This project focused on understanding how ribbed or roughened surfaces enhance heat transfer in fluid channels—a principle directly applicable to improving cooling in nuclear reactor components. Using advanced computational fluid dynamics (CFD) simulations, the study compared detailed three-dimensional (3D) and simplified two-dimensional (2D) models of ribbed channels to assess the accuracy and efficiency of 2D simulations. The project also explored how different thermal and near-wall conditions affect heat transfer and flow patterns. The findings demonstrated that 2D simulations can accurately represent the core flow behaviour of 3D rib-roughened channels, reducing computational time and cost without significant loss of accuracy. This is particularly valuable in nuclear thermal-hydraulic analyses, where computational efficiency is essential for safety and design optimisation. The research further showed that the specific thermal boundary conditions applied to the ribs—whether heated or insulated—had only minor effects on overall heat transfer, though they influenced local temperature gradients near the ribs. However, the choice of turbulence model and near-wall treatment proved critical; low-Reynolds-number models captured the complex flow separation and reattachment more accurately than high-Reynolds-number models using standard wall functions. In the nuclear sector, these results are particularly relevant to the design of fuel assemblies and coolant channels in advanced gas-cooled reactors (AGRs) and next-generation nuclear systems. The study’s approach enables engineers to model turbulent heat transfer more efficiently while maintaining fidelity in predicting temperature and flow fields, which is crucial for improving thermal performance and component longevity in reactor cores.