Towards the direct numerical simulation of nucleate boiling flows (original) (raw)
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Nucleate boiling simulation using interface tracking method
Nuclear Engineering and Design, 2020
The development and validation of 3D multiphase computational fluid dynamics (M-CFD) models and physics-informed data-driven modeling require data of high-quality and high-resolution. Considering the difficulties in acquiring the corresponding experimental data in prototypical conditions, two-phase boiling simulations by Interface Tracking Method (ITM) based models can be used to generate high-resolution numerical data in a consistent and relatively economical manner. A boiling model is developed in one of the ITM-based multiphase-flow solvers, named PHASTA, to investigate the nucleate boiling phenomenon. The interaction between bubbles forming at adjacent nucleation sites is investigated with this ITM boiling model. Nucleate pool boiling simulations with multiple nucleation sites are presented in this paper and influences of site distance, neighboring bubble size and contact angle effect are investigated. The presented boiling model can conduct boiling simulation on 3D unstructured computational meshes. These simulation results improve our understanding of the physical mechanisms of the nucleate boiling phenomenon and provide high-resolution numerical data for M-CFD validation and advanced boiling model development.
A new conservative phase change model for nucleate boiling
Proceedings of 20th International Conference on Nuclear Energy for New Europe 2011
A new mass-conservative phase change model has been developed for the nucleate boiling simulation. The conservative CIP scheme is used for surface tracking in order to satisfy the mass conservation exactly. As the phase change model, a sharp-interface model is developed, in which the phase change rate can be computed from the heat flux to the interface in a straightforward manner. The developed numerical method is verified for one dimensional phase change problem, and three dimensional bubble growth problem in superheated liquid in unbounded domain. Following these verifications, a saturated nucleate pool boiling simulation is conducted, using a micro region model which can treat the micro physics close to the wall.
Numerical Study of Nucleate Boiling Flows Using ANSYS Fluent
Proceedings of the 4th World Congress on Momentum, Heat and Mass Transfer, 2019
In the recent decade, computational fluid dynamics has emerged as a tool to improve our understanding of boiling heat transfer. In the nuclear industry, for ins instance, high fidelity modelling of the critical heat flux has stimulated much interest in modelling boiling flows. In this paper, we evaluate the accuracy of the boiling models implemented in the ANSYS Fluent software against experimental data. The boiling model is based on the heat flux partitioning approach and accommodates the heat flux due to single-phase convection, quenching and evaporation. Extensive validations carried out for a range of 2d, and 3d boiling flows demonstrate that the boiling models can correctly predict the vapour volume fraction distribution. The numerical results in all the cases are in good agreement with the experimental data.
Numerical Investigation of Boiling
Bulletin of the American Physical Society, 2012
In this work, we study different phenomena that occur during nucleate boiling. We numerically investigate boiling using two phase flow direct numerical simulation based on a level set / Ghost Fluid method. This method allows us to follow the interface and to make accurate geometric calculation as for bubble curvature. Nucleate boiling on a plate is not only a thermal issue, but also involves multiphase dynamics issues at different scales and at different stages of bubble growth. As a consequence, we divide the whole problem and investigate separately the different phenomena considering their nature and the scale at which they occur. First we analyse the boiling of a static bubble immersed in an overheated liquid. We perform numerical simulations at different Jakob numbers in the case of strong discontinuity of density through the interface. These simulations permit us to estimate the accuracy of our numerical method dealing with phase change in the context of two phase flow direct n...
International Journal of Heat and Mass Transfer, 2013
The increasing industrial applications of boiling heat transfer call for high fidelity and efficient numerical predictions, of which a hybrid scheme simulation combining CFD and boiling model is a promising candidate. To this end, the current research put forth a dynamical boiling model. The model dynamically integrates the sub-processes associated with a boiling cycle, including those of the formation of a thermal boundary layer, the evaporation of a sublayer film, the growth and detachment of a bubble as well as the concomitant heat transfer. In the bubble growth period the growth rate is given by summing the evaporation over the vapor-liquid interface surrounded by a micro sublayer film, a macro film in the thermal boundary layer, and bulk fluid respectively. The computation solves transient governing equations for the instantaneous distribution and heat transfer of the micro sublayer film. It also works out automatically an apparent contact angle. The bubble detachment is processed in a new way that calculates the various forces acting on the bubble to trace the detaching process. Numerical results of the boiling from single nuclei agree with experimental data with reasonable accuracies. Comments are given about the possible improvement of the model and the further development toward practical hybrid simulations of the boiling phenomena.
