ANALYSIS OF COMPONENT EXERGETIC EFFICIENCY CHAMBER CONVECTIVE DRYER

Abstract

A methodology for calculating individual components of the exergy balance and the exergy coefficient of useful action for non-stationary heat and mass transfer processes, in particular drying processes, is proposed. It is shown that the analysis of the drying process by exergetic characteristics is more effective than by thermal characteristics, as it makes it possible to estimate both internal and external losses, as well as the potential of energy flows. Calculations of exergetic and thermal efficiency of the chamber convective dryer were performed on the basis of the proposed methodology. It was established that when the temperature of the incoming heat carrier changes from 5 to 35°С, the exergetic efficiency of the drying unit changes within 4...16%, while the thermal efficiency determined using heat balance equations is about 50%. It is shown that with an increase in the temperature of the surrounding environment, the exergetic efficiency of chamber drying units decreases significantly, and the thermal efficiency changes within 5%, while it increases with an increase in the temperature of the heat carrier at the input, and decreases with an increase in the temperature of the heat carrier at the outlet in such the very limits. Exergy losses in drying plants are due to losses caused by flows of substances that carry exergy out of the system, losses as a result of heat exchange at a finite temperature difference, or mass exchange at a finite concentration difference, as a result of mechanical friction and hydraulic resistance, chemical reactions in non-equilibrium conditions, reduction of the magnetic or electric field under the action of electric resistance, etc. To increase the exergy efficiency of chamber drying units, it is necessary to reduce the exergy losses in the heaters, therefore it is preferable not to use steam heaters, it is worth giving preference to electric heaters or pyrolysis boilers of indirect air heating. It is also necessary to reduce heat loss during mixing of spent and fresh heat carrier, to reduce the temperature of the incoming heat carrier.