Сельскохозяйственные машины и технологии (Jun 2016)
Research of moisture transfer in grain at oscillating drying
Abstract
Among the innovative modes of seeds and grain drying the priority belongs to the oscillating one. But the modes with periodic lying allowing to increase significantly efficiency of seeds and grain drying including the increased moisture are least studied. Researches of moisture transfer are necessary for justification of the modes of safe and intensive drying. Realization of these modes allows to define heat-transfer coefficient and lying periods duration. It is caused by need of decrease in a gradient of surface moisture content and temperature of grain. Drying duration can be defined by equation which enter diffusion coefficient, the caryopsis radius, hull thickness (the dehydrated zone) and the size of moisture content of a kernel and a hull. After moisture evaporation intensity and safety of drying decrease therefore the lying is necessary for moisture redistribution. Under certain conditions width of an evaporation zone turns out to be much less characteristic size of the dried-up body so this zone can be replaced, for example, with grain hull thickness. On the basis of an admissible moisture removal and density of a thermal stream at intensive drying analytical expression was received. It can be used for calculation of the maximum heat-transfer coefficient and, respectively, of the drying agent speed which depends on its height, a specific surface of grain and a share of the warmth required for moisture evaporation. For conditions of drying of grain in the grain dryers the speed of the drying agent should not exceed 0.6 m per a second. The authors defined values of admissible size of heat-transfer coefficient (no more than 40 W per sq. m in terms of one degree) and lyings duration which is equal 10 min. The ratio of duration of the period of heating and cooling of grain is equal 10:10, optimum value of this ratio is 15:20.
