Performance characteristics of solar drying system for agricultural products

Drying has important influences on agricultural products' quality and storage. Drying characteristics of different agricultural products vary. Temperature and velocity of drying airflow affect greatly drying quality and drying efficiency of agricultural products. Two types of solar drying systems for different drying temperature requirement were designed and characterized in this paper: solar air drying system with plate air collector and solar parabolic trough concentrating drying system. In solar air drying system with plate air collector, the drying oven has two ventilation modes. With top inlet and bottom outlet ventilation mode, the overall temperature in drying oven is relatively high, however large vertical temperature difference exists in drying oven. With bottom inlet and top outlet ventilation mode, the temperature in drying oven is uniformity, however relatively low. In notoginseng drying experiment, the drying time is shortened to half of that in nature drying. The average thermal efficiency is 66.5%. The solar trough concentrating drying system utilizes a low cost and reliable V-type metal cavity to collect solar irradiation. In the system, the heat conducting oil can be heated to 230 degrees C, and the air flow from heat exchanger reaches above 200 degrees C. The tobacco shred drying experiments verifies that the drying temperature of the system meets the tobacco shred drying requirement. Solar trough concentrating drying system matchts the drying temperature scope of 80 degrees C similar to 200 degrees C.