article · Environmental Progress & Sustainable Energy
A solar dryer featuring a zigzag airflow pathway was developed and evaluated for drying henna leaves under Egyptian climatic conditions. The design guides heated air alternately above and below drying trays to enhance contact between air and the product. Testing evaluated performance across two airflow rates, three layer thicknesses, and four tray positions, with conditions monitored using an Arduino-based data logger. The system successfully lowered henna leaf moisture content from 62.7 percent to below 5 percent wet basis. Drying durations varied from 10 hours at the highest airflow and thinnest layer to 26 hours at lower airflow and maximum thickness. Maximum solar collector energy efficiency reached 67.8 percent, whilst drying room exergy efficiency spanned from 25.27 to 86.66 percent. Environmental analysis revealed that higher layer thickness reduced the energy payback period to 3.27 years, with lifetime carbon dioxide mitigation reaching almost 2400 kilograms.
Traditional open-air drying of agricultural products can be slow and vulnerable to contamination. This research demonstrates an efficient, renewable alternative using a modified airflow configuration. By improving heat transfer and cutting drying duration, the system preserves product quality while providing measurable reductions in operational energy payback times and carbon dioxide emissions.
This technology represents an applied and tested prototype for agricultural processors and producers of botanical products such as henna. It enables low-carbon, controlled drying using solar energy and low-cost Arduino monitoring. Practical adoption would require moving from field experimental trials to standardised commercial units tailored to smallholder or industrial agricultural facilities in high-sunlight regions.
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Abstract This study developed and evaluated a solar dryer with a zigzag airflow pathway for drying henna leaves under Egyptian climatic conditions. The system was designed to improve air‐product contact in tray drying by directing heated air alternately above and below the drying trays. Drying experiments were conducted at two airflow rates, 0.09 and 0.14 m 3 /s, three‐layer thicknesses, 2, 4, and 6 cm, and four tray positions. An Arduino‐based local data‐logging system was used to record temperature and relative humidity during drying. Henna leaf moisture content decreased from 62.7% to below 5% wet basis. The shortest drying time was 10 h at 0.14 m 3 /s and 2 cm layer thickness, whereas the longest drying time was 26 h under the lowest airflow and highest loading condition. The corrected peak drying rate ranged from approximately 0.28 to 0.35 g water g −1 dry matter h −1 . The maximum solar‐collector energy efficiency reached 67.8%, while the drying‐room exergy efficiency ranged from 25.27% to 86.66%, depending on airflow rate, layer thickness, and tray position. Higher airflow enhanced useful energy recovery, but its effect was interpreted as a balance between increased mass flow rate, shorter air residence time, and improved vapor removal. A simplified environmental assessment showed that the energy payback time decreased from 9.83 years at 2 cm layer thickness to 3.27 years at 6 cm layer thickness, while lifetime CO 2 mitigation reached up to 2399.2 kg CO 2 .
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DOI: 10.1002/ep.70634
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