Browsing by Author "SHIEH, WJ"

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A NUMERICAL STUDY OF TRANSIENT NATURAL-CONVECTION UNDER TIME-DEPENDENT GRAVITATIONAL ACCELERATION FIELD
(1991-12-01)
FU, WS
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SHIEH, WJ
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交大名義發表
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機械工程學系
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National Chiao Tung University
A transient natural convection caused by abruptly heating of a vertical wall in a square enclosure which is under time-dependent gravitational acceleration field is studied numerically. During the computing process, a penalty finite element method is adopted to solve the governing equations. The factor of the time-dependent gravitational acceleration is included in Rayleigh number, therefore two variation of Rayleigh number are considered, one is from 10(5) via 10(6) to -10(5) and the other is from 10(4) via 10(5) to -10(4). Since the variations of flow field and temperature distribution of the fluid in the square enclosure are complicated and unpredictable, the isotherms, streamlines and time dependent heat transfer rate are examined for investigating the heat transfer mechanism during the transient process. The results show that the agreement of the heat transfer rate of this study with that of quasi-steady state is mainly dependent on the response of the variation rate of boundary layer along the vertical walls to that of time-dependent gravitational acceleration.
A PENALTY FINITE-ELEMENT METHOD FOR NATURAL-CONVECTION HEAT-TRANSFER IN A PARTIALLY DIVIDED ENCLOSURE
(1988-05-01)
FU, WS
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SHIEH, WJ
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交大名義發表
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機械工程學系
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National Chiao Tung University
A STUDY OF THERMAL-CONVECTION IN AN ENCLOSURE INDUCED SIMULTANEOUSLY BY GRAVITY AND VIBRATION
(1992-07-01)
FU, WS
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SHIEH, WJ
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交大名義發表
;
機械工程學系
;
National Chiao Tung University
Thermal convection in a two-dimensional square enclosure induced simultaneously by gravity and vertical vibration is investigated numerically. A penalty finite element method with a Newton-Raphson iteration algorithm and a backward difference scheme dealing with the time term are adopted to solve the governing equations. In order to investigate the effects of the vibration frequency and Rayleigh number on the thermal convection in the enclosure, the vibration frequency is varied from 1 to 10(4) and three different values of the Rayleigh number of 0, 10(4) and 10(6) are considered. According to the results, the thermal convection can be divided into five regions: (i) quasi-static convection; (ii) vibration convection; (iii) resonant vibration convection; (iv) intermediate convection; and (v) high frequency vibration convection. In the high Rayleigh number (= 10(6)) case, the gravitational thermal convection dominates, and the vibration motion does not enhance the heat transfer rate remarkably. In contrast, in the low Rayleigh number (=10(4)) case, except in the quasi-static convection region, the vibration thermal convection is dominant, and the vibration enhances the heat transfer rate significantly. In addition, two analytic methods are proposed to predict the frequencies of the quasi-static convection and resonant vibration convection regions, respectively. The values predicted by the two methods are in agreement with that obtained from the numerical method.
A TRANSIENT NATURAL-CONVECTION IN A UNIFORMLY HEATED ENCLOSURE UNDER TIME-DEPENDENT GRAVITATIONAL ACCELERATION FIELD
(1990-07-01)
FU, WS
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SHIEH, WJ
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交大名義發表
;
機械工程學系
;
National Chiao Tung University
ENHANCEMENT OF NATURAL-CONVECTION HEAT-TRANSFER OF AN ENCLOSURE BY A ROTATING CIRCULAR-CYLINDER
(1994-09-01)
FU, WS
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CHENG, CS
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SHIEH, WJ
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交大名義發表
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機械工程學系
Enhancement of natural convection heat transfer in an enclosure by a rotating cylinder is investigated numerically. A penalty finite-element method with a Newton-Raphson iteration algorithm is adopted to solve the governing equations with the boundary conditions, and the accuracy of solutions is sensitively affected by the grid system combining curve-sided and rectangular quadrilateral elements. Since the flow fields of fluids are induced by mutual interaction between the natural convection and the rotating cylinder, the contribution of the rotating cylinder to natural convection heat transfer depends on the direction of rotation of the cylinder. For the counter-clockwise rotating cylinder situation, the contribution is found to be substantial when the value of Gr/Re2 is larger than 100: however, for the clockwise rotation cylinder situation, the contribution is hardly found even when the value of Gr/Re2 is equal to 1.
TRANSIENT LAMINAR NATURAL-CONVECTION IN A PARTITIONED ENCLOSURE HEATED BY UNIFORM FLUX
(1990)
FU, WS
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PERNG, JC
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SHIEH, WJ
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交大名義發表
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機械工程學系
TRANSIENT LAMINAR NATURAL-CONVECTION IN AN ENCLOSURE FROM STEADY FLOW STATE TO STATIONARY STATE
(1990-09-01)
FU, WS
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KAU, TM
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SHIEH, WJ
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交大名義發表
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機械工程學系
TRANSIENT LAMINAR NATURAL-CONVECTION IN AN ENCLOSURE PARTITIONED BY AN ADIABATIC BAFFLE
(1989)
FU, WS
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PERNG, JC
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SHIEH, WJ
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交大名義發表
;
機械工程學系
TRANSIENT THERMAL-CONVECTION IN AN ENCLOSURE INDUCED SIMULTANEOUSLY BY GRAVITY AND VIBRATION
(1993-01-01)
FU, WS
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SHIEH, WJ
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機械工程學系
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Department of Mechanical Engineering
Transient thermal convection in a two-dimensional square enclosure induced simultaneously by gravity and vibration is investigated numerically. The enclosure, which is filled with air under a terrestrial environment, is insulated at both horizontal walls and kept at constant temperature at the vertical walls. For time t = 0, the fluid is stationary with the same temperature as the vertical walls T(c); as t > 0, the left wall temperature is raised to T(h) and the enclosure is vibrated with a constant frequency OMEGA and amplitude b simultaneously. In order to study the effect of vibration frequency on the transient thermal convection, four vibration frequencies (100, 900, 1100, 5000) are considered with fixed Rayleigh number (Ra = 10(4)) and vibrational Grashof number (G = 10(6)). The results show that the transient process, from the stationary state to the steady flow state, is shortened by increasing the vibration frequency, and both the flow field and heat transfer mechanism are mainly determined by the vortex shedding rate, which has the same frequency as the vibration frequency near the upper and lower corners of the hot wall. For omega = 100, a single main cell is formed and alternates the rotating direction with the variation of the buoyancy force direction. For omega = 5000, the buoyancy force induced by the vibration is definitely dominant and the development of temperature distribution from left to right sides is initially symmetric at the center line of the vertical wall; afterwards, an instability of the thermal boundary layer causes an overshoot of the total Nusselt number and an increase of flow intensity before the periodic solution is approached. For omega = 900 and 1100, the vortices shed continuously and alternately from the upper and lower corners near the hot wall, which causes the variation of the total Nusselt number to be irregular and inconsistent on the hot and cold walls for the omega = 900 case; for the omega = 1100 case the total Nusselt number varies irregularly in the transient processes, but a periodic solution is obtained at steady state.