Nucleate boiling flow – experimental investigations and wall heat flux modelling for automotive engine applications

Numerical simulation of boiling flow and heat transfer presents a number of unique challenges in both theoretical modeling and developing robust numerical methodology. The major difficulty arises due to the heat transfer and phase changes between heated walls and fluid (liquid and vapor). Furthermore, modeling of the liquid-vapor interfacial transfers of momentum, heat and mass proves to be equally challenging. The multiphase boiling modeling approach described in this paper has been found to be capable of addressing these issues and is therefore suitable for inclusion in an advanced general purpose CFD solver. In the present approach, boiling flows are modeled within the framework of the Eulerian multifluid model. The governing equations solved are phase continuity, momentum and energy equations. Turbulence effects can be accounted for using mixture, dispersed or per-phase multiphase turbulence models. Wall boiling phenomena are modeled using the baseline mechanistic RPI model for nucleate boiling, and its extensions to non-equilibrium boiling and critical heat flux regime. A range of sub-models are considered to account for the interfacial momentum, mass and heat transfer, and flow regime transitions. An advanced numerical scheme has been developed for solving the model equations which can handle the heat partition between heated walls and fluid, provide for wall and interfacial mass transfer source terms in phase volume fraction equations, and address the coupling between the phase change rates and the pressure correction equation. The wall boiling models and numerical algorithm have been implemented in an advanced, general-purpose CFD code, FLUENT. Validations have been carried out for a range of 2D and 3D boiling flows, including pressurized water through a vertical pipe with heated walls, R-113 liquid in a vertical annulus with internal heated walls, a 3D BRW core channel geometry with vertical heated rods, and water in a vertical circular pipe under critical heat flux and post dry-out conditions. The results demonstrate that the wall boiling models are able to correctly predict the wall temperature and vapor volume fraction distribution. The predictions in all the cases are in reasonable good agreement with available experiments. Tests also indicate that the present implementation is fast and robust, as compared to previous approaches. All the cases are able to be simulated with the use of the FLUENT steady-state multiphase solver with reasonable numbers of iterations.

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The Onset of Flow Instability in Uniformly Heated Horizontal Microchannels

Journal of Heat Transfer ◽

10.1115/1.521442 ◽

1999 ◽

Vol 122 (1) ◽

pp. 118-125 ◽

Cited By ~ 96

Author(s):

J. E. Kennedy ◽

G. M. Roach, ◽

M. F. Dowling ◽

S. I. Abdel-Khalik ◽

S. M. Ghiaasiaan ◽

...

Keyword(s):

Heat Flux ◽

Flow Instability ◽

Experimental Parameter ◽

Nucleate Boiling ◽

Wall Heat Flux ◽

Exit Pressure ◽

Channel Exit ◽

Demand Curves ◽

Parameter Ranges ◽

Heated Length

Onset of nucleate boiling and onset of flow instability in uniformly heated microchannels with subcooled water flow were experimentally investigated using 22-cm long tubular test sections, 1.17 mm and 1.45 mm in diameter, with a 16-cm long heated length. Important experimental parameter ranges were: 3.44 to 10.34 bar channel exit pressure; 800 to 4500 kg/m2s mass flux (1 to 5 m/s inlet velocity); 0 to 4.0 MW/m2 channel wall heat flux; and 7440–33,000 Peclet number at the onset of flow instability. Demand curves (pressure drop versus mass flow rate curves for fixed wall heat flux and channel exit pressure) were generated for the test sections, and were utilized for the specification of the onset of nucleate boiling and the onset of flow instability points. The obtained onset of nucleate boiling and onset of flow instability data are presented and compared with relevant widely used correlations. [S0022-1481(00)02101-0]

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Advances in Modeling Critical Heat Flux in LWR Boiling Flows With the NEK-2P CFD Code

Volume 8: Computational Fluid Dynamics (CFD); Nuclear Education and Public Acceptance ◽

10.1115/icone26-81910 ◽

2018 ◽

Author(s):

Adrian Tentner ◽

Prasad Vegendla ◽

Ananias Tomboulides ◽

Aleks Obabko ◽

Elia Merzari ◽

...

