Geometrical study of ventilation system openings of pump room in nuclear power plant

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Alexandria Engineering Journal (2018) xxx, xxx–xxx
H O S T E D BY
Alexandria University
Alexandria Engineering Journal
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ORIGINAL ARTICLE
Geometrical study of ventilation system openings
of pump room in nuclear power plant
H.A. Refaey a,*, A.M. Refaey b, M.M. Kandil b, M.A. Moawed a
a
b
Mechanical Eng. Department, Faculty of Engineering of Shoubra, Benha University, 11629 Cairo, Egypt
Department of Safety Engineering, Egyptian Nuclear and Radiological Regularly Authority, 11762 Cairo, Egypt
Received 10 May 2017; revised 11 September 2017; accepted 14 November 2017
KEYWORDS
Nuclear power plant;
Numerical;
CFD;
Pump room;
Vents locations
Abstract Fire safety is important throughout the lifetime of nuclear power plant (NPP), from
design to construction throughout plant operation. The integrity of the shutdown cables located
in the pump room in NPPs is very important in the fire protection system. Therefore, the present
numerically study investigates the effect of outlet vent opening geometry and the location of the
ventilation system specifications on the heat transfer in pump room during a fire. Threedimensional ANSYS- FLUENT Computational Fluid Dynamics with Realizable k–e turbulence
model is employed in the present work. The results found that the geometry (aspect ratio) of the
outlet opening vent has major effects on the shutdown cable protection from fire according to their
locations. Furthermore, as the aspect ratio for outlet vent decreases, then the suction of hot gasses
from the upper half of the room is improved. Consequently, the temperature of the heat source and
target decreases. When the two inlet and outlet vents are located at a same lower level from the
ground the inlet velocity should be 1.25 m/s, while, when the two vents are located at two different
level the inlet velocity should be 0.75 m/s in order to protect the shutdown cable insulation.
Ó 2018 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an
open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
An uncontrolled fire in a nuclear facility can be a very energetic event. The majority of fire dynamics, fire risk evaluations
are focused on electrical cables because of their thermal
fragility and must be examined within the fire safety analysis.
The shutdown cables within the pump room of NPP must be
protected by fire barrier system. Therefore, the ventilation sys-
* Corresponding author.
E-mail address: [email protected] (H.A. Refaey).
Peer review under responsibility of Faculty of Engineering, Alexandria
University.
tem in the pump room is essential for the protection of the
cables. This technique is considered as a passive fire safety.
In NPP, it is necessary to ensure that the plant buildings are
protected from fire by divide it into fire compartments and fire
cells for fire protection [1]. The aim is to segregate important
items from high fire loads and segregate redundant safety systems from each other. The segregation reduces the risk of fires
spreading and minimize secondary effects to prevent common
failures. Moreover, building structures should be suitable to
resist fire by making the fire stability rating (load bearing
capacity) of the building structures higher than the fireresistance rating of the fire compartment itself. In addition
to, noncombustible or fire retardant and heat resistant materials are required to be used as far as practicable throughout the
https://doi.org/10.1016/j.aej.2017.11.016
1110-0168 Ó 2018 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article in press as: H.A. Refaey et al., Geometrical study of ventilation system openings of pump room in nuclear power plant, Alexandria Eng. J.
(2018), https://doi.org/10.1016/j.aej.2017.11.016
2
H.A. Refaey et al.
plant and in particular in locations such as in the reactor containment and the control room [2]. The NPP buildings must be
divided into fire zones and take especially interested for the
confined fire zones which are represented inside their fire analysis hazard (FHA) [3]. This is very important to support design
basis accident (DBA) and engineering review to regulatory
decision making.
The fire zones are classified into four categories based on
whether safe shutdown functions and radioactive materials
exist in the target fire zones or compartments. Table 1 represents the characteristics of fire zones or compartments with
their specific functions and major concerns for fire risk management according to the Korean standard NPPs (KSNP)
[4]. As shown in Table 1, the pump room is a special zone
because it contains many shutdown cables which play a major
role to ensure safety analysis during the fire. Moreover, the
room has a high thermal load due to leakage of lubrication
oil from the pump and it has an impact on the vital places
inside it. Therefore this research is concerned with the ventilation system inside the design base accident of the room to protect the shutdown cables during fires from damage.
