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TOPIC 3.1 - Flow Measurement.pptx

  1. 1. Topic 3.1: Process Measuring Instruments Faculty of Chemical and Process Engineering Technology BVF2124 FIELD INSTRUMENTATION DEVICES & CONTROL
  2. 2. Elements of a Process Control System 4) Final Control Element 3) Controller 2) Measuring Element 1) Process
  3. 3. Process Instrumentation & Measurement • Flow Measurement • Level Measurement • Pressure measurement • Temperature measurement
  4. 4. Chapter 3.1: FLOW MEASUREMENT
  5. 5. OBJECTIVES After you study this sub-chapter, you should be able to: 1. Define flow measurement. 2. Describe the importance of flow measurement. 3. Explain the basic operation, list the advantages and disadvantages of each flow measurement device.
  6. 6. TOPIC COVERED • Fundamental of Flow Measurement • Flow Measuring Devices: 1. Differential Pressure Flowmeter - Orifice 2. Velocity-type Flowmeter -Turbine, Electromagnetic, Ultrasonic Flowmeters 3. Variable area Flowmeter - Rotameter • How to Choose the right Flowmeter?
  7. 7. Fundamental of Flow Measurement • What is flowrate? - Amount of material passing one point for certain time. • Give one simple method to measure water flowrate from tap water. • Flowmeters help to determine how much fluid is passing through
  8. 8. • Why flow is an important parameter? - Most process involves moving material from one part of the plant to another. • A fluid can be defined as any substance that can flow and thus the term applies both to liquids and gases. Fundamental of Flow Measurement
  9. 9. Why Custody Transfer • Measure material present in a tank • Billing purposes Monitor the process • Provide information about the process • Ensure that the process is operating satisfactorily Safety • Ensure that critical portions of the process operate safely • Over/under flow WHY MEASURE FLOW ?
  10. 10. FUNDAMENTAL OF FLOW MEASUREMENT Fluid type Viscosity Specific Gravity Density Flow Profile Reynold’s Number Mass per unit volume of a fluid Ratio of the density of a fluid to the density of a reference fluid Measure of fluid’s tendency to resist a shearing force or to resist flow Clean Fluid, Dirty Fluid, Slurry, Steam Characterizes the behavior of a fluid as it flows through a pipe (e.g: smooth or turbulent, symmetrical or asymmetrical) Ratio of the inertial force to the viscous force in the flow stream.
  11. 11. Clean Fluid Dirty Fluid Slurry Steam High viscosity Fluid Foam TYPE OF FLUID
  12. 12. TYPE OF FLOW MEASUREMENT Volumetric Flow Q = A V = ft = ft sec * * ² ft sec ³ where: Q = volumetric flow A = cross sectional area ( ft ) V = average fluid velocity ( ) ft sec ft sec ³ ²
  13. 13. TYPE OF FLOW MEASUREMENT Mass Flow where: m = mass flow ( )  = density ( ) Q = average fluid velocity ( ) A = cross sectional area ( ft ) V = average fluid velocity ( )  lbs sec ² ft sec ft sec m = Q  = A V  = ft =  * * * ² ft sec * * lbs ft³ lbs sec lbs ft³
  14. 14. CLASS OF FLOW MEASUREMENT Differential Pressure (DP) Flowmeter Velocity Flowmeter Mass Flowmeter Volumetric Flowmeter • Orifice plate • Venturi tube • Flow nozzle • Wedge • V-cone • Rotatometer • Pitot tube • Annubar • Magnetic Flowmeter • Vortex Flowmeter • Turbine Flowmeter • Ultrasonic Flowmeter • Coriolis Flowmeter • Thermal Flowmeter • Positive displacement flowmeter
  15. 15. FLOW MEASUREMENT USING Differential Pressure (DP) Transmitter Based on Bernoulli Principle - Velocity is increased after passing the obstruction while pressure is decreased. Primary element --> Placed in the process pipe to restrict the flow and create a differential pressure Measure the differential pressure (ΔP) caused by an obstruction in the flow stream Secondary element --> Measures the differential pressure and transmits the result to a control system
  16. 16. DP Flowmeter Venturi tube Orifice plate Flow nozzle Rotatometer V-cone Pitot tube FLOW MEASUREMENT USING Differential Pressure (DP) Transmitter
  17. 17. FLOW MEASUREMENT USING Differential Pressure (DP) Transmitter Venturi Orifice Nozzle V-cone l Rotatometer Pitot Tube
  18. 18. FLOW MEASUREMENT USING Differential Pressure (DP) Transmitter & Orifice Fluid velocity increases and pressure decreases as fluid passes through the orifice, which creates a pressure drop.
