Double-Pass Solar Collectors with Porous Media Suitable for Higher-Temperature Solar-Assisted Drying Systems

A high-performance solar collector suitable for a solar-assisted drying system was designed, fabricated, and tested. Solar-assisted drying systems consist of the solar collector array, auxiliary heater, drying chamber, and the air distribution systems. The solar collector was a double-pass solar collector and has upper and lower channels. The lower channel of the solar collector was filled up with porous media, which also acts as a storage medium. The outlet temperature and the performance of the system increased with the presence of the porous media. The collector width and length are 120 and 240 cm , respectively. The upper channel depth is 3.5 cm and the lower channel depth is 10.5 cm . The solar collector array consists of six solar collectors, arranged as two banks of three collectors in series. The collectors were joined in series using internal manifolding. A temperature of 90°C can be reached at a solar radiation level of 800 W∕ m2 , ambient temperature of 30°C , and mass flow rate of 0.06 kg∕s . The solar-assisted drying system was used for drying of oil palm fronds from moisture content of about 63% to moisture content of about 15%, for a drying time of about 7 h . The overall system efficiency is about 25%.