Airflow characteristics in the outlet region of a vortex room air diffuser

摘要

For turbulent type clean rooms, terminal devices with high diffusion performance are required because the supply flow rate is usually provided only in the margin value. Vortex diffuser is generally assumed with high diffusion performance. However, its detailed technology data are not available. In this study, the airflow characteristics in the outlet region of a generic vortex diffuser were experimentally and numerically investigated. The zonal hybrid meshes were used in grid generation, where the regions around the disk and the guide vanes were meshed with tetrahedral cells, the inlet duct of the diffuser and the room space were meshed with hexahedra cells. The prismatic (or wedge) cells were used as the transitional cells to enable a change in cell type from hexahedra to tetrahedral. Such arrangement of the cell types has been found to be ideal for analysis of room air movement due to an air diffuser. Corresponding airflow measurements were conducted by using a three-dimensional ultrasonic anemometer. In the region very adjacent to the ceiling (0.05 m from the ceiling), the velocity magnitude was conducted by using a hot-wire anemometer. The results show that the flow pattern in the vicinity of outlet region for vortex diffuser is three-dimensional and highly turbulent. The experimental results were found to agree well with the results of the numerical analysis. The K value of the vortex diffuser investigated is in the range 2.1-2.3. It is concluded that the zonal hybrid meshes are well suited for analysis of the complicated flow structure issuing from the vortex diffuser. This study also shows that the vortex diffuser has a greater entrainment ratio than that of a multi-cone circular ceiling diffuser, due to the influence of the stationary twists guide vanes. Therefore, the vortex diffuser is a good option as a terminal device for turbulent type clean room.