Mathematical Relationship Predicting Grain Separation in Combines

ABSTRACT TO achieve the proper design of a combine straw walker that can efficiently separate the grain from the plant material, the physical process of this separation must be understood. An equation, which describes the physical separation of the grain from the plant material was derived in terms of many parameters typically omitted by researchers. The derived equation included the parameters width of separation, material flow rate, bulk density of the material, thickness of the separation layer, and a diffusion coefficient. Using published data, the model was evaluated in terms of material flow rate and straw walker length. The R^ values for length for all data sets were greater than 0.99, and significant at the 99.9% level (a = 0.001). In addition to the initial derivation, variables in the separation function were related to the rate of material flow and the type of plant material. The flow rate relationship also gave a high R^ (0.90) and was significant at the 95% level (a = 0.05). It was also shown that grain size and straw type has an effect on rate of separation.