orifice meter experiment

• Measurement and Metrology
• Material Science
• Thermodynamics

Orifice Meter: Definition, Construction, Working, Experiment, Derivation, Formula, Advantages, Application [Notes & PDF]

Table of Contents

The orifice Meter is a topic of fluid machinery and it is a device that is used to measure the flow rate or average velocity of the flowing fluid (Liquid or gases) in a pipe.

Here the orifice plate is used for the restriction in the direction of the fluid flow. Therefore the restriction process we also called Orifice Plate. The restriction effect results in pressure drops of the flowing fluid.

The drop in pressure is associated with the rate of flowing fluid or the average velocity of the fluid.

Now lets see definition,

Orifice Meter Definition:

The orifice Meter or Plate can be defined as the device in Fluid Mechanics and machinery which is used for measuring the flowing fluid rate or in other terms the average velocity. The orifice meter or Plate works on the principle of Bernoulli’s theorem and that is the sum of all the energy at a point is equal to the sum of all the energy at point 2 .

Orifice Meter or Plate Types:

There are 4 different types that include Eccentric, Conical, Sharp Edge, Segmental, and Quadrant Orifice Plate.

Eccentric Orifice Plate:

It is used for measuring fluids who carry small amount of or gases with small amounts of liquid and non-abrasive solids. It has a round opening (bore) tangent to the inside wall of the pipe.

Conical Orifice Plate:

Conic Edge orifice plate is useful for lower Reynolds numbers. It has a 45° bevel facing upstream into the flowing stream.

Segmental Orifice Plate:

The segemental plate is also used for measuring fluids that is liquid or gases carry non-abrasive impurities such as light slurries or exceptionally dirty gases.

Quadrant Orifice Plate:

This orifice is used for high viscosity Fluids .

Now moving to construction,

Orifice Meter Construction or Parts:

Orifice Meter Consists of following four Parts :

• Inlet Suction
• Orifice Plate
• Flow Conditioner and
• Outlet section

Inlet Section:

The name inlet section means the fluid will enter into the orifice meter through the inlet section.

Orifice Plate:

The orifice plate is situated between the inlet and outlet and the plate is used to generate pressure drop that will enable the flow rate. The orifice plate construction: It is thin size having one hole from that the water will pass.

Flow Conditioner:

The flow conditioner is used to increase the linear flow in the inlet section of the meter tube. The flow conditioner is installed nearly the inlet section of the meter tube.

Outlet Section:

Now Here in the outlet section, the pressure of the fluid is being discharged and determined.

Orifice Meter Working Principle:

The working of the orifice meter is based on the principle of Bernoulli’s equation.

As you can see in the diagram there is a pipe in which fluid is passing from one side to another side that is an inlet to outlet. The manometer is attached hereto measure the pressure differences between two-point.

Now we place an orifice plate which is thin in size and having a small hole in between through which the fluid will pass. Now when the increases in the velocity, the decrease in the pressure and it is vice versa.

The place of the orifice plate in the pipe only determines the flow rate or discharge at that point only. The discharge can be calculated by the formula and that will be explained in the derivation section.

Orifice Meter hydraulic coefficient:

There are four hydraulic coefficient of Orifice meter and those are:

• Coefficient of Contraction
• Coefficient of Velocity
• Coefficient of Resistance
• Coefficient of Discharge

Coefficient of Contraction:

Coefficient of contraction can be defined as the ratio of the area of the jet at vena contracta to the area of Orifice.

Coefficient of Velocity:

Coefficient of discharge can be defined as theratio of actual velocity of jet at vena contracta to the theoretical velocity of the jet.

Coefficient of Resistance:

Coefficient of resistance can be defined as the ratio of loss of head in the orifice to the head of water available at the exit of the orifice.

Coefficient of Discharge:

The coefficient of discharge can be defined as the ratio of Qact (actual discharge) to the Qthe (theoretical discharge).

Now our main topic derivation,

Orifice Meter Derivation or Experiment:

As you can see in the diagram,

d1= Inlet section diameter P1= Inlet section pressure v1= Inlet section velocity of the fluid A1= Inlet section Area d2= Outlet section diameter P2= Outlet section pressure v2= Outlet section velocity of the fluid A2= Outlet section Area Cd= Coefficient of discharge

There are some assumption to derive orifice meter discharge and that is

• Fluid must be ideal
• Fluid flow irritation. steady and continuous
• The inner surface must be frictionless

Bernoulli’s Therom: In an ideal that is an incompressible fluid, the sum of all pressure energy, kinetic energy, and Potential energy is equal in section 1 will be the same as in section 2

Now applying the Bernoulli’s equation in this at point 1 and 2:

Here h is the differential head.

And A0 is the area of orifice and Cc is coefficient of contraction. Cc=A2/A0

Now the continuity equation which is A1v1=A2v2

Therefor the discharge is,

If Cd is the coefficient of discharge for orifice meter then,

Now the above equation we will use the Cc value in the discharge Q therefore we will get the value of discharge is,

Here the Cd value will be low as compare to Cd value of Venturimeter.

Orifice Meter Formula:

From the below formula you can easily calculate the actual discharge of Orifice Meter.

Orifice Meter Specification:

The specification of orifice Meter or Plate is:

• The length of the Orifice can be from 10 mm to 800 mm.
• The diameter of the orifice plate can be 0.5 times the diameter of the pipe though it may vary from 0.4 to 0.8 times.
• Up to 800 degrees celsius Operating Temperature.
• The Operating Pressure is up to 400 bar.

Orifice Meter Advantages:

The following advantages of Orifice meter is:

• The Orifice meter is very cheap compared to other flow meters like the venturi meter and so on.
• The direction possibility can be vertical, horizontal, and inclined.
• The space required for installation is less.
• It is usually thin enough to fit between an existing pipe.
• The maintenance cost is low.
• It offers very less pressure drop.
• The construction and design of this orifice meter are very simple.
• It is capable to determine a wide range of flow rates that the main advantages.

Orifice Meter Disadvantages:

The following disadvantages of Orifice Meter is:

• Due to limitations in the vena-contracta length, the minimum pressure for reading the flow is sometimes difficult.
• In the Venturi meter, downstream pressure can be recovered. But In Orifice meter downstream pressure can not be recovered in Orifice Meters.
• It requires a single phase of liquid.
• The orifice Accuracy can be affected by the viscosity, density, and pressure of the fluid.
• It requires a straight pipe for good precision and accuracy.
• The 40% to 90% overall head loss of the differential pressure.
• The obtained coefficient of discharge is low.

Orifice Meter Application:

The main application of orificemeter is used at several places to measure flow rates such as Water Treatment Plants, Natural Gas, Petrochemicals, Oil Filtration Plants, and Refineries.

Internal Resources: Pump vs Compressor Francis Turbine Pelton Wheel Turbine Types of Fluid Flow

So finally our article ends here. I have also explained another flow meter that is the venturi meter you can read that too. And if you like the article then do not forget to spread the love.

Related Article:

Types of Fluid Flow: Definition and Example [Notes & PDF]

Diesel cycle: definition, process, pv and ts diagram, derivation, efficiency, application [notes & pdf], er. amrit kumar.

Amrit Kumar is a Mechanical Engineer and founder of Themechanicalengineering.com. I have done a Diploma and Engineering degree in Mechanical and writes content since 2016.

