Height of Water Jet from Pressure in Domestic Water Pipes

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Discussion Overview

The discussion revolves around determining the height reached by a jet of water from a domestic water pipe under pressure, using Bernoulli's equation. Participants explore the application of the equation, the definitions of pressure, and the assumptions involved in the calculations.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant proposes using Bernoulli's equation to relate the pressures and heights in the water jet scenario, questioning the appropriate value for P2.
  • Another participant suggests that P1 and P2 should both be defined consistently as absolute pressures, indicating that gauge pressure could also be used.
  • A participant challenges the definitions of Z1 and V2, asserting that Z1 should be the height of the water surface and V2 should be zero at the maximum height of the jet.
  • Another participant argues that Bernoulli's equation should be applied between two steady points, noting that the flow may not be steady at points along the jet and suggesting the need for kinematic equations to find the maximum height after determining the exit velocity.

Areas of Agreement / Disagreement

Participants express differing views on the definitions of pressure and the application of Bernoulli's equation, indicating that there is no consensus on these points. The discussion remains unresolved regarding the correct approach to the problem.

Contextual Notes

There are unresolved assumptions regarding the definitions of pressure (absolute vs. gauge) and the conditions under which Bernoulli's equation can be applied. The discussion also highlights potential limitations in the assumptions about steady flow and the treatment of the water jet.

hfatehi
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Homework Statement


The pressure in domestic water pipes is typically 60 psi above the atmospheric pressure. If the viscous effects are neglected, determine the height reached by a jet of water through a small hole in the top of the pipe.


Homework Equations


I am using the Bernoullis equation;
(P1/Rho) + gZ1 + (V1^2/2) = (P2/Rho) + gZ2 + (V2^2/2)


The Attempt at a Solution



I take
Z1 = 0 (surface of the pipe)
V2 = 0 (Max height)
P1 = Atmospheric pressure + 60 = 74.7 psi
g = 32.174 ft/sec^2
question is what should P2 be? will it be just atmospehric pressure or will it be 0
 
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well, since you defined P1 to be absolute pressure, then so should you define P2

you could have just taken gauge pressure, it's up to you

but being consistent is the most important thing
 
hfatehi said:

Homework Statement


The pressure in domestic water pipes is typically 60 psi above the atmospheric pressure. If the viscous effects are neglected, determine the height reached by a jet of water through a small hole in the top of the pipe.


Homework Equations


I am using the Bernoullis equation;
(P1/Rho) + gZ1 + (V1^2/2) = (P2/Rho) + gZ2 + (V2^2/2)


The Attempt at a Solution



I take
Z1 = 0 (surface of the pipe)
V2 = 0 (Max height)
P1 = Atmospheric pressure + 60 = 74.7 psi
g = 32.174 ft/sec^2
question is what should P2 be? will it be just atmospehric pressure or will it be 0

Let's make life easier by using gauge pressure . Also you defined Z1 and V2 incorrectly.
 
May i asked why is Z1 and V2 wrong. My understanding is that at the surface of pipe where the hole is we take that point as Z1 and the height of the water at MAX as Z2. hence Z1 will be our reference point of 0. Also i thought that the velocity of the particle at its highest point in the trejactory is 0. please correct me
 
Bernoulli's equation (in that form) has to be applied between two points in a steady flow (with the exception of obtaining an approximate answer for 'quasisteady' flows) , I don't believe that any point in the jet besides the very base of it can be considered steady (since it diffuses).

So you will have to use bernoulli's equation to find the velocity of the water at the point where it leaves the pipe, then apply the kinematics equations to find the maximum height.
 

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