The fundamental idea behind and use of a thermal anemometer
One: The basic principle of thermal anemometer:
1. A thin metal wire is placed in the fluid, and the wire is heated by current to make its temperature higher than the temperature of the fluid, so the wire anemometer is called. When the fluid flows through the wire in the vertical direction, it will take away part of the heat of the wire and reduce the temperature of the wire.
2. According to the theory of forced convection heat exchange, there is a relationship between the lost heat Q and the fluid velocity v. A standard probe consists of a short, thin wire stretched between two brackets. Metal wire is usually made of platinum, rhodium, tungsten and other metals with high melting point and good ductility.
3. According to different purposes, the head can also be made into double wire, triple wire, oblique wire, V shape, X shape, etc. In order to increase the strength, a metal film is sometimes used instead of a metal wire, and a thin metal film is usually sprayed on a thermally insulating substrate, which is called a hot film probe. Probes must be calibrated before use.
4. Static calibration is carried out in a special standard wind tunnel, and the relationship between flow velocity and output voltage is measured and drawn as a standard curve; dynamic calibration is carried out in a known fluctuating flow field, or in the anemometer heating circuit Add a pulsating electrical signal to the center to check the frequency response of the line anemometer. If the frequency response is not good, it can be improved with the corresponding compensation circuit.
Two: The use of thermal anemometer:
1. Anemometers are widely used and can be used flexibly in all fields. They are widely used in electric power, steel, petrochemical, energy-saving and other industries. There are other applications in the Beijing Olympic Games, such as sailing competitions, rowing competitions, and field shooting competitions. Anemometers and other anemometers need to use an anemometer to measure.
2. There are many industries that need to use anemometers. Recommended industries: fishing, various fan manufacturing industries, industries that require ventilation and exhaust systems, etc.
3. Anemometer The working principle of the heat-sensitive probe of the anemometer is based on the cold impact airflow taking away the heat on the heating element. With the help of an adjustment switch to keep the temperature constant, the adjustment current is proportional to the flow rate.
4. When the thermal probe is used in turbulent flow, the airflow from all directions impacts the thermal element at the same time, which will affect the accuracy of the measurement result. When measuring in turbulent flow, the indication value of the thermal anemometer flow sensor is often higher than that of the rotary probe.
