Two-Phase Critical Flow under Diabatic Conditions

1969 ◽  
Vol 184 (3) ◽  
pp. 127-133
Author(s):  
A. E. Bergles ◽  
J. T. Kelly
Keyword(s):  
Experimental Investigation ◽  
Equilibrium Model ◽  
Small Diameter ◽  
Critical Flow ◽  
Subcooled Boiling ◽  
Flow Conditions ◽  
Two Phase ◽  
Wide Range ◽  
Good Agreement ◽  
Non Equilibrium

This paper summarizes an experimental investigation of steam-water critical flow in heated tubes. A wide range of data was taken for water at pressures below 100 lbf/in2 (abs.) in tubes of small diameter. It is demonstrated that critical flow conditions can occur in subcooled boiling at low exit subcoolings. At equilibrium qualities below about 0·04, the data differ significantly from adiabatic data for a similar exit geometry. The deviations can be explained in terms of the additional non-equilibrium effects present in heated flows. For higher qualities, the diabatic data are in good agreement with adiabatic data, and can be approximately predicted by a slip equilibrium model.

Analysis of two phase critical flow with a non-equilibrium model

2021 ◽  
Vol 372 ◽  
pp. 110998
Author(s):  
Hong Xu ◽  
Aurelian Florin Badea ◽  
Xu Cheng
Keyword(s):  
Equilibrium Model ◽  
Critical Flow ◽  
Two Phase ◽  
Non Equilibrium

A Choking Model With Thermal Non-Equilibrium for Initially Subcooled Water

2018 ◽  
Author(s):  
Lv Yufeng ◽  
Zhao Minfu ◽  
Li Weiqing
Keyword(s):  
Bubbly Flow ◽  
Flow Regimes ◽  
Critical Flow ◽  
Vapor Bubbles ◽  
Two Phase ◽  
Subcooled Water ◽  
Wide Range ◽  
Frictional Forces ◽  
Flow Closure ◽  
Non Equilibrium

Mechanical non-homogeneous and thermal non-equilibrium phenomenon exists in two-phase critical flow compared with single phase flow. A one-dimensional two-fluid critical flow model is developed for initially subcooled water flowing in pipe or orifices. The model accounts for thermal nonequilibrium between the liquid and vapor bubbles and for interphase relative motion. In this model, an improved correlation to calculate flashing inception location and surperheat is proposed. The model consists of six conservation equations as well as a seventh equation representing bubble growth in bubbly flow. Closure of the set of governing equations is performed with constitutive relationships which determine the interfacial momentum terms due to mass exchange, wall to liquid and wall to vapour frictional forces, liquid to gas interfacial force and interfacial heat transfer rate. The model considers the development of three flow regimes, namely, bubbly, churn and annular flow regimes. Model predictions compare favorably with experimental data over a wide range of pressures and pipe diameters and lengths.

Two-Phase Critical Flow Simulations by Using a New Non-Equilibrium Model and a Modified Equilibrium Model

2010 ◽  
Author(s):  
Moon-Sun Chung ◽  
Sung-Jae Yi ◽  
Keun-Shik Chang
Keyword(s):  
Phase Change ◽  
Equilibrium Model ◽  
Phase Changes ◽  
Critical Flow ◽  
Vapor Generation ◽  
Two Phase ◽  
Subcooled Liquid ◽  
Equilibrium Parameter ◽  
Phase Mixture ◽  
Non Equilibrium

An accurate prediction of a critical flow discharged from a pressurized pipe system is of most importance in such a safety analysis of nuclear power plants, since it provides the transient boundary conditions during the depressurization transients initiated by a pipe break in primary or secondary systems and during the over-pressurization transients resulting in a relief of coolant through valves. Mass and energy discharge through the opening of pressure boundary affects the system thermal hydraulic responses, that is, phase changes and flow distribution in the system, and the mass inventory remaining in the system necessary to remove core decay heat of a nuclear reactor. Therefore, the safety significance relating to the critical flow led to a development of various empirical and mechanistic critical flow models. However, the accuracies of these models are still in question especially during two-phase critical flow condition. A good example of that is a homogeneous equilibrium model (HEM). The HEM is the basis of several system codes, such as early versions of RELAP, for nuclear loss-of-coolant accident (LOCA). The major non-equilibrium phenomena that are ignored in the HEM are vapor bubble nucleation and interface heat, mass, and momentum transfer. Henry-Fauske empirically handled non-equilibrium vapor generation by introducing a non-equilibrium parameter that allows only a fraction of the equilibrium vapor generation to occur. This approach boils down in essence to a correlation of the deviation between the measured flow rate and the prediction from the HEM: The details of the flow path do not have to be worked out and only needs to know the upstream conditions. However, if we treat non-equilibrium phenomena with this model, it requires an empirical database of the non-equilibrium parameters or their correlations that are so far unknown. Further, because the coefficients are not applied separately to the subcooled liquid and two-phase mixture, we have not been able to treat the non-equilibrium phenomena with the phase change properly. For this reason, we propose the non-equilibrium parameters for subcooled liquid and two-phase mixture, respectively, and then we adopt their combinations according to the flow conditions through the phase change process using the RELAP5/MOD3 code. In addition, we discuss the assessment results of Marviken LBLOCA tests using these non-equilibrium parameter sets with those from the non-equilibrium model by Trapp-Ransom and Chung et al.

