Performance enhancement of the hybrid solar dryer (HSD) for commercial drying of high- value Agricultural produce in Uganda

Abstract

Post-harvest losses of fruits and vegetables is major hindrance in development of Uganda’s agricultural sector. The need to ensure that well-functioning solar dryers are available in the market is an important step in addressing this problem. In a bid to enhance the performance of the exiting HSD in Uganda, the objectives of this study were to; 1) establish the appropriate drying chamber geometry and parameters, 2) redesign the biomass burner, and 3) compare the performance of the old HSD with the improved HSD. For the study; literature review, numerical analysis, modelling and simulation using SolidWorks, and experimental analysis were conducted. Data was collected from the old HSD at Kayunga and Kasese, and the improved HSD at Makerere University Agricultural Research Institute Kabanyolo (MUARIK). Temperature and humidity recordings were obtained using TemLog 20H data loggers for 6 days. Data analysis was conducted using Excel 2019. Parabolic shape was found to be the most appropriate because of its capacity to capture most of the solar radiation and ensure good temperature distribution. Numerical analysis established the temperature of hot air exiting the heater exchanger at 92.30 ℃ to be sufficient for pineapple drying. The length of the heat exchanger was increased from 0.7 m to 1.0 m and this caused a temperature increment of 18.44 ℃ causing a significant difference in the drying chamber temperature (p≤0.05). Dry run test revealed temperature increment of 27% (13.5 ℃) for the improved HSD compared to the old HSD. The highest temperature for the improved HSD was recorded at 63.5 ℃ at 2pm, and was close to the highest limit of 65 ℃ for safe drying of pineapples. There was a significant difference (p=0.006) between temperature distribution of the improved HSD and Old HSD (p-Value =0.048). The highest recorded temperature difference was 5.4 ℃ (63.5 ℃ for experimental and 68.9 ℃ for simulation), and both recorded at 2 pm. This close difference indicates that the simulation process was fairly accurate. Overall, the capacity of the HSD has been improved to process 300 kg of pineapples for a period of 10 hours. The improved HSD can easily be adopted to process other high value crops. Given that the study utilized mostly locally available materials, the improved HSD is recommended for promotion and adoption by commercial farmers in Uganda.