Pressure drop along a tube of unkown length containing turbulent flow

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Discussion Overview

The discussion revolves around calculating the pressure at each end of a pipe with turbulent flow, where the length of the pipe is unknown. Participants explore the implications of various parameters such as viscosity, density, temperature differences, and flow rates on the pressure calculations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about calculating pressure at the ends of a pipe without knowing its length, given parameters like viscosity, density, temperature difference, and diameter.
  • Another participant suggests considering the type of fluid, its density variation with temperature, mass/volumetric flow rate, and assumptions about inlet or outlet pressure.
  • A third participant mentions the use of the Darcy-Weisbach equation for pipe flow and provides a link to examples.
  • Further clarification is provided regarding the fluid being oil, with an assumption of constant density and a known mass flow rate, but uncertainty remains about the assumptions regarding pressure.
  • One participant proposes using a non-dimensionalized Navier-Stokes equation to address the problem, particularly in the context of temperature gradients, and suggests using Femlab for simulations.

Areas of Agreement / Disagreement

Participants express various viewpoints and approaches to the problem, with no consensus reached on a specific method or solution. Multiple competing ideas remain regarding the calculations and assumptions needed.

Contextual Notes

Participants mention the influence of temperature on viscosity and density, but the exact effects and relationships are not fully explored. There are also unresolved questions about the assumptions necessary for calculating pressure gradients.

Who May Find This Useful

Individuals interested in fluid dynamics, particularly those dealing with turbulent flow in pipes and the effects of temperature on fluid properties.

scott_for_the_game
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How do u calc pressure at each end of pipe if u know its turbulent and u don't know the length.

Just got viscosity, density, temp diff at one end, D.

Cheers.
 
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hmm... Things I am thinking include:

what is your fluid?
How does it's density change with temperature?
what is your mass/volumetric flow rate?
Can you make any assumptions about either the inlet or outlet pressure?
How did you calculate your Re to determine turbulence without a velocity?
 
what is your fluid?
How does it's density change with temperature?
what is your mass/volumetric flow rate?
Can you make any assumptions about either the inlet or outlet pressure?
How did you calculate your Re to determine turbulence without a velocity?

the fluid is an oil.
density is assumed constant.
u've got mass flow rate.
Not sure about assumptions.
Calc Re from mass flow rate.
The only thing involving temp which i have no idea what its influence is.. is there's a difference in temp at one end of the pipe of like 45K.
u know viscosity is half the value at other end.

What formulas would i need to use and does it involve iterating.
And u want pressure gradient ratio of two ends.
 
I would use a non dimensionalized Navier Stokes to solve for this sort of thing, but with the case that you are speaking involving temperature gradients, I might suggest using Femlab to do this sort of thing.
 

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