Kandil et al. [5] numerically performed a fire simulation to
declare the recital of the suppose fire and its products inside
standard cable spreading room of NPP. In addition to, the
relation between the fire and different air flow rate from the
mechanical ventilation to an exhaust system. The simulation
used CFAST zone model as fire hazarded analysis. The results
showed that the mechanical ventilation with certain air flow
rate has a primary effect on the air inflow into the compartment and hence the oxygen and carbon concentration. The
optimum results to prevent the re-ignition to occur after the
doors opened were produced for air flow rate (between 2 m/s
and 4 m/s). Rahman et al. [6] numerically presented the mixed
convection in a vented enclosure. Various inlet port configurations are extensively studied with the change of governing
parameters. The results showed that by increasing Reynolds
and Richardson numbers the convective heat transfer became
predominant over the conduction heat transfer. Furthermore,
Table 1
the rate of heat transfer from the heated wall significantly
depends on the position of the inlet port. Empirical correlations have been developed.
Kagou et al. [7] numerical simulated the fire phenomenon
concerning fire outbreak in confined enclosures by using Fire
Dynamics Simulator (FDS). The results obtained were compared with experimental results and it was satisfactory but it
needed a heat flow sensitivity analysis. Cai and Chow [8] predicted the HRR of gasoline pool fire by using FDS. The prediction was then used as an ignition source for the numerical
studies on wood chipboard. The results demonstrated the
capability of FDS program to predict the HRR during the fire
growth period. The results were compared with experimental
data and it was found that the HRR curve has a better agreement with experiments.
Siddapureddy and Prabhu [9] reported a numerical and
experimental study of thermal packages engulfed in pool fires
tests. The adiabatic surface temperature concept was used to
simplify the thermal test problem. The computed AST from
fire simulations and the measured AST are within 6%. Mouangue et al. [10] numerically simulated an unexpected fire occurring in a one-way tunnel to investigate the critical velocity of
the ventilation airflow. Two different values of HRR;
43.103 kJ/kg and 19.103 kJ/kg were used and the critical velocity in the upstream side of the tunnel was 1.34 m/s and 1.12 m/
s, respectively.
Sahu et al. [11] performed experimental and numerical studies for a compartment with different door sizes with different
HRR using diesel as fuel. The results revealed that the refined
mesh near the fire source improved the accuracy of the numerical simulation. Cai and Chow [12] used CFD to predict the
HRR for liquid fuel model in FDS with different ventilation
factors. Five different fire scenarios with different ventilation
conditions were investigated. The resulted showed a linear
correlation which could be fitted for the relationship between
the intake air flow rate and the ventilation factor.
Herein in the present paper study ventilation of pump room
in NPP using the passive technique. In most cases of fire
Classification of fire zones.
Fire zone or
compartment
Specific function
Major concerns for fire risk management
Example of fire zone
Special zone
Safe shutdown function and radioactive
material control
– Charging pump room
– Residual heat removal
pump room
Red zone
Safe shutdown function
Yellow zone
radioactive material control
White zone
Simple roles
1. at fire, transfer to redundant safe
shutdown train
2. Protection of one of redundant safe
shutdown trains
3. Protection of radioactive material
release
4. Security of fire zone integrity
1. At fire, transfer to redundant safe
shutdown train
2. Protection of one of redundant safe
shutdown trains
3. Security of fire zone integrity
1. Protection of radioactive material
release
2. Security of fire zone integrity
1. Protection of heat and smoke
propagation
2. Security of fire zone integrity
– Central chiller water
equipment room
– Auxiliary feed water pump
room
– Spent material treatment
facilities
– Spent fuel storage room
– Turbine hall
– Water treatment area.
Please cite this article in press as: H.A. Refaey et al., Geometrical study of ventilation system openings of pump room in nuclear power plant, Alexandria Eng. J.
(2018), https://doi.org/10.1016/j.aej.2017.11.016
Geometrical study of ventilation system openings
conditions in NPP, a large effort has been done for achieving
passive fire protection. These efforts depend on estimation the
possible parameters and conditions of the ventilation system
inside any closed room during the fire occurrence. Moreover,
most fire studies concentrated on the effects of ventilation
parameter of causing and controlling the fire, and the fire heat
transfer through the louvers. Furthermore, the ventilation
studies concentrated on the effects of heat transfer to improve
the air quality of rooms and ventilation of the building (air
condition). In addition to, some of the previous researches
concerns on HRR and on the ventilation of an open tunnel
and or in compartments with different fuel as a heat source.
