| Fluidization technology has many advantages, it has been put into application in many fields and for a long time. Due to its special properties, nanoparticles have been the focus of research and application since it was discovered. There are some nanoparticles can achieve agglomerate particulate fluidization as nanoparticle agglomerates under certain conditions, the formation of agglomerate particulate fluidization is closely related to properties and dynamics behavior of the nanoparticle aggregations, in order to understand the dynamic characteristics of nanoparticle aggregations, we should better understand the dynamic characteristics of single nanoparticle aggregation, for this purpose, based on the free setting experiment of nanoparticle fluidized bed agglomerate of size between 1-2mm, we studied the setting behavior of aggregation and interaction of two-phase under setting process.The diameter of the primary particle is 25 nm, the hydrophilic nano-SiO2 particles are fluidized, and the fluidized agglomerates under the bottom of fluidized are picked as the research object, the physical parameters were measured and influence on these parameters of fluidization velocity and fluidization time are analyzed. The setting behavior of agglomerate and the relationships between terminal velocity, drag coefficient and physical parameters, flow state are studied in settling tube combined with PIV which was used to take pictures of agglomerate under free setting process and IPP6.0 which was used to analyze the images. The differences between the solid ball and agglomerate are illustrated through theoretical research and experimental data, of which the reasons are analyzed too.Experimental study found that under the experimental condition in this paper, the diameters of fluidized agglomerates under the bottom of fluidized bed showed a narrow Gaussian distribution, agglomerate density is among the range of 60-130kg/m~3, the average density is 96.55 kg/m~3.The void rates of these agglomerates are above 93%, the average void rate was 96.5%, indicating that the agglomerates have typical developed pore structure. Assuming that the basic unit size is constant, the permeability values calculated using the Limit Dilute model and the Brinkman model are the smallest, and the calculated values of the two are the closest. The permeability value calculated by Kozeny-Carman model was the maximum, the calculated values using the Davies equation is between the top three. In spite of the differences, the results calculated by different models are still kept at an order of magnitude. Permeability increases with the increase of the void ratio and the particle size of the basic unit, and the permeability values vary by several orders of magnitude with different basic unit sizes. This also shows the importance of the basic unit size, which calls for the full understanding of the internal structure of the agglomerate. Agglomerate and solid sphere are very different compared from physical parameters.Re are beyond the range of laminar flow when the agglomerates reached the terminal velocity. Terminal velocity and drag coefficient ratio between agglomerate and solid ball with the same density and size was not affected by particle size, which may be attributed to the narrow range of particle size. The Ω<1 may be directly related to the flow through the internal voids of agglomerate, four most-accepted permeability models are employed, and it is realized that the size of basic unit has significant effect on Ω. Exact understanding of the size of basic unit is the foundation to accurately identify which permeability model is more proper to be employed. The Ω>1 is mainly due to the irregular shape of agglomerate, however, the internal void of agglomerate still has effect on the two-phase interaction at this time. Agglomerate and solid ball are different from the point of view of dynamics, and this difference may be related to the void structure and the irregular shape of the agglomerate. |
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