Keyword(s):

Heat Flux ◽

Critical Heat Flux ◽

Vertical Channel ◽

Nucleate Boiling ◽

Heated Wall ◽

Transfer Model ◽

Axial Distribution ◽

Two Phase ◽

Wide Range ◽

Boiling Flow

The paper focuses on the extension of the NEK-2P Wall Heat Transfer model, which was initially developed for the analysis of Critical Heat Flux (CHF) under Dryout (DO) conditions to the simulation of CHF under Departure from Nucleate Boiling (DNB) conditions. The paper presents results of recent NEK-2P analyses of several CHF experiments including both DO and DNB conditions. The CHF experiments analyzed have measured the axial distribution of wall temperatures in two-phase boiling flow in a vertical channel with a heated wall. The axial distribution of the calculated wall temperatures is compared with the corresponding experimental data. Reasonably good agreement with measured data is obtained in predicting the CHF location and post CHF wall temperature magnitudes illustrating the ability of the NEK-2P code and Extended Boiling Framework (EBF) models to simulate the CHF phenomena for a wide range of thermal-hydraulic conditions.

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Flow Boiling in Minichannels of Copper, Brass, and Aluminum Round Tubes

ASME 2nd International Conference on Microchannels and Minichannels ◽

10.1115/icmm2004-2381 ◽

2004 ◽

Cited By ~ 3

Author(s):

K. H. Bang ◽

W. H. Choo

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Mass Flux ◽

Boiling Heat Transfer ◽

Flow Boiling ◽

Nucleate Boiling ◽

Wall Heat Flux ◽

Vapor Quality ◽

Transfer Coefficients ◽

Flow Boiling Heat Transfer

The past work on flow boiling heat transfer in minichannels ranging one to three millimeters of hydraulic diameter has indicated that the local heat transfer coefficients are largely independent of mass flux and vapor quality, but mainly a function of wall heat flux. The present work is a revisit of flow boiling in minichannels by conducting experiment using 1.67 mm inner diameter tubes of three different materials; aluminum, brass, and copper, to investigate an effect of the tube inner surface conditions with the focus on an effect on nucleate boiling. Tests were conducted for R-22, a fixed mass flux of 600 kg/m2s, 5∼30 kW/m2 of wall heat flux, 0.0∼0.9 of local vapor quality. The present experimental data confirmed that the flow boiling heat transfer coefficient in a minichannel varies only by heat flux, independent of mass flux and vapor quality. The effect of tube material was found small for the tubes used in the present work. The present data were well predicted by the correlation proposed by Tran et al. (1996).

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Heat Transfer and Wall Heat Flux Partitioning During Subcooled Flow Nucleate Boiling—A Review

Journal of Heat Transfer ◽

10.1115/1.2349510 ◽

2006 ◽

Vol 128 (12) ◽

pp. 1243-1256 ◽

Cited By ~ 59

Author(s):

Gopinath R. Warrier ◽

Vijay K. Dhir

Keyword(s):

Heat Transfer ◽

Experimental Data ◽

Heat Flux ◽

Nucleate Boiling ◽

Wall Heat Flux ◽

Forced Flow ◽

Mechanistic Models ◽

Subcooled Flow ◽

Flux Partitioning ◽

Empirical And Mechanistic Models

In this paper we provide a review of heat transfer and wall heat flux partitioning models/correlations applicable to subcooled forced flow nucleate boiling. Details of both empirical and mechanistic models that have been proposed in the literature are provided. A comparison of the experimental data with predictions from selected models is also included.

