Ndubisi A. Aviara

Influence of Cultivar on the Predictive Performance of a Moisture Transport Model Developed for Parboiled Paddy Drying

A mathematical model for predicting moisture profile in parboiled paddy during drying was developed using the prolate spheroidal coordinate system. The model was solved using the Crank Nicolson central difference scheme and the variation of its predictive potential with paddy cultivar was investigated. Parboiled paddy drying was carried out at 60°C using a cabinet tray dryer. The variation of the moisture ratio of different paddy cultivars (Banki, De-gold, and Liberia) with time and drying rate and with time and moisture content was determined. Model validation was carried out using residual plots, root mean square deviation, and coefficient of determination. The parboiled Banki, De-Gold, and Liberia paddy cultivars had equivalent diameters of 3.73, 4.75, and 3.68 mm, prolate spheroidal geometric dimensions (equatorial and polar radii) of 1.16 and 4.78 mm, 1.22 and 5.45 mm, and 3.10 and 3.92 mm, and effective moisture diffusion coefficient of 2.81934 × 10−10, 5.71515 × 10−10, and 3.77336 × 10−10 m2/s, respectively. Drying of parboiled paddy occurred in the falling rate phase with initial period of induction and critical moisture content that varied with cultivar. The residual plots showed that the model was acceptable for predicting moisture transport in all the cultivars during drying. Comparison of the observed and predicted moisture ratios showed low root mean square deviation and high coefficient of determination, which varied with cultivar indicating that the predictive potential of the model was cultivar dependent.

Modeling for Drying of Thin Layer of Native Cassava Starch in Tray Dryer

Ndubisi A. Aviara*, Joseph C. Igbeka Department of Agricultural and Environmental Resources Engineering, University of Maiduguri, Maiduguri, Nigeria Department of Agricultural and Environmental Engineering, University of Ibadan, Ibadan, Nigeria Received: June 27th, 2016; Revised: August 31st, 2016; Accepted: October 12nd, 2016 Purpose: The drying of a thin layer of native cassava starch in a tray dryer was modeled to establish an equation for predicting the drying behavior under given conditions. Methods: Drying tests were performed using samples of native cassava starch over a temperature range of 40-60°C. We investigated the variation in the drying time, dynamic equilibrium moisture content, drying rate period, critical moisture content, and effective diffusivity of the starch with temperature. The starch diffusion coefficient and drying activation energy were determined. A modification of the model developed by Hii et al. was devised and tested alongside fourteen other models. Results: For starch with an initial moisture content of 82% (db), the drying time and dynamic equilibrium moisture content decreased as the temperature increased. The constant drying rate phase preceded the falling rate phase between 40-55°C. Drying at 60°C occurred only in the falling rate phase. The critical moisture content was observed in the 40-55°C range and increased with the temperature. The effective diffusivity of the starch increased as the drying temperature increased from 40 to 60°C. The modified Hii et al. model produced randomized residual plots, the highest R2, and the lowest standard error of estimates. Conclusions: Drying time decreased linearly with an increase in the temperature, while the decrease in the moisture content was linear between 40-55°C. The constant drying rate phase occurred without any period of induction over a temperature range of 40-55°C prior to the falling rate period, while drying at 60°C took place only in the falling rate phase. The effective diffusivity had an Arrhenius relationship with the temperature. The modified Hii et al. model proved to be optimum for predicting the drying behavior of the starch in the tray dryer.

Moisture-dependent Physical Properties of Detarium microcarpum Seeds

Physical properties of Detarium microcarpum seed were investigated as a function of moisture content with a view to exploring the possibility of developing its bulk handling and processing equipment. In the moisture range of 8.2%–28.5% (d.b.), the major, intermediate and the minor axes increased from 2.95–3.21 cm, 1.85–2.61 cm, and 0.40–1.21 cm respectively. The arithmetic mean, geometric mean and equivalent sphere effective diameters determined at the same moisture level were significantly different from each other with the arithmetic mean diameter being of the highest value. The seed can be described as an irregularly shaped spherical disc. In the above moisture range, the surface area, one thousand seed weight, particle density and porosity increased linearly with moisture content from 354.62-433.19 cm2, 3.184-3.737kg, 1060-1316 kg/m3 and 30% to 53.1% respectively, while bulk density decreased with increase in moisture content from 647.6-617.2 kg/m3. Angle of repose increased linearly with moisture content from 13.9o-28.4o. Static and kinetic coefficients of friction increased linearly with moisture content and varied with structural surface. Highest value of static coefficient of friction at each moisture level in the above range was on galvanized steel sheet, while the lowest value was on fiber glass. For the kinetic coefficient of friction, the highest values were on Hessian bag material, while the lowest values were on fiber glass.

Measurement of Engineering Properties Necessary to the Design of Drumstick (Moringa oleifera L.) Pod Sheller

, 2015Purpose: Designing equipment for processing, sorting, and other post-harvest operations of agricultural products requires information about their physical properties. This study was conducted to investigate some of the mechanical and physical properties of Moringa oleifera L . pods and seeds. Methods: Properties such as the length, width, thickness, bulk density, porosity, mass, static coefficient of friction, and angle of repose were determined as a function of moisture content. Statistical data and force-deformation curves obtained at each loading orientation and moisture level were analyzed for bioyield point, bioyield strength, yield force, rupture point, and rupture strength using a testrometric machine. Result: The basic dimensions (length, width, and thickness) of moringa pods and seeds were found to increase linearly from 311.15 to 371.45 mm, 22.79 to 31.22 mm, and 22.24 to 29.88 mm, respectively, in the moisture range of 12 to 49.5% d.b. The coefficient of friction for both pods and seeds increased linearly with an increase in moisture content on all the surfaces used. The highest value was recorded on mild steel, with 0.581 for pods and 0.3533 for seeds, and the lowest on glass for pods, with a value of 0.501, and of 0.2933 for seeds on galvanized steel. The bioyield and rupture forces, bioyield and rupture energies, and deformation of the pods decreased with an increase in moisture content to a minimum value, then increased with further decrease within the moisture content range, while the yield force increased to a maximum value and then decreased as the moisture content increased. Conclusion: These results will help to determine the most suitable conditions for processing, transporting, and storing moringa pods, and to provide relevant data useful in designing handling and processing equipment for the crop.Keywords: Angle of Repose, Deformation, Drumstick pod sheller, Moisture content, Moringa oleifera