Designing the structure and determining the mode characteristics of the grain dryer based on thermosiphons

Energy consumption, environmental issues, product quality are actual problems related to grain drying processes. It is necessary to pay attention to designing new structures of energy-efficient grain dryers. A structure of an energy-efficient grain dryer based on thermosiphons has been designed; its energy consumption is 3.5...6.8 MJ/kg depending on surface temperature and air flow rate. The dryer includes a layer heater, a drying chamber, a heat generator, a heater, a noria for loading the product, and fans. The structural features of the dryer allow the drying process to be carried out without direct contact between the combustion gases and the product. The efficiency of the designed structure was evaluated for such indicators as heat transfer coefficients to the grain flow, specific energy costs, moisture content, the relative humidity of the air leaving the dryer. The values of coefficients of the heat transfer to the grain flow vary within 36...58 W/m2K at speeds 2.5...8 mm/s. An increase in the flow rate by 3.2 times leads to an increase in the heat transfer coefficient by 1.6 times. The moisture content of the air at the outlet of the dryer reaches 60 g/kg, while the relative humidity is 90 %, which is several times higher than the parameters for convective mine grain dryers. Energy consumption for drying at the surface temperature of thermosiphons Ts=142.9 °C for various grain flow rates is close to a minimum. The energy consumption is lower than in existing convective dryers. 21 % is spent on heating grain in the dryer; 54 % ‒ on moisture evaporation; and 23.6 % are losses. If we consider the energy spent on moisture evaporation usable, the efficiency of convective dryers is only 40 % while that of dryers based on thermosiphons is 54.1 %. It is expected that the designed structure could be a solution for small farmers in the post-harvest drying process