Final Report

Megan Davisson, Jameson Hunter, Cameron Magolan, & Julia Parker

University of Kentucky

April 2019

Executive Summary

Corn is commonly dried in Nigeria by placing whole cobs along the roadside to dry in the sun (Adedeji, 2018). Roadside drying is inefficient, taking anywhere between three days to more than a week, and exposes the grain to contaminants, animals, and theft. We were assigned with designing a new method of drying ear corn in Nigeria. Our design was to be under $200, easily built and maintained with local materials by the farmers, an improvement upon traditional roadside drying methods, utilize passively produced electricity, and have a capacity that matched the production of an average Nigerian corn farmer.

Our proposed solution holds 8 bushels of eared corn with electricity produced by a solar panel. Our final design exceeds the $200 limit because we did not have access to the same scrap materials that Nigerian farmers would be able to salvage to reduce cost. After testing, we concluded that our solution could dry 8 bushels of eared corn given 17.5 hours of sunlight. However, due to complications testing indoors, we recommend further testing of our system outdoors during the summer months in Kentucky to determine if the drying time could be decreased.

Introduction

A single-family Nigerian farmer produces approximately 240 bushels of corn and stores approximately 60% (144 bushels) of their harvest (Adedeji, 2018). Harvesting was done in batches of nearly 8 bushels, effectively spreading the 144 bushels to be dried over a period of 18 days (McNeill, 2018). A bushel of corn was assumed to be 60 ears, each measuring 7 inches in length and 2 inches in diameter (Showalter, 1964). The moisture content of freshly harvested corn was approximately 25% and must be reduced to 14% for proper storage (University of Nebraska-Lincoln, 2016). Current drying methods on single-family Nigerian farms can lead to unnecessary post-harvest losses of grain due to spoilage from slow drying times and contamination (Adedeji, 2018).

Our design was an indirect-type active solar energy dryer. It includes a drying chamber, solar collector, 410 CFM fan, and a 50 W solar panel. Under ideal conditions, our design was expected to dry 8 bushels per 17.5 hours of sunlight. This rate would reduce grain losses due to spoilage while the enclosed design would reduce environmental contamination.

Our total costs for materials of the grain drying system was $437.48. This cost was higher than our $200 limit set by the customer due to project constraints such as, being required to purchase all necessary items rather than having the ability to utilize salvaged materials. Faculty members familiar with grain drying in Nigeria note that the farmers would be able to use leftover and salvaged materials to limit costs to $200 (McNeill, 2018).

Relevant Standards

  1. Corn must be dried and stored at 14% moisture content (University of Nebraska-Lincoln, 2016).
    • This was used for the engineering analysis and target testing condition.
  2. The Nigerian Building Code
    • This structure would not be occupied by humans; thus, this standard does not apply to our design (Mimiko, 2006).

Solution Proposed

SEE APPENDIX B FOR DRAWINGS

Drying Chamber

    • Capacity: 8 Bushels
    • Moisture Removed: 71.6lbs (University of Nebraska-Lincoln) (Flycarpet Inc.) (Henderson) (Marshal)
    • Size: 4’X5’X6.5’
    • Volume of Chamber: 60 ft3
    • Details: Four doors, angled roof for air flow, and four chicken wire shelves placed 6” apart. The cobs are placed 1/2in apart.

Solar Collector

    • Volume Required: 5117 m3 D.A. (Flycarpet Inc.) (Henderson) (Marshal)
    • Velocity: 410 CFM
    • Temperature and Relative Humidity Entering Collector: 25℃, 85% (TuTiempo)
    • Temperature and Relative Humidity Entering Chamber: 52℃, 63% (Flycarpet Inc.) (Henderson) (Marshal)
    • Temperature and Relative Humidity Exiting Chamber: 36℃ 61.4% (Flycarpet Inc.) (Henderson) (Marshal)
    • Size: 3’X6’X 4.75”
    • Details: Wood frame, 1” thick cardboard insulation, scrap metal, and greenhouse film

Expected Drying Time: 17.5 hours

Wiring Diagram


Figure 1. Wiring Diagram of the Solar Panel to Fan for Direct Current

Results

Phase 1: Solar Panel

Setup.

The solar panel was placed in a sunny spot at a 52 ̊ angle from the horizontal (“How to Figure the Correct Angle for Solar Panels”, n.d.). The current, voltage output, and light intensity were measured every thirty minutes for approximately 4 hours. The weather data was also recorded using the US National Weather Service website set for Lexington, KY.

Conclusions.

The voltage was as expected (Figure 2). The current was measured using an open circuit current, therefore there are discrepancies between our measurements and the solar panel specification sheet. Overall, the solar panel was operating as specified.

Figure 2. Solar Panel Raw Data from Testing Phase

Phase 2: Drying Chamber with Solar Collector Attached

Setup.

