Multiphase VOF modeling of heat transfer phenomena in annular flows of pure fluids and zeotropic mixtures

This doctoral dissertation presents an integrated framework for the advanced numerical investigation of multiphase flow dynamics and phase change phenomena in heat exchangers operating with low-global warming potential (GWP) fluids. The study focuses primarily on the annular flow regime while addressing the unique challenges presented by zeotropic mixtures, ultimately providing novel insights to inform the design and optimization of sustainable refrigeration and heat pump systems. Central to this research is the development of a high-fidelity computational fluid dynamics (CFD) model within the OpenFOAM environment. The model employs the Volume of Fluid (VOF) method in conjunction with non-equilibrium formulations, which together enable the accurate resolution of the complex interactions between fluid waves and phase transitions occurring in microchannels. Specifically, in the annular flow regime, the formation of a thin liquid film along the channel walls surrounding a central vapour core is exploited to enhance heat transfer during the evaporation process.