Subcooled Boiling Research Articles

Investigation of Wall Boiling Closure, Momentum Closure and Population Balance Models for Refrigerant Gas–Liquid Subcooled Boiling Flow in a Vertical Pipe Using a Two-Fluid Eulerian CFD Model

The precise design of heat exchangers in automobile air conditioning systems for more sustainable electric vehicles requires an enhanced assessment of CFD mechanistic models for the subcooled boiling flow of pure eco-friendly refrigerant. Computational Multiphase Flow Dynamics (CMFDs) relies on two-phase closure models to accurately depict the complex physical phenomena involved in flow boiling. This paper thoroughly examines two-phase CMFD flow boiling, incorporating sensitivity analyses of critical parameters such as boiling closures, momentum closures, and population balance models. Three datasets from the DEBORA experiment, involving vertical pipes with subcooled boiling flow of refrigerant at three different pressures and varying levels of inlet liquid subcooling, are used for comparison with CFD simulations. This study integrates nucleate site density and bubble departure diameter models to enhance wall boiling model accuracy. It aims to investigate various interfacial forces and examines the S-Gamma and Adaptive Multiple Size-Group (A-MuSiG) size distribution methods for their roles in bubble break up and coalescence. These proposed approaches demonstrate their efficacy, contributing to a deeper understanding of flow boiling phenomena and the development of more accurate models. This investigation offers valuable insights into selecting the most appropriate sub-closure models for both boiling closure and momentum closure in simulating boiling flows.

Numerical Study on Subcooled Boiling Flow and Heat Transfer Characteristics in Helical Cruciform Fuel Assembly

The helical cruciform fuel rod is a new fuel design. Its advantages include a large surface area–to-volume ratio, short thermal conductivity distance, and no need for grid spacers. This new fuel rod can effectively improve the hydraulic performance of nuclear reactors. To study the performance of the helical cruciform fuel assembly, the subcooled boiling flow and heat transfer characteristics of this assembly are analyzed in the present work based on computational fluid dynamics. The results indicate that the temperature distribution of the central rod wall surface in the circumferential direction has inhomogeneity and periodicity. The fluid’s temperature and velocity distribution in the cross section are high in the center and low elsewhere, and the fuel rod’s torsional orientation is compatible with the velocity vector’s direction. The vapor volume fraction on the wall of the center rod of the fuel assembly is the highest, and the vapor volume fraction in the mainstream area is relatively low. This work provides a reference for further research on helical cruciform fuel assemblies in the thermal analysis of nuclear reactors.

NUMERICAL STUDY OF THE EFFECT OF TUBE WALL ON SUBCOOLED BOILING AT THE END OF A LASER WAVEGUIDE

Results of numerical simulations of the laser-induced boiling at the end of a waveguide placed inside the tube are presented. The effect of the tube wall on the vapor bubble evolution and characteristics of the cumulative jet forming as a result of its collapse was studied. Particularly, it was found that while the tubes of large radii insignificantly affect the velocity of the cumulative liquid jet, in the relatively narrow tubes the jet may not form at all. The effect of the tubes of moderate radii comes down to the decrease of the jet velocity compared to the case without the tube. A possible physical explanation of such influence of tube walls is proposed. Numerical results on laser-induced boiling inside the tubes are summarized in the regime diagram in the tube radius-waveguide radius plane.

Further Study and Development of Correlations for Heat Transfer during Subcooled Boiling in Plain Channels

The author’s published correlations for subcooled boiling in channels are further studied and developed in this work. The areas explored include choice of equivalent diameters for annuli and partially heated channels, effects of flow direction, micro-gravity, and orientation of heated surface. A new correlation is developed, which is a modification of the author’s earlier correlation. The author’s previous correlations and the new correlation are compared with a very wide range of test data for round tubes, rectangular channels, and annuli. Several other correlations are also compared with the same data. The authors’ correlations provide good agreement with data, the new correlation giving the least deviation. The data included hydraulic diameters from 0.176 to 22.8 mm, reduced pressure from 0.0046 to 0.922, subcooling from 0 to 165 K, mass flux from 59 to 31,500 kgm−2s−1, all flow directions, and terrestial to micro gravity. The new correlation has mean absolute deviation (MAD) of 13.3% with 2270 data points from 49 sources. Correlations by others had MAD of 18% to 116%. The results are presented and discussed.

