Modelling of the Near-Wall Liquid Velocity Field in Subcooled Boiling Flow

2005 ◽  
Author(s):  
Franz Ramstorfer ◽  
Bernd Breitscha¨del ◽  
Helfried Steiner ◽  
Gu¨nter Brenn
Keyword(s):  
Experimental Data ◽  
Surface Roughness ◽  
Flow Velocity ◽  
Liquid Flow ◽  
Axial Velocity ◽  
Velocity Profiles ◽  
Subcooled Boiling ◽  
Test Channel ◽  
Boiling Flow ◽  
Near Wall

The subject of the present work is the modelling of the liquid streamwise flow velocity in the two-phase boundary layer in subcooled boiling flow under the influence of the vapor bubbles. Subcooled boiling flow experiments were carried out in a horizontal test channel in order to investigate the interaction between the bubbles and the liquid phase. The heater surface was located at the bottom of the test channel. The near-wall liquid flow velocity was measured using a two-component laser-Doppler anemometer. Based on the experimental data a model is proposed to describe the impact of the gaseous phase on the motion of the liquid in the subcooled boiling regime. It was observed that the axial velocity profiles near the wall follow a logarithmic law similar to that used in turbulent single-phase flow over rough surfaces. Based on this finding it is suggested to model the influence of the bubbles on the liquid flow analogously to the effect of a surface roughness. The correlation developed for an equivalent surface roughness associated with the bubbles yields good agreement of the modeled axial velocity profiles with the experimental data.

Velocity and Temperature Profiles in Turbulent Boundary Layer Flows Experiencing Streamwise Pressure Gradients

1997 ◽  
Vol 119 (3) ◽  
pp. 433-439 ◽  
Author(s):  
R. J. Volino ◽  
T. W. Simon
Keyword(s):  
Experimental Data ◽  
Pressure Gradient ◽  
Velocity Profiles ◽  
Temperature Profiles ◽  
Pressure Gradients ◽  
Mean Velocity ◽  
Law Of The Wall ◽  
Prandtl Numbers ◽  
Energy Equations ◽  
Near Wall

The standard turbulent law of the wall, devised for zero pressure gradient flows, has been previously shown to be inadequate for accelerating and decelerating turbulent boundary layers. In this paper, formulations for mean velocity profiles from the literature are applied and formulations for the temperature profiles are developed using a mixing length model. These formulations capture the effects of pressure gradients by including the convective and pressure gradient terms in the momentum and energy equations. The profiles which include these terms deviate considerably from the standard law of the wall; the temperature profiles more so than the velocity profiles. The new profiles agree well with experimental data. By looking at the various terms separately, it is shown why the velocity law of the wall is more robust to streamwise pressure gradients than is the thermal law of the wall. The modification to the velocity profile is useful for evaluation of more accurate skin friction coefficients from experimental data by the near-wall fitting technique. The temperature profile modification improves the accuracy with which one may extract turbulent Prandtl numbers from near-wall mean temperature data when they cannot be determined directly.

Bubble Diameter Effects on CFD Simulation for Subcooled Boiling Flow in Rolling Circular Tube

2017 ◽  
Author(s):  
Sheng Xu ◽  
Liang-ming Pan ◽  
Yu Yang ◽  
Dewen Yuan ◽  
Jianjun Xu ◽  
...  
Keyword(s):  
Experimental Data ◽  
Void Fraction ◽  
Bubble Diameter ◽  
Low Pressure ◽  
Subcooled Boiling ◽  
Rolling Condition ◽  
Mean Diameter ◽  
Calculation Results ◽  
Boiling Flow ◽  
Fluctuation Amplitude

