In the present study, a complex geometry, high-temperature heat pipe was investigated. The heat pipe was designed to be used in a thermal energy storage for concentrating solar power systems. It consists of a primary heat pipe and an array of secondary heat pipes. In the complex heat pipe, all thermal energy applied to the evaporator is transferred to the condenser via phase change and vapor/liquid flow of the working fluid. Some part of the heat absorbed by the heat engine and the excess heat is used to charge the phase change material through secondary heat pipes. Due to the complex geometry of the heat pipe, a new numerical approach was developed. The developed model provides a way to find the non-uniformed condensate velocity profile at the condenser sections. The effects of the heat input and main condenser geometry were investigated on hydrodynamics and thermal behavior of the heat pipe. The results show that changing the main condenser inlet shape from sharp corner to tapered corner improves the performance of the heat pipe.