Momentum Conservation Flashcards
What is Newtons 2nd Law?
The rate of change of momentum is equal to the sum of the forces
What are the forces acting a fluid?
- Pressure
- Gravity
- Density differences
- Friction/Viscosity
- Forces exerted by a solid surface e.g., a water jet hitting a flat plate
How is momentum calculated?
m*U in the x direction
How can sum of momentum be found?
Finding the integral of Ο*U dv
What is the surface force?
Due to stress, proportional to total surface area in which it acts
What are body forces?
Forces acting on a fluid mass
What is the unsteady momentum equation?
ππ (πππβ πππ’π‘) + π
When can we expect the pressure in a moving fluid to be hydrostatic?
As long as the vertical acceleration π_π is negligibly small.
When is vertical acceleration negligible?
If the streamlines
are nearly horizontal without significant curvature
What is pressure like in closed conduits?
Constant
What does S stand for in the momentum equation?
The sum of horizontal forces
What is the force like in converging pipes?
- Neglect friction losses
- Flow driven by pressure differences
- Force exerted by pipe onto fluid
- Flow accelerates so resultant force exists on the fluid
How do you find surface area?
PR where P = ΟD
What does shear stress exert?
A force over an area
What gives a larger pressure gradient?
More friction
What is the pressure gradient equal to?
P1-P2/L
What is the definition for momentum conservation?
The rate of change in momentum over time inside a control volume is balanced by the change in momentum flux, and the sum of forces acting in the x-direction.
What is the partial derivative?
Itβs derivative concerning one of those variables, with the others, held constant
How is pressure drop related to velocity?
(f/D)(rhoU^2/2)
- f is the friction coefficient
What happens to momentum in 2D?
Changes in magnitude and direction
What is the Reynolds transport theorem?
The Reynolds transport theorem is used to transform from system to control volume for integral analysis
