Air jets in ventilation applications

Abstract: The purpose of air distribution systems for HVAC is tocreate proper air quality and thermal conditions in an occupiedzone. In mixing type air distribution systems air is suppliedinto a room through various types of outlets and distributed byturbulent air jets. These air jets are the primary factorsaffecting room air motion. The ASHRAE handbook recognises fourmajor zones of maximum velocity decay along a jet.Although numerous theoretical and experimental studies havebeen conducted to develop turbulent air jet theory from the1930's, air jet performance in the further field from theoutlet is still not well understood.Many studies were therefore carried out, and the followingconclusions can be drawn from them:    The end centerline velocities of zone 3 for both "free"jet and wall jet could strongly depend on the outletvelocities and room size.    TheK-value of wall jets could be a function of bothoutlet velocities and outlet size.    It is very important to choose suitable sampling time toevaluate jet performance.    CFD can not always be used to predict jet behaviour,especially for the jet with low outlet velocity and in thearea far away from the outlet. However, for a two-dimensionwall jet, CFD could be a powerful tool for designers.KEYWORDS: air jet, centerline velocity,K-velocity, air diffuser, ventilation, measurement,CFD