Flow measurementFlow measurement

Flow measurementFlow measurement

Important variable in plant operationImportant variable in plant operation Measured primarily for determining Measured primarily for determining

the amount of fluid flowing the amount of fluid flowing

Fluid typesFluid types

Less or highly viscousLess or highly viscous Clear or opaqueClear or opaque Clean or dirtyClean or dirty Wet or dryWet or dry Erosive or corrosiveErosive or corrosive

Fluid flow typeFluid flow type

Stream line or viscous or laminarStream line or viscous or laminar TurbulentTurbulent Combined viscous or turbulentCombined viscous or turbulent

Fluid flow – steam lineFluid flow – steam line

Occurs at low velocitiesOccurs at low velocities All parts flowing in one direction All parts flowing in one direction

parallel to walls parallel to walls Change in cross section means Change in cross section means

change in direction of flowchange in direction of flow Pressure drop Pressure drop ∞∞ flow velocity flow velocity

Fluid flow - turbulentFluid flow - turbulent

Liquid behaves as independent Liquid behaves as independent entitiesentities

Pressure varies with Kinetic energyPressure varies with Kinetic energy Prop. To square of turbulent flow Prop. To square of turbulent flow

velocityvelocity

Flow meterFlow meter

Flow measured as a quantity or rate Flow measured as a quantity or rate of flowof flow

In terms of weight or flowIn terms of weight or flow

Types of flow metersTypes of flow meters

Head type metersHead type meters Rota meter (variable –area type)Rota meter (variable –area type) Electromagnetic typeElectromagnetic type Mechanical typeMechanical type AnemometerAnemometer Ultrasonic flow meterUltrasonic flow meter Vortex flow meterVortex flow meter

Head type flowmeterHead type flowmeter

Produce a pressure difference when Produce a pressure difference when fluid flow is maintained through themfluid flow is maintained through them

Diff. Pressure propotional to square Diff. Pressure propotional to square of flow rateof flow rate

Uses Bernoulli’s theoremUses Bernoulli’s theorem

Bernoulli's theormBernoulli's theorm

Bernoulli’s theormBernoulli’s theorm

Pressure head + velocity head + Pressure head + velocity head + elevation head (at a point) = elevation head (at a point) =

pressure head + velocity head + pressure head + velocity head + elevation head ( at some other point) elevation head ( at some other point) + loss due to friction+ loss due to friction

Bernoulli’s theormBernoulli’s theorm

For in compressible liquidFor in compressible liquid

Q = EAQ = EA22 sqrt ( (2gP sqrt ( (2gPdd)/ )/ ρρ))

For compressible liquidFor compressible liquid

Q = EAQ = EA2 2 φφ sqrt ( (2gP sqrt ( (2gPdd)/ )/ ρρ11))

Head flow meter -typesHead flow meter -types

Orifice meterOrifice meter VenturimeterVenturimeter Flow nozzleFlow nozzle Pitot tubePitot tube

Orifice metersOrifice meters

Orifice metersOrifice meters

Head type meter used for large Head type meter used for large &medium pipes&medium pipes

Orifice plate- inserted to pipe to Orifice plate- inserted to pipe to create a partial restriction to flowcreate a partial restriction to flow

Pressure before orifice plate rises Pressure before orifice plate rises and pressure after it reduces but and pressure after it reduces but velocity increasesvelocity increases

Pressure differncesPressure differnces

Position where velocity is maximum Position where velocity is maximum & static pressure is min is known as & static pressure is min is known as vena contractavena contracta

Diff. Pressure calculationDiff. Pressure calculation

Orifice meterOrifice meter

Usually pressure tapping is at a Usually pressure tapping is at a distance D & D/2 for up stream & distance D & D/2 for up stream & down streamdown stream

D- diameter of pipeD- diameter of pipe For pipe size 0.05m or moreFor pipe size 0.05m or more Orifice to pipe diameter is 0.6Orifice to pipe diameter is 0.6

Friction & contraction effects are Friction & contraction effects are considered. So new term is considered. So new term is incorporated called discharge co-incorporated called discharge co-efficient ©efficient ©

C varies with Reynolds's no.C varies with Reynolds's no.

Q = 2.35 X 10 Q = 2.35 X 10 -3-3 c d c d22 E E √√ (P (Pdd / /ρρ))

Flow measurementFlow measurement

ConstructionConstruction

Normal thickness -0.015 m for pipe Normal thickness -0.015 m for pipe with diameter 0.15 m & 0.003 for with diameter 0.15 m & 0.003 for largerlarger

Materials used bronze, stainless Materials used bronze, stainless steel, phosphor bronze, gun metal steel, phosphor bronze, gun metal etc.etc.

Orifice plate & flangesOrifice plate & flanges

Types of orifice platesTypes of orifice plates

Types of orifice plateTypes of orifice plate

If fluid contains suspended If fluid contains suspended materials , particles tend to settle materials , particles tend to settle down in orifice,- to avoid this- down in orifice,- to avoid this- segmented or ccentric type usedsegmented or ccentric type used

AdvantageAdvantage

Simple, reliableSimple, reliable

DisadvantageDisadvantage

Poor accuracy, Poor accuracy, poor calibrationpoor calibration maintenance problemsmaintenance problems

Venturi meterVenturi meter

Three sections- venturimeterThree sections- venturimeter

Converging conical section at up Converging conical section at up streamstream

Cylindrical throat- provides a panel Cylindrical throat- provides a panel for measurement- pressure for measurement- pressure decreased- flow rate steadydecreased- flow rate steady

Diverging recovery outletDiverging recovery outlet

Principle- Bernoulli's theormPrinciple- Bernoulli's theorm

dimensionsdimensions

Throat to diameter ratio 0.25 to 0.75Throat to diameter ratio 0.25 to 0.75 Discharge co-efficient – 0.9 to 1.0Discharge co-efficient – 0.9 to 1.0 Made of cast iron, gun metal, Made of cast iron, gun metal,

stainless steelstainless steel May be circular, square or May be circular, square or

rectangularrectangular

featuresfeatures

Calculation similar to orifice plateCalculation similar to orifice plate Better than orifice meterBetter than orifice meter

Flow nozzleFlow nozzle

Flow nozzleFlow nozzle

Flow nozzleFlow nozzle

Principle- Bernoulli’s theoremPrinciple- Bernoulli’s theorem SimpleSimple Used in higher velocities, difficult to Used in higher velocities, difficult to

maintain, costlymaintain, costly Used in gasesUsed in gases

Pitot tubePitot tube

Pitot tubePitot tube

Cylindrical probe inserted into fluidCylindrical probe inserted into fluid Velocity head converted into impact Velocity head converted into impact

pressurepressure Diff b/w static pressure & impact Diff b/w static pressure & impact

pressure- proptional to flow pressure- proptional to flow

By introduction of pitot tubeBy introduction of pitot tube

Pitot tubePitot tube

FeaturesFeatures

Easy to installEasy to install No pressure lossNo pressure loss Sensitive to up stream disturbanceSensitive to up stream disturbance Not used for sticky and dirty fluidsNot used for sticky and dirty fluids

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