Response surface optimization of Bambara nut kernel yield as affected by speed of rotation, and impeller configurations

Abstract

The number of impeller slots, slot angle (angulations), and rotational speed are some of the operational parameters that influence kernel yield of centrifugal impact nut shellers. The effects of these three parameters on Bambara nut kernel extraction using a horizontal placed centrifugal Bambara nutcracker with a capacity of 150.6 kg/hr at a speed of 2200 rpm was determined using a split plot factorial experimental design. The dehulling efficiency increased with increase in rotational speed and number of impeller slots with a maximum value of 90.5% obtained at the highest speed of 2251 rpm, 75 ° angulations and 4 impeller slots while the minimum dehulling efficiency was 59% obtained at the lowest speed of 1125.8 rpm, 60 ° angulations, and 2 impeller slots. This range of values produced an extraction yield of 79.7– 84.5% and broken kernel of 11–59.6%. The results were fitted and responses were plotted and statistically analyzed to obtain the relationships between the variables. The optimum range of dehulling efficiency was 75.67–87.94% at rotational speed of 1956.42 -2135.74 rpm, angulations of 67.82 °–90 ° and 2–4 impeller slots. The optimum kernel yield ranged from 83.54–84.98% at 1125.8–1228.78 rpm, 47–90 ° and 2 -4 slots while the optimum kernel damage was 12.56 -15.19% at 1126.46–1131.3 rpm, 2–4 slots and 90 ° angulations. However, from the coefficient Table, it was only the speed and interaction of speed and angulations that significantly affected the nut dehulling efficiency and kernel yield respectively at p < 0.05. Keywords: Bambara bean, Nutcracker, Shelling, Modeling, Kernel extraction