Prediction of Boiling and Critical Heat Flux Using an Eulerian Multiphase Boiling Model

2011 ◽  
Author(s):  
Huiying Li ◽  
Sergio A. Vasquez ◽  
Hemant Punekar ◽  
R. Muralikrishnan
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Wall Temperature ◽  
Volume Fraction ◽  
Turbulence Models ◽  
Nucleate Boiling ◽  
Model Parameters ◽  
Cross Sectional ◽  
Bulk Fluid ◽  
Good Agreement

The present paper concerns the development and validation of an Eulerian multiphase boiling model to predict boiling and critical heat flux within the general-purpose computational fluid dynamics (CFD) solver FLUENT. The governing equations solved are generalized phase continuity, momentum and energy equations. Turbulence effects are accounted for using mixture, dispersed or per-phase multiphase turbulence models. Wall boiling phenomena are modeled using the baseline mechanistic nucleate boiling model, developed in Rensselaer Polytechnic Institute (RPI). Modifications have been introduced to the quenching heat flux model to achieve mesh-independent solutions. The influences of boiling model parameters have also been systematically investigated. To model non-equilibrium boiling and critical heat flux, the PRI model is extended to the departure from nucleate boiling (DNB) by partitioning wall heat flux to both liquid and vapor phases and considering the existence of thin liquid wall film. Topological functions are introduced to consider the wall boiling regime transition from the nucleate boiling to critical heat flux (CHF), and the corresponding flow regime change from bubbly flows to mist flows. A range of sub-models are implemented to model the interfacial momentum, mass and heat transfer and turbulence-bubble interactions. To validate the Eulerian multiphase boiling model, it has been used to predict nucleating boiling and critical heat flux in a range of 2D and 3D boiling flows. The examples presented in the paper include: (1). Nucleate boiling of sub-cooled water in an upward heated pipe; (2) R113 liquid flows through a vertical annulus with internal heated walls; (3). 3D boiling flows in a rectangular-sectioned duct; and (4). Critical heat flux and post dryout in vertical pipes. The results demonstrate that the model is able to predict reasonably well the distributions of wall temperature, the bulk fluid sub-cooling temperature and cross-sectional averaged vapor volume fraction in the vertical pipe. The computed profiles of the vapor volume fraction, liquid temperature, and the liquid and vapor velocity profiles are generally in good agreement with available experiments in the 2D annular case. In the 3D rectangular duct, the cross-sectional averaged vapor volume fractions are well captured in all the ten cases under investigation. In the case of critical heat flux and post dryout, the model is also able to predict reasonably well the location and the temperature rise under critical heat flux conditions. The computed wall temperature distributions along the pipes are in overall good agreement with available experiments.

Prediction of critical heat flux in flow boiling process under the effect of different operating parameters

2020 ◽  
pp. 095765092096223
Author(s):  
Ehsan Abedini ◽  
Mohammad Behboudi ◽  
Arash Mohammadi Karachi ◽  
Reza Hamidi Jahromi ◽  
Kianoush DolatiAsl
Keyword(s):  
Heat Flux ◽  
Surface Roughness ◽  
Critical Heat Flux ◽  
Wall Temperature ◽  
Flow Boiling ◽  
Turbulence Models ◽  
Fluid Flows ◽  
Channel Length ◽  
Heated Wall ◽  
Boiling Process

In the present study numerical simulation of flow boiling process has been conducted for evaluation of critical heat flux conditions under the effect of different parameters (mass flux, heat flux, channel length and surface roughness). Comparison between the results of the present study and previous researches were done. The comparison shows a good agreement between the present study and previous researches. The three different turbulence models (k-epsilon, k-omega and Reynolds Stress) are considered for simulation of boiling heat transfer and CHF phenomenon. The highest accuracy of simulation is obtained by k-epsilon model. The results express that the wall temperature value of tube with adiabatic and heated boundary conditions for first and second half of the tube is lower than the wall temperature when the fluid flows only in the heated wall section. Reduction of velocity value also leads to reduction of maximum wall temperature value and CHF value. Decreasing Roughness value as an effective parameter leads to an increase in wall temperature. Maximum value of the wall temperature, after CHF point, also increases with increase in heat flux value. CHF depends on the surface roughness and rises with increasing roughness value.

Advanced Computational Modeling of Multiphase Boiling Flow and Heat Transfer

2010 ◽  
Author(s):  
Huiying Li ◽  
Sergio A. Vasquez ◽  
Peter Spicka
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Volume Fraction ◽  
Nucleate Boiling ◽  
General Purpose ◽  
Phase Changes ◽  
Pressurized Water ◽  
Flow And Heat Transfer ◽  
Boiling Flow

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.

