In terms of thermodynamics and heat transfer, heat pipes such as closed two-phase thermosyphon are of great importance in saving energy. In this study, a computational fluid dynamics model for simulation of a thermosyphon heat pipe with two-phase flow including phase change heat transfer was developed. The study has mainly focused on the effects of volume concentrations of Nanoparticles and the operating temperature on the heat transfer performance of the thermosyphon. The analysis was performed to compare heat transfer performance between a solid copper tube and a thermosyphon heat pipe which contained deionized water and graphene oxide(GO)/water Nanofluid as its working fluids. Based on a...