MARKOV CHAIN MODEL OF PARTICULATE SOLIDS BATCH DRYING IN A CONICAL FLUIDIZED BED

DOI: 10.6060/tcct.20165912.5489
Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2016. V. 59. N 12. P. 93-99

The objective of the present study is to develop a model to describe the hydrodynam-ics, heat and mass transfer in a conical fluidized bed with particles of strongly variable prop-erties. The proposed model is based on the Markov chains approach, and the wet potato mono-sized cubes are used as the model material. Shrinkage of potato samples during the process of drying is taken into account to improve the adequacy of simulation. Thus, the three new factors that influence the process are taken into account: variation of the superfi-cial gas velocity over the bed height due to its conical shape, variation of particles mass due to drying and variation of particle size due to its shrinkage. The bed is presented as two par-allel chains of perfectly mixed cells: one chain for particulate solids, and one chain for the drying gas. The evolution of particulate solids distribution over its chain is describes with the matrix of transition probabilities, which is state dependent and varies with time. The heat and mass transfer between adjacent cells of the both chains is describes with the common rela-tions of heat and mass transfer. The model allows predicting the drying kinetics if the coeffi-cients of heat and mass transfer are known. The correlations to calculate the drag force coef-ficient, Nusselt and Sherwood numbers, the coefficients of shrinkage and of diffusivity were borrowed from literature. The model was validated at the lab scale fluidized bed dryer with the conical shape of reactor. A good agreement between obtained experimental and calculat-ed results is achieved.

Key words: fluidization, Markov chain, state vector, matrix of transition probabilities, drying, moisture content, kinetics

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