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Bergagio, M., Fan, W., Thiele, R. & Anglart, H. (2020). Large eddy simulation of thermal mixing with conjugate heat transfer at BWR operating conditions. Nuclear Engineering and Design, 356, Article ID 110361.
Open this publication in new window or tab >>Large eddy simulation of thermal mixing with conjugate heat transfer at BWR operating conditions
2020 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 356, article id 110361Article in journal (Refereed) Published
Abstract [en]

Thermal fatigue occurs in most metals under cyclic heat loads and can threaten the structural integrity of metal parts. Detailed knowledge of these loads is of utter importance to prevent such issues. In this study, a large eddy simulation (LES) with wall-adapting local eddy viscosity (WALE) subgrid model is performed to better understand turbulent thermal mixing in an annulus with a pair of opposing cold inlets at a low axial level (z = 0.15 m) and with a pair of opposing hot inlets at a higher axial level (z = 0.80 m). Each inlet pair is 90 degrees from each other in the azimuthal direction. Conjugate heat transfer between fluid and structure is accounted for. The geometry simplifies a control-rod guide tube (CRGT) in a boiling water reactor (BWR). LES results are compared with measurement data. This is one of the first times BWR conditions are met in both experiments and LES: pressure equals 7.2 MPa, while the temperature difference between hot and cold inlets reaches 216 K. LES temperatures at the fluid-structure interface are fairly correlated with their experimental equivalents, with regard to mean values, local variances, and dangerous oscillation modes in fatigue-prone areas (z = 0.65 - 0.67 m). An elastic analysis of the structure is performed to evaluate stress intensities there. From them, cumulative fatigue usage factors (CUFs) are estimated and used as screening criteria in the subsequent frequency analysis of temperature time series at the fluid-structure interface. The likelihood of initiating a fatigue crack is linked to the maximum CUF, which is 3.2 x 10(-5) for a simulation time of similar to 10 s.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2020
Keywords
Turbulent mixing, Conjugate heat transfer, LES, WALE SGS model, High cycle thermal fatigue
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-266514 (URN)10.1016/j.nucengdes.2019.110361 (DOI)000503842900011 ()2-s2.0-85073569453 (Scopus ID)
Note

QC 20200205

Available from: 2020-02-05 Created: 2020-02-05 Last updated: 2020-02-17Bibliographically approved
Fan, W. & Anglart, H. (2020). varRhoTurbVOF: A new set of volume of fluid solvers for turbulent isothermal multiphase flows in OpenFOAM. Computer Physics Communications, 247, Article ID 106876.
Open this publication in new window or tab >>varRhoTurbVOF: A new set of volume of fluid solvers for turbulent isothermal multiphase flows in OpenFOAM
2020 (English)In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 247, article id 106876Article in journal (Refereed) Published
Abstract [en]

The volume of fluid (VOF) method is a popular approach for multiphase flow modeling. The open-source computational fluid dynamics (CFD) software, OpenFOAM, implements a variety of VOF-based solvers and provides users a wide range of turbulence models. Since isothermal multiphase flows under the VOF framework belong to the variable-density incompressible flow category, the isothermal VOF-based solvers in OpenFOAM fail to use the correct turbulence models. varRhoTurbVOF is designed to solve this issue and with the hope to replace all the corresponding existing solvers in the future. With the object-oriented paradigm, varRhoTurbVOF guarantees the usability, reusability and maintainability of the codes. Aside from turbulence modeling, all other features in the original solvers are preserved in varRhoTurbVOF. Program summary: Program Title: varRhoTurbVOF Program Files doi: http://dx.doi.org/10.17632/4t8z8vzyvs.1 Licensing provisions: GPLv3 Programming language: C++ Supplementary material: http://dx.doi.org/10.17632/7mp25kyb4p.4 Nature of problem: Under the VOF framework, the flow of the isothermal mixture belongs to the variable-density incompressible flow category. For such flows, VOF-based solvers of OpenFOAM fail to construct the correct governing equations for turbulence modeling. varRhoTurbVOF contains a set of newly designed VOF-based solvers which could use the desired governing equations for turbulence quantities. Solution method: varRhoTurbVOF creates a new class for variable-density incompressible turbulence models, which allows reusing the existing turbulence model template classes. A set of VOF-based solvers are then created to be able to construct variable-density incompressible turbulence models.

