evaluation technique of the reacting force on jet

U.P.B. Sci. Bull., Series C, Vol. 76, Iss. 2, 2014
ISSN 2286 – 3540
Tiberiu GYONGYOŞI1, Ştefan NICOLICI2, Valeriu Nicolae PANAITESCU3, Ilie
The analysis of the possible cause generating the collector pipe failure of the
Degasser-Condenser equipment at CANDU 6 NPP implies checking its mechanical
resistance. During execution of the degassing function, the normal jet force which
act direct on collector pipe in each nozzle area, bends it. The characterization of the
minimum cross section geometry (shape and size determination) of the fluid passage
through the nozzle, together with the analytical and numerical models for the
reacting force evaluation of the jet is presented in this paper.
The paper has original contributions in the domain and is dedicated to
specialists working in the research and technological engineering.
Keywords: collector pipe, nozzle, minimum flow section, reacting force on jet
1. Introduction
At CANDU 6 NPP the Degasser – Condenser equipment is a component
part of a safety system from primary heat transport system. The DegasserCondenser behaves cyclic for a settled time as degasser, and as condenser for the
rest. The pressure is controlled by heat supply brought by electric heaters and by
cooling primary agent injection. To behave like a degasser, the sample of cooling
primary agent has to indicate a limit concentration of the solution gases.
Increasing of the pressure level in Degasser-Condenser over a threshold value
releases the injection of cooling primary agent in spray tank, injection that stops
when the steam pressure from the vessel decreases under the maximum value. The
gases are removed from cooling agent by their part pressure drop, above liquid
surface [1]. This is thermally made in a steam environment when the partial gases
pressure towards the steam pressure became practically zero [1]. To remove the
gases from the primary agent a necessary condition is a large contact area of the
IDT I, The Out of Reactor Department, Institute for Nuclear Research Piteşti, Romania, e-mail:
tiberiu.gyongyoş[email protected]
Assist., Energy Generation and Utilisation Department, University POLITEHNICA of Bucharest,
Romania, e-mail: [email protected]
Prof., The Hydrokinetics, Hydraulic Machines and Environment Engineering Department,
University POLITEHNICA of Bucharest, Romania, e-mail: [email protected]
Prof., Energy Generation and Utilisation Department, University POLITEHNICA of Bucharest,
Romania, e-mail: [email protected]
Tiberiu Gyongyoşi, Ştefan Nicolici, Valeriu Nicolae Panaitescu, Ilie Prisecaru
agent with the steam environment and a great difference between the partial
pressures of the gases in the liquid/ steam environment [2]. The complete
removing of the gases from the liquid environment requires a long time, during
the finite available time for degassing the gases could be removed up to a cut
fraction from their initial concentration [1]. In our case, the increase of the contact
area between water and steam is carried out through spraying the cooling primary
agent in particles reduced at “fog” stage [2] by special nozzles.
Apparently, the cooling agent jet at nozzle outlet can be considered
harmless. Loosing the collector pipe integrity, well in advance of reaching its
design lifetime, imposed paying a proper attention to evaluation of the reacting
force of the jet that came out from nozzle.
The paper describes the determination method of the components for
calculating the forced flow section of the cooling agent through nozzle and the
evaluation technique of the normal jet value. The elements on view are part of
own analysis of a case study completed with proposal of resizing solution of spray
collector pipe [2].
2. Geometrical adapted description. Nozzle details
The spray collector is a subassembly made of a thick wall pipe (de/di = 1.2
> 1.1) [3], along it are N nozzles thread fitted (2) whereby the cooling primary
agent injection is made, as fine drops, in the steam environment of the DegasserCondenser, injection required for execution of degassing function, see Fig. 1.
Fig.1. The spray collector pipe – adapted chart
At one end, the spray collector pipe (5) is assembled by a special sleeve
(1) to the pressure vessel wall and, the other pipe end, plugged by a cover (4) is
simply supported (3) being locked for both loading generated by the reacting force
of the water jet, injected through nozzles during the short time executing
degassing function and thermal elongation. The nozzles (2) are assembled
alternative on the collector pipe, at equiangular and equally spaced, obtaining a
symmetry around those placed as „six hour” (Fig. 1), to provide the greater
contact area between water and steam. The cooling primary agent is passing from
the collector through the adapted nozzle, as it can be seen in the Fig. 2.
