Axisymmetric TLM model for water vapor soaking of white rice

Abstract

An earlier-developed, two-dimensional, orthogonal TLM grid, using axisymmetric elements, has been used to model moisture diffusion during long-grain white rice soaking in moist still air. Previously, soaking of rice in water was shown to depend largely on the diffusion properties of moisture inside the kernel. However, in the case of water vapor soaking, the experimental soaking curves can only be approximated very closely by assuming a surface resistance. Further, this analysis shows that the resistance to moisture transfer to the surface, which is represented by a mass-transfer coefficient, is the controlling factor. As a consequence of this resistance at the surface, which dominates the internal resistance to moisture diffusion, almost no concentration gradients occur inside the kernel. Finally, using an Arrhenius-type equation, an exponential relationship between the mass-transfer coefficient and the inverse of the absolute temperature was found.