Effects of doorsill jet injection on fume cupboard containment.

The flow separation and its accompanied recirculation induced when the airflow passes over the inappropriately designed doorsill of a chemical fume cupboard are the key factors which would lead to deterioration of the cupboard performance. In order to alleviate the contaminant leakage of the fume cupboard induced by inherent aerodynamic deficiency, a technique using doorsill jet injection is developed and validated. A planar jet is ejected upward through a slot located across the inner surface of the doorsill of a full-scale, transparent fume cupboard and is ejected upward. The laser-light-sheet-assisted smoke flow visualization is performed to explore the physical mechanism of changing and controlling the flow structure. It is found that the upward injected jet is curved by the airflow drawn into the sash opening and forms a layer of clean air which can isolate the contaminant and alleviate the diffusion through the recirculating vortex on the doorsill, if the jet velocity is properly adjusted. The tracer gas concentration measurements present extraordinarily satisfactory results--the order of magnitude of the leakage of tracer gas near the doorsill may be reduced from original levels of approximately 10(2) to approximately 10(-2) p.p.m. Except for the experimental fume cupboard used for development of technique, two commercial fume cupboards are employed for verifications and comparisons on the proposed method. Tests about the two modified commercial fume cupboards demonstrate good agreement to those of the model fume cupboard.