scholarly journals CFD investigation of sub-cooled boiling flow using a mechanistic wall heat partitioning approach with Wet-Steam properties

2018 ◽  
Vol 10 (4) ◽  
pp. 239-258 ◽  
Author(s):  
M Promtong ◽  
SCP Cheung ◽  
GH Yeoh ◽  
S Vahaji ◽  
J Tu
Keyword(s):  
Void Fraction ◽  
Flow Boiling ◽  
Force Balance ◽  
Heated Wall ◽  
Working Fluid ◽  
Group Model ◽  
Wet Steam ◽  
Bubble Interactions ◽  
Boiling Flow ◽  
Heat Partitioning

In this paper, the mechanistic wall heat partitioning approach was used to capture the complex heat and mass transfer in sub-cooled boiling flows. In order to accommodate the changes of local variables to be relevant to the physical properties of sub-cooled fluids, the Wet-Steam (IAPWS-IF97) is used as the working fluid. Currently, the approach is evaluated based on the bubble sliding along the wall before lifting-off, which is usually found in the flow boiling situations. In the simulation, the closure mechanistic models, including the fractal analysis, the force balance and the mechanistic frequency, were coupled with the Eulerian–Eulerian two-fluid framework, while the Shear Stress Transport model was used as a turbulent modelling closure. The Multiple Size Group model was introduced to handle the bubble interactions and predict the bubble size distribution. Moreover, the effect of adopting the sub-cooled liquid properties into the modelling was investigated and compared with the experiments over a wide range of flow conditions. Specifically, the predicted void fraction and the sub-cooling temperature near the heated wall were precisely compared with the cases of using the constant-property liquid. Overall, the satisfactory agreements were found between the experiments and the predictions of the liquid temperature, void fraction, interfacial area concentration, Sauter mean diameter and bubble and liquid velocities with the exception of the case of high heat and mass fluxes. To enhance the current prediction accuracy for a situation of having a high superheating temperature, more bubble interactions on the boiling wall, such as merging of the bubbles while sliding, need to be considered. Furthermore, to assess the model capability, this mechanistic approach will be introduced to elucidate the sub-cooled boiling flow in situations of using different fluids in the near future.

Visualization of FC-72 Flow Boiling in Parallel- and Counter-Flow Plate Heat Exchangers

2014 ◽  
Author(s):  
Kohei Koyama ◽  
Yuya Nakamura ◽  
Hirofumi Arima
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Flow Pattern ◽  
Void Fraction ◽  
Flow Boiling ◽  
Plate Heat Exchanger ◽  
Parallel Flow ◽  
Working Fluid ◽  
Counter Flow ◽  
Plate Heat

This study investigates FC-72 (Perfluorohexane) flow boiling in a plate heat exchanger. A plate heat exchanger which has a transparent cover plate is manufactured to visualize boiling two-phase flow pattern of the working fluid FC-72 heated by hot water. Titanium is used for heat transfer plate, which has micro pin-fin structure on the heat transfer surface to enhance heat transfer. Experiment is conducted for parallel- and counter-flow arrangements to compare thermal and hydraulic performances. Flow boiling is photographed by a digital camera and instantaneous images are processed to classify flow pattern and to measure void fraction in the heat exchanger. Flow rates and temperatures of FC-72 and hot water at inlet and outlet of the heat exchanger are simultaneously measured to obtain overall heat transfer coefficient. Two-phase flow pattern of FC-72 flow boiling and void fraction along flow direction as well as thermal performance are discussed. Experimental results show that bubbly flow, slug flow, and churn flow are observed for the experimental range of this study. Extent of churn flow in the parallel-flow heat exchanger is larger than that of the counter-flow one due to generated bubbles at upstream region in working fluid channel. Void fraction of the parallel-flow plate heat exchanger increases rapidly compared with that of the counter-flow one due to location of onset of nucleate boiling. Overall heat transfer coefficients for the parallel-flow arrangement is larger than that of the counter-flow due to destruction of thermal boundary layer. The experimental results show that flow arrangement of a plate heat exchanger has the potential to improve its thermal performance.

