Theses and Dissertation

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Browsing Theses and Dissertation by Author "Mgaya, Gelion"

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    Thermal Performance and Techno-Economic Analysis of Solar-Biogas Hybrid Dryer for Drying Agricultural Products
    (NM-AIST, 2025-07) Mgaya, Gelion
    Traditional drying methods, such as solar and fossil fuel-based mechanical drying, are widely used for agricultural products. However, these methods often yield low-quality dried products, which negatively impact market value and consumer satisfaction. Hybrid solar drying technology offers an alternative by enhancing drying efficiency and improving product quality. Despite growing interest in Hybrid solar drying technology, Sub-Saharan Africa lacks experimental studies on biogas-supplemented solar dryers. In addition, while a considerable body of literature addresses the use of biogas for heating in drying applications, only a few studies have explored its potential as a supplemental energy source for solar drying systems.Therefore, this study evaluates the thermal performance and techno-economic feasibility of a solar-biogas hybrid dryer designed to maintain stable drying conditions by supplementing solar energy with biogas during low solar irradiance. Drying experiments using 100 grams of lemongrass were conducted to compare the hybrid dryer with traditional open sun drying. After four hours, the tray samples in the hybrid dryer had lost 75% of their initial moisture, resulting in a 28% reduction in drying time compared to open sun drying. The hybrid dryer showed an average drying rate of 0.31% min⁻¹, compared to 0.27% min⁻¹ for open sun. Ambient conditions averaged a temperature of 31.04°C and a relative humidity of 47.36%. Inlet temperatures for trays 1, 2 and 3 were 53.7°C, 55.96°C and 55.73°C, respectively. The system achieved a thermal efficiency of 34.2% and an average exergy of 0.26 kJ/kg. Quality analysis revealed improved nutrient content, with hybrid-dried lemongrass containing 42.2% carbohydrates, compared to 40.5% in open-sun samples and 10.3% in fresh samples. Potassium and phosphorus were well retained, while copper levels were 1.63 mg/100 g and 1.13 mg/100 g for hybrid and open sun samples, respectively. A techno-economic analysis revealed a 2.3-g year payback period and a 43% return on investment, highlighting the viability of biogas assisted hybrid systems for sustainable agricultural drying