Sizing, Testing and Optimization of a Geothermal Maize Grain Dryer: Use of Geothermal-Heated Water
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Date
2025-03
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Kenyatta University
Abstract
Geothermal energy is a renewable form of energy that can be utilized for drying agricultural
products like horticultural crops and grains. Utilization of geothermal energy to dry agricultural
products requires the design of a properly sized geothermal crop dryer that meets the specific
requirements for drying crops. In this study, the objective was to size, test, and optimize a
geothermal maize dryer deployed at the Menengai Geothermal Project site in Nakuru County,
Kenya. The components of the dryer consisted of a dryer cabinet, a water-to-air heat exchanger,
drying trays and a fan unit specially fabricated to assess the drying time of the geothermal dryer.
The study involved describing the heat transfer principles and equations to design these dryer
components. The fabricated dryer was used to dry a batch of maize grain, evenly distributed
between two trays, to lower the moisture content of the maize to 13% to allow for longer-term
storage. The heat exchanger was used to dry air which was used as the drying medium. The sized
fan unit was then used to blow the heated air over the maize grains. The geothermal water (brine)
obtained from a discharging well at the Menengai Geothermal Project site provided the source of
heat. The study investigated how the total drying time of the geothermal dryer varied at different
grain layer depths, drying air temperatures, and air velocities. The study also sought to optimize
the drying process and minimize the total drying time for the given geothermal dryer size using
the Taguchi method to determine the optimal combination of the three parameters. Minitab 20
software was used for optimization and Analysis of Variance (ANOVA) was performed using R 4.2.3 software to test for significance of varying the parameters on the drying time. From the
design, a geothermal maize dryer with 0.55m (L) × 0.25m (W) × 1m (H) dimensions and a drying
capacity of 40kg was designed, tested, and optimized for drying maize grains to a moisture content
of 13% moisture content wet bulb. The dryer had an axial fan with a power rating of 0.035kW and
a heat exchanger with an overall heat transfer coefficient of 86.8 W/m2
K. From analysis, drying
time reduced with increased temperature from 40ºC to 45ºC by 30 minutes while the drying time
was constant from 45ºC to 50ºC at 5 hours. The least drying time of 4 ½ hours was achieved with
a drying air velocity of 0.5 m/s while maximum drying time of 5 ½ hours was achieved with a
drying air velocity of 0.2m/s. As the grain depth was increased, the drying time increased from 4
½ hours at 0.1m to 5 hours with grain depths of both 0.15m and 0.2m. Results for the optimal
combination of the parameters using the Taguchi Method found that the optimal combination of
parameters for the geothermal dryer were drying air temperature at 50ºC, drying air velocity at
0.5m/s, and grain depth at 0.1m which would result in the minimum total drying time. ANOVA
analysis showed that varying the drying air temperature and the drying air velocity had a significant
impact on the total drying time. This study advances knowledge by presenting a systematic
approach to designing and optimizing geothermal maize drying systems to enhance energy
agricultural drying technology. The findings promote sustainable agriculture and food security by
demonstrating geothermal energy as a cost-effective, eco-friendly alternative to fossil-fuel powered drying. The optimized dryer benefits small-scale farmers and agribusinesses by reducing
post-harvest losses and improving grain storage.
Description
A Thesis Submitted in Partial Fulfilment of the Requirements for the Award of the Degree of Master of Science in Renewable Energy Technology in the School of Engineering and Architecture of Kenyatta University March, 2025
Supervisors;
1.Booker Onyango Osodo
2. Willis Jakanyango Ambusso