Bulk density and friction coefficients of selected minor millet grains and flours

The bulk density, coefficient of static friction and coefficient of internal friction were determined for the grains and flours of barnyard millet (Echinochola colona), finger millet (Eleusine coracana), foxtail millet (Sestaria Italid), kodo millet (Paspalum sorobiculatum), little millet (Panicum Miliare) and poroso millet (Panicum miliaceum) in the moisture contents of 8.7%, 11.1%, 16.3%, 22% and 28.2% d.b for the grains and 11.1%, 17.6%, 25%, 33.3% and 42.8% d.b for the flours. The bulk density of the millet grains, in this moisture range decreased linearly from 888.7–750.1, 794.9–740.3, 746.7–626.3, 810.1– 681.3, 748.1–570.3 and 820.9–762.1 kg/m3, respectively, for the barnyard millet, finger millet, foxtail millet, kodo millet, little millet and poroso millet. The bulk density of the millet flours increased logarithmically with the increase in moisture content, in the moisture content range studied. It increased from 483.1–523.4, 486.5–530.8, 502.6–534.9, 511.2–550.8, 508.4–551.7 and 498.3–541.8 kg/m3, respectively, for the flours of barnyard millet, finger millet, foxtail millet, kodo millet, little millet and poroso millet. The coefficient of static friction increased in the range, 0.26–0.62 for the grains and 0.62–1.13 for the flours with increase in moisture content. For both grains and flours, mild steel surface offered the maximum friction followed by galvanized steel, aluminium and stainless steel. The coefficient of internal friction ranged 0.59–1.25 and 0.73–1.16 for the millet grains and flours, respectively, in the moisture content range of 11.11–42.86% d.b. Both the values of coefficient of static friction and coefficient of internal friction exhibited a linear relationship with moisture content with higher coefficient of fit.