Physical properties of cowpea (Vigna sinensis L.) seed

The physical properties of cowpea seed were evaluated as a function of moisture content. The average length, width and thickness were 9.92 mm, 6.87 mm and 6.06 mm, respectively, at 12.01% d.b. moisture content. In the moisture range from 12.01% to 38.90% dry basis (d.b.), studies on rewetted cowpea seed showed that 1000 seed mass increased from 209.23 g to 256.88 g, the projected area from 22.59 to 32.72 mm2, the sphericity from 0.781 to 0.799, the porosity from 50.64% to 51.49% and the terminal velocity from 9.31 m s−1 to 9.61 m s−1. The static coefficient of friction of cowpea seed increased the linearly against surfaces of four structural materials, namely, rubber (0.364–0.394), aluminium (0.212–0.296), stainless steel (0.176–0.238) and galvanised iron (0.324–0.36) as the moisture content increased from 12.01% to 38.90% d.b. The bulk density decreased from 569.9 to 535.6 kg m−3 and the true density from 1154.8 to 1104.1 kg m−3, respectively, with an increase in moisture content from 12.01% to 39.90% d.b.