This scientific study provides a comprehensive investigation of the exergy losses that occur during the operation of low-potential solar and air-based drying systems. It covers the nature and primary sources of these losses, as well as the theoretical evaluation methods. Low-potential dryers operate at relatively low temperatures in the range of 40–65 °C. While these low-temperature processes may be highly energy efficient, they often result in low exergy efficiency. Therefore, identifying and reducing exergy losses in drying systems can significantly enhance the scientific and practical relevance of the process. A theoretical model is used to present the exergy potential of solar radiation, the exergy of the air streams entering and exiting the dryer, the binding energy of moisture in the dried product and the general exergy balance equation. When evaluating exergy losses, the main variables considered are the maximum useful utilisation level of solar radiation, the optical coefficients of the absorber surface, the air velocity inside the drying chamber, the moisture transfer rate and the heat transfer coefficients. Additionally, the structural dimensions of the dryer, the material of the transparent cover, the ventilation regime and the humidity and temperature of the air mixture are shown to have a significant impact on exergy efficiency on a scientific basis.

Solar dryer, solar collector, thermal stability

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