The working mode and purpose of the anemometer
1. Working mode
The anemometer has two operating modes:
1. Constant current method, also known as constant current method, means that the current of the heated metal wire remains constant, and the temperature of the metal wire decreases as the gas carries away some of the heat. The higher the flow rate, the more the temperature decreases; When the temperature changes, the resistance changes and the voltage at both ends changes. Therefore, the temperature of the metal wire can be measured to determine the magnitude of the flow rate.
2. Constant temperature method, also known as constant resistance method (i.e. constant temperature method), changes the heating current to supplement the heat carried away by the gas, while keeping the temperature of the metal wire unchanged (also known as the resistance value of the metal wire unchanged), such as maintaining 150 ℃,; At this point, the larger the flow rate, the greater the required heating current. The magnitude of the flow rate can be determined based on the required applied current (heating current value). The constant temperature type is more widely used than the constant current type.
2. Purpose
The main uses of anemometers are as follows:
1. Measure the speed and direction of average flow.
2. Measure the pulsation velocity and its spectrum of the incoming flow.
3. Measure the Reynolds stress in turbulence and the velocity and time correlations between two points.
4. Measure the wall shear stress (usually using a hot film probe placed flush with the wall, similar to the principle of velocity measurement).
5. Measure fluid temperature (by measuring the variation curve of probe resistance with fluid temperature in advance, and then determining the temperature based on the measured probe resistance), in addition to this, many professional applications have been developed
