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1.
A review of recombination coefficients of neutral oxygen atoms for various materials
Domen Paul, Miran Mozetič, Rok Zaplotnik, Gregor Primc, Denis Đonlagić, Alenka Vesel, 2023, review article

Abstract: Relevant data on heterogeneous surface recombination of neutral oxygen atoms available in the scientific literature are reviewed and discussed for various materials. The coefficients are determined by placing the samples either in non-equilibrium oxygen plasma or its afterglow. The experimental methods used to determine the coefficients are examined and categorized into calorimetry, actinometry, NO titration, laser-induced fluorescence, and various other methods and their combinations. Some numerical models for recombination coefficient determination are also examined. Correlations are drawn between the experimental parameters and the reported coefficients. Different materials are examined and categorized according to reported recombination coefficients into catalytic, semi-catalytic, and inert materials. Measurements from the literature of the recombination coefficients for some materials are compiled and compared, along with the possible system pressure and material surface temperature dependence of the materials’ recombination coefficient. A large scattering of results reported by different authors is discussed, and possible explanations are provided.
Keywords: heterogeneous surface recombination, recombination coefficient, surface catalicity, catalytic efficiency, atom loss coefficient, oxygen, neutral atoms, plasma
Published in DKUM: 21.03.2024; Views: 113; Downloads: 4
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2.
New technique to evaluate the overall heat loss coefficient for a flat plate solar collector
Amor Bouhdjar, Hakim Semai, Aissa Amari, 2021, original scientific article

Abstract: Low-temperature solar systems mostly use flat plate solar collectors. Good design and correct dimensioning of a solar heat generator are based on precise knowledge of the characteristics of the flat plate solar collector on site. The present work considers a flat plate solar air collector, a flat plate solar water collector, and a flat plate solar water collector with air absorber cooling. The investigation intends to shed light on a procedure to determine the overall heat loss coefficient and the heat removal factor using recorded system temperatures, operating parameters, and environmental data. The Hottel-Whillier-Bliss equation gives the collector useful energy. This expression is used to generate a correlation for the collector efficiency through a linear fitting. We calculate the overall heat loss coefficient of the collector from the slope of the collector efficiency curve. However, we need to know the heat removal factor of the collector. In this study, we present a new technique to calculate the heat removal factor. Then we deduce the collector overall heat loss coefficient. Results show that, very often, the overall heat loss coefficient for the flat plate solar air collector and the flat plate solar water collector determined with this new method is higher than the one calculated with the empirical formula proposed by Klein. However, the experimental overall heat loss coefficient for the flat plate solar water collector with air absorber cooling is smaller than the one calculated with the empirical formula proposed by Klein. The analysis shows that the overall heat loss coefficient determined with the new technique seems more realistic since all phenomena occurring during the heat transfer from solar irradiance incident on the absorber plate and transmitted to the transport fluid are considered.
Keywords: flat plate solar collector, overall heat loss coefficient, heat removal factor
Published in DKUM: 10.11.2023; Views: 133; Downloads: 6
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