Abstract
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.
Highlights
Air flow measurement at the outlets of air terminal devices installed in ventilation systems is very difficult
Adjustment of combined inlet-and-exhaust ventilation systems requires that the air flow rate be measured at the outlets or inlets of anemostats, diffusers, and ventilation grilles
This difference in flows significantly complicates the measuring process, since the air must first be collected in a single channel, and directed to the probe of the measuring device. In this case, such a matching device, or, in other words, an air collector, must have a minimum aerodynamic resistance in order to prevent the air flow rate from dropping on elements of inlet-and-exhaust ventilation systems. Another requirement for an air collector is the absence of reverse flows and turbulence at its outlet, since they can introduce a significant error in the measurement of the air flow rate
Summary
Air flow measurement at the outlets of air terminal devices installed in ventilation systems is very difficult. 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). The parabolic air collector was chosen as the rational one It has low aerodynamic resistance and good air flow distribution. 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.
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