Modeling and sensitivity analysis of the thermal behavior of solar air heaters for various selectivity, nature, and glazing

Solar energy is one of the sustainable energy sources, and Solar Air Heaters (SAHs) are among the key solar energy applications. SAHs are crucial for different applications due to their simplicity and minimal cost, with a wide variation in their performance based on the type and structure of the absorber plates and glass covers. This work aims to develop an extensive theoretical model to understand the heat transfer dynamics within SAHs and develop an empirical equation to find the optimal thermal efficiency of SAHs for various glass covers and the selectivity and structure of absorber plates. This is coupled with an attempt to quantitatively understand the correlation between different parameters and their effect on thermal efficiency through sensitivity analysis. Hence, employing the weather data for Amman, Jordan, for one year, this work investigates the performance of SAH under the simultaneous influence of selectivity and structure of absorber plates with the number of glass covers. The developed model utilises the energy balance equation and the isotropic diffuse model. The developed model and analysis show that the number of covers has an opposite effect on the performance of SAHs. Hence, the model converges to an optimal number of covers with the largest thermal efficiency. It is found that this optimal number is two covers for low-emittance absorber plates and three covers for high-emittance absorber plates. Moreover, the model shows that for flat SAHs, the highest efficiency is achieved with a combination of three covers and high-emittance absorber plates. In contrast, it is found that for corrugated SAHs, the efficiency is maximum with a combination of two glass covers and low-emittance absorber plates.