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Differential Pressure Flow Measurement
Nov 21, 2019

1.       General description

Differential pressure flow measurement (differential pressure flow) is one of the most common techniques for measuring flow in a closed pipe. There are many reasons why differential pressure flow technology is widely used.

1)     The technology is based on well-known laws of physics, especially the laws of physics relating to fluid dynamics and mass transfer phenomena;

2)      A long history of use has also contributed to the development of standards for the manufacture and use of differential pressure flow meters;

3)     Manufacturers offer a wide range of options for general purpose and specialty instrumentation and installation options;

4)     Differential pressure flow technology for high accuracy and repeatability.

2.       The history of differential pressure flow

The flow measurement originated thousands of years ago, when the Egyptians began to make a rough prediction of the harvest based on the relative height of the spring flood of the Nile. Later, the Romans designed ditches to provide drinking water to the city, so the need to monitor steady flow became important. The operator roughly measures the flow using the flow through the orifice or the obstacle well. The marking on the wall of the fluid medium, the flow intensity through the orifice, etc. gives a rough flow measurement. Newton discovered the law of universal gravitation in 1687, which led physicists and mathematicians to put forward theories about motion and force, and finally promoted the development of quantitative flow.

Bernoulli principle

Daniel Bernoulli is a Swiss mathematician who studies fluid mechanics. His work is centered on energy conservation and has achieved a critical breakthrough for the first time in the development of flow measurement technology. He discovered the Bernoulli principle, which states that the sum of the energy in the flow must remain constant regardless of the conditions. This means that the sum of the static energy (pressure), kinetic energy (flow rate) and potential energy (altitude) of the upstream and downstream are equal, especially the differential pressure flow.

Reynolds number

Osbourne Reynolds is not a physicist, but a mechanic. The most famous is his research on the fluid flow in the pipeline, more specifically the flow transition between laminar flow and turbulent flow. The Reynolds number is a numerical quantification of the ratio of inertial force to viscous force. In short, the Reynolds number describes the flow characteristics of a fluid. The Reynolds number is a key concept in the design of flow meters and can be used as a constraint on the flowmeter's range of applications.

3.       Pressure

What is stress? Pressure refers to the amount of force acting on a specified area.

1)     When the force increases or the area decreases, the pressure increases;

2)     When the force is reduced or the area is increased, the pressure is reduced;

3)     Measuring pressure helps prevent excessive pressure on the equipment and causes damage;

4)     Measuring pressure helps prevent accidental pressure or pressure release, causing personal injury.

Why measure pressure?

1)     safety

2)     Process efficiency

3)     save costs

Safety: Pressure measurement helps prevent overpressure on pipes, tanks, valves, flanges and other equipment, minimizes equipment damage, controls liquid level and flow, and helps prevent accidental pressure or pressure Release and personal injury.

Process efficiency: In most cases, productivity is highest when pressure (and other process variables) are maintained at a specific value or within a small range of values.

Cost savings: Pressure or vacuum equipment (eg pumps and compressors) consume a lot of energy. Energy cost savings can be reduced through pressure optimization.