Coupled Mass and Heat Transfer in Multiphase Flows Using a Generalized Multiphase Modelling Approach

Multiphase flows are fundamental to both natural phenomena and industrial applications, with particular significance in nuclear thermal hydraulics where they influence subcooled boiling, condensation, and critical safety scenarios such as Pressurised Thermal Shocks (PTS) and Loss-Of-Coolant Accidents (LOCA). Accurate prediction of these flows is essential for reactor safety, as flow regimes and interfacial dynamics directly influence heat and mass transfer, structural integrity, and operational efficiency. However, the complex multiscale nature of multiphase flows, ranging from dispersed bubbles to large segregated interfaces, presents significant challenges for conventional Computational Fluid Dynamics (CFD) models.
This research focuses on the development and enhancement of the Generalised Multifluid Modelling Approach (GEMMA) to overcome these limitations. GEMMA combines interface-averaging and interface-resolving methods, enabling accurate simulation across different interfacial scales. The study extends GEMMA in three key stages: (1) coupling GEMMA with Large Eddy Simulation (LES) using a dynamic Sub-Grid Scale (SGS) to evaluate multiphase flow predictions in adiabatic systems with diverse interface morphologies, (2) incorporating phase-change heat transfer using regime-specific closures coupled with LES to capture turbulence in thermal flows, and (3) enhancing boiling models through mechanistic force-balance and correlation-based approaches, including an extended wall boiling model for slug flow, to predict bubble dynamics, heat partitioning, and flow boiling transitions.
The enhanced GEMMA model demonstrates robust predictive capabilities for multiphase flows with complex interfacial structures, including subcooled and high-volume-fraction nucleate boiling. Its integration with LES and advanced boiling models provides a novel, computationally efficient, and high-fidelity framework for simulating turbulent multiphase flows, significantly improving safety analyses and performance predictions in nuclear thermal hydraulics and related industrial applications.