Abstract The detailed flow structure and heat transfer characteristics in a newly designed heat transfer surface geometry were investigated. The surface geometry proposed is the combination of a conventional dimple cavity with a protrusion structure mounted within it. The underlying design concept of this surface geometry aims to enhance the flow mixing and the corresponding heat transfer in the flow-recirculating region that is generated by a conventional dimple cavity. Four different protrusion heights were considered as the main design parameter of the present study. The numerical simulations were carried out with a Reynolds number of 2800 and Prandtl number of 0.71 (air) corresponding to the mean velocity and channel height. The calculated pressure drop and heat-transfer capacity were assessed in terms of the Fanning friction factor and Colburn j factor. The overall performances, estimated in terms of area goodness factor for several protrusion-in-dimple cases, were higher than that found by a conventional dimple. Compared to the conventional dimple case, the pressure drop and heat-transfer capacity were slightly augmented in the case of a protrusion height of 0.05 since this leads to an improvement in the mixing of the turbulent flow in the dimple cavity.