SOURCE:

Faculty: Engineering
Department: Mechanical Engineering

CONTRIBUTORS:

Nwadike, E. C.
Enibe, S. O.
Nwabanne, J. T.

ABSTRACT:

This work focusedon the drying characteristics and modelling of aerial yam and water yam using convectional hot air and solar dryer. The raw unblanched and blanched samples were dried using convective hot air and solar dryer. Fan speed, temperature and slice thickness were varied for convectional hot air dryer, while fan speed, mass of sample and slice thickness were varied for solar dryer, to determine the change in moisture content. The thermo gravimetric analysis (TGA), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) was done to determine the thermal stability, functional groups and surface morphology respectively for each sample. The phytochemical composition and proximate compositions of the samples were carried out to determine the phytochemicals and proximate components of the samples. Mechanical and thermal properties of the samples were analyzed to determine the behaviour of the samples under stress and heat respectively. Drying kinetic models were evaluated to determine the models that best explain the drying process, while finite element analysis was done to determine the thermo physical characteristics (effective diffusivity (Deff), shrinkage kinetics and mass transfer coefficient) of the samples. Response surface methodology (RSM) via central composite design (CCD) was used to optimize the drying process. Sensory test, using a designed questionnaire, was done to determine the acceptability of flour produced from the dried products. TGA results showed that water yam and aerial yam consisted of two and three drying regions respectively. The thermal decomposition temperature of water yam was 389.5 °C, while that of aerial yam was 432.7 °C, which showed that the thermal stability was higher in aerial yam than in water yam. FTIR results revealed the presence of some important functional groups such as esters, ethers and nitro-compounds, and show that drying at this temperature (40-70oC) do not alter the nutrient components of this variety of yams. The SEM results showed that important cells were not destroyed at the drying temperature. The results also revealed the presence of important phytochemicals (tannin, Flavonoid, glycoside, saponin, alkaloids e.t.c) in both water yam and aerial yam samples. Proximate analysis of the samples showed that both samples contain moderately high water contents in raw form. The mechanical and thermal properties of the samples were significantly influenced by drying, while batch studies on the drying process also showed that increase in temperature and air speed increased the drying process, but decreases with increase in slice thickness for convectional hot air dryer. Increase in fan speed increased the drying rate of the samples for solar dryer but decreased with increase in slice thickness of the samples. The kinetic study showed that the best model for water yam and aerial yam was Logarithmic model with correlation coefficient of 0.9995 and 0.9991 respectively. The finite element result showed that Deff at 68.58 oC and 60.56 oC were 2.5487×〖10〗^(-10)m2s-1 and 2.0809×〖10〗^(-10)m2s-1 respectively for water yam, and 1.4381×〖10〗^(-10)m2s-1 and 1.2241×〖10〗^(-10)m2s-1 for aerial yam at the same respective temperatures. The RSM revealed optimum drying conditions of 60oC, 2.0 m/s and 3.5 mm for blanched and 60oC, 2.4 m/s and 2.0 mm for unblanched sample dried byconvectional hot air dryer, and 71g, 1.5 m/s and 3.2 mm for the blanched and 70g, 1.5 m/s and 3.0 mm for unblanched samples dried with solar dryer.The Hedonic test results showed wide acceptability of the colour, aroma, texture and general appearance of blanched samples more than the unblanched samples of the yam species. In conclusion, the economic advantages of these yam species can be optimized by blanching and computer based finite element modeling should be employed in making decisions on the handling, storage and distribution/exportation of these important agro-products.