Eulerian two-fluid model coupled with wall boiling model was employed to calculate the three dimensional flow field and local parameter distribution with different bubble diameter models in circular tube under static and rolling condition. The wall boiling model utilized in this study was validated by Bartolomei experiment data, and a good agreement can be obtained. The calculation results of local void fraction are compared with experiment data to verify the accuracy of the numerical calculation for subcooled boiling flow under rolling condition. The Zeitoun bubble mean diameter model which the most recommended correlation for bubble diameter under low pressure and several fixed bubble diameters are applied to simulate the same condition in low pressure. These results are compared, include the distribution of void fraction, velocity distribution and radial flow induced by rolling motion. A good agreement with the experimental data has been achieved when Zeition bubble mean diameter and 2 mm fixed bubble diameter are used to describe vapor diameter in static condition. The local void fraction fluctuation has the same period with the rolling motion, and the fluctuation amplitude increases with the increase of rolling amplitude and rolling frequency. The difference shown in rolling condition between calculation results and experimental data demonstrates that better agreement with the experimental data has been achieved in the near-wall region about local void fraction which has bigger fluctuation amplitude. Higher void fraction has gotten using Zeition bubble mean diameter model to describe bubble diameter in subcooled boiling flow, tiny difference has showed in temperature, velocity and radial velocity in different bubble diameter model. Accurate vapor diameter model or method to describe vapor diameter coupled with suitable interphase force model is needed in rolling condition under low pressure to fit the calculation of subcooled boiling better under rolling condition.

Turbulent Subcooled Boiling Flow—Experiments and Simulations

2001 ◽  
Vol 124 (1) ◽  
pp. 73-93 ◽  
Author(s):  
R. P. Roy ◽  
S. Kang ◽  
J. A. Zarate ◽  
A. Laporta
Keyword(s):  
Prandtl Number ◽  
Axial Velocity ◽  
Liquid Velocity ◽  
Laser Doppler Velocimeter ◽  
Transfer Model ◽  
Turbulent Heat ◽  
Turbulent Prandtl Number ◽  
Subcooled Boiling ◽  
Dual Sensor ◽  
Boiling Flow

Experiments and simulations were carried out in this investigation of turbulent subcooled boiling flow of Refrigerant-113 through a vertical annular channel whose inner wall only was heated. The measurements used, simultaneously, a two-component laser Doppler velocimeter for the liquid velocity field and a fast-response cold-wire for the temperature field, and a dual-sensor fiberoptic probe for the vapor fraction and vapor axial velocity. In the numerical simulation, the two-fluid model equations were solved by the solver ASTRID developed at Electricite´ de France. Wall laws for the liquid phase time-average axial velocity and temperature were developed from the experimental data, and the turbulent Prandtl number in the liquid was determined from the wall laws. The wall laws and turbulent Prandtl number were used in the simulations. The wall heat transfer model utilized the measured turbulent heat flux distribution in the liquid. Results from the simulations were compared with the measurements. Good agreement was found for some of the quantities while the agreement was only fair for others.

Subcooled Boiling Flow Heat Transfer From Plain and Enhanced Surfaces in Automotive Applications

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Franz Ramstorfer ◽  
Helfried Steiner ◽  
Günter Brenn ◽  
Claudius Kormann ◽  
Franz Rammer
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Nucleate Boiling ◽  
Heated Wall ◽  
Transfer Model ◽  
Subcooled Boiling ◽  
Cooling Systems ◽  
Porous Coatings ◽  
Transfer Rates ◽  
Boiling Flow

The requirement for the highest possible heat transfer rates in compact, efficient cooling systems can often only be met by providing for a transition to subcooled boiling flow in strongly heated wall regions. The significantly higher heat transfer rates achievable with boiling can help keep the temperatures of the structure on an acceptable level. It has been shown in many experimental studies that special surface finish or porous coatings on the heated surfaces can intensify the nucleate boiling process markedly. Most of those experiments were carried out with water or refrigerants. The present work investigates the potential of this method to enhance the subcooled boiling heat transfer in automotive cooling systems using a mixture of ethylene-glycol and de-ionized water as the coolant. Subcooled boiling flow experiments were carried out in a vertical test channel considering two different types of coated surfaces and one uncoated surface as a reference. The experimental results of the present work clearly demonstrate that the concept of enhancing boiling by modifying the microstructure of the heated surface can be successfully applied to automotive cooling systems. The observed increase in the heat transfer rates differ markedly for the two considered porous coatings, though. Based on the experimental data, a heat transfer model for subcooled boiling flow using a power-additive superposition approach is proposed. The model assumes the total wall heat flux as a nonlinear combination of a convective and a nucleate boiling contribution, both obtained from well-established semiempirical correlations. The wall heat fluxes predicted by the proposed model are in very good agreement with the experimental data for all considered flow conditions and surface types.

