| The application of lipid wall materials has prompted the emergence of hot melt fluidized bed coating technology.As an advanced technology for preparing microcapsules,it is widely used in food,pharmaceutical,chemical and other industries.In this study,a bottom-spray experimental spray granulator designed and manufactured by ourselves was used to coat the citric acid powder with a lipophilic molten fat(stearic acid)as the wall material and a citric acid powder as the core material.The atomized molten wall material in the coating process was in contact with the fluidized core material to embed the core material.the process involves microscopic phenomena such as birth and death between the particles,and this microscopic phenomenon was what the Population Balance Model(PBM)needs to express.Therefore,it was necessary to introduce PBM in the research process of this subject to reflect the birth and death process of particles during the coating process of hot melt fluidized bed.In the use of the population balance equation,there are unknown parameters such as nucleation constants and coalescence constants.These parameters need to be determined in order to solve the population balance equation.In order to solve the PBM,it was discretized.the growth of the particles was mainly caused by particle coalescence,Therefore,this paper only considers the coalescence of particle growth during the hot melt fluidized bed coating process.The coalescence kernel of the particles was the Equi-partition of Kinetic Energy(EKE)kernel described on the basis of the kinetic theory of gas.The main purpose of this paper was to incorporate the EKE kernel into a Discretized Population Balance(DPB)Model to fit the mass-based experimental data,and to obtain the coalescence rate constant.The known coalescence kernel was incorporated into the PBM and the Quadrature Method of Moments(QMOM)was used to solve the equation to explore the change of the first 6 moments with time in the particle growth process.This study provides a theoretical basis for the growth of particles during hot melt fluidized bed coating process.The research results show that under the experimental conditions of bed temperature of 45?,fan frequency of 25 Hz,atomization pressure of 0.2 MPa and feed liquid flow of 4 ml/min,the amount of atomized droplets increases with the increase of coating time,the particle size as a whole shows a trend of increasing gradually.The particle size distribution curve of citric acid is obviously a single peak,which showed a trend of normal distribution.The Discrete Population Balance model is fitted with the mass-based particle size distribution of the citric acid particles during the experiment to obtain the coalescence rate constant ?0.Under the coalescence rate constant,by comparing the simulation results with the experimental results,it is found that the data in both cases are basically consistent.The coalescence rate constant ?0 is verified and an effective coalescence kernel function is obtained.Based on the Quadrature Method of Moments,the number of particles does not change during the growth of the particles.the number of particles gradually decreases with the increase of coating time during particle coalescence,and m1 and m2 are also reduced.Although the particles coalescence during the coating process,the total volume remained constant after coalescence,so the total volume of the particles(m3)has not change.In addition,the moments above the 3rd order increase with time. |
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