IMPACTS OF DRYING AIR TEMPERATURE, BED DEPTH AND AIR FLOW RATE ON WALNUT DRYING RATE IN AN INDIRECT SOLAR DRYER

Walnut is one of the world's top 20 agricultural products and is consumed mostly as dried [3]. This product must be dried with great care to maintain its quality. Walnut products are traditionally spread on open space for a long time to reduce the kernel moisture content to a safe level. Due to direct sun radiation and some environmental impacts such as long time exposure the quality of the products may be degraded. Application of renewable energy such as solar energy may be an appropriate substitution for traditional methods.In this research a new pilot size walnut indirect solar batch type dryer was designed and fabricated. The effect of crucial factors affecting drying time namely: drying air temperature (T1:37o C; T2:39o C and T3:41oC), drying air flow rate (F1: 0.065 m3/s, F2: 0.075 m3/s, F3: 0.09 m3/s) and bed depth (D1: 2 layers, D2: 4 layers and D3: 6 layers) were evaluated. The experimental results showed that, the effect of above factors on walnut moisture loss are significant. With increasing drying air temperature, drying air flow rate and number of layers, the amount of average moisture loss decreased from 37% (d.b) to 9% (d.b) at 3 hrs. Performance of dryer was determined at temperature 41oC, air flow 0.09m3/s, 2 layers depth.