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About me, My name is Amrit Kumar. I have studied Mechanical Engineering and on this platform, I try to share the content in detail and in a good format. My aim is to provide useful and engaging content to our readers. I have been on this journey since 2016.

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Experiment on Orifice Meter in Laboratory

• Author : --> Farhan Khan
• --> Posted On : June 11, 2021
• Updated On : June 11, 2021

Table of Contents

The performance of this experiment targets the following objectives:

• To measure the volume flow rate or discharge through a pipe having a pressurized fluid flow
• To comprehend the abstraction of vena contracts in pipe flows
• To determine the coefficient of discharge of an orifice meter

Related Theory

An orifice is simply an aperture or hole and for flow measurement, it can be installed in a fluid tank (at the base or side) through which water is expelled out in the form of a jet.

Orifices are used to measure the discharge or volumetric rate of flow through tanks, reservoirs, or any fluid receptacle.

Evidently, the flow through an orifice depends upon the diameter and type of orifice as well as the head of fluid present above it.

Orifice Meter:

An orifice meter or orifice plate is also a discharge measuring device employed in a pipe to create a pressure gradient by altering the pipe cross-section at the point it is installed. The differential pressure head is measured using a manometer and the discharge through the pipe cross-section can easily be calculated.

The figure above shows an orifice meter connected in a pipe of diameter D containing a fluid flowing under the influence of pressure forces.

Due to the presence of the orifice plate, the pipe’s diameter reduces. Consequently, the velocity of fluid shows an instantaneous surge, thereby dropping the fluid pressure at the contracted section.

The differential pressure becomes eminent on the limbs of the manometer in the form of a pressure step-down. The manometric fluid in both limbs of the manometer shows a difference in the levels which is noted down.

D =Diameter of pipe

A 1 = Area of pipe at inlet

d o = Diameter of orifice

A 2 = Area of pipe at vena contracta

h = Pressure difference in the limbs of manometer

The theoretical discharge through the pipe cross-section can be calculated as;

The actual discharge can be determined by recording the time to fill a known volume of fluid in the volumetric tank.

Vena Contracta

When an orifice meter is installed in a pipe, the cross-section contracts. Consequently, the streamlines come close to each other. The section where the streamlines come the closest possible is termed the vena contracta. The velocity of fluid at this section shows an instantaneous hike followed by a pressure decrement.

The figure above shows the graphical trend of pressure variation across the orifice plate. It can be seen that at the contracted section, the pressure magnitude is the least after which the pressure head is restored but to decremented value in comparison to the pressure at the inlet. This is because of frictional losses incurred as the fluid traverses the pipe length.

Coefficient of Discharge, C d

The coefficient of discharge of an orifice meter is the ratio of the actual discharge to the theoretically-calculated volume flow rate. Mathematically, it is given as;

• Hydraulic bench , to measure the actual volume flow rate
• Stopwatch, to record the time taken to fill the tank to the required depth
• Orifice meter apparatus

Test Procedure

• Start the pump and by using the discharge control valve, adjust the flow rate and measure it by noting down the time taken (t) to fill the volumetric tank in the hydraulic bench to a known depth.
• Calculate the actual discharge as follows;
• Before allowing the fluid to flow into the orifice meter apparatus, ensure that the pipelines are free from air bubbles. To do so, turn on the air-release valves to allow the air bubbles to traverse the pipe length to enter the tank.
• Open the valve of the orifice meter pipeline to allow water to flow through the orifice plate.
• The manometer present below shows a pressure drop. Record the level of manometric fluid in both limbs of the manometer in order to determine the differential pressure head .
• Calculate the theoretical discharge as follows;

• Determine the coefficient of discharge of the orifice meter by taking the ratio of actual discharge to the theoretical one.
• Repeat the above process for a different discharge value. To alter the flow rate, rotate the discharge control valve either clockwise or anticlockwise.
• Average out the value of the coefficient of discharge of the orifice meter.

Observations and Calculations

Inlet diameter of pipe = D =

Area of pipe at inlet = A 1 = (π*D 2 )/4

Type of orifice plate used:

Diameter of orifice = d o =

Area of orifice = A 2 = (π*d o 2 )/4

Formulae Used:

The formula for calculating the differential head is based on the assumption that the flow through the pipe is from left to right such that the left limb of the manometer connected at the pipe inlet shows a higher value of pressure head than the right limb connected at the contracted section.

Coefficient of Discharge of the orifice meter =

Precautions

• The availability of water in the sump tank should be ensured prior to pumping the water.
• The meniscus of the manometer should be read carefully.
• It is preferable to wear safety goggles and gloves while handling hydraulic fluids.
• It is imperative to remove the air bubbles in the pipelines that may otherwise yield misleading results.
• The coefficient of discharge of an ideal pipe is 1. This is because the theoretical and actual flow rate values coincide. However, the existence of such a pipe is hypothetical and energy or frictional losses during the flow of fluid can be minimized but not eliminated.
• Depending upon the viscosity of the fluid and its Reynold number, different types of orifice plates can be used. These include segmental, eccentric, conical, and quadrant orifice plates.
• Orifice meters can serve to measure the discharge through water treatment plants, filtration plants, oil refineries, etc.

Farhan is a highly experienced civil engineer from the Southern side of Texas and has been associated with ConstructionHow since 2020. Over almost a decade, his wide span of expertise enabled him to bring forth his fair share of stories and experiences related to the most iconic engineering examples worldwide. He has also contributed to online and offline publications on requests. Engineering is his passion, which is why he chose to become part of our honorable team of industry experts looking to provide authentic and credible guidelines to the reader.

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Experiment #6: Orifice and Free Jet Flow

1. introduction.

An orifice is an opening, of any size or shape, in a pipe or at the bottom or side wall of a container (water tank, reservoir, etc.), through which fluid is discharged. If the geometric properties of the orifice and the inherent properties of the fluid are known, the orifice can be used to measure flow rates. Flow measurement by an orifice is based on the application of Bernoulli’s equation, which states that a relationship exists between the pressure of the fluid and its velocity. The flow velocity and discharge calculated based on the Bernoulli’s equation should be corrected to include the effects of energy loss and viscosity. Therefore, for accurate results, the coefficient of velocity ( C v ) and the coefficient of discharge ( C d ) should be calculated for an orifice. This experiment is being conducted to calibrate the coefficients of the given orifices in the lab.

2. Practical Application

Orifices have many applications in engineering practice besides the metering of fluid flow in pipes and reservoirs. Flow entering a culvert or storm drain inlet may act as orifice flow; the bottom outlet of a dam is another example. The coefficients of velocity and discharge are necessary to accurately predict flow rates from orifices.

3. Objective

The objective of this lab experiment is to determine the coefficients of velocity and discharge of two small orifices in the lab and compare them with values in textbooks and other reliable sources.

The coefficients of velocity and discharge are determined by measuring the trajectory of a jet issuing fluid from an orifice in the side of a reservoir under steady flow conditions, i.e., a constant reservoir head.

5. Equipment

The following equipment is required to perform the orifice and free jet flow experiment:

• F1-10 hydraulics bench;
• F1-17 orifice and free jet flow apparatus, with two orifices having diameters of 3 and 6 mm;
• Measuring cylinder for flow measurement; and
• Stopwatch for timing the flow measurement.

