An investigation on pistachio drying in a solar dryer equipped with an air to air waste heat recovery system

Only a small percentage of provided thermal energy is used for the drying process in the hot air dryers while, a large fraction is lost via the dryer walls and exhaust air. The present study developed a solar dryer with a simple heat recovery system for pistachio drying. The evaluation tests were conducted at different levels of drying temperature (55, 65 and 75 OC) and air flow rate (0.045, 0.065 and 0.085 kg/s). The results showed that rising the temperature from 55 to 65 OC caused a reduction of 57.61% in drying time, 24.32% in solar fraction, 6.8% in recovery fraction and 2.56% in the collector efficiency. Meanwhile, average electricity consumption at temperature of 75 OC was 1.9 times more than that at 55 OC. Increasing the air flow rate from 0.045 to 0.085 kg/s improved collector efficiency and recovery fraction while it led to a reduction of 20.54% in solar fraction. Totally, it can be said that the waste heat recovery system accounted for about 28.58% of total energy needed for pistachio drying. The results also indicated that both shell splitting number and pistachio kernel strength increased at the higher air temperatures.