S2: Fluids Flashcards
What’s the first law of thermodynamics?
Change in energy of a system is equal to the difference between energy input and energy output
Delta Esys= Wnet in + Qnet in
What is the net work done in terms of energy?
Mech energy transfers in/out is net work done
What’s net heat added in terms of energy transfers
Thermal energy in/our is net heat added
What are the 3 forms of fluid energy?
Internal, kinetic, potential
Define specific energy
Fluid energy per unit mass
What are the 4 forms of work?
Shaft work, pressure work, viscous work, other work
What’s shaft power and it’s equation?
•
Wshaft = wTshaft = 2pie
•
x n x Tshaft
What’s the equation for work done by pressure forces
SWpressure = Pd9 = PAds
What’s the equation for rate of pressure work
•
Wpressure = PA ds/dt = PAV
For steady flow what’s the equation for mass flow rate?
•
m= row1A1V1 = row2A2V2
Where is the kinetic energy correction factor used?
What’re the values for laminar and turbulent flow?
When there’s incompressible flow with none uniform velocity at 1 and 2
L= 2 T= 1.04-1.10
How does fluid flow in an open channel?
Fluid flows under gravity
How does fluid flow in a closed pipe?
Pressure difference drives flow
What shaped pipes withstand highest internal pressure?
Circular
What are the 2 types of viscous flow?
Turbulent and laminar
Which type of flow (turbulent / laminar) has the sharpest nose?
Laminar
Turbulent is almost flat
For steady state flow, what is shear force proportional to?
Shear rate
Mue u/y
Shear force = Mue dux/dy
When does Newton’s law of viscosity (shear force proportional to shear rate) not apply and apply?
Applies- Newtonian fluids (gas, water, petrol)
Doesn’t- non Newtonian fluids (toothpaste, painting, marmalade, polymers)
What’s the diff between laminar and turbulent flow?
Laminar- flows in layers
Turbulent- layers mix at macroscopic level
What are the 4 factors that affect the type of fluid flow?
Velocity
Density
Kinematic viscosity
Diameter (geometry)
What values should be given to Reynolds number for each flow type?
<2000 laminar
2000-4000 transition flow
> 4000 turbulent flow
What equation describes how long a fluid will take to reach full flow?
Le/D = 0.06 Re laminar
Le/D = 4.4 Re ^1/6 turbulent
In pipes, what does the friction force depend on?
Solid characteristics
- geometry, size : D
- particle toughness : K (increases as pipe ages)
Fluid characteristics
- density
- viscosity
Relative velocity
-solid vs liquid v
What’s the equation for relative toughness?
K/D
