A two-dimensional model of grain storage with dynamic visualisation: predictions for temperature, moisture content, germination and respiration--a case study for rapeseed

摘要

The work presented here describes the development of a two-dimensional (r-z plane) simulation model of a cylindrical silo. The model assumes axi-symmetric conditions throughout. The heat and mass-transfer equations were solved for the case of uniform vertical flow, using the "up-wind" difference technique employed in computational fluid dynamics. This describes the ventilated case and the unventilated case, when the velocity is set to zero and the heat and mass transfer is assumed to be driven purely by diffusion. For the ventilated case, aerodynamic dispersion terms were incorporated. These describe the enhancement of heat and moisture diffusion by the mixing of air in its tortuous path through the grains. The program can simulate the storage ofwheat, barley and rapeseed, using subroutines for each set of properties. The solution of the energy and moisture balance equations provides the temperature and moisture fields over a vertical section through the silo axis. Subroutines to predict germination (viability) and respiration (mould growth) are then used to calculate the percentage viability and cumulative dry matter loss. Using contourmapping software, the temperature, moisture content, viability and cumulative dry matter loss are displayed in two dimensions. The program is then used to investigate the holding of high moisture rapeseed before drying, with air flows of 0, 5, 10 and 15 m~3/h tonne.