Design, experimental investigation and analysis of a solar drying system

In this experimental study, a new type solar dryer has been designed and manufactured by using double-pass solar air collector, heat pump and photovoltaic unit. The performance of solar dryer has been tested for carrot drying. In drying system, double-pass solar air collector (DPSAC) has provided the system heat energy requirement for drying process. Constant drying air temperature has been provided with PID (proportional-integral-derivative) control. Carrot slices were dried from initial moisture content 7.76 g water/g dry matter (dry basis) to final moisture content 0.1 g water/g dry matter (dry basis) at 50 °C drying air temperature and variable air volume. Velocity of air has been changed depending upon air inlet temperature of drying cabinet. During the drying operation, the air velocity was measured 0.4–0.9 m/s. The thermal efficiency of the double-pass collector was calculated from 60% to 78% according to experimental results. Carrot slices were dried at 220 min by using double-pass solar air collector in solar-heat pump dryer. Consequently, system (solar-heat pump dryer) can be comfortably operated without the need to the heat pump under normal ambient air conditions.

► Design and testing of a new type solar dryer by using a double pass solar collector.
► Developing of an automatic control system for constant drying air temperature via process control equipment.
► All energy requirements of drying system have been supplied from solar energy.
► Investigation of carrot drying behaviors such as moisture content, moisture ratio and drying rate.