Browsing by Author "Yang, SJ"

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A new model for heat transfer of fins swinging back and forth in a flow
(2001-05-01)
Fu, WS
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Yang, SJ
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機械工程學系
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Department of Mechanical Engineering
In this paper, a new concept of an electronic device cooling method is proposed. In this method, extremely thin fins are used for swinging back and forth in a flowing fluid. The boundary layers attaching on the fins are then contracted and disturbed, and the heat transfer rate of the fins can be enhanced remarkably. The dynamic behavior between the fins and fluid is classified into a class of the moving boundary problems. A Galerkin finite element formulation with an arbitrary Lagrangian-Eulerian kinematic description method is adopted to solve this problem. The parameters of velocities of the fluid and the swinging speed of the fins are employed to investigate the variations of the flow and thermal fields. The results show that the velocity and thermal boundary layers may be contracted and disturbed, which results in a significant heat transfer enhancement, being attained. (C) 2001 Elsevier Science Ltd. All rights reserved.
A numerical investigation of effects of a moving operator on airflow patterns in a cleanroom
(2002-07-01)
Yang, SJ
;
Fu, WS
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機械工程學系
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Department of Mechanical Engineering
The variations of the airflow induced by a moving operator in a cleanroom installed with a curtain were studied numerically. This situation is cataloged to a class of the moving boundary problems. An arbitrary Lagrangian-Eulerian kinematic description method is utilized to describe the flow field and a penalty finite element formulation with moving meshes is adopted to solve this problem. The effects of the moving operator and curtain on the airflow patterns under different distances from the workbench to the curtain with the moving speed of the operator equal to 2.0 and Reynolds number Re = 500 are taken into account. The results show that recirculation zones are formed around the operator and workbench due to the movement of the operator. The recirculation zones are not favorable to the cleanroom because they may induce a local turbulent flow and entrain and trap contaminants. These phenomena are remarkably different from those of the moving operator assumed as stationary in the cleanroom. Based on the length of the curtain, it is useful for protecting the operator from the hazardous gases. (C) 2002 Elsevier Science Ltd. All rights reserved.
A numerical study of effects of the swinging amplitude of fins on heat transfer characteristics in a flow
(2001-11-01)
Fu, WS
;
Yang, SJ
;
機械工程學系
;
Department of Mechanical Engineering
A new method for enhancing heat transfer of a finned heat sink is proposed in this study. In this method, extremely thin fins are installed in the finned heat sink, and these fins may swing back and forth in a flow because of the fluid flowing pass them. As a result, the velocity and thermal boundary layers attached on the fins are then contracted and disturbed, and the heat transfer rate of the fins can be enhanced. The variations between the fluid and fins are dynamic and belong to a kind of the moving boundary problems. The arbitrary Lagrangian-Eulerian (ALE) kinematic description method is available and adopted to describe the flow and thermal fields, and the governing equations are solved using the Galerkin finite element method with moving meshes. The effects of variations in the Reynolds number, swinging speed and amplitude of the fins on the heat transfer of the fins are investigated. The results show that the velocity and thermal boundary layers may be contracted and disturbed as the fins swing with a large speed, and the heat transfer rates are remarkably affected by the swinging speed and amplitude of the fins.
A numerical study of the effects of a moving operator on particles in a cleanroom with a curtain
(2002-02-01)
Fu, WS
;
Chen, SF
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Yang, SJ
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機械工程學系
;
Department of Mechanical Engineering
The motion of airflow and particles induced by a moving operator in a cleanroom installed with a solid worktable and a vertical isolating curtain were studied numerically. This situation is classified as a kind of moving boundary problem, and a Galerkin finite element formulation with an arbitrary Lagrangian-Eulerian kinematic description method is adopted to analyze this problem. Two different moving speeds of the operator under Reynolds number Re = 500 and Schmidt number Sc = 1.0 are taken into consideration. The results show that recirculation zones, which are disadvantageous to remove the particles, are observed around the operator and near the worktable. The behavior of the operator usually prevents the particles from being removed, and the higher moving speed of the operator demonstrates that the removal of particles becomes more difficult. These phenomena are quite different from those that regard the moving operator as stationary in the cleanroom.
