Assessment of temperature-based and vapor-pressure-driven models for CFD simulation of volatile species deposition

The transport and deposition of volatile fission-product species under strong thermal gradients is a safety relevant issue in lead-bismuth eutectic (LBE) systems, yet reliable kinetic models for their treatment in computational fluid dynamics (CFD) simulations remain limited. In this work, two complementary modeling strategies for the deposition of PbI 2 are implemented and assessed within a common CFD framework. The first approach is a phenomenological temperature-based model in which deposition is represented by temperature-activated source terms calibrated against experimental observations. The second approach is a vapor-pressure-based kinetic model derived from the Hertz–Knudsen–Schrage formulation, which explicitly links phase change to thermodynamic driving forces and allows for re-evaporation. Both models are implemented in the in-house solver T-Flows and assessed by comparison with thermosublimatography experiments under varying carrier-gas flow rates and experiment durations. The temperature-based model reproduces the main trends of the reference experiment and long-duration deposition profiles, and shows robust behavior within its calibration regime. The vapor-pressure-based model captures reversible phase-change effects and reproduces the experimentally observed decrease in deposition temperature with increasing experiment duration, but systematically predicts broader downstream deposition tails, indicating that the effective condensation kinetics remain slower than in the experimental system. The results highlight complementary strengths of the two approaches: the temperature-based model is well suited for robust engineering-oriented assessments after calibration, while the vapor-pressure-based formulation provides a more physically grounded framework for future extension toward multi-species and multi-phase thermodynamic coupling. The study provides a basis for further development of CFD models for volatile species behavior in complex LBE environments.