Choosing a Universal Air Collector Design for a Cylindrical-Shaped Hot-Wire Anemometer

Air flow measurement at the outlets of air terminal devices installed in ventilation systems is very difficult. At the outlets of anemostats, swirl diffusers, grilles,  the air flow can swirl, contract, or expand sharply, change its direction, etc., which causes great measurement errors. Therefore, it was necessary to develop a universal measuring device that would make it possible to measure air flow rate with high accuracy. It should consist of an air collector (for collecting and rectifying air flow) and a sensor for measuring air flow rate (integral hot-wire anemometer). Several air collector designs have been investigated. The parabolic air collector was chosen as the rational one. It has low aerodynamic resistance and good air flow distribution. To reduce the influence of turbulence and air swirling, a cylindrical stilling channel with a built-in rectifying grille is connected to the air collector. Experimental studies on various air distribution devices made it possible to obtain a refined calibration dependence for an integral hot-wire anemometer, the dependence being used to calculate air flow rate. The influence of the aerodynamic resistance of an airflow meter on air flow rate is taken into account with the help of a correction that must be introduced into the values measured.