Increasing the thermal efficiency of a solar air heater coated with a functional nanocomposite ceramic film

Abstract

Relevance: solar air heaters are widely used in low-potential thermal systems, and their practical importance in industry, agriculture, and construction is steadily increasing. However, the practical thermal efficiency of these devices is significantly limited by radiative and convective heat losses occurring at the absorber surface. In the literature, various design solutions aimed at improving efficiency have been proposed, including the installation of turbulators in the flow channel, the creation of artificial roughness, and the complication of airflow direction. Nevertheless, such approaches often lead to increased pressure losses and higher structural complexity of the system. Therefore, improving the thermal efficiency of solar air heaters without modifying their geometric structure by means of modifying the physical properties of the absorber surface is considered an актуальная scientific and practical problem.

Aim: the objective of this study is to analyze the thermal efficiency of a solar air heater with a metal absorber coated with a thin ceramic composite film based on an energy balance model and to compare its performance with that of a solar air heater of simple design under identical operating conditions.

Methods: In this study, the thermal processes of the solar air heater were analyzed using an energy balance model based on the law of conservation of energy. The ceramic composite film was considered as a selective surface, and its influence on the solar radiation absorptivity coefficient (α) and the emissivity coefficient (ε) was taken into account. The outlet air temperature and thermal efficiency indicators for the conventional absorber and the ceramic-coated absorber were determined and compared under identical operating conditions.

Results: the calculation results showed that the thermal efficiency of the solar air heater coated with a ceramic composite film increases by 17–19% compared to a solar air heater of simple design. This increase is explained by the enhancement of the solar radiation absorptivity coefficient and the reduction of the emissivity coefficient of the absorber surface. It was established that the proposed approach allows an increase in the thermal efficiency of the device without changing the geometry of the flow channel and without additional pressure losses, which represents a significant practical advantage.