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Degha2010-SubcooledBoiling.pdf
Journal of Electron Devices, Vol. 7, 2010, pp. 240-245
© JED [ISSN: 1682 -3427 ]
Journal of Electron Devices
www.jeldev.org
Numerical Study of Subcooled Boiling In Vertical Tubes Using Relap5/Mod3.2
A.L. Degha l*, A. Chaker **
Nuclear research center, Djelfa, Algeria
Physical Energy laboratory, Mentouri University, Constantine, Algeria
e-Mail: [email protected]*
[email protected]**
Received 7-11-2009
Abstract--This paper presents a numerical study for prediction of
the void fraction in subcooled boiling flow in the vertical pipes using
the Relap5/Mod3.2 code system. This last is used for the study of the
safety reactors, is an advanced computer code designed for bestestimate thermal hydraulic analysis of transient in light water reactor.
Relap5 models represent the physical processes of critical flow,
vertical or horizontal stratified flow, and heat transfer from heat
structure. The numerical results agree satisfactorily with those of
experimental and numerical results available in the literature.
I.
INTRODUCTION
Subcooled boiling occurs in many practical applications, such as
in nuclear reactors, heat exchangers, steam generators and
various power generation systems. Prediction of the void fraction
profile and others parameters in the subcooled boiling flows is
essential for design and safety analysis of such system, like
nuclear reactors and significant in test to many process industrie
[1].
In the nuclear area, interest in the precise prediction of two-phase
flow behaviors in subcooled flow boiling is of great importance
to the safety analysis of nuclear reactors. Many years of
extensive research work have been performed with the aim of
developing and verifying various thermal-hydraulics codes, such
as, TRAC, CATHARE and ATHLET and RELAP5 [14].
The prediction of void fraction in subcooled boiling flow in
vertical pipes and channels has been the subject of numerous
studies in the literature. Most of these studies are based on
empirical correlations due to the complex nature of the
subcooled boiling process. Zuber & al. developed an
expression for the axial void fraction considering the relative
velocity between two phases. Kroger and Zuber [3] developed
an empirical formulation for the axial void fraction in a pipe
depending on temperature, flow and local relative velocity.
Levy [4] developed a formulation for the vapor volumetric
fraction. Hu and Pan [5] developed a mechanistic model
derived from a one-dimensional two-phase model. Zeitoun and
Farouki [6] also developed a one-dimensional two-phase model
that accounts for interfacial mass energy transport between two
phases. Lai and Farouk [7] applied an advanced two phase
model to subcooled boiling flow in a pipe.
A.L.Deghal, nuclear research center, BP 180 Ain Oussera Djelfa Algeria (email: [email protected]).
A.chaker, Mentourie University, Constantine, 25000 Algeria. She is now with
the Department of energetically Physics (e-mail: [email protected])
This model was very useful for predicting the axial and
radial void fraction profile, temperature distribution and
velocity profile in the pipe. M.D.Mat & al [8] used a
bubble-induced turbulence model in subcooled boiling of
water in a vertical pipe.
This study is focalized on the analysis of the numerical
results for subcooled boiling in vertical tubes using
Relap5/Mod3.2 thermal-hydraulic computer code; this last,
is an analysis code system of realistic evaluation level. The
main results of this study are compared with the
experimental results of C.Bartolemi & al [1], and the
numerical results of Larson and L.Tong [2] and
M.Z.Podoswski & al [9]. The comparison shows that there
is a good concordance between the Relap5/Mod3.2 results
and literature operation data.
II. PROBLEM DESCRIPTION
Processes in a boiling flow, heterogeneous bubble
nucleation occurs within small pits and cavities on the heater
surface where these nucleation sites are activated and when
the temperature of the surface exceeds the saturation
temperature of the liquid at the local reassure. Here, bubbles
are detached from the heated surface due to the forces acting
on them in the axial and normal directions, which include
buoyancy, drag, lift, surface tension, capillary force,
pressure force, excess pressure force and the inertia of the
surrounding [2]. If at the same location, the temperature of
the bulk fluid remains below saturation, the boiling process
is known as subcooled boiling flow. Subcooled boiling flow
can usually be characterized by a high-temperature twophase region near the heated wall and a low-temperature
single-phase liquid away from the heated surface. Fig. 1
illustrates a typical axial development of the subcooled
boiling process along the heated channel. It begins at a point
called the onset of nucleate boiling (ONB). As it continues
downstream from the ONB point, the void fraction begins to
increase sharply at a location called the net vapor generation
(NVG). The NVG point is the transition between two
regions: low void fraction region followed by a second
region, in which the void fraction increases significantly.
Because of the bulk liquid remain mainly subcooled,
bubbles migrated from the heated surface are subsequently
242
condensed and the rate of collapse is dependent on the Engineering Laboratory (INEL) for the US Nuclear
Regulatory Commission (NRC). Code uses include analysis
extent of the liquid subcooling. [2].
required to support rulemaking, licensing audit calculation,
evaluation of accident mitigation strategies, evaluation of
operator guidelines, and experiment planning analysis.
