Research On The Fluidization Characteristics Of Carbon Nanotubes In A Non-distributed Plate Cone Fluidized Bed

As a new type of material,carbon nanotubes have attracted more and more attention from scientific researchers due to their unique physical and chemical properties.The main macro-preparation method of carbon nanotubes is chemical vapor deposition,and Fluidized bed is the key equipment of this method.The fluidization characteristics of carbon nanotubes in a fluidized bed are critical to the preparation of carbon nanotubes.This paper mainly studies the fluidization characteristics of carbon nanotubes in a fluidized bed from the aspects of bed pressure drop,bed expansion behavior,and pressure fluctuation signal.At present,most of the fluidized beds used for the preparation of carbon nanotubes are fluidized beds with distributor.In the current research on the use of a tapered fluidized bed without a distributor for the preparation of carbon nanotubes.The characteristics of carbon nanotubes in a fluidized bed with a diameter of 50 mm have been thoroughly studied.However,in order to realize an industrial production of carbon nanotubes,the fluidized bed needs to be scaled up step by step.In this paper,focusing on the scientific problem of the influence of the amplification process on the fluidization characteristics,based on the study of the fluidization characteristics of the carbon nanotubes in the fluidized bed with a diameter of 50 mm,the kinetics of the fluidization of carbon nanotubes in a bed with a diameter of 100 mm was studied in detail.It lays a theoretical foundation for realizing the industrial scale-up of the tapered fluidized bed without a distributor.In order to deeply explore the fluidization characteristics of carbon nanotubes in the tapered fluidized bed without a distributor,different types of carbon nanotubes in it with a diameter of 100 mm have been studied on the cold fluidization of the cone and column.A computational fluid dynamics(CFD)simulation study has been carried out on the fluidization of carbon nanotubes in a two-dimensional bed using ANSYS fluent software,and a detailed comparison with the experiment has also been carried out;the wavelet analysis is used to analyze the gas and carbon nanotubes in the three-dimensional tapered fluidized bed without a distributor.The pressure signal of the two-phase flow is analyzed for multi-scale characteristics.The main research contents of this paper are as follows.Firstly,the different types of carbon nanotubes are researched in a three-dimensional cold experiment.The expansion characteristics of carbon nanotubes in the tapered fluidized bed without a distributor are studied in detail.The bed pressure drop and expansion rate of different types of carbon nanotubes at different initial bed heights and different input air volumes are measured in detail and their fluidization behavior is explored.Their minimum fluidization velocity is obtained by calculation and experiment.Secondly,the CFD simulation research on different types of carbon nanotubes is carried out.The expansion behavior of carbon nanotubes under different operating conditions is explored,and detailed comparisons are made with experiments.It was found that the three drag force models can make a more accurate prediction of the bed expansion rate,but the Wen-Yu drag force model can simulate and predict the bubble behavior more accurately.Finally,a differential pressure sensor is used to collect the pressure signals of different types of carbon nanotubes,different initial bed heights,and different collection points of carbon nanotubes in the bed.A multi-scale characteristic of carbon nanotubes is analyzed in the three-dimensional cold fluidized bed.This study found that the pressure fluctuations at the signal collection points and different locations can reflect the flow status in the bed;multi-scale characteristic analysis can accurately predict the transition of the bed flow status for different bed heights and different types of carbon nanotubes.