Numerical study of convective heat transfer in static arrangements of particles with arbitrary shapes:A monolithic hybrid lattice Boltzmann-finite difference-phase field solver

A compressible lattice Boltzmann-finite difference method is extended by the phase-field approach into a monolithic scheme to study fluid flow and heat transfer through regular arrangements of solid bodies of circular,elliptical and irregular shapes.The advantage of using the phase-field method is demon-strated both in its simplicity of accounting for flow and thermal boundary conditions at solid surfaces with irregular shapes and in the capability of generating such complex-shaped objects.For an array of discs,numerical results for the overall solid-to-gas heat transfer rate are validated via experiments on flow through arrays of hot cylinders.The thus validated compressible LB-FD-PF hybrid scheme is used to study the dependence of heat transfer on flow and thermal boundary conditions(Reynolds number,temperature difference between the hot solid bodies and the inlet gas),porosity as well as on the shape of solid objects.Results are rationalized in terms of the residence time of the gas close to the solid body and downstream variations of gas velocity and temperature.Perspective for further applications of the proposed methodology are also discussed.

Spatially resolved investigation of flame particle interaction in a two dimensional model packed bed

This study investigates the interaction between a premixed methane-air flame and particles inside a model packed bed.The opacity of the spherical packed beds to visible light poses a major barrier to the implementation of highly resolved optical diagnostics,so that no detailed experimental data were so far available for the validation of numerical simulation.Here,a two-dimensional cylindrical packed bed design is set up,which enables direct line-of-sight optical measurements without loss of spatial reso-lution over the fluid region between the particles.In this study,the case of cold metallic cylindrical particles(T=377 K)relevant to start-up of a reactor is investigated using internal particle cooling,which also allows cylinder specific heat transfer rate measurements by differential temperature measurements on the coolant streams.The two dimensional assumption is first verified by measuring the inflow ve-locity and cylinder temperature profile along the cylinders.Chemiluminescence imaging is then per-formed using a telecentric lens to observe the position and geometry of the two-dimensional flame front with respect to the surrounding cylinders without loss of resolution.Simultaneously,the cylinder-specific flame to cylinder heat transfer rates and cylinder surface temperature are measured.As the flame is closely surrounded by the three cooled cylinders,intense heat transfer is observed in this region corresponding to 25±2.5%of the flame thermal power.Flames were stabilised at different positions depending on inflow velocity and equivalence ratio,and a direct correlation between flame to cylinder stand-off distance and the heat transfer rate normalised to the flame thermal power was found for both top and side cylinders.Also,sidewall quenching distances to the curved cylinder surfaces were evaluated,and seem to be influenced by the presence of a warm recirculation zone behind the cylinders.This investigation provides fully resolved flame front position and heat transfer rates for a known geometry and cylinder thermal boundary conditions,and provides validation data for numerical simulations of this high flame particle coupling case.