Designing a solar-powered sweet potato storage unit using simulation

The importance of sweet potato storage for food security

Sweet potato (Ipomoea batatas Lam) roots are rich in carbohydrates and can produce more edible energy per hectare than wheat, rice, or cassava. In addition, sweet potatoes contain substantial amounts of proteins, vitamins, and minerals and can play a key role in famine relief.

The roots can be stored for up to one year if the right procedures and storing conditions are in place. Immediately after harvest, the roots should be cured, allowing cuts, bruises, and skinned areas on the roots to heal. The speed of the healing process is driven by temperature, humidity, and aeration. If curing is not done properly, sweet potatoes will not store well.

Using simulation tools to design an environmentally controlled sweet potato storage unit

An environmentally controlled, solar-powered sweet potato storage unit, developed using Rocky coupled with Ansys Fluent, has brought significant benefits to farmers and rural enterprises in Kenya. Sweet potatoes can be stored in the unit for up to a year, and farmers can adjust the unit to ensure optimal air temperature, humidity, and ventilation.

Through multiphysics simulation enabled by Discrete Element Method (DEM) coupled with Computational Fluid Dynamics (CFD), a sweet potato storage unit was dimensioned specifically for farmers and rural enterprises in sub-Saharan Africa.

Figure 1: A dry shipping container will be used for the storage unit and its interior.

This unit can cure up to 5000 kg of roots at a temperature of 28°C and a relative humidity of 85%. For storage, the unit can maintain the temperature at 15°C and the relative humidity at 85%. The system was built using a 6-m intermodal dry freight container designed to be affordable, durable, and easy to operate. Components were selected so that the unit can be manufactured and repaired locally without the need for special imported items.

How coupled DEM-CFD simulation helped develop the storage unit

The challenges when designing this kind of equipment are:

Dimension the ventilators

Assure uniform airflow and temperature + relative humidity distribution

If Ansys Fluent would have been used alone, the sweet potatoes would have to be modeled as porous media. This simplification reduces accuracy and increases errors. For that reason, it was used Ansys Fluent coupled 2-way with Rocky. This simulation allowed the interaction between the air and the roots and not only estimated the uniformity of air temperature in the chamber, but estimated the actual temperature of the roots, providing much greater insights.

The simulation results helped us dimension the size of the fans and identify where to install air guides to assure uniformity of temperature.

Figure 2: Ansys Rocky coupled with Ansys Fluent was used to simulate a sweet potato storage unit.

Benefits of the storage unit for farmers in sub-Saharan Africa

A curing and storing unit suitable for village-based enterprises in sub-Saharan Africa reduces postharvest losses and allows more efficient use of the fields during the rainy season, fostering food security and improving the livelihood of rural populations. Its adoption has allowed farmers in Kenya to harvest sweet potatoes at optimal maturity, freeing up fields for other crops. Finally, the ability to store crops for up to a year has enabled those farmers to sell sweet potato roots later in the season, bringing additional income and reducing waste.

Marcelo Precoppe

Crop Postharvest Technologist, University of Greenwich

Precoppe holds a Ph.D. in Agricultural Sciences from the University of Hohenheim, Stuttgart, Germany. He joined the Natural Resources Institute at the University of Greenwich in 2017 as a Crop Postharvest Technologist. Earlier, between 2014 and 2016, Dr. Precoppe was a postdoctoral fellow at the International Institute of Tropical Agriculture (IITA). Before joining lITA, Dr. Precoppe worked as a researcher at the University of Hohenheim in Germany and, between 2004 and 2006, he managed the University of São Paulo training farm on sustainable agriculture and rural development.