Experimental study of unsteady thermal characteristics and rotation induced stabilization of air convection in a bottom heated rotating vertical cylinder

Abstract

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.