Effect of moisture content and feed rate on size reduction of pearl millet

Abstract

Pearl millet at various moisture content (6.2, 9.4 and 12.3%, db) and feed rates (3, 6 and 9 kg/h) was ground using hammer mill and its physical properties viz. arithmetic mean diameter, geometric mean diameter, thousand grain weight, aspect ratio, specific surface area, surface area and bulk density were studied. Sieve analysis results showed that the increase in moisture content produced more medium sized particles with decreased percent weight retained in pan. Bond’s work index, Kick’s constant and average particle size were increased with the decrease in total surface area at higher moisture levels. The highest energy (2.34 KWh/kg) was consumed for 12.3% moisture content. Various grinding characteristics were significantly affected by moisture content and feed rate either individually or in combination and correlated in terms of Bond’s work index, Kick’s constant, total surface area, average particle size, effectiveness of milling and bulk density. Milling loss was found to be higher at lower moisture level and decreased with the increase of moisture content as well as feed rate. The loose and compact bulk density was ranged between 46.8-199.5 kg m-3and 53.5-254.1 kg m-3, respectively among the entire sieve fractions. Water absorption capacity increased with the decrease in particle size.