Abstract
Temperature and moisture content are the most importantfactors which govern the
quality of grain during stora. Seasonal variations in ambient temperaturés can cause safe
moisture contents of stored grain to become unsafe due to migration or redistribution of
moisture within the storage. In this study the moisture migration process is primarily
considered as the diffusive and convective transport of water vapor through the intergranular spaces of the bulk grain where grain moisture itself acts as a source or sink for.the
water vapor.
A mathematical model of moisture migration is developed by reflecting the change in
air moisture on the grain moisture through the sorption isotherm. The effect of temperature
gradients on moisture migration is simulated through the source term. The differential
equations for energy are developed by using moisture dependent thermal properties and by"
considering the latent heat of vapórization as a source. Natural convection Darcy flows are
computed by solving an equation for the pressure, which represents the continuity
eguation. The resylting unsteady, nonlinear, coupled differential- equations with time
vàrying boundary temperatures are solved numerically using the control-volume scheme.
Natural convection moisture migration is also experimentally simulated under
laboratory.conditions by maintaining a temperature gradient across a column of corn and
wheat. In the case of wheat, moisture migration is largely governed by the diffusion while
the effect of natural convection is moré prominent in the case of corn. Heat transfer.is
predominantly governed by conduction in both grains. The experimental and predicted
results show good agreement.
Using actualweather data for St. Paul, Minnesota, the numerical models are applied.
to various actual situations to predict the patterns of temperature, moisture and natural
convection flows in stored grain. "These predictions indicate that cooling of grain to 0°С
during the fall season can keep grain moistures under stable conditions for thie entire year.
It is. also shown that moisture migration occurs in all sizes of bins and starts accumulating
earlier in smaller bins.