Study of gas radiation effect on the performance of single-pass solar heaters with an air gap

A. Hosseinkhani and S.A. Gandjalikhan Nassab

Energy, 2024, vol. 294, issue C

Abstract: This paper investigates the performance of solar gas heaters that utilize an air gap between the glass cover and the absorber, along with radiating gas. By using a participating fluid as the working gas, thermal radiation can be absorbed, emitted, and scattered, enhancing the heat transfer between the absorber and the flowing gas. Free convection airflow inside the air gap adds to the forced convection airflow through the solar collector's duct. The study utilizes the κ-ε model and the discrete ordinate method for radiative intensity computation to analyze the flow and energy equations. Numerical results indicate a significant increase in thermal efficiency, particularly at lower gas mass flow rates, when employing radiating gases with high radiative absorption coefficients. The research shows about 40% improvement in thermal efficiency is obtained in test cases at a gas mass flow rate of 0.01 kg/s. A gas flow optical thickness of τ = 2 is found to be optimal among the investigated parameters. In addition, this paper demonstrates high efficiency of up to 70% for plane solar collectors without the need for configuration changes by using working gases with high radiative properties, such as pressurized CO2.

Keywords: Solar; Solar gas heater; Radiation; Turbulent flow; Efficiency; Air gap (search for similar items in EconPapers)
Date: 2024
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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:294:y:2024:i:c:s0360544224006959

DOI: 10.1016/j.energy.2024.130923

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