| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 94 === An innovative chemical fume hood which operates based on the aerodynamic principle of air-curtain isolation is developed. The flow visualization and tracer-gas test methods are performed to diagnose the flow characteristics and containment performance of the air-curtain hood. A real-size, transparent air-curtain hood and a commercial grade conventional chemical fume hood are constructed for experimental study. The experimental results of the conventional hood are used for comparison. Through the application of the laser-assisted smoke flow visualization method, the characteristic flow patterns are clearly observed and recorded. The results presented that the conventional fume hood has several regions that the pollutants issued from the smoke ejector placed in the fume hood would leak or disperse out of the sash opening due to some inherent flow physics. Firstly, the geometric arrangement of the conventional fume hood would inevitably induce several large recirculation regions inside and behind the sash. The large recirculating bubble may induce turbulent dispersion and leakage of the pollutants when the sash is open or in opening process. Secondly, around the doorsill and the side poles of the fume hood, there are high risks of pollutant leakage. These local leakages are induced by existence of local recirculation bubble, which are formed when the inlet flows pass over the non-aerodynamically-streamlined (bluff) bodies of the hood structure. The bluff bodies would induce significant flow separation and subsequently lead to flow recirculation. From the flow visualization results, these local flow recirculations obviously bring large amount of in-hood pollutants out to the atmosphere through the sash opening. These global and local flow deficits are not easy to overcome. Contradictorily, the flow fields of the air-curtain hood shows no global recirculations. The local recirculation bubbles may exist, although much weaker. No apparent traces of the in-cabinet released smoke particles are entrained out of the hood and go into these local recirculation bubbles. It seems that the leakage of the air-curtain hood would be less than that of the traditional fume hood if the aerodynamic consideration can be extended to an extent of the mass transport. The tracer-gas concentration measurements present extra-ordinarily satisfactory results. By employing both the ANSI/ASHRAE 110-1995 and prEN14175-3 standard methods to test the performance of the air-curtain fume hood under both the static and dynamic situations, the leakages of the tracer gas approach almost null. The observed flow patterns and the measured tracer-gas concentrations are closely related.
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