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

摘要

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℃ can be reached at a solar radiation level of 800 W/m~2, ambient temperature of 30℃, 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%.