Relap5/Mod3.2 has also been used as the basic for a nuclear
plant analyzer. Specific applications have included
simulation of transients in LWR systems such as loss of
coolant. Relap5/Mod3.2 is a highly generic code that, in
addition to calculating the behavior of a reactor coolant
system during a transient, can be used for simulation of a
wide variety of hydraulic and thermal transients in both
nuclear and nonnuclear system involving mixture of steam
and water. The Relap5/Mod3.2 hydro-dynamic model is
based on non-homogeneous, no equilibrium, six equations
system for the two phases system that solved by a fast,
partially implicit numerical scheme to permit economical
calculation of system transients. The general solution
procedure is to subdivide the system into a number of
control volumes connected by flow paths. The code
includes many generic components models from which
general systems can be simulated. The component models
include pumps, valves, pipes, heat structures, reactor point
kinetics, separators, control system components, etc. The
conduction heat transfer model is one-dimensional, using a
Fig. 1 Subcooled flow boiling regions
staggered mesh to calculate temperatures and heat flux
vectors [10, 11].
Subcooled flow boiling in this work was considered in a
vertical heated pipe. Subcooled water enters the pipe from the
bottom. Uniform heat flux boundary conditions are applied
B. Tube Modeling
along the pipe wall. A 24 mm diameter pipe for the cases 1, 2,
The aim of this work is the numerical study of numerical
3 and 15.4mm for the case4 are considered. The pipe length
study of subcooled boiling in vertical tubes using
section is 2m. Specified pressure conditions were applied in
Relap5/Mod3.2. The nodalisation of the tube for the
the exit of the pipe. The numerical simulations were done at
Relap5/Mod3.2 code is given in the Figur.2. The philosophy
three pressure levels, namely, 1.5, 3.0, and 4.5MPa. For each
of using Relap5/Mod3.2 code consists in subdividing the tube
pressure, three values of wall heat flux were considered,
in volumes of control connected by junctions of flow. The
namely, 380 and 790 kW/m2 for the first, second and third
2
tube model includes 8 regular volumes, 7 junctions and 8 heat
cases, and 570 kW/m for the fourth case. These cases are
structures. The heat structure included in the model simulate
chosen so that the predictions can compare with the
the behavior of the material mass, and heat transfer between
experimental results from [1], and the numerical results of [2]
the material mass and the fluid in the tube. The thermoand [9]. The inlet qualities and calculated subcooling and
hydraulic conditions at the inlet and outlet of the pipe were
temperatures are shown in Table1.
imposed by the Time-Dependent Volume, Time-Dependent
Junction and Single Junction model, component TMDV-100
Table1
and TMDJ-110, TMDV-200 et SJ-120. The heat densities
Cases Considered
involved between the thermal flux and the external tube
Cases
Inlet sub T
Inlet T
Outlet P
G
q
surface are imposed by table entry.
(°C)
(°C)
(MPa)
(kg/m2.s)
(kW/m2)
A.L. Degha et al, Journal of Electron Devices, Vol. 7, 2010, pp. 241-244
Case1a
Case1b
Case2a
Case2b
Case3a
Case3b
Case4
22.6
50.9
25.0
48.1
24.0
50.0
64.5
177.4
149.1
210.0
186.9
231.0
205.0
465.5
1.5
1.5
3.0
3.0
4.5
4.5
4.5
890
890
890
890
890
890
900
380
790
380
790
380
790
570
III. NODALISATION AND SIMULATION
A. Presentation of Relap5/Mod3.2
The light water reactor (LWR) transient analysis code,
Relap5/Mod3.2, was developed at the Idaho National
243
A.L. Degha et al, Journal of Electron Devices, Vol. 7, 2010, pp. 241-244
Water outlet
TDV-200
SJ-120
Heat Structure
2m
uniforme Flux
1
2
3
4
5
6
7
8
TDJ-110
TDV-100
Water inlet
The effects of the exit pressure, inlet subcooling and wall heat
flux on the subcooled flow boiling can be determined from the
results of these cases. The estimate axial void fraction
distribution along the pipe for the all cases is given in the
figure 2. The numerical results of this study are compared
with the experimental data of Bertolemei and Chanturiya [1],
and the numerical data of Lai and Frouk [7] and Larsen and
Tong [2].
It is seen that the main results gotten by the code
Relap5/Mod3.2 of this work and the data of [1], [2] and [7]
are in good agreement. So there is somewhat lower than the
experimental data [3] at the bottom half of the pipe, the
predictions at the upper half of the pipe are, however, agrees
well with the results data. The differences are considered
acceptable. The deviations are essentially due to the models of
heat transfer used by the code Realp5/Mod3.2. The present
results estimate the initial point of vapor generation better in
all the cases compared whit the experience data.
0,5
Fig.2 Nodalization scheme of the pipe.
Ref.1
Ref.9
Relap5
0,4
Case 4
Void fraction
IV. RESULTS AND DISCUSSION
The code system Relap5/Mod3.2 was applied to predict the
void fraction for subcooled flow boiling in a vertical pipe
for different flow and wall heat flux conditions. There is
four cases were considered for the vertical pipe as shown in
Table1. Lower inlet subcooling and lower wall heat flux
were considered for cases 1a, 2a and 3a. Higher inlet
subcooling and higher wall heat flux were given to cases 1b, 2b,
3b and 4.
