Do you know what anemometers are used for
The basic principle of an anemometer is to place a thin metal wire in a fluid and heat the wire with an electric current to make its temperature higher than the temperature of the fluid. Therefore, a metal wire anemometer is called a "hot wire". When the fluid flows through the metal wire in a vertical direction, it will take away some of the heat from the wire, causing the temperature of the wire to decrease.
The purpose of the anemometer is:
1. Measure the average velocity and direction of flow.
2. Measure the pulsating velocity of incoming flow and its spectrum.
3. Measure the Reynolds stress in turbulence and the velocity and time correlation between two points.
4. Measure wall shear stress (usually using a hot film probe placed flush with the wall, similar to the principle of hot wire velocity measurement).
5. Measure fluid temperature (by measuring the change curve of probe resistance with fluid temperature in advance, and then determining the temperature based on the measured probe resistance).
Introduction to the classification of anemometers
1. Wind cup anemometer
It is the most common type of anemometer. The rotary anemometer was first invented by Robinson in England, with four cups at the time and later changed to three cups. Three parabolic or hemispherical empty cups fixed on the frame with mutual complementarity are all aligned on one side, and the entire frame, along with the air cup, is mounted on a freely rotating axis. Under the action of wind, the wind cup rotates around its axis, and its speed is proportional to the wind speed. The speed can be recorded using electrical contacts, speed measuring generators, or photoelectric counters.
2. Propeller anemometer
It is an anemometer with a set of three or four bladed propellers rotating around the horizontal axis. The propeller is installed at the front of a wind vane, so that its rotating plane is always facing the direction of the incoming wind speed, and its speed is proportional to the wind speed.
3. Hot wire anemometer
A metal wire heated by an electric current is dissipated by the flowing air. The heat dissipation rate is linearly related to the square root of the wind speed, and then linearized through an electronic circuit (for easy calibration and reading) to create a hot wire anemometer. There are two types of hot wire wind speed scoring: side heating and direct heating. A side heating hot wire is usually made of manganese copper wire, with a resistance temperature coefficient close to zero. It is also equipped with a temperature measuring element on its surface. Direct heating hot wires are mostly platinum wires, which can directly measure the temperature of the hot wire itself while measuring wind speed. Hotwire anemometers have high sensitivity at low wind speeds and are suitable for measuring small wind speeds. Its time constant is only a few percent of a second, making it an important tool for atmospheric turbulence and agricultural meteorological measurements.