Growth and fatigue properties of pulsed laser deposited Pb1-xLax(ZryTiz)O-3 thin films with [001] preferred orientation
(1996-12-01)
Lin, WJ
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Tseng, TY
;
Wu, YZ
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Lin, SP
;
Tu, SL
Growth of [00/] preferentially oriented Pb1-xLax(ZryTiz) O-3 (PLZT) thin films was carried out by using targets of either tetragonal or rhombohedral structure. The tetragonal films grew in a similar manner to the rhombohedral films. Both the substrate temperature (500 or 550 degrees C) and oxygen pressure (0.1 mbar, 10 Pa) required stringent control in order to deposit [00/]-textured PLZT thin films. The ferroelectric and fatigue properties were examined. The films deposited on YBa2Cu3O7-x and CeO2 coated silicon (YBCO/CeO2/Si) substrates possessed substantially lower remanent polarization than those grown on YBCO coated SrTiO3 (YBCO/STO) substrates; this is ascribed to inferior crystallinity of the PLZT/BCO/CeO2/Si films. The remanent polarization of tetragonal PLZT films was degraded insignificantly up to 10(8) polarization switching cycles, whereas that of rhombohedral PLZT films was already reduced to 80% of the initial value after 10(8) cycles. Low endurance of rhombohedral films was ascribed to the periodic stress induced when the inclined spontaneous polarization vector (P=[111]) switched. On the other hand, high endurance of tetragonal films was explained by the fact that the spontaneous polarization vector (P=[001]) lies along the film's normal such that switch cycles cause no lateral stress.
Heat transfer induced by a body moving in opposition to a flowing fluid
(2001-01-01)
Fu, WS
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Yang, SJ
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機械工程學系
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Department of Mechanical Engineering
The heat transfer problem of a body moving in opposition to a flowing fluid in a channel is investigated numerically. This problem belongs to a class of the moving boundary problems and an arbitrary Lagrangian-Eulerian method with a Galerkin finite element method is adopted to analyze this problem. Several different moving Velocities of the body and Reynolds numbers are taken into consideration. The results show that the fluid simultaneously replenishes the vacant space induced by the movement of the body and new recirculation zones are formed around the body. These phenomena are quite different from those of the body fixed in the flowing fluid. Heat transfer rates of the body are enhanced remarkably as the body moving in opposition to the flowing fluid. In the computing range, the mean global Nusselt number Nu can be estimated by an equation of 0.664(Re V-b)(1/2) - 1.34. (C) 2000 Elsevier Science Ltd. All rights reserved.
High performance non-alloyed pseudomorphic high electron mobility transistors
(1996-07-01)
Peng, CK
;
Lan, WH
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Tu, SL
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Yang, SJ
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Chen, SS
We have studied the InAs/GaAs strained layer superlattice (SLS) structures as non-alloyed contacts applied to pseudomorphic high electron mobility transistors (PHEMTs) grown by the molecular beam epitaxy (MBE) system. Transmission line measurements with four point configurations showed that specific contact resistances between 6.6 x 10(-7) and 2.6 x 10(-6) Omega cm(2) were obtained for the as-grown devices, with a linear correlation coefficient of 0.997. D.c. measurements of the as-grown PHEMT with 1 mu m gate showed a transconductance of 240 ms mm(-1). Microwave measurements on the same device showed a cut-off frequency of 19 GHz and a maximum power gain frequency of 42 GHz. These results are comparable with those of devices with the conventional contact scheme. Meanwhile, since the non-alloying process maintains excellent surface morphology and sharp metal pad edges, AuGeNi type metals can be used in small dimension devices. In contrast, the conventionally alloyed devices showed rough surface morphology and zigzag edges, which may affect device processing and limit the usefulness of AuGeNi metal as the ohmic contact in small dimension devices.