6. Equipment Description

The orifice and free jet flow apparatus consists of a cylindrical head tank with an orifice plate set into its side (Figure 6.1). An adjustable overflow pipe is adjacent to the head tank to allow changes in the water level. A flexible hose attached to the overflow pipe returns excess water to the hydraulics bench. A scale attached to the head tank indicates the water level. A baffle at the base of the head tank promotes smooth flow conditions inside the tank, behind the orifice plate. Two orifice plates with 3 and 6 mm diameters are provided and may be interchanged by slackening the two thumb nuts. The trajectory of the jet may be measured, using the vertical needles. For this purpose, a sheet of paper should be attached to the backboard, and the needles should be adjusted to follow the trajectory of the water jet. The needles may be locked, using a screw on the mounting bar. The positions of the tops of the needles can be marked to plot the trajectory. A drain plug in the base of the head tank allows water to be drained from the equipment at the end of the experiment [6].

The orifice outflow velocity can be calculated by applying Bernoulli’s equation (for a steady, incompressible, frictionless flow) to a large reservoir with an opening (orifice) on its side (Figure 6.2):

where h is the height of fluid above the orifice. This is the ideal velocity since the effect of fluid viscosity is not considered in deriving Equation 1. The actual flow velocity, however, is smaller than v i and is calculated as:

C v is the coefficient of velocity , which allows for the effects of viscosity; therefore,  C v <1. The actual outflow velocity calculated by Equation (2) is the velocity at the vena contracta, where the diameter of the jet is the least and the flow velocity is at its maximum (Figure 6.2).

The actual outflow rate may be calculated as:

where A c is the flow area at the vena contracta. A c  is smaller than the orifice area,   A o (Figure 6.2), and is given by:

where C c is the coefficient of contraction; therefore, C c  < 1.

Substituting v  and A c  from Equations 2 and 4 into Equation 3 results in:

The product C v C c is called the coefficient of discharge, C d ; Thus, Equation 5 can be written as:

The coefficient of velocity, C v , and coefficient of discharge, C d , are determined experimentally as follows.

7.1.  Determination of the Coefficient of Velocity

If the effect of air resistance on the jet leaving the orifice is neglected, the horizontal component of the jet velocity can be assumed to remain constant. Therefore, the horizontal distance traveled by jet (x) in time (t) is equal to:

The vertical component of the trajectory of the jet will have a constant acceleration downward due to the force of gravity.  Therefore, at any time, t, the y-position of the jet may be calculated as:

Rearranging Equation (8) gives:

Substitution of t and v from Equations 9 and 2 into Equation 7 results in:

Equations (10) can be rearranged to find C v :

7.2.  Determination of the Coefficient of Discharge

8. Experimental Procedure

This experiment will be performed in two parts. Part A is performed to determine the coefficient of velocity, and Part B is conducted to determine the coefficient of discharge.

Set up the equipment as follows:

• Locate the apparatus over the channel in the top of the bench.
• Using the spirit level attached to the base, level the apparatus by adjusting the feet.
• Connect the flexible inlet tube on the side of the head tank to the bench quick-release fitting.
• Place the free end of the flexible tube from the adjustable overflow on the side of the head tank into the volumetric. Make sure that this tube will not interfere with the trajectory of the jet flowing from the orifice
• Secure each needle in the raised position by tightening the knurled screw.

Part A: Determination of coefficient of velocity from jet trajectory under constant head

• Install the 3-mm orifice in the fitting on the right-hand side of the head tank, using the two securing screws supplied. Ensure that the O-ring seal is fitted between the orifice and the tank.
• Close the bench flow control valve, switch on the pump, and then gradually open the bench flow control valve. When the water level in the head tank reaches the top of the overflow tube, adjust the bench flow control valve to provide a water level of 2 to 3 mm above the overflow pipe level. This will ensure a constant head and produce a steady flow through the orifice.
• If necessary, adjust the frame so that the row of needles is parallel with the jet, but is located 1 or 2 mm behind it. This will avoid disturbing the jet, but will minimize errors due to parallax.
• Attach a sheet of paper to the backboard, between the needles and board, and secure it in place with the clamp provided so that its upper edge is horizontal.
• Position the overflow tube to give a high head (e.g., 320 mm). The jet trajectory is obtained by using the needles mounted on the vertical backboard to follow the profile of the jet.
• Release the securing screw for each needle, and move the needle until its point is just immediately above the jet. Re-tighten the screw.
• Mark the location of the top of each needle on the paper. Note the horizontal distance from the plane of the orifice (taken as ) to the coordinate point marking the position of the first needle. This first coordinate point should be close enough to the orifice to treat it as having the value of y=0. Thus, y displacements are measured relative to this position.
• The volumetric flowrate through the orifice can be determined by intercepting the jet, using the measuring cylinder and a stopwatch. The measured flow rates will be used in Part B.
• Repeat this test for lower reservoir heads (e.g., 280 mm and 240 mm)

Repeat the above procedure for the second orifice with diameter of 6 mm.

Part B: Determination of coefficient of discharge under constant head

• Position the overflow tube to have a head of 300 mm in the tank. (You may have to adjust the level of the overflow tube to achieve this.)
• Measure the flow rate by timed collection, using the measuring cylinder provided.
• Repeat this procedure for a head of 260 mm.

The procedure should also be repeated for the second orifice.

9. Results and Calculations

Please visit this link for accessing excel workbook for this experiment.

9.1. Results

Use the following tables to record your measurements.

Raw Data Table: Part A

Raw Data Table: Part B

9.2.     Calculations

Calculate the values of (y.h) 1/2  for Part A and discharge ( Q ) and ( h 0.5 ) for Part B. Record your calculations in the following Result Tables.

The following dimensions of the equipment are used in the appropriate calculations. If necessary, these values may be checked as part of the experimental procedure and replaced with your measurements [6]. – Diameter of the small orifice: 0.003 m – Diameter of the large orifice: 0.006 m – Pitch of needles: 0.05 m

Result Table- Part A

Result Table- Part B

Use the template provided to prepare your lab report for this experiment. Your report should include the following:

• Table(s) of raw data
• Table(s) of results

Part A : On one chart, plot a graph of x values (y-axis) against (y.h) 1/2 values (x-axis) for each test. Calculate the slope of these graphs, using the equation of the best-fit for your experimental data and by setting the intercept to zero. Using Equation 11, calculate the coefficient of velocity for each orifice as:

Part B : Plot Q values (y-axis) against (h) 0.5 values (x-axis). Determine the slope of this graph, using the equation of the best- fit for your experimental data and by setting the intercept to zero. Based on Equation 12, calculate the coefficient of discharge for each orifice, using the equation of the best-fit for your experimental data and the following relationship:

• Find the recommended values for C v  and C d    of the orifices utilized in this experiment from reliable sources (e.g., textbooks). Comment on the agreement between the textbook values and experimental results, and give reasons for any differences.
• Comment on the significance of any experimental errors.

Applied Fluid Mechanics Lab Manual Copyright © 2019 by Habib Ahmari and Shah Md Imran Kabir is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Orifice Meter: Definition, Construction, Working, Experiment, Derivation, Formula, Advantages, Application

What is an orifice meter .

