parameters, the inlet pressure is approximately 0.2 PSI higher than the outlet pressure, with a linear pressure drop along the tube's length. Assumptions about temperature and water properties are necessary for accuracy. This method provides a reasonable approximation of internal pressure based on the provided data.
PaulB
Messages
12
Reaction score
0
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.
 
Physics news on Phys.org
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?
 
Last edited by a moderator:
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.
 
  • Like
Likes 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?
 
  • Like
Likes russ_watters
Dullard said:
what are your Length and Flowrate?
Dullard said:
what are your Length and Flowrate?
 
  • #10
Dullard said:
what are your Length and Flowrate?
Length is 0.3 m, flowrate is 8 mL/minute. How can I calculate the answer?
 
  • #11
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...).
 
  • Like
Likes russ_watters
Back
Top