Calculate Force on Steel Wall from Water Flow

[neilmark]

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?

 

[JaredJames]

Do you know how to work out the pressure of the fluid leaving the pipe?

 

[neilmark]

Not sure I follow you there??

 

[JaredJames]

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.

 

[russ_watters]

Static pressure at the end of the pipe is zero, but there is velocity pressure, which you can calculate with Bernoulli's equation.

 

[sophiecentaur]

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)