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Computational fluid dynamics and population balance modelling of nucleate boiling of cryogenic liquids: Theoretical developments

The Journal of Computational Multiphase Flows ◽

10.1177/1757482x16674217 ◽

2016 ◽

Vol 8 (4) ◽

pp. 178-200 ◽

Cited By ~ 2

Author(s):

Guan Heng Yeoh ◽

Xiaobin Zhang

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Nucleate Boiling ◽

Nucleation Site ◽

Heat Transfer Process ◽

Wall Heat Flux ◽

Heated Wall ◽

Balance Model ◽

Bulk Liquid ◽

Two Phase

The main focus in the analysis of pool or flow boiling in saturated or subcooled conditions is the basic understanding of the phase change process through the heat transfer and wall heat flux partitioning at the heated wall and the two-phase bubble behaviours in the bulk liquid as they migrate away from the heated wall. This paper reviews the work in this rapid developing area with special reference to modelling nucleate boiling of cryogenic liquids in the context of computational fluid dynamics and associated theoretical developments. The partitioning of the wall heat flux at the heated wall into three components – single-phase convection, transient conduction and evaporation – remains the most popular mechanistic approach in predicting the heat transfer process during boiling. Nevertheless, the respective wall heat flux components generally require the determination of the active nucleation site density, bubble departure diameter and nucleation frequency, which are crucial to the proper prediction of the heat transfer process. Numerous empirical correlations presented in this paper have been developed to ascertain these three important parameters with some degree of success. Albeit the simplicity of empirical correlations, they remain applicable to only a narrow range of flow conditions. In order to extend the wall heat flux partitioning approach to a wider range of flow conditions, the fractal model proposed for the active nucleation site density, force balance model for bubble departing from the cavity and bubble lifting off from the heated wall and evaluation of nucleation frequency based on fundamental theory depict the many enhancements that can improve the mechanistic model predictions. The macroscopic consideration of the two-phase boiling in the bulk liquid via the two-fluid model represents the most effective continuum approach in predicting the volume fraction and velocity distributions of each phase. Nevertheless, the interfacial mass, momentum and energy exchange terms that appear in the transport equations generally require the determination of the Sauter mean diameter or interfacial area concentration, which strongly governs the fluid flow and heat transfer in the bulk liquid. In order to accommodate the dynamically changing bubble sizes that are prevalent in the bulk liquid, the mechanistic approach based on the population balance model allows the appropriate prediction of local distributions of Sauter mean diameter or interfacial area concentration, which in turn can improve the predictions of the interfacial mass, momentum and energy exchanges that occur across the interface between the phases. Need for further developments are discussed.

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Wall Heat Flux Partitioning During Subcooled Flow Boiling at Low Pressures

Heat Transfer: Volume 2 ◽

10.1115/ht2003-47156 ◽

2003 ◽

Cited By ~ 11

Author(s):

Nilanjana Basu ◽

Gopinath R. Warrier ◽

Vijay K. Dhir

Keyword(s):

Heat Flux ◽

Flow Boiling ◽

Nucleate Boiling ◽

Wall Heat Flux ◽

Superheated Liquid ◽

Pressure Data ◽

Vapor Generation ◽

Subcooled Flow Boiling ◽

Wall Superheat ◽

Subcooled Flow

In this work a mechanistic model for nucleate boiling heat flux as a function of wall superheat has been developed. The premise of the proposed model is that the entire energy from the wall is first transferred to the superheated liquid layer adjacent to the wall. A fraction of this energy is then utilized for vapor generation. Contribution of each of the heat transfer mechanisms — forced convection, transient conduction, and vapor generation, has been quantified in terms of nucleation site densities, bubble departure and lift off diameters, bubble release frequency, flow parameters like velocity, inlet subcooling, wall superheat, and fluid and surface properties including system pressures. To support the model development, subcooled flow boiling experiments were conducted at pressures of 1.03 to 3.2 bar for a wide range of mass fluxes (124 to 926 kg/m2s), heat fluxes (2.5 to 90 W/cm2) and for contact angles varying from 30° to 90°. Model validation has been carried out with low-pressure data obtained from present work and the wall heat flux predictions are within ± 30% of experimental values. Application of the model to high-pressure data available in literature also showed good agreement, signifying that the model can be extended to all pressures.

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