Bubble Sliding Characteristics and Dynamics of R134a during Subcooled Boiling Flow in a Narrow Gap

The numerical method was used to study bubble sliding characteristics and dynamics of R134a during subcooled flow boiling in a narrow gap. In the numerical method, the volume of fraction (VOF) model, level set method, Lee phase change model and the SST k − ω turbulent model were adopted for the construction of the subcooled flow boiling model. In order to explore bubble sliding dynamics during subcooled flow boiling, the bubble sliding model was introduced. The bubble velocity, bubble departure diameter, sliding distance and bubble sliding dynamics were investigated at 0.2 to 5 m/s inlet velocities. The simulation results showed that the bubble velocity at the flow direction was the most important contribution to bubble velocity. Additionally, the bubble velocity of 12 bubbles mostly oscillated with time during the sliding process at 0.2 to 0.6 m/s inlet velocities, while the bubble velocity increased during the sliding process due to the bubble having had a certain inertia at 2 to 5 m/s inlet velocities. It was also found that the average bubble velocity in flow direction accounted for about 80% of the mainstream velocities at 0.2 to 5 m/s. In the investigation of bubble sliding distance and departure diameter, it was concluded that the ratio of the maximum sliding distance to the minimum sliding distance was close to two at inlet velocities of 0.3 to 5 m/s. Moreover, with increasing inlet velocity, the average sliding distance increased significantly. The average bubble departure diameter obviously increased from 0.2 to 0.5 m/s inlet velocity and greatly reduced after 0.6 m/s. Finally, the investigations of the bubble sliding dynamics showed that the surface tension dominated the bubble sliding process at 0.2 to 0.6 m/s inlet velocities. However, the drag force dominated the bubble sliding process at 2 to 5 m/s inlet velocities.

Performance Comparison of ANN-Based Model and Empirical Correlations for Void Fraction Prediction of Subcooled Boiling Flow in Vertical Upward Channel

The accurate prediction of void fraction parameter in subcooled boiling flow is very important for nuclear safety since it has significant influences on the mass flow rate, the onset of two-phase flow instability, and the heat transfer characteristics in a nuclear reactor core. Many different models and empirical correlations have been established over a variety of input conditions; however, this classical approach could lead to unsatisfactory prediction due to the uncertainties of model parameter and model forms. To cope with these limitations, Artificial Neural Network (ANN) is a powerful machine learning tool for modeling and solving non-linear and complicated physical problems. Therefore, this work is aim at developing an ANN-based model to predict the local void fraction of subcooled boiling flows. The comparison results of the performance between the ANN-based model and empirical correlations for the void fraction prediction of subcooled boiling in vertical upward channel showed the potential use of ANN-based model in the Computational Fluid Dynamics (CFD) codes to accurately simulate the subcooled boiling phenomena.

Visualization Experiment of Subcooled Boiling in Rectangular Channel

Visualization Experiment of Subcooled Boiling in Rectangular Channel

Mechanism study of the Full-cycle Growth process based on Bubbles Thermodynamics in Low-pressure Subcooled Boiling Condition

Mechanism study of the Full-cycle Growth process based on Bubbles Thermodynamics in Low-pressure Subcooled Boiling Condition

Development of FEM Calculation Methods to Analyse Subcooled Boiling Heat Transfer in Minichannels Based on Experimental Results

