Numerical study of two-phase streams in a linear solar concentrator with a new S-shaped absorber. Application: Direct Steam Generation
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Date
2023
Authors
ACHI Alladdine
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Abstract
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.
Key words: Boiling flow, DSG, Parabolic trough, DISS test facility, S-shaped absorber,
coiled tube, Monte Carlo Ray Tracing method.