Enhancement of thermohydraulic performance in 3D pipe based on different concavity dimpled surfaces: Numerical and experimental investigation

This study examines the thermal-hydraulic performance of enhanced tubes featuring concavity dimpled surfaces. The primary goal is to determine the optimal geometric design that improves heat transfer. The research employs a dual approach, integrating both numerical simulations and experimental data to validate the results. Water is used as the working fluid under varying Reynolds numbers (4000-15000) and inlet temperature (298 K). The study reveals that the shape of the dimples significantly impacts heat transfer, with concave shapes demonstrating superior performance. While the number of cylindrical dimples has a limited effect on heat transfer, the arrangement and number of dimples in other configurations play a crucial role. In a study of enhanced cylindrical tubes, the maximum heat transfer enhancement, approximately 50% relative to a smooth pipe, was achieved with five dimples. This finding suggests that for cylindrical configurations, a specific number of concavities is optimal for disrupting the thermal boundary layer and augmenting heat transfer. The highest performance evaluation factor (PEF) of 1.408 was achieved with the spherical dimple shape (SDS) configuration. This optimal performance occurred at a Reynolds number (Re) of 4000 and a dimple diameter of 2 mm. The PEF is a crucial metric in thermal engineering that quantifies the trade-off between the desired heat transfer enhancement and the undesirable increase in pressure drop, providing a single value to assess the overall efficiency of an enhanced heat transfer surface. A PEF greater than 1.0 indicates that the heat transfer enhancement outweighs the penalty of increased pumping power due to pressure drop. This study provides valuable insights into optimizing heat exchanger performance by analyzing the influence of various parameters, such as dimple shape, size, and arrangement, on thermal and hydraulic characteristics. Increasing the number and size of dimples, within reasonable limits, can effectively enhance the overall thermo-hydraulic performance of heat exchangers.