  19. 19. Orifice plate • An orifice plate is a thin disk diameter which is inserted in the pipe perpendicular to the flow stream. It acts as the primary element of a DP flowmeter. • Fluid velocity increases and pressure decreases as fluid passes through the orifice, which creates a pressure drop . • It is commonly used when the flow is continuous and occupies the entire pipe • Typical orifice meter has a concentric, eccentric and segmental
  20. 20. Figure 2: schematic diagram of orifice meter Figure 1: Orifice meter Video
  21. 21. Advantages Disadvantages • Recommended for clean and dirty liquids and some slurry services • Most commonly used flow sensor - inexpensive, easy to install, no moving part, simple configurations, required less maintenance. • Compatible with most pipe sizes • Accuracy are poor at low flowrates • Easily gets clogged due to impurities in gas or in unclear liquids Orifice plate
  22. 22. • Variable area flow meters operate at a constant differential pressure (ΔP) and the area changes with the flowrate. • The area will increase as the flowrate through the meter increases to preserve a constant ΔP. FLOW MEASUREMENT USING Variable area type flowmeter
  23. 23. • An industrial flowmeter used to measure the flowrate of liquids and gases. • The rotameter consists of a tube and float. • The direction of flow in the vertical conic tube is from the bottom to the top • Falling and rising action of float provides a measure of flowrate. • The upward flowing media lifts the float for as long as necessary to reach an equilibrium. Rotameter
  24. 24. TYPE OF MATERIALS • The two basic components of every rotameter are the tapered metering tube and float • Tapered tube may be made of :  Glass tubes (for accurate reading)  Metal tubes (for corrosive conditions)  Plastic tubes ( for low cost)
  25. 25. Advantages Disadvantages • All rotameters are low cost compared to other flow measurement devices • Reliability combines for an extremely low cost ownership. • Long last expectancy brings low life cycle cost. • Simple to install and maintain. • When opaque fluid is used, float may not be visible • It must be installed in vertical position only • Limited to low temperatures Rotameter
  26. 26. Typical units used to represent velocity are ft/s and m/s Velocity is the speed of a fluid flowing past a stationary point in a process pipe Producing an output based upon fluid velocity that is linear to the volumetric flow rate FLOW MEASUREMENT USING Velocity type flowmeter
  27. 27. In a vortex flowmeter an obstruction, or “bluff body,” is placed across the pipe bore perpendicular to the fluid flow. FLOW MEASUREMENT USING Velocity type flowmeter Vortex flowmeter
  28. 28. A slow moving putt barely displaces the molecules of air The higher velocity of a chip shot causes irregular eddies to form behind the ball The velocity associated with a drive is sufficient to cause a strong, regular vortex formation behind the ball The analogy of a golf ball moving through the air is useful in describing vortex formation: FLOW MEASUREMENT USING Vortex flowmeter Principle of operation
  29. 29. When a flowing medium strikes a non-streamlined bluff object, it separates, moves around the object and passes downstream. At the point of contact with the object, vortex swirls separate from the body on alternating sides. This separation causes a local increase in pressure and a decrease in velocity on one side and a decrease in pressure and an increase in velocity on the opposite side. FLOW MEASUREMENT USING Vortex flowmeter Principle of operation
  30. 30. FLOW MEASUREMENT MASS FLOWMETER The continuing need for more accurate flow measurements in mass-related processes (chemical reactions, heat transfer, etc.) has resulted in the development of mass flowmeter. Some of the most common mass flowmeter are: Coriolis flowmeter Thermal flowmeter
  31. 31. Thermal Flowmeter Coriolis Flowmeter FLOW MEASUREMENT MASS FLOWMETER
