Mathematical models based on heat transfer and coupled heat and mass transfers for rapid high temperature treatment in fluidized bed: Application for grain heat disinfestation

This study sought to develop a mathematical model of rapid, high temperature heat treatment of stored grains in a fluidized bed. The model was intended to evaluate dynamic changes in temperature distributions inside grain kernel, and grain and exit air temperatures. No differences in temperature profiles within individual paddy kernels obtained from either analytical or numerical solutions for one- and two-dimensional heat diffusion models were found. Cylindrical coordinates gave clearer pictures of temperature profiles than spherical coordinates, and the former was chosen for the model. Thin-layer heat diffusion alone is inadequate for explaining transport phenomena in a fluidized bed; it must be incorporated into a deep bed model. The loss of as little as 1.0% dry basis moisture content from the grain surface during heating significantly affected the predictiveness of the model. Therefore, a model coupling heat and mass transfer performs much better in predicting grain and exit air temperatures than one that neglects the effect of moisture loss, when compared with the experimental results. The results showed agreement between the measured and predicted results, although the predicted results tended toward over-estimation. The results indicate that the model is a powerful tool for disinfestation applications, to predict the exposure time required to obtain lethal temperatures throughout grain kernel, so ensuring the total mortality of insects within it.