Modelling of Boiling Flows for Nuclear Thermal Hydraulics Applications—A Brief Review

Abstract

The boiling process is utterly fundamental to the design and safety of water-cooled fission reactors. Both boiling water reactors and pressurised water reactors use boiling under high-pressure subcooled liquid flow conditions to achieve high surface heat fluxes required for their operation. Liquid water is an excellent coolant, which is why water-cooled reactors can have such small sizes and high-power densities, yet also have relatively low component temperatures. Steam is in contrast a very poor coolant. A good understanding of how liquid water coolant turns into steam is correspondingly vital. This need is particularly pressing because heat transfer by water when it is only partially steam (‘nucleate boiling’ regime) is particularly effective, providing a great incentive to operate a plant in this regime. Computational modelling of boiling, using computational fluid dynamics (CFD) simulation at the ‘component scale’ typical of nuclear subchannel analysis and at the scale of the single bubbles, is a core activity of current nuclear thermal hydraulics research. This paper gives an overview of recent literature on computational modelling of boiling. The knowledge and capabilities embodied in the surveyed literature entail theoretical, experimental and modelling work, and enabled the scientific community to improve its current understanding of the fundamental heat transfer phenomena in boiling fluids and to develop more accurate tools for the prediction of two-phase cooling in nuclear systems. Data and insights gathered on the fundamental heat transfer processes associated with the behaviour of single bubbles enabled us to develop and apply more capable modelling tools for engineering simulation and to obtain reliable estimates of the heat transfer rates associated with the growth and departure of steam bubbles from heated surfaces. While results so far are promising, much work is still needed in terms of development of fundamental understanding of the physical processes and application of improved modelling capabilities to industrially relevant flows.

Modelling of free bubble growth with Interface Capturing Computational Fluid Dynamics

“…Interfaceresolving CFD, and other approaches such the Lattice Boltzmann method (Li et al, 2020), are promising tools for simulating two-phase flows of real fluids with large density ratios and interfacial evaporation. The perspectives of the work are applications to modelling of boiling phenomena, which are integral part of power generation, e.g., water-cooled nuclear reactors (Giustini, 2020), and thermal management technologies (Karayiannis and Mahmoud, 2017). Welch and Wilson (2000) appear to be the first to introduce mechanistic phase change in Interface Capturing (VOF) two-phase flow simulation.…”

CFD Assessment of the Bubble Flow in a 3D Rectangular Column

“…Si,k = SL+ SD + STDF + SWL + SVM (6) For this equation, the right-hand terms have included things like virtual mass forces, wall lubrication, turbulence dispersion, and lift and drag.…”

“…The extensive theoretical and experimental study focuses on the flow in a bubble column. The main goal of these studies was to find the fluid dynamics and flow regimes that have a big effect on the interfacial area in terms of gas-liquid, heat, and mass transfer rates, which are important for how bubble column reactors work [5][6][7][8][9][10][11][12].…”

Pool Boiling Heat Transfer Performance and Bubble Dynamics from Pin Fin-Modified Surfaces with Geometrical Shape Variation

“…Several industrial applications rely on boiling heat transfer to achieve high heat flux removal for their applications, for instance, nuclear power plants [3], cryogenic applications [4], and server cooling [5]. In server cooling, high heat removal is utterly vital to keep the performance of the computer by maintaining the junction temperature within the allowable criterion.…”