Therefore, the main objective of the present research is to
cover the lack of previous studies by taking into consideration
the effect of the ventilation system openings in terms of openings location to protect the vital goal (insulation of the shutdown cable) in the pump room of NPP. In addition,
minimizes the impact of the fire on the target. Moreover, find
out the optimum ventilation inlet air velocity during the fire
that reduces the fire influence on the shutdown cables.
2. General description of model
The aerodynamic behavior of lubricating oil fire in the standard pump compartment of nuclear power plant is studied.
Fig. 1
3
The compartment is of fire-resistive construction and contains
an emergency core cooling system pump and a single tray containing safe-shutdown cables that are protected by an ERFBS.
The pump is surrounded by a dike designed to contain any
lubricating oil that may leak or spill, with a maximum capacity
of 190 L. The compartment contains one smoke detector and
one sprinkler. The compartment is mechanically ventilated.
The fire occurs when pumping oil leaks into the dike area
and ignites. Large oil fires are likely to cause flashover conditions. Actually, flashover refers to the rapid transition from the
growth period of a fire (pre-flashover) to the fully developed
fire (post-flashover). A flashover condition is typically expected
when the hot gas layer temperature reaches 500 °C or greater
[13]. In the present study, the flashover conditions have not
been reached in all simulation. Because one of the aims of
the study is to control the ventilation parameters in order to
prevent the flashover to occur in the pump room. Consequently, the shutdown cable in NPP will be protected.
The paper studies the best position of the inlet and outlet
vents of the ventilation system inside a standard pump room
through expected fire results from leakage of oil lubrication
from the pump. This is an important step in the design base fire
accident for the insulation of the shutdown cable to confident
its safety during the fire. The influences of geometry (aspect
ratio), position and inlet flow velocity on the insulation of
Illustration of the pump room for group II.
Please cite this article in press as: H.A. Refaey et al., Geometrical study of ventilation system openings of pump room in nuclear power plant, Alexandria Eng. J.
(2018), https://doi.org/10.1016/j.aej.2017.11.016
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H.A. Refaey et al.
Table 2
Description of vent positions for the two groups.
Case
Group I
Group II
Position of inlet and outlet vent
Fig. 2
The outlet vent geometries.
shutdown cable are numerically investigated. Eight different
domains of the vent opening location are numerically studied.
Therefore, two groups with different locations of inlet and
outlet vent with aspect ratios [1, 2, 0.5, circle] are studied. Furthermore, the effect of air inlet velocity that reduces the fire
influence on insulation temperature of the shutdown cables is
studied.
Therefore, a CFD simulation of pump room with its all
contents from the source of fire and ventilation system (inlet
and outlet opening vent) and insulation of shutdown cables
is presented. The details of the pump room are shown in
Fig. 1. The following subsections describe in details the present
CFD domain for the pump room.
2.1. Geometries description and classifications
Table 2 represents the positions of the inlet and outlet vents in
the pump room. There are two groups with different geometry
of outlet vent. The two groups are described as follow:
Group (I): Inlet and outlet openings vents are located at the
same level measured from the ground.
Group (II): Inlet and outlet opening vents are located at different levels measured from the ground.
As shown in Table 2, each group has four configurations
(C1, C2, C3, and C4) depending on the aspect ratio (ratio
between width to height of the opening vent) [1, 2, 0.5, and circle]. For group I, both holes are located on the same level
which measured from the ground level. For group II, both
holes are located at a different height measured from the
ground level. For all CFD simulation runs the inlet velocity
is ranged from 0.5 to 1.75 m/s.
As can be noticed from Fig. 1, the inlet vent is on the righthand wall and it is near to the ground. The inlet vent has a
fixed square shape (0.5 m). Regarding the outlet vent, it is on
the left-hand wall and its position depends on the group as represented in Table 2. Moreover, Fig. 2 represents the outlet vent
used geometry. All the shown geometries have equal total cross
sectional area. So that, the effect of outlet vent geometry could
be studied. In addition to, the effect of ventilation inlet velocity
on the shutdown cable temperature during the fire is also
studied.
