Study On Fluidization Characteristics Of Mixed Particles In Two-dimensional Fluidized Bed

At present,the world energy field is facing many challenges.How to use the limited resources efficiently has become the primary problem in industry.Fluidization technology has the advantages of simple operation,fast and effective.It also plays an important role in enhancing mass transfer and heat transfer,so as to maximize the benefits of industry.In the past 100 years,researchers have done a lot of researches on fluidization technology,which has also led to the rapid development of industrial production.The study of fluidization characteristics in fluidized beds can provide theoretical guidance for industrial applications,especially the minimum fluidization velocity and bubble behavior of particles in fluidized beds,which plays an important role in fluidization operation.Previous studies have mostly focused on traditional cylindrical fluidized beds.With the development of industry,new two-dimensional fluidized beds have emerged,especially in the field of photochemical catalysis.However,there are few studies on mixed particles in two-dimensional fluidized bed,so this paper focuses on the fluidization characteristics of different types of binary mixed particles in two-dimensional rectangular fluidized bed,providing technical guidance for fluidization development.This work was carried out in a transparent two-dimensional rectangular fluidized bed.Different types of particles were selected: glass beads,quartz sand,sawdust,glutinous rice flour and millet.The flow characteristics,bubble characteristics and mixing properties of binary mixed particles with different particle sizes,densities and types in a two-dimensional fluidized bed were studied systematically.The relationship between bed pressure drop and gas velocity was measured by velocity-reducing method.Combined with bubbling phenomenon in fluidized bed,the minimum fluidization velocity of mixed particles was studied.By comparing with the calculation results of the minimum fluidization velocity correlation proposed by predecessors,the difference was analyzed and the mixing ratio R was introduced.According to the experimental results,the minimum fluidization velocity formula for binary mixed particles was fitted.The relationship between the expansion ratio of mixed particle bed and particle properties and particle composition was studied.The results show that the smaller the particle size,the larger the expansion ratio of the bed;the smaller the particle density,the larger the expansion ratio of the bed;and the larger the particle viscosity,the smaller the expansion ratio of the bed.The CCD camera was used to photograph bubbles in fluidized bed,and MATLAB image processing program was used to process bubbles images.The bubble properties of mixed particles in fluidization process,such as bubble diameter and bubble rising speed,were studied.The effects of gas velocity,mass ratio and particle size on bubble diameter and rising velocity in a two-dimensional bed were studied.The correlation between bubble diameter and rising velocity was fitted according to the experimental results.With the help of image processing technology,the mixing behavior of mixed particles in fluidization was studied.The results show that for the mixed particles of glass beads and sawdust,serious segregation occurs in the bed when the mass content of sawdust exceeds 15%,and for the mixed particles of glass beads and glutinous rice flour,segregation occurs when the content of glutinous rice flour is 12%.In addition,the method of calculating variance of instantaneous pressure drop was used to study the pressure fluctuation of the bed,and the pressure fluctuation data under different conditions were obtained,and the influencing factors were analyzed.