Place, publisher, year, edition, pages
Elsevier B.V., 2020
Keywords
CFD, OpenFOAM, Turbulence modeling, Variable-density incompressible flow, VOF, C++ (programming language), Incompressible flow, Isotherms, Multiphase flow, Object oriented programming, Open source software, Open systems, Reusability, Turbulence models, Governing equations, Incompressible turbulence, Multi-phase flow models, Object oriented paradigm, Variable density, Volume of fluid method, Volume of fluids, Computational fluid dynamics
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-263257 (URN)10.1016/j.cpc.2019.106876 (DOI)000503093400023 ()2-s2.0-85071451876 (Scopus ID)
Note

QC 20191106. QC 20200109

Available from: 2019-11-06 Created: 2019-11-06 Last updated: 2020-01-09Bibliographically approved
Li, H. & Anglart, H. (2019). Dryout prediction with CFD model of annular two-phase flow. Nuclear Engineering and Design, 349, 20-26
Open this publication in new window or tab >>Dryout prediction with CFD model of annular two-phase flow
2019 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 349, p. 20-26Article in journal (Refereed) Published
Abstract [en]

Two-phase flow and heat transfer are of interest to industrial applications due to its high efficiency. In a diabatic annular two-phase flow, the liquid film is depleted by both entrainment of liquid droplets and by evaporation. When the liquid film experiences almost complete depletion and cannot cover the wall, the heat transfer between the fluid and the channel wall significantly deteriorates, leading to the onset of boiling transition called dryout. While the dryout is milder than the departure from nucleate boiling (DNB) occurring in low quality two-phase flows, it could still challenge and damage the channel wall. As a result, the dryout occurrence needs to accurately predicted and avoided in practice, such as in boiling water reactors (BWRs). Research interests haven been recently focused on dryout prediction with annular flow modeling, with three fields of gas, droplets and liquid film accounted for. In the current study, one unified computational fluid dynamics (CFD) model for annular flow was developed for dryout applications. The model is employing a separate solver of two-dimensional conservation equations to predict propagation of a thin boiling liquid film on solid walls. The film model is coupled to a solver of three-dimensional conservation equations describing the gas core, which is assumed to contain a saturated mixture of vapor and liquid droplets. All the major interaction phenomena between the liquid film and the gas core flow have been accounted for, including the liquid film evaporation as well as the droplet deposition and entrainment. The resultant unified framework for annular flow has been applied to the swam-water flow with conditions typical for a BWR. The simulation results for the liquid film flow and dryout occurrence show favorable agreements with the available experimental data.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Annular two-phase flow, Dryout prediction, Liquid film, Droplet deposition and entrainment
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-252582 (URN)10.1016/j.nucengdes.2019.04.020 (DOI)000468113300003 ()2-s2.0-85064430579 (Scopus ID)
Note

QC 20190611

Available from: 2019-06-11 Created: 2019-06-11 Last updated: 2019-06-11Bibliographically approved
Anglart, H. (2019). Initial entrained fraction at onset of annular flow. In: 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 20192019,: . Paper presented at 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2019; Marriott Portland Downtown WaterfrontPortland; United States; 18 August 2019 through 23 August 2019 (pp. 1023-1034).
Open this publication in new window or tab >>Initial entrained fraction at onset of annular flow
2019 (English)In: 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 20192019,, 2019, p. 1023-1034Conference paper, Published paper (Refereed)
Abstract [en]

One of the frequently employed current models to predict the occurrence of dryout in boiling annular flows is using conservation equations to determine the liquid film mass flux. The accuracy of predictions of dryout depends to a large extend on the initial conditions, which are employed in the model. In this paper it is shown that the accuracy of predictions can be significantly improved if the initial entrained fraction of liquid is correlated to the flow conditions at the onset of annular flow. Using experimental data for liquid film flow rates in pipes with variable power distributions, a new closure relationship for the initial entrained fraction of liquid at the onset of annular flow is proposed.

National Category
Mechanical Engineering Energy Engineering
Identifiers
urn:nbn:se:kth:diva-268323 (URN)2-s2.0-85073715098 (Scopus ID)
Conference
18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2019; Marriott Portland Downtown WaterfrontPortland; United States; 18 August 2019 through 23 August 2019
Note

QC 20200310

Available from: 2020-03-10 Created: 2020-03-10 Last updated: 2020-03-10Bibliographically approved
Fan, W., Li, H. & Anglart, H. (2019). Numerical investigation of spatial and temporal structure of annular flow with disturbance waves. International Journal of Multiphase Flow, 110, 256-272
Open this publication in new window or tab >>Numerical investigation of spatial and temporal structure of annular flow with disturbance waves
2019 (English)In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 110, p. 256-272Article in journal (Refereed) Published
Abstract [en]

