TITLE:
Determination of the Drying Kinetics Modeling and Activation Energy of Medium-Grain and Long-Grain Rough Rice under Isothermal Conditions
AUTHORS:
Sammy Sadaka, Vinay Kalyankar
KEYWORDS:
Drying Kinetics, Effective Moisture Diffusivity, Long-Grain Rice, Medium-Grain Rice, Activation Energy
JOURNAL NAME:
Open Journal of Applied Sciences,
Vol.12 No.5,
May
31,
2022
ABSTRACT: The available literature revealed a gap in reporting the rough rice
drying kinetics parameters under isothermal conditions, particularly for
Arkansas medium- and long-grain varieties. Therefore, medium-grain (RO170112
and Titan) and the long-grain (Diamond and Wells) rough rice varieties were
dried under isothermal conditions. The drying process occurred under 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, and 100°C in a system emulating the thermogravimetric
analyzer. Drying kinetics models were studied for four well-known models: Page,
Newton, Logarithmic, and Henderson & Pabis. The drying kinetics constants
were determined for the four studied models. The initial moisture content of
rough rice was 28.2% db. Profound moisture reduction was observed during the
first three hours of drying, followed by less moisture content reduction. The
results showed that at the drying temperature of 100°C and after 6 hours of the drying process,
the lowest moisture content reached 13.9% (db) for Titan rough rice. The drying
rate of rough rice ranged between 7.41 and 2.01%/h during the first hour of
drying under the studied temperature range of 40°C to 100°C. The drying
rate was higher with the higher temperature levels during the first three
hours. Among all the studied models, the Page, Newton, and Logarithmic models
best fit 25%, 25%, and 50% of the twenty-eight studied cases. The challenge
that arose from these results led to evolving a mathematical solution by
joining the three models in one equation. The combined model showed the best
fit for all the studied cases, with R2 ranging between 0.9999 and
0.9954 for the medium- and long-grain rice varieties. Increasing the drying
temperature increased the effective moisture diffusivity values. The highest
effective moisture diffusivity of 18.104 × 10-9 m2/s was
obtained at the drying temperature of 100°C for medium-grain rice, Titan. The activation energy values ranged between
17.77 and 24.48 kJ/mol for the four rough rice varieties.