A passive micromixer combined with two different mixing units was designed by submerging planar structures, and its mixing performance was simulated over a wider range of the Reynolds numbers from 0.1 to 80. The two submerged structures are a Norman window and rectangular baffles. The mixing performance was evaluated in terms of the degree of mixing (DOM) at the outlet and the required pressure load between inlet and outlet. The amount of submergence was varied from 30 μm to 70 μm, corresponding to 25% to 58% of the micromixer depth. The enhancement of mixing performance is noticeable over a wide range of the Reynolds numbers. When the Reynolds number is 10, the DOM is improved by 182% from that of no submergence case, and the required pressure load is reduced by 44%. The amount of submergence is shown to be optimized in terms of the DOM, and the optimum value is about 40 μm. This corresponds to a third of the micromixer depth. The effects of the submerged structure are most significant in the mixing regime of convection dominance from Re = 5 to 80. In a circular passage along the Norman window, one of the two Dean vortices burst into the submerged space, promoting mixing in the cross-flow direction. The submerged baffles in the semi-circular mixing units generate a vortex behind the baffles that contributes to the mixing enhancement as well as reducing the required pressure load.

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An air-turbine and associated air supply tube was optimized as a dental air-turbine handpiece system. The system consists of an air-turbine with an impeller and a housing, and an air supply tube which supplies compressed-air to the air-turbine. The flow characteristics of the dental air-turbine handpiece system were investigated using ANSYS CFX. The study aimed to find the significant design parameters, and optimize them in terms of the maximum torque. The number of blades, the blade angle of the impeller and the gap between the impeller and the housing were chosen as the three major design parameters. The design of experiment technique was used to optimize two dental air-turbine handpiece systems: Type 1 was an air turbine alone and Type 2 was the air-turbine with an air supply tube. The optimization results showed that the gap between the impeller and the housing was not a significant parameter for Type 1. The maximum torque was lower for Type 2 than for Type 1. The optimized optimum blade number was the same for both types, but the blade angle and the gap differed between the two types. The blade angle and blade number were significant for Type 1, and all three design parameters were significant for Type 2. The performance improvement was greater for Type 2 than for Type 1. The performance of both optimized handpiece systems was reviewed in terms of the experimental measurements of noise level, rotational speed, and withdrawal force.

The air-interlacing process provides assurance in the downstream performance in weaving and knitting without changing the properties of the synthetic yarn. The air-interlacing nozzle is an important component for improving the performance in the air-interlacing process. The airflow inside the air-interlacing nozzle is investigated to design an optimum yarnchannel shape of the nozzle. The width and height of the yarn-channel and inlet pressure are the design variables of the air-interlacing nozzle. The design variables are evaluated by the vorticity. The design of experiments (DOE) approach is utilized to study the influence of the nozzle configuration. Minitab is used as a practical and effective tool in optimizing the nozzle geometry to improve performance. Computational simulations of the impinging airflow inside the nozzle are undertaken using ANSYS CFX. The airflow characteristics such as the vorticity, shock wave, and velocity distributions were discussed. Various cross-sectional shapes of the yarn-channel are investigated with the same inlet pressure. The cross-sectional shape of Shape 6 which has high vorticity is observed to find optimal configurations for the nozzle of the air-interlacing process. The design variables of the nozzle are the width and the height of the yarn-channel and the inlet pressure. The reason for the evaluation of the performance of the nozzle is the maximization of the vorticity. The response surface method (RSM) is applied for the shape optimization. The vorticity cannot increase at the high inlet pressure due to the shock wave. The air-interlacing nozzle, with optimum configurations, is verified numerically and experimentally.