CSP systems based on Parabolic-Trough Collectors (PTCs) account for a representative share of the global solar thermal capacity installed. Most of the existing PTC power plants use synthetic oil as heat transfer fluid. However, water can be alternatively used, where both single and two-phase flow occur. This technology is called Direct Steam Generation (DSG) and it presents some advantages in terms of system overall efficiency and plant cost reduction. Nevertheless, some complexities inherent to two-phase flow have to be addressed to succeed in the commercial deployment of DSG. The development of numerical codes to model such systems is of key importance to put new insights into them. Both, the thermal-hydraulic and optical modeling are of relevance.
Conventional parabolic-trough reflectors concentrate solar radiation on absorber tubes following a characteristic pattern with a non-homogeneous distribution in the angular direction. It means that the bottom half of the absorber tube receives much more flux than the upper half. Under specific two-phase flow patterns (e.g. stratified flow) the refrigeration of the absorber tube is not homogeneous and thermal bending may take place. This problem can also be reported in single-phase flow conditions (e.g. superheated steam), where a significant thermal gradient at the cross-sectional plane of the absorber tube can be critical. A new technique called Inverse Monte Carlo Ray Tracing (IMCRT) method is proposed in this thesis. It aims to design new reflector geometries so that a more homogeneous distribution of concentrated solar radiation on the absorber tube can be accomplished. In line with this, new reflector geometries have been proposed with the same aperture width as the LS-3 design for the same absorber design, where quasi-constant flux distribution is achieved within a specific angular range.
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