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ISSN Druckformat: 2152-5102
ISSN Online: 2152-5110
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Suppression of Secondary Flow through Sidewall Converging in Model Horizontal Longitudinal MOCVD Processes
ABSTRAKT
Experimental flow visualization has been conducted to investigate how the sidewall converging affects the buoyancy induced return flow structure and stabilization of vortex flow in mixed convection of gas in a horizontal rectangular duct. The buoyancy driven secondary flow including the return flow and vortex flow is driven by a heated circular disk embedded in the bottom plate of the duct, simulating that in a horizontal longitudinal MOCVD reactor. Specifically, the sidewalls of the duct are inclined toward the duct core so that the gas flow in the duct is accelerated, causing the local buoyancy-to-inertia ratio to decrease in the main flow direction. In the experiment the Reynolds and Rayleigh numbers of the flow at the duct inlet are respectively varied from 5.1 to 51.2 and from 7200 to 21000, and the duct aspect ratio is reduced from 20 at the inlet to 16 or 12 at the exit. The results show a substantial delay in the onset of the return flow and the effective suppression of the buoyancy driven unstable longitudinal and transverse vortex flows by the sidewall converging. Moreover, the sidewall converging can weaken the return flow more effectively at slightly higher Reynolds numbers. An empirical equation is provided to correlate the present data for the onset condition of the return flow in the converging duct. The reduction in the size and intensity of the return flow is prominent. Besides, the onsets of longitudinal and transverse vortex rolls are delayed substantially.