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Venturimeter Definition Parts Working Equation Applications Installation With PDF Written by Anup Kumar Deyin Instrumentation Mechanical Pipeline Piping Design Basics Piping Interface Venturimeter is a type of flowmeter that works on the principle of Bernoulli s Equation This device is widely used in the water chemical pharmaceutical and oil gas industries to measure the flow rates of fluids inside a pipe The pipe cross sectional area is reduced to create a pressure difference which is measured with a manometer to determine the rate of fluid flow So the venturi meter is a differential head type flowmeter that converts pressure energy into kinetic energy Types of Pipes Classification of Video Player is loading Pause Unmute Loaded 0 37 Remaining Time 9 06 Fullscreen Types of Pipes Classification of Pipes PDF The principle of the Venturimeter was demonstrated by Giovanni Batista Venturi Hence the name Venturimeter But it was first used in practical metering applications by Clemens Herschel In this article we will explore the parts working principles equations and applications of the Venturimeter Venturimeter Diagram and Parts A venturimeter consists of four parts 1 Cylindrical Inlet Section 2 Conical convergent Section 3 Cylindrical throat and 4 Conical divergent outlet Fig 1 below shows a typical venturimeter diagram with its parts Fig 1 Typical Venturimeter Diagram with Parts There are two tappings on the venturi meter for pressure measurement the upstream pressure tapping is located at a distance of one half of pipe diameter D 2 upstream of the convergent entry while the downstream pressure tapping is located in the throat d 2 as shown in Fig 1 Cylindrical Entrance Section Venturimeter entrance is a straight cylindrical section with a length equal to 5 to 8 times the pipe diameter Convergence Conical Section In this section the venturi meter tube diameter gradually decreases The conical angle is normally 210 20 While the liquid flows inside the venturimeter the velocity of fluid increases at the expense of a decrease in pressure Cylindrical Throat Throat consists of the minimum venturemeter diameter In the throat section the velocity is maximum and pressure is minimum Normally throat diameter 1 3 to 1 4th of inlet pipe diameter Diverging Conical section At this section of venturimeter the tube diameter gradually increases So the pressure is build up again to the original inlet pressure The cone angle is 5 70 British Standard BS 1042 specifies two conical angles 5 70 and 14 150 for the outlet cone Materials for Venturimeter Small size venturimeter are made of brass glass or bronze and large venturimeters are made of cast iron steel or stainless steel Working principle of Venturimeter When a fluid flows through a venturimeter it accelerates in the convergent section and then decelerates in the divergent section The pressure difference between an upstream section and the throat is measured by a manometer Using that differential pressure applying Bernoulli s Equation and Contininuity Equitation the volumetric flow rate can be estimated In the next section the equations of venturimeter to find the discharge value are discussed Venturimeter Equations Bernoulli s principle states the relation between pressure P kinetic energy and gravitational potential energy of a fluid inside a pipe The mathematical formula of Bernoulli s equation is given as Advertisements Where p pressure inside the pipe density of the fluid g gravitational constant v velocity z elevation or head a cross sectional area of the pipe d diameter of the pipe Suffixes 1 and 2 are used to denote two different areas 1 denotes the cylindrical inlet section and 2 denotes the throat section Now as the pipe is horizontal there is no difference in the elevation of the pipe centerline So z1 z2 Re arranging the above equation we get the following p1 p2 g v22 v12 2g p1 p2 g is the difference of pressure heads in sections 1 and 2 which is equal to h that can be measured in the differential manometer So the above equation becomes h v22 v12 2g eqn 1 Now applying continuity equations between the same sections 1 and 2 we get a1v1 a2v2 or v1 a2v2 a1 Putting this value of v1 in eqn 1 and solving we get So the rate of flow through the throat Q can be calculated as Q a2v2 Substituting the above value of v2 we get This Q represents the theoretical discharge of Venturi Meter in ideal conditions But in actual practice there will always be some frictional loss Hence the actual discharge will always be less than the theoretical discharge So to calculate the actual discharge the above Q value is multiplied by Cd called the Coefficient of discharge of venturimeter So the actual flow rate through the throat of the venturimeter will be given by the following equation Coefficient of Discharge of Venturimeter Cd The coefficient of discharge for Venturimeter Cd is defined as the ratio of the actual flow rate through the venturi meter tube to the theoretical flow rate So the venturi meter discharge coefficient is given by Cd Qact Q As Qactual will always be less than Qtheoretical due to frictional losses the value of Cd is always less than 1 0 The typical range of the discharge coefficient of a Venturi meter is 0 95 0 99 but this can be increased by proper machining of the convergent section The value of venturimeter discharge coefficient differs from one flowmeter to the other depending on the venturimeter geometry and the Reynolds number ISO 5167 code provides the values of venturimeter discharge coefficients For accurate flow measurement normally straight length requirement upstream and downstream of venturimeter is specified Types of Venturimeters Normally three types of venturimeters are available Horizontal Venturimeter This type of venturimeter has the highest kinetic energy and the lowest potential energy Vertical Venturimeter This type has the maximum potential energy and the minimum kinetic energy Inclined Venturimeter Both potential and kinetic energy are in between the above two types mentioned Applications of Venturimeter Venturimeters find wide application in fluid industries The major application of venturimeters include Used in Engine Carburetors Automobile Sector to measure airflow Used in process industries Process and Power Piping Industries to measure and control process flow In the medical industry blood flow in the arteries is measured by venturimeters Measures the fluid flow inside pipelines Oil Gas Industries Broadly the use of

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