0,3
0,2
0,1
0,0
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
Z (m)
0,5
0,6
Ref.2
Ref.1
Relap5
Case 1b
Void fraction
0,5
Case 1a
0,4
Void fraction
Ref.2
Ref.1
Relap5
0,4
0,3
0,3
0,2
0,1
0,2
0,0
0,1
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
Z (m)
0,0
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
Z (m)
0,5
0,5
Ref.2
Ref.1
Relap5
0,4
Ref.2
Ref.1
Relap5
0,4
Case 2b
Void fraction
Void fraction
Case 2a
0,3
0,2
0,3
0,2
0,1
0,1
0,0
0,0
0,0
0,2
0,4
0,6
0,8
1,0
Z (m)
1,2
1,4
1,6
1,8
2,0
0,0
0,2
0,4
0,6
0,8
1,0
Z (m)
1,2
1,4
1,6
1,8
2,0
0,5
A.L. Degha 0,5et al, Journal
of Electron Devices, Vol. 7, 2010, pp. 241-244
Ref.2
Ref.2
Ref.1
Relap5
0,4
Ref.1
Relap5
0,4
Case 3a
Case 3b
0,3
Void fraction
Void fraction
244
0,2
0,1
0,3
0,2
0,1
0,0
0,0
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
Z (m)
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
Z (m)
Fig.3 Comparison of axial void fraction
V. CONCLUSION
This work is focused on the numerical study of subcooled
boiling in vertical tubes using the thermal hydraulic code
system Relap5/Mod3.2. The validation of the results has been
made with comparing the theoretical results of the
RELAP5/Mod3.2 code whit the experimental and numerical
data in the literature with the same conditions of experience
(pressure, mass flow rate, tube diameter and heat flux), for a
vertical tube heated uniformly in steady-state. The gotten
theoretical results are in good agreement with the data. The
present results estimate the initial point of vapor generation
better in all the cases compared with the experience data. Is
show the reliability of the thermo hydraulic code Relap5 in
the analysis of subcooled boiling flow.
VI. REFERENCES
[1] C.C .Bartolemei and V.M.Chanturiya, 1967, “Experimental
study of true void fraction when boiling subcooled water in
vertical tubes”, Thermal Engng, vol.14, pp.123-128.
[2] P.S.Larsen and L.S.Tong, 1969, “Void fraction in subcooled
flow boiling”, J. Heat Transfer, November, pp.471-476.
[3] P.G.Kroges and Zuber, 1968, “an analysis of the effects of
various parameters on the average void fractions in subcooled
boiling”, Journal of heat and heat transfer, vol.11, pp.211-233.
[4] S.Lavy, 1967, “Forced convection subcooled boiling prediction
of vapor volumetric fraction”, International journal of heat and
mass transfer, vol.10, pp.951-965.
[5] Hu, L.W, and pan, 1995, “Prediction of void fraction in
convective subcooled boiling channels using a one dimensional
tow fluid model”, Journal of heat transfer, vol.117, pp.799-803.
[6] O.Zeitoun, M.Shoukri, 1997, “Axial void fraction profile in low
pressure subcooled flow boiling”, Int.J.Heat and Mass Transfer,
Vol.40, N 4, pp.869-879.
[7] J.C.Lai and B.Farouk, 1993, “Numerical simulation of subcooled
boiling and heat transfer in vertical ducts”, Int. J. Heat and Mass
Transfer, vol.36, N° 6, pp.1541-155.
[8]
M.D.Mat, K.Aldas and Y.Kaplan, 2002, “Numerical
investigation of subcooled boiling in vertical pipe using a
Bubble-Induced Turbulence Model”, Turkish J. Eng. Science,
vol.26, pp.275-28.
[9] M.Z.Podowski and N.Kurul, 1990, “Multidimensional effects in
forced convective subcooled boiling”, 9th International Heat
Transfer Conference, August, Jerusalem.
[10] R. C. Borges, F. D’Auria & A. C. M. Alvim, 2000,
“RELAP5/MOD3.2 Post Test Simulation and Accuracy
Qualification of LOBI TEST A1-93”, Relap5 International Users
Seminar, Sept. 12-14, USA
[11] The RELAP5 Development Team, RELAP5/Mod3.2 Code
Manuals, 1998, NUREG/CR-5535 Report, Vols. 1-5, Idaho
National Engineering Laboratory. USA
[12] C.C.St Pierre and S.G.Bankoff, 1967, “Vapor volume profiles in
developing two-phase flow”, Int. J .Heat and Mass transfer, vol.10,
pp.237-249.
[13] L.A.Payan & al, 2005, “Critical heat flux prediction for water
boiling in vertical tubes of steam generator”, In. J. Of Thermal
Science, vol.44, pp.179-188.
[14] G.H.Yeoh and J.Y.Tu, 2006, “Two-fluid and population balance
models for subcooled boiling flow”, Applied Mathematical
Modeling, vol.30, pp.1370-139.
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