Flow Measurements • Identify an effect that depends on flowrate – Mixing of two streams – Feed rate into a combustion chamber – Heat exchangers – Velocity • Flowmeters – Size – Accuracy – Media – Cost – Pressure drop – Pressure losses
Dec 23, 2015
Flow Measurements• Identify an effect that depends on flowrate
– Mixing of two streams– Feed rate into a combustion chamber– Heat exchangers– Velocity
• Flowmeters– Size– Accuracy– Media– Cost– Pressure drop– Pressure losses
Magnetic Flowmeter
Faraday’s Law
Conductive fluid moving through a magnetic field induces a voltage.
• Non-streamlined object placed in the middle of a flow stream
• Vortices are shed alternately downstream of the object.
• Frequency of the vortex shedding is directly proportional to the velocity of the liquid flowing in the pipeline.
• Ultrasonic, electric, or fiber optic transducers
Vortex Shedding
Flow through a Nozzle
1
1
1
1
v
A
m
2
2
2
2
v
A
m
a.) Continuity
mass in = mass out
b.) Bernoulli’s equation
Total pressure is constant throughout
If incompressible fluid (like water):
P2
A
A1
1YCAQ
FlowalReFor
IdealP2
A
A1
1AvAQ
RateFlow
P2
A
A1
1v
2
1
2
2
2
1
2
222
2
1
2
2
Flow through a Nozzle
Y = Compressibility Factor
=1 for incompressible flow or when DP<< Pabs
C= Discharge Coefficient
=f(Re) and
nature of specific flow meter
Flow Types – Reynolds Number
• Reynolds number is a ratio of inertial to viscous flows
• Re < 2000 – Laminar Flow• Re > 4000 – Turbulent Flow