Sang-Min Lee, Jin-Won Lee
Bibliographic info:
Ashrae 2005 Winter meeting, technical and symposium papers, Orlando, February 2005

In a local exhaust ventilation system, the exhaust air velocity decreases very rapidly with distance from the exhaust inlet.One possible way of maintaining a high capture velocity far from the exhaust inlet is the use of vortex flow, usually called a "vortex ventilation system", which has a rotating annular disk installed in the exhaust inlet. Through numerical and experimental analysis, an optimal shape of the disk is developed and its performance is represented based on the operating parameter D, which is the ratio of the displacement flow rate by the fins on the disk to the exhaust flow rate. Compared with the simple exhaust, the vortex ventilation system gives more than twice as large a capture depth and more than ten times as large a capture volume. The main mechanism for the improved performance is the displacement flow propagating radially around the exhaust inlet and thus inducing a secondary air flow under the hood.