Drying is an effective means of reducing moisture content of perishable fruit and vegetables to a safe storage level and reduce post harvest loss. This study was conducted to evaluate a solar tunnel dryer for drying cabbage in comparison to traditional open sun drying at the advanced drying lab of the Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh. Salt pre-treated cabbage was used for drying inside the dryer and open sun drying. The parameters like solar radiation, temperature, relative humidity, and moisture content were measured using standard instruments during the experiments. The results showed that the maximum peak temperature inside the drying chamber was 45 °C during mid-day (12 pm) when solar radiation was 600 w/m2 and in an average inside temperature was approximately 30°C to 40°C in a full sunny day (9:00 AM to 04:00 PM) when average solar radiation was 321±115 W/m2. The moisture content of sliced cabbage was reduced initially 94.42, 90.18, and 92.24 % (w.b.) to 4.85, 15.84, and 15.71% (w.b.), and drying time of the dryer was 28, 21, and 19 hours in 1st, 2nd, and 3rd trials, respectively. The drying rate and drying efficiency were found 0.15 kg/hr. and 8.22 %, respectively in tunnel dryer and 0.02 kg/hr. and 3.38 %, respectively in open sun drying. The color and texture of the solar tunnel dried cabbage were better than the open sun drying method. Further experiments are required for estimating drying capacity with the operating cost of the solar tunnel dryer when the dryer will be used with its full capacity.
Key words: Solar drying, Cabbage, Drying efficiency, moisture content
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