Study On The Heat And Mass Transfer Of Shrinkable MSW Matrixes At Medium Temperature Air Convection

Drying process is the neccessary stage before the Municipal Solid Waste (MSW) incineration and its combustion efficiency is mainly determined by the quality of dry process. Serious contraction occurred in the consideration of MSW is a kind of porous materials which has the high moisture content. For this reason, this paper focus on the internal heat and mass transfer characteristic of shrinkable MSW matrixes during hot air convection drying.The hot air convection drying experimental study of the MSW matrixes has been carried out and the influence rules of moisture migration characteristic by hot air tempertature, windspeed, matrixes kinds and geometric factor were obtained. Also, the shrinkage characteristic was obtained. Result shows the linear relationship between shrinkage factor and weight loss ratio (R2>0.95), the MSW matrixes volume reduced was approximately equal to the volume of water loss. Through the orthogonal experimental results of range and variance analysis, it shows that temperature, windspeed and weight loss ratio has significant effect on the shrinkage factor (α=0.05),the temperature and thickness has significant effect on drying time.Based on the Fick law and energy conservation equation, the mathematical model has been built. Calculating programme has been designed base on the MATLAB, through the implicit finite difference method, the internal temperature and moisture distribution were obtained, moisture content and temperature on the convection boundary shows the step-like changes. Through the comparison between experimental value and calculating value found that average effective moisture diffusivity was an increasing function about moisture content and temperature, value range is 3.245×10-8～20.576×10-8m2/s. Throught the dynamic analysis, the Arrhenius equations were obtained. Under conditions in this study, the apparent activation energy range is 10～22kJ.After dimensionless rewrite about the governing equation and series analysis, law of internal heat and mass transfer were obtained. Bi and Bim series were 100～101, it shows that heat and mass transfer were governed by the internal conduction and diffusion, external drying conditions (hot air velocity and relative humidityof dring air) has limit affect about internal heat and mass transfer process. Under conditions of this study, surface heat transfer coefficient of matrixes is 9.5～184.5W/(m2·K) and surface mass transfer coefficient of matrixes is 6.2×10-6～7.4×10-4m/s.