Numerical analysis of heat transfer enhancement and flow characteristics inside cross-combined ellipsoidal dimple tubes

The heat transfer and flow characteristics have been numerically investigated in the cross-combined dimple tube with the k-ε model, and the enhancement model based on composite-shape surface technologies is established for the first time. The results indicate that the heat transfer index, friction factor and performance evaluation criteria increase tremendously by comparing with the single ellipsoidal dimple tube at considered operating conditions. In particular, the heat transfer enhancement rises by 18.8–48.3%, and an average of 24.8%, when compared with the traditional single ellipsoidal tube. 3D simulation is carried out to elaborate the influence mechanism of dimples on the thermal performance and concludes that dimples can further enhance heat transfer through changing temperature distribution and increasing the gradient of the core region at the dimple section. The concave surface profile can disturb steady flow and boundary layer development to enhance the mixture of hot fluid and cold fluid. Additionally, the effects of geometric parameters on thermal and hydraulic performances are discussed to reveal that the larger quantity and volume of dimples lead to a better comprehensive thermo-hydraulic performance.