DESIGN AND EVALUATION DIRECT SOLAR- DRYER TO DRY RED ONIONS SLICES

Abstract

An direct solar–electrical dryer has been designed and constructed at a Zagazig City of , Sharkia governorate, Egypt. Solar dryer consists of solar flat plate air collector with V-corrugated absorption plate in conecation with drying tray uint. The red onions most popular to consumer no dayes in the Zagazig City so that it was chosen to experiment. The new dryer prototype was tested its efficiency for drying red onions slices 5 &10 mm to study the effect of drying air velocities (0.4,0.5 and 0.6 m/s) at air temperature (40.82,42.37 and 43.81)respectiviely.The qualitative analysis for drying of onions slices 5 mm showed that initial moisture content of about 88% (wet basis) was reduced to final moisture content of about (10%,12% and 16%) for velocities (0.4,0.5 and 0.6 m/s),while it were (16%,18% and 20.8%) for onions slices 10 mm respectiviely.The average percent of dryer efficiency was found to be 16.07, 12.83 and 12 % for air speed 0.4,0.5 and 0.6 m/s respectiviely. In order to estimate and select the suitable form of solar drying curves, five different mathematical models, were compared according to their coefficient of determination R2, MBE, RMSE, %E and chi square X2 to estimate experimental drying curves. The page and Modified page II model in this condition proved to be the best for predicting drying behavior of red onions slices 5 and 10 mm with (R2 = 0.9961 and 0.9899) and (X2 = 0.000121 and 0.000423).The effective moisture diffusivity (Deff) was obtained using Fick’s diffusion equation and its value varied from 1.46× 10-9 to 1.59× 10-9 m2/s and 5.25× 10-9 to 5.72× 10-9 m2/s. The temperature dependence of the diffusivity coefficients was described with the activation energy (Ea) value of 21.33 kJ/mol and 19.14 kJ/mol for red onions slices 5 and 10mm.Finally an economic evaluation was calculated using the criterion of payback period which is found very small 1.84 years compared to the life of the dryer 25 years.