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Principles and Practice of Flow Meter Engineering L K Spink: Everything You Need to Know about Flow Measurement and Calibration


Principles and Practice of Flow Meter Engineering by L.K. Spink




Introduction




Flow meter engineering is the science and art of measuring the rate or quantity of fluid flowing through a pipe or a channel. It is a vital aspect of many industrial processes, such as oil and gas production, water supply and treatment, chemical manufacturing, power generation, food processing, etc. Flow meters are devices that measure the flow of fluids by using various physical principles, such as pressure difference, velocity, rotation, displacement, etc.




PRINCIPLES AND PRACTICE OF FLOW METER ENGINEERING L K SPINK.15



Flow meter engineering is not a new field. It has a long history that dates back to ancient times when people used simple methods to measure the flow of water in rivers or canals. However, the modern development of flow meter engineering began in the 18th century with the invention of the venturi tube by Giovanni Battista Venturi and the pitot tube by Henri Pitot. Since then, many types of flow meters have been invented and improved to meet the diverse needs and challenges of different applications.


One of the pioneers of flow meter engineering was Leland Kenneth Spink (1898-1975), an American engineer who worked for the Foxboro Company for over 40 years. He wrote several books and papers on flow meter engineering, including the classic "Principles and Practice of Flow Meter Engineering" which was first published in 1943 and has been revised several times since then. This book covers the theory and practice of various types of flow meters, such as orifice plate, venturi tube, pitot tube, turbine, positive displacement, etc. It also discusses the factors affecting flow meter performance and accuracy, such as fluid properties and conditions, flow meter design and installation, flow meter calibration and maintenance, etc. The book is widely regarded as a comprehensive and authoritative reference for flow meter engineers and users.


Types of flow meters and their applications




Orifice plate flow meters




How they work




An orifice plate flow meter is one of the most common types of differential pressure flow meters. It consists of a thin metal plate with a hole (orifice) in the middle that is mounted across a pipe. As the fluid flows through the pipe, it has to pass through the orifice which creates a pressure difference between the upstream and downstream sides of the plate. The pressure difference is proportional to the square of the flow rate, according to the Bernoulli's principle. The pressure difference can be measured by a differential pressure transmitter or a manometer and converted to a flow rate by using a calibration equation or a flow coefficient.


Advantages and disadvantages




Some of the advantages of orifice plate flow meters are:



  • They are simple, cheap, and easy to install and maintain.



  • They can measure a wide range of flow rates and fluid types, such as liquids, gases, and steam.



  • They can withstand high temperatures and pressures.



  • They have a low pressure loss compared to other differential pressure flow meters.



Some of the disadvantages of orifice plate flow meters are:



  • They require a straight pipe section before and after the orifice plate to ensure a fully developed and stable flow profile.



  • They are sensitive to changes in fluid properties and conditions, such as density, viscosity, temperature, pressure, etc.



  • They are prone to erosion, corrosion, and clogging of the orifice due to abrasive or dirty fluids.



  • They have a low accuracy and repeatability compared to other types of flow meters.



Examples of use cases




Some of the typical applications of orifice plate flow meters are:



  • Measuring the flow of natural gas in pipelines or wells.



  • Measuring the flow of steam in power plants or boilers.



  • Measuring the flow of water in irrigation systems or water treatment plants.



  • Measuring the flow of air in HVAC systems or combustion processes.



Venturi tube flow meters




How they work




A venturi tube flow meter is another type of differential pressure flow meter. It consists of a tube with a converging section, a throat, and a diverging section that is mounted across a pipe. As the fluid flows through the tube, it accelerates in the converging section and reaches its maximum velocity at the throat. This causes a pressure drop at the throat which is measured by a differential pressure transmitter or a manometer. The pressure drop is proportional to the square of the flow rate, according to the Bernoulli's principle. The pressure drop can be converted to a flow rate by using a calibration equation or a flow coefficient.


