Modeling of Physical and Compressive Test Properties of Tigernut Using Response Surface Approach

The Engineering data of tiger nut cultivated in Africa is of high importance in facilitating the design of machineries for its effective and efficient cultivation, processing, handling, storage, and postharvest activities in general. This study is aimed at determining and modeling of the physical and compressive test properties of tiger nuts as influenced by size, moisture level and loading pattern. Applying Standard procedures and a 3,4,3 response surface factorial design, the Tiger nuts were cleaned of all foreign materials and sorted into three different sizes of 6mm, 9mm and 12mm, and conditioned into four different moisture levels of 7%, 10%, 13% and 16% respectively. The results shows that the arithmetic mean diameter (AMD) ranged from 7-14.867 (mm), geometric mean diameter (GMD) ranged from 6.982-14.853 (mm), sphericity (S) ranged from 0.931-1.011, surface area (SA) ranged from 153.216 -693.382 (mm2) and the aspect ratio (AR) ranged from 0.926-1.106. The mass (M) of 1000 tiger nut ranged from 201-1061 (g), volume (V) ranged from 25-96 (cm3), bulk density (BD) ranged from 0.634-0.979 (g/cm3), solid density (SD) ranged from 0.712-0.989 (g/cm3) and porosity (P) ranged from 11.08-21.45. The angle of repose ranged (AOR) from 20.58o-28.85o while the coefficient of friction (CF) on galvanized steel and stainless-steel surfaces ranged from 0.222-0.352 and 0.201-0.02 respectively. It was observed that, as sizes and moisture level increases, AMD, GMD, S, SA, AR, M, V, BD, SD and CF all increases respectively while both P and AOR decreases as the size and moisture level increases. It was revealed that the maximum compressive stress ranged from 0.26392-2.12026 (MPa), compressive strain at maximum compressive stress ranged from 1.20168-4.58292 (mm/mm). Energy at maximum compressive stress ranged from 0.02298-0.50274 (J), the compressive load at maximum compression stress ranged from 27.5937-232.257 (N), the extension at maximum compressive stress ranged from 0.30271-4.01056 (mm). The compressive stress at break ranged from 0.20376-1.75422 (MPa). The compressive load at break ranged from 25.2221-200.257 (N). The compressive strain at break ranged from 1.39935-5.79384 (mm/mm). The compressive extension at break ranged from 0.24417-3.55188 (mm). The energy at break ranged from 0.02113-0.33018 (J). The compressive stress at yield ranged from 0.24918-2.37054 (MPa) while the compressive load at yield ranged from 15.9373-210.693 (N). ANOVA result reveals that moisture level and tiger nut sizes have significant effects on the physical properties of tiger nut measured except on sphericity. Moisture level, tiger nut sizes and loading pattern have significant effects on the compressive test properties of tiger nut tested at 95% confidence level except for Energy at maximum compressive stress and Energy at break where loading have no significant effect at 95% confidence level. Empirical models were developed for the measured Engineering properties. The experimental data generated from this study serves as strong tools for the design and development of tiger nut postharvest machineries such as an oil and milk extractor among others.