Date of Degree
MS (Master of Science)
Occupational and Environmental Health
T. Renee Anthony
The objective of this study was to determine whether improvements could be made to increase the capture distance of traditional local exhaust ventilation (LEV) hoods by designing a circular slotted-hood. The criterion of success for this study was to achieve increases in capture velocity at an upstream distance equal to the diameter of the hood (11 inches). By increasing capture velocity further from the face, contaminant capture could take place at distances more convenient to the circular slotted-hood operator while maintaining adequate suction. This was to be achieved by the addition of two slots and a flange to a traditional conical hood opening. Three plates were designed to change the geometry of a plain conical hood (slot area: 0.1334, 0.0963 and 0.0694 ft2). They were tested at different airflow rates (243, 347, 467, 647, 897 cubic feet per minute) for a set number of distances from the hood face using a thermal anemometer. Three-dimensional maps of performance were created for visual comparisons, and t-tests were conducted to analyze performance by comparison of velocity at any point upstream of the hood. Velocity contours illustrated that two of the three designs had greater capture velocities compared to the standalone conical hood, and paired t-tests confirmed the significance (p<0.05). Each of the new designs failed to significantly increase capture distance further than 11 inches from the hood. However, increased velocities occurred near the hood opening (within 5 inches). These modest improvements for the largest slot design increases operating pressures by approximately 0.1" wg @ 250 cfm but 1.1" wg @ 650 cfm. Implementing these new designs would increase capture velocities close to the hood, although this advantage is offset by the cost it would require to compensate for the pressure loss incurred.
Copyright 2011 Matthew Lucas Hibbs
Hibbs, Matthew Lucas. "Capture velocity with slot entry to conical hood." thesis, University of Iowa, 2011.