Prediction of specific energy consumption in milling process using some physical and mechanical properties of alfalfa grind

Abstract Estimating energy consumption in milling process of chopped alfalfa using some physical and mechanical properties would be useful and cost effective. The objective of this study was to determine the relationship between specific energy consumption in milling and physical (bulk density) and mechanical properties (cohesion, coefficient of internal friction, adhesion and coefficient of external friction) of alfalfa grind. Rectangular bales (at moisture content of 13.3% wet basis) were chopped with a screen size of 18 mm and divided into three portions. The hammer mill screen sizes of 2.38, 3.36 and 4.76 mm were selected to grind the alfalfa chops at moisture content of 8% (w.b.). Mechanical properties of alfalfa grind were determined using a shear box apparatus. An experimental watt-hour meter was used to measure energy consumption in grinding operation. According to the correlation coefficients (Pearson's matrix), it was found that all the physical and mechanical properties significantly (P<0.001) correlated with the specific energy consumption. Coefficients of internal friction and external friction on polished steel were negatively correlated with the specific energy consumption (-0.839 and -0.593, respectively). The results showed that coefficient of internal friction with a linear regression explained the variations of the specific energy consumption by 70%. After removing coefficient of internal friction from variables, bulk density (ρ b ) explained the variations of the specific energy consumption by 76% with exponential regression. So, bulk density is a key factor to estimate energy consumption in milling process