Even though two-phase heat transfer of refrigerants in minichannel heat sinks has been studied extensively, there is still a demand for improvements in overall thermal performance of miniature heat transfer exchangers. Experimental investigation and sophisticated heat transfer calculations with respect to heat transfer devices are still needed. In this work, a time-dependent experimental study of subcooled boiling was carried out for FC-72 flow in a heat sink, comprising of five asymmetrically heated minichannels. The heater surface temperature was continuously monitored by an infrared camera. The boiling heat transfer characteristics were investigated and the effect of the mass flow rate on the heat transfer coefficient was studied. In order to solve the heat transfer problem related to time-dependent flow boiling, two numerical methods, based on the FEM were applied, and based on the Trefftz functions (FEMT) and using the ADINA program. The results achieved with these two calculation methods were explored with an emphasis on the impact of the mass flow rate (range from 5 to 55 kg/h) on the resulting heat transfer coefficient. It was found that, with increasing mass flow, the heat transfer coefficient increased. Good agreement was found between the heat transfer coefficients, determined according to two numerical methods and the simple 1D calculation method.

Numerical Simulation of Subcooled Boiling in Swing Rectangular Channel based on Non-Equilibrium Thermal Model

Theoretical analysis on the fluid flow in a vertical rectangular channel under swing motion is performed to establish the mathematical model which is based on Eulerian two-fluid framework and non-equilibrium subcooled boiling model. It is analyzed that the flow and heat transfer characteristics and the force of the fluid under the condition of forced flow and swing motion condition. The results show that, for the existence of Coriolis force, the period of acceleration of the fluid is 1/2 of the period of swing angle, and the phase differ. In the rectangular channel, the angle of pressure isoline and horizontal line is sinusoidal likely, which is behind the swing angle phase; Due to the influence of the periodic force field, with the increase of the swing angle, the bubbles in the rectangular channel move to one side, and the wall temperature also increases, which leads to the deterioration of heat transfer; In a swing period, the vapor volume fraction at the outlet and the pressure drop between the inlet and outlet of the rectangular channel fluctuate, and the vapor volume fraction is located at the minimum pressure drop, and the vapor volume fraction at the outlet fluctuates in a trough type.

Prediction of Critical Heat Flux for Subcooled Flow Boiling in Annulus and Transient Surface Temperature Change at CHF

The ability to predict critical heat flux (CHF) is of considerable interest for high-heat equipment, including nuclear reactors. CHF prediction from a mechanistic model for subcooled flow boiling in rod bundles still remains unsolved. In this paper, we try to predict the CHF in an annulus, which is the most basic flow geometry simplified from a fuel bundle, using a liquid sublayer dryout model. The prediction is validated with both water and R113 data, showing an accuracy within ±30%. After the CHF in an annulus is calculated successfully, a near-wall vapor–liquid structure is proposed on the basis of the liquid sublayer dryout model. Modeling of heat transfer modes over the heating surface at CHF is performed, and predictions of the changes in liquid sublayer thickness and heater surface temperature at the CHF occurrence point are carried out by solving the heat conduction equation in cylindrical coordinates with a convective boundary condition, which changes with the change in flow pattern over the heating surface. Transient changes in the liquid sublayer thickness and surface temperature at the CHF occurrence point are reported.

Comparison of Intergroup Mass Transfer Coefficient Correlations in Two-Group IATE for Subcooled Boiling Flow

The interfacial area concentration (IAC) is of vital importance in determining the interfacial transfer terms of mass, momentum, and energy between phases in the two-fluid model. The two-group (2-G) interfacial area transport equation (IATE) dynamically models the IAC evolution of large and small bubbles, and the intergroup transfer bookkeeps the mass transferring between two groups. Different intergroup mass transfer coefficient correlations are employed in the 2-G IATE model, which include one old correlation and three new correlations previously developed by the authors. The two-group IATE is benchmarked with subcooled boiling experimental dataset. The group-1 interfacial area concentration results show that the three modified correlations improve the physically incorrect prediction by the old correlation. With the modified correlations, the 2-G IATE is foundationally capable of predicting the group-1 interfacial area concentration in subcooled boiling flow.