An orifice meter is a type of flow measurement device used to determine the flow rate of fluids, such as gases or liquids, through a pipeline or duct. It consists of a specially designed plate called an orifice plate, which is installed in the flow path. The orifice plate has a precisely machined hole, known as the orifice, through which the fluid passes.

Table of Contents

When fluid flows through the orifice, it creates a pressure drop across the plate. This pressure drop is related to the flow rate according to Bernoulli’s principle. By measuring the pressure drop across the orifice plate, along with other parameters such as temperature and fluid properties, the flow rate can be calculated using empirical equations or standardized tables.

Orifice meters are widely used in various industries, including oil and gas, chemical, and water utilities, for measuring and controlling fluid flow. They are relatively simple and cost-effective devices, but they require careful calibration and consideration of factors such as fluid viscosity, temperature, and pipe size to ensure accurate measurements.

Other types of flow measurement devices include Venturi meters, flow nozzles, and magnetic flow meters, each with their own advantages and applications. The choice of the appropriate flow measurement device depends on factors such as the type of fluid, flow rate range, accuracy requirements, and installation constraints.

Must Read : Optical Flat

orifice meter parts

An orifice meter typically consists of the following parts:

• Orifice Plate: This is the primary component of the orifice meter and is a flat circular plate with a precisely machined orifice (hole) in the center. The orifice plate creates a restriction in the flow, causing a pressure drop. It is typically made of stainless steel or other suitable materials.
• Pipe Sections: Orifice meters are installed within a pipeline. The meter includes two straight pipe sections: the upstream pipe section, which is the section of pipe just before the orifice plate, and the downstream pipe section, which is the section of pipe just after the orifice plate. The length of these pipe sections is essential for accurate flow measurement.
• Flanges: Flanges are used to connect the orifice meter to the pipeline. They are usually made of metal and provide a secure and leak-tight connection. Flanges allow for easy installation, removal, and maintenance of the orifice meter.
• Tappings: Tappings are small holes or pressure connections located on the upstream and downstream sides of the orifice plate. They are used for pressure measurement and are connected to pressure transmitters or manometers to measure the pressure difference across the orifice.
• Pressure Taps: Pressure taps are small holes located in the pipe walls at specific positions. They are used to connect pressure measuring devices, such as pressure transmitters or gauges, to measure the upstream and downstream pressures.
• Support Brackets: Support brackets are used to hold the orifice plate in place within the pipeline. They ensure proper alignment of the orifice plate and prevent any movement or vibration during operation.
• Gaskets and Bolts: Gaskets and bolts are used to create a seal between the flanges, ensuring a leak-tight connection. The gaskets are placed between the flanges, and the bolts are tightened to secure the orifice meter in place.
• Instrumentation: Orifice meters are typically connected to instrumentation devices for data collection and measurement. These instruments can include pressure transmitters, differential pressure transmitters, flow computers, and data acquisition systems.

It’s important to note that the specific design and components of an orifice meter can vary based on factors such as the application, fluid properties, and industry requirements.

orifice meter working principle

The working principle of an orifice meter is based on the measurement of the pressure drop across a constriction created by an orifice plate in a fluid flow. Here’s a step-by-step explanation of the working principle:

• Fluid Flow: The fluid (liquid, gas, or steam) flows through a pipeline where the orifice meter is installed. The flow can be either horizontal or vertical.
• Constriction by Orifice Plate: The orifice plate, a flat circular plate with a precisely machined hole (orifice) in the center, is placed perpendicular to the flow direction. The orifice creates a constriction that narrows the flow path, resulting in increased fluid velocity and a pressure drop across the plate.
• Pressure Measurement: Pressure taps are located upstream and downstream of the orifice plate, typically at 0.5 pipe diameters away from the plate. Pressure measuring devices, such as pressure transmitters or gauges, are connected to these taps to measure the respective pressures.
• Differential Pressure Calculation: The difference in pressure between the upstream and downstream sides of the orifice plate is determined by subtracting the downstream pressure from the upstream pressure. This differential pressure (ΔP) is proportional to the square of the fluid velocity through the orifice.
• Flow Rate Calculation: Using Bernoulli’s equation, the differential pressure (ΔP) is related to the fluid flow rate (Q). By applying the appropriate fluid properties, such as density and fluid characteristics, and using equations or flow coefficient charts, the flow rate can be calculated.
• Calibration and Correction: Orifice meters require calibration to establish a relationship between the differential pressure and the actual flow rate. Calibration factors, such as discharge coefficient and expansion factor, are applied to correct for the flow profile, fluid properties, and other factors that may affect the accuracy of the measurement.
• Data Interpretation: The differential pressure measurement and calibration factors are used to determine the actual flow rate of the fluid through the orifice meter. The flow rate can be displayed, recorded, or used for further process control or analysis.

It’s important to note that the accuracy of the flow measurement with an orifice meter depends on various factors such as the orifice plate design, flow conditions, fluid properties, and the accuracy of pressure measurement instruments. Proper installation, calibration, and adherence to recommended guidelines are crucial for obtaining accurate flow measurements using an orifice meter.

Orifice Meter or Plate Types

Apologies for the confusion in my previous response. You are correct. There are various types of orifice plates used in orifice meters. Here are the four commonly used types:

• Eccentric Orifice Plate: An eccentric orifice plate is designed with the orifice opening offset from the center of the plate. This offset helps to reduce the effects of erosion and clogging by allowing debris or particulate matter to pass through without directly impacting the orifice. It is often used in applications where the fluid may contain solids or particles.
• Conical Orifice Plate: A conical orifice plate has a conical-shaped orifice hole, with the diameter gradually reducing in the downstream direction. This design helps in minimizing the pressure recovery losses and provides a smoother flow transition, reducing the potential for flow disturbances and turbulence.
• Sharp-Edged Orifice Plate: A sharp-edged orifice plate has a circular orifice opening with a sharp, straight edge. It is the most common and widely used type of orifice plate. The sharp edge creates a distinct and well-defined flow restriction, allowing for accurate measurement of flow rates. However, it is more prone to erosion and can be affected by fluid properties, such as viscosity.
• Segmental Orifice Plate (Quadrant Orifice Plate): A segmental or quadrant orifice plate is designed with a segment of the circular orifice removed, creating a semi-circular orifice opening. This design is primarily used in applications where the flow contains solids or viscous fluids. It helps to reduce the buildup of debris and provides better resistance to erosion.

Each type of orifice plate has specific advantages and considerations based on the fluid characteristics, flow conditions, and application requirements. The selection of the appropriate orifice plate type depends on factors such as the nature of the fluid, potential for erosion or clogging, desired accuracy, and maintenance considerations.