International Journal of Heat and Mass Transfer, 2017
A numerical simulation method to model nucleate pool boiling from multiple nucleation sites has been developed and applied to different boiling-water regimes, ranging from discrete bubbles to the vapor mushroom region. The method is based on an interface tracking method in which the liquid-vapor interface is resolved by a color function within the framework of Computational Fluid Dynamics (CFD). Conjugate heat transfer between the wall and the fluid is included in order to capture the temperature field appropriately, since this has a significant influence on the bubble growing process. The microlayer, which is the thin liquid film existing beneath a growing bubble, is taken into account using a specialized model specifically developed by the authors. A validation case is chosen to test the model, based on an experiment by Gaertner, featuring the boiling of water from a heated, horizontal plate under atmospheric pressure. Estimation of the nucleation site density and the local activation temperatures are taken from experimental measurement, and introduced into the simulation through an in-built, nucleation-site model. The applied heat flux ranges from 50 to 300 kW/m 2 , the heat-transfer surface being of dimensions 20 mm  20 mm. The computed heat transfer coefficient agrees well with the measured value, demonstrating the capability of the described CFD model to predict boiling heat transfer in a mechanistic sense for the flow regimes examined. Comparison of bubble shapes between experiment and computation also shows good agreement. In addition, a variety of statistical data, such as the heat flux partitioning and the ratio of vapor-to-liquid area over the heat transfer surface, which cannot be measured in the experiments, but can be derived from the results of the simulations.
Volume 3, 2004
Numerical simulations of boiling flows are discussed. The change of phase from liquid to vapor and vice-versa usually takes place in a highly unsteady manner where the phase boundary is very convoluted. Direct numerical simulations therefore require the accurate solution of the Navier-Stokes equations and the energy equation in each phase and the correct incorporation of the unsteady phase boundary. Such simulations, where the motion of an unsteady phase boundary is followed for a sufficiently long time to allow computation of average heat transfer are very recent. Here, we will describe one method that has been used successfully to simulate boiling flows and show a few examples of studies using the method.
Modeling of Subcooled Nucleate Boiling with OpenFOAM
Within the course of this master thesis project, subcooled nucleate boiling in a vertical pipe has been modeled using CFD. The modeling has been carried out within the OpenFOAM framework and a two-phase Eulerian approach has been chosen. The code can be used to predict the distribution of the local flow parameters, i.e. the void fraction, the bubble diameter, the velocity of both liquid and gas, the turbulent intensity as well as the liquid temperature. Special attention has been devoted to the phenomena which govern the void fraction distribution in the radial direction. Two different solvers have been implemented and the simulations have been performed in two dimensions.
Boiling heat transfer modelling: A review and future prospectus
Thermal Science
This paper reviews the current status of boiling heat transfer modelling, discusses the need for its improvement due to unresolved intriguing experimental findings and emergence of novel technical applications and outlines the directions for an advanced modelling approach. The state-of-the-art of computational boiling heat transfer studies is given for: macro-scale boiling models applied in two-fluid liquid-vapour interpenetrating media approach, micro-, meso-scale boiling computations by interface capturing methods, and nano-scale boiling simulations by molecular dynamics tools. Advantages, limitations and shortcomings of each approach, which originate from its grounding formulations, are discussed and illustrated on results obtained by the boiling model developed in our research group. Based on these issues, we stress the importance of adaptation of a multi-scale approach for development of an advanced boiling predictive methodology. A general road-map is outlined for achieving th...
Multiphase Science and Technology, 2011
Predictions of local boiling flow processes leading to DNB conditions are considered. The work was performed within the NURESIM project in the frame of sixth European Framework Program. This paper focuses on the RANS approach as being the most reliable for simulation of realistic bubbly flows. New physical models developed within the NURESIM project are presented and tested on various single-channel boiling experiments, differing in geometry, working fluid and operating conditions. The applicability of the model for boiling in fuel rod bundles under industrial conditions has been demonstrated.