Numerical methodology for performance assessment and gradient-based optimization of brazed plate heat exchangers

This thesis presents a comprehensive numerical methodology for the performance assessment and gradient-based optimization of brazed plate heat exchangers. Motivated by the growing industrial demand for predictive, high-fidelity simulation tools, the research develops a computational framework capable of accurately capturing the complex thermo-hydraulic behaviour of corrugated geometries and enabling informed design improvements through physics-based optimization. The proposed multi-step CFD-based approach integrates forming simulations to reconstruct plate geometries, thereby preserving the geometric fidelity of the corrugation as produced by manufacturing. This realistic reconstruction forms the basis for subsequent CFD analyses, allowing an accurate description of both the thermal and hydraulic performance of BPHEs through full-plate investigations with direct industrial applicability. Two corrugation geometries were investigated: a dimpled plate, representing an alternative plate design, and a chevron-type plate, corresponding to the most widely used corrugation in industrial plate heat exchangers. The methodology was validated for both geometries through systematic and consistent comparison of pressure-drop and thermal-performance predictions with experimental data provided by the industrial partner Danfoss. Furthermore, a detailed study of the mechanisms governing heat transfer and pressure loss across different corrugation types was conducted based on insights derived from CFD simulations. For the dimpled geometry, additional Large Eddy Simulation analyses were performed to further investigate the influence of different turbulence-modelling approaches, thereby extending the understanding of the inherent unsteady flow structures characteristic of corrugated channels and their impact on local heat-transfer behaviour. Building upon this foundation, a gradient-based adjoint optimization framework was implemented and applied to the chevron-type plate for geometry refinement aimed at enhancing thermo-hydraulic performance. Two operating scenarios were examined: a water-to-water configuration, and a CO₂-to-water configuration representative of transcritical heat-recovery applications. The study introduced alternative objective-function formulations and corresponding boundary setups, departing from conventional approaches commonly employed in gradient-based optimization of heat exchangers. These cases demonstrated the capability of the proposed method to produce meaningful shape modifications, resulting in measurable improvements in heat-transfer performance. Overall, the research establishes a validated, computationally robust, and physically interpretable workflow that bridges high-fidelity CFD analysis with gradient-based shape optimization for BPHEs. The developed methodology provides a strong foundation for future advancements in digital, optimization-driven design of high-performance plate heat exchangers.