Calculate Force on Steel Wall from Water Flow

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Discussion Overview

The discussion revolves around calculating the force exerted by water flowing from a pipe onto a steel wall located 1.2 meters away. Participants explore the principles of fluid dynamics, including pressure, momentum, and the application of Bernoulli's equation, in the context of this scenario.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents the scenario of water flowing from a 750mm diameter pipe at a flow rate of 152 l/s and seeks assistance in calculating the force on the wall.
  • Another participant inquires about how to determine the pressure of the fluid exiting the pipe.
  • A participant clarifies that pressure is defined as force per unit area and suggests that knowing the pressure and area can help calculate the force at the pipe's exit.
  • It is noted that static pressure at the end of the pipe is zero, but velocity pressure can be calculated using Bernoulli's equation.
  • One participant argues that the static pressure can be neglected at a distance of 1 meter from the nozzle, emphasizing that the force required to stop the mass of water upon hitting the wall is what matters.
  • This participant proposes a method to calculate force based on the rate of change of momentum, suggesting that the force can be derived from the speed of the jet and the mass flow rate of the water.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of static pressure and the methods for calculating the force. There is no consensus on a single approach or solution, and multiple perspectives on the problem remain present.

Contextual Notes

Participants discuss various assumptions, such as the neglect of static pressure and the conditions under which the calculations are made. The discussion does not resolve these assumptions or the mathematical steps involved.

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We have a water pipe which is 750mm diameter assumed running full with a flow rate of 152l/s. When the water exits the pipe there is a steel wall approx 1.2m in front of it and I need to determine the force that the water exerts on the wall?

I have claulcated that the water is running at 0.067m/s.

Can anyone help?
 
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Do you know how to work out the pressure of the fluid leaving the pipe?
 
Not sure I follow you there??
 
Pressure is force per unit area.

If you know the pressure and the area of the end of the pipe you can get the force at the point of leaving the pipe.

I suppose if you know the mass flow rate you could get the momentum also.
 
Static pressure at the end of the pipe is zero, but there is velocity pressure, which you can calculate with Bernoulli's equation.
 
By the time you are 1m away from the nozzle, I think you can neglect the static pressure as the jet will have spread outwards as soon as it exits the hole. All that counts is the force needed to stop the mass of water as it hits the wall.

The Force is the rate of change of Momentum, P.
P = Speed change X Mass
and Force = P/time
So Force = Speed change X Mass per second
Work out the speed of the jet (Volume per second / Area of Pipe) now multiply by the mass per second (Volume in one second X density). Assuming the water is brought to rest, then the change is from P to zero, this is the value of the force. (Someone will point out that there is a simplified version of this but I think this is more straightforward)
 

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