  Heat pipes can efficiently and passively remove heat in nuclear
microreactors. Nevertheless, the flow dynamics within heat pipes present a
significant challenge in designing and optimizing them for nuclear energy
applications. This work aims to explore the vapor core of heat pipes through
comprehensive two- and three-dimensional simulations, with a primary focus on
modeling the pressure recovery observed in the condenser section. The goal is
to establish improved correlations for one-dimensional heat pipe codes. The
simulations are validated against experimental data from a vapor pipe
documented in the literature. The turbulence model is employed in the
two-dimensional simulations through the open-source spectral-element code
Nek5000. This model provides insights into pressure recovery within heat pipes
with low computational cost. In addition, Large Eddy Simulations (LES) are used
to capture turbulent flow features in a three-dimensional vapor pipe model,
utilizing the code NekRS. Using LES is crucial for comprehending the impact of
laminar-to-turbulent transition on pressure recovery. A simulation framework is
created to model the heat pipe's vapor core, laying the foundation for an
enhanced understanding of heat pipe behavior. The ultimate goal is to improve
and optimize heat pipe designs, provide data to validate lower-fidelity
approaches and enhance their performance in nuclear reactors.
