Browsing by Author "Ker, YT"

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A combined numerical and experimental study of air convection in a differentially heated rotating cubic cavity
(1996-10-01)
Ker, YT
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
A combined numerical and experimental study was carried out to investigate the steady convective flow structure and the how stability in an inclined cubic air cavity subject to differential heating across a pair of side walls and subject to rotation about an axis which is normal to the insulated bottom wall and through the geometric center of the cavity. In the numerical simulation the three-dimensional Navier-Stokes and energy equations were directly solved by the projection method for the vertical cavity (phi = 0 degrees). While in the experimental study the air temperature in the cavity at selected locations was detected for both steady and unsteady flows. Results were obtained for Delta T = 10 degrees C and 4.6 degrees C, Omega from 0 rpm to 453 rpm and phi from 0 degrees to 75 degrees. The numerical results clearly revealed the complex multicellular flow structure in a vertical cavity at low rotation rates in which the mutual interactions of the thermal buoyancy, Coriolis force and rotational buoyancy are important. The experimental data suggested that the air flow can be stabilized by the cavity rotation when the rotation rate is low. But al high rotating speed the cavity rotation produced destabilizing effects. Copyright (C) 1996 Elsevier Science Ltd.
Experimental observation and conjugated heat transfer analysis of vortex flow development in mixed convection of air in a horizontal rectangular duct
(1996-11-01)
Lin, WL
;
Ker, YT
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
A combined flow visualization and conjugated heat transfer analysis was carried out to study the axial evolution of the buoyancy induced secondary vortex flow in a mixed convective air flow through a bottom heated horizontal rectangular duct. In the experiment the cross plane secondary flow was visualized at selected cross-sections. While in the conjugated analysis, the unsteady three-dimensional Navier-Stokes and energy equations for the flow were coupled with the unsteady two-dimensional conduction equations for the solid walls and were solved together numerically. Results were obtained for the Reynolds number ranging from 35 to 102 and Grashof number from 1600 to 5.8 x 10(5), covering the steady and time periodic flows. Both the experimental and numerical results clearly showed the generation of the longitudinal vortex rolls in the entry half of the duct and the merge of these rolls downstream. At higher buoyancy-to-inertia ratio more rolls were generated and they merged into fewer and larger rolls. Significant conjugated heat transfer effects were noted from the numerical results. Copyright (C) 1996 Elsevier Science Ltd.
Experimental observation and conjugated heat transfer analysis of vortex flow development in mixed convection of air in a horizontal rectangular duct
(1996-11-01)
Lin, WL
;
Ker, YT
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
A combined flow visualization and conjugated heat transfer analysis was carried out to study the axial evolution of the buoyancy induced secondary vortex flow in a mixed convective air flow through a bottom heated horizontal rectangular duct. In the experiment the cross plane secondary flow was visualized at selected cross-sections. While in the conjugated analysis, the unsteady three-dimensional Navier-Stokes and energy equations for the flow were coupled with the unsteady two-dimensional conduction equations for the solid walls and were solved together numerically. Results were obtained for the Reynolds number ranging from 35 to 102 and Grashof number from 1600 to 5.8 x 10(5), covering the steady and time periodic flows. Both the experimental and numerical results clearly showed the generation of the longitudinal vortex rolls in the entry half of the duct and the merge of these rolls downstream. At higher buoyancy-to-inertia ratio more rolls were generated and they merged into fewer and larger rolls. Significant conjugated heat transfer effects were noted from the numerical results. Copyright (C) 1996 Elsevier Science Ltd.
Experimental study of unsteady thermal characteristics and rotation induced stabilization of air convection in a bottom heated rotating vertical cylinder
(1998-06-01)
Ker, YT
;
Li, YH
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
Flow stabilization by cavity rotation in convection of air (Pr = 0.7) in a vertical circular cylinder heated from below is studied experimentally. The cylinder is rotated at a constant speed about its own axis. In the experiment the time variations of the air temperature at selected locations in the cylinder are measured. Results are obtained for a cylinder with diameter D = 5 cm, height H = 10 cm, imposed temperature difference Delta T = 5 degrees C to 15 degrees C and rotation rate Omega from 0 to 346.1 rpm. The experimental data clearly show the stabilization of the thermal buoyancy driven irregular flow by the cavity rotation when the rotation rate is in certain ranges. For a given Delta T two different ranges of Omega exist for the flow to be stabilized. Outside these ranges the flow oscillates periodically or quasi-periodically in time. At given Delta T and Omega the temperature oscillation at various locations exhibits some change in amplitude but negligible change in frequency. However, change of the oscillation frequency with the rotation rate is nonmonotonic and is rather significant at high rotation rates. But this frequency change with the imposed temperature difference is small. (C) 1998 Elsevier Science Ltd. All rights reserved.
