Investigation of flow generated by the collision of two opposed ceiling-attached jets from radial vortex diffusers

Abstract

Thermal comfort in rooms with mixing air distribution systems is greatly influenced by air jets issuing from ceiling diffusers. Jets are often attached to ceilings, and as the attached jets collide with each other and generate flow, here called a merged jet, directed vertically and towards the occupied zone. In this research, air velocity and turbulence intensity were measured in the zone of the attached jets from two adjacent vortex ceiling diffusers and in the zone of the merged jet under isothermal conditions using omnidirectional anemometers. The jet characteristics, uniformity, similarity zone, spread rate, the position of virtual origin, centerline and profile distribution for velocity and turbulence intensity, were investigated in the ceiling-attached jet and the merged jet. The aim is to understand better the interactions between air jets created by diffusers and provide tools to designers of air distribution systems to estimate thermal comfort in the zone of the merged jet. Moreover, the results can be used to verify numerical models (CFD) and improve the reproduction of airflow characteristics created by diffusers. Velocity and turbulence intensity profiles show the presence of the similarity zone extending to the occupied zone, which is encouraging in terms of using well-known decay and profile equations to approximate velocity distribution, which has been done here. The draught rate index (DR) distribution in the merged jet was calculated from the measurement data. However, there is no known simple model to estimate turbulence intensity, which has a significant impact on the DR in the jet zone.