Velocity Field in Turbulent Subcooled Boiling Flow

1997 ◽  
Vol 119 (4) ◽  
pp. 754-766 ◽  
Author(s):  
R. P. Roy ◽  
V. Velidandla ◽  
S. P. Kalra
Keyword(s):  
Shear Stress ◽  
Velocity Field ◽  
Liquid Flow ◽  
Single Phase ◽  
Laser Doppler Velocimeter ◽  
Subcooled Boiling ◽  
Boiling Flow ◽  
Phase Liquid ◽  
Single Phase Liquid Flow ◽  
Two Fluid

The velocity field was measured in turbulent subcooled boiling flow of Refrigerant-113 through a vertical annular channel whose inner wall was heated. A two-component laser Doppler velocimeter was used. Measurements are reported in the boiling layer adjacent to the inner wall as well as in the outer all-liquid layer for two fluid mass velocities and four wall heat fluxes. The turbulence was found to be inhomogeneous and anisotropic and the turbulent kinetic energy significantly higher than in single-phase liquid flow at the same mass velocity. A marked shift toward the inner wall was observed of the zero location of the axial Reynolds shear stress in the liquid phase, and the magnitude of the shear stress increased sharply close to the inner wall. The near-wall liquid velocity field was quite different from that in single-phase liquid flow at a similar Reynolds number. Comparison of the measurements with the predictions of a three-dimensional two-fluid model of turbulent subcooled boiling flow show reasonably good agreement for some quantities and a need for further development of certain aspects of the model.

Alternate Scales for Turbulent Boundary Layer on Transitional Rough Walls: Universal Log Laws

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Noor Afzal
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Surface Roughness ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Skin Friction ◽  
Velocity Profiles ◽  
Pressure Gradients ◽  
Wall Roughness ◽  
Extensive Experimental Data

The present work deals with four new alternate transitional surface roughness scales for description of the turbulent boundary layer. The nondimensional roughness scale ϕ is associated with the transitional roughness wall inner variable ζ=Z+∕ϕ, the roughness friction Reynolds number Rϕ=Rτ∕ϕ, and the roughness Reynolds number Reϕ=Re∕ϕ. The two layer theory for turbulent boundary layers in the variables, mentioned above, is presented by method of matched asymptotic expansions for large Reynolds numbers. The matching in the overlap region is carried out by the Izakson–Millikan–Kolmogorov hypothesis, which gives the velocity profiles and skin friction universal log laws, explicitly independent of surface roughness, having the same constants as the smooth wall case. In these alternate variables, just above the wall roughness level, the mean velocity and Reynolds stresses are universal and do not depend on surface roughness. The extensive experimental data provide very good support to our universal relations. There is no universality of scalings in traditional variables and different expressions are needed for inflectional type roughness, monotonic Colebrook–Moody roughness, k-type roughness, d-type roughness, etc. In traditional variables, the velocity profile and skin friction predictions for the inflectional roughness, k-type roughness, and d-type roughness are supported well by the extensive experimental data. The pressure gradient effect from the matching conditions in the overlap region leads to the universal composite laws, which for weaker pressure gradients yields log laws and for strong adverse pressure gradients provides the half-power laws for universal velocity profiles and in traditional variables the additive terms in the two situations depend on the wall roughness.

scholarly journals Experimental study on the correlation of subcooled boiling flow in horizontal tubes

2020 ◽  
pp. 339-339
Author(s):  
Qi Jing ◽  
QingGuo Luo
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Flow Velocity ◽  
Cylinder Head ◽  
Nucleate Boiling ◽  
Coolant Flow ◽  
Inlet Temperature ◽  
Subcooled Boiling ◽  
Water Jacket ◽  
System Pressure

Subcooled boiling is the most effective form of heat exchange in the water jacket of the cylinder head. Chen's model is the most widely used correlation for predicting boiling heat transfer, but the selection of the correlation for the nucleate boiling is controversial. The work of this paper is to simulate the heat transfer process in the water jacket of the cylinder head with a horizontal rectangular channel that is heated on one side. Using the coolant flow velocity, inlet temperature and system pressure as variables, the heat flux and heat transfer coefficient were obtained. The results show that the increase of the coolant flow velocity can effectively promote the convection heat transfer, and the change of inlet temperature and system pressure will affect the occurrence of nucleate boiling. However, the Chen?s model predictions doesn?t fit well with the experimental data. Four nucleate boiling correlations were selected to replace Chen's model nucleate boiling correlation. The correlation proposed by Pioro coincides best with the experimental data. The mean error after correction is 18.2%.

