Grain drying in stationary bins with solar heated air

Abstract

In Brazil, most of the grains are dried naturally in the fields or on concrete floors; recently continuous type of driers have been used extensively. However, the drying of grains in silos has not been adopted yet, in spite of the good ambient conditions. This paper presents results from the drying of 600 kg of “carioca” dry beans in a round bin with a perforated floor, using solar energy as the only supplemental heat source. The performance of the flat plate collectors is analysed; the drying data is analysed with the basic equations of transfer complemented with newly proposed empirical equations describing the thin layer drying and equilibrium data. The agreement between experimental and theoretical results is quite satisfactory, justifying the utilization of this model for simulation studies. The net effect of the solar energy was to accelerate by about 4 times-the drying rates of grains in the top of the bin; the use of average inlet conditions, as compared to the inlet varying conditions, was also satisfactory after 26 hr of drying over a period of three days. Although the overall efficiency of the collecting system was good, the design of ducting, the bin and collector materials and geometry can be improved.