2.2. Ventilation
Inside the room, there is one supply and one return air vent,
each with an area of 0.25 m2, with the change of air speed from
0.5 to 1.75 m/s. The inlet and outlet opening vent in the pump
room is square (0.5 m). The components in the pump room are
shown in Fig. 1. The ventilation system continues to operate
during the fire, with no changes brought about by firerelated pressure effects. This does not imply that the fire does
not impact the ventilation system, but rather than there is typically limited information about the ventilation network that
connects to a given compartment.
2.3. Fire (heat source)
The fire starts according to a release of 190 L of lubricating oil
which spill at the dike. Lubricating oil is a mixture of hydrocarbons, mostly alkanes. For the purpose of modeling, the
lubrication oil has the following chemical formula C14H30 with
a density of 0.76 kg/L. This oil has a specified burning rate of
0.039 kg/m2/s which is applied directly in the model over an
area of 2.75 m2 yielding a burning rate of 0.107 kg/s and,
which means that the oil burns at a rate of 0.141 L/s. In the fire
scenarios simulation study, it is assumed that fire is initialized
and grow till it reaches its full developed stage with maximum
Heat Release Rate (HRR) from burning the used lubrication
oil. In the present simulation, a steady state condition is used
and the amount of HRR is equal to 120 kW/m3.
2.4. Insulation of cable tray
The insulation of the cable tray is considered as the main target
to be prevented from burning. The single cable tray in this
compartment is filled with PE/PVC cables with copper conductors. The damage criterion is the point at which the cable
Please cite this article in press as: H.A. Refaey et al., Geometrical study of ventilation system openings of pump room in nuclear power plant, Alexandria Eng. J.
(2018), https://doi.org/10.1016/j.aej.2017.11.016
Geometrical study of ventilation system openings
5
temperature reaches 205 °C [13]. The cable tray is protected by
an ERFBS, which is consisted of two layers of ceramic fiber
insulation blankets, covered by 0.0254 mm foil to withstand
temperature. This insulation temperature is supposed not
exceed about 200–205 °C according to the design base accident
for even reflected on heat rate released from the fire in end.
bulent dissipation rate 0.7. The turbulent intensity for all runs
is 5%; (the ratio of the root-mean-square of the velocity fluctuations to the mean free stream velocity) [14]. The simulations
presented in this work have been performed on Intel Core TM
i7 eight core 2.2 GHz PC.
3.1. Flow governing equations used in CFD modeling
3. Numerical approach and assumptions
For the present study, three-dimensional ANSYS-FLUENT
Computational Fluid Dynamics (CFD) simulation model is
used. The CFD simulation with Realizable k–e turbulence
model is employed with standard wall functions. Turbulent
flow is assumed for all runs due to high flow rates, leading
to the Reynolds-Averaged Navier–Stokes equations (RANS),
which are then discretized by the finite volume method.
First order upwind schemes is selected for turbulent kinetic
energy and turbulent dissipation rate. The second order
upwind schemes is selected for momentum and energy to
compute the field variables. The pressure-velocity coupling
algorithm is the SIMPLE scheme (Semi-Implicit-method for
Pressure Linked Equations), and all under-relaxation factors
are set as a default except turbulent kinetic energy 0.7 and tur-
The CFD flow pressure based solver based on finite volume
method is used in the present work to solve ReynoldsAveraged Navier–Stokes (RANS) equations. The flow is
assumed as steady and incompressible. The conservation equations of continuity, momentum, and energy are represent as
follow [14]:
Continuity equation:
@Ui
¼0
@xi
Momentum equation:
@Ui
@P
@
@Ui @Uj
qu0i u0j
¼
þ
l
þ
qUi
@xi
@xj @xi
@xj @xi
ð2Þ
Energy equation:
2350
780
C2
1950
C1
C4
Cc
1750
C3
C1/2
C2
C1
680
Temperature, K
2150
Temperature, K
ð1Þ
1550
1350
Cc
C4
C3
C1/2
580
480
1150
950
750
0.25
0.5
0.75
1
1.25
1.5
1.75
380
0.25
Inlet velocity, m/s
0.5
0.75
1.5
1.75
b
750
8.5
C2
C2
C1
C1
650
Cc
C4
hav, w/m2.K
Temperature, K
1.25
Inlet velocity, m/s
a
C3
C1/2
550
8
Cc
C4
C3
C1/2
7.5
7
450
6.5
350
0.25
0.5
0.75
1
1.25
Inlet velocity, m/s
c
Fig. 3
1
1.5
1.75
15000
25000
35000
45000
55000
65000
Reynolds number
d
Effect of inlet vent velocity for group (I) on the temperature of (a) heat source (b) room (c) target and (d) heat transfer coefficient.
