Calculating Drag Through A Pipe

[tomtomtom1]

MODERATOR NOTE: NO TEMPLATE - MISPLACED HOMEWORK
Hi All
I was hoping someone could help with the following problem:-

Concrete is being pumped along a pipe. All of the concrete that is more then 10cm from the wall of the pipe is moving at 0.2m/s, and the material in contact with the pipe wall is not moving. Assuming that the concrete has a viscosity of 5 Pa s, calculate the drag on each square meter of the surface of the pipe.

I know that the Viscosity = Shear Stress / Shear Strain
and Shear Stress = Force / Area
and Shear Strain = Change in Length / Original Length

But that it is.

The answer is meant to be:-
Shear stress = Viscosity x ((V1 – V2) / dy)
Shear stress = 5 x (0.2 / 0.1)
Shear stress = 10 N/m2

I assume the pipe diameter to be 20cm giving me an Area of 0.03146m^2

I'm not sure where to take it from here.

Any ideas?

Thank you.

 

[Chestermiller]

MODERATOR NOTE: NO TEMPLATE - MISPLACED HOMEWORK
Hi All
I was hoping someone could help with the following problem:-

Concrete is being pumped along a pipe. All of the concrete that is more then 10cm from the wall of the pipe is moving at 0.2m/s, and the material in contact with the pipe wall is not moving. Assuming that the concrete has a viscosity of 5 Pa s, calculate the drag on each square meter of the surface of the pipe.

I know that the Viscosity = Shear Stress / Shear Strain
and Shear Stress = Force / Area
and Shear Strain = Change in Length / Original Length

This is not correct. Viscosity = Shear Stress / Shear Rate (i.e., velocity gradient)

But that it is.

The answer is meant to be:-
Shear stress = Viscosity x ((V1 – V2) / dy)
Shear stress = 5 x (0.2 / 0.1)
Shear stress = 10 N/m2

The velocity gradient is $\Delta V/\Delta y$, which is 0.2/0.1 = $2 s^{-1}$
So the shear stress is the same as the drag force per unit area = 10 N/m^2 = 10 Pa

I assume the pipe diameter to be 20cm giving me an Area of 0.03146m^2

I'm not sure where to take it from here.

You don't need the pipe surface area. You already have your answer.