Browsing by Author "Yin, CP"

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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.
Improvement in wafer temperature uniformity and flow pattern in a lamp heated rapid thermal processor
(2000-07-01)
Yin, CP
;
Hsiao, CC
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
An experimental lamp heated, rapid thermal processor (RTP) for an 8-in single silicon wafer was designed and established to investigate the thermal and flow characteristics in the processing chamber by transient temperature measurement and flow visualization. Experiments were carried out to explore the effects of placing a highly conducting copper plate right below the wafer on the uniformity of the wafer temperature and effects of the showerhead on the resulting flow distribution in the processing chamber. The measured data indicated that adding the copper plate can effectively reduce the nonuniformity of the wafer temperature. Besides, using a showerhead with finer holes in it results in a better flow distribution in the processor. (C) 2000 Elsevier Science B.V. All rights reserved.
Stabilization of buoyancy-driven unstable vortex flow in mixed convection of air in a rectangular duct by tapering its top plate
(2000-02-01)
Tseng, WS
;
Lin, WL
;
Yin, CP
;
Lin, CL
;
Lin, TF
Stabilization of the buoyancy-driven unstable mixed convective vortex air flow in a bottom heated rectangular duct by tapering its top plate is investigated experimentally. Specifically, the duct is tapered so that its aspect ratio at the duct inlet is 4 and gradually raised to 12 at the exit of the duct. In the study the secondary flow in the duct is visualized and the steady and transient thermal characteristics of the flow are examined by measuring the spanwise distributions of the time-average temperature. The effects of the Reynolds and Grashof numbers on the vortex flow structure are studied in detail. Moreover, the spanwise-averaged Nusselt numbers for the horizontal rectangular and tapering ducts are also measured and compared. Furthermore, the time records of the air temperature are obtained to further detected the temporal stability of the flow. Over the ranges of the Re and Gr investigated for 5 less than or equal to Re less than or equal to 102 and 1.0X10(4)less than or equal to Gr less than or equal to1.7X10(5), the vortex flow induced in the rectangular duct exhibits temporal transition from a steady laminar to time periodic and then to chaotic state at increasing buoyancy-to-inertia ratio. Substantial change in the spatial structure of the vortex flow is also noted to accompany this temporal transition. The results for the tapering duct indicate that more vortex rolls can be induced due to the increase in the aspect ratio of the duct with the axial distance. But the vortex rolls are weaker and are completely stabilized by the tapering of the top plate.
Subcooled flow boiling heat transfer of R-134a and bubble characteristics in a horizontal annular duct
(2000-06-01)
Yin, CP
;
Yan, YY
;
Lin, TF
;
Yang, BC
;
機械工程學系
Experiments were carried out to investigate the subcooled flow boiling heat transfer and visualize the associated bubble characteristics for refrigerant R-134a flowing in a horizontal annular duct having inside diameter of 6.35 mm and outside diameter of 16.66 mm. The effects of the imposed wall heat flux, mass flux, liquid subcooling and saturation temperature of R-134a on the resulting nucleate boiling heat transfer and bubble characteristics were examined in detail. In the experiment significant hysteresis was noted in the boiling curves during the onset of nucleate boiling (ONB) especially at low saturation temperature and high subcooling. The temperature undershoot at ONE is rather large for most cases. The boiling heat transfer was slightly higher for a lower saturation temperature and was little affected by the mass flux. However, for a higher subcooling of the refrigerant better heat transfer results. Furthermore, the flow visualization revealed that at higher imposed wall heat flux the heated surface was covered with more bubbles and the bubble generation frequency is higher. But the size of the bubbles departing from the heated surface was only slightly affected by the imposed heat flux. At high mass flux and subcooling the bubble generation was suppressed to a noticeable degree. Besides, the bubbles are much smaller at a higher subcooling. Finally, empirical correlations for the heat transfer coefficient and bubble departure diameter in the subcooled flow boiling of R-134a were proposed. (C) 2000 Elsevier Science Ltd. All rights reserved.