Saturation Boiling Critical Heat Flux of PF-5060 Dielectric Liquid on Microporous Copper Surfaces

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Mohamed S. El-Genk ◽  
Amir F. Ali
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Inclination Angle ◽  
Nucleate Boiling ◽  
Dielectric Liquid ◽  
Copper Surfaces ◽  
Inclination Angles ◽  
Surface Inclination ◽  
Effect Of Surface ◽  
Good Agreement

Pool boiling experiments are performed to investigate potential enhancement of critical heat flux (CHF) of PF-5060 dielectric liquid on microporous copper (MPC) surfaces and the effect of surface inclination angle. The morphology and microstructure of the MPC surfaces change with thickness. The experiments tested seven 10 × 10 mm MPC surfaces with thicknesses from 80 to 230 μm at inclination angles of 0 deg (upward facing), 60 deg, 90 deg (vertical), 120 deg, 150 deg, 160 deg, 170 deg, and 180 deg (downward facing). CHF increases as the thickness of the surface increases and/or the inclination angle decreases. The values in the upward facing orientation are 36–59% higher than on smooth Cu. For all surfaces, CHF values in the downward facing orientation are approximately 28% of those in the upward facing orientation. A developed CHF correlation, similar to those of Zuber and Kutateladze, accounts for the effects of inclination angle and thickness of the MPC surfaces. It is in good agreement with experimental data to within ±8%. Still photographs of nucleate boiling on the MPC surfaces at different inclinations help the interpretation of the experimental results.

Boiling Heat Transfer and Critical Heat Flux Enhancement of Upward- and Downward-Facing Heater in Nanofluids

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Muhamad Zuhairi Sulaiman ◽  
Masahiro Takamura ◽  
Kazuki Nakahashi ◽  
Tomio Okawa
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Flux Enhancement ◽  
Optimum Configuration ◽  
Wall Superheat ◽  
Nucleate Boiling Heat Transfer

Boiling heat transfer (BHT) and critical heat flux (CHF) performance were experimentally studied for saturated pool boiling of water-based nanofluids. In present experimental works, copper heaters of 20 mm diameter with titanium-oxide (TiO2) nanocoated surface were produced in pool boiling of nanofluid. Experiments were performed in both upward and downward facing nanofluid coated heater surface. TiO2 nanoparticle was used with concentration ranging from 0.004 until 0.4 kg/m3 and boiling time of tb = 1, 3, 10, 20, 40, and 60 mins. Distilled water was used to observed BHT and CHF performance of different nanofluids boiling time and concentration configurations. Nucleate boiling heat transfer observed to deteriorate in upward facing heater, however; in contrast effect of enhancement for downward. Maximum enhancements of CHF for upward- and downward-facing heater are 2.1 and 1.9 times, respectively. Reduction of mean contact angle demonstrate enhancement on the critical heat flux for both upward-facing and downward-facing heater configuration. However, nucleate boiling heat transfer shows inconsistency in similar concentration with sequence of boiling time. For both downward- and upward-facing nanocoated heater's BHT and CHF, the optimum configuration denotes by C = 400 kg/m3 with tb = 1 min which shows the best increment of boiling curve trend with lowest wall superheat ΔT = 25 K and critical heat flux enhancement of 2.02 times.

Study on Subcooled-Forced Flow Boiling Heat Transfer and Critical Heat Flux of Solid-Water Two-Phase Mixture

1999 ◽  
Author(s):  
Yasuo Koizumi ◽  
Hiroyasu Ohtake ◽  
Manabu Mochizuki
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Liquid Layer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Forced Flow ◽  
Superheated Liquid ◽  
Flow Boiling Heat Transfer

Abstract The effect of solid particle introduction on subcooled-forced flow boiling heat transfer and a critical heat flux was examined experimentally. In the experiment, glass beads of 0.6 mm diameter were mixed in subcooled water. Experiments were conducted in a range of the subcooling of 40 K, a velocity of 0.17–6.7 m/s, a volumetric particle ratio of 0–17%. When particles were introduced, the growth of a superheated liquid layer near a heat trasnsfer surface seemed to be suppressed and the onset of nucleate boiling was delayed. The particles promoted the condensation of bubbles on the heat transfer surface, which shifted the initiation of a net vapor generation to a high heat flux region. Boiling heat trasnfer was augmented by the particle introduction. The suppression of the growth of the superheated liquid layer and the promotion of bubble condensation and dissipation by the particles seemed to contribute that heat transfer augmentation. The wall superheat at the critical heat flux was elevated by the particle introduction and the critical heat flux itself was also enhanced. However, the degree of the critical heat flux improvement was not drastic.

scholarly journals Determination of Pool Boiling Critical Heat Flux Enhancement in Nanofluids

2007 ◽  
Author(s):  
Bao H. Truong
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Porous Coating ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Sem Images ◽  
Heat Transfer Coefficients ◽  
Nucleate Boiling Heat Transfer

Nanofluids are engineered colloids composed of nano-size particles dispersed in common fluids such as water or refrigerants. Using an electrically controlled wire heater, pool boiling Critical Heat Flux (CHF) of Alumina and Silica water-based nanofluids of concentration less than or equal to 0.1 percent by volume were measured. Silica nanofluids showed a CHF enhancement up to 68% and there seems to be a monotonic relationship between the nanoparticle concentration and the magnitude of enhancement. Alumina nanofluids had a CHF enhancement up to 56% but the peak occurred at the intermediate concentration. The boiling curves in nanofluid were found to shift to the left of that of water and correspond to higher nucleate boiling heat transfer coefficients in the two-phase flow regime. Scanning Electron Microscopy (SEM) images show a porous coating layer of nanoparticles on wires subjected to nanofluid CHF tests. These coating layers change the morphology of the heater’s surface, and are responsible for the CHF enhancement. The thickness of the coating was estimated using SEM and was found ranging from 3.0 to 6.0 micrometers for Alumina, and 3.0 to 15.0 micrometers for Silica.

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