dc.description.abstract |
Drying of maize grain is considered an important process in reducing aflatoxins effects
on Maize Mechanical drying is recommended over natural drying during wet weather
but is costly and energy intensive. Comprehensive understanding of convective water
activity during grain drying is critical to the development of more efficient drying
process particularly for cobbed maize. The main objective of this study was to analyse
batch dehydration of cobbed maize to help understand the dynamics of low temperature
processing to facilitate the development of appropriate on-farm drying technologies.
The specific objectives were (i) Experimental measurements of drying characteristics
and process conditions during batch drying of cobbed maize at low temperatures,(ii)
Analysis of the temperature distribution and velocity field of drying air in the batch
drier using CFD software (ANSYS Fluent) and (iii) Validation of drying model using
experimental results from batch drying at an industrial seed processing facility.
Empirical data was obtained using temperature, relative humidity, velocity and
moisture content sensors. The sensors were applied within the actual cobbed maize
drying operations at Kenya Seed Company Ltd. - Kitale in November 2018.The results
showed drying chamber temperatures in the range of 30 - 35 o C while the relative
humidity varied from 15 – 35%. The initial moisture content of the Kernels and cob
were 19%wb and 38%wb, respectively, reducing to 12%wb for both components after
70hours of dehydration. Numerical modeling was performed using CFD software
(ANSYS Fluent 19R1). For ease of analysis, a 2D geometrical model was developed in
accordance with the actual parameters of the drying chamber that was used in the
experimental analysis. ANSYS CFD-Post was applied to visualize contours, streamline
and vector plots inside the drying chamber at superficial air flows of 1m/s, 5m/s and
10m/s, for scenarios with and without the product. The simulated pressure and velocity
contours showed lower airflow along the walls and at the corners, consistent with the
findings of other studies on non-circular geometries. Similar trends were observed at
the increased airflow settings. Non-uniform airflows cause uneven dehydration which
presents a challenge for optimal termination of batch operations where over-drying is
avoided. The Midili model best fitted the drying kinetics of cobbed maize with R 2 and
RMSE values of 0.946 and 0.0127, respectively showing good agreement between the
mathematical model and the experimental data. The study concluded that the geometry
significantly affects the distribution of air velocity and temperature during drying
process and that Midili Model best fits on the drying curves of cobbed maize. Further
research is recommended to assess the impact of moisture content, cob size and fines /
shell out on batch drying kinetics. |
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