The solar collector and drying chamber were placed in an environmental chamber and connected using 8” metal ducting. The conditions in the chamber were set to 25 ℃ and 85% relative humidity. 8 bushels of corn were placed on the drying racks. 1875 W of heat lamps were position above the solar collector to simulate the sun. A HOBO device was placed on the top shelf in the middle of the drying chamber to record the temperature and relative humidity in the drying chamber throughout testing. An ear of corn on the top and bottom shelves were marked using zip ties. The marked ears were placed the furthest distance away from the inlet air duct to ensure uniform drying. 10-15 kernels were taken from the marked ears every hour and placed in a labeled ziplocked bag until the sample could be placed in the moisture content reader. It took two hours per sample to determine the moisture content of the corn. The bottom shelf samples were tested first.

Conclusions.

Figure 5 shows a decrease in the moisture content of the corn for both the top and bottom shelf samples. The bottom shelf dried by approximately 1.5% whereas the top shelf dried by approximately 3%. Because testing each sample took 2 hours to run, and we had 18 samples to run, which were spread out among a couple days, it is possible that the top shelf samples could have lost moisture outside of the drying chamber. The samples were stored in single use plastic bags to minimize this risk, however. Based on our data, some of our corn was able to reach the desired 14% moisture content at the end of an 8-hour period.

Figure 4 shows the relationship between the temperature and relative humidity in the environmental chamber (T ec & RH ec) versus the temperature and relative humidity of our designed drying chamber (T dc & RH dc). To simulate Nigerian weather conditions, our initial conditions in the environmental chamber were set to 25 ℃ and 80% RH, however, the chamber was not able to hold these conditions. Consequently, the test performed did not accurately depict the location our design was built for. As the figure illustrates, the temperature grew fairly rapidly (nearly 6 ℃) inside the entire environmental chamber due to the heat lamps positioned above the solar collector. The increase in temperature caused a decrease in the relative humidity as expected. While our conditions didn't match that of Nigeria, our drying chamber and solar collector set up did perform as designed. The temperature in the drying chamber after about an hour was consistently 1 ℃ above that of the ambient air. The relative humidity in the drying chamber after about an hour was also consistently about 1% higher than that of the ambient air, signifying that the air was picking up the moisture from the corn. We would expect the temperature and relative humidity differences to be larger if the drying chamber was placed in the sun.

The heat lamps placed so closely to the solar collector caused some of the plastic to melt. The original 400 CFM fan purchased operated as expected. We adjusted our final design to 410 CFM to eliminate the inverter. It is also important to note that the initial moisture content of the corn was not at the desired 25% moisture content.

Figure 3. Raw Data of 1st Test in Drying Chamber

Figure 4. Graph of Temperature and Relative Humidity of the Drying Chamber (dc) and Environmental Chamber (ec)

Figure 5. Graph of Corn Moisture Content Over Time in Trial 1

Phase 3: Solar Collector Alone

Setup.

The 1875 W of heat lamps were placed above and parallel to the solar collector. The solar collector was run with the fan turned on for approximately one hour. The HOBO was placed directly below the outlet of the fan to read the temperature and relative humidity of the air leaving the solar collector.

Conclusion.

The plateau in the middle of the graph is the maximum amount of heating that occurred. Once we observed the graph had plateaued for 10 minutes, we turned off the heat lamps and let the system cool. It took approximately 30 minutes to reach the maximum temperature.

Ambient conditions:

● Temperature: 23 ℃

● Relative Humidity: 39.5%

Maximum heating:

● Temperature: 24.54 ℃

● Relative Humidity: 33.95%

Amount changed:

● Temperature: +1.54 ℃

● Relative Humidity: -5.55%

Discussion

To simulate the sun in Nigeria, we needed 1200 W/m2, or 2400 W total, for our solar collector. After extensive research and discussion with trusted faculty, we incorporated five 375 W heat lamp bulbs for a total of 1875 W into out testing design to simulate Nigerian solar conditions. This was the maximum load that could safely be utilized inside the environmental chamber without fear of electrical failure within the environmental chamber. This ultimately failed due to the environmental chamber’s inability to maintain controlled conditions due to stress brought on by the heat lamp bulbs.

During the first round of testing, we chose to measure the moisture content of the corn on the top most and bottom most shelves in the chamber due to our assumption based on proximity to the air duct; the top most shelf would take the slowest amount of time to dry versus the bottom most shelf drying the quickest. However, as this first test concluded we had to mitigate the stress on the chamber caused by the heat lamp bulbs. We chose to mimic the heat of the solar collector with a small space heater for the second round of testing, but the heater failed within the first two hours of testing due to lack of proper air flow across its face, which resulted in an unusable testing sample. After exhausting our options to test the grain drying chamber, and the corn turning into a biological hazard, we stopped testing.

Although our system's components worked properly individually, further testing would need to be conducted, with all components connected, in an environment more closely resembling Nigeria to conclude this as a feasible design.

