Development of the Universal Air Collector Design for Measuring the Flow Rate of Swirling Air Flow Using an Integral Thermoanemometer

Abstract

Measurement of the swirling air flow rate and average speed of air at air distribution units of ventilation systems is a rather difficult task due to the fact that the air flow enters the measuring device at different angles. As a result, significant measurement errors can occur when using point thermoanemometers or other flow meters. The use of integral anemometers facilitates the measurement process. However, it is necessary to eliminate the errors associated with changes in the angle of the air flow to the sensing element of the measuring device. To do this, it is necessary to ensure a rectilinear structure of the air flow using a transitional air collector and rectifier. The aim of this paper is to develop a design of an air collector device that will allow to measure the flow rate of a swirling air flow. The objectives of the paper are to optimize the geometrical parameters of the air collector to ensure a rectilinear flow, minimize its dimensions and aerodynamic drag. The correctness of the air collector design was evaluated by matching the calibration characteristic of the probe of an integral thermoanemometer in the presence of a vortex diffuser in front of the air collector and in its absence. The proposed device has a rectangular shape and consists of a receiver, a rectifying grid, a chamber, an accelerating and stabilizing section, at the outlet of which a thermoanemometer probe is installed. The receiver and the accelerating section are tapered along their length, while the chamber and the stabilizing section have a constant cross-section. The rectifying grid is installed inside the chamber and has a square-shaped honeycomb structure. Several options of the air collector design with different geometrical parameters were studied using computer modelling. The dependence of aerodynamic drag on air flow was plotted. The optimal design of the air collector was chosen, for which a life-size physical model was created. The calibration characteristics of the measuring probe with an air collector were experimentally obtained when a swirling air flow was applied. The developed universal air collector allows the air flow rate measurement at the outlets of almost any air distribution devices of ventilation systems of buildings.