evelopment and Premiliarily validation of an Efficient Alkali Metal Heat Pipe Analysis Model for Long Time Transient Simulations

Heat pipe cooled microreactors (HP MicroRx) are highly suitable for applications in space power, military installations, marine energy, and more. A key aspect in the safety analysis of HP MicroRx is the efficient modeling of heat pipes and their coupling with the solid reactor core. When a heat pipe starts from a cold state, the working fluid in the vapor core goes through various stages ranging from rarefied vapor flow to continuous vapor flow, making the analysis of transient heat pipe behaviors a challenge. This work aims at developing a HP MicroRx core analysis model based on the coupling of the ANSYS/Fluent and a newly developed transient heat pipe analysis code HePIRE-HA. A compressible two-equation model for the heat pipe vapor core is formulated and solved together with the heat pipe wall and wick using a fully-implicit solution scheme. An interface tracking scheme is developed to handle the transition of the rarefied vapor state to the continuous vapor state. This transition scheme is demonstrated to work reasonably well and shown great efficiency. The coupling of ANSYS/Fluent and HePIRE-HA is achieved through the User Defined Function (UDF) capability of ANSYS/Fluent. A series of verification and validation studies are conducted to assess the performance and capabilities of the newly developed model. Results show that the new coupling model predicts the transient response of HP MicroRx core reasonably well and provides a reliable tool for the design and safety analysis of HP MicroRx.