Study of design and fabrication of an indirect solar dryer

Abstract

This work presents an experimental investigation of an indirect forced-convection solar dryer incorporating an innovative active-wall concept, in which the sun-facing wall of the drying chamber is replaced by a wall-integrated flat-plate air solar collector, enabling the recovery of solar energy otherwise lost through the dryer envelope. Two absorber configurations were tested: a flat-plate absorber and a tubular absorber integrating parallel rough-surfaced aluminium tubes. Laboratory tests demonstrated that the tubular configuration achieves a superior thermal efficiency of 72% versus 68% for the flat-plate design, with a more uniform temperature distribution and a broader optimal operating range. The complete solar drying system comprising the primary collector coupled with the active-wall chamber was subsequently tested outdoors at the University of Tlemcen in June, under real solar irradiance conditions, using banana slices and mint leaves as drying products. Outdoor experiments confirmed the operational feasibility of the system, with the primary collector delivering outlet temperatures of 54 °C and 72 °C for the flat-plate and tubular configurations respectively. However, the wall-integrated secondary collector exhibited a limited thermal contribution under the current serial airflow arrangement, as the pre-heated air arriving from the primary collector frequently exceeded the secondary absorber temperature, resulting in a net heat loss. A circuit inversion (Tamb → C2 → C1 → chamber) is proposed as a priority design improvement to address this limitation.