Simulation Of Fluid Flow Characteristics In Spherical Particles Packed Bed

Several techniques have been developed for impurity removal from the water solution to face the challenging technical problem of wastewater treatment.As a typical method of wastewater treatment,the adsorption method has problems such as incomplete adsorption and inhomogeneous particle stacking in the adsorption process,which can further result in high radial pressure deviation values in the bed,heterogeneous fluid distribution,and other disadvantageous situations.In this paper,the hydrodynamic characteristics of a bed of spherical particles packed in a dynamic adsorption device are investigated for this type of problem,with the dynamic adsorption device as a model.A combination of theoretical calculations and empirical formulas is used to verify the feasibility of the simulation results.Firstly,the bypass flow characteristics of the particles in the packed bed inside the device are analyzed.On this basis,the actual filling is simulated and the internal void(pore)structure and flow characteristics are further investigated.Secondly,modification of the parameters of the porous media model was completed based on the data obtained from the simulation,further the distribution of pressure and velocity were investigated in the porous media model.With this paper,it is beneficial to provide theoretical guidance for the optimization of the packed bed structure.It is known from the analysis of the bypassing flow of spherical particles that the effect of bypassing drag of the sphere is small when the Reynolds number Re is lower,there is an obvious flow vortex does not appear,and the flow velocity and pressure values on both sides of the porous sphere are generally the agreement.Reversed symmetric vortices started to be observed in the back part of the sphere as Re increased.High pressure is observed on the front surface of the porous sphere,and the pressure changes decrease as the distance between the fluid and the sphere is increased.To the left of the tangent point of the upper hemisphere,i.e.nearα=292.5°,the peak velocity of the bypass is observed.The simulation results of the bed structure which was built from DEM showed that the overall error of the global void fraction from DEM simulation was less than 7%compared with the empirical formulations.A decrease in the local void fraction of the bed oscillates from wall to bed center along the radial direction,which is in general agreement with the prediction of the empirical correlation and demonstrates the feasibility of this method.Furthermore,through comparing the pressure drop and friction coefficient obtained from the simulation with the calculated values from the conventional empirical correlation equation.The empirical formula is shown to be applicable in the range of D/d ratios and particle Reynolds number Re_m.Whereas Ergun’s empirical correlation equation has the highest relative error(RE),Foumeny’s empirical correlation equation has the greatest applicability.It can be seen from the analysis of the velocity that there are inhomogeneities in the distribution of fluid characteristics.The tendency of the fluid to flow into the particle gap indicates that the distributions of fluid velocity for different D/d ratios are related to the distribution of void fraction,and the distributions of radial velocity for different D/d ratios are linked to the structure of the packed bed.Results of the current study of fluid flow characteristics in packed beds employing the porous media model indicate that the model is not appropriate for packed beds with D/d<3.The variation of the resistance coefficient has a negligible effect on the velocity and pressure drop inside the porous media region of the bed,and the variation of the velocity and pressure drop is associated mainly with the global void fraction.It is also known that the increased the global void fraction,the greater the flow velocity and the lower the pressure drop in the bed region.In this paper,we have calculated that the error between the fitting equations and the DEM simulation results is within 6%,which can satisfy the error required for engineering applications.It is employed to analyze spherical particle-packed beds with D/d ratios greater than 3.