Browsing by Author "Lai, Yu-Chih"

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A mixed convection in a reciprocating Pi shape channel with opposite direction of gravity and inlet cooling fluids
(2009-04-01)
Fu, Wu-Shung
;
Lian, Sin-Hong
;
Lai, Yu-Chih
;
機械工程學系
;
Department of Mechanical Engineering
A numerical study is executed to investigate heat transfer mechanisms of a reciprocating channel cooled by fluids. The problem of the reciprocating piston is a moving boundary problem, and the Finite Element Method and arbitrary Largragian-Eulerian Kinematics method are then utilized. Due to the high temperature of the channel, a mixed convection is taken into consideration for simulating a more realistic situation. Directions of inlet cooling fluids and gravity are opposite. Concerning important parameters of the Reynolds number and Grashof number, reciprocating frequency and amplitude are examined. Thermal stratification layers which are found firmly on the top surface are deeply dependent on the magnitude of Gr/Re(2) ratio which directly affects the heat transfer mechanisms.
An enhancement of the back region forced convection heat transfer rates of a reciprocating curved channel with a rib by the ALE method
(2013-12-01)
Fu, Wu-Shung
;
Lai, Yu-Chih
;
Huang, Shang-Hao
;
機械工程學系
;
Department of Mechanical Engineering
An enhancement of the back region forced convection heat transfer rates of a reciprocating curved channel with a rib by the ALE method is investigated numerically. In order to avoid damage caused by a huge difference of heat transfer rates between the front and back regions of a reciprocating curved channel, a rib is selected and installed at an appropriate location to enhance the heat transfer rate of the back region. In the ALE method, the generalized minimal residual method preconditioned by the mesh free pressure convection-diffusion in which the pressure terms are arranged in a finite element linearized matrix system is used to solve governing equations. The results show that the heat transfer rate of the back region is indeed enhanced by the installation of the rib at an appropriate location. (C) 2013 Elsevier Ltd. All rights reserved.
An investigation of a mixed convection in a boolean OR shape channel moving with a reciprocating motion
(2009-11-01)
Fu, Wu-Shung
;
Lian, Sin-Hong
;
Lai, Yu-Chih
;
機械工程學系
;
Department of Mechanical Engineering
This study focuses on utilizing numerical calculation to investigate the heat transfer mechanisms in a shape reciprocating channel system comprised of a horizontal channel at the bottom and vertical channels on both left and right sides. The issue is considered one kind of moving boundary problems and the finite element and Arbitrary Lagrangian-Eulerian (ALE) kinematic methods can be applied to this study. Due to the high temperature at the bottom surface of the horizontal channel and the direction of inlet cooling fluids in the same direction of the gravity, the heat transfer mechanisms induced by the mixed convection flow become extremely complex. The results show that thermal layers near the heat surface are disturbed drastically and the effect of reciprocating motion upon the heat transfer mechanisms strongly depends on a relationship between Reynolds and Grashof numbers. (C) 2009 Elsevier Ltd. All rights reserved.
An investigation of flow reversal of mixed convection in a three dimensional rectangular channel with a finite length
(2013-09-01)
Fu, Wu-Shung
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Lai, Yu-Chih
;
Huang, Yun
;
Liu, Kuan-Lan
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機械工程學系
An investigation of flow reversal of mixed flow in a three dimensional channel is studied numerically. At a high Richardson number, natural convection dominates the flow and thermal fields of mixed convection. Behaviors of the residual mass flow rate produced by the difference of the strength of natural and forced convections coexisting in mixed convection are worthy to be examined deeply for industrial applications. Due to the necessity of considering the fluid compressibility, methods of the Roe scheme, preconditioning and dual time stepping are adopted to solve governing equations. The results show that at a high Richardson number situation, via the outlet in large quantities of fluids are sucked into the channel from the outside that causes the flow and thermal fields in the channel to be unsteady and vice versa. (C) 2013 Elsevier Ltd. All rights reserved.
Effects of a porous medium on forced convection of a reciprocating curved channel
(2014-11-01)
Fu, Wu-Shung
;
Chen, Chung-Jen
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Lai, Yu-Chih
;
Huang, Shang-Hao
;
機械工程學系
Enhancement of heat transfer rates of a reciprocating curved channel partially installed by a porous medium is investigated numerically. The distribution of heat transfer rates on the heat surface of the reciprocating curved channel is rather non-uniform that easily causes a thermal damage to destroy the channel. A method of using the porous medium to enhance heat transfer rates of the channel is then developed to solve the thermal damage. The arbitrary Lagrangian-Eulerian method is firstly modified for treating a moving boundary problem of the porous medium. Main parameters of Reynolds numbers, porosities, frequencies and amplitudes are examined. The results show that the enhancements of heat transfer rates of most porous medium situations are achieved. However, heat transfer rates of a few porous medium situations are unexpectedly inferior to those of without porous medium situations. (C) 2014 Elsevier Ltd. All rights reserved.
Estimation of turbulent natural convection in horizontal parallel plates by the Q criterion
(2013-07-01)
Fu, Wu-Shung
;
Lai, Yu-Chih
;
Li, Chung-Gang
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機械工程學系
;
Department of Mechanical Engineering
An investigation of estimation of turbulent structures of natural convection in horizontal parallel plates by the Q criterion is studied numerically. It is difficult to adopt a definite criterion like the critical Reynolds number adopted in forced convection to distinguish laminar and turbulent flows of natural convection in horizontal parallel plates because the angle between directions of the buoyancy force and main stream flow is changed in the whole process of the flowing. The Q criterion is then used to make up for a deficiency of the definite criterion and examines mechanisms of the occurrence of rotation behaviors which are often regarded as turbulent structures in detail. Methods of the Roe scheme, preconditioning and dual time stepping matching the method of LUSGS are simultaneously used to solve a low speed compressible flow. As well, non-reflecting boundary conditions are held at apertures to prevent the reflection caused by pressure waves. Under a low height situation, the shear force is dominant and then a few rotation behaviors are observed near the central region where flow directions are changed. Oppositely, the space is almost filled with active rotation behaviors because natural convection fully develops in a high height situation. (C) 2013 Elsevier Ltd. All rights reserved.