Fabrication and Performance Evaluation of a Semi-Automatic Electric Cabinet Dryer for Carrot, Cabbage and Tomato

In many parts of the world, the journey from farm to table is fraught with loss. Fresh vegetables, rich in nutrients and vital for food security, often spoil before they can be eaten. This happens because these crops are highly perishable; without proper storage or processing, they rot, wasting the water, land, and labor invested in growing them. In lower-income regions, where refrigeration and advanced storage facilities are often scarce, this problem is especially acute. One of the oldest and most effective ways to stop this spoilage is drying. By removing water from the food, the environment becomes inhospitable to the bacteria and molds that cause decay, and the food becomes lighter and easier to store or transport. While drying is a simple concept, doing it well requires control. Traditional open-air drying relies on the weather, which can be unpredictable, and exposes food to dust and insects. Modern solutions often involve machines that use heated air to speed up the process, but these can be expensive or complex to build. The challenge for small-scale farmers and local communities is finding a way to dry food that is affordable, reliable, and capable of handling different types of vegetables without requiring expensive technology.

A team of researchers in Rwanda set out to address this challenge by designing, building, and testing a simple, semi-automatic electric cabinet dryer. Their goal was to create a machine that could be constructed from locally available materials and used to preserve common vegetables like carrots, cabbage, and tomatoes. They began by creating a detailed three-dimensional model of the device, which took the form of a wooden box roughly the size of a large suitcase. Inside this cabinet, they installed a heating element, a fan to circulate the warm air, and wire-mesh trays to hold the vegetables. The system was equipped with sensors to monitor the temperature and humidity inside the chamber, along with a control panel that allowed the operator to set the desired conditions. The entire machine was assembled in a carpentry workshop, using timber for the structure and standard electrical components for the heating and control systems. The total cost to build the prototype was 84,755 Rwandan francs, a sum that the researchers noted was heavily influenced by the price of the electrical parts, which made up the vast majority of the hardware cost.

To see how well this homemade machine worked, the researchers conducted a series of tests using fresh produce purchased from a local market. They prepared samples of carrots, cabbage, and tomatoes, washing and peeling them before placing them on the trays. Each test run lasted for sixteen minutes, during which the machine heated the air to temperatures between 49 and 55 degrees Celsius. The researchers carefully weighed the vegetables before and after each run to measure how much water had been removed. They also tracked the temperature and humidity inside the cabinet throughout the process. The results showed that the dryer functioned as intended, successfully removing moisture from all three types of vegetables. However, the speed at which the water left the food varied significantly depending on the crop.

The most striking finding was that the vegetables did not dry at the same rate, even though they were subjected to the same heat and airflow. Cabbage proved to be the easiest to dry, losing nearly half of its initial weight in just sixteen minutes. Carrots performed moderately well, losing about one-third of their weight in the same time. Tomatoes, by contrast, dried much more slowly, shedding only about 15 percent of their weight. The researchers observed that the air inside the cabinet was significantly drier when drying tomatoes compared to the other two crops, yet the tomatoes still lost moisture at the slowest pace. This suggests that the structure of the tomato itself—perhaps its skin or the thickness of its flesh—creates a barrier that makes it harder for water to escape, regardless of how dry the surrounding air is. In contrast, the leafy structure of the cabbage allowed water to evaporate quickly. The carrots fell somewhere in between, though the results for carrots showed more variation from one test to another, likely because the size and shape of the carrot pieces were not perfectly uniform.

While the machine successfully demonstrated that it could dry these vegetables, the researchers were careful to note the limits of their study. The tests were short, lasting only sixteen minutes, which is far less time than is needed to dry vegetables completely for long-term storage. Consequently, the numbers they recorded represent the initial speed of drying rather than the final efficiency of the process. They also estimated the electricity used rather than measuring it directly with a meter, meaning they could not yet calculate exactly how much energy was required to remove a specific amount of water. Despite these limitations, the project proved that a low-cost, locally built dryer can be a functional tool for reducing post-harvest losses. The study suggests that for small-scale processors in Rwanda and similar settings, such a device offers a practical way to preserve surplus produce. However, to make the system truly efficient, future improvements would need to focus on standardizing the size of the vegetable pieces, better controlling the humidity inside the chamber, and measuring energy use more precisely. The work confirms that with the right design, simple technology can play a significant role in securing food supplies and supporting local agriculture.