| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 102 === Experimental analysis was conducted in the present research to study the flow and leakage characteristics of a specially designed desk-top fume hood. The hood was designed to reduce the negative effect of containment spillage induced by the boundary-layer separation of flow, which was commonly observed in the aerodynamic phenomena. The design features of the hood include (1) an rearward-offset elongate suction slot at the ceiling, (2) an half-circle flange at the inlet of the hood, (3) two side guard plates, their leading edges were arranged with boundary-layer separation controllers (BSC), (4) two triangular platelets installed at the junctions of the hood and two guard plates. The laser-light-sheet smoke flow visualization technique and tracer-gas (SF6) concentration detection method were employed to characterize the properties of the hood. The results of flow visualization showed that the rearward-offset elongate suction slot enable the flow drawn from the front area of the hood to be inclined rearward when the flow goes toward the suction flow. The half-circle flange at the inlet of the hood and the BSCs at the leading edges of the guard plates effectively postponed the boundary-layer separation of the flow into the hood and away from the inlet of the hood. The postponement of the boundary-layer separation point is beneficial to reducing the leakage levels of containments due to the reverse and vortical flows induced by boundary-layer separation at the inlet. The triangular platelets presented effects of reducing the containment leakage induced by three-dimensional turbulent flow structure around the juncture of the hood and the guard plates. The results of tracer-gas concentration measurements showed that the aerodynamically improved desk-top fume hood operated at a suction velocity of 6 m/s present almost null leakage levels (< 0.005 ppm) for both the unoccupied and occupied tests. Operating the hood at a higher suction velocity would increase its robustness. The flow rate, pressure drop, and flow work corresponding to 6 m/s of suction velocity were 5.0 m3/min, 88 Pa, and 7.4 Watt, respectively, which were relatively smaller than the conventionally used chemical fume hoods.
|
|---|
