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.