What is flow meter?
is a device that measures how much liquid or gas is passing through a pipe in a given time period.
By measuring flow rates, flow meters
provide important visibility into the direction of flow within pipelines, drainage systems, and other types of infrastructure. In turn, they help operators determine if a system is properly balanced, ensure that each endpoint is adequately supplied, identify excessive flow rates that could damage a pipe, and more.
Different types of flow meter
Rotameter is based on the throttling principle to measure the flow of fluid, but it is changing the fluid flow area to maintain a constant differential pressure above and below the rotor, so it is also known as a variable flow area constant differential pressure flowmeter, as well as float flowmeter.
Structure of rotameter
In a vertical conical tube expanding from bottom to top, the gravity of the float with a circular cross-section is carried by the liquid power, the float is free to rise and fall in the conical tube. In the flow rate and buoyancy under the action of up and down, and float weight balance, through the magnetic coupling transmitted to the flow rate indicated with the dial. Metal rotameter is the most commonly used in industry, for small pipe diameter corrosive media usually with glass material, due to the fragility of the glass material itself, the key control points are also used in full titanium and other precious metals for the material of the rotameter.
Rotor flowmeter is based on the float position measurement of a variable area flow meter. Its all-metal structure, and modular concept design, so its pressure loss is small, and the range ratio is large (10:1). At the same time, the instrument is easy to install and maintain, can be widely used in complex, harsh environments, and a variety of media conditions in the flow measurement and process control.
Feature of rotameter
Rotameter is the most common type of flow meter used in industry and laboratories. It has a simple structure, intuitive as well as small pressure loss, easy maintenance, and other characteristics. Rotor flowmeter is suitable for measuring the small flow through the pipe diameter D < 150mm, and can also measure the flow of corrosive media. When the use of flowmeter is generally installed in the vertical direction of the pipe section, the fluid medium from the bottom up through the rotor flowmeter, the rotor flowmeter by special design can be installed horizontally or on the bottom of the vertical installation.
Working principle of rotameter
Rotameter consists of two parts, one of which is a gradually expanding conical tube from the bottom up, and the other part is placed inside the conical tube and can move freely up and down along the centerline of the rotor inside the tube. When measuring the flow of fluid, the measured fluid from the lower end of the tapered tube of the rotameter, the flow of fluid impacting the rotor, and produces a force (the size of this force varies with the size of the flow); when the flow is large enough, the resulting force will lift the rotor, and make it rise. At the same time, the measured fluid flows through the annular section between the rotor and the tapered tube wall, when there are three forces acting on the rotor: a)the dynamic pressure of the fluid on the rotor, b) the buoyancy of the rotor in the fluid, c) the gravity of the rotor itself. When the flow meter is installed vertically, the center of gravity of the rotor and the tapered tube axis will coincide, and the three forces acting on the rotor are along the direction parallel to the tube axis. When these three forces are balanced, the rotor floats smoothly in a position within the cone tube. For a given rotor, the size and shape of the rotor has been determined, so its buoyancy in the fluid and its own gravity are known constants, and only the dynamic pressure of the fluid on the float varies with the magnitude of the incoming flow. Thus, as the inflowing flow velocity becomes larger or smaller, the rotor will move up or down and the flow cross-sectional area at the corresponding position changes until the flow velocity becomes the corresponding velocity at equilibrium and the rotor stabilizes in its new position. For a given rotor, the position of the rotor in the conical tube corresponds to the magnitude of the fluid flow through the conical tube.
To make the rotor in the center line of the tapered tube up and down movement does not touch the wall, usually using two methods: one is equipped with a guide mandrel in the center of the rotor to keep the rotor in the center line of the tapered tube for up and down movement, the other is in the rotor disc edge open a slanting groove when the fluid flows through the rotor from the bottom up, one side around the rotor, and at the same time through the slanting groove to produce a counter-thrust, so that the rotor around the center line Non-stop rotation, you can keep the rotor in the work does not touch the wall. Rotor flowmeter rotor material can be made of stainless steel, aluminum, bronze, etc.
Venturi meter is a commonly used device to measure the flow of pressurized pipes, is a differential pressure flowmeter. It is commonly used to measure the flow of air, natural gas, gas, water, and other fluids. It includes 3 parts, which are installed in the need to measure the flow of the pipe.
Working principle of Venturi meter
As a new generation of differential pressure flow measurement instruments, the basic measurement principle of the Venturi meter is based on the law of energy conservation - Burr's Equation of Effort and the flow continuity equation. The inner Venturi consists of a circular measuring tube and a special core placed inside and coaxial to the measuring tube. The radially outer surface of the special core has a similar geometric profile to the inner surface of the classic venturi, and the inner surface of the measuring tube constitutes a reducer ring-shaped overflow gap. The fluid flow through the inner venturi tube throttling process with the fluid flow through the classic venturi tube, annular orifice plate throttling process is basically similar. This structural feature of the inner venturi makes it not exist in the process of using similar orifice plate throttle sharp edge abrasion and dirt accumulation problems and can be effective flow adjustment (rectification) of the fluid velocity distribution gradient and the possible existence of various non-axisymmetric velocity distribution in the tube before throttling, so as to achieve high accuracy and high stability of flow measurement.
Air flow meter
Air flow meter is a device that measures airflow, i.e., how much air flows through a tube. It does not measure the amount of air passing through the tube, but the amount of air flowing through the device per unit of time. Thus, an airflow meter is just one application of a mass flow meter for a particular medium. Typically, the units in air mass flow measurement are expressed in kilograms per second (kg/s).
Air meters are used in many manufacturing processes to monitor air (compressed, forced or ambient air). In many industries, preheated air (called "combustion air") is added to boiler fuel before the fuel ignites to ensure the proper ratio of fuel to air to produce an effective flame. Pharmaceutical plants and coal pulverizers use forced air as a means of forcing particle movement or ensuring a dry atmosphere. Airflow is also monitored in mining and nuclear environments to ensure personnel safety.
Working principle of air flow meter
In the use of an air flow meter, the gas flow through the meter pushes the turbine blades to rotate. The number of impeller revolutions is proportional to the volume of gas passing through the air meter. A specially designed, patented deflector frame is installed at the inlet of the meter to accelerate the gas flow into the meter as the flow rate increases. The design of the guide frame eliminates any potential fluid disturbances, such as vortex or asymmetric flow. The push on the turbine blades is also increased at the same time. This ensures that the flowmeter measures with high accuracy within the allowable error range, even in low flow conditions. The flow acting on the turbine blades is axial and the turbine is mounted on the main drive shaft, which is equipped with high-strength ball bearings. After the gas passes through the turbine blades, the rotation of the turbine blades is decelerated by the gear set. The pressure in the inlet channel of the air flow meter is returned, and the channel design ensures the optimal flow pattern.
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