Discrete element method as an approach to model the wheat milling process

Abstract

It is a well-known phenomenon that break-release, particle size, and size distribution of wheat milling are functions of machine operational parameters and grain properties. Due to the non-uniform characteristics and properties of wheat kernels, the kernel physical and mechanical properties affect the size reduction process. This research was the first to test the functionality of the discrete element method (DEM) to simulate the 1st break wheat roller milling process. DEM models of 1st break wheat milling were developed by incorporating the bonded particle model along with the spherical-shaped and kernel-shaped particle models. The models simulated hard red winter (HRW) wheat milling at 12%, 14%, and 16% moisture content and was validated using lab scale milling trials. The spherical-shaped approach simulated the size reduction of a spherical cluster of mono-sized particles with uniform bond strength throughout the kernel. At 16% moisture content, this spherical-shaped kernel model resulted in an average particle size of 438μm with a deviation of prediction of 177%. The prediction error was reduced to 144% with a mean PSD of 372μm by modifying the shear modulus and coefficient of restitution values. With the kernel-shaped model, a bonded cluster resembling a wheat kernel in shape and size was used with a random distribution of particle bond strengths in the kernel. Even though the model predicted a 1st break particle size of 413μm, which had a deviation of 139% from the lab scale milling results, the model satisfactorily predicted the variation in particle size distribution from 1st break milling with moisture content.