Abstract
One of the key tasks of modern grain processing equipment is to increase the efficiency of drying in bunker installations with a ring-cylindrical grain bed. The aim of this study was to investigate the unsteady processes of heat and mass transfer in the annular layer of grain in a bin-type dryer with a radial supply of drying agent to assess the uniformity of temperature and moisture distribution and determine the effect of drying parameters on dehydration efficiency. To improve the energy efficiency and quality of drying, a two-level mathematical model was proposed to study the processes of internal heat and mass transfer and external heat and mass transfer. At the first level, the drying kinetics of a single grain in the form of a sphere in contact with a drying agent of constant temperature and humidity was modelled. The second level described the process of filtration drying of a dense ring-cylindrical layer of grain with a radial supply of the drying agent. The thermophysical coefficients of the models were identified based on the results of field experiments. The obtained analytical and numerical solutions of the presented mathematical models made it possible to determine the rational design parameters and calculate energy-efficient operating modes of bunker-type grain dryers depending on the initial grain parameters. It was substantiated that the highest efficiency is achieved when using a periodic circulation mode, which ensures uniform heating and dehydration of the grain mass along the radial coordinate of the bed. The dependences of the influence of temperature, moisture content and air filtration rate on the exposure of grain drying in the bed were determined, which allows for flexible control of the drying process depending on the operating conditions. The study results confirmed that the use of a batch-circulating drying mode allows achieving high uniformity of the final grain moisture content, increasing the energy efficiency of the process and significantly reducing the unevenness of grain heating compared to traditional continuous modes of drying grain in a thick radial layer. The results can be used both for the modernisation of existing drying plants and for the design of new energy-saving grain dryers