Mixed-flow dryers are of great importance in worldwide agriculture for the drying of grain, corn, and rice. Unfavorable dryer designs can result in uneven particle and air flow distributions and, thereby, cause inhomogeneous gas–solids contact and drying conditions. As a consequence, the grain drying can locally be very uneven with high fluctuations of the moisture distribution over the dryer cross section. The main reasons are design and construction of the dryer apparatus and the discharge device. A new mixed-flow dryer design has been developed that promises more homogeneous drying, higher energy efficiency, and increased product quality. Firstly, the new dryer design was proved with respect to particle flow. For this purpose, a new test dryer was constructed. A series of particle flow experiments was performed using colored tracer particles. The flow of the tracer particles was observed through a transparent acrylic front wall by image analysis. Based on a comparison with the traditional design, the advantages and disadvantages of the new design were evaluated. The experimental investigations were accompanied by numerical simulations of the particle flow pattern using the discrete element method. The effects of design properties and different air duct arrangements were studied. The present results show that we are at the beginning of a new development concerning the optimization of mixed-flow drying apparatuses.

Keywords: Discrete element method, Dryer design, Mixed-flow grain dryer, Particle flow, Tracer technique

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