Experimental study of heat transfer of a sphere levitating in a channel

The paper presents experimental results on heat transfer rate for a spherical body under the condition of aerodynamic lifting (free levitation) in airflow within a diffuser channel. The temperature of the heated surface and the sphere rotation speed were measured by contactless methods. It was found that for a broad range of airflow speed, the sphere rotational motion by two coordinates develops. This drastically alters the flow dynamics around the sphere: there is no stationary separation zones both in the frontal and rear parts. The heat transfer coefficient was investigated using the nonstationary method at different initial temperatures of the sphere surface and at Reynolds numbers for the airflow. For the sake of comparison, a similar study was conducted for a rigidly fixed sphere under the same conditions. It was proved that the free aerodynamic levitation of a sphere allows leveling the surface temperature field and enhancing the heat transfer (compared to a flow past an immovable sphere). Experimental results on heat transfer demonstrate that the cooling time becomes shorter and the Nusselt number increases with the rotation speed by 300–600 %.