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Fluid statics : fluid at rest
force/ pressure/ head
Fluid dynamics :
hydrodynamics/
aerodynamics
Motion transport (flow)
Fluid statics
• Pressure = normal force exerted by fluid
/ unit area
• Absolute, gauge, vacuum pressure
• Pressure measurement devices: U-tube
manometer, barometer
• Hydrostatic force, buoyant force
Fluid dynamics
Motion transport (flow)
Internal flow, velocity profile, pressure drop, friction loss
Bernoulli’s equation
https://www.accessengineeringlibrary.com/content/book/9780071422949/toc-chapter/chapter6/section/section2#/p200139d889206_6014
Classification of fluid flows
• Viscous flow region/ inviscid flow region
• Internal flow/ external flow
• Compressible /incompressible flow
• Laminar / turbulent flow
• Natural/forced flow
• Steady /unsteady flow
https://www.theengineerspost.com/types-of-fluid-flow/
TYPES OF FLUID FLOW AND REYNOLDS NUMBER
• Two types of fluid flow : laminar and turbulent flow.
– Laminar flow: flow at low velocities where the layers
of fluid seem to slide by one another without eddies
or swirls being present (viscous flow)
– Turbulent flow: flow at higher velocities where
eddies are present giving the fluid a fluctuating
nature
• The Reynolds number used to characterize the regimes
of flow.
• As the velocity was increased, laminar flow becomes
turbulent flow.
– The velocity at which the flow changes is known as
the critical velocity
TYPES OF FLUID FLOW AND REYNOLDS NUMBER
The experiments of Reynolds
https://theconstructor.org/practical-guide/hydraulics-lab/reynolds-experiment/2052/
https://www.aps.org/publications/apsnews/202003/history.cfm
TYPES OF FLUID FLOW AND REYNOLDS NUMBER
• Transition from laminar to turbulent in tubes is function of:
– velocity, density, viscosity of the fluid
– the tube diameter
• These variables are combined into the Reynolds number, which is
dimensionless:
– NRe is the Reynolds number
– D is the diameter in m
– is the fluid density in kg/m3
– is the fluid viscosity in Pas
– v is the average velocity of the fluid in m/s
• Units in the cgs system, D in cm, in g/cm3, in g/cms, v in cm/s.
• Units in the English system, D is in ft, in lbm/ft3, in lbm/fts, v in
ft/s.
DvN Re
TYPES OF FLUID FLOW AND REYNOLDS NUMBER
• For a straight circular pipe
– Reynolds number less than 2100 - the flow will be laminar.
– Reynolds number over 4000, the flow will be turbulent.
– In between, which is called the transition region, the flow can be
viscous or turbulent, depending upon the apparatus details.
ExampleWater at 303 K is flowing at the rate of 10 gal/min in a
pipe having an inside diameter (ID) of 2.067 in.
Calculate the Reynolds number using both English
units and SI units.
• Solution:
s/ft957.0ft 0233.0
1
s
ft0223.0 pipe,in velocity
ft 0233.04
)172.0(
4
D pipe of area sectional-cross
ft 172.012
2.067 D diameter, pipe
s/ft 0223.0s 60
min1
gal 7.481
ft 1
min
gal0.10rate flow
2
3
222
33
v
SolutionWater at 303 K (30°C),
density, = 0.996(62.43) lbm/ft3
viscosity, = (0.8007 cp)(6.719710-4 lbm/ftscp = 5.3810-4 lbm/fts
Finally,
Hence, the flow is turbulent
If using SI unit:
density, = 0.996(100) kg/m3 = 996 kg/m3
D = (2.067 in.)(1 ft/12 in.)(1 m/3.2808 ft) = 0.0525 m
v = (0.957 ft/s)(1 m/3.2808 ft) = 0.2917 m/s
= (0.8007 cp)(110-3 kg/mscp = 8.00710-4 kg/ms = 8.00710-4
Pas
4
m
4-
3
mRe 10905.1
s/ftlb105.38
)/ftlb 43.62996.0(ft/s) 957.0(ft) 172.0(
DvN
4
4-
3
Re 10905.1skg/m108.007
)kg/m 996(m/s) 2917.0(m) 0525.0(
DvN