Characterization of a combined downward jet for protected zone ventilation reducing exposure risk of occupants to indoor pollutants

The objective of the dissertation is to characterize the air distribution of a combined downward jet and to obtain a model of the velocity distribution. The objective is achieved through analyzing the initial outlet conditions of the diffusers, the velocity decay from the two flows, measuring the deflection of flow and finally modelling the dimensionless velocity profile of the flow using the excess velocity method on the co-flow. The combined downward jet is a possible improvement of the protected occupied zone ventilation, which aim to lower the exposure of contaminants to the occupant. Urbanization and stricter regulation on energy use of ventilation systems increase the risk of indoor exposure to pollutants and airborne pathogens. Ventilation systems that address the problem are needed. A combined downward jet is formed by introducing a plane jet from a slot diffuser and a co-flow from a perforated plate diffuser. Anemometers and a smoke machine is used to measure and analyze the flow. The combined downward jet deflects away from the co-flow and the deflection angle increase with higher co-flow velocity, while the velocity decay decrease. The expansion rate of the velocity profile, measured at y1/2, increase up to 2.5 times that of a plane jet without co-flow. There is likely the plane jet steal momentum from the co-flow, and the rate increase with the co-flow velocity. The excess velocity method show promise in creating a model for the combined downward jet, however with unanswered potential limitations. Future work need to analyze the interaction the plane jet has on the co-flow, and the co-flow needs accurate models for its velocity decay