| Summary: | 碩士 === 中原大學 === 機械工程研究所 === 106 === Diffuser is widely used in industry and the flow behavior within is commonly investigated. For example, the bolts can be pre-coated with some adhesive plastics to increase the clamping force and reduce the occurrence of loosen and falling fasteners. During the coating process, the air-particle mixtures are ejected from the coating diffuser toward the preheated bolts. However, an accumulation of particles is encountered near the outlet of the coating nozzle, which reduces the uniformity of particle distribution on the bolt surface. This phenomena has been proven to reduce the expected clamping force by experiments.
Therefore, this thesis would find out the strategy to avoid the accumulation of particles and improve the uniformity of the diffuser by using computational fluid dynamic (CFD) simulation. Influence of the angle and the length of diffuser, the Reynolds number, the baffles and the mixing zone on the flow behaviors are systematically investigated. In general, the flow structure within the diffuser can be categorized into four types accordingly and the critical parameters are fully detected. The accumulation of particles can be prevented as the secondary flow near the outlet is absent, and the ‘unstall’ type is found to have better uniformity.
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