| The liquid-solid fluidized bed heat exchanger is a kind of technology which combines the fluidized bed technology with the heat exchanger closely and has the characteristics of high-efficiency heat transfer.It has a broad application prospect in the field of making ice slurry.However,the distributor inside the liquid-solid fluidized bed heat exchanger is the bottleneck restricting the technical performance.In this paper,based on the previous experimental research,the uniformity of particle distribution in the downflow chamber is analyzed by improving the experimental device,using different particle materials and using the flow field simulation software.By comparing and analyzing the four key factors influencing the flow field in the lower fluidization tank of the liquid-solid fluidized bed,namely the installation position of the nozzle,the length of the lower straight pipe section of different lower fluidization tanks,the presence or absence of the flow cap and the structure of the distributor to study its effect on the flow field in the lower fluidization tank.The main work carried out in this paper is as follows:(1)Experimental study on the minimum fluidization velocity,terminal velocity and expansion index of particles.Three kinds of bearing steel with diameter of 1,2 and3 mm,density of 7729 kg/m~3,zirconia of 4123 kg/m~3 and alumina of 2364 kg/m~3 were used,respectively.The experiment was carried out in a vertical glass cylindrical riser with inner diameter of 60 mm and height of 1.45 m.The volume fraction of fixed bed was 10%,15%,20%,25%and 30%,respectively.The minimum fluidization velocity is predicted by measuring the bed pressure drop,and compared with the theoretical calculation results of Wen Yu formula,Richardson et al.formula and Chen et al.formula.The comparison results show that the experimental value is in good agreement with the theoretical value,and the deviation of Chen et al.formula is the smallest.The experimental results show that the increase of particle size and density are the main reason for the increase of the minimum fluidization velocity,which is independent of the volume fraction of particles in the bed.This paper discusses the accuracy of the common terminal velocity formula and expansion index formula used to calculate spherical particles,and obtains the terminal velocity and expansion index formula with high accuracy which are applicable to the engineering field.(2)The installation position of the nozzle,the different height of the lower straight pipe section of the lower fluidization box,and the presence or absence of the flow cap affect the flow field in the lower pipe box.Place the nozzle in 5 different positions of the downcomer,namely left end,middle end,right end,right end 10mm right side and right end 20mm right side,respectively.Make the particles circulate normally,the lower straight pipe section of the lower fluidization box adopts 5 different schemes of 50,75,100,125 and 150 mm,respectively,and it is found that the particles are most evenly distributed in the interior when the height is 100 mm,the analysis of the two conditions when there is a choke cap and no choke cap in the lower fluidization box shows that the particles in the lower fluidization box are mostly concentrated directly under the heat exchange tube in the middle with the choke cap,and the distribution effect is better.(3)A comparative study of different distributor structures.Comparative analysis of variable aperture distribution plates and equal aperture distribution plates,the distribution grids with small grid sides of 2,4,6,and 8 mm,respectively,and the circular table-shaped distributors with inclination angles of 45°,52.5°,and 60°,respectively.The influence of the distribution uniformity shows that the distribution grid with a small grid side length of 4 mm has the best distribution effect. |
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