Please cite this article in press as: H.A. Refaey et al., Geometrical study of ventilation system openings of pump room in nuclear power plant, Alexandria Eng. J.
(2018), https://doi.org/10.1016/j.aej.2017.11.016
6
H.A. Refaey et al.
480
C2
Cc
C4
C3
C1/2
1200
C2
C1
Cc
C4
C3
C1/2
460
C1
Temperature, K
Temperature, K
1400
1000
800
440
420
400
380
360
340
600
0.25
0.5
0.75
1
1.25
Inlet velocity, m/s
1.5
0.25
1.75
0.5
0.75
1
1.25 1.5
Inlet velocity, m/s
a
b
460
8.5
420
400
hav, w/m2.k
C2
C1
Cc
C4
C1/2
C3
440
Temperature, K
1.75
8
C2
C1
Cc
C4
C3
C1/2
7.5
380
360
7
340
320
0.25
0.5
0.75
1
1.25
Inlet velocity, m/s
1.5
1.75
6.5
15000
25000
35000 45000 55000
Reynolds number
c
65000
d
Fig. 4 Effect of inlet vent velocity for group (II) on the temperature of (a) heat source (b) room (c) target and (d) heat transfer
coefficient.
qCp Ui
@T @T @T
0
0
¼
k
qCp ui Ti þ Sh
@xi @xi @xj
ð3Þ
The realizable r-e transport equations for the turbulent
kinetic energy equation and the dissipation rate equation
respectively are representing as follow:
Turbulent kinetic energy equation:
@
@
@
l @k
ðqkÞ þ
þ Gk þ Gb
ðqkuj Þ ¼
lþ t
@t
@xj
@xj
rk @xj
qe YM þ Sk
ð4Þ
Dissipation rate of turbulent kinetic energy equation:
@
@
@
l @e
ðqeÞ þ
þ qC1 Se qC2
ðqeuj Þ ¼
lþ t
@t
@xj
@xj
re @xj
lt ¼ qCl
k2
e
e2
e
pffiffiffiffi þ C1e C3e Gb þ Se
k
k þ me
ð5Þ
ð6Þ
where Ui and T are the time-averaged velocity and temperature
and Sh is the heat source term. q, k, p, l and R are the density,
thermal diffusivity, static pressure, viscosity and gas constant,
respectively. u0i ; u0j ,T0 , qu0i u0j ,qcp u0i T0 are the fluctuating velocities, temperature, average Reynolds stresses and the turbulent
heat fluxes, respectively. Gk represents the generation of turbulence kinetic energy due to the mean velocity gradients, Gb is
the generation of turbulence kinetic energy due to buoyancy,
and YM represents the contribution of the fluctuating dilatation in compressible turbulence to the overall dissipation rate.
The model coefficients are C1e = 1.44, C2 = 1.9, rj = 1.0 and
re = 1.2.
4. Results and discussion
The simulations are carried out for mixed convection in the
pump room. The inlet and outlet vent are located at different
positions with different geometries in the room while fire
source of the room is fixed. The effects of the outlet vent geometry, locations and Reynolds number on the heat transfer characteristics are presented. The following sections explain the
importance of the positions of the ventilation system openings
during the fire. In addition to, it show the effect of the ventilation system openings on the temperature of the insulated control cables (target) which response on the shutdown of the
NPP. Furthermore, the influence of the air dynamic flow and
the heat transfer on the target exists in the pump room is
discussed.
4.1. Inlet and outlet vent at same position with different aspect
ratios (Group I)
Fig. 3 shows the effect of inlet air velocity on the heat source,
room, target temperatures, and the heat transfer coefficient for
Please cite this article in press as: H.A. Refaey et al., Geometrical study of ventilation system openings of pump room in nuclear power plant, Alexandria Eng. J.