  32. 32. Electromagnetic Flowmeter • Use Faraday’s Law of electromagnetic induction to determine the flow of liquid in a pipe. • In this flowmeter, a magnetic field is generated by electric coils and channelled into the liquid flowing through the pipe. • Flow of a conductive liquid through the magnetic field will cause a voltage signal to be sensed by electrodes located on the flow tube walls. • When the fluid moves faster, more voltage is generated . • The developed voltage is linearly proportional to the volumetric flow rate • The electronic transmitter process the voltage signal to determine liquid flow. Video
  33. 33. Advantages Disadvantages • Can be used in hazardous environments or measure corrosive or slurry fluid flow • Low maintenance cost because of no moving parts • More accurate than differential pressure meter (orifice, venturi and flow nozzle) since this flow meter does not introduce any pressure drop • Material must be liquid that conduct electricity • Requires electrical conductivity of fluid higher than 3 µS/cm in most cases, (particle caused bias in reading). • Expensive Magnetic Flowmeter
  34. 34. Turbine Flowmeter • Turbine meters have a spinning rotor with blades that is mounted on bearings in a housing on the central longitudinal axis of the pipeline. • The rotor spins as water or other fluid passes over it. • Blade movement is often detected magnetically, where the movement of rotor generates a pulse • The pulse frequency is proportional to the velocity of the fluid. When the fluid moves faster, more pulses are generated • Speed of rotation of rotor proportional to the volumetric flow rate.
  35. 35. Advantages Disadvantages • Turbine meter excel at measuring steady, high-speed flows of liquid and gas. • Widely used in utility applications to measure the amount of water used in commercial and industrial buildings. • Have excellent accuracy • The size (diameter) same as the pipe in which they are fitted, and pressure loss is quite low. • limited to clean fluid, require maintenance at their bearing from time to time and expensive. • Not suitable for high viscosity fluids Turbine Flowmeter
  36. 36. Ultrasonic Flowmeter • Ultrasonic flowmeters can be categorized into two types based on the installation method: clamped-on and inline. • The clamped-on type is located outside of the pipe and there are no wetted parts. It can easily be installed on existing piping systems without worrying about corrosion problems. • Clamped-on designs also increase the portability of the flowmeter. • The inline type, on the other hand, requires fitting flanges or wafers for installation. However, it usually offers better accuracy and its calibration procedures are more straightforward.
  37. 37. • A pair of transducers is placed on the pipe wall, one on the upstream and the other on the downstream. • Flowrate is measured based on the time for the sound to travel between a transmitter and a receiver • The time for acoustic waves to travel from the upstream transducer to the downstream transducer, td is shorter than the time it requires for the same waves to travel from the downstream to the upstream, tu. transmitter receiver Ultrasonic Flowmeter
  38. 38. Advantages Disadvantages • No obstruction in the flow path • No pressure drop, no moving parts • Low maintenance cost • Can be used to measure corrosive or slurry fluid flow. • Higher initial cost • Measuring accuracy easy influenced by the installation and environment. Ultrasonic Flowmeter
  39. 39. How to choose the flowmeter? • The purpose of the measurement and the physical characteristics of the fluid being measured are the two main considerations.
  40. 40. Some specifics to consider are: • Type of the fluid being measured (air, water, gas, oil, etc.) • Fluid condition (clean, dirty, viscous, slurry, corrosive, conductive etc.) • Measurement device accuracy, turndown ratio (rangeability) and reliability • Total cost involve (equipment cost, total cost installation, maintenance cost, and operating cost)- cheap or expensive? • Type of construction materials (stainless steel, fiberglass, etc.) • Pressure loss (high, low, intermediate?)
  41. 41. Orifice plate Vortex Flowmeter Venturi meter Turbine flowmeter Electromagnetic flowmeter Flow Nozzle Time Transit Model Doppler Electromagnetic flowmeter