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A numerical model for simultaneous heat and mass transfer was developed for solar drying of spherical objects and the object considered is green peas. Solar collector outlet temperature is assumed as drying chamber temperature and justified through energy balance equations. Assumptions are imposed on heat and mass transfer governing equations without losing the physics of the problem. Discretization is performed by finite difference method with implicit scheme. To generalize, the governing equation and boundary conditions are non-dimensionalized. The set of finite difference equations was solved by Tridiagonal Matrix Algorithm and a computer code in MATLAB was developed to solve them. The drying curves showed two stages of drying, initial, and secondary drying stage. At all drying temperatures and drying time, the center moisture was maximum and it was minimum at the boundary. A percentage of 85.67 surface moisture content and 25.33% center moisture was eliminated in the first 1 hr at 348 K. The product should be dried up to 7.45, 4.74, and 3.74 hr at air drying temperatures of 318, 333, and 348 K respectively, to maintain 10% of the product's initial moisture content. The result is compared with the experimental result from literature and they are found to be in good agreement. [ABSTRACT FROM AUTHOR] more...

Freeze drying is a highly advanced dehydration technique used for preserving pharmaceuticals, human organs transplanted to others and highly heat sensitive food products. During the freeze drying, there are two layers formed namely dried region and frozen region. In this present work, a numerical model is developed to estimate the temperature distribution of both regions. The sample object considered is skimmed milk. The transient heat conduction equations are solved for both regions of dried and frozen region. The interface layer between the two region is considered as moving sublimation front as same as the realistic case. Radiative boundary condition at the top and convective boundary condition at the bottom are considered. The model has been solved by finite difference method and the scheme used is backward difference in time and central difference in space (implicit scheme), which generates set of finite difference equations forming a Tri-Diagonal Matrix. A computer program is developed in MATLAB to solve the tri-diagonal matrix. The temperature distribution along the length of the product with varying chamber pressures and the sublimation front temperature with time are estimated. The transient effect of sublimation front movement was estimated with different applied chamber pressure. It was noticed that at lower pressure the sublimation rate is very fast. [ABSTRACT FROM AUTHOR] more...