Droplet entrainment is a crucial process for annular flow in terms of heat and mass transfer. Disturbance wave is believed to be a fundamental phenomenon which is closely related to entrainment. A 3D numerical simulation on disturbance waves and entrainment is carried out by using volume of fluid (VOF) method where no periodic boundary condition is used. Since VOF tracks the interface implicitly, a systematic method is developed for post-processing, with which disturbance waves. ripples, base film, and entrainment process are clearly visualized, and the stochastic and chaotic nature of two-phase flow is confirmed. Surfacewise distributions are generated for main wave parameters, and the streamwise developments of such quantities are shown to be consistent with experimental observations. Predictions for main wave parameters are in reasonable agreement with the experiment and empirical correlations. Current work shows the capability and promising application of investigating disturbance waves and entrainment with VOF method.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Disturbance wave, Entrainment, VOF, Periodic boundary
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-240699 (URN)10.1016/j.ijmultiphaseflow.2018.10.003 (DOI)000452945400019 ()2-s2.0-85054441195 (Scopus ID)
Note

QC 20190110

Available from: 2019-01-10 Created: 2019-01-10 Last updated: 2019-11-18Bibliographically approved
Fan, W., Li, H. & Anglart, H. (2019). Prediction of annular two-phase flow with heat transfer. In: 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2019: . Paper presented at 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2019, 18 August 2019 through 23 August 2019 (pp. 5230-5238). American Nuclear Society
Open this publication in new window or tab >>Prediction of annular two-phase flow with heat transfer
2019 (English)In: 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2019, American Nuclear Society , 2019, p. 5230-5238Conference paper, Published paper (Refereed)
Abstract [en]

This paper is presenting recent development of mechanistic models to predict annular two-phase flows and heat transfer. The main interest in simulation of such phenomena results from the need to accurately predict the onset of dryout. In heat exchange devices where the heat flux - rather than the temperature - is controlled (such as, e.g., boiling water reactors) the occurrence of dryout may lead to severe damage of equipment, since the temperature of heated wall can significantly increase and the wall can be melted through. The difficulty in simulation of dryout stems from the fact that it is influenced by phenomena, for which the length scales are ranging from microns to meters. The thickness of the liquid film just before the onset of dryout can be just a few microns, whereas the entrained fraction of liquid is governed by two-phase flow in channels with a few meters in length. To cope with such big characteristic-length span, Computational Fluid Dynamics (CFD) codes are proposed. This approach allows to resolve the phenomena close to the wall and also to account for far-field effects related to the flow history. It is shown that with a proper choice of the level of approximation, and with appropriate closure relationships, CFD codes can be used to predict the occurrence of dryout, taking into account, between others, the effect of disturbance waves, the influence of channel geometry and the presence of flow obstacles.

Place, publisher, year, edition, pages
American Nuclear Society, 2019
Keywords
Annular flow, Disturbance waves, OpenFOAM, Transient dryout, Boiling water reactors, Computational fluid dynamics, Forecasting, Heat flux, Heat transfer, Heating equipment, Hydraulics, Liquid films, Phase meters, Annular flows, Annular two-phase flow, Characteristic length, Computational Fluid Dynamics codes, Dry-out, Entrained fractions, Two phase flow
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-268499 (URN)2-s2.0-85073732416 (Scopus ID)
Conference
18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2019, 18 August 2019 through 23 August 2019
Note

QC 20200402

Available from: 2020-04-02 Created: 2020-04-02 Last updated: 2020-04-02Bibliographically approved
Fan, W. & Anglart, H. (2019). Progress in Phenomenological Modeling of Turbulence Damping around a Two-Phase Interface. FLUIDS, 4(3), Article ID 136.
Open this publication in new window or tab >>Progress in Phenomenological Modeling of Turbulence Damping around a Two-Phase Interface
2019 (English)In: FLUIDS, ISSN 2311-5521, Vol. 4, no 3, article id 136Article in journal (Refereed) Published
Abstract [en]

The presence of a moving interface in two-phase flows challenges the accurate computational fluid dynamics (CFD) modeling, especially when the flow is turbulent. For such flows, single-phase-based turbulence models are usually used for the turbulence modeling together with certain modifications including the turbulence damping around the interface. Due to the insufficient understanding of the damping mechanism, the phenomenological modeling approach is always used. Egorov's model is the most widely-used turbulence damping model due to its simple formulation and implementation. However, the original Egorov model suffers from the mesh size dependency issue and uses a questionable symmetric treatment for both liquid and gas phases. By introducing more physics, this paper introduces a new length scale for Egorov's model, making it independent of mesh sizes in the tangential direction of the interface. An asymmetric treatment is also developed, which leads to more physical predictions for both the turbulent kinetic energy and the velocity field.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
two-phase flow, CFD, phenomenological modeling, turbulence damping, Egorov's model, asymmetric treatment
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-262799 (URN)10.3390/fluids4030136 (DOI)000488029400011 ()2-s2.0-85071514977 (Scopus ID)
Note

QC 20191021

Available from: 2019-10-21 Created: 2019-10-21 Last updated: 2019-10-21Bibliographically approved
Anglart, H. (2019). Progress in understanding and modelling of annular two-phase flows with heat transfer. Nuclear Engineering and Design, 345, 166-182
Open this publication in new window or tab >>Progress in understanding and modelling of annular two-phase flows with heat transfer
2019 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 345, p. 166-182Article in journal (Refereed) Published
Abstract [en]

