The Numerical Simulation Of Pneumatic Drying

Pneumatic drying, also known as "instant dry", dispersed the granularmaterials in high-speed hot air (air, inert gas, gas, or other hot gases), is adrying method which in pneumatic conveying process. Due to its directcontacting with each other, the relatively high speed and large contact area,strengthened the mass and heat transfer process; Also due to the shortresidence time and low temperature, particularly suitable for processingheat-sensitive, easily oxidized and combustible materials. Pneumaticdrying has a wide range of applications in industries such aspharmaceuticals, plastics, food, fertilizers and dyes. But the design of thepneumatic drying process mainly relies on experiments and experience,lack of understanding of the nature of the drying and the correspondingtheoretical basis, not only wasting a lot of manpower, materials and energy, but also subject to the limitations of experimental and analysismethods,and make the process development, enlarging, controling andoptimization difficult. As the base of particle kinetic theory and theEulerian multiphase model, the use of computational fluid dynamics,numerical simulation of the pneumatic drying process in the vertical tube,around the proposition carried out the following research:Establishing the mathematical model of pneumatic drying in thevertical tube. Based on Euler two-fluid theory, using computational fluiddynamics methods to build a mathematical model for the pneumaticdrying of wet particles in the two-dimensional vertical pipe, and bywriting the user defined function to describe the required phase transitionmodel.Checking the model of pneumatic drying in the vertical tube. The useof pre-processing software to create the geometric model of the verticaldrying tube, and divided the grid. According the experimental conditionsprovided by J. Baeyens et.al,simulated the polyvinyl chloride drying process in the vertical tube. The experimental data contains the measuredgas temperature、particle moisture and evaporation rate compared with thenumerical simulation results, and obtained a better consistency, and haveproved the feasibility of the model.The application of mathematical models in the vertical tube. By themodel, simulated the polycarbonate drying process in the vertical tube ofpilot plant test, got the richer simulation values, including axial and radialdistribution of pressure field, velocity field, humidity field andtemperature field,and the drying effect for the changes in operatingparameters including gas temperature, gas velocity, particle size andoutside heating and provided support for the scheme of pilot tests.This study related to fluid mechanics, pneumatic transport, multiphaseflow theory, computing and unit operations. Theoretical study hasacademic value for pneumatic conveying drying process and numericalcalculation, and significance for guidance of a certain project.