Properties of Cowpeas (var. Minica Beans)

Abstract

In order to design a thresher for Minica beans grown in Guyana, the following properties were needed: the average energy absorbed by a bean before cracking, static and dynamic moduli of elasticity, threshability using belts and aerodynamic lift of beans and pods. This paper reports on the design of the equipment required for each of these tests and the test results. The average energy required to cause fracture of a single bean at 11% m.c.w.b. under quasi-static load was on average 0·007 N m compared with 0·004 N m for impact loading. The dynamic modulus of elasticity under impact loading was on average 876 MN/m2compared with 97 MN/m2for quasi-static compressive loading. Threshability with a rubbing action was found to be most effective when the pods had an initial crack; 98% of the pods could then be threshed. Aerodynamic tests showed that the terminal velocity of the beans was 9 m/s on average and, under the conditions at which the experiments were carried out, a vertical air velocity of 6 m/s on average provided effective separation of the threshed pods from the beans.