How Duct Anemometers Work
The practice of measuring the airflow velocity in the pipeline by the anemometer proves that the 16mm probe of the anemometer is the most widely used. Its size not only ensures good permeability, but also can withstand a flow velocity up to 60m/s. As one of the feasible measurement methods, the air flow velocity measurement in the pipeline is suitable for air measurement by the indirect measurement procedure (grid measurement method).
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. When using thermal probes in turbulent flow, airflow from all directions impinges on the thermal element simultaneously, which can affect the accuracy of the measurement results. When measuring in turbulent flow, the indication value of the thermal anemometer flow sensor is often higher than that of the rotary probe. The above phenomenon can be observed in the pipeline measurement process. Depending on the design of the managed pipe turbulence, it can occur even at low speeds.
Therefore, the anemometer measurement process should be carried out on the straight part of the pipeline. The starting point of the straight line should be at least 10×D (D=pipe diameter in CM) before the measurement point; the end point should be at least 4×D behind the measurement point. The fluid cross-section must not be obstructed in any way
Anemometer Measurements in Extraction Exhaust
The vent will greatly change the relatively balanced distribution of the airflow in the duct: a high-speed area is generated on the surface of the free vent, and the rest is a low-speed area, and a vortex is generated on the grid. According to the different design methods of the grid, at a certain distance (about 20cm) in front of the grid, the airflow section is relatively stable. In this case, the aperture wheel of a large anemometer is usually used for measurement. This is because the larger bore is able to average the unbalanced flow rate and calculate its average value over a larger range.