Orifice Meter hydraulic coefficient

The orifice meter has four hydraulic coefficients that are commonly used to describe its performance. Here’s a brief explanation of each coefficient:

• Coefficient of Contraction (C): The coefficient of contraction represents the ratio of the minimum cross-sectional area of the orifice to the area of the pipe. It takes into account the contraction of the fluid stream as it passes through the orifice. The coefficient of contraction is denoted by the symbol “C” and is typically less than 1.
• Coefficient of Velocity (Cv): The coefficient of velocity is a dimensionless parameter that relates the actual velocity of the fluid at the vena contracta (the point of maximum constriction) to the theoretical velocity based on the cross-sectional area of the orifice. It accounts for the change in fluid velocity as it passes through the orifice. The coefficient of velocity is denoted by the symbol “Cv” and is also typically less than 1.
• Coefficient of Resistance (Cr): The coefficient of resistance is a measure of the pressure loss or resistance caused by the orifice plate in the fluid flow. It represents the ratio of the pressure drop across the orifice to the dynamic pressure of the fluid. The coefficient of resistance is denoted by the symbol “Cr” and is dimensionless.
• Coefficient of Discharge (Cd or Cc): The coefficient of discharge, sometimes referred to as the coefficient of discharge (Cd) or coefficient of contraction (Cc), relates the actual flow rate through the orifice to the theoretical flow rate based on the cross-sectional area of the orifice. It takes into account the combined effect of the contraction and velocity factors. The coefficient of discharge is denoted by either “Cd” or “Cc” and is typically less than 1.

These coefficients are determined through calibration and are used in the calculation of flow rates in an orifice meter. They vary depending on factors such as the design of the orifice plate, flow conditions, and fluid properties. Proper calibration and application of these coefficients are crucial for accurate flow measurement using an orifice meter.

Orifice Meter Derivation or Experiment

The derivation of the orifice meter formula involves the application of Bernoulli’s equation and the conservation of mass principle. Here’s a brief explanation of the derivation:

• Bernoulli’s Equation: Bernoulli’s equation relates the pressure, velocity, and elevation of a fluid in a streamline. For an incompressible fluid flowing through a pipe with no elevation change, the equation can be simplified to:

P + 0.5ρv^2 = constant

Where P is the pressure, ρ is the density of the fluid, and v is the velocity of the fluid.

• Conservation of Mass: According to the conservation of mass principle, the mass flow rate (m_dot) through a pipe is constant. The mass flow rate is given by:

m_dot = ρ * A * v

Where A is the cross-sectional area of the pipe and v is the velocity of the fluid.

• Application of Bernoulli’s Equation: Consider a fluid flowing through a pipe with an orifice plate. The fluid approaches the orifice with a certain velocity (v1) and pressure (P1) and passes through the orifice, resulting in a velocity (v2) and pressure (P2) downstream.

Applying Bernoulli’s equation to the upstream and downstream sections, neglecting elevation changes, and assuming no energy losses, we have:

P1 + 0.5ρv1^2 = P2 + 0.5ρv2^2

• Pressure Differential: The pressure differential (ΔP) across the orifice is given by:

ΔP = P1 – P2

Rearranging the Bernoulli’s equation, we get:

ΔP = 0.5ρ(v1^2 – v2^2)

• Substituting the Mass Flow Rate: Substituting the expression for mass flow rate into the pressure differential equation, we have:

ΔP = 0.5 * (m_dot / A) * (v1 + v2) = 0.5 * ρ * A * (v1 + v2) * (v1 – v2)

• Coefficient of Discharge: The coefficient of discharge (Cd) is introduced to account for the effects of the orifice plate geometry and flow conditions. It is defined as the ratio of the actual flow rate (Q) to the theoretical flow rate based on the orifice area (A). Therefore, Q = Cd * A * √(2ΔP / ρ).

Combining the equations, we arrive at the final orifice meter formula:

Q = Cd * A * √(2ΔP / ρ)

This equation allows us to calculate the flow rate through an orifice meter using the known values of Cd, A, ΔP, and ρ.

It’s important to note that the derivation and formula assume ideal conditions and may require adjustments and corrections for real-world factors and specific applications. Additionally, calibration of the orifice meter is necessary to determine the actual value of Cd for accurate flow measurements.

Orifice Meter Formula

The flow rate through an orifice meter can be calculated using the following formula:

Where: Q is the flow rate (volume per unit time, such as cubic meters per second) Cd is the coefficient of discharge A is the area of the orifice opening ΔP is the pressure differential across the orifice ρ is the density of the fluid

In this formula, Cd represents the combined effect of the coefficient of contraction, coefficient of velocity, and other factors that influence the flow measurement accuracy. The value of Cd is typically determined through calibration.

To use the formula, you need to ensure that the units of measurement are consistent. For example, the area A should be in square meters, the pressure differential ΔP in Pascals, and the density ρ in kilograms per cubic meter.

It’s important to note that the orifice meter formula assumes certain ideal conditions, such as a fully developed flow profile, negligible pipe friction losses, and incompressible fluid flow. In practical applications, corrections and adjustments may be required to account for real-world factors and improve the accuracy of the flow measurement.

application of orifice meter

The orifice meter is a commonly used device for measuring the flow rate of fluids, particularly in industrial and process control applications. Here are some key applications of orifice meters:

• Flow Measurement in Pipelines: It is widely used for measuring the flow rate of liquids, gases, and steam in pipelines. They can be installed in various industries such as oil and gas, chemical, power generation, water treatment, and HVAC systems. Orifice meters provide a cost-effective solution for measuring flow rates and are relatively easy to install and maintain.
• Process Control: It play a crucial role in process control by providing accurate and reliable flow measurements. They are often integrated into control systems to monitor and regulate the flow of fluids in industrial processes. By measuring the flow rate, orifice meters help ensure proper process control, optimize efficiency, and maintain product quality.
• Energy Management: It is used in energy management systems to measure the flow of steam, gas, or liquids in power plants and industrial facilities. Accurate flow measurement enables operators to track energy consumption, identify potential energy losses, and optimize energy usage.
• Custody Transfer: In industries where the accurate measurement of fluid flow is critical for financial transactions, such as oil and gas production, custody transfer applications utilize orifice meters. These meters provide precise measurements that can be used for billing purposes between different entities involved in the transfer of fluids.
• Environmental Monitoring: It can be employed in environmental monitoring applications to measure the flow rate of various gases and liquids. This is particularly important in wastewater treatment plants, air pollution monitoring stations, and other environmental control systems.
• Research and Development: It is often used in research and development settings to study fluid dynamics and conduct experiments involving flow rate measurements. They provide researchers with valuable data on fluid behavior, pressure differentials, and flow characteristics.

It’s worth noting that while orifice meters are widely used, they do have limitations and may not be suitable for certain applications. Factors such as fluid properties, pressure conditions, and required accuracy should be considered when selecting a flow measurement device.

advantages of orifice meter

Here are some advantages of using orifice meters:

• Cost-Effective: It is relatively inexpensive compared to other flow measurement devices, making them a cost-effective choice for many applications. Their simple design and construction contribute to their affordability.
• Wide Range of Applications: It can be used to measure the flow rate of various fluids, including liquids, gases, and steam. They are suitable for a wide range of industries, such as oil and gas, chemical, power generation, and water treatment.
• Simple Installation: It is straightforward to install and can be easily integrated into existing pipelines or process systems. They typically require minimal space and have a compact design.
• Low Maintenance: It has a simple design with no moving parts, reducing the need for frequent maintenance or calibration. This results in lower maintenance costs and increased operational efficiency.
• Reliable and Accurate: It offer reliable and accurate flow measurements when properly installed and calibrated. They provide consistent results over time, making them a trusted choice for many industrial applications.
• Wide Range of Sizes: It is available in a wide range of sizes to accommodate various flow rates. This flexibility allows for customization based on specific application requirements.
• Wide Availability: It is widely available from multiple manufacturers, making them easily accessible for procurement and replacement purposes.
• Compatibility with Different Fluids: It can be used with a wide range of fluids, including corrosive and abrasive substances. By selecting appropriate materials for construction, they can withstand challenging fluid conditions.
• Pressure and Temperature Measurement: In addition to flow rate measurement, orifice meters can provide valuable information about the pressure and temperature of the fluid being measured, contributing to a more comprehensive understanding of the process.

