A new moisture equilibration theory to predict moisture movement in a non-aerated grain mass

摘要

A previously developed finite element model of the heat, mass, and momentum transfer during aerated and non-aerated grain storage was used to investigate the traditional theory of moisture migration. Moisture migration is defined as movement of excessive moisture in a grain mass during non-aerated storage that can lead to spoilage. Very little moisture accumulation at the exposed top surface of the bulk (less than 0.1 percentage points) was predicted for a non-aerated bin with a diameter of 5.5 m and an eave height of 11.0 m in Indianapolis, IN during 12 months of storage. However, in a bin with a diameter of 11.0 m and an eave height of 11.0 m the grain in the top center of the bin increased in moisture content by 1.3 percentage points. The modelused permeable boundaries that allowed natural convection currents to originate and flow into the headspace and plenum air. It was determined that moisture "migration" in the traditional sense did not occur, instead a more realistic theory of moisture equilibration between the grain mass and headspace and plenum air was developed. Moisture accumulation in the upper portions of a grain mass occurred primarily due to natural convection currents that entered and exited the headspace. Depending on the binsize, very little moisture accumulation at the grain surface was caused by the traditional moisture migration theory. By controlling the equilibrium relative humidity of the headspace, moisture accumulation in a bin could be minimized. Permeability had amajor influence on the predicted moisture accumulation due to the higher natural convection currents. Neglecting solar radiation and assuming impermeable boundary conditions led to a significantly lower average com temperature and a smaller amount of moisture accumulation than realistic boundary conditions. Three bin sizes were simulated to determine the effect of bin size on predicted moisture accumulation and average com temperature. The surface area to volume ratio had a more significant impact on the average corn temperature and moisture accumulation than height to diameter ratio.