Advantages and disadvantages




Some of the advantages of venturi tube flow meters are:



  • They have a high accuracy and repeatability compared to other differential pressure flow meters.



  • They have a low pressure loss compared to other differential pressure flow meters.



  • They are less sensitive to changes in fluid properties and conditions, such as density, viscosity, temperature, pressure, etc.



  • They are less prone to erosion, corrosion, and clogging of the throat due to abrasive or dirty fluids.



Some of the disadvantages of venturi tube flow meters are:



  • They are more expensive and complex than orifice plate flow meters.



  • They require more space and piping than orifice plate flow meters.



  • They still require a straight pipe section before and after the venturi tube to ensure a fully developed and stable flow profile.



Examples of use cases




Some of the typical applications of venturi tube flow meters are:



  • Measuring the flow of liquids with high viscosity or solids content, such as oil, slurry, pulp, etc.



  • Measuring the flow of gases with high humidity or condensation, such as steam, flue gas, etc.



  • Measuring the flow of fluids with low Reynolds numbers or laminar flows, such as blood, air, etc.



Pitot tube flow meters




How they work




it by the cross-sectional area of the pipe. The velocity can also be measured by using a pitot-static tube which combines a pitot tube and a static tube in one device.


Advantages and disadvantages




Some of the advantages of pitot tube flow meters are:



  • They are very simple, cheap, and easy to install and maintain.



  • They can measure high flow velocities and turbulent flows.



  • They have a negligible pressure loss compared to other differential pressure flow meters.



  • They can measure the flow profile in a pipe or a channel by using multiple pitot tubes at different locations.



Some of the disadvantages of pitot tube flow meters are:



  • They have a low accuracy and repeatability compared to other types of flow meters.



  • They require a straight pipe section before and after the pitot tube to ensure a fully developed and stable flow profile.



  • They are sensitive to changes in fluid properties and conditions, such as density, viscosity, temperature, pressure, etc.



  • They are prone to erosion, corrosion, and clogging of the opening due to abrasive or dirty fluids.



Examples of use cases




Some of the typical applications of pitot tube flow meters are:



  • Measuring the airspeed of aircrafts or wind tunnels.



  • Measuring the flow of gases in pipes, ducts, or stacks.



  • Measuring the flow of liquids in pipes, weirs, or open channels.



Turbine flow meters




How they work




A turbine flow meter is a type of rotary flow meter that measures the volumetric flow rate of fluids by using a turbine or a fan that rotates at a speed proportional to the fluid velocity. The turbine or fan is mounted on a shaft that is connected to a magnetic pickup or an optical sensor that generates an electrical signal as the blades pass by. The frequency of the signal is proportional to the rotational speed of the turbine or fan, which is proportional to the volumetric flow rate of the fluid. The frequency can be converted to a flow rate by using a calibration equation or a K-factor.


Advantages and disadvantages




Some of the advantages of turbine flow meters are:



  • They have a high accuracy and repeatability compared to other types of flow meters.



  • They have a high rangeability and turndown ratio compared to other types of flow meters.



  • They have a low pressure loss compared to other types of flow meters.



  • They can measure bidirectional flows by using dual turbines or sensors.



Some of the disadvantages of turbine flow meters are:



  • They are expensive and complex than other types of flow meters.



  • They require a straight pipe section before and after the turbine to ensure a fully developed and stable flow profile.



  • They are sensitive to changes in fluid properties and conditions, such as density, viscosity, temperature, pressure, etc.



  • They are prone to wear, damage, and fouling of the turbine due to abrasive or dirty fluids.



Examples of use cases




Some of the typical applications of turbine flow meters are:



  • Measuring the flow of liquids with low viscosity and high purity, such as water, fuel, oil, etc.



  • Measuring the flow of gases with low density and high velocity, such as air, nitrogen, oxygen, etc.