It’s important to note that while orifice meters offer several advantages, they also have limitations. These include pressure drop across the meter, sensitivity to pipe conditions, and potential inaccuracies in the presence of pulsating flows or non-uniform velocity profiles. Proper installation, calibration, and consideration of these limitations are necessary for accurate and reliable measurements.

disadvantages of orifice meter

Certainly! Here are some disadvantages of using orifice meters:

• Pressure Drop: It create a pressure drop in the fluid flow due to the restriction caused by the orifice plate. This pressure drop can result in energy loss in the system, especially in applications where maintaining high fluid pressure is crucial.
• Turndown Ratio Limitation: It has a limited turndown ratio, which refers to the range of flow rates they can accurately measure. Operating the meter outside its specified turndown range can lead to decreased accuracy and reliability of the measurements.
• Sensitivity to Fluid Properties: It can be sensitive to changes in fluid properties such as viscosity, density, and temperature. Variations in these properties can affect the accuracy of the flow measurements. Compensation factors or corrections may be required to account for such changes.
• Flow Condition Requirements: It require specific flow conditions, particularly a fully developed flow profile with uniform velocity distribution across the pipe cross-section, for accurate measurements. Flow disturbances, such as turbulence or swirl, can lead to inaccuracies.
• Potential for Plugging or Fouling: It can be susceptible to plugging or fouling when used with fluids containing suspended solids, debris, or contaminants. These obstructions can affect the accuracy of the measurements and require regular maintenance or cleaning.
• Installation and Piping Considerations: The accuracy of orifice meter measurements can be influenced by the installation conditions, such as the presence of upstream and downstream piping configurations, valves, elbows, or reducers. These factors can introduce flow disturbances and affect the meter’s performance.
• Limited Range of Fluids: While orifice meters are compatible with a wide range of fluids, certain types of fluids, such as highly corrosive or erosive substances, may require special materials or coatings for the orifice plate and other components, increasing the cost and complexity of the meter.
• Calibration Requirements: It need periodic calibration to ensure accurate measurements. This involves removing the meter from the pipeline and conducting calibration tests using a reference standard. Calibration can be time-consuming and may require specialized equipment and expertise.
• Non-Linear Flow Profile: It inherently create a non-linear flow profile downstream of the orifice plate, with the highest velocity at the center and lower velocities near the pipe walls. This non-linear profile can affect the accuracy of the measurements, especially if the flow rate is low.

Understanding these disadvantages and their potential impact on specific applications is crucial when selecting and using orifice meters. Proper installation, regular maintenance, and adherence to recommended guidelines can help mitigate these limitations and ensure accurate flow measurements.

orifice meter is used to measure

An orifice meter is primarily used to measure the flow rate of fluids, such as gases or liquids, through a pipeline or duct. By measuring the pressure drop across the orifice plate, the flow rate can be determined using empirical equations or standardized tables. The orifice meter provides a cost-effective and widely used method for flow measurement in various industries, including oil and gas, chemical, and water utilities.

Orifice Meter Specification

Orifice meters typically have specific specifications that define their design and performance characteristics. Here are some common specifications associated with orifice meters:

• Orifice Plate Size: The orifice plate size refers to the diameter of the orifice opening. It is specified based on the pipe size and the desired flow range. Common sizes range from a few millimeters to several inches.
• Material of Construction: The material of construction for the orifice plate and other components of the orifice meter is specified based on factors such as the fluid being measured, temperature, pressure, and corrosiveness of the environment. Common materials include stainless steel, carbon steel, brass, and various alloys.
• Pressure Rating: The pressure rating indicates the maximum pressure that the orifice meter can withstand without compromising its integrity. It is specified in units of pressure, such as PSI (pounds per square inch) or bar.
• Accuracy Class: The accuracy class defines the level of accuracy that can be achieved with the orifice meter. It specifies the acceptable level of deviation between the measured flow rate and the actual flow rate. Common accuracy classes include ±0.5%, ±1.0%, and ±2.0%.
• Temperature Range: The temperature range specifies the minimum and maximum temperatures at which the orifice meter can operate effectively and reliably. It is important to ensure that the orifice meter is suitable for the temperature range of the fluid being measured.
• Flow Range: The flow range indicates the minimum and maximum flow rates that the orifice meter is designed to measure accurately. It is typically specified in units of volume per unit of time, such as liters per minute or cubic meters per hour.
• Installation Requirements: The orifice meter specifications may include installation requirements such as the recommended length of straight pipe sections upstream and downstream of the orifice plate, flow conditioning elements, and alignment considerations.
• Calibration and Certification: Orifice meters may require periodic calibration to maintain their accuracy. Specifications may include details about calibration procedures, frequency, and traceability to national or international standards. Some orifice meters may also come with certification documents to demonstrate compliance with specific industry standards or regulations.

It’s important to note that specific orifice meter specifications may vary depending on the manufacturer, application, and industry requirements. It is advisable to consult the manufacturer’s documentation or industry standards for the precise specifications of a particular orifice meter.

Reference : https://www.sciencedirect.com/topics/engineering/orifice-meter

Sanjeev Kumar

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VENTURI METER AND ORIFICE PLATE LAB REPORT

Venturi meter effect and orifice plate effects are two main and very important phenomena in the fluid mechanics sub-field of mechanical engineering. 

In this post, the effect of the venturi meter and orifice plate on the fluid flow will be discussed and complete work will be presented in the form of a report. 

According to Michael Reader-Harris (n.d), a Venture meter is an instrument used to study the flow of fluid when it passes through the converging section. 

There is an increase in the velocity and decrease in the pressure of the flowing fluid when the area available to flowing fluid decreases, this effect is called the venture effect named after the physicist who first introduces this theory. 

According to Michael Reader-Harris (n.d), an Orifice plate is an instrument used for three different applications one to measure the flow rate, second to restrict the flow, ad third to reduce the pressure of the flowing fluid. 

It depends on the orifice plate-associated calculation method that either the mass flow rate or the volumetric flow rate is used for calculation. 

It uses the Bernoulli experiment which shows the relationship between velocity and pressure for a flow of fluid . When one increases then the second one decrease.

• The Thin Plate, Concentric Orifice
• Eccentric Orifice Plates
• Segmental Orifice Plates
• Quadrant Edge Plate
• Conic Edge Plate

Theory of  Venturi Meter and Orifice Plate

Procedure  venturi meter and orifice plate.

To set up the orifice tube and venture meter apparatus two tubes were connected one on each of the outlet and inlet of the apparatus. 

The tube which was connected to the venture meter outlet was further connected to the measuring tank. 

To level the orifice meter and venture tube apparatus, adjustable screws are provided at the apparatus.

The apparatus was connected to the power source to run the motor for the water supply. The bench valve and the control valve of the apparatus were open to let the water move into the tube and to remove all the air pockets.

