Numerical investigation of heat resistances in uniform dense granular flows along a vertical plate

Abstract

Moving bed heat exchangers have been the economic alternatives for the granular flow in industries. To predict the heat transfer coefficients, a better understanding is required of the contact resistance (1/hws) and the penetration resistance (1/hso). In this work, the heat transfer coefficients were simulated using the finite volume method to investigate these resistances in both ordered and random packing sphere particles. It was found that, the 1/hws is determined by the effective thermal conductivity in the wall region, of which the thickness is around 3/22 particle diameters. Moreover, the 1/hso is affected by the heat capacity, thermal conductivities and particulate structures. The effect is reflected by two modified equivalent heat absorption coefficients (1/p1 and 1/p3) in granular flows. Generally, p1 is smaller in the ordered structure because the peak local solid fraction is higher, while p3 is smaller in the random structure due to the lower average porosity.