Evaluation technique of the reacting force on jet at spray collector nozzle
Fig.2. Nozzle – adapted chart
Fig.3. Detail (inlet of the cooling primary agent in the
The geometrical layout of the primary agent inlet from the collector pipe
into nozzle is utmost complex, see Fig. 3.
The precise settlement of the slits and their sizing (even when the nozzle is
in disassembled condition) was for a while an issue because, without these
information the flow section couldn’t be calculated.
3. The complete characterization of the real flow section
In the first step, the characterization of the flow section assumes to
perform the two slits projection in the cross section on the flowing alignment.
Performing of these projections is difficult due to complexity of the slit geometry.
Thereby, it has been adopted as a possible solution, the replacement of the cooling
primary agent with a light beam produced by a spot [4]. Two spot lights have been
obtained on the plane surface, see Fig. 4.
The light beam was replaced with the light generated by a LED [4].
Looking into the nozzle, from the outlet, one can observe in series the presence of
two light slits antipodal placed, having the shape showed in the Fig. 5.
Fig.4. The projection of the light beam on the plane surface
Tiberiu Gyongyoşi, Ştefan Nicolici, Valeriu Nicolae Panaitescu, Ilie Prisecaru
Fig.5. The projection of the real flow section on
the plane surface
Fig.6. Viewing the light slit wing sizes
Sizing of the width “a” and of the thickness “g” of the light slit projection
in plane has no problem [4]. Two identical slits can’t be seeing together because
the exit hole diameter from nozzle doesn’t allow it. It has been attempted shooting
a light slit as control sample [4]. No more than one of light slit wing has been
obtained, see Fig. 6.
4. The evaluation technique of the normal jet force
At nozzle outlet, the jet has the shape shown in Fig. 7. The characteristic
of this shape is the vena contracta diameter [5].
Fig.7. The jet shape at nozzle outlet
From the beneficiary’s data the primary cooling agent parameters are the
average flow per hour through nozzle Qh and the average flow per hour through
the collector pipe, Qhc [2].
Using this data one can calculate:
¾ the rate of cooling primary agent through collector:
ν1 =
3600S c
where: Sc is the flow section through collector:
Evaluation technique of the reacting force on jet at spray collector nozzle
Sc =
πd c2
and dc is the inner pipe diameter of the collector pipe [2];
¾ the rate of primary cooling agent through nozzle depends on the area of
the minimum flow section:
ν2 =
3600S de
where: Sde represents the minimum flow section area:
S de = 2ag + 2 g (a − g )
where: a is the slit wing width and g is the slit wing thickness;
¾ the vena contracta diameter is [5]:
d dν = 0.65d i
¾ the vena contracta cross section area can be calculated as:
πd 2
S dν = dν
¾ the rate of primary cooling agent at nozzle outlet:
ν3 =
3600S dν
¾ the hole area at nozzle outlet:
πd 2
S= i
where: di is the hole diameter at nozzle outlet [2], see Fig. 2.