Annular two-phase flows with heat transfer play important role in many industrial applications. In particular, thermal margins of Boiling Water Reactors (BWR) are entirely determined by this type of flow and heat transfer conditions. To avoid dryout, a liquid film must be present on heated rods of BWR fuel assemblies during normal operation. The present paper describes the recent progress in understanding and modelling of the governing phenomena of annular two-phase flow and heat transfer. A special attention has been devoted to experimental observations that have the most significant influence on the adopted modelling approach. The primary goal is to pave a path to mechanistic modelling of dryout and post-dryout heat transfer applicable to nuclear fuel assemblies. Current Computational Fluid Dynamics (CFD) approaches to model the governing phenomena are presented and their further improvements are suggested.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Annular flow, Droplets, Dryout, Liquid film, Post-dryout
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-246448 (URN)10.1016/j.nucengdes.2019.02.007 (DOI)000460659300015 ()2-s2.0-85062033228 (Scopus ID)
Note

QC 20190319

Available from: 2019-03-19 Created: 2019-03-19 Last updated: 2019-03-27Bibliographically approved
Spirzewski, M., Anglart, H. & Stano, P. M. (2019). Uncertainty and sensitivity analysis of a phenomenological dryout model implemented in DARIA system code. Nuclear Engineering and Design, 355, Article ID UNSP 110281.
Open this publication in new window or tab >>Uncertainty and sensitivity analysis of a phenomenological dryout model implemented in DARIA system code
2019 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 355, article id UNSP 110281Article in journal (Refereed) Published
Abstract [en]

Uncertainties of numerical predictions play important role in assessment of safety margins in nuclear reactors. In this paper uncertainties of the predictions of the Hewitt-Govan model, which is used to determine the entrainment and deposition rates in phenomenological dryout model, are presented and discussed. Results of the global uncertainty analysis are shown in terms of trends of uncertainty values with respect to the pressure, mass flux and inlet subcooling. Regions of large and small uncertainties are identified and presented in a tabular form. Application of the global sensitivity analysis methods allowed to quantify the sources of uncertainties with high accuracy over large spectrum of experimental conditions. Since the present analysis required calculation of millions of cases, a dedicated fast-running three-field computational code called DARIA has been developed for that purpose. The analysis revealed that the uncertainties of dryout prediction are predominantly resulting from uncertainties of the coolant mass flow rate. The most obvious implication of the presented work is that, when applying the current methodology to predict dryout in rod bundles, the most important parameter, affecting the accuracy of predictions, is the distribution of coolant flow between sub-channels.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Dryout, Uncertainty, Sensitivity, DARIA
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-264330 (URN)10.1016/j.nucengdes.2019.110281 (DOI)000493898800044 ()2-s2.0-85071336374 (Scopus ID)
Note

QC 20191202

Available from: 2019-12-02 Created: 2019-12-02 Last updated: 2019-12-02Bibliographically approved
Anglart, H., Li, H. & Niewinski, G. (2018). Mechanistic modelling of dryout and post-dryout heat transfer. Paper presented at 13th Conference on Research and Development in Power Engineering (RDPE), NOV 28-DEC 01, 2017, Warsaw, Poland. Energy, 161, 352-360
Open this publication in new window or tab >>Mechanistic modelling of dryout and post-dryout heat transfer
2018 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 161, p. 352-360Article in journal (Refereed) Published
Abstract [en]

In this paper a new mechanistic model for the diabatic annular two-phase flow is presented and applied to prediction of dryout and post-dryout heat transfer in various channels. The model employs a computational fluid dynamics code - OpenFOAM (R) - to solve the governing equations of two-phase mixture flowing in a heated channel. Additional closure laws have been implemented to calculate the location of the dryout and to predict wall temperature in the post-dryout region. Calculated results have been compared with experimental data obtained in pipes and good agreement between predictions and measurements has been achieved. The presented model is applicable to complex geometries and thus can be used for prediction of post-dryout heat transfer in a wide variety of energy conversion systems.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Dryout, Post-dryout, Annular flow, Liquid film, Droplets
National Category
Energy Systems
Identifiers
urn:nbn:se:kth:diva-237091 (URN)10.1016/j.energy.2018.07.011 (DOI)000446148400031 ()2-s2.0-85053079758 (Scopus ID)
Conference
13th Conference on Research and Development in Power Engineering (RDPE), NOV 28-DEC 01, 2017, Warsaw, Poland
Note

QC 20181024

Available from: 2018-10-24 Created: 2018-10-24 Last updated: 2018-10-24Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-5595-1952

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