scholarly journals Simulation of Boiling Flow Experiments Close to CHF with the Neptune_CFD Code

2008 ◽  
Vol 2008 ◽  
pp. 1-8 ◽  
Author(s):  
Boštjan Končar ◽  
Borut Mavko
Keyword(s):  
Volume Fraction ◽  
Flow Boiling ◽  
Three Dimensional ◽  
Heated Wall ◽  
Wall Region ◽  
Two Phase ◽  
Subcooled Flow Boiling ◽  
Boiling Flow ◽  
Flow Experiments ◽  
Near Wall

A three-dimensional two-fluid code Neptune_CFD has been validated against the Arizona State University (ASU) and DEBORA boiling flow experiments. Two-phase flow processes in the subcooled flow boiling regime have been studied on ASU experiments. Within this scope a new wall function has been implemented in the Neptune_CFD code aiming to improve the prediction of flow parameters in the near-wall region. The capability of the code to predict the boiling flow regime close to critical heat flux (CHF) conditions has been verified on selected DEBORA experiments. To predict the onset of CHF regime, a simplified model based on the near-wall values of gas volume fraction was used. The results have shown that the code is able to predict the wall temperature increase and the sharp void fraction peak near the heated wall, which are characteristic phenomena for CHF conditions.

A Mechanistic Model for Predicting Subcooled Boiling Flow

2003 ◽  
Author(s):  
G. H. Yeoh ◽  
J. Y. Tu
Keyword(s):  
Void Fraction ◽  
Liquid Velocity ◽  
Fluid Model ◽  
Mechanistic Model ◽  
Three Dimensional ◽  
Annular Channel ◽  
Heat Fluxes ◽  
Group Model ◽  
Subcooled Boiling ◽  
Boiling Flow

Population balance equations combined with a three-dimensional two-fluid model are employed to predict subcooled boiling flow at low pressure in a vertical annular channel. The MUSIG (MUltiple-SIze-Group) model implemented in CFX4.4 is extended to account for the wall nucleation and condensation in the subcooled boiling regime. Comparison of model predictions against local measurements is made for the void fraction, bubble Sauter diameter and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcoolings. Good agreement is achieved with the local radial void fraction, bubble Sauter diameter and liquid velocity profiles against measurements. However, significant weakness of the model is evidenced in the prediction of the vapor velocity. Work is in progress to circumvent the deficiency of the extended MUSIG model by the consideration of an algebraic slip model to account for bubble separation.

Subcooled Flow Boiling in a Rectangular Channel With Added Turbulence and Longitudinal Vortices

2012 ◽  
Author(s):  
Gregor Bloch ◽  
Christina Jochum ◽  
Tobias Schechtl ◽  
Thomas Sattelmayer
Keyword(s):  
Isotropic Turbulence ◽  
Flow Boiling ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Vertical Channel ◽  
Nucleate Boiling ◽  
Secondary Flows ◽  
Heated Wall ◽  
Working Fluid ◽  
Flow Velocities

Experiments are conducted to analyze the influence of turbulence and secondary flows on heat transfer and CHF in sub-cooled flow boiling. Inserts creating turbulence and stationary vortices are placed below a vertical channel with a heated wall and upward flow direction with flow velocities up to 1.2 m/s. The boiling chamber is of square shape with inner dimensions of 40 × 40 mm2. Boiling regimes range from onset of nucleate boiling up to fully developed film boiling. Influence of the inserts is measured for varying flow velocities and subcooling from 4 K to 27 K. Flow parameters are measured with Particle Image Velocimetry (PIV). A decay of nearly isotropic turbulence within only few diameters is observed, while stationary swirls exhibit longer penetration depths. Boiling experiments are conducted with unsteady heating with a low boiling hydrocarbon (dodekafluoromethylpentanone) as working fluid. Results from boiling experiments show a positive influence of the inserts on the boiling process, increasing with higher subcooling and flow velocities.

