Thèse de Doctorat

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Browsing Thèse de Doctorat by Author "ACHI Alladdine"

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    Numerical study of two-phase streams in a linear solarconcentrator with a new S-shaped absorber. Application: Direct Steam Generation
    (2023) ACHI Alladdine
    This numerical study focuses on the feasibility of the new solar receiver proposed and patented by Demagh Yassine in 2015 for linear concentrating modules. After the promising numerical results obtained in single-phase flow with synthetic oil, it was interesting to move towards the Direct Steam Generation (DSG) in parabolic trough collectors by adopting the scenario where this absorber would replace the conventional straight one in a full-scale installation like the DISS test facility in Almeria, Spain. First, the mathematical model was validated by comparison with experimental data for boiling flows in straight and coiled horizontal tubes at a laboratory scale and followed by validation under actual conditions in the commercial scale of the DSG in the DISS facility. Preforming 3D simulations in the OpenFOAM environment, the obtained numerical results were more than satisfactory. In the second step, the previously validated model is used to perform simulations of DSG in the DISS facility parabolic trough collector equipped with the new S-curve absorber in replacement of the conventional straight one; the same (actual) operating conditions are adopted for both absorbers for better performance comparison. The curved shapes of the tube greatly disturb the stratified flow by converting it into a stratified wavy and slug flows, further improving the evaporative heat transfer coefficient. It is evident that a penalty accompanies any improvement in thermal performance in terms of pressure drops, but it remains entirely acceptable. The S-curved absorber is not recommended when the conventional straight absorber can provide an annular flow alone, which is not always true.