A new circular tube with delta-winglet vortex generators is proposed in order to improve the thermal hydraulic performance for energy conservation. The delta-winglet vortex generators are punched out from the fin which inserted in the center of the circular tube. Three-dimensional numerical investigation is performed to study the thermal hydraulic characteristics of the circular tube with delta-winglet vortex generators. The effects of attack angle (beta = 15 deg, 30 deg, 45 deg, and 60 deg) and pitch (P = 1D, P = 2D, P = 3D, and P = 4D) of delta-winglet vortex generators on heat transfer and fluid flow are examined in detail. The mechanism of heat transfer enhancement is analyzed based on the viewpoint of field synergy principle. The results demonstrate that delta-winglet vortex generators generate swirling motion of flow to enhance the fluid flow mixing in circular tube resulting in heat transfer augmentation with a moderate pressure drop penalty. It was found that the Nusselt number increase with the increasing attack angle and decreasing pitch of the delta-winglet vortex generators. The mechanism of heat transfer enhancement in circular tube by using delta-winglet vortex generators can be well explained by field synergy principle. (C) 2017 Published by Elsevier Ltd.