Doctoral Degrees (Mechanical and Mechatronic Engineering)

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Browsing Doctoral Degrees (Mechanical and Mechatronic Engineering) by Subject "Air-cooled condenser"

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    Optimisation towards a wind resistant air-cooled condenser for the modern energy sector.
    (Stellenbosch : Stellenbosch University, 2021-12) Marincowitz, F. S.; Owen, Michael ; Muiyser, Jacques; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Past research has shown that wind negatively affects the thermal performance of an air-cooled condenser (ACC) and increases dynamic fan blade loading. Several different wind-effect mitigation measures have been investigated, including cruci- form screens, perimeter screens, walkways, deflector plates, alternative fan rota- tional speeds or blade angles and different module array configurations. However, these investigations were performed using different ACC configurations, consider- ing mainly ACC thermal performance as an evaluation metric and mostly neglecting dynamic fan blade loading. This study investigated three promising externally in- stalled wind-effect mitigation mechanisms (cruciform screens, perimeter screens and walkways) with the aim of identifying general guidelines on how these miti- gation measures could be optimally combined to improve the thermal performance and reduce dynamic fan blade loading. The study focuses on ACCs for the modern energy sector in which smaller solar thermal and natural gas combined cycle power plants are largely replacing large fossil-fuelled plants. A 3 × 6-cell ACC, typical of ∼ 100 MW plants, was therefore selected for investigation. An efficient computational fluid dynamics-based numerical ACC model, incorpo- rating the extended actuator disk fan model, was developed for this investigation. A multi-objective optimisation was performed using a genetic algorithm combined with a meta-modelling approach to identify optimal wind-mitigation solutions for two realistic wind distributions. This was done to identify generalised optimum so- lutions that improve ACC thermal performance and reduce dynamic blade loading in windy conditions, without causing a hindrance in calm conditions. The optimal solutions from these two demonstrative examples provided the required information to identify general guidelines for wind-effect mitigation on the ACC in question. The combination of a cruciform screen and a walkway is always recommended. The cruciform screen should have a height of 0.35 ≤ Hcs/Hp ≤ 0.50 and a solid- ity of 0.75 ≤ αcs ≤ 1.0. The width of the walkway should be within the range 0.30 ≤ Lww/d f ≤ 0.50. A perimeter screen is only recommended if dynamic blade loading is expected to be a significant issue, or is still an issue after installing the combination of cruciform screen and walkway. If a non-retractable perimeter screen is considered, the solidity of this screen should be αps ≈ 0.4, with a screen height of between 0.6 ≤ Hps/Hp ≤ 1.0. However, a retractable screen is an attractive option, as such a screen can be deployed only at higher wind speeds (vw > 6 m/s). In the case of a retractable screen, a larger solidity screen of 0.5 ≤ αps ≤ 0.6 spanning the full length of the ACC (Hps/Hp = 1.0) should be used to most effectively reduce dynamic blade loading for short periods of time. It was shown that, for a wind- effect mitigation measure solution that falls within these ranges, an improvement in the ACC’s average thermal effectiveness of up to 19% is possible for a high wind speed condition, while also reducing the blade loading by 22%.