Particle shape effect on hydrodynamics and heat transfer in spouted bed:A CFD-DEM study

Spouted bed has drawn much attention due to its good heat and mass transfer efficiency in many chemical units.Investigating the flow patterns and heat and mass transfer inside a spouted bed can help optimize the spouting process.Therefore,in this study,the effects of particle shape on the hydrodynamics and heat transfer in a spouted bed are investigated.This is done by using a validated computational fluid dynamics-discrete element method(CFD-DEM)model,considering volume-equivalent spheres and oblate and prolate spheroids.The results are analysed in detail in terms of the flow pattern,microstruc-ture,and heat transfer characteristics.The numerical results show that the prolate spheroids(Ar=2.4)form the largest bubble from the beginning of the spouting process and rise the highest because the fluid drag forces can overcome the interlocking and particle-particle frictional forces.Compared with spherical particles,ellipsoidal spheroids have better mobility because of the stronger rotational kinetic energy resulting from the rough surfaces and nonuniform torques.In addition,the oblate spheroid system exhibits better heat transfer performance benefiting from the larger surface area,while prolate spheroids have poor heat transfer efficiency because of their orientation distribution.These findings can serve as a reference for optimizing the design and operation of complex spouted beds.

Investigation of mini-hydrocyclone performance in removing small-size microplastics

Large amounts of microplastics(MPs)have been found in rivers and oceans,bringing great harm to aquatic animals,plants,even human beings.However,the effective removal method of MPs,especially those with small sizes(5-20 μm)is still lacking.This work presents mini-hydrocyclones to remove 10 μm(average size)diameter MPs.The removal performance of nine mini-hydrocyclones with different diameters of spigot and vortex finder is examined experimentally and numerically.The performance of the designed cyclones is evaluated in terms of recovery,water split,concentration ratio and pressure drop.The results show that mini-hydrocyclones are applicable to removing small-size MPs with the maximum concentra-tion ratio at 2.16 and the particle recovery at 51%.The flow characteristics inside the mini-hydrocyclones are analyzed in detail.It is shown that the distributions of water axial velocity and radial velocity could collectively affect the behaviors of small-size MPs in mini-hydrocyclones.Specifically,a larger amount of water split could entrain more fine particles to underflow.Meanwhile,a less frequent alternation of radial velocity between the positive and negative directions on the same side of the cyclone should benefit the removal of small-size MPs.

A Pseudopotential Lattice Boltzmann Analysis for Multicomponent Flow

This paper presents a pseudopotential lattice Boltzmann analysis to show the deficiency of previous pseudopotential models,i.e.,inconsistency between equilibrium velocity and mixture velocity.To rectify this problem,there are two strategies:decoupling relaxation time and kinematic viscosity or introducing a system mixture relaxation time.Then,we constructed two modified models:a two-relaxationtime(TRT)scheme and a triple-relaxation-time(TriRT)scheme to decouple the relaxation time and kinematic viscosity.Meanwhile,inspired by the idea of a system mixture relaxation time,we developed three mixture models under different collision schemes,viz.mix-SRT,mix-TRT,and mix-TriRT models.Afterwards,we derived the advection-diffusion equation for the multicomponent system and derived the mutual diffusivity in a binarymixture.Finally,we conducted several numerical simulations to validate the analysis on these models.The numerical results show that these models can obtain smaller spurious currents than previous models and have a wider range for the accessible viscosity ratio with fourth-order isotropy.Compared to previous models,presentmodels avoid complex matrix operations and only fourth-order isotropy is required.The increased simplicity and higher computational efficiency of these models make them easy to apply to engineering and industrial applications.