Evaluation of Moisture Diffusion Coefficient of Cylindrical Bodies Considering Shrinkage During Natural Convection Drying
2011
Rahman, Najmur | Kumar, Subodh
An analytical diffusion model which considers the influence of the external resistance to mass transfer, sample finite geometry and shrinkage is proposed to simulate drying kinetic curves of cylindrical bodies. The convective mass transfer coefficients, hm at air-solid interface obtained from natural convection drying experiments on potato cylinders of length 0.05m and diameter 0.01m at different air drying temperatures were used for the model evaluation. Using Levenberg-Marquardt algorithm for optimization, an empirical relation describing effective diffusion coefficient of potato as a function of air temperature and material moisture content is proposed for finite and infinite cylinders with and without considering shrinkage. The significance of material moisture content in the proposed diffusion coefficient relation is demonstrated through a comparison between the predicted and experimental moisture content ratios. The mean effective diffusion coefficient, Deff for finite shrinking cylindrical bodies is found to vary from 3.93 to 8.63 x 10-10 m2/s for the temperature range of 40 to 60°C. In addition, the assumption of infinite geometry instead of finite one in the model evaluation results in an overestimation of Deff. However, lower values of Deff are obtained when shrinkage effect is taken into account in the analysis, irrespective of the product size considered.
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