  • Measuring the flow of cryogenic fluids with low temperature and high pressure, such as liquid nitrogen, liquid oxygen, etc.



Positive displacement flow meters




How they work




the volumetric flow rate of fluids by using a series of chambers or gears that capture and release a fixed amount of fluid with each rotation or reciprocation. The number of rotations or reciprocations is counted by a mechanical register or an electronic sensor that generates an electrical signal. The number of rotations or reciprocations is proportional to the volumetric flow rate of the fluid. The signal can be converted to a flow rate by using a calibration equation or a K-factor.


Advantages and disadvantages




Some of the advantages of positive displacement flow meters are:



  • They have a high accuracy and repeatability compared to other types of flow meters.



  • They can measure low flow rates and viscous fluids that are difficult for other types of flow meters to measure.



  • They do not require a straight pipe section before and after the meter to ensure a fully developed and stable flow profile.



  • They can measure bidirectional flows by using dual chambers or gears or sensors.



Some of the disadvantages of positive displacement flow meters are:



  • They are expensive and complex than other types of flow meters.



  • They have a high pressure loss compared to other types of flow meters.



  • They are sensitive to changes in fluid properties and conditions, such as density, viscosity, temperature, pressure, etc.



  • They are prone to wear, damage, and fouling of the chambers or gears due to abrasive or dirty fluids.



Examples of use cases




Some of the typical applications of positive displacement flow meters are:



  • Measuring the flow of liquids with high viscosity and solids content, such as oil, slurry, pulp, etc.



  • Measuring the flow of gases with low velocity and high pressure, such as natural gas, propane, etc.



  • Measuring the flow of water for domestic or industrial use, such as billing, irrigation, etc.



Factors affecting flow meter performance and accuracy




Fluid properties and conditions




Density, viscosity, temperature, pressure, etc.




The performance and accuracy of flow meters depend on the properties and conditions of the fluid being measured. Some of the important factors are:



  • Density: The mass per unit volume of a fluid. It affects the pressure drop across differential pressure flow meters and the rotational speed of turbine and positive displacement flow meters. Density changes with temperature and pressure and must be measured or corrected for accurate flow measurement.



  • Viscosity: The resistance of a fluid to flow or shear stress. It affects the pressure drop across differential pressure flow meters and the rotational speed of turbine and positive displacement flow meters. Viscosity changes with temperature and must be measured or corrected for accurate flow measurement.



  • Temperature: The degree of heat or coldness of a fluid. It affects the density, viscosity, pressure, and volume of a fluid. Temperature changes can cause thermal expansion or contraction of the fluid and the flow meter components. Temperature must be measured or corrected for accurate flow measurement.



  • Pressure: The force per unit area exerted by a fluid on a surface. It affects the density, volume, and compressibility of a fluid. Pressure changes can cause cavitation or flashing in differential pressure flow meters and affect the accuracy of turbine and positive displacement flow meters. Pressure must be measured or corrected for accurate flow measurement.



How to measure and correct them




To measure and correct the effects of fluid properties and conditions on flow meter performance and accuracy, some methods are:



  • Using auxiliary devices such as thermometers, pressure gauges, densitometers, viscometers, etc. to measure the fluid properties and conditions at the point of measurement or at a reference point.



  • Using correction factors or equations to adjust the measured flow rate based on the measured fluid properties and conditions.



  • Using online calculators or software to perform the correction calculations automatically.



the fluid properties and conditions automatically.


Flow meter design and installation




Size, shape, material, location, etc.




The performance and accuracy of flow meters also depend on the design and installation of the flow meter itself. Some of the important factors are:



  • Size: The diameter of the flow meter should match the diameter of the pipe or the channel where it is installed. A mismatch can cause turbulence, distortion, or leakage of the flow and affect the accuracy of the flow measurement.



  • Shape: The shape of the flow meter should be compatible with the shape of the pipe or the channel where it is installed. A mismatch can cause obstruction, restriction, or misalignment of the flow and affect the accuracy of the flow measurement.



