Transient heat conduction and hotspot development prediction in a flaking roll with revolving heat flux and convection boundary conditions

In the oilseed crushing industry, flaking rolls sometimes develop hotspots that cause high thermal stresses. Soybean flakes on contact with hotspots crumble to powder, which is unsuitable for oil extraction. Transient heat conduction equations with revolving boundary conditions were solved using the finite element method. Simulations demonstrated that hotspots arise due to heat flow in three dimensions from the source toward the roll ends and the curved surface. An estimate eat flux value of 56 kW/m(2) yielded surface temperature values near observed values. Perturbations performed to the base values showed that a 10% increase in thermal conductivity caused a 6-8% reduction in peak thermal gradient, whereas a 20% increase in heat-transfer coefficient caused less than 2% reduction in peak thermal gradient. Therefore, thermal conductivity is a more sensitive parameter affecting thermal gradients than the heat-transfer coefficient. A small change in heat-transfer coefficient caused by aspirating air through the flake outlet of the roll stands would not cause a significant reduction in temperature and thermal gradients in rolls. The higher thermal gradients observed near the outer surface of rolls suggest that casting rolls with subsurface layers of higher thermal conductivity would make rolls less prone to forming hotspots.