Performance enhancement approaches for tube-and-fin heat exchangers by different dimple-protrusion configurations

Tube-and-fin heat exchangers are widely used in various industries, where fin-side heat transfer enhancement is crucial for energy saving and has long been a key research focus in this field. The dimple-protrusion structure has attracted considerable attention due to its low flow resistance and significant heat transfer enhancement. However, systematic studies on the influence of dimple-protrusion geometric parameters on the thermo-hydraulic performance of tube-and-fin heat exchangers remain scarce. Therefore, this study employs numerical simulation to systematically investigate different dimple-protrusion shapes, including ellipsoidal dimple-protrusion, negative eccentricity teardrop dimple-protrusion, positive eccentricity teardrop dimple-protrusion, ridged dimple-protrusion, and spherical dimple-protrusion. The influence of ellipsoidal dimple-protrusion depth on fluid thermal performance is also explored. Results show that increasing the depth enhances flow disturbances, generating more intense longitudinal vortices. These vortices effectively disrupt the thermal boundary layer and increase the intensity of the secondary flow within the channel, thereby significantly enhancing heat transfer. The optimal thermal performance factor of JF w = 1.189 occurs at the depth of b = 1.01 mm. The spherical dimple-protrusion achieves the highest heat transfer enhancement, with a 23.89% increase in Nu compared with the conventional plain fin, while f increases by 25.45% accordingly. However, the ellipsoidal dimple-protrusion achieves the optimal comprehensive heat transfer performance, with its JF w being 18.90% and 3.39% higher than that of the plain fin and the spherical dimple-protrusion, respectively.