Chapter 2-4

Question 1

What is viscosity?

How can you calculate it?

Answer 1

It is the measure of the shear force per unit area that is needed to drag one layer of fluid past another layer of fluid one unit distance away.

t = u * dv/dy
t = tau (shear force)
u= dynamic viscosity 
dv= change in velocity 
dy= change in height.

Question 2

Q= ?

F=?

H=?

Answer 2

Q=AV

F=p*Q( V2 - V1)

H= P/(pg) + V^2/(2g) + z

Question 3

What are the differences between steady and unsteady flows?

What are the differences between uniform and non-uniform flow?

Answer 3

In steady flows, the properties do not change with time whereas in unsteady flows they do.

Unifrom: properties don’t change with position
dV/dS = 0
Non-uniform flow: properties change with position.
dV/dS doesn’t = 0

V= velocity vector
S= arc length along a streamline

Question 4

To =?

To is the mean stress on fluid at the boundary

Answer 4

To = -A / Pw  *  dP*/dx
A=cross-sectional area\
Pw= wetted perimeter
dP*/dx = pressure gradient 
P*= P + p*g*z

Question 5

To (for a circular section) =?

Answer 5

To = -r/2 * dP/dx
r=radius of the pipe.
dP/dx = pressure gradient
P= P + pg*z

Question 6

Hagen-poiseuille Equation
u=?
u is the dynamic viscosity

When is u the max?
When is u=0?

Answer 6

u = 1/(4u) * dp/dx * (R^2 - r^2)

u is maxed when r=0

u=0 when r=R

Question 7

Hagen-poiseuille Equation

Q=?

Answer 7

Q= (piR^4) / (8u) * (/\P*)/L

/\P* = P1* - P2*
L= length of pipe

Question 8

Hagen-poiseuille Equation
hf=?
(Head loss)
Shat flow is this for?

Answer 8

hf= (32*v*L*V) / (g * d^2)
v= kinematic viscosity
V= mean pipe velocity
d= diemeter

ONLY FOR LAMINAR FLOW

Question 9

Re < 2000 = ?
2000 < Re < 4000 = ?
Re > 4000 = ?

Re =?

Answer 9

Re < 2000 = Lamiar flow
2000 < Re < 4000 = Transitional flow
Re > 4000 = Turbulent flow.

Re = ( V*d) / v = ( p*V*d) / u
v= kinematic viscosity
u= dynamic viscosity
V= mean pipe velocity

Question 10

The Darcy Equation
hf = ?

What flow does this work for?

Answer 10

hf = Y * (L * V^2) / ( 2gd)
Y is lambda

Laminar and turbulent.

Question 11

How can you calculate Lambda (Y)?

Answer 11

Y = 64 / Re

Question 12

How to use the Moody diagram?

Answer 12

Relative roughness on the right selects a line.
The frictional factor is Lambda (Y)
And Reynolds number is at the bottom
Draw on the turbulence line which is where all the lines become flat. (use this as a first guess of Re when needed)