Experimental study of the forces associated with mixed convection from a heated sphere at small Reynolds and Grashof numbers. Part I: cross-flow

The present paper addresses the issue of mixed convection from a small heated sphere in cross-flow configuration. The sphere is suspended in an electrodynamic chamber (EDC), where it is heated by a focused laser beam up to several hundred degrees above room temperature. As a result, there is free convection from the sphere, with the Grashof number smaller than 0.01. Then, a horizontal forced flow is applied and gradually increased in a quasi-static manner. Horizontal flow velocities are in the range 0–0.1 m/s, providing very low particle Reynolds numbers, usually less than 0.5. The effects of the free convection on the drag force, and of the forced flow on the free convection, are assessed measuring continuously the horizontal and vertical forces experienced by the sphere. It is shown quantitatively how the forced flow suppresses the free convection. A similarity law is suggested for the behavior of horizontal and vertical forces at various particle temperatures.