MOISTURE TRANSPORT CAUSED BY NATURAL-CONVECTION IN GRAIN STORES

Observations suggest that natural convection in grain stores produces moisture movement. The process is very slow but the moisture content of the grain can change enough during months of storage to influence the quality of the grain. The equations which describe this process are presented in this paper. The fact that the movement of moisture is very slow is used to simplify the equations of heat and moisture transfer. The simplified equations have the same form as the equations used to describe heat transfer alone. Standard methods for solving heat transfer equations were used to solve the simplified equations. The method is shown to be reasonably accurate by comparing the results with experimental data. Also, the equations were used to simulate the movement of moisture in a grain bin where some data were recorded. Overall, the simulation was reasonably accurate; in particular it showed that the moisture was moved to the top-centre of the bin. But there was not enough information (such as weather data and packing density) to give a very accurate simulation. Earlier work suggests that heat is normally transported by conduction in grain stores. In this paper, it is shown that natural convection can significantly affect heat transfer in the presence of moisture movement. This is achieved by using an approximate analysis of the heat and mass transfer equations which shows that conduction normally dominates the process. However, convection is important if the resistance to airflow is low enough and if the radius of the storage bin is approximately equal to the height of the bin. © 1997 Elsevier Science Ltd. All rights reserved.