Performance Efficiency of an Energy-Saving Mini Dryer with a Combined Heat Supply System

Abstract. The paper presents the description and operating principle of energy-saving mini-grain dryers for drying small grain batches on farms using conductive and convective drying methods and the process of grain cooling with heat obtained from a traditional heat source and a heat carrier prepared with a solar collector or a charged heat storage. (Research purpose) To develop and study a compact energy-saving grain dryer, with a heat supply system based on both a traditional source and a heat transfer fluid heated by a solar collector or a charged heat storage. (Materials and methods) The authors have carried out experimental studies of the drying process of wheat grain to determine the effectiveness of the developed unit for grain drying; the main condition for saving energy has been taken as the minimization of the total unit cost of the evaporation of one kilogram of moisture. (Results and discussion) The authors have conducted a two-factor experiment to determine the main optimal parameters affecting the grain drying process - the speed of grain movement in the conductive chamber and the temperature of the heating surface of its casing based on the calculated mathematical model. In the first variant, the drying process was carried out only by the conductive method using the heat from a traditional energy source. In the second variant, the drying was carried out by successive use of conductive and convective methods, and the grain was cooled using both thermal energy received from a traditional source and solar radiation heat along with the heat of the spent heat carrier. (Conclusions) The study has revealed that the most effective option in terms of saving thermal energy is grain drying with the consistent use of conductive and convective drying methods followed by grain cooling. The heat supply of the drying unit was partially carried out by using the heat of solar radiation and the heat obtained from the spent coolant recycling. In this optimal variant, the heat consumption for evaporation of one kilogram of moisture from the grain is minimal and amounts to 1.53-2.50 MJ per kilogram with a grain movement speed of in the dryer of 0.007-0.011 m per second and a heating surface temperature of 85-91 degrees Celsius.

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