To raise the water level in the manometer tubes the control valve was closed gradually and when the height of the water level was enough high then the bench valve was gradually closed. 

With both valves closed there was static water in the meter at a moderate pressure

The flow rate of the water was recorded and the height of the water level was also recorded in all the tubes

The difference between the heights of the water level and the flow rate will change upon opening any one of the apparatus valves. 

The flow rate was calculated by noticing the time required to fill the tank of a known weight and at the same time the level of the water in the manometer tubes was also recorded

The same process is repeated for different flow rates

Sample Calculations for Venturi Meter and Orifice Plate

Experimental results  venturi meter and orifice plate.

Discussion Venturi Meter and Orifice Plate

2. Result shows that with a decrease in the flow rate, the value of the ∆h also decreases. So it can be said from the results that the difference in the height of the water level is directly proportional to the flow rate.

3. Change in the height of the water column of the venture meter is much less than the change in the height of the water column in the orifice plate this is because the difference in diameter of the areas of the orifice is much more than the venture meter. 

So we can say that the difference in height of the water column is directly proportional to the difference in the diameter of the area.

Conclusion  Venturi Meter and Orifice Plate

An experiment was conducted to find the overall meter coefficient C in the venture meter and orifice tube and results show that the flow rate and ∆h are directly proportional to each other and along with this ∆h and the ∆d are also directly proportional to each other. Both these things are important as they are used to calculate the overall meter coefficient C

4 comments:

error analysis?

NICE INFORMATION

Thank you so much. This will really help with my Lab report!!

Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Orifice, Nozzle and Venturi Flow Rate Meters

The orifice, nozzle and venturi flow rate meters makes the use of the bernoulli equation to calculate fluid flow rate using pressure difference through obstructions in the flow..

In a flow metering device based on the Bernoulli Equation the downstream pressure after an obstruction will be lower than the upstream pressure before. To understand orifice, nozzle and venturi meters it is necessary to explore the Bernoulli Equation.

• The Bernoulli Equation

Assuming a horizontal flow (neglecting the minor elevation difference between the measuring points) the Bernoulli Equation can be modified to:

p 1 + 1/2 ρ v 1 2 = p 2 + 1/2 ρ v 2 2                             (1) where p = pressure  (Pa, psf (lb/ft 2 )) ρ = density   (kg/m 3 , slugs /ft 3 ) v = flow velocity (m/s, ft/s)

The equation can be adapted to vertical flow by adding elevation heights :

p 1 + 1/2 ρ v 1 2 + γ h 1 = p 2 + 1/2 ρ v 2 2 + γ h 2                      (1b)

γ = specific weight of fluid (kg/m 3 , slugs/ft 3 )

h = elevation (m, ft)

Assuming uniform velocity profiles in the upstream and downstream flow - the Continuity Equation can be expressed as

q = v 1 A 1 = v 2 A 2                                   (2) where q = flow rate   (m 3 /s, ft 3 /s) A = flow area   (m 2 , ft 2 )

Combining (1) and (2) , assuming A 2 < A 1 , gives the "ideal" equation:

q = A 2 [ 2(p 1 - p 2 ) /ρ(1 -(A 2 / A 1 ) 2 ) ] 1/2                                  (3)

For a given geometry (A) , the flow rate can be determined by measuring the pressure difference p 1 - p 2 .

The theoretical flow rate q will in practice be smaller ( 2 - 40% ) due to geometrical conditions.

The ideal equation (3) can be modified with a discharge coefficient:

q = c d A 2 [ 2 (p 1 - p 2 ) /ρ (1 -(A 2 / A 1 ) 2 ) ] 1/2                                   (3b) where c d = discharge coefficient

The discharge coefficient c d is a function of the jet size - or orifice opening - the

area ratio = A vc / A 2 where A vc = area in "vena contracta"   (m 2 , ft 2 )

" Vena Contracta " is the minimum jet area that appears just downstream of the restriction. The viscous effect is usually expressed in terms of the non-dimensional parameter Reynolds Number - Re .

Due to the Benoulli and the Continuity Equation the velocity of the fluid will be at it's highest and the pressure at the lowest in " Vena Contracta ". After the metering device the velocity will decrease to the same level as before the obstruction. The pressure recover to a pressure level lower than the pressure before the obstruction and adds a head loss to the flow.

Equation (3) can be modified with diameters to:

q = c d (π / 4) D 2 2 [ 2 (p 1 - p 2 ) / ρ (1 - d 4 ) ] 1/2                                       (4) where D 2 = orifice, venturi or nozzle inside diameter (m, ft) D 1 = upstream and downstream pipe diameter  (m, ft) d = D 2 / D 1 diameter ratio π = 3.14...

Equation (4) can be modified to mass flow for fluids by simply multiplying with the density:

m = c d (π / 4) D 2 2 ρ [ 2 (p 1 - p 2 ) / ρ (1 - d 4 ) ] 1/2                                     (5) where m = mass flow (kg/s)

When measuring the mass flow in gases, its necessary to considerate the pressure reduction and change in density of the fluid. The formula above can be used with limitations for applications with relatively small changes in pressure and density.

The Orifice Plate

The orifice meter consists of a flat orifice plate with a circular hole drilled in it. There is a pressure tap upstream from the orifice plate and another just downstream. There are in general three methods for placing the taps. The coefficient of a meter depends on the position of the taps.

• Flange location - Pressure tap location 1 inch upstream and 1 inch downstream from face of orifice
• " Vena Contracta " location - Pressure tap location 1 pipe diameter (actual inside) upstream and 0.3 to 0.8 pipe diameter downstream from face of orifice
• Pipe location - Pressure tap location 2.5 times nominal pipe diameter upstream and 8 times nominal pipe diameter downstream from face of orifice

The discharge coefficient - c d - varies considerably with changes in area ratio and the Reynolds number . A discharge coefficient c d = 0.60 may be taken as standard, but the value varies noticeably at low values of the Reynolds number.

The pressure recovery is limited for an orifice plate and the permanent pressure loss depends primarily on the area ratio. For an area ratio of 0.5 the head loss is about 70 - 75% of the orifice differential.

• The orifice meter is recommended for clean and dirty liquids and some slurry services.
• The rangeability is 4 to 1
• The pressure loss is medium
• Typical accuracy is 2 to 4% of full scale
• The required upstream diameter is 10 to 30
• The viscosity effect is high
• The relative cost is low

Example - Orifice Flow

An orifice with diameter D 2 = 50 mm is inserted in a 4" Sch 40 steel pipe with inside diameter D 1 = 102 mm . The diameter ratio can be calculated to

d = (50 mm) / (102 mm)

  = 0.49

From the table above the discharge coefficient can be estimated to approximately 0.6 for a wide range of the Reynolds number.

