Moisture content and residence time distributions in mixed-flow grain dryers

Unfavourable designs of mixed-flow grain dryers can cause inappropriate residence time distributions, locally different drying conditions and, hence, inhomogeneous drying. To study the effect of design elements and different air duct arrangements, residence time experiments, grain drying experiments and discrete element simulations were conducted both at pilot and industrial scale. These investigations revealed that present dryer designs give broad distributions of residence time, moisture content, and grain temperature. This is a consequence of different drying histories for individual grains. This variation is mainly influenced by the air duct arrangement applied but is affected by other structural and operating parameters as well. Uneven drying is one of the main reasons for elevated energy demands which are still comparatively high in mixed-flow dryers. A future goal will be to develop improved designs of mixed-flow dryers.