A Heat and Mass Transfer Model of Peanut Convective Drying Based on a Two-Component Structure

In order to optimize the convective drying process parameters of peanuts and to provide a theoretical basis for the scientific use of energy in the drying process, this study took single-particle peanuts as the research object and analyzed the heat and mass transfer process during convective drying. In addition, a 3D two-component moisture heat transfer model for peanuts was constructed based on the mass balance and heat balance theorem. Moreover, the changes in the internal temperature and concentration fields of peanut pods during the whole drying process were investigated by simulations using COMSOL Multiphysics. The model was validated by thin-layer drying experiments, compared with the one-component model, and combined with low-field NMR technology to further analyze the internal moisture distribution state of peanut kernel drying process. The results show that both models can effectively simulate the peanut thin-layer drying process, and consistency is found between the experimental and simulated values, with the maximum errors of 10.25%, 9.10%, and 7.60% between the simulated moisture content and the experimental values for the two-component model, peanut shell, and peanut kernel models, respectively. Free water and part of the weakly bound water was the main water lost by peanuts during the drying process, the change in oil content was small, and the bound water content was basically unchanged. The results of the study provide a theoretical basis to accurately predict the moisture content within different components of peanuts and reveal the mechanism of moisture and heat migration during the drying process of peanut pods.

A 3-Dimensional Body Fitted Simulation of Heat and Mass Transfer in Rice Kernel during Hot Air Drying Process

A precise geometry model of the rice kernel is necessary to predict the moisture content and temperature distribution, or even drying stress in the kernel. In this study, a three-dimensional body fitted model of brown rice (Chunyou 84) kernel was developed by using image processing method, and the COMSOL Multiphysics software was used to simulate the drying process of the brown rice and compared with the experimental results. The maximum deviation between the simulated and experimental results was about 8%. During the drying process, the temperature gradient in the rice kernel only occurred a few minutes at the initial drying period (0–6.5 min, at 45 °C), while the moisture content gradient lasted in the whole drying process. Simulation and experimental results showed that the hot air temperature was one main factor governing the drying process of the brown rice.