An investigation into the proportional discharge of air from side outlets on a small-scale terminal ventilation duct

Abstract

This investigation relates to a small-scale air duct of rectangular cross-section with variably sized rectangular apertures pitched evenly along one face of the duct. Measurements of air velocities were made mainly with a hot-wire anemometer and to a lesser extent with a pitot-static tube. Details are given of the calibration and use of these instruments together with an outline of the precautions which must be taken to ensure reliability of results. Aperture air flow patterns determined by the use of the hot-wire anemometer were found to be complex and dependent primarily on the interrelated factors of duct gauge static pressure, aperture size, and that fraction of the approaching air which escaped through an aperture. It was established that aperture air volume flow could be determined accurately from a single, half-height, horizontal traverse of an aperture with the hot-wire probe and consequently the expenditure of time and effort required for a multi-row traverse was eliminated. Some evidence was found to support the supposition that variation in the magnitude of the total duct air flow does not affect the proportions into which it is divided by fixed aperture settings. Relationships between non-dimensional parameters were determined from which a method was devised by which the requisite aperture areas associated with specified aperture proportional air flows were predicted.