Influence of crystal structure on the fatigue properties of Pb1-xLax(Zr-y,Ti-z)O-3 thin films prepared by pulsed-laser deposition technique
(1997-05-01)
Lin, WJ
;
Tseng, TY
;
Lin, SP
;
Tu, SL
;
Chang, H
Lead lanthanum zirconate titanate (Pb1-xLax(Zr-y,Ti-z)O-3, PLZT) films containing [00l] preferentially oriented grains were produced successfully on YBa2Cu3O7-x-coated (YBCO-coated) SrTiO3, (STO) or YBCO/CeO2-coated silicon substrates; films containing randomly oriented grains were created on platinum-coated silicon substrates. The latter possessed significantly inferior ferroelectric properties, a fact ascribed to the presence of a paraelectric phase (TiO2,) at the PLZT/platinum interface. On the other hand, the PLZT/YBCO/STO films exhibited better electrical properties than did the PLZT/YBCO/CeO2/Si films, and this phenomenon was attributed to better alignment of the grains in normal and in-plane orientations. In terms of fatigue properties, the [00l] textured films that were deposited on YBCO/CeO2/Si substrates possessed substantially superior polarization-switching-cycle endurance versus the randomly oriented films grown on Pt(Ti)/Si substrates. Moreover, the tetragonal films behaved much more satisfactorily than did the rhombohedral PLZT films. The ferroelectric parameters of tetragonal PLZT films showed no significant degradation up to 10(9) polarization switching cycles, whereas the remnant polarization and coercive force of the rhombohedral PLZT films had already degraded to 80% of their initial values after 10(8) cycles.
Influence of crystal structure on the fatigue properties of Pb1-xLax(Zr-y,Ti-z)O-3 thin films prepared by pulsed-laser deposition technique
(1997-05-01)
Lin, WJ
;
Tseng, TY
;
Lin, SP
;
Tu, SL
;
Chang, H
Lead lanthanum zirconate titanate (Pb1-xLax(Zr-y,Ti-z)O-3, PLZT) films containing [00l] preferentially oriented grains were produced successfully on YBa2Cu3O7-x-coated (YBCO-coated) SrTiO3, (STO) or YBCO/CeO2-coated silicon substrates; films containing randomly oriented grains were created on platinum-coated silicon substrates. The latter possessed significantly inferior ferroelectric properties, a fact ascribed to the presence of a paraelectric phase (TiO2,) at the PLZT/platinum interface. On the other hand, the PLZT/YBCO/STO films exhibited better electrical properties than did the PLZT/YBCO/CeO2/Si films, and this phenomenon was attributed to better alignment of the grains in normal and in-plane orientations. In terms of fatigue properties, the [00l] textured films that were deposited on YBCO/CeO2/Si substrates possessed substantially superior polarization-switching-cycle endurance versus the randomly oriented films grown on Pt(Ti)/Si substrates. Moreover, the tetragonal films behaved much more satisfactorily than did the rhombohedral PLZT films. The ferroelectric parameters of tetragonal PLZT films showed no significant degradation up to 10(9) polarization switching cycles, whereas the remnant polarization and coercive force of the rhombohedral PLZT films had already degraded to 80% of their initial values after 10(8) cycles.
Modeling mechanical stress effect on dopant diffusion in scaled MOSFETs
(2005-01-01)
Sheu, YM
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Yang, SJ
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Wang, CC
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Chang, CS
;
Huang, LP
The effect of shallow trench isolation mechanical stress on MOSFET dopant diffusion has become significant, and affects device behavior for sub-100-nm technologies. This paper presents a stress-dependent dopant diffusion model and demonstrates its capability to reflect experimental results for a state-of-the-art logic CMOS technology. The proposed stress-dependent dopant diffusion model is shown to successfully reproduce device characteristics covering a wide range of active area sizes, gate lengths, and device operating conditions.
Numerical investigation of heat transfer from a heated oscillating rectangular cylinder in a cross flow
(2001-05-11)
Yang, SJ
;
Fu, WS
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機械工程學系
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Department of Mechanical Engineering
A numerical simulation is performed to study the flow structures and hear transfer characteristics of a heated transversely oscillating rectangular cylinder in a cross flow. The variations of pow and thermal fields are classified into a class of the moving boundary problems, The moving interfaces between the fluid and rectangular cylinder have been considered. An arbitrary Lagrangian-Eulerian (ALE) kinematic description method is adopted to describe the pow and thermal fields,A penalty consistent finite element formulation is applied to solve the governing equations, The subsequent developments of the vortex shedding and heat transfer characteristics around rite heated rectangular cylinder are presented in detail. The effects of Reynolds number, oscillating amplitude, oscillating speed. blockage ratio, and aspect ratio on the flow structures and heat transfer characteristics are examined. The results show that the interaction between the oscillating rectangular cylinder and vortex shedding from the rectangular cylinder dominates tire state of the wake, The flow and thermal fields may approach a periodic state with time. The heat transfer around the rectangular cylinder performance is enhanced remarkably.
