Indirect conduction in gas–solids systems: Static vs. Dynamic effects

Abstract

Conductive mechanisms play an integral role in the transfer of heat through dense gas-solid systems. In particular, the conduction occurring through a thin layer of fluid between the solids (indirect) can become the primary mode for heat transfer within gas-solid systems. However, attempts to evaluate the effect of surface roughness and fluid lens thickness (theoretical inputs) on indirect conduction have been restricted to static, single-particle cases. By contrast, here we quantify these effects for dynamic, multi-particle systems using a non-dimensional, average heat transfer coefficient that is obtained via techniques commonly employed by classic kinetic theory.Analytical predictions for the impact of theoretical inputs on indirect conduction are compared to outputs from computational fluid dynamics -discrete element method simulations. The analytical predictions are in agreement with simulations and show that indirect conduction in static systems is most sensitive to surface roughness, while dynamic systems are sensitive to the fluid lens thickness.

Infrared temperature measurements and DEM simulations of heat transfer in a bladed mixer

“…We instead consider an “effective” thermal conductivity between particles. Previous study has examined heat transfer from the particle to the gas to the particle and incorporated this in DEM 31,34,39 . It is of interest to examine such “more sophisticated” models which include heat transfer from the particles to the gas, frictional heating, and particle roughness, to see whether they better capture experimental results or if the added complexity does not warrant the additional parameters in the model.…”

“…In summary, the model is rather straightforward, and we acknowledge that literature exists with more complex heat transfer models that account directly for heat transfer in the interstitial gas, 17,31 frictional heating, 32 radiation, 33 nonuniform particle heating, 16 particle roughness, 34 and interparticle porosity, 35 among others. Implementing a model that encompasses all aspects of heat transfer would be ideal but this study serves as a first step to comparing simulations and experiments for heat transfer in a bladed mixer, so we have only considered direct (particle–particle) conduction without the complexities of the interstitial gas, frictional heating, and other effects.…”

“…Previous study has examined heat transfer from the particle to the gas to the particle and incorporated this in DEM. 31,34,39 It is of interest to examine such "more sophisticated" models which include heat transfer from the particles to the gas, frictional heating, and particle roughness, to see whether they better capture experimental results or if the added complexity does not warrant the additional parameters in the model. In a real drying process, there is liquid, gas, and solid particles and heat transfer through all three phases should be considered.…”

Study on Segregation and Heat Transfer of Polydisperse Particles in a Three-Dimensional Rotating Drum by Using the DEM

“…Based on the simulation conditions of this work, the heat transfer model is simplified as follows: The gas is stagnant in the rotating drum, and the thermal conductivity of the solid is much higher than that of gas (λ s /λ g > 14,000). The convective heat transfer rate is much lower than the conductive heat transfer rate, and the convective heat transfer is ignored The heat radiation from the side wall to the particle can be neglected when dealing with solid materials with temperatures below 700 K …”

“…The convective heat transfer rate is much lower than the conductive heat transfer rate, and the convective heat transfer is ignored. 33 2. The heat radiation from the side wall to the particle can be neglected when dealing with solid materials with temperatures below 700 K. 34 3.…”