Evaluation of Thin Layer Drying Process for Paddies and Determining and Appropriate Grain Thin Layer Depth Using a Naural Convection Pilot Solar Dryer

Rice is only second to wheat as a major food for Iranians. It has to be dried for processing and/or storing due to excessive moisture content after harvesting. In most parts of Iran, rice is sun-dried by spreading it on the ground under solar radiation which leads to excessive losses such as attacking birds and rodents, grain contamination, wind and rainfall hazards, as well as thermal and moisture stresses. The present research aims to investigate the feasibility of thin layer solar drying process of rough rice to determine the appropriate bed depth of seed. A mixed mode passive solar dryer was used. In this system, hot air is provided by natural convection through an air solar collector. Thin-layer drying process was investigated using the thin layer mathematical models (Newton and Page models). One of the main aims of this research was to find an appropriate depth that can be regarded as thin layer. Therefore, bed grain depths of 2, 4 and 6 cm were selected for the experiments. The results illustrated that the bed depth of 2 cm showed the thin layer drying behavior whereas bed depths of 4 and 6 cm did not.