Some Measurements in Subcooled Flow Boiling of Refrigerant-113

1991 ◽  
Vol 113 (1) ◽  
pp. 216-223 ◽  
Author(s):  
A. Hasan ◽  
R. P. Roy ◽  
S. P. Kalra
Keyword(s):  
Flow Boiling ◽  
Fluid Model ◽  
Annular Channel ◽  
Heated Wall ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Boiling Flow ◽  
Phase Temperature ◽  
Two Fluid Model ◽  
Two Fluid

Measurements of local vapor phase residence time fraction, liquid phase temperature, and heated wall temperature were carried out in subcooled flow boiling of Refrigerant-113 through a vertical annular channel. Data are reported for two fluid mass velocities and two pressures over a range of wall heat flux. Estimates of typical vapor bubble size and velocity are given. Some comparisons with a one-dimensional two-fluid model of subcooled boiling flow are also presented.

CFD simulation of subcooled boiling flow in PWR 5 ⨯ 5 rod bundle

Kerntechnik ◽  
2021 ◽  
Vol 86 (1) ◽  
pp. 24-32
Author(s):  
B. Ren ◽  
Y. Dang ◽  
F. J. Gan ◽  
P. Yang
Keyword(s):  
Void Fraction ◽  
Cfd Simulation ◽  
Phase Distribution ◽  
Flow Boiling ◽  
Fluid Model ◽  
Three Dimensional ◽  
Spacer Grid ◽  
Pressurized Water ◽  
Rod Bundle ◽  
Boiling Flow

Abstract This paper describes the computational fluid dynamics (CFD) methodology to simulate the boiling flow in a typical Pressurized Water Reactor (PWR) 5 ⨯ 5 rod bundle. The method includes the Eulerian-Eulerian two-fluid model coupled with the improved wall heat partitioning model. The NUPEC PWR Subchannel and Bundle Test (PSBT) International Benchmark are used for validation. The simulated surface averaged void fraction agree well with the experimental data, which indicate the promising application of the present method for modeling the boiling flow in the fuel rod bundle. The main emphasis of current research has been given to the analysis of the phase distribution around and downstream the spacer grid, the effect of the spacer grid structure, including the mixing vanes, the springs and the dimples on the void fraction distribution is investigated. The findings can contribute to a better understanding of three dimensional flow boiling characteristics and can be used to assist in optimizing the spacer grid.

scholarly journals Predicting Critical Heat Flux With Multiphase CFD: 4 Years in the Making

2017 ◽  
Author(s):  
Emilio Baglietto ◽  
Etienne Demarly ◽  
Ravikishore Kommajosyula
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Heated Surface ◽  
Force Balance ◽  
Modeling Framework ◽  
Lift Off ◽  
Limiting Condition

Advancement in the experimental techniques have brought new insights into the microscale boiling phenomena, and provide the base for a new physical interpretation of flow boiling heat transfer. A new modeling framework in Computational Fluid Dynamics has been assembled at MIT, and aims at introducing all necessary mechanisms, and explicitly tracks: (1) the size and dynamics of the bubbles on the surface; (2) the amount of microlayer and dry area under each bubble; (3) the amount of surface area influenced by sliding bubbles; (4) the quenching of the boiling surface following a bubble departure and (5) the statistical bubble interaction on the surface. The preliminary assessment of the new framework is used to further extend the portability of the model through an improved formulation of the force balance models for bubble departure and lift-off. Starting from this improved representation at the wall, the work concentrates on the bubble dynamics and dry spot quantification on the heated surface, which governs the Critical Heat Flux (CHF) limit. A new proposition is brought forward, where Critical Heat Flux is a natural limiting condition for the heat flux partitioning on the boiling surface. The first principle based CHF is qualitatively demonstrated, and has the potential to deliver a radically new simulation technique to support the design of advanced heat transfer systems.

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