Full mechanism modeling of contact thermal resistance with stagnant fluids in thermal discrete element method

After reexamining three mechanisms of thermal resistance in packed bed: particle-particle conduction through a finite contact area (PPA), conduction through a contact point (PPP), and through stagnant fluids near the contact point (PFP), a full mechanism model of contact thermal resistance (CTR) and the effective thermal conductivity (ETC) of particles with stagnant interstitial fluid is proposed here for thermal discrete particle simulations (TDEM). The current model agrees with experimental data of various conductivity ratios and void fractions, and can be applied for both dense and dilute gas-particle systems. It shows that the PPA mechanism is dominating when the conductivity ratio of particle-to-fluid κ is greater than 104. Moreover, when κ < 2000, the PPP mechanism becomes dominant and the PPA mechanism can be neglected. All these mechanisms incorporated in current model can be naturally imbedded in thermal discrete thermal method (TDEM).