Fluctuating characteristics and rotation induced stabilization of thermal buoyancy driven water flow in a vertical rotating cylinder
(2001-03-01)
Yin, CP
;
Ker, YT
;
Huang, TH
;
Lin, TF
;
機械工程學系
An experimental study was carried out here to investigate the fluctuating characteristics and stabilization of the thermal buoyancy driven unstable water flow in vertical closed circular cylinders heated from below by rotating the cylinder about its vertical axis. Results for the time variations of the water temperature at selected locations were obtained for the imposed temperature difference DeltaT ranging from 5 degreesC to 15 degreesC and the cavity rotation rate Ohm from 0 to 300 rpm for a cylinder with diameter D = 5 cm, height H = 10 cm and Ohm varying from 0 to 210 rpm for another cylinder with D = 2.5 cm and H = 5 cm. Based on the data for the time records of the water temperature, the flow suppression by the cylinder rotation causes the time-average temperature distributions along the cylinder axis for high rotation rates to become linear. Besides, the flow can be stabilized by the cylinder rotation when the rotation rate is in certain ranges. Significant dependence of the oscillation amplitude with the space is revealed. But the entire how oscillates at nearly the same frequency when the flow is time periodic. Moreover, non-monotonic variations of the oscillation frequency with the rotation rate are clearly shown. Based on the present data, a flow regime map and correlations delineating the stable and unstable states in the vertical rotating cylinders containing water are also provided. (C) 2001 Elsevier Science Ltd. All rights reserved.
Rotation induced stabilization of air convection in a bottom heated diverging cylinder rotating about its own axis
(1998-12-01)
Ker, YT
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
Rotation induced stabilization of air convection in a vertical, diverging cylinder heated from below and rotated steadily about its own axis is studied experimentally. The cylinder has a smaller circular cross section at its bottom end. In the experiments, the transient variations of the air temperature at selected locations are measured to explore the effects of rotation rate and diverging angle on the temporal stability of the flow. Data are collected for the diverging angle varied from 0-30 degrees, imposed temperature difference from 5-15 degrees C and rotation rate up to 346.1 rpm. The measured data show that the ranges of the rotation rate to stabilize the flow are wider for diverging cylinders than those fora right cylinder at xi = 0 degrees. Thus, it is possible to use a crucible with a diverging section to grow large and high quality bulk crystals. A power spectrum density analysis of the data for the unstable flow at high rotation rates indicates that the flow oscillation is mainly time periodic and dominated by a single fundamental frequency: Moreover, the oscillation frequency varies nonmonotonically with the rotation rate. Flow regime maps delineating stable and unstable states are also provided for practical applications. (C) 1998 Elsevier Science Ltd. All rights reserved.
Time-averaged and reverse transition in oscillatory air convection in a differentially heated rotating cubic cavity
(1997-09-01)
Ker, YT
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
An experimental study was carried out to investigate the time-averaged and unsteady thermal characteristics in an inclined cubic air cavity, subject to differential heating across a pair of side walls and subject to rotation about an axis which is normal to the insulated bottom wall and through the geometric center of the cavity. Specifically, the air temperature in the cavity at selected locations was measured for both steady and unsteady flows. Results were obtained for the cavity height H=10 and 15 cm, temperature difference Delta T ranging from 2 to 10 degrees C, rotation rate Omega from 0 to 452.9 rpm and inclined angle phi from 0 to 90 degrees (heated from below). Time records of the air temperature showed the presence of the how re-stabilization in two different ranges of the rotation rates. Thus, the transient oscillatory flow can be stabilized by increasing the cavity rotation when the rotation rate is in these ranges. This flow restabilization is more pronounced for a higher inclined angle. Moreover, a power spectrum density analysis of the time records indicated that at low rotation rates the amplitudes of the temperature oscillation are location dependent, but the oscillation frequencies at various locations for a given set of Delta T, Omega and phi are the same. (C) 1997 Elsevier Science Ltd.
Time-averaged and reverse transition in oscillatory air convection in a differentially heated rotating cubic cavity
(1997-09-01)
Ker, YT
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
An experimental study was carried out to investigate the time-averaged and unsteady thermal characteristics in an inclined cubic air cavity, subject to differential heating across a pair of side walls and subject to rotation about an axis which is normal to the insulated bottom wall and through the geometric center of the cavity. Specifically, the air temperature in the cavity at selected locations was measured for both steady and unsteady flows. Results were obtained for the cavity height H=10 and 15 cm, temperature difference Delta T ranging from 2 to 10 degrees C, rotation rate Omega from 0 to 452.9 rpm and inclined angle phi from 0 to 90 degrees (heated from below). Time records of the air temperature showed the presence of the how re-stabilization in two different ranges of the rotation rates. Thus, the transient oscillatory flow can be stabilized by increasing the cavity rotation when the rotation rate is in these ranges. This flow restabilization is more pronounced for a higher inclined angle. Moreover, a power spectrum density analysis of the time records indicated that at low rotation rates the amplitudes of the temperature oscillation are location dependent, but the oscillation frequencies at various locations for a given set of Delta T, Omega and phi are the same. (C) 1997 Elsevier Science Ltd.