Recommendation

To further conclude the feasibility of our design, we recommend a full system test with all components placed in an exposed location during a Kentucky summer. The test must include fresh corn off of the stalk as close to 25% moisture content as possible. The solar panel angle should be adjusted to match the summer recommendation found on How to Figure the Correct Angle for Solar Panels. The solar collector should be placed on the side that would receive the most sun. A HOBO should be placed in the drying chamber to record the temperature and relative humidity. Weather data should be recorded similar to that of the solar panel data table (Figure 2). A “quality of corn” metric should be established to test for grain spoilage. Finally, we recommend taking samples from all four shelves and combining them into a representative sample to ensure proper drying. These testing parameters should be run in triplicate at the very least to ensure proper analyses can be made for the corn samples.




Figure 6. Graph of Temperature Over Time in the Solar Collector

Manufacturability

Not Applicable to this design.

Environmental Sustainability

The grain dryer was designed to be low-cost and environmentally sustainable. One of the main goals in our design was to utilize recycled material as much as we could. This helps maintain a reduced cost for building the system as well as a reduction of waste production. One of the restrictions in our design was to create a system that could work independently of public utilities due to the scarcity of a reliable power source in rural Nigeria. All heat used in the drying process is collected from the sun. The only powered implement used is a DC fan that runs off of electricity sourced by a solar panel.

Ethical, Health, and Safety

  1. Injuries During Construction: The builders are advised to wear proper safety equipment while building (gloves, eye protection, closed-toed shoes, etc.).
  2. Pests/Rodents: Drying chamber placed up off the ground, and the piping air holes for the solar collector were drilled too small for most rodents to enter.
  3. Sickness: When testing, we had to worry about moldy corn, so we wore latex gloves and carpenters’ masks.
  4. Death by Crushing if Structure Fails: We followed typical framing guidelines with 2x4’s and 16d nails.
  5. Cuts Caused by Metal Roof: We wore heavy duty leather gloves and long sleeves/pants when handling the metal roofing. We would recommend painting the edges of the roof a bright color to further protect people from running into an edge once constructed.
  6. Burns Caused by Metal Ducting and Roof: This was not a concern during the construction because we built it indoors. However, we would advise people to wear gloves, long sleeves, and pants while the device is in the sun.
  7. Product Restriction Approximately 8 bu. of Corn: The chamber can theoretically hold more than 8 bushels of corn but exceeding the designed 8 bushel limit will not guarantee the expected results. The recipient is advised not to exceed this limit.
  8. Mold growth in chamber: We are aware this a possibility, but we did not know how to address this.

Economics

Tabulated below is a complete list of the materials bought and used to build the grain dryer we designed (Table 1).

Table 1. Grain Drying Bill of Materials

Updated Bill of Materials

Conclusion

The indirect-type active solar energy dryer we designed met the majority of the constraints required by the customer. Our dryer had to not exceed a maximum cost of $200, be an improvement upon traditional roadside drying methods, be independent of public electrical utilities, be capable of drying and storing corn on its cob that has been produced by the average Nigerian farmer, and had to have materials that were sourced locally to the farmers’ area. The final dryer we built and tested cost a total of $438 due to the inability to utilize salvaged material. In order to decrease drying time to a reasonable amount, we added a solar panel and fan to our design to create forced convection which may not be materials that are as easily accessible to a rural farmer’s area. Aside from failing to meet these two requirements, we successfully met the remaining ones listed above. The as-built grain dryer has been calculated to dry grain in approximately 17.5 hours. This is less than our initial calculations during the design phase, but ultimately more efficient than the 3-5 days that roadside drying required.

Next Steps

Due to the complex nature of testing our design indoors, we recommend that testing continue outdoors during the summer months in Kentucky. According to Dr. Adedeji, the climate of Kentucky during the peak summer months (June-August) is similar to the average Nigerian climate (2018). This will yield the most realistic and accurate results from our design, allowing for any changes that may be necessary to improve the design to be made.

Future iterations of this design should also address the issues we faced with our first design. The high cost could be mitigated by utilizing as much scrap material as possible, as well as using leftover pieces from the first design. The solar collector could be improved by increasing its heat capacity. This could be done by improving its insulation and replacing the greenhouse film with glass sheeting or plexiglass. A thicker glazing material across the top of the collector would allow for more air to remain trapped within the layers of the collector rather than escaping through the plastic film, which could help force more air into the drying chamber. The next iteration should also address the issue of loose kernels in the chamber. When the corn was being moved in or out of the drying chamber, kernels would often fall off. These kernels would scatter across the bottom of the chamber and sometimes into the fan inlet on the bottom of the chamber. In the next iteration of this design, a permeable barrier should be placed over the fan inlet to prevent corn from becoming lodged in the ducting leading to the solar collector.

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