Experimental Research On Nanoparticle Fluidization Behavior

Nanoparticle fluidization has been the focus of research and application due to its special advantage such as high efficiency and high cost performance,but nanoparticles are easy to form funnel-shaped sedimentation in the bottom of fluidized bed,fluidization quality decreases,the nanoparticle has been limited to mass fluidize for a long time.About this problem,we design the divice of whirlwind flow,it can improve the quality of nanoparticle fluidization by accessing the high speed airflow to the tangential bottom of the fluidized bed.We adopt the 25 nm initial diameter of SiO₂ nanoparticle to carry out the experiment,compare the experimental parameters such as fluidized height,partial pressure drop,particle size,porosity and solid fraction,and analyze the impact of the gas velocity,initial bed height on the nanoparticle fluidization behavior.On basis of the research,we add the whirlwind flow in the fluidization,and study the improvement of fluidization behavior.In addition,under the premise of keeping the total flow,we analyze the discrepancy of different air distribution ratio,and find the optimal experimental conditions.Experimental study found that the minimum fluidization velocity curve of nanoparticle is different from other of particles due to the deposition at bottom.With the decrease of fluidization velocity,the curve of bed pressure drop does not exist obvious turning point to determine the minimum fluidization velocity,and the influence of the deposition at bottom decrease with the increase of initial bed height.After adding the device of whirlwind flow,under the premise of keeping total flow,the whirlwind flow break the deposition in the bottom,promote the measurement of the minimum fluidization velocity,but it will be researched on judgement of the minimum fluidization velocity with two copies airflow.The fluidization velocity and initial bed height are main factors that affect the fluidization behavior of nanoparticles.They affect the change of drag force between gas and solid phase directly or indirectly,and they cause changes of many parameters in the process of nanoparticle fluidization.We found that the inflation of nanoparticle promoted with the increase of fluidization velocity and initial bed height,the inhomogeneity of axial distribution of nanoparticle weaken.At same time,we use wavelet transform to analyze the fluctuations of partial pressure drop.We found that the fluidization velocity and initial bed height contributed the growth of degree of disorder during the nanoparticle fluidization,increase the frequency and exchange capacity along the axial in the middle and low frequency range,thus speeding up the grow process of agglomeration during fluidization.The average size of agglomeration increases.For the deposition of agglomeration in the bottom of fluidization,the experiment adds the whirlwind flow device.We found that whirlwind flow increase the quality of nanoparticles from multiple aspects.From the macro phenomenon,on the one hand,whirlwind flow break the deposition in the bottom of fluidized bed,delayed the decline process of fluidization height.The whirlwind flow enhances the fluidization percentage of nanoparticle,and material distribution is more balanced.On the other hand,by the interactions of fluidization flow and whirlwind flow,it enhances the degree of turbulence in the middle and high frequency region,the range of frequency is expanded about the gas-solid interaction.From the point of agglomeration behavior,the addition of whirlwind flow decreases the average size of agglomeration,prolongs the fluidization of nanoparticle,it makes easier to enter into a state of dynamic stability.In addition,under the premise of keeping total flow,the nanoparticle fluidization behaviors exist the best point as the percentage of whirlwind flow increases.When the percentage of whirlwind flow is 30%,the average agglomeration size is smallest,the axial exchange capacity is most,the partial pressure drop is biggest,axial distribution of nanoparticle is most homogeneous,the whirlwind flow improve the quality of nanoparticle fluidization from several aspects furthest.