If the fluid is water with density 1000 kg/m 3 and the pressure difference over the orifice is 20 kPa (20000 Pa, N/m 2 ) - the mass flow through the pipe can be calculated from (5) as

m = 0.6 (π / 4) (0.05 m) 2 (1000 kg/m 3 ) [ 2 (20000 Pa) / (1000 kg/m 3 ) (1 - 0.49 4 ) ] 1/2      

   = 7.7 kg/s

Orifice Calculator

The orifice calculator is based on eq. 5 and can be used to calculate mass flow through an orifice.

c d - discharge coefficient

D 2 - orifice diameter (m)

D 1 - pipe diameter (m)

p 1 - upstream pressure (Pa)

p 2 - downstream pressure (Pa)

ρ - density of fluid (kg/m 3 )

Typical Orifice K v Values

• American Society of Mechanical Engineers (ASME). 2001. Measurement of fluid flow using small bore precision orifice meters. ASME MFC-14M-2001.
• International Organization of Standards (ISO 5167-1:2003). Measurement of fluid flow by means of pressure differential devices, Part 1: Orifice plates, nozzles, and Venturi tubes inserted in circular cross-section conduits running full. Reference number: ISO 5167-1:2003.
• International Organization of Standards (ISO 5167-1) Amendment 1. 1998. Measurement of fluid flow by means of pressure differential devices, Part 1: Orifice plates, nozzles, and Venturi tubes inserted in circular cross-section conduits running full. Reference number: ISO 5167-1:1991/Amd.1:1998(E).
• American Society of Mechanical Engineers (ASME). B16.36 - 1996 - Orifice Flanges

The Venturi Meter

In the venturi meter the fluid is accelerated through a converging cone of angle 15-20 o and the pressure difference between the upstream side of the cone and the throat is measured and provides a signal for the rate of flow.

The fluid slows down in a cone with smaller angle ( 5 - 7 o ) where most of the kinetic energy is converted back to pressure energy. Because of the cone and the gradual reduction in the area there is no "Vena Contracta". The flow area is at a minimum at the throat. High pressure and energy recovery makes the venturi meter suitable where only small pressure heads are available.

A discharge coefficient c d = 0.975 can be indicated as standard, but the value varies noticeably at low values of the Reynolds number .

The pressure recovery is much better for the venturi meter than for the orifice plate.

• The venturi tube is suitable for clean, dirty and viscous liquid and some slurry services.
• Pressure loss is low
• Typical accuracy is 1% of full range
• Required upstream pipe length 5 to 20 diameters
• Viscosity effect is high
• Relative cost is medium
• International Organization of Standards - ISO 5167-1:2003 Measurement of fluid flow by means of pressure differential devices, Part 1: Orifice plates, nozzles, and Venturi tubes inserted in circular cross-section conduits running full. Reference number: ISO 5167-1:2003.
• American Society of Mechanical Engineers ASME FED 01-Jan-1971. Fluid Meters Their Theory And Application- Sixth Edition

Nozzles used for determining fluid's flowrate through pipes can be in three different types:

• The ISA 1932 nozzle - developed in 1932 by the International Organization for Standardization or ISO. The ISA 1932 nozzle is common outside USA.
• The long radius nozzle is a variation of the ISA 1932 nozzle.
• The venturi nozzle is a hybrid having a convergent section similar to the ISA 1932 nozzle and a divergent section similar to a venturi tube flowmeter.

• The flow nozzle is recommended for both clean and dirty liquids
• The relative pressure loss is medium
• Typical accuracy is 1-2% of full range
• Required upstream pipe length is 10 to 30 diameters
• The viscosity effect high
• The relative cost is medium

Example - Kerosene Flow Through a Venturi Meter

The pressure difference dp = p 1 - p 2 between upstream and downstream is 100 kPa (1 10 5 N/m 2 ) . The specific gravity of kerosene is 0.82 .

Upstream diameter is 0.1 m and downstream diameter is 0.06 m .

Density of kerosene can be calculated as:

ρ = 0.82 (1000 kg/m 3 )     = 820 (kg/m 3 )

• Density, Specific Weight and Specific Gravity - An introduction and definition of density, specific weight and specific gravity. Formulas with examples.

Upstream and downstream area can be calculated as:

A 1 = π ((0.1 m)/2) 2     = 0.00785 (m 2 ) A 2 = π  ((0.06 m)/2) 2     = 0.002826 (m 2 )

Theoretical flow can be calculated from (3):

q = A 2 [ 2(p 1 - p 2 ) /ρ(1 -(A 2 /A 1 ) 2 ) ] 1/2 q = (0.002826 m 2 ) [2 (10 5 N/m 2 ) / (820 kg/m 3 )(1 - ( (0.002826 m 2 ) / (0.00785 m 2 ) ) 2 )] 1/2     = 0.047 (m 3 /s)

For a pressure difference of 1 kPa (0,01x10 5 N/m 2 ) - the theoretical flow can be calculated:

q = (0.002826 m 2 ) [2 (0.01 10 5 N/m 2 ) / (820 kg/m 3 )(1 - ( (0.002826 m 2 ) / (0.00785 m 2 ) ) 2 )] 1/2     = 0.0047 (m 3 /s)

The mass flow can be calculated as:

m = q ρ     = (0.0047 m 3 /s) (820 kg/m 3 )     = 3.85 (kg/s)

Flow Rate and Change in Pressure Difference

Note! - The flow rate varies with the square root of the pressure difference.

From the example above:

• a tenfold increase in the flow rate requires a one hundredfold increase in the pressure difference!

Transmitters and Control System

The nonlinear relationship have impact on the pressure transmitters operating range and requires that the electronic pressure transmitters have the capability to linearizing the signal before transmitting it to the control system.

Due to the non linearity the turn down rate is limited. The accuracy strongly increases in the lower part of the operating range.

• More about Flow Meters as Orifices, Venturi meters, and Nozzles
• Fluid Mechanics
• T he Continuity Equation
• TurnDown Ratio and Flow Measurement Devices - An introduction to Turn Down Ratio and flow measurement accuracy.

Related Topics

Flow measurements, related documents, california pipe flow metering method, comparing flowmeters, flowmeter - accuracy, flowmeters - turndown ratios, fluid flow - equation of continuity, fluid flowmeters - comparing types, jet propulsion, liquid flow from containers - emptying time, orifice air discharge vs. pressure, pitot tubes, steam flow - orifices, steam leaks through orifices, u-tube differential pressure manometers, velocity-area flowmetering.

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EXPERIMENT No.1 FLOW MEASUREMENT BY ORIFICEMETER

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Nithiaprathap Paneerselvam

ephrem dama

In this chapter, however, a method of expressing the loss using an average flow velocity is stated. Studies will be made on how to express losses caused by a change in the cross sectional area of a pipe, a pipe bend and a valve, in addition to the frictional loss of a pipe. Consider a case where fluid runs from a tank into a pipe whose entrance section is fully rounded. At the entrance, the velocity distribution is roughly uniform while the pressure head is lower by V 2 /2g. As shown in below Figure ,the section from the entrance to just where the boundary layer develops to the tube centre is called the inlet or entrance region, whose length is called the inlet or entrance length. For steady flow at a known flow rate, these regions exhibit the following: Laminar flow:A local velocity constant with time, but which varies spatially due to viscous shear and geometry. Turbulent flow: A local velocity which has a constant mean value but also has a statistically random fluctuating component due to turbulence in the flow. Typical plots of velocity time histories for laminar flow, turbulent flow, and the region of transition between the two are shown below .

Jemary Roca

Hernan Pita Benavides

boniface fidelis

Mohammed Ziauddin Ahmed

savery chhin

Mike Kabinga

Michael Johnson

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