Pressure Drop Calculation Using U-Tube Manometer

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Discussion Overview

The discussion revolves around calculating the pressure drop between two points in a pipe carrying water using a U-tube manometer. Participants explore the relationship between the densities of the fluids involved and the implications for measurement accuracy.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions whether the density (p) in the pressure drop equation refers to the density of the manometer fluid or the water flowing through the pipe.
  • Another participant asserts that the pressure drop can be expressed as p1 - p2 = gh(density(manometer fluid) - density(water).
  • A subsequent reply reiterates the previous equation and specifies that in their case, the manometer fluid has a lower density than the water.
  • Another participant cautions against using a manometer fluid with a lower density than the fluid in the pipe, explaining that a higher density fluid is preferable for more compact measuring instruments.

Areas of Agreement / Disagreement

Participants express differing views on the appropriate choice of manometer fluid density relative to the fluid in the pipe, indicating a lack of consensus on the best practices for pressure drop measurement.

Contextual Notes

There are unresolved assumptions regarding the implications of using different fluid densities in the manometer and how this affects the accuracy of pressure measurements.

Physicist3
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I have been told to calculate the pressure drop between two points in a pipe carrying water using a U-tube manometer. I understand that the pressure drop (P1 - P2) is given by pgh and that h is the difference in manometer fluid levels and g is gravity, but is p the density of the manometer fluid or the water flowing through the pipe?
 
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Exactly, p1-p2 = gh(density(manometer fluid) - density(water))
 
pukb said:
Exactly, p1-p2 = gh(density(manometer fluid) - density(water))

In the case I am referring to, the manometer fluid has a lower density than the water. For a pipe, is the pressure drop measured using a utube manometer simply ρmanometergh?
 
it is not a good idea to use a fluid of lower density in manometer than the density of fluid in the pipe. a higher density fluid is used to make measuring instruments smaller. for example, mercury will require a space 13.6 times smaller than water for same pressure rise or drop.
 

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