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Journal of Flow Visualization and Image Processing
SJR: 0.161 SNIP: 0.312 CiteScore™: 0.1

ISSN Druckformat: 1065-3090
ISSN Online: 1940-4336

Journal of Flow Visualization and Image Processing

DOI: 10.1615/JFlowVisImageProc.v15.i4.20
pages 301-312

OBSERVATION OF THERMALS IN MIXED CONVECTIVE GAS FLOW OVER A MODEL HEATED SUBSTRATE

Jyh-Long Tuh
Department of Living Services Industry, Asia-Pacific Institute of Creativity Miaoli, Taiwan 35153, ROC

ABSTRAKT

Experimental flow visualization has been carried out to investigate the characteristics of thermals and their relation to the evolution of longitudinal roll patterns in mixed convection of air over a circular heated plate mounted on the bottom of a horizontal flat duct. The results reveal that thermals with three different appearances are observed in the progression of end view flow photos, namely, the knotted thermals situated slightly beyond the onset point, the subsequent mushroom-shape thermals in the core region of the duct, and the deformed thermals located at each far side of lateral extension upon the heated plate. It is noted that on top of the heated surface, regular thermals arrange in unequal distance and lose their spanwise symmetry slightly. Moreover, the onset points of thermals all land on the circular heated disk and are in a shape of a concave downward curve in the flow direction. At higher buoyancy the generated knotted thermals unsteadily oscillate up and down and move spanwisely in the region slightly beyond the onset point which in turn results in meandering of the smoke streaks on top view accompanied by the bifurcation points of rising thermals to move back and forth in the axial direction. This explains the snaking motion proposed in the literature. Besides, coexistence and new generation of thermals are observed in the intermittent transition.


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