Fluid Mechanics Flashcards
Liquids are considered…
… incompressible
Gases are considered…
… compressible
Viscosity
a measure of resistance to flow
Dynamic (absolute) viscosity
ratio of shearing stress to rate of shearing strain
Newtonian fluids
rate of shearing strain is constant for a given temperature
The viscosity of most liquids decreases significantly with…
… increase in temperature
The viscosity of most gases increases mildly with…
… an increase in temperature
Fluid
a substance that will deform readily and continuously when subjected to shear force
Absolute pressure
measured from a vacuum
Gage pressure
uses atmospheric pressure as datum
Vacuum
negative gage pressure
In a capillary tube, a liquid will rise when…
… adhesive forces dominate
In a capillary tube, a liquid will fall when…
… cohesive forces dominate
The center of pressure is always…
… below the centroid except when the surface is horizontal
Buoyant force is equal to…
… the weight of the fluid displaced by the object
Inviscid
viscosity is assumed negligable
The sum of the hydraulic grade line and velocity head is the…
… energy grade line
Reynolds number (Re)
ratio of inertial forces to viscous forces in fluid flow
Moody diagrams are used to…
… determine the friction factor
Hazen-Williams equation
used to determine head loss in a system
For pipes in series…
… volumetric flow rates and head loss are equal
For pipes in parallel…
… total volumetric flow rate and head loss are additive
Pumps
add energy to liquid systems
Compressors
add energy to gases
Dynamic pump
energy is added by a set of blades (impellers, vanes) that are attached to a rotating shaft turned by a motor
Centrifugal pump
impeller attached to a rotating shaft with fixed housing
Pump efficiency
ratio of power gained by fluid to shaft power delivered to pump
Pumps in a parallel configuration have…
… equivalent head delivered, but total volumetric flow rate is calculated as the sum of the individual flow rate delivered by each pump
Cavitation
system pressure is less than or equal to the vapor pressure of the liquid, causing the liquid to form small bubbles of vapor which reduce pump efficiency
Impulse turbine
low-discharge, high-head devices in which high-speed jets of water impact bucket-shaped vanes to rotate turbine
Froude number (Fr)
ratio of inertial forces to gravitational forces
Critical flow occurs when…
… Fr = 1
Hydraulic jump
occurs when flow transitions from supercritical to subcritical flow (often seen under sluice gates)
Mannings equation
expresses stream velocity during uniform flow
Weirs are used to…
… determine flow rate in open channels
Darcy-Weisbach
Used to calculate head loss due to friction
