Calculation And Research On The Heat And Mass Transfer Of The Corn Vacuum Drying And The Tower Drying Equipment

Corn is a very important food product and industrial raw material.It contains a high level of moisture content when it is harvested.It needs drying to the safe moisture content.And then it can being a long-term storage.Compared to the traditional hot air drying,the vacuum drying technology of the corn has a lot of benefit,including low temperature drying,a better quality of the drying corn,heating the medium can be recycled,low energy consumption,no emissions and so on.The continuous vacuum drying technology that conbined the largy-scale prodction technology can improve the drying efficiency and productivity.But the current research on the internal heat and mass transfer of the corn vacuum drying is still deficient,failed to form a complete theory that can be used to guide the drying produce.The corn continuous vacuum drying equipment still lack mature design methods and theoretical basis,and the tower vacuum drying equipment design is still not perfect.In order to further research the heat and mass transfer mechanism of the corn vacuum drying process,the related factors which affecting the drying effect of the tower drying equipment,we made certain efforts to provide a theoretical basis for improving drying technology and drying process,saving development costs,reducing energy consumption,protecting the environment and improving the quality of the drying corn.In this paper,the main research work is as follows:We constructed the corn partical 3D solid geometry model based on the CT scanning method,established the heat and mass transfer equations based on the existing theoretical models,determined the boundary conditions of the vacuum drying model based on the experimental conditions,and established the 3D solid heat and mass transfer process calculation model of the corn vacuum drying.Through the simulation,we got the influence of the radiation plate temperature,the vacuum chamber pressure,the initial temperature and the initial moisture content during the corn vacuum drying.So that,we can further understand the mechanism of the corn vacuum drying,provide the technology curves that the dry warehouse design and simulation required.We conducted several corn vacuum drying experiments,got the average drying curves under the same drying condition,and compared with the simulation results of the vacuum drying heat and mass transfer model,in order to modify the model internal parameter.Through this method,we can get the heat and mass transfer model which can correctly reflect the corn vacuum drying.So that,we can ensure that the simulations of the vacuum drying model can reflect the actual drying process,and can be used to guide the actual drying production.We established a simplified structural model of the corn vacuum drying tower,builded the mass transfer model of the vacuum drying tower during the vacuum drying based on the porous media flow model and the fitting equations of the corn partical temperatures and the drying curves of the heat and mass transfer model calculation during the vacuum drying.Through the simulation,we analysis the effect of the position of the exhaust port,the vacuum degree of the exhaust port and the drying temperature to the flow field of of the vacuum drying tower during the vacuum drying.And we choosed the better program of the exhaust port position,proposed the theory evidence of the equipment design and the technical parameters of the drying tower.For example,in the 200t corn tower vacuum drying equipment,we putted forward the overall design scheme and technical parameters,completed the single structure size calculation,the heat and mass calculations of the overall and binned,and the performance design of the condensers,the heating pumps,the water heaters and the cool warehouse.We demonstrated the the proper design process and design methods of the corn tower vacuum drying equipment,in order to provide some guidance and reference for future equipment design.