Research On The Drag Force Model Of Nanoparticle Agglomerates Based On Fractal Dimension

The internal structure of nanoparticle fluidization agglomerates is relatively complex.At present,there is no reasonable description of its internal structure.In this paper,the structure characteristics of nanoparticle aggregates are described by fractal theory.Based on fractal theory,the nanocluster structure model is constructed.The distribution of porosity and permeability in the cluster is described,and the flow and force of the cluster are analyzed.By analyzing the flow and stress state of the cluster under different Reynolds number and fractal dimension,a cluster drag force model based on fractal dimension under different Reynolds conditions was established.In this paper,the flow and pressure characteristics of the gas passing through a single nanparticle agglomerate under different working conditions are studied.The velocity and pressure distribution of the fluid and the variation of the drag coefficient are analyzed.The drag system based on the Reynolds number and the fractal dimension is obtained by comparing with the experimental and simulation results in other literature.At low Reynolds number,the smaller the average permeability of the aggregates with high fractal dimension,the harder the gas permeates the nanoclusters,and the gas flows around the agglomerate surface.The drag coefficient of nanomagglomerate increases with the increase of fractal dimension,and the drag coefficient is less than the drag coefficient of solid ball under the same condition,that is,the drag coefficient ratio is always less than 1.The drag coefficient ratio at low Reynolds number is independent of Reynolds number and it is only related to the fractal dimension or permeability ratio affecting the permeability of the agglomerate.Different permeability models have great influence on drag coefficient ratio,and the applicable conditions of different permeability models are different.At moderate Reynolds number,after passing through the nano agglomerate,the gas will flow back to the inner part of the nano agglomerate in addition to the flow and penetration.This phenomenon may cause the drag coefficient to be larger than the drag coefficient of the solid ball at a certain Reynolds number and fractal dimension,and the drag coefficient ratio is more than 1.The drag coefficient ratio decreases with the increase of permeability ratio to the peak value and tends to be stable.In this paper,agglomerate drag force model with different Reynolds conditions is established on the basis of fractal dimension,which can describe the fractal structure of the nano agglomerate while describing the flow characteristics and the stress characteristics of the agglomerate.The model is more accurate for describing the hydrodynamic characteristics of nanoclusters,and can provide a reference for the study of the flow and stress of agglomerate.