Capture envelope of an exhausted opening under cross draft an experimental approach.

The exterior hood has been used extensively in the local exhaust devices to capture a variety of contaminants generated in a working-site. The performance of a hood can be measured by either how well it captures the contaminants or how far away it can perform an effective capture. It has been known theoretically that in the presence of an uniform cross draft a capture envelope will form in front of an exhausted opening(2, 3). All streamlines inside an envelope will lead into the opening; otherwise, those outside the envelope will lead to infinity downstream. Therefore, a contaminant inside the envelope tends to be captured by the opening. In this study, the capture envelope formed under the combination of exhaust airflow generated by an exterior hood and a uniform cross draft is observed in a wind tunnel.