A two-dimensional model to calculate the radial heat transfer coefficient in a heat pipe evaporator with trapezoidal grooves is extended to highly efficient so-called ‘Re-Entrant’ groove geometries. Results from the model are compared with experimental values. Good agreement is found. For further theoretical studies the heat transfer model is combined with liquid flow characteristics in axial groove direction. Based on these numerical studies, an advanced capillary structure is developed to improve the heat transfer coefficient. The new structure consists of the Re-Entrant grooves with additional micro grooves which are manufactured on top of them. It is modeled in a first attempt by superposition of two two-dimensional heat transfer models. A parameter study shows that for certain dimensions of the micro grooves the overall evaporative heat transfer coefficient considerably increases compared to the standard Re-Entrant groove geometry.