(239h) Effect of Particle Surface Roughness on Wall to Particle Heat Transfer

Solid drying commonly involves heat transfer between a hot wall and particles. Hence, accurate prediction of overall wall to particle heat transfer coefficient is crucial to the process. For granular materials, microscopic particle properties (size, shape, surface roughness, etc.) play a significant role in determining the bulk (macroscopic) behavior. Therefore, careful consideration of each of the particle-scale properties is critical in particulate heat transfer. The effects of particle size on particle-wall heat transfer have been investigated extensively in past works; however, the effects of particle surface roughness and shape have not been well established. This work is mainly focused on linking particle surface roughness to macroscopic particle-wall heat transfer, which impacts the contact area between particles and their separation distance. Experiments were designed to operate in wall- conduction dominant regime. For particle characterization, the roughness of spherical glass particles was modified and asperity heights were measured. Asperity heights of the particles were determined from atomic force microscopy topographic maps of the surfaces. Wall-to-particle heat transfer coefficients for different particle roughness levels were compared, allowing for the sensitivity of heat transfer to surface roughness to be established. The experimental results were then validated using the discrete element simulations, which take the measured roughness values as inputs.