(2018), https://doi.org/10.1016/j.aej.2017.11.016
Geometrical study of ventilation system openings
Fig. 5
7
Temperature contours of the four configurations (C2, C1, C3 and C4).
group I. The figure demonstrates that as the air inlet velocity
increases the temperature of heat source, target, and room
decreases gradually. The temperature of the insulation (target)
has its lower value as the aspect ratio decreases (configuration
C3). This can be attributed to, the center of configuration C3 is
far from the ground level, which results in decreasing the density between upper and lower part of fire room. Consequently,
the hot gasses mounting accumulates on the ceiling of the
room and descends out of the nearest air outlet vent for the
ventilation system. For configuration C1, heat source temperature increased, because, the aspect ratio for inlet is similar to
the outlet and there is a short pass between them, which
decreases the heat exchange rate between room space and ventilation air. In addition to, configuration C4 with circular
shape has the best heat transfer rate.
4.2. Effect of height between inlet and outlet vent (group II)
Fig. 4 represents the temperature of heat source, room, and
target as a function of air inlet velocity for the four configurations of group II. It is noticed that, as the aspect ratio increases
the temperature decrease for target and room during the fire.
This can be attributed to the plume releases from fire, then
the hot gasses which upward to room ceiling ‘‘stratification
hot gasses”. So that, the best configuration for target and
room, in this case, is configuration C2. By increasing the inlet
velocity more than 1 m/s there is no effect of the vents opening
in the room and the target as shown in Fig. 4(b and c). Fig. 4(a
and d) illustrates that the configuration C4 represents the lowest temperature of the heat source. This could be attributed to
the difference between inlet and outlet vent geometry which
make eddy currents, which improves heat transfer coefficient.
4.3. The temperature distribution in pump room during fire for
group I&II
Fig. 5 shows that at the lowest inlet velocity for each group to
protect the target and also the effect of the geometry of ventilation openings on the distribution of temperature at the middle of the room. The arrangement of each figure according to
the lowest temperature is for each configuration. In group I, at
inlet velocity, 1.25 m/s for the ventilation system, the temperature of the target is protected, and the best configuration is C3
at the aspect ratio 1/2, where it shows a maximum space with
less temperature. In group II, at inlet velocity, 0.75 m/s for the
ventilation system, the temperature of the target is protected,
and the best configuration is C2 at the aspect ratio 2, where
it shows a maximum space with less temperature in Fig. 5
(b). This Figure shows a higher space for temperature distribution above the heat source. It is meaning that the location of
inlet and outlet vent improves the heat transfer coefficient at
low inlet velocity. In addition to, Fig. 6 represents velocity distribution in a plane passes through the mid points of inlet and
outlet vents. Furthermore, the figure shows the stream lines
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H.A. Refaey et al.
a
b
Inlet velocity = 0.75 m/s
C2
Fig. 6
c
(a, b) Velocity vectors and contours for mid plane passes through inlet and outlet vents (c) Stream lines starts from inlet.
starts from the inlet vent. It can be noticed that the velocity is
small in the whole plane except near the inlet and exit vents.
This distribution explains the reduction in the temperature
above the heating source.
5. Conclusions
This study shows the effect of Geometry (aspect ratio) and
location of the outlet vent and inlet vent for ventilation system
inside a standard pump room. Two different groups with variable aspect ratio are studied. It can be expected the fire results
from leakage of oil lubrication of pump, in order to protect the
vital target for safe shutdown of a nuclear power plant. The
obtained results can be divided into two branches.
5.1. Results from group I
- as the aspect ratio for outlet vent decreases, then the suction of hot gasses from the upper half of the room is
improved. Consequently, the temperature of the heat
source and target decreases.
- For this group, the best outlet vent is that one with lowest
aspect ratio, But to protect the shutdown cable insulation,
the inlet velocity should be 1.25 m/s.
5.2. Results from group II
- By increasing the aspect ratio for outlet vent, then the hot
gases suction for the upper half of the room is improved.
Consequently, the temperature of the heat source and target decreases particularly at configuration Cc, where the
outlet vent has a circle shape.
- For this group, the best outlet vent is that one with highest
aspect ratio. But to protect the shutdown cable insulation,
the inlet velocity should be 0.75 m/s which leads to decrease
of heat rate release for the fire.
Generally, for both of the represented groups the following
results are obtained:
- The difference between the aspect ratio for inlet and outlet
vent leads to occurring of eddy currents in the room, so
that, the turbulent flow occurs and it leads to improvement
of heat transfer coefficient in the pump room.
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