  • Material: The material of the flow meter should be suitable for the type and condition of the fluid being measured. A mismatch can cause corrosion, erosion, or contamination of the flow meter or the fluid and affect the accuracy of the flow measurement.



  • Location: The location of the flow meter should be chosen to ensure a stable and representative flow profile. A poor location can cause interference, noise, or vibration of the flow meter or the fluid and affect the accuracy of the flow measurement.



How to select and install them properly




To select and install flow meters properly, some methods are:



  • Using manufacturer's specifications and recommendations to choose the appropriate size, shape, material, and location of the flow meter for a given application.



  • Using industry standards and best practices to follow the proper installation procedures and guidelines for a given type of flow meter.



  • Using professional services or experts to assist with the selection and installation of flow meters if needed.



Flow meter calibration and maintenance




Methods, standards, frequency, etc.




The performance and accuracy of flow meters also depend on the calibration and maintenance of the flow meter over time. Some of the important factors are:



  • Methods: The methods of calibrating and maintaining flow meters vary depending on the type and design of the flow meter. Some common methods are using reference standards, test benches, provers, master meters, etc.



the application and the regulation of the flow measurement. Some common standards are ISO, ASTM, API, OIML, etc.


  • Frequency: The frequency of calibrating and maintaining flow meters varies depending on the type and design of the flow meter, the usage and condition of the fluid, and the quality and reliability of the flow measurement. Some common frequencies are annual, biannual, quarterly, monthly, etc.



How to calibrate and maintain them regularly




To calibrate and maintain flow meters regularly, some methods are:



  • Using manufacturer's specifications and recommendations to choose the appropriate methods, standards, and frequency of calibration and maintenance for a given type of flow meter.



  • Using industry standards and best practices to follow the proper calibration and maintenance procedures and guidelines for a given type of flow meter.



  • Using professional services or experts to assist with the calibration and maintenance of flow meters if needed.



Conclusion




Flow meter engineering is a complex and dynamic field that requires a thorough understanding of the principles and practice of various types of flow meters, such as orifice plate, venturi tube, pitot tube, turbine, positive displacement, etc. It also requires a careful consideration of the factors affecting flow meter performance and accuracy, such as fluid properties and conditions, flow meter design and installation, flow meter calibration and maintenance, etc. By following the guidelines and recommendations provided in this article, one can select, install, use, calibrate, and maintain flow meters effectively and efficiently for different applications.


FAQs




Here are some frequently asked questions about flow meter engineering:



  • What is the difference between mass flow rate and volumetric flow rate?



Mass flow rate is the amount of mass of a fluid passing through a cross-sectional area per unit time. It is expressed in units such as kg/s or lb/min. Volumetric flow rate is the amount of volume of a fluid passing through a cross-sectional area per unit time. It is expressed in units such as m3/s or ft3/min. Mass flow rate is independent of fluid density, while volumetric flow rate depends on fluid density.


  • What is Reynolds number and why is it important for flow measurement?



Reynolds number is a dimensionless number that characterizes the flow regime of a fluid. It is defined as the ratio of inertial forces to viscous forces in a fluid. It is calculated as Re = ρVD/μ where ρ is density, V is velocity, D is diameter, and μ is viscosity. Reynolds number indicates whether the flow is laminar (smooth), turbulent (chaotic), or transitional (mixed). Reynolds number affects the pressure drop across differential pressure flow meters and the accuracy of other types of flow meters.


  • What are some advantages and disadvantages of differential pressure flow meters?



Differential pressure flow meters are based on measuring the pressure difference across a constriction in a pipe or a channel. Some advantages are that they are simple, cheap, easy to install and maintain, can measure a wide range of flows and fluids, can withstand high temperatures and pressures. Some disadvantages are that they require straight pipe sections before and after the constriction to ensure stable fl


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