Numerical solutions were also used to solve the partial differential
equations with mixed boundary conditions, and
the corresponding results were compared with the computed
results obtained from analytical solutions (Eqs.
(14) and (17)). The finite-difference approach was used to
discretize the derivative in partial differential equations into
a system of algebraic equations, the well-known Crank–
Nicholson implicit method was chosen to solve spherical
coordinate problems and an explicit method for cylindrical
coordinate problems. To simulate a heat diffusion thinlayer
model, it is reasonably assumed that air temperature
remains unchanged when passing through a thin layer of
grain; thus, the thermodynamic properties of air used for
calculation can be evaluated at the inlet air temperature