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Syafruddin Hasan

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SystemsSystemsConceptsConcepts

• Automated systems Automated systems that control flow rates that control flow rates or volume employ the or volume employ the following components:following components:– A SourceA Source– A PathA Path– A Control FunctionA Control Function– An ActuatorAn Actuator– A Measuring InstrumentA Measuring Instrument

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Reasons for ControlReasons for Control

• To ensure the correct proportions of raw materials To ensure the correct proportions of raw materials are combined during the manufacturing processare combined during the manufacturing process

• To ensure that ingredients are supplied at the To ensure that ingredients are supplied at the proper rate during the mixing and blending of the proper rate during the mixing and blending of the materialsmaterials

• To prevent a high flow rate than might cause To prevent a high flow rate than might cause pressure or temperatures to become dangerous, pressure or temperatures to become dangerous, overspills to occur, or machines to overspeedoverspills to occur, or machines to overspeed

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Flow Units of Flow Units of MeasurementMeasurement

• Common classifications used to Common classifications used to determine flow instruments are:determine flow instruments are:– Volumetric flow rate - in cubic feet, gallons, Volumetric flow rate - in cubic feet, gallons,

or liters per unit of time (this is an or liters per unit of time (this is an inferredinferred measurement)measurement)

– Mass flow rate - pounds, tons, grams, or Mass flow rate - pounds, tons, grams, or kilograms per unit of timekilograms per unit of time

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Solid Flow MeasurementSolid Flow Measurement• Solid materials that are measured for mass flow rate are Solid materials that are measured for mass flow rate are

typically small particles, powder, pellets, or crushed typically small particles, powder, pellets, or crushed materialsmaterials

• Conveyors are usually used to transport these materialsConveyors are usually used to transport these materials

• Mass flow rate calculation:Mass flow rate calculation:

F =WS

L

F = Mass flow rate in lb/min

W = Weight of a material on a section of length

S = Conveyor speed in ft/min

L = Length of weighing platform

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Solid Flow MeasurementSolid Flow Measurement

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Fluid Flow MeasurementFluid Flow Measurement

• Important terms:Important terms:– Velocity - speed at which a fluid Velocity - speed at which a fluid

moves through a pipemoves through a pipe– Density - weight per unit volumeDensity - weight per unit volume– Viscosity - Ease of flow of a fluidViscosity - Ease of flow of a fluid– Pipe size - Diameter of the pipe Pipe size - Diameter of the pipe

carrying the fluidcarrying the fluid

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Reynolds’ NumberReynolds’ Number

• A numerical scheme that A numerical scheme that represents the four preceding represents the four preceding factors on fluid flow (R number)factors on fluid flow (R number)

R =VDp

u

V = Velocity

R = Reynolds’ Number

D = Pipe inside diameter

p = Fluid density

u = Liquid viscosity

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Application of Reynolds’ Application of Reynolds’ NumberNumber• The R-number is used to identify the type of The R-number is used to identify the type of

flow likely to occur in a process: flow likely to occur in a process: laminar laminar flow,flow, turbulent turbulent flow, orflow, or transition transition flowflow

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Fluid Flowmeter Fluid Flowmeter ClassificationClassification• One method of classifying One method of classifying

flowmeters is to divide them into flowmeters is to divide them into the following categories:the following categories:– Differential PressureDifferential Pressure– Positive DisplacementPositive Displacement– VelocityVelocity– Direct Reading MassDirect Reading Mass

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Differential Pressure Differential Pressure FlowmeterFlowmeter

• Most common type of flowmeterMost common type of flowmeter

• A restriction called an A restriction called an orifice orifice is placed on is placed on the flowthe flow

• An orifice plate has a specified size hole An orifice plate has a specified size hole bored through it, through which the liquid bored through it, through which the liquid must flowmust flow

• Using Bernoulli’s Principle, the differential Using Bernoulli’s Principle, the differential pressure is measured across the restriction pressure is measured across the restriction and flow rates may be calculatedand flow rates may be calculated

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Flow Restrictor TypesFlow Restrictor Types

• Conventional orifice plate

• Flow nozzle restrictor

• Venturi tube restrictor

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RotameterRotameter

• Also known as a Also known as a variable area variable area flowmeterflowmeter

• The float, when no The float, when no flow is present, flow is present, settles at a location settles at a location in the tube with the in the tube with the same diameter as same diameter as has the tubehas the tube

• As flow increases, As flow increases, the float raises to a the float raises to a higher level in the higher level in the tubetube

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Positive Displacement Positive Displacement MethodsMethods

• Rotary instruments that mechanically Rotary instruments that mechanically make direct measurements to the make direct measurements to the fluid by separating the fluid into fluid by separating the fluid into segments of known valuessegments of known values

