Reynolds Number - Instrumentation Engineering
REYNOLDS NUMBER
Reynolds number is a ratio of the
inertial force to the viscous force in a fluid flow. Irish innovator Osborne Reynolds first
noticed this ratio. The Reynolds number is used to determine whether a fluid is
laminar or turbulent. It is dependent upon the viscosity of a fluid. So we can
determine the Reynolds number in some different cases.
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Osborne Reynolds |
CASE I: No Viscosity is Present
Flow profile moves parallel if there is no viscosity and there
will be no distortion in the flow profile. It will move straight, it means the
flow profile will be rectilinear.
FB = FI
– FV max
FC = FI
CASE II: Viscosity is Present
There is a viscous force, acting on the particle in the
opposite direction of the movement of the particle.
Here we get parabolic profile when its –
(i)
Viscosity
is low
(ii)
Absolute
viscosity is high
Parabolic profile is also known as Laminar flow profile.
CASE III: Viscosity is in between zero and Absolute viscosity (A.V) [0<viscosity<A.V]
When the velocity is high the viscosity will be low and vice
versa. Here these profile are called as Turbulent flow profile.
Here we get turbulent profile when its –
(i)
Velocity
is very high
(ii)
Viscosity
is very low
FORMULA
Reynolds number = Internal force / Viscous force
RN = FI / Fr
RN = (ρvD)/µ
Where, ρ = Density of the fluid
v = Average
velocity of the fluid
D = pipeline
diameter
µ = Absolute
viscosity
Reynolds number and Flow profile
If,
RN <
2000 = Flow profile is laminar
RN > 4000
= flow profile is turbulent
If, the Reynolds number of the fluid is between 2000 and
4000, the flow profile is a complex mixture of laminar flow and turbulent flow,
which is called Transition region.
In this state we can’t use any flow meter.
CONCLUSION
For industrial purpose RN is made above 10,000.
If we assume that the fluid has no viscous force ( Fr ),
then
Fr = 0
So, Reynolds number, RN = FI / Fr
So, RN =
infinite (∞)
Then it is known as Rectilinear flow profile.
It means, the turbulent flow profile is in between the
rectilinear and the laminar flow profile.
Read Also,
Specific Gravity of Fluid : http://www.theincredibletruths.com/2018/09/specific-gravity-industrial.html
Specific Gravity of Fluid : http://www.theincredibletruths.com/2018/09/specific-gravity-industrial.html
RTD Wiring : http://www.theincredibletruths.com/2018/08/rtd-wiring-color-code.html
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