Development of an auxiliary heating system for a solar dryer in Bangladesh

Abstract Solar dryers are a convenient option for drying fruits and vegetables, but they largely depend on climatic conditions. Climate dependency makes them vulnerable to dry products and maintain the quality of the products accurately. To mitigate this problem, an electric auxiliary heating system (AHS) was designed, constructed, and tested for a solar dryer in Bangladesh. The developed system had three parts: an auxiliary heating unit, an air duct, and hot air convection pipes. The performance testing of the AHS was done in three experimental trials. The average air velocity from the auxiliary heating unit was found to be between 3.57 and 3.80 m s −1 . Trial runs showed a maximum drying temperature of 66.97°C, while the average value remained between 35.10 and 43.26°C. During the off‐sunshine hours, the AHS rose the average temperature by 1.00–12.84°C above ambient and continued the drying operation. Overall, the solar dryer with AHS saved 30%–36% sunshine hours than open sun drying, and its efficiency was estimated as 14.55%–21.9%. Regression analysis showed that the Page and Modified Page models were suitable for predicting the drying kinetics of cabbage samples. Through the results of the study, the developed AHS showed potential for significantly improving the solar drying process. It could be an effective measure for establishing a weather‐independent drying solution to reduce the postharvest losses of perishable agro‐products. Further improvements to the auxiliary heating unit, implying an Internet of Things (IoT)‐based control system will facilitate an improved and user‐convenient drying operation. Practical Applications Postharvest losses are prevalent for perishable agricultural products (fruits and vegetables) in Bangladesh and are considered a prime reason for the inhabitants to consume a less nutritious diet than recommended. An appropriate dry chain technology that is affordable, weather‐independent, continuous, and fast in operation could be the optimal solution to this problem. Numerous types of solar hybrid dryers with different additional heating sources (electricity, biomass, LPG, etc.) have been investigated around the world. However, the extent of these research endeavors is very limited in Bangladesh. The study was thus conducted to develop a novel auxiliary heating system for a solar dryer in Bangladesh and check its technical viability. Our results indicate that an electric auxiliary heating system can be an efficient option for drying fruits and vegetables irrespective of the weather and can substantially reduce postharvest losses in Bangladesh.