A study on flow stratification in a space using displacement ventilation

摘要

This paper presents a theoretical analysis approach and experimental results on the stratified flow in a reduced-scale model using mechanical and natural displacement ventilation. Theoretical analysis is based on fundamental conservation equations and turbulent plume theory. The salt-bath technique is employed to conduct the analogous experiments to building ventilation problems and the reduced-scale acrylic model is used to observe the flow patterns in the laboratory. The light-attenuation method is used to analyze flow stratification in the analogous experiments. The model is divided into two rooms, which have the same cross-section area and volume, by an interior divider. The room having a buoyancy source is denoted as the 'forced room', and the other room is denoted as the 'supply room', which provides a constant flow rate into the space for mechanical displacement ventilation cases. This research focuses on analyzing convection flow properties and stratification distribution in the forced room. The research results show that the stratified flow in the forced room is controlled by the supply flow rate and slightly by the buoyancy source strength for mechanical displacement ventilation. The flow properties are normalized to be dimensionless parameters under the condition of a fixed buoyancy flux, and the dimension-less interface level and the dimensionless reduced gravity of the buoyant layer change with the dimensionless flow rate. As the supply flow rate increases, the stability of stratification becomes weak and there is an intermediate stratified layer formed between the fresh ambient and polluted buoyant layers. This study shows that the stability of stratification and the thickness of the intermediate stratified layer are dependent on the ratio of buoyancy force to inertia force in the room using displacement ventilation.