MOISTURE DEPENDENT ENGINEERING PROPERTIES OF AFRICAN LOCUST BEAN SEED (Parkia biglobosa) RELEVANT TO PROCESSING MACHINE DESIGN

Abstract

The physical, mechanical, aerodynamic and flow properties of locust bean seed (Parkia biglobosa) relevant to the development of a processing machine for the seed were determined in this study. These properties were determined in the moisture content range of 4.27% to 19.65% w.b. Locust bean seeds were obtained from Saki in Oyo State. The moisture content and physical properties were determined using American Society of Agricultural Engineer’s Standard. Universal testing machine was used to determine the mechanical properties. Terminal velocity was determined using a wind tunnel and data was analyzed using ANOVA. The major, intermediate, minor axes, geometric mean diameter of locust bean seed increased linearly from 0.94 to 1.17 cm, 0.76 to 0.96 cm, 0.45 to 0.60 cm, 0.69 to 0.87 cm, respectively. The porosity and aspect ratio decreased with increase in moisture content from 43.25 to 40.29% and 2.08 to 1.95, respectively. The static angle of repose increased with increase in moisture content level from 18.270 to 27.640. Seeds became sticky when moisture content increases, affecting free flow and piling at rest, and increased angle of repose. The coefficient of static friction on plywood, galvanized iron, mild steel, glass and stainless surfaces increased with increase in moisture content from 0.35 to 0.47, 0.34 to 0.43, 0.35 to 0.44, 0.25 to 0.36 and 0.33 to 0.41, respectively. The increase was due to increased adhesion between the seeds and the test surfaces at high moisture levels while surface smoothness reduced adhesion, accounting for the decrease in static friction on stainless steel and glass. The terminal velocity of the seed ranged from 1.48 to 2.76 m/s2 while drag coefficient decreased with increase in moisture level from 0.39 to 0.10. Compressive test shows that the compressive stress result of the seed in longitudinal orientation has the highest compressive strength compared to transverse orientation at higher moisture content level of 8.64, 12.63, 16.29 and 19.65% w.b and lower for moisture content level of 4.27% while the least deformation value of 0.79 and 1.32 mm was recorded for transverse and longitudinal orientation at moisture content level of 16.29 and 12.63 % w.b respectively, while the highest deformation value of 1.65 and 1.84 mm) was recorded for transverse and longitudinal orientation at moisture content level of 12.63 and 16.29% w.b. The flow properties parameters of milled locust bean seed which are bulk density, tapped density, angle of repose, hausner ratio and carr’s compressibility index increased with increase in moisture level from 0.55 to 0.61 g/cm3, 0.66 to 0.81 g/cm3, 44.70 to 46.390, 1.21 to 1.34 and 17.13 to 24.90 % respectively. A scientific data for the selected engineering properties of locust bean seeds useful for optimal machine design has been generated. These properties are useful for the design of storage facilities and dehullers