Pressure Drop Across a Change in Diameter

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Discussion Overview

The discussion revolves around calculating the pressure drop across an abrupt change in diameter in piping systems, specifically for water. Participants explore fluid dynamics concepts, including relevant equations and their implications in a horizontal system.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant seeks assistance in calculating pressure drop due to a change in pipe diameter, indicating limited experience in fluid dynamics.
  • Another participant presents a formula for pressure drop, expressing uncertainty about its English terminology and referencing their notes in Italian.
  • A participant questions the meaning of ΔH in the presented formula, suggesting it relates to potential energy changes, and notes that their system is horizontal, implying ΔH may be zero.
  • Another participant clarifies that ΔH represents pressure drop expressed as a length, and references Bernoulli's equation to support their explanation.
  • A further response challenges the interpretation of H, stating it does not necessarily refer to height and explaining that engineers often treat pressure drop as a length for simplicity.

Areas of Agreement / Disagreement

Participants express differing interpretations of the equations and concepts involved, particularly regarding the meaning of ΔH and its application in a horizontal system. No consensus is reached on the correct interpretation or application of the formulas discussed.

Contextual Notes

Participants acknowledge limitations in their understanding of the terminology and the context of the equations, particularly due to language barriers and the horizontal nature of the system being discussed.

nlis12
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Greetings,

I have very little experience with fluid dynamics and I was wondering how I can calculate a pressure drop across an abrupt change in diameter of the piping used for water.

Any help is appreciated!

Thanks!
 
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I looked my notes on fluid dynamics by my professor and I found this formula

##ΔH = \frac {(V_1-V_2)^2} {2g}##

Then ##ΔP = \rho g ΔH## where ##\rho## is the density of the fluid.

I'm sorry that I can't give you any reference, but my notes are in italian... and I don't know the name of this formula in english! :(
 
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dRic2 said:
I looked my notes on fluid dynamics by my professor and I found this formula

##ΔH = \frac {(V_1-V_2)^2} {2g}##

Then ##ΔP = \rho g ΔH## where ##\rho## is the density of the fluid.

I'm sorry that I can't give you any reference, but my notes are in italian... and I don't know the name of this formula in english! :(

Thank you very much for your reply.
But I wonder what the H stands for?
I think your equation determines the pressure drop due to a change in potential energy.
Unfortunately, my system is perfectly horizontal, or I can assume Delta H is zero, so I have no losses due to potential energy changes. (I think)

Regards!
 
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nlis12 said:
I think your equation determines the pressure drop due to a change in potential energy.
Unfortunately, my system is perfectly horizontal

No, H is a misleading letter but It doesn't refer to the heights necessarily. It's just that egineers like to work with the pressure drop as it was a length thus they divided it but ##\rho## and ##g##(that are constant).

This is the simplest explanation I can think of.
 
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