Effect of fluctuation on heat transfer enhancement of a spherical particle

Abstract

Heat transfer of a particle in turbulent flows is essential, while the study on the effect of turbulent fluctuation on the heat transfer enhancement of a spherical particle is rarely reported. In this work, a 4.4 mm copper particle with a small Biot number was subject to a near homogenous and isotropic turbulent flow field to investigate the heat transfer behaviors. The detailed flow characteristics were measured with the Particle Image Velocimetry (PIV). As the fan speed increases, both the fluctuating velocity (urms) and the time-averaged velocity (uave) increase quickly at first and then slowly. When the furnace temperature increases, both urms and uave barely change. For all conditions, urms is apparently larger than uave. As for the particle heating experiment, the heating rate increases with the fan speed and the furnace temperature. Based on the measured results of the flow field and the particle temperature, a modified correlation for predicting Nusselt number was proposed to describe the effect of the turbulent fluctuation on the heat transfer of a single spherical particle. The newly proposed correlation was further validated by particle heating experiments of a 2 mm copper sphere in this work and direct numerical simulation results from the literature.