Phenomena Identification and Ranking Table (PIRT) for heat pipes

Abstract

Heat pipes are advanced passive thermal management devices that utilize phase change and capillary action to achieve efficient heat transfer. However, due to the complexity of the phenomena coupled in heat pipes, including capillary, phase change, turbulence, and compressibility effects, there are high uncertainties in the predictability of their operational regimes and performance. This PIRT exercise, conducted as a collaborative effort involving the Department of Energy (DOE) Microreactor Program (MRP), the Nuclear Regulatory Commission (NRC), and university partners systematically identifies, reviews, and prioritizes critical phenomena affecting the operation of heat pipes based on their importance and knowledge levels. Additional analyses and discussions are provided for phenomena with high importance and low knowledge, such as wick de-wetting, critical heat flux, contact angles, and pressure dynamics. The discussions include recognizing challenges and proposing future research directions for both modeling/simulation and experimental efforts. Additionally, the article addresses phenomena with medium importance and low knowledge that could impact heat pipe operation during non-normal or transient conditions, including frozen startup, laminar to turbulent transition, geyser boiling, wick priming, under-filling conditions, surface roughness of the wick, non-condensable gases trapped in the wick, and the timescales of startup and shutdown. This comprehensive evaluation serves as a valuable resource for guiding future research and development efforts, supporting the successful integration of heat pipes into nuclear reactors, and contributing to the advancement of heat pipe technologies in safety-critical industries.