Two-Phase, Two-Component Critical Flow in a Venturi

1972 ◽  
Vol 94 (1) ◽  
pp. 147-151 ◽  
Author(s):  
R. V. Smith
Keyword(s):  
Gas Phase ◽  
Gas Flow ◽  
Critical Flow ◽  
Flow Conditions ◽  
Transfer Coefficients ◽  
Two Phase ◽  
One Dimensional ◽  
Flow Equations ◽  
Heat Transfer Coefficients ◽  
Wide Range

This paper reports the results of an analytical and experimental investigation whose object was to test the hypothesis that the flow of the gas phase controls critical and near critical two-phase flow for cases where the gas flow is essentially in separate streams. The results substantiate the hypothesis. The analytical results also indicate that one dimensional flow equations with reasonably accurate estimates for the droplet size and for the drag and heat transfer coefficients will adequately describe critical and near critical flow over a wide range of flow conditions.

On the Analysis of Critical Flow Discharged From a Pressurized Pipe System Using a HEM

2009 ◽  
Author(s):  
Moon-Sun Chung ◽  
Sung-Jae Lee
Keyword(s):  
Phase Change ◽  
Equilibrium Model ◽  
Critical Flow ◽  
Vapor Generation ◽  
Two Phase ◽  
Subcooled Liquid ◽  
Pipe System ◽  
Equilibrium Parameter ◽  
Phase Mixture ◽  
Non Equilibrium

An accurate prediction of a critical flow discharged from a pressurized pipe system is of most importance in such a safety analysis of nuclear power plants, since it provides the transient boundary conditions during the depressurization transients initiated by a pipe break in primary or secondary systems and during the over-pressurization transients resulting in a relief of coolant through valves. Mass and energy discharge through the opening of pressure boundary affects the system thermal hydraulic responses, that is, phase changes and flow distribution in the system, and the mass inventory remaining in the system necessary to remove core decay heat of a nuclear reactor. Therefore, the safety significance relating to the critical flow led to a development of various empirical and mechanistic critical flow models. However, the accuracies of these models are still in question especially during two-phase critical flow condition. A good example of that is a homogeneous equilibrium model (HEM). The HEM is the basis of several system codes, such as early versions of RELAP, for nuclear loss-of-coolant accident (LOCA). The major non-equilibrium phenomena that are ignored in the HEM are vapor bubble nucleation and interface heat, mass, and momentum transfer. Henry & Fauske empirically handled non-equilibrium vapor generation by introducing a non-equilibrium parameter that allows only a fraction of the equilibrium vapor generation to occur. This approach boils down in essence to a correlation of the deviation between the measured flow rate and the prediction from the HEM: The details of the flow path do not have to be worked out and only needs to know the upstream conditions. However, if we treat non-equilibrium phenomena with this model, it requires an empirical database of the non-equilibrium parameters or their correlations that are so far unknown. Further, because the coefficients have not been applied separately to the subcooled liquid and two-phase mixture, we have not been able to treat the non-equilibrium phenomena with the phase change properly. For this reason, we propose the non-equilibrium parameters for subcooled liquid and two-phase mixture, respectively, and then we adopt their combinations according to the flow conditions through the phase change process using the RELAP5/MOD3 code. In addition, we discuss the assessment results of Marviken LBLOCA tests using these non-equilibrium parameter sets with those from the non-equilibrium model by Trapp & Ransom and Chung et al.

Experimental Measurements and CFD Evaluation of the Onset Flow Boiling at Low Pressure and High Subcooling Flow of R-11 Within Vertical Annulus

2014 ◽  
Author(s):  
Y. Bouaichaoui ◽  
R. Kibboua ◽  
M. Matkovič
Keyword(s):  
Heat Flux ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Fluid Model ◽  
Computer Code ◽  
Computational Method ◽  
Subcooled Boiling ◽  
Two Phase ◽  
Local Flow ◽  
Wide Range

The knowledge of the onset of subcooled boiling in forced convective flow at high liquid velocity and subcooling is of importance in thermal hydraulic studies. Measurements were performed under various conditions of mass flux, heat flux, and inlet subcooling, which enabled to study the influence of different boundary conditions on the development of local flow parameters. Also, some measurements have been compared to the predictions by the three-dimensional two-fluid model of subcooled boiling flow carried out with the computer code ANSYS-CFX-13. A computational method based on theoretical studies of steady state two phase forced convection along a test section loop was released. The calculation model covers a wide range of two phase flow conditions. It predicts the heat transfer rates and transitions points such as the Onset of Critical Heat Flux.

Investigation of the Influence of Elevated Pressure on Subcooled Boiling Flow—Model Evaluation Toward Generic Approach

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Sara Vahaji ◽  
Sherman Chi Pok Cheung ◽  
Guan Heng Yeoh ◽  
Jiyuan Tu
Keyword(s):  
Mechanistic Model ◽  
Elevated Pressure ◽  
Nucleation Site ◽  
Empirical Models ◽  
Mechanistic Modeling ◽  
Force Balance ◽  
Balance Model ◽  
Subcooled Boiling ◽  
Flow Conditions ◽  
Wide Range

Modeling subcooled boiling flows in vertical channels has relied heavily on the utilization of empirical correlations for the active nucleation site density, bubble departure diameter, and bubble departure frequency. Following the development and application of mechanistic modeling at low pressures, the capability of the model to resolve flow conditions at elevated pressure up to 10 bar is thoroughly assessed and compared with selected empirical models. Predictions of the mechanistic and selected empirical models are validated against two experimental data at low to elevated pressures. The results demonstrate that the mechanistic model is capable of predicting the heat and mass transfer processes. In spite of some drawbacks of the currently adopted force balance model, the results still point to the great potential of the mechanistic model to predict a wide range of flow conditions in subcooled boiling flows.

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