Numerical determination of the volumetric heat transfer coefficient in fixed beds of wood chips

Abstract The aim of this work is to build CFD tools to study heat transfer in packed beds during the thermochemical upgrading process of woody biomass. For that purpose, a numerical workflow capable of investigating heat transfer phenomena inside a packed bed was developed. First, the bed is generated using a Discrete Element Method (DEM) code. Then, a steady-state Direct Numerical Simulation (DNS) solver is used to acquire the flow patterns inside the pores of the bed. Finally, the heat equation is solved for the particles and the fluid in a coupled manner. The results are thoroughly validated against two benchmark cases: flow around a sphere and flow through a packed bed of spheres. The importance of accounting for internal heat resistance for substrates with high Biot number (e.g. wood) is highlighted. Furthermore, the heat transfer phenomena inside a packed bed of torrefied wood chips are investigated. Values of the heat transfer coefficient are also provided ( ≃ 5 W/m 2 /K, for Re i 5, 7.7 for Re = 10). Another interesting finding is the effect of channeling in this type of beds and its impact on the temperature field of the wood chips.