Estimation And Reliability Analysis Of Moisture Diffusion Coefficient

The moisture diffusion coefficient is an important mass transfer characteristics parameter to calculation, simulation of material in the drying and processing, the accurate estimation of moisture diffusion coefficient to improve the drying efficiency, optimal drying parameters, design, select the appropriate dryer are essential. Now there are a lot kinds of model to estimate the moisture diffusion coefficient, but few analysis on the model reliability, this paper is studied the problem.Firstly, the moisture diffusion coefficient estimation model at home and abroad were reviewed, the theoretical basis and the applicable conditions of the model were carried on the summary. And the moisture diffusion coefficient estimation involves the partial differential equations of discrete method, least squares optimization, wet air and wet material and other basic properties were introduced.Secondly, the Crank equation to estimate the moisture diffusion coefficient was used in the reliability analysis. Use of water diffusion within the material to follow the second Fick diffusion law, the material-air convection drying quality model, peas, cylindrical and slab potato were simulated test, and the numerical results into Crank equation for moisture diffusion coefficients of the three different materials were estimated. The estimate moisture diffusion coefficient and the numerical simulation experiment using reference moisture diffusion coefficient was compared, the results show that:moisture diffusion coefficient dependence on the initial moisture content, relative humidity and hot air velocity is mainly due to the drying of the material is the actual boundary condition of dry material not Crank equation model assume boundary conditions without resistance. Choose hot air speed is larger, the initial moisture content and relative humidity is lower by Crank equation to estimate the moisture diffusion coefficient, the more close to its real value, this indicates that the Crank equation needs further improvement.Finally, the estimation of hot air convection drying convective mass transfer coefficient and the moisture diffusion coefficient of Bi-G correlation feasibility was analyzed. First, use the exponential function of plums, potato and cylindrical banana dry experimental data were fitted, using Bi-G correlation to estimate the mass transfer coefficient and the moisture diffusion coefficient. Then the estimates was substituted into Fick diffusion law in the material-hot air convection in the quality boundary conditions equation of plum, potato and cylindrical banana were numerically simulated and the numerical calculation results were compared with the drying experimental data.The results showed that:the exponential function fitting drying experimental data well is not the sufficient condition for the Bi-G correlation to estimate the convective mass transfer coefficient and the moisture diffusion coefficient, Bi-G correlation can not be used to estimate the convective mass transfer coefficient and the moisture diffusion coefficient.