Browsing by Author "Wu, PW"

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Effects of lobe geometry on the mixing flow in multilobe mixers
(2001-01-01)
Tsui, YY
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Wu, PW
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機械工程學系
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Department of Mechanical Engineering
This study is concerned with a numerical investigation of the mixing flow in multilobe mixers. Predictions are obtained using a finite-volume method which incorporates a second-order difference scheme. The irregular boundaries are fitted by curvilinear nonorthogonal grids and the grid points are arranged in the collocated manner. A method is described to generate suitable three-dimensional grids to cover both the lobe region and the mixing duct. Computations ave undertaken to examine the effects of lobe geometry on the mixing performance. Results indicated that the convex lobe contour can lead to stronger vortex flow and, thus, better mixing because of its large slope. As for the geometry of the lobe trailing edge, a sinusoidal shape with wide peak region gives rise to roell-organized vortices and the mixing performance is enhanced. Also revealed is the mechanism which, resulting in efficient mixing in the mixer, is clearly identified.
Heat transfer enhancement by multilobe vortex generators: Effects of lore parameters
(2000-05-12)
Tsui, YY
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Leu, SW
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Lin, CC
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Wu, PW
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機械工程學系
A three-dimensional computational method is developed to study the flow and heat transfer in a circular tube with a multilobe vortex generator inserted. Governing equations are discretized by the finite volume technique. The irregular lobe geometry is treated using curvilinear nonstaggered grids. Examination of the flow field reveals that the radial and counterradial flows induced inside and outside the lobe are forced to form axial vortices downstream of the vortex generator Because of the transport of the high-speed, low-temperature core flow toward the tube wad by the vortex, heat transfer is enhanced. Also because of the vortex flow, the high-temperature wall flow is carried away from the wall to mix with the low-temperature core flow. Consequently, very effective augmentation in the heat transfer and mixing of flow temperature results. It is shown also that since the slope of the lobe is increased by enlarging the lobe penetration, reducing the lobe length, and making a concave contour geometry, the circulation, representing the strength of the axial vortex induced by the lobe, is promoted, leading to higher heat transfer and flow mixing By increasing the lobe number both the circulation and Nusselt number (Nu) decrease because of the narrowed lobe passage.
Investigation of the mixing flow structure in multilobe mixers
(1996-07-01)
Tsui, YY
;
Wu, PW
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交大名義發表
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機械工程學系
;
National Chiao Tung University
A computational procedure is described to study the mixing flow in a multilobe turbofan mixer. The predictions have been obtained using a finite volume method to solve the density-weighted time-averaged Navier-Stokes equations, Turbulence is characterized by the k-epsilon eddy viscosity model, To fit the irregular boundaries of the flowfield, curvilinear nonorthogonal coordinates are employed, The robustness of the computational procedure is enhanced by making use of nonstaggered grids. In the calculation the computational domain contains not only the mixing duct but also the lobe itself, Three kinds of configuration are under consideration: a confluent mixer, a convoluted mixer, and a forced miser, Results show that the streamwise vortex generated at the trailing edge is the most prominent flow structure for the forced mixer, responsible for the effective mixing, The strength of the streamwise vortex can be characterized by the circulation. A parameter termed mixedness is defined to describe the effects of the mixing process. In addition to the streamwise vortex, normal vortices are generated by the velocity difference in the shear layer between the core and fan streams. To illustrate the mechanism of the mixing procedure, velocity vectors and contours of streamwise and normal vorticities and turbulence contours on transverse planes at selected axial locations are presented, The roles played by the streamwise vortex and the normal vortex are clearly identified.
Potassium ion recognition by 15-crown-5 functionalized CdSe/ZnS quantum dots in H2O
(2006-01-21)
Chen, CY
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Cheng, CT
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Lai, CW
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Wu, PW
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Wu, KC
Based on 15-crown-5 functionalized CdSe/ZnS quantum dots (QDs), we report a novel fluorogenic sensor to probe K+ ions in H2O; recognition of K+ can be achieved via the Forster type of energy transfer between two different color QDs, so that [K+] of the order of 10(-6) M can be promptly detected.