Thermal performance of optimum thermal energy storage in natural convective solar crop dryer

A solar crop dryer using phase change material as thermal energy storage was developed to naturally regulate the drying and also maintain the quality of dried crop. The solar dryer included flat plate solar collector, packed bed phase change energy storage, drying plenum with crop trays and natural ventilation duct based on phase change material. Dryer was designed such that it had collector area of 1.5 m², six crop trays with an effective area of 0.50 x 0.75 m², could hold 12 kg of fresh leaves vegetables and herbs. The dryer was attached with the provision of variable capacity of packed bed thermal energy storage from 0 to 48 kg and 0 to 32 kg phase change material (PCM) below drying chamber and in natural ventilation duct, respectively. The phase change material stored the thermal energy during sunshine hours and released the latent and sensible heat after sunset, thus dryer was effectively operative further for next 5–6 hours. The temperature in drying chamber was observed 6°C higher than the ambient temperature after sunshine hours till the mid night during the month of June and November at Jodhpur.