Upload
baldwin-robertson
View
218
Download
1
Embed Size (px)
Citation preview
Mechanics of Fluids
I.GNANASEELANlecturer,
department of mechanical Engineering, Parisutham institute of technology and science
Mechanics of Fluids
SEQUENCE OF CHAPTER 1 IntroductionObjectiveHistoryDefinition of a fluidDimension and unitsFluid propertiesContinuum Concept of system and control
volume
Introduction• Defined: the science that deals with the forces on fluids and
their actions.• Fluids: a substance consisting of particles that change their
position relative to each other.• A substance that will continuously deform when shear stress
is applied to it.• Solids resist stress, do not easily deform.
Objectives
Identify the units for the basic quantities of time, length, force and mass.
Properly set up equations to ensure consistency of units.
Define the basic fluid properties.
Identify the relationships between specific weight, specific gravity and density, and solve problems using their relationships.
History
Fluid Mechanics 5
Faces of Fluid Mechanics
Archimedes(C. 287-212
BC)
Newton(1642-1727)
Leibniz(1646-1716)
Euler(1707-1783)
Navier(1785-1836)
Stokes(1819-1903)
Reynolds(1842-1912)
Prandtl(1875-1953)
Bernoulli(1667-1748)
Taylor(1886-1975)
Fluid Mechanics
• Definition– The study of liquids and gases at rest (statics) and in
motion (dynamics)
• Engineering applications– Blood in capillaries– Oil in pipelines– Groundwater movement– Runoff in parking lots– Pumps, filters, rivers, etc.
States of Matter
• Fluids (gasses and liquids) and solids• What’s the difference?– Fluid particles are free to move among themselves
and give way (flow) under the slightest tangential (shear) force
FluidSolid
Shear Stress
Classes of Fluids
– Liquids: Close packed, strong cohesive forces, retains volume, has free surface
• Liquids and gasses – What’s the difference?
Liquid
Free Surface
Gas
Expands
– Gasses: Widely spaced, weak cohesive forces, free to expand
Common Fluids
• Liquids:– water, oil, mercury, gasoline, alcohol
• Gasses: – air, helium, hydrogen, steam
• Borderline: – jelly, asphalt, lead, toothpaste, paint, pitch
Dimensions and Units
• The dimensions have to be the same for each term in an equation
• Dimensions of mechanics are– length– time– mass– force– temperature
aF m aF m
L
T
M
MLT-2
Dimensions and Units
Quantity SymbolDimensionsVelocity V LT-1
Acceleration a LT-2
Area A L2
Volume L3
Discharge Q L3T-1
Pressure p ML-1T-2
Gravity g LT-2
Temperature T’ Mass concentration C ML-3
Dimensions and Units
Quantity Symbol DimensionsDensity ML-3
Specific Weight ML-2T-2
Dynamic viscosity ML-1T-1
Kinematic viscosity L2T-1
Surface tension MT-2
Bulk mod of elasticity E ML-1T-2
These are _______ properties!fluidHow many independent properties? _____ 4
Fluid Properties
• Density: Mass per unit volume– How large is the volume?• Too small: # molecules changes continuously• Large: # molecules remains almost constant
– At these scales, fluid properties (e.g., density) can be thought of as varying continuously in space.
V
m
VV
*lim
Density
• Mass per unit volume (e.g., @ 20 oC, 1 atm)– Water water = 1000 kg/m3
– Mercury Hg = 13,500 kg/m3
– Air air = 1.22 kg/m3
• Densities of gasses increase with pressure• Densities of liquids are nearly constant
(incompressible) for constant temperature• Specific volume = 1/density
Specific Weight
• Weight per unit volume (e.g., @ 20 oC, 1 atm)
water = (998 kg/m3)(9.807 m2/s)
= 9790 N/m3
[= 62.4 lbf/ft3]air = (1.205 kg/m3)(9.807 m2/s)
= 11.8 N/m3
[= 0.0752 lbf/ft3]
]/[]/[ 33 ftlbformNg
Specific Gravity
• Ratio of fluid density to density at STP(e.g., @ 20 oC, 1 atm)
3/9790 mkgSG
liquid
water
liquidliquid
– Water SGwater = 1– Mercury SGHg = 13.6– Air SGair = 1
3/205.1 mkgSG
gas
air
gasgas
Ideal Gas Law
• Equation of state
TnRpV n MRRRTp n /,
Rn = universal gas constant
M = molecular weight of the gas