Suppression of Vortex Flow Resulting from a Round Jet of Air Impinging onto a Heated Horizontal Disk Confined in a Vertical Cylindrical Chamber by Disk Rotation

• Main Authors: Wen-Hsien Lo, 羅文賢
• Other Authors: Tsing-Fa Lin
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/49780753298375342957

碩士 === 國立交通大學 === 機械工程系所 === 93 === An experiment combining flow visualization and temperature measurement is carried out in the present study to explore the possible suppression of the buoyancy-driven stable and unstable vortex flow resulting from a round jet of air impinging onto a heated horizontal disk in a vertical cylindrical chamber by the disk rotation. In this study the experiment is mainly conducted for the jet flow rate varied from 0 to 12.0 slpm (standard liter per minute) with two different injection pipes (diameter 10.0 and 22.1 mm) and the temperature difference between the disk and the air injected into the chamber is varied from 0 to 25.0℃ at a fixed jet-to-disk separation distance of 20.0 mm. The disk rotation speed is varied from 0 to 50 rpm. Thus the jet Reynolds number, Rayleigh number and rotational Reynolds number range respectively from 0 to 1,623, from 0 to 18,790, and from 0 to 3,892. The results from the flow visualization clearly show that typically the steady mixed convective air jet impinging onto the rotating disk consists of three circular vortex rolls. The inner vortex roll is generated by the deflection of the impinging jet at the disk surface and hence termed as the inertia-driven vortex roll. The middle vortex roll is mainly formed by the centrifugal pumping action produced by the disk rotation and hence termed as the rotation-induced roll. The buoyancy-induced vortex roll resulting from the temperature difference between the heated disk and the inlet air prevails in the outer zone of the processing chamber. At a high disk rotation rate, the buoyancy roll can be significantly suppressed and even wiped out by the disk rotation. Besides, the primary inertia-driven roll is stretched out to become slender and weaker. Moreover, the inertia-driven secondary, tertiary, and quaternary rolls dominated at high Rej can be entirely wiped out. We further note that the disk rotation can effectively suppress the inertia-driven and/or buoyancy-driven time-dependent and nonperiodic vortex flows. The unstable vortex flows can be completely stabilized by the disk rotated at a high speed and the flows become steady. The disk rotation can also reduce the radial temperature variation in the flow and significantly delay the onset of the buoyancy-driven roll. Based on the present data, a flow regime map is provided to delineate the the axisymmetric and nonaxisymmetric vortex flows with various disk rotation rates for H=20.0 mm.