Transcript CL-232 Lab - Chemical Engineering, IIT Bombay

CL-232 Lab
Experiment FM-202 : Nature of Flow
Staff
TA’S
Mr. Amit Shinde
Munish Kumar Sharma
Mr. B.G. Parab
Laxman R. Bhosale
Objectives
• To visually observe laminar and turbulent flow patterns
• To determine the upper and lower critical Reynolds number
• Experimentally determine the friction factor and compare
with model prediction
Schematic diagram
Theory
• Fluid flow in a pipe may be laminar or turbulent depending
upon the conditions of flow.
• At low fluid velocities, the fluid moves without lateral mixing
and without any eddies formation. The streamlines remain
distinct from one another over the entire length (Laminar
flow).
• At high fluid velocities, eddies form in the fluid under motion
causing lateral mixing and formation of eddies. The flow is
chaotic (Turbulent flow).
Reynolds no.
• Reynolds no. is used to characterize the flow:
NRe = D v ρ/ μ
Where
D = dia of the pipe;
v = avg. velocity of fluid;
μ = dynamic viscosity
For a pipe flow:
NRe < 2100
2100 < NRe < 4000
NRe > 4000
(Laminar regime)
(Transition regime)
(Turbulent regime)
• NRe, upper critical:
flow behavior change Laminar to Turbulent
NRe, lower critical:
flow behavior change Turbulent to Laminar
Friction factor
• Friction factor (f) is defined as the ratio of wall shear stress
to the product of the density and velocity head. It is given by
the following relation:
f =
ΔP gc D/ 2 L ρ V2
Where
ΔP = pressure drop across pipe; L = length of pipe;
D = dia of pipe; V = average velocity of fluid; ρ = fluid density
Model (Theoretical) predictions of friction factor:
f = 16/ NRe
f = 0.046 NRe-0.2
f = 0.0014 + (0.125 / NRe0.32)
(Laminar flow)
( 50000 < NRe < 106)
(3000 < NRe < 3×106)
Observations
• Measure h1 (pressure head in Tank-1) and h2 (pressure head in
Tank-2) for laminar flow.
• Start increasing the flow rate through discharge valve and take h1
and h2 again and measure the flow rate.
• Take atleast 10 such readings and one extra reading at maximum
flow rate.
• Now start decreasing the flow and repeat the above step again. The
flow will shift from turbulent to laminar once again.
• Calculate the Reynolds no. for every reading and characterize the
flow.
• Report NRe,
upper critical
and NRe,
lower critical
values.
• Calculate the friction factor experimentally and compare it with the
model predictions on a log-log plot.