Porous Media, Heat And Mass Transfer Process Of Numerical Simulation - Tobacco Curing Process Simulation Technology

The cumulate tobacco leaves in loose tobacco curing barn can be regarded as evenly distributed porous medium. During the process of thermal wind drying, the heat and mass are transferring among also. Normally, the work capacity is big and errors come out easily in experimental data collection and analysis, because of the complexity and randomcity of the porous medium structure. But the development of computer fluid dynamics (CFD) can make it be a possibility to induct the technique of computer fluid simulation to the drying research filed of curing barn.This article systematically analyzes the heat and mass transfer mechanism in porous medium drying. It starts from the physical environment of the research object (the cumulate tobacco leaves), synthetically considers the computer fluid dynamics theory, the multiphase flowing theory, and the phase transition theory, founds and describes the mathematic model and the controlling equation for the heat and mass regularity during the cumulate loose leaves drying process in curing barn. The solving and data processing for the heat and mass transferring during leaves drying are carried out through the preprocessor GAMBIT, the equation solver FLUENT and the Post processor TECPLOT. In order to describe the mass transfer and the energy transfer when the leaves moisture transpired, a phase transition model needs to be found, to compile the UFD source program of this processing and let its data communicate with that of equation solver. Based on the curing barn with a 80kg/m3 of tobacco loading density, a 0.3m/s of wind speed among the leaves, it makes a numerical simulating study on the velocity field, pressure field, temperature field and consistency field, and get every field's distribution nephogram along the height of the curing barn, then analyze the numerical simulating results. The study result of the numerical simulation shows that in the cumulate loose leaves zone, wind speeds even, vertical temperature variation between 2～3℃, horizontal temperature variation less than 1℃, temperature even, will make a better Synchronization drying for all leaves in the curing barn. The temperature got from numerical simulation is almost identical with that from actual measure; the difference between the two is less than 6%.It makes use of the FLUENT simulation to analyze the impact that happened to the drying capability of loose leaves curing barn by the drying manipulating parameters, such as wind speed among the leaves and the tobacco loading density. The study result of numerical simulation shows that when the wind speed among the leaves is 0.3m/s. the dry and wet difference in the curing barn will be much more reasonable and the leaf quality after drying will be much better. Secondly, It simulates analyzing the different temperature distribution states under different tobacco loading densities, and based on synthetically considering the temperature distribution and drying efficiency in the curing barn, a 75～85kg/m3 of tobacco loading density for a single cote in loose leaves curing barn is deemed to be suitable. Then on the basis of the above drying parameters, it further discusses the impact that the sealing property (heat insulation capability of wall) and the wind spreading around property (the wind spreading property of ground slope) effect on the drying capability. The simulating result indicates that it would be much favorable for the synchronous drying for the tobacco leaves if the ground slope is about 4.2～5%, and a 6～8cm gap between the leaves cumulate zone and wall is remained when loading, as they make that in the available zone of leaves cumulating, the wind speed among the leaves and the complanate temperature in the curing barn even.The numerical simulating technique can factually reflect the whole process of cumulate loose leaves in curing barn, provide the betterment of the drying techniques and the optimization of the curing barn structure with favorable theoretical basis, as well as can popularize to apply to other drying systems of intensive barn. Therefore, this technique is of important practical significance for improving the drying quality of the curing barn, and should be mastered by most of researchers in tobacco industry.