Drying of hot chilli using solar tunnel drier

A mixed mode type forced convection solar tunnel drier was used to dry hot red and green chillies under the tropical weather conditions of Bangladesh. The drier consisted of transparent plastic covered flat-plate collector and a drying tunnel connected in series to supply hot air directly into the drying tunnel using two fans operated by a photovoltaic module. The drier had a loading capacity of 80 kg of fresh chillies. Moisture content of red chilli was reduced from 2.85 to 0.05 kg kg−1 (db) in 20 h in solar tunnel drier and it took 32 h to reduce the moisture content to 0.09 and 0.40 kg kg−1 (db) in improved and conventional sun drying methods, respectively. In case of green chilli, about 0.06 kg kg−1 (db) moisture content was obtained from an initial moisture content of 7.6 kg kg−1 (db) in 22 h in solar tunnel drier and 35 h to reach the moisture content to 0.10 and 0.70 kg kg−1 (db) in improved and conventional sun drying methods, respectively. The use of a solar tunnel drier and blanching of sample led to a considerable reduction in drying time and dried products of better quality in terms of colour and pungency in comparison to products dried under the sun. The solar tunnel drier and blanching of chilli are recommended for drying of both red and green chillies.