Micro-Scale Simulations of Boiling Heat Transfer via a Volume of Fluid Approach: Application to Pool Boiling and Flow Boiling

The current trend in the electronics industry is to offer products that are progressively smaller and more powerful, resulting to an exponential increase in the generated residual heat.Effective and environmental-friendly cooling of electronic components is of upmost importance for the Thermal Management of Data Centres, Fuel Cells, Insulated-Gate Bipolar Transistors, Lithium-Ion Batteries and a variety of other important technological applications.Boiling heat transfer has been proven as one of the most efficient cooling strategies for such High-Power Density Electronics.However, such thermal management solutions that rely on the phase-change of a working fluid, are not yet used fully in practice.This is due to a lack of deep understanding of the underpinned complex flow and transport processes and a corresponding lack of reliable and easy-to-use thermal design tools.The cooling efficiency of phase-change heat transfer devices and components depends mainly on phenomena occurring at very small scales, such as bubble nucleation and bubble growth characteristics.Therefore, a parallel effort on developing interlinked (i) suitable theoretical models, (ii) specialized 3D, high-fidelity numerical simulations and (iii) accurate experiments is required to make a real breakthrough on understanding the underlying mechanisms of heat transfer during phase-change, especially in small scales.Here, an enhanced customised Volume of Fluid (VOF) based numerical simulation framework that has been developed in the general context of the OpenFOAM CFD Toolbox is presented.The proposed enhancements include: i) implementation of a treatment for spurious velocities dampening (a well-known defect of VOF methods) [1], ii) implementation of an accurate dynamic contact angle sub-model to account for wettability effects [2], [3], iii) implementation of a phase-change model that accounts for boiling and condensation [4] and iv) implementation of conjugate heat transfer between solid and two-phase fluid domains [5].Various applications of the proposed numerical simulation framework for boiling heat transfer are also presented [6]-[8], and the main limitations of the proposed numerical simulation methodology are discussed.Finally, some recommendations for future directions towards a multiscale modelling methodology that will couple the proposed VOF method with mesoscale simulations for boiling heat transfer [9], are proposed.