1 Syafruddin Hasan

2 Systems Concepts Automated systems that control flow rates or volume employ the following components: Automated systems that control flow rates or volume employ the following components: –A Source –A Path –A Control Function –An Actuator –A Measuring Instrument

3 Reasons for Control To ensure the correct proportions of raw materials are combined during the manufacturing process To ensure the correct proportions of raw materials are combined during the manufacturing process To ensure that ingredients are supplied at the proper rate during the mixing and blending of the materials To ensure that ingredients are supplied at the proper rate during the mixing and blending of the materials To prevent a high flow rate than might cause pressure or temperatures to become dangerous, overspills to occur, or machines to overspeed To prevent a high flow rate than might cause pressure or temperatures to become dangerous, overspills to occur, or machines to overspeed

4 Flow Units of Measurement Common classifications used to determine flow instruments are: Common classifications used to determine flow instruments are: –Volumetric flow rate - in cubic feet, gallons, or liters per unit of time (this is an inferred measurement) –Mass flow rate - pounds, tons, grams, or kilograms per unit of time

5 Solid Flow Measurement Solid materials that are measured for mass flow rate are typically small particles, powder, pellets, or crushed materials Solid materials that are measured for mass flow rate are typically small particles, powder, pellets, or crushed materials Conveyors are usually used to transport these materials Conveyors are usually used to transport these materials Mass flow rate calculation: Mass flow rate calculation: 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

6 Solid Flow Measurement

7 Fluid Flow Measurement Important terms: Important terms: –Velocity - speed at which a fluid moves through a pipe –Density - weight per unit volume –Viscosity - Ease of flow of a fluid –Pipe size - Diameter of the pipe carrying the fluid

8 Reynolds’ Number A numerical scheme that represents the four preceding factors on fluid flow (R number) A numerical scheme that represents the four preceding factors on fluid flow (R number) V = Velocity R = Reynolds’ Number D = Pipe inside diameter p = Fluid density u = Liquid viscosity

9 Application of Reynolds’ Number The R-number is used to identify the type of flow likely to occur in a process: laminar flow, turbulent flow, or transition flow The R-number is used to identify the type of flow likely to occur in a process: laminar flow, turbulent flow, or transition flow

10 Fluid Flowmeter Classification One method of classifying flowmeters is to divide them into the following categories: One method of classifying flowmeters is to divide them into the following categories: –Differential Pressure –Positive Displacement –Velocity –Direct Reading Mass

11 Differential Pressure Flowmeter Most common type of flowmeter Most common type of flowmeter A restriction called an orifice is placed on the flow A restriction called an orifice is placed on the flow An orifice plate has a specified size hole bored through it, through which the liquid must flow An orifice plate has a specified size hole bored through it, through which the liquid must flow Using Bernoulli’s Principle, the differential pressure is measured across the restriction and flow rates may be calculated Using Bernoulli’s Principle, the differential pressure is measured across the restriction and flow rates may be calculated

12 Flow Restrictor Types Conventional orifice plate Flow nozzle restrictor Venturi tube restrictor

13 Rotameter Also known as a variable area flowmeter Also known as a variable area flowmeter The float, when no flow is present, settles at a location in the tube with the same diameter as has the tube The float, when no flow is present, settles at a location in the tube with the same diameter as has the tube As flow increases, the float raises to a higher level in the tube As flow increases, the float raises to a higher level in the tube

14 Positive Displacement Methods Rotary instruments that mechanically make direct measurements to the fluid by separating the fluid into segments of known values Rotary instruments that mechanically make direct measurements to the fluid by separating the fluid into segments of known values Two types of PD flowmeters are rotary-vane and lobed impeller Two types of PD flowmeters are rotary-vane and lobed impeller

