Research On Packing Structure And Internal Heat Transfer Of Porous Media Combustion

Porous media combustion is a promising new combustion technology.Compared with free space combustion,it has many potential advantages.In recent years,with the deepening of the theory and technology of porous media combustion,domestic and foreign researchers have applied it to the combustion of natural gas and mash gas.However,because porous media has both a solid-phase framework part and a non-solid-phase pore part,it is necessary to thoroughly explore the particle accumulation structure and the fluid flow and fluid flow in the porous medium in order to fully understand the combustion characteristics of porous media.Heat transfer characteristics.In order to deeply explore the fluid flow and heat transfer characteristics of porous media,it is very difficult to accurately describe porous media because the porous media are very complex and irregular in structure.Based on the actual particle accumulation type porous media accumulation structure,this paper establishes a random accumulation of particles porous media structure model,and combines computational fluid dynamics to numerically simulate the particle accumulation structure,porosity,and fluid flow and heat transfer process in the porous media.Research,the main tasks completed in this paper are as follows:Firstly,the discrete element method(DEM)is used to establish a particle packing structure model similar to the real random porous media.Because the discrete element method(DEM)is used to simulate the process of particle falling and accumulating,it is necessary to complete the particle accumulation model with 3D modeling software after the particle falling and accumulating is stable,so as to reconstruct the final accumulation structure.Therefore,the DEM model is highly similar to the actual porous media accumulation structure,and the particle accumulation structure has distinct randomness.Secondly,based on the geometric model of random packing structure,the characteristics of fluid flow and pressure distribution in porous media bed with different number of particles were studied.Finally,based on the above analysis,the heat transfer characteristics in the porous media bed are analyzed,and the influence of gas velocity on the fluid flow field and temperature field in the porous media is described in detail.The results are as follows:(1)The discrete element method was used to construct a random accumulation model with the number of particles(N)N=100-500,and the overall porosity of the resulting accumulation model was compared with the experimental results of the radial porosity distribution in the literature.The porous medium accumulation structure in the porous medium burner is more consistent with the actual packing structure in the actual burner.(2)The pressure drop of the stacked bed with different numbers of particles at the same inlet speed increases roughly linearly with the increase of the number of particles stacked;there is a low-velocity zone or even fluid stagnation at the wake of the particles and the end of the bed with different numbers of particles Zone: The average circumferential velocity of the beds with different particle numbers has the same trend as the radial porosity distribution.(3)The pressure drop of the stacked bed fluctuates more violently as the inlet velocity increases,which is conducive to the mixing of different fluids in the bed;the axial average turbulent kinetic energy and the axial average turbulent dissipation rate change in the stacked bed at different inlet velocities The trends are roughly the same,and the greater the fluctuation of the turbulent kinetic energy and the turbulent dissipation rate as the inlet velocity increases,this reflects the larger spatial distortion in the randomly packed bed,resulting in extremely high local dissipation rates,which may affect The combustion process has an impact.(4)The high temperature area is concentrated in the center of the cylinder structure,and the range decreases with the increase of the inlet velocity.The low-speed zone at the particle wake causes the uneven distribution of the bed heat,and forms a detailed local high temperature area at the particle wake,which aggravates the uneven distribution of bed temperature.(5)A long and narrow low temperature zone appears in the stacked bed close to the tube wall,and the area of the long and narrow low temperature zone becomes larger with the increase of the inlet speed;due to the unevenness of the randomly stacked particles in the bed,the heat is inclined to the isothermal surface in the bed.,And the tilt angle gradually decreases with time.