orifice meter by Gulshan Athbhaiya .pptx

An orifice meter is a device used to measure the flow rate of a fluid (liquid or gas) in a pipe. It operates on the principle of differential pressure, which is derived from Bernoulli's theorem.

How It Works
An orifice meter consists of a thin circular plate with a hole, or orifice, in the center. This plate is installed inside a pipe.

When the fluid flows through the pipe, its velocity increases as it passes through the narrow opening of the orifice. This increase in velocity causes a corresponding drop in the fluid's pressure, which is measured by pressure taps located before and after the plate. The lowest pressure point is reached at a location slightly downstream of the orifice, known as the vena contracta.

By measuring this differential pressure across the orifice, the flow rate of the fluid can be calculated. The relationship between the flow rate and the pressure drop is described by a formula that incorporates a coefficient of discharge (C_d), which accounts for energy losses due to turbulence and friction.

Types of Orifice Plates and Applications
There are different types of orifice plates designed for specific applications:

Concentric plates: The most common type, used for clean liquids and gases.

Eccentric plates: Used for fluids containing non-abrasive solids or gases with some liquid, as the off-center hole allows for drainage.

Segmental plates: Ideal for fluids with a high concentration of solids or a second phase (like a slurry), as the segment shape minimizes the buildup of material.

Quadrant edge plates: Used for measuring viscous fluids at low Reynolds numbers.

Orifice meters are widely used in various industries, including petroleum refineries, water treatment plants, and natural gas transmission, due to their simple design and cost-effectiveness.

1. Orifice Meter By Gulshan Athbhaiya Assistant Professor, YBN University, Ranchi

2. An orifice meter is a device used to measure the flow rate of a fluid (liquid or gas) in a pipe. It works on the principle of differential pressure measurement based on Bernoulli's theorem . Bernoulli's theorem is a fundamental principle in fluid dynamics that describes the relationship between pressure, velocity, and height for a flowing fluid. It states that for a steady, incompressible, and non-viscous fluid flow, the sum of the fluid's pressure energy, kinetic energy, and potential energy per unit volume remains constant along a streamline. This principle is a direct application of the conservation of energy for a fluid in motion. As the fluid flows, any increase in its speed (kinetic energy) must be accompanied by a decrease in its pressure or potential energy. The Equation The mathematical expression of Bernoulli's theorem is the Bernoulli equation : P + 1/2pv 2 + pgh = constant Where: • P = static pressure of the fluid p = density of the fluid • v = velocity of the fluid g = acceleration due to gravity • h = height of the fluid from a reference point Each term in the equation represents a form of energy per unit volume: P: Pressure energy 1/2pv 2 : Kinetic energy pgh : Potential energy

3. An orifice meter is a device used to measure the flow rate of a fluid by creating a pressure drop across a specially designed plate inserted into a pipe. Its construction is centered around three main components: a straight pipe section, an orifice plate, and pressure taps. Orifice Plate This is the heart of the orifice meter. It's a thin, circular plate with a hole, or orifice , in the center. The plate is typically made of a strong material like stainless steel to withstand the pressure and fluid flow. The orifice's diameter is smaller than the pipe's diameter, which creates the necessary constriction. There are several types of orifice plates, each suited for different applications: Concentric Orifice Plate: The most common type. The hole is in the exact center of the plate, making it suitable for measuring the flow of clean, non-viscous liquids, gases, and steam. Eccentric Orifice Plate: The hole is offset from the center, positioned tangent to the inner wall of the pipe. This design helps prevent the buildup of solids or debris in fluids containing suspended particles. Segmental Orifice Plate: The hole is a segment of a circle. This is also used for fluids with a high concentration of solids or slurries. Quadrant-Edge Orifice Plate: The upstream edge of the hole is rounded. This design is specifically used for measuring the flow of viscous fluids at low Reynolds numbers.

4. Pressure Taps Pressure taps are small holes drilled into the pipe on either side of the orifice plate. They are connected to a differential pressure measuring instrument, like a manometer or a pressure transmitter, to measure the pressure difference. The location of these taps is crucial for accurate measurement and is standardized. The most common types are: Flange Taps: Located one inch upstream and one inch downstream of the orifice plate. This is the most popular configuration for large pipes. Vena Contracta Taps: The upstream tap is located about one pipe diameter before the plate, while the downstream tap is placed at the point of minimum pressure, known as the vena contracta . Corner Taps: Taps are placed immediately at the upstream and downstream faces of the orifice plate. They are typically used for smaller pipe diameters. Installation The orifice plate is typically installed between two pipe flanges, with the orifice fitting ensuring it is precisely centered within the pipe. For accurate measurements, it is essential to have a sufficiently long, straight run of pipe both before and after the orifice meter to ensure a fully developed flow profile and minimize turbulence caused by bends, valves, or other fittings.

5. How it Works The main component of an orifice meter is an orifice plate , which is a thin circular plate with a hole, or orifice, in the center. This plate is installed inside a pipe perpendicular to the flow of the fluid. As the fluid flows through the pipe, the orifice plate creates a constriction, forcing the fluid to accelerate as it passes through the smaller opening. According to Bernoulli's principle, as the velocity of the fluid increases, its static pressure decreases. Therefore, the pressure of the fluid just before the orifice is higher than the pressure at a point slightly downstream of the orifice, where the fluid velocity is at its maximum (a point known as the vena contracta ). This difference in pressure, or differential pressure, is measured by a manometer or a differential pressure transmitter connected to pressure taps on either side of the orifice plate. The flow rate of the fluid can then be calculated by correlating this differential pressure with the known characteristics of the orifice plate and the fluid.

6. Advantages Disadvantages Simple and Cost-Effective: It has a simple design and is relatively inexpensive to manufacture and install. Significant Pressure Loss: The sharp constriction causes a large pressure drop, which is not fully recovered downstream. This leads to energy loss in the system. Easy to Maintain: The orifice plate can be easily replaced or maintained. Low Discharge Coefficient: The coefficient of discharge is lower compared to other flow meters like a Venturi meter, indicating higher energy losses. Versatile: It can be used for a wide range of fluids, including liquids, gases, and steam. Different types of orifice plates (e.g., eccentric, segmental) can be used for specific applications like those with dirty fluids or slurries. Sensitivity to Fluid Properties: Its accuracy can be affected by changes in fluid properties such as viscosity and density. Standardized: Its design and calculations are standardized, making it a widely accepted and predictable method for flow measurement. Susceptibility to Clogging: The orifice plate can get clogged when measuring fluids with suspended particles.

7. Applications Orifice meters are used in various industries for process control and measurement, including: Oil and Gas: For measuring the flow of crude oil and natural gas. Water Treatment: To monitor flow rates in water treatment and distribution systems. Chemical and Petrochemical: For controlling the flow of various chemicals during production. Power Plants: For measuring the flow of steam and cooling water.

8. Thank You!