Determination of Moisture and Temperature Variation in Wet Grains Over Time and Space to Effect Desiccant Drying
Abstract
The aim of this study was to establish the best position to place super absorbent polymer
(SAP)in an experimental granary for effective and economical drying. To achieve the aim of
the study moisture migration and temperature distribution in stored wet grain was determined
over time. Also determined was the best position for placing SAP in the silo for use in a direct
solar drying grain silo. Results from experiments conducted were used to evaluate performance
of the SAP in grain drying. The study was carried out in the University of Nairobi, Department
of Environmental and Biosystems Engineering, Upper Kabete Campus.
An experimental silo was designed. From the design, three experimental silos were fabricated.
The initial experiment was conducted to determine moisture migration within the silos without
use of Super Absorbent Polymer (SAP). In a second experiment drying was conducted using
sun and super absorbent polymer placed inside the silo. The silo was evaluated in fifteen
different sections. The sections were: East (top, central and bottom), West (top, central and
bottom), North (top, central and bottom) South (top, central and bottom) and Center (top,
central and bottom). Thermometers were placed in each section and readings taken in the
morning, midday and evening. Modeling was done using regression analysis (MS Excel 2010)
based on the minimization of sum of squares by adjusting the model constants. The
coefficient of determination (R2), were used to evaluate the goodness of fit of the
mathematical model to the actual data. The model considered for this study was: second
degree polynomial regression model.
The results exhibited that drying occurred faster at the top compared to the center and bottom
sections. This was due to the fact that the top section was open hence moisture easily escaped
to the atmosphere aided by the high vapor pressure gradient between the grains at the top
surface of the silo and the atmospheric air. Second degree polynomial regression model
produced the highest values of R2 for experiment with SAP and the that without.
~ vi ~
Generally, it was established from the research that there is a significant difference in the
moisture content with depth in the three layers investigated during the entire drying period.
There was a high moisture depletion in the top layer while there was a high moisture
concentration at the center and bottom section with the central section having the highest. This
was a clear indication that the SAP ought to be placed in the center section and partly bottom
section as these were the areas with high moisture concentration. From the two sets of
experiments conducted it was revealed that the silo with SAP had a steeper and smoother
negative gradient as compared to that without; whose curves showed a series of negative and
positive gradients. This indicated that SAP was able to take up extra moisture that emigrated
into the center and bottom section and those that were brought about by moisture diffusion.
The research work indicated that SAP can be used in drying maize grains. Future research work
should consider passing preheated air in the grain to optimise moisture absorption by SAP and
improve air circulation in the silo.
Keywords
Absorption, desiccant, drying, grain, migration, moisture, Super Absorbent Polymer,
temperature.
Publisher
University of Nairobi
Rights
Attribution-NonCommercial-NoDerivs 3.0 United StatesUsage Rights
http://creativecommons.org/licenses/by-nc-nd/3.0/us/Collections
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