Prediction of Sliding Bubble Coalescence Rate During Subcooled Flow Boiling in Narrow Rectangular Channel

Prediction of Sliding Bubble Coalescence Rate During Subcooled Flow Boiling in Narrow Rectangular Channel

Experimental Investigation of Local Two-Phase Parameters in a 4 × 4 Rod Bundle Channel Under a Subcooled Boiling Flow

Experimental Investigation of Local Two-Phase Parameters in a 4 × 4 Rod Bundle Channel Under a Subcooled Boiling Flow

Verification of Pressure Loss Evaluation Method for High Temperature and High Pressure Evaporator Tubes Including Subcooled Boiling Region

Verification of Pressure Loss Evaluation Method for High Temperature and High Pressure Evaporator Tubes Including Subcooled Boiling Region

Effect of Different Blister Positions on Void Fraction Distribution Under Subcooled Boiling Conditions in Narrow Rectangular Channel

Effect of Different Blister Positions on Void Fraction Distribution Under Subcooled Boiling Conditions in Narrow Rectangular Channel

Numerical Simulation of Subcooled Boiling Considering Bubble Sliding Behavior in Conventional Channels

Numerical Simulation of Subcooled Boiling Considering Bubble Sliding Behavior in Conventional Channels

Bubble Parameters in an Inclined Rectangular Channel with Downward-Facing Heated Wall Under the Subcooled Boiling Flow Condition

Bubble Parameters in an Inclined Rectangular Channel with Downward-Facing Heated Wall Under the Subcooled Boiling Flow Condition

Evaluation on Coupling of Wall Boiling and Population Balance Models for Vertical Gas-Liquid Subcooled Boiling Flow of First Loop of Nuclear Power Plant

An accurate prediction of the interphase behaviors of the vertical gas-liquid subcooled boiling flow is meaningful for the first loop of a nuclear power plant (NPP). Therefore, the interphase behaviors including the bubble size distribution in the first loop of the NPP are analyzed, evaluated, and validated using various wall boiling models coupled with the population balance model (PBM) kernels in this paper. Firstly, nondimensional numbers of the first loop of the NPP and DEBORA (Development of Borehole Seals for High-Level Radioactive Waste) experiment test cases are analyzed with approximation. Secondly, five active nucleation site density models Nn coupled with the PBM kernel combination, four kernel combinations (C1~C4) with the Nn models are calculated and analyzed. Lastly, various behaviors including the bubble size distribution Sauter mean diameter (SMD) dp, void fraction α, gas superficial velocity jg, and liquid superficial velocity jl are compared and validated with the experimental data of the DEBORA-1 (P = 2.62 MPa). The results indicate that the two Nn models are suitable for the calculations of thefirst loop of the nuclear power plant. For instance, for the bubble size distribution SMD dp, the specified Nn model with C1 (maximum relative error 9.63%) has relatively better behaviors for the first loop of the NPP. Especially, the combination C1 is applicable for the calculation of the bubble size distribution dp, void fraction α and liquid superficial velocity jl while C4 is suitable for the calculation of the gas superficial velocity jg. These results can provide guidance for the numerical computation of the subcooled boiling flow in the first loop of the NPP.

Application of Artificial Neural Network for Prediction of Local Void Fraction in Vertical Subcooled Boiling Flow

This paper presents the feasibility study of potential application of multi-layer feed-forward Artificial Neural Networks (ANN) to predict local void fraction of subcooled boiling flows in vertical upward annular channel. A total of 638 experimental data points performed at KAERI and reported in literature was selected for training and testing ANN model. The seven basic parameters are chosen to be input variables and then the optimal structure of ANN which consist of two hidden layers with 131 neurons was determined based on traditional Trial-and-Error method after balancing the trade-off between the performance and training time. Results showed that the ANN model is capable to accurately predict the local void fraction with R2 value of 0.99931 for training data, R2 value of 0.99483 for testing data and R2 value of 0.99828 for all data. Also, it proved that the ANN training will be more effective with an extensive experimental database.