the fluid mass blowing out as jet through nozzle during
time period Δt2 (Δt2 = Δt3) is finding during period time Δt1 into collector pipe:
ρSν 1Δ t1 = ρSν 3 Δ t3
Δt1 ν 3
Δt3 ν 1
where: ρ is the primary cooling agent density (from thermo-dynamic nomograms
[6] at pressure and temperature at which degassing is made);
¾ variation rate of the cooling primary agent impulse along entire line passed through the
nozzle outlet is equal to force acting on the fluid [5]:
F = ρSν 22
Δt 3
¾ according to the third Newton’s law, on the rest of the system (the
collector pipe) acts an equal and opposed force [5]. The reacting jet force
through the nozzle central placed:
Tiberiu Gyongyoşi, Ştefan Nicolici, Valeriu Nicolae Panaitescu, Ilie Prisecaru
Δt 3
¾ the reacting jet force for the nozzles placed under an angle „α”, referring to
the nozzle placed at „six hour”:
N 2 = ρSν 22 1 cos α
Δt 3
5. The finite element analysis
N 1 = ρSν 22
A finite element (FE) analysis has been performed for the collector pipe
assembly and the maximum von Misses stresses and the maximum deflection of
the pipe nozzle have been obtained. The FE analysis includes several steps [7]:
¾ creation of the geometric model
¾ meshing;
¾ elaboration of the physical model, i.e. material data, loads and boundary
conditions inclusion;
¾ solving of the FE model;
¾ determination of the fatigue usage factor according to the ASME
A FE model was prepared to represent the nozzle pipe (Fig. 9). Solid 187
element has been used to idealize the geometry. The mesh characteristics are:
¾ number of nodes: 372307
¾ number of elements: 230344
¾ minimum element quality: 0.295
The cinematic conditions and the applied loads of the model are shown in
Fig. 9. The Degasser-Condenser vessel nozzle has zero imposed displacements
and the pipe end cover is represented by cylindrical type support. The nozzle
loads are applied to the FEM in the correspondent pipe orifices. Some graphical
results are presented below (Figs. 9 and 10) denoting the pipe deformations and
stresses pattern for the loads shown in Fig. 8.
Fig.8. The boundary conditions and the loads imposed on the FE model
Evaluation technique of the reacting force on jet at spray collector nozzle
Fig.9. Example of nozzle pipe deflections
Fig.10. Equivalent stresses pattern on pipe nozzle
The main objective of the FE analysis was to calculate the maximum pipe
deflections and the maximum von-Misses stress for various velocities of the jet
passing through the pipe orifices. To account for different jet conditions the
reaction force for each orifice was varied from 10 to 200 N. The numerical results
are given in Table 1.
Reaction force [N]
Table 1
Numerical FE analysis results
Maximum von -Misses stress[MPa] Maximum deflection [mm]
6. Conclusion
The analysis of the event root cause of the Degasser-Condenser nozzle
pipe failure leads to the need of mechanical resistance checking. Corresponding to
the assembling positions, the nozzle – collector pipe section is of least resistance.
To come out the cracking in this area and even the pipe breaking a mechanical
bending load has to exist, that have to be considered. The bending load is
generated by a combined action of the jet reacting and collector pipe weight forces
distributed between the bearings. The reacting forces value could be the direct
cause of the event. To evaluate the jet reacting force value it was required to build
a calculus model. Further, to evaluate the maximum stresses and deflections of the
pipe a finite element model has been developed.
The calculus model was based on the impulse setting given by the fluid
mass blowing out as jet through the nozzle and the maximum flow rate value. The
maximum primary flow rate is given by its passage through the minimum cross
section area of the nozzle.
The complex shape of the nozzle makes the complete characterization of
its internal geometry to be problematic. At the nozzle inlet we do not have two
bands half-coil but one single piece that splits the fluid valve in two parts, leading
Tiberiu Gyongyoşi, Ştefan Nicolici, Valeriu Nicolae Panaitescu, Ilie Prisecaru
to two antipodal slits. The jet exit from the nozzle full tapered shaped with an
angle γ carrying out the “fog” spray required by the degassing function. The
minimum flow section into the nozzle is not circular, it is resulting from
projections of the flow section surfaces on the plane normal to the flow direction.
A dismantling or cutting of the nozzle on the generatrix wouldn’t solve the issue
of the minimum flow section value determination. An experimental reproduction
of the process would require conformation to geometrical and physical conditions
and also afferent instrumentation. Neglecting the execution costs of such
experiment, we can affirm that, the experiment and its results wouldn’t lead to
reacting forces determination in due time. The approach presented in this paper is
original. Therefore, for a direct data results about the shape and sizes of the flow
hole, we proceeded to the replacement of the cooling agent, at the nozzle inlet,
with monochromatic light generated by a led. The results obtained allowed a
quick setting of the minimum flow section area. The calculus model proposed
allowed obtaining the force acting on the fluid when it passes through spray
collector nozzle and implicitly the reacting force evaluation on the absolute jet
need for checking of the collector pipe mechanical resistance.
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