Lecture 25 Flashcards
What is viscosity?
The resistance of a fluid to flow or an applied force
What causes viscosity?
The intermolecular friction within a fluid
How does viscosity differ from pressure?
They are both measurements of force over area, however viscosity applies internal stresses in the perpendicular and parallel planes whereas pressure only occurs stress in the parallel direction
What is the expression of applied stress?
Strain
What is dynamic viscosity?
Applied stress divided by the rate of applied stress
How does deformation work in dynamic viscosity?
The rate of deformation is proportional to the rate of applied stress
What is the difference between dynamic and kinematic viscosity?
Absolute viscosity is a measure of a fluids resistance to flow
Kinematic viscosity is a ration between the viscous and inertial forces
What does viscosity determine?(four factors)
Fluid movement speed
Levels of mixing and exchange within the fluid
The forces that the fluid applies
How well the fluids transport material
What does Reynolds number determine?
Reynolds number determines whether the flow is laminar or turbulent
What is the equation for Reynolds number?
Re= Ud/v
Where u= speed of fluid
D=size of fluid
=kinetic viscosity
What causes viscosity in laminar flows?
Molecular molecular diffusion
What causes viscosity in turbulent flows?
Eddie’s
Which flow is more efficient at spreading, moving and dispersing material?
Turbulent flows
What is an eddy flow?
An eddy flow is simply a flow within the main flow that differed from the flow direction of the main one
What is a interstitial fluid?
The fluid that occupies the space between particles in a fluid dominated flow
What are the three ways of particle motion?
Bedload transport
Suspended load transport
Saltation load transport
Explain lift force in suspension flows?
The shape of oval particles force fluids to flow downwards and move around them. The fluid exerts an equal and opposite force to the one that diverts it, and thus force lifts the particle in suspension (it’s the lift force). The speed difference between the top and bottom fluid (around the particle) also contributes to lifting
Why do particles not remain in suspension in saltation flows?
The lift force raises particles, but the shear stresses are too great to keep particles in suspension. The weight of the particle vs the energy of fluid mechanism also plays a part
What is suspension dependant on in particle transport?
The buoyancy of the particle and the viscosity of the fluid
What is stokes law?
Fall speed= 1/18 x (solid density -fluid density)/ viscosity
X gravity x cross sectional area
What else determines suspension besides buoyancy?
Momentum
Describe the process of lofting in volcanic eruptions
Heavier particles interrupting fluids fall out of suspension, and the volcanic cloud condenses, becoming less dense than surrounding air. This causes it it re- rise