Numerical simulation for variations of airflow induced by an object getting in and out of a workbench
(2001-05-11)
Fu, WS
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Yang, SJ
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機械工程學系
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Department of Mechanical Engineering
The variations of airflow patterns induced by an object getting in and out of a workbench in a vertical laminar flow cleanroom are studied numerically. This subject is an important issue of microcontamination control for fabrication of precision devices. The characteristic of the variations of the airflow is dynamic and is a type of moving boundary problem. An arbitrary Lagrangian-Eulerian (ALE) kinematic description method is employed to describe the flow field, and a penalty finite element formulation with moving meshes is adopted to solve this problem, Three different moping speeds of the moving object with Reynolds number Re =500 are considered. The results show that the formation of recirculation zones, which inhibit removing contaminants, is remarkably dependent upon the moving speed of the object getting in and out of the workbench.
Numerical simulation of flow structures around an oscillating rectangular cylinder in a channel flow
(2005-04-01)
Yang, SJ
;
Chang, TR
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Fu, WS
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機械工程學系
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Department of Mechanical Engineering
In this paper, the flow structures of a confined flow over a transversely oscillating rectangular cylinder are investigated numerically. The flow characteristics are dynamic and are classified as a moving boundary problem. An arbitrary Lagrangian-Eulerian (ALE) kinematic description method is used to describe the flow field and a Galerkin finite element formulation with moving meshes is employed to solve the governing equations. The effects of the oscillating speed, frequency and aspect ratio on the flow field are examined. The initiation and subsequent developments of the vortex shedding are investigated in details. The results indicate that the vortices shedding from the rectangular cylinder are entrained by the motion of the rectangular cylinder, and the interactions between the oscillating rectangular cylinder and shedding vortices dominate the state of the wake. The vortex shedding frequency is gradually changed to match the rectangular cylinder oscillating frequency, and the flow field may approach a periodic motion with time. The mechanisms of the vortex shedding from an oscillating rectangular cylinder are different from those of an oscillating circular cylinder.
Numerical simulation of heat transfer induced by a body moving in the same direction as flowing fluids
(2000-05-01)
Fu, WS
;
Yang, SJ
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機械工程學系
;
Department of Mechanical Engineering
Variations of flow held and heat transfer induced by a body moving in the same direction as flowing fluids in a channel were studied numerically This situation is cataloged to a kind of moving boundary problem and an arbitrary Lagrangian-Eulerian description method with a Galerkin finite element formulation is adopted to analyze this problem. Several different moving velocities of the body and Reynolds numbers are taken into consideration, The results show that the fluids simultaneously complement the vacant space induced by the movement of the body and new recirculation zones are formed near the body. These phenomena are remarkably different from those of the moving body regarded as a stationary body in the flowing fluids by a relative velocity viewpoint. Heat transfer rates of the body are enhanced significantly as the body moves rapidly, but the slight enhancement is indicated as the body moves slower than the flowing fluids, In the computing range, the mean global Nusselt numbers Nu can be approximately expressed as the form of Nu = 0.62 Re*(1/2) - 2.95.
Numerical study of variations of airflow induced by a moving automatic guided vehicle in a cleanroom
(2002-01-01)
Yang, SJ
;
Chen, SF
;
Fu, WS
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機械工程學系
;
Department of Mechanical Engineering
The variations of airflow induced by a moving automatic guided vehicle (AGV) in a vertical laminar flow cleanroom are studied numerically. From a viewpoint of fluid mechanics, the characteristic of the variations of the airflow induced by a moving object is dynamic and is classified as a moving boundary problem. A Galerkin finite element formulation with an arbitrary Lagrangian-Eulerian (ALE) kinematic description method is adopted to analyze this problem. Three different moving velocities of the AGV under Reynolds number Re=500 and two different positions of the wafer cassette are considered. The results show that the formation of recirculation zones, which are disadvantageous for removing contaminants, is remarkably dependent on the moving velocity of the AGV and the position of the wafer cassette.
Role of haptoglobin in formation of atherosclerosis
(2001-03-07)
Mao, SJT
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Yang, SJ
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Wu, CH
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交大名義發表
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National Chiao Tung University