Author ORCID Identifier

https://orcid.org/0000-0002-1093-6852

Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture; Engineering

Department/School/Program

Biosystems and Agricultural Engineering

First Advisor

Dr. Michael Montross

Second Advisor

Dr. Samuel McNeill

Abstract

Grain in Africa and indeed most developing parts of the world are stored in polypropylene or jute bags arranged in stacks of varied dimensions in naturally ventilated warehouses. This practice is, however, associated with high postharvest losses due to poor temperature and moisture management during storage. This constitutes a major economic and food security challenge in these countries. Therefore, this study characterizes changes in moisture content and temperature occurring in a stack of bagged corn by determining the permeability of bag materials that influence moisture transfer and developing a mathematical model of heat and mass transfer which incorporates the unique physical and thermal properties of bagged corn in storage.

Water vapor transmission rate and permeability of woven polypropylene bags and jute bags increase with an increase in vapor pressure deficient of the storage environment. Water vapor transmission rate was linearly correlated with vapor pressure deficit. The development of a monitoring device capable of acquiring temperature and relative humidity data from specific locations within the stack and its deployment for field use is also discussed in terms of providing data for analyzing the bagged grain ecosystem and also for validating the mathematical model.

A comprehensive analysis of the effect of changing environmental conditions on temperature and moisture distribution as well as insect population in bagged corn is discussed. Small stacks of bagged corn (54 bags of 40 kg capacity arranged in two stacks) and a large stack (192 bags of 40 kg capacity) stored under naturally ventilated warehouses in Nigeria and US respectively were used. Generally, bagged corn temperatures followed the trends of the air temperature surrounding the bags with no differences between individual bags in the small stack. Moisture content increased uniformly in the small stacks and the warm conditions within the bags encouraged the proliferation of insects, of which maize weevil Sytophilus zeamais was the most predominant. These contributions are unique as it marks the first time that temperature and moisture distribution in a stack of bagged grain is critically studied for the purpose of improving management.

Validation of the mathematical model was performed with experimental data from the two storage studies. There was a close agreement between the predicted and experimental data in terms of describing the temperature distribution within the stack of bagged corn, although predicted temperatures in the small stack showed higher standard errors. The average standard error between the experimental and predicted temperatures was 1.2 °C (0.8 to 2.1 °C). The average standard error between the measured moisture content and predicted equilibrium moisture content (EMC) was 1.0 percent point (0.8 to 1.1 %). The prediction accuracy of the model was improved with the use of experimental values for the physical and thermal properties of bagged corn. The monitoring systems and mathematical model will contribute to improved management of bagged grain in naturally ventilated warehouses.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.458

Funding Information

National Institute of Food and Agriculture, U.S. Department of Agriculture Multistate Project Program under 1002344. (2017 - 2020)

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