Drying of Sultana seedless (Vitis vinifera L.) grape variety in indirect drying chamber using solar air collector with conic dimpled absorber: The case of end-season drying

The main functions of mechanical drying are to extend the drying season, prevent reduction in dry product mass due to immature harvest, and obtain high-quality products without exposure to rainy weather conditions. A SAC with a conic dimpled absorber-assisted indirect solar dryer was designed, manufactured, and tested for the Sultana Seedless grapes under the end-season conditions. Also, the effect of medicinal chamomile oils on the color quality of raisins was investigated. While the first three days of the drying experiment were reminiscent of summer, the remaining days were characteristic of autumn. The thermal efficiency of the collector at a flow rate of 0.05 kg/s was realized as 66.33 % and 48.27 % on average during the days (between hours of 10:00–15:00), depending on the psychrometric conditions. The moisture content of the grapes (22.5 brix) decreased from 3.37 to 0.22 kgw/kgsm and lasted for 272 h/12 days. It has been revealed that the collector efficiency and drying time were significantly affected by the psychrometric conditions, and the use of medicinal chamomile oil in dipping pretreatment increased the color quality of raisins. Effective use of the SAC in the end-season drying process should be increased by techniques such as serial connection and heat storage.