Heat And Mass Transfer Performance Of Centrifugal Fluidized Bed Dryer

Firstly, the fluid dynamics performance of the Centrifugal Fluidized Bed Dryer is studied in the paper, especially for the ball of particles and the mass of particles, and compared with the result in different conditions, such as altering the height of the shaft, changing the direction of gas velocity, at last, the correlation of the minimum fluidization velocity is obtained. Then, the experimental methods of drying curves and heat transfer are developed in the Centrifugal Fluidized Bed Dryer on the basis of the study. More than ten kinds of particles with different characters, taking batch-operating method, are chosen to do drying experiment. The particles studied range from 1.80mm to 6.43mm in size, and the particle density varies from 890kg/rn3 to 2670kg/rn3, so that the particles studied have the better representatives. According to the difference of the content of water, the drying curves of green bean having the longer drying period of constant rate and molecule sieves having the drying period of apparent falling rate are drawn in non-direct method. Its calculating process is as follows: according to the balance of water is found, according to the slope of curve x-t , the drying rate: dt is acquired. According to the feature of equipment, the drying stage of constant rate is chosen to study. and its mathematical model calculating the coefficient of heat transfer between the fluid and particles is obtained by theoretical analysis and derivation: Experiment and theoretical analysis present the factors, which have a great influence on the coefficient of connective heat transfer between gas and particles. The paper incorporated them as five dimensionless groups according to the dimensional analysis, that is Nu=f(Re, Pr, Fc, HId). The corresponding correlation of the drying stage of constant rate is obtained by the regression of experimental date: According to the principle of the wet bulb thermometer having dry and moist temperature, the coefficient of mass transfer: is obtained. The corresponding correlation is acquired by the same method above: sh=5.587Re 0.398 Fc0375 (Hdj) 1.018 verify the reality of experimental result. The experimental result indicate: 1) The Centrifugal Fluidized Bed Dryer is very fit for the drying or pre-drying of materials with high unbound water content, the drying time is short and the capability of product is very well. 2) Yellow bean, d=6.43mm, is also fluidized well in the equipment. 3) The factors, which have influence on the heat and mass transfer performance are complicated in the Centrifugal Fluidized Bed Dryer. The main factors are presented in the paper by experiments and analysis: the velocity of gas~the speed of rotating drum..the height of the bedthe characteristics of particles as well as the construction and size of the equipment. 4) The mass and heat transfer rates in the Centrifugal Fluidized Bed Dryer are higher than that in the Conventional Fluidized Bed. 5) The drying curves of the Centrifugal Fluidized Bed indicate it can effectively restrain from generating.. flowing of the gas balloon and floating~ putting through of the particles.