Analysis of Gas Entrainment Phenomenon From Free Liquid Surface for a Sodium-Cooled Fast Reactor Design: Validation of Velocity Profile and Strouhal Number in a Flow Field

2020 ◽  
Author(s):  
Mao Uchida ◽  
Moe Hirakawa ◽  
Aaru Sano ◽  
Keisuke Inoue ◽  
Takaaki Sakai ◽  
...  
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Flow Velocity ◽  
Liquid Surface ◽  
Velocity Profiles ◽  
Reactor Vessel ◽  
Flow Channel ◽  
Wake Flow ◽  
Gas Entrainment ◽  
Piv Method

Abstract Gas entrainment (GE) from cover gas, which is an inert gas to cover sodium coolant in a reactor vessel, is one of key issue for Sodium-cooled fast reactors (SFRs) design to prevent unexpected effects to core reactivity. In this research series, evaluation method has been investigated for surface dimple depth growth of unstable drifting vortex dimples on the liquid surface in the reactor vessel. By using a computational fluid dynamics (CFD) code, analyses have been conducted to estimate the drifting vortex on water experiments in a circulating water tunnel. The unstable drifting flow vortexes on the water surface were generated as wake vortexes behind a plate obstacle. Downward flow velocity was induced by bottom slit flow pass along the flow channel. In the previous study, the onset conditions of the gas entrainment were evaluated based on existing non-dimensional numbers method by using the STREAM-VIEWER code. However, the CFD predication accuracy of the detail flow field itself was not clear especially for vortex frequency in the wake flow and detail velocity profiles in the flow channel. In this study, to clarify the accuracy of CFD analysis, Strouhal numbers of vortex frequency and detail flow velocity profiles were compared with experimental data which were measured by Particle Image Velocimetry (PIV) method. As the results, the Strouhal numbers of the vortex frequency behind the plate obstacle reasonably agreed with experimental data. Prediction accuracy for the velocity profiles in the flow channel were also confirmed by comparisons with measured data by the PIV method.

Investigation on Variations of Void Fraction in a Subcooled Boiling Channel Under Vertical Forced Excitations

2021 ◽  
Vol 143 (6) ◽  
Author(s):  
Shao-Wen Chen ◽  
Wei-Cheng Lee ◽  
Yu-Hsien Chang ◽  
Ailing Ho ◽  
Jin-Der Lee ◽  
...  
Keyword(s):  
Heat Flux ◽  
Void Fraction ◽  
Experimental Tests ◽  
Dominant Frequency ◽  
Heat Fluxes ◽  
Fluid Temperature ◽  
Subcooled Boiling ◽  
Wall Superheat ◽  
Boiling Flow ◽  
Near Wall

Abstract Experimental tests were carried out to investigate the vertically forced excitation effects on the subcooled boiling flow. The heated circular channel with an inner diameter of 11.9 mm was operated with various heat fluxes (q″ ≈ 14.6–41.1 kW/m2) and inlet flow conditions (vin ≈ 0.21–0.42 m/s) under various vertical forced excitations (f ≈ 0–1.63 Hz), and the time variations of void fraction, near-wall fluid temperature and pressure were recorded during the tests. Fast Fourier transform (FFT) was applied to extract the dominant frequency from the transient signals, and the variations of averages and standard deviations of test data were obtained for analysis. Under lower heat flux, lower flow, and lower void conditions, the time-averaged void fraction may decrease under forced excitations, and the dominant frequencies of void variations were identical to those of forced excitations. However in higher heat flux and higher void conditions, the void fraction can slightly increase under forced excitations, but the excitation frequencies may not be clearly observed in the void FFT plots. In general, the transient and time-averaged void fraction can be affected by forced excitations, and the void variation trends are similar to those of near-wall fluid temperature, which implies the void variations may be related to the changes of thermal boundary layer thickness. Besides, the potential variations of void fraction were estimated by assuming changes of heat transfer coefficient and/or wall superheat, which appear similar trends to the observed void variations in the present tests.

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