An Effective Moisture Diffusivity of a Hybrid Double Pass Collector-Solar Dryer for Tomato Slices Drying

This study tries to analysis the thermal performance of the newly fabricated compact hybrid double pass collector-solar dryer using a wavy absorber. Energy and exergy efficiencies of the solar collector, drying chamber and drying process were performed during drying of tomato slices and compared with the open sun drying in the same conditions. The experiments were performed during spring seasons with the least available amount of solar energy. Mathematical modelling of drying kinetics was tested and used to evaluate the effective moisture diffusivity. The results show that a tomato slice reaches the equilibrium moisture content of 8.9% (wet basis) after just 7–8 h of operating time, depending to the trays positions. The average effective diffusivity of tomato reaches 1.657 × 10^–10 and 1.518 × 10^–10 m²/s for open sun and hybrid solar dryer, respectively. The average exergy efficiencies reach 2.32, 49 and 27% for solar collector, drying chamber and drying process, respectively. Low exergy efficiency is therefore observed in the solar collector which requires more efficient insulation. Exergy efficiencies of drying chamber and drying process decreases significantly during the operating periods of auxiliary system. The thermal energy input becomes important and thermal losses increase.