Specific energy consumption for reducing the size of alfalfa chops using a hammer mill

Measuring the energy requirement for alfalfa size reduction could be important for downstream processes such as densification. Alfalfa chops passed through sieve sizes of 18 mm (SS18mm), 15 mm (SS15mm) and 12 mm (SS12mm) were ground using a hammer mill (1.1 kW) with four screen sizes of 1.68, 2.38, 3.36 and 4.76 mm. Results showed that alfalfa chops with sizes of SS18mm and SS12mm had the highest and lowest specific energy (30.96 and 5.06 kJ kg−1), respectively. Exponential relationships between the specific energy requirement and the hammer mill screen sizes were obtained with coefficients of determination (R2) values ranging from 0.94 to 0.98. The data on specific energy was fitted to Bond, Rittinger and Kick models. The Rittinger model was the best fitted model with R2 > 0.94 for the three sizes of alfalfa chop. A linear model relating the specific energy to the ratio of initial to final screen sizes using the combined data predicted more accurately the specific energy values than all three models.