A study on stratification in a space using displacement ventilation

• Main Authors: Chih-lung Lin, 林志龍
• Other Authors: Yi-Jiun Peter Lin
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/rusy56

碩士 === 國立臺灣科技大學 === 機械工程系 === 100 === The purpose of this research is to study the stratified flow in a space using displacement ventilation. The salt-bath technique was employed to conduct the experiments and the acrylic reduced-scale model was used to observe the flow patterns. Dye attenuation technique was used to analyze the light intensity data from the recorded images. A partition with an opening was placed in the middle of the rectangular acrylic model to divide the model into two individual chambers. The chamber having a constant buoyancy source is denoted as the forced room, and the other chamber is denoted as the supply room, which supplies fresh water at different flow rates. According to two different connection opening sizes on the partition, the experiments are categorized as DCDV(I) and DCDV(II) two series and the flow pattern in the forced room is investigated. Flow visualization technique is used to observe the flow pattern and the interface level, and the densimeter is used to measure the fluid density. The density plume as a buoyancy source is placed on the ceiling of the forced room and it proceeds in the same direction as that of the gravity force. For thermal plume, the buoyant fluid is ascending and opposite to the proceeding direction of the salt plume in the experiments. But the coordinates of the experiments and the theoretical model are consistent in this study. The results show that the properties of the occupied region in the forced room can be controlled by the volume flow rate of the supply room and the buoyancy strength in the forced room. Experimental results are in reasonable agreement with the theoretical model. As the supply volume flow rate increases, the distance between the interface level and the source increases and the stability of the stratification becomes weaker. The stratification stability depends on the inertial force of the incoming flow and the buoyancy force of the outgoing flow of the forced room. The results show that the interface stability is disturbed when the inflow supply rate increases. The increase of the inflow inertial force would gradually exceed the buoyancy force to drive the outflow, and a mixing layer is formed between two homogeneous layers. The thickness of the mixing layer and the logarithm of the ratio of buoyancy force to inertial force have a linear relationship.