• Two types of PD flowmeters are Two types of PD flowmeters are rotary-vane rotary-vane and and lobed impellerlobed impeller

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PD PD FlowmetersFlowmeters

Rotary-vane Flowmeter Lobed impeller flowmeter

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Velocity Velocity MetersMeters

• Velocity meters measure the velocity of fluids directlyVelocity meters measure the velocity of fluids directly

• The most common type of velocity meter is the The most common type of velocity meter is the turbine turbine flowmeterflowmeter

• Essentially, the turbine flowmeter is a flow-powered generatorEssentially, the turbine flowmeter is a flow-powered generator

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Electronic Electronic SensorsSensors• Several electronic flowmeters are Several electronic flowmeters are

available at this time:available at this time:– The coriolis meterThe coriolis meter– The rotor flow detectorThe rotor flow detector– The electromagnetic flow detectorThe electromagnetic flow detector– The thermal flowmeterThe thermal flowmeter– The vortex flowmeter The vortex flowmeter – The ultrasonic flowmeterThe ultrasonic flowmeter– The time-of-flight meterThe time-of-flight meter

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Coriolis Coriolis MetersMeters• Built around a U-shaped tube that liquid flows throughBuilt around a U-shaped tube that liquid flows through

• The tube is caused to vibrate by induction of fluctuating currentsThe tube is caused to vibrate by induction of fluctuating currents• Flow through the tube causes it to twist proportionally to the flow. Flow through the tube causes it to twist proportionally to the flow.

The distortion of the tube is detected by magnetic sensors and the The distortion of the tube is detected by magnetic sensors and the resultant signal is conditioned and sent to control equipmentresultant signal is conditioned and sent to control equipment

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Electromagnetic Electromagnetic Flow DetectorsFlow Detectors

• Electromagnetic flow Electromagnetic flow detector is a transducer detector is a transducer that converts the flow rate that converts the flow rate of a conductive substance of a conductive substance into a voltageinto a voltage

• Based upon Faraday’s law Based upon Faraday’s law of inductionof induction

• Used for difficult and Used for difficult and corrosive liquids and corrosive liquids and slurriesslurries

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Thermal Thermal FlowmetersFlowmeters• Thermal flowmeters use a thermistor Thermal flowmeters use a thermistor

inserted into the flow streaminserted into the flow stream

• Liquid in the flow stream carries Liquid in the flow stream carries away heat from the thermistor, away heat from the thermistor, thereby raising its resistance, which thereby raising its resistance, which unbalances a bridge circuitunbalances a bridge circuit

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Vortex FlowmeterVortex Flowmeter

• A blunt object is placed A blunt object is placed in the flow path of the in the flow path of the liquid, and as liquid is liquid, and as liquid is forced around the forced around the object, vortices are object, vortices are formedformed

• The number of vortices The number of vortices formed downstream is formed downstream is directly proportional to directly proportional to the flow rate; the the flow rate; the vortices cause a change vortices cause a change in the pressure at the in the pressure at the vortices’ location, which vortices’ location, which is then measuredis then measured

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Ultrasonic Ultrasonic FlowmetersFlowmeters

• Using the Using the Doppler EffectDoppler Effect, ultrasonic , ultrasonic flowmeters measure flow by analyzing the flowmeters measure flow by analyzing the frequency shift of induced sound waves in frequency shift of induced sound waves in a flow process. The frequency shift is a flow process. The frequency shift is directly proportional to the flow rate of the directly proportional to the flow rate of the liquidliquid

• This method is only used on liquids that This method is only used on liquids that have particles present, not for clear liquidshave particles present, not for clear liquids

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Time-of-Flight FlowmeterTime-of-Flight Flowmeter

• For clear liquid flow measurements For clear liquid flow measurements using ultrasonic principles, the time-of-using ultrasonic principles, the time-of-flight flowmeter is usedflight flowmeter is used

• It is based upon the principle that the It is based upon the principle that the speed of sound transmitted in the speed of sound transmitted in the direction of flow will increase, and direction of flow will increase, and decrease if transmitted against the flowdecrease if transmitted against the flow

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Selecting a FlowmeterSelecting a Flowmeter

• Is the fluid a gas or a Is the fluid a gas or a liquid?liquid?

• Is the fluid corrosive?Is the fluid corrosive?

• Is the fluid conductive Is the fluid conductive or not?or not?

• Does the fluid contain Does the fluid contain a slurry or large solids?a slurry or large solids?

• What is the viscosity What is the viscosity of the fluid?of the fluid?

• Will the fluid density Will the fluid density or viscosity change?or viscosity change?

• Is there a need for a Is there a need for a noninvasive noninvasive approach?approach?

• What is the cost?What is the cost?

When selecting a flowmeter, the following issues need to be considered: