Comparative study on the thermal–hydraulic performance of tubes enhanced with three different types of teardrop protrusions

An attractive approach for improving heat transfer in tubes is creating protrusions on the inner surface of tubes. Protrusions can have various shapes. One of the attractive shapes in the literature is a teardrop. For a teardrop protrusion, different teardrop tails have been used in the literature, but no study has considered the effects of the type of these tails on the thermal–hydraulic performance of these protrusions. In this paper, three types of teardrop protrusions were defined to numerically study the effects of changing the tail curves of a teardrop protrusion on thermal–hydraulic performance. One of these teardrop protrusions with an elliptic tail is novel and not similar to any teardrop protrusion reported in the literature. The heat transfer performance of these teardrop protrusions is compared with each other and with ellipsoidal protrusions in a Reynolds number (Re) range of 10,000 to 40,000. The realisable k–ε model and the periodic boundary conditions were adopted for the numerical model. Six different tube configurations with different protrusion pitches were considered for each protrusion shape. The results showed that using a curved tail for teardrop protrusions results in better performance than a straight tail, which was the most used shape in the literature. Tear-circle protrusions with circular tail curves were superior to all protrusion shapes (other teardrop and ellipsoidal protrusions) considered in this study at the entire Re range. A tube enhanced with tear-circle protrusions with the optimum pitch improved thermal–hydraulic performance by up to 54% compared to a smooth tube.