Flow and Separation Characteristics of Three-Dimensional Negatively Buoyant Wall Jets

This paper reports a study of the behavior of cold air jets, specifically three-dimensional, incompressible, negatively buoyand, turbulent wall jets, and their separation from horizontal surfaces. With a cold-air distribution system, both the supply air temperature and flow rate are lower than in conventional systems for the same cooling load. The cold air is supplied to a zone at temperaturesbetween 39 degrees F and 49 degrees F (3 degrees C and 9 degrees C) instead of the conventional 55 degrees F (13 degrees C). As the building's ventilation and cooling airflow supply temperature and flow rate are reduced below the conventional values, indoor thermal environment considerations become increasingly important. An analysis using integral forms of the momentum and energy equations ispresented for determination of the separation point of buoyand turbulent wall jets. The analysis shows that the separation point is a function of the outlet Richardson number in addition to the geometry of the outlet diffuser or nozzle. Also reported in this paper is an experimental investigation of the mixing and separation of three-dimensional buoyand turbulent wall jets discharging into alarge room. Velocity and temperature difference profiles and half-width growth rates for these jets are presented. The separation distances are also measured, and compared to the predicted results.