15 PD Flowmeters Rotary-vane Flowmeter Lobed impeller flowmeter

16 Velocity Meters Velocity meters measure the velocity of fluids directly Velocity meters measure the velocity of fluids directly The most common type of velocity meter is the turbine flowmeter The most common type of velocity meter is the turbine flowmeter Essentially, the turbine flowmeter is a flow-powered generator Essentially, the turbine flowmeter is a flow-powered generator

17 Electronic Sensors Several electronic flowmeters are available at this time: Several electronic flowmeters are available at this time: –The coriolis meter –The rotor flow detector –The electromagnetic flow detector –The thermal flowmeter –The vortex flowmeter –The ultrasonic flowmeter –The time-of-flight meter

18 Built around a U-shaped tube that liquid flows through Built around a U-shaped tube that liquid flows through The tube is caused to vibrate by induction of fluctuating currents The tube is caused to vibrate by induction of fluctuating currents Flow through the tube causes it to twist proportionally to the flow. The distortion of the tube is detected by magnetic sensors and the resultant signal is conditioned and sent to control equipment Flow through the tube causes it to twist proportionally to the flow. The distortion of the tube is detected by magnetic sensors and the resultant signal is conditioned and sent to control equipment

19 Electromagnetic Flow Detectors Electromagnetic flow detector is a transducer that converts the flow rate of a conductive substance into a voltage Electromagnetic flow detector is a transducer that converts the flow rate of a conductive substance into a voltage Based upon Faraday’s law of induction Based upon Faraday’s law of induction Used for difficult and corrosive liquids and slurries Used for difficult and corrosive liquids and slurries

20 Thermal Flowmeters Liquid in the flow stream carries away heat from the thermistor, thereby raising its resistance, which unbalances a bridge circuit Liquid in the flow stream carries away heat from the thermistor, thereby raising its resistance, which unbalances a bridge circuit Thermal flowmeters use a thermistor inserted into the flow stream Thermal flowmeters use a thermistor inserted into the flow stream

21 Figure Thermal flowmeter

22 A blunt object is placed in the flow path of the liquid, and as liquid is forced around the object, vortices are formed A blunt object is placed in the flow path of the liquid, and as liquid is forced around the object, vortices are formed The number of vortices formed downstream is directly proportional to the flow rate; the vortices cause a change in the pressure at the vortices’ location, which is then measured The number of vortices formed downstream is directly proportional to the flow rate; the vortices cause a change in the pressure at the vortices’ location, which is then measured

23 Ultrasonic Flowmeters Using the Doppler Effect, ultrasonic flowmeters measure flow by analyzing the frequency shift of induced sound waves in a flow process. The frequency shift is directly proportional to the flow rate of the liquid Using the Doppler Effect, ultrasonic flowmeters measure flow by analyzing the frequency shift of induced sound waves in a flow process. The frequency shift is directly proportional to the flow rate of the liquid This method is only used on liquids that have particles present, not for clear liquids This method is only used on liquids that have particles present, not for clear liquids

24 The Doppler ultrasonic flowmeter

25 Time-of-Flight Flowmeter For clear liquid flow measurements using ultrasonic principles, the time-of-flight flowmeter is used For clear liquid flow measurements using ultrasonic principles, the time-of-flight flowmeter is used It is based upon the principle that the speed of sound transmitted in the direction of flow will increase, and decrease if transmitted against the flow It is based upon the principle that the speed of sound transmitted in the direction of flow will increase, and decrease if transmitted against the flow

26 Time-of-Flight flowmeter

27 Is the fluid a gas or a liquid? Is the fluid a gas or a liquid? Is the fluid corrosive? Is the fluid corrosive? Is the fluid conductive or not? Is the fluid conductive or not? Does the fluid contain a slurry or large solids? Does the fluid contain a slurry or large solids? What is the viscosity of the fluid? What is the viscosity of the fluid? Will the fluid density or viscosity change? Will the fluid density or viscosity change? Is there a need for a noninvasive approach? Is there a need for a noninvasive approach? What is the cost? What is the cost? When selecting a flowmeter, the following issues need to be considered: