U.S. patent application number 14/390634 was filed with the patent office on 2015-04-09 for emergency cooling system using a loop thermosyphon.
This patent application is currently assigned to FUJIKURA LTD.. The applicant listed for this patent is FUJIKURA LTD.. Invention is credited to Masahiro Matsuda, Masataka Mochizuki, Randeep Singh.
Application Number | 20150096721 14/390634 |
Document ID | / |
Family ID | 49300530 |
Filed Date | 2015-04-09 |
United States Patent
Application |
20150096721 |
Kind Code |
A1 |
Mochizuki; Masataka ; et
al. |
April 9, 2015 |
EMERGENCY COOLING SYSTEM USING A LOOP THERMOSYPHON
Abstract
An emergency cooling system for cooling an object certainly and
rapidly in case a temperature of the object is accidentally raised
abnormally. A loop thermosyphon is formed by connecting an
evaporating portion with a condensing portion through a vapor pipe
and a return pipe in a manner to form a cyclic conduit. A
condensable working fluid circulates within the loop thermosyphon
to be evaporated by a heat of the cooling object at the evaporating
portion, and to be condensed at the condensing portion to radiate
the heat conducted from the cooling object. A switching valve is
disposed on the return pipe to selectively allow the working fluid
in a liquid phase to be returned from the condensing portion to the
evaporating portion. Heat transfer pipes to which the heat of the
cooling object is conducted are arranged in the evaporating
portion. Heat transfer protrusions are formed on an inner wall of
the heat transfer pipe to penetrate through dews of the working
fluid, and a preheating portion to which the heat of the cooling
object is conducted is formed within a portion of the return pipe
connected to the heat transfer pipe.
Inventors: |
Mochizuki; Masataka;
(Koto-ku, JP) ; Singh; Randeep; (Koto-ku, JP)
; Matsuda; Masahiro; (Koto-ku, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIKURA LTD. |
Koto-ku Tokyo |
|
JP |
|
|
Assignee: |
FUJIKURA LTD.
Koto-ku, Tokyo
JP
|
Family ID: |
49300530 |
Appl. No.: |
14/390634 |
Filed: |
April 2, 2013 |
PCT Filed: |
April 2, 2013 |
PCT NO: |
PCT/JP2013/060095 |
371 Date: |
October 3, 2014 |
Current U.S.
Class: |
165/104.24 |
Current CPC
Class: |
Y02E 30/30 20130101;
F28D 15/06 20130101; Y02E 30/40 20130101; G21C 15/18 20130101; F28D
15/0266 20130101; G21C 15/12 20130101 |
Class at
Publication: |
165/104.24 |
International
Class: |
F28D 15/02 20060101
F28D015/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 6, 2012 |
JP |
2012-087466 |
Claims
1. An emergency cooling system, comprising: a loop thermosyphon, in
which an evaporating portion at which heat exchange with a cooling
object takes place is connected with a condensing portion at which
a heat radiation takes place through a vapor pipe and a return pipe
in a manner to form a cyclic conduit; a condensable working fluid
circulating within the loop thermosyphon to be evaporated by a heat
of the cooling object at the evaporating portion, and to be
condensed at the condensing portion to radiate the heat conducted
from the cooling object; a switching valve that is disposed on the
return pipe to selectively allow the working fluid in a liquid
phase to be returned from the condensing portion to the evaporating
portion; characterized by: a heat transfer pipe, which is arranged
in the evaporating portion and to which the heat of the cooling
object is conducted; a heat transfer protrusion that is formed on
an inner wall of the heat transfer pipe to penetrate through a dew
of the working fluid; and a preheating portion, which is formed
within a portion of the return pipe connected to the heat transfer
pipe, and to which the heat of the cooling object is conducted.
2. The emergency cooling system as claimed in claim 1, wherein the
condensing portion is situated higher than the evaporating portion;
and further comprising a storage tank for holding the working fluid
in the liquid phase that is connected with a lower portion of the
condensing portion.
3. The emergency cooling system as claimed in claim 1, wherein the
cooling object includes a containment for holding an atomic
fuel.
4. The emergency cooling system as claimed in claim 1, wherein the
evaporating portion is comprised of: an upper header pipe; an lower
header pipe; and a plurality of the heat transfer pipes arranged in
parallel with one another while being connected with the upper
header pipe and the lower header pipe; and wherein the condensing
portion is comprised of: another upper header pipe; another lower
header pipe; a plurality of a radiating pipes arranged in parallel
with one another while being connected with said another upper
header pipe and said another lower header pipe; and a plurality of
radiator fins mounted on the radiating pipes to radiate the heat to
the air.
5. The emergency cooling system as claimed in claim 1, wherein the
preheating portion is formed within the portion of the return pipe
extending inside of the cooling object.
6. The emergency cooling system as claimed in claim 1, wherein the
preheating portion includes a meander pipe formed by bending the
return pipe.
Description
TECHNICAL FIELD
[0001] This invention relates to an emergency cooling system using
a loop thermosyphon for circulating working fluid transporting heat
between an evaporating portion and a condensing portion.
BACKGROUND ART
[0002] The thermosyphon is a heat transfer device comprised of a
sealed conduit and a working fluid encapsulated therein such as
water, alcohol or ammonium. In the thermosyphon, a heat
transportation is provided by an vaporization of the working fluid
caused by locally applying a heat to the conduit, and a
condensation of the vapor migrated to a site where a temperature
and a pressure are low. Generally, in order to facilitate the
vaporization of the working fluid and to allow the vapor to flow
entirely in the conduit, non-condensable gas is evacuated from the
conduit and only the working fluid is encapsulated in the
thermosyphon. In the thermosyphon, the condensed working fluid is
returned to the evaporating portion utilizing a capillary pressure
or gravitationally. For example, a porous material such as a mesh,
a sintered metallic sheet, a wire strand, narrow grooves etc. may
be used as a wick for returning the working fluid to the
evaporating portion. Alternatively, in case of returning the
working fluid gravitationally to the evaporating portion, the
condensing portion is situated higher than the evaporating portion.
The thermoelectric element thus structured may also be called a
heat pipe. Especially, in the heat pipe adapted to gravitationally
return the liquid phase working fluid to the evaporating portion, a
heat transporting direction is limited to a vertical direction from
the upper side to the lower side. Therefore, the heat pipe of this
kind is called a thermosyphon.
[0003] Basically, a straight or curved pipe is used as a container
(or a casing) of the heat pipe or the thermosyphon. One end of the
container is placed at a site where the temperature is high to
serve as the evaporating portion (or heating portion), and other
end of the container is placed at a site where the temperature is
low to serve as the condensing portion (or cooling portion). In the
container this structured, the working fluid vaporized at the
evaporating portion flows toward the condensing portion, and the
flow rate of the fluid reaches sonic speed. Then, the working fluid
condensed at the condensing portion is returned to the evaporating
portion through the wick provided on an inner wall of the
container. If a flow channel for the vaporized working fluid and a
flow channel for the condensed working fluid are too close to each
other, a flow of the condensed working fluid toward the evaporating
portion may be hindered by the vapor flow. In this case, the
working fluid cannot be delivered sufficiently to the evaporating
portion thereby deteriorating a heat transporting performance.
[0004] On the other hand, the loop heat pipe or thermosyphon is
formed into a cyclic structure while connecting the evaporating
portion with the condensing portion by a vapor pipe and a return
pipe. That is, the flow channel for the vaporized working fluid and
the flow channel for the condensed working fluid are sufficiently
isolated from each other. Therefore, in the loop heat pipe or
thermosyphon, the flow of the condensed working fluid toward the
evaporating portion will not be hindered by the vapor flow so that
the heat transporting performance can be enhanced. One example of a
heat accumulation type steam generator using the loop heat pipe is
described in Japanese Patent Laid-Open No. 10-2501 discloses.
[0005] In the loop heat pipe taught by Japanese Patent Laid-Open
No. 10-2501, a switching valve is disposed in the fluid return pipe
for returning the working fluid from the condensing portion to the
evaporating portion. Therefore, a dryout of the heat pipe may be
achieved by closing the switching valve to block the working fluid
flowing toward the evaporating portion. Consequently, the working
fluid disappears from the evaporating portion so that a heat
transportation of the heat pipe is stopped. The heat transportation
may be restarted by opening the switching valve thereby allowing
the working fluid to flow downwardly toward the evaporating
portion. Consequently, the working fluid is vaporized at the
evaporation portion to resume the heat transportation. In this
situation, however, the working fluid is delivered to the
evaporating portion in the dry condition. Therefore, if the
temperature of the evaporating portion is too high, an evaporation
of the working fluid may be disturbed by a vapor film covering the
dew drop of the working fluid. Such phenomenon is called
Leidenfrost phenomenon. If the dew drop is covered with the vapor
film, the working fluid cannot be contacted with an inner wall of
the evaporating potion. Therefore, it is difficult for the working
fluid to be heated and evaporated. Japanese Patent Laid-Open No.
7-103679 describes a structure to prevent the Leidenfrost
phenomenon. According to the teachings of Japanese Patent Laid-Open
No. 7-103679, a structure comprises a needlelike protrusion formed
by cutting and bending a tip of the metal strand of a mesh body,
and the protrusion penetrates into the dew to transfer the heat
directly to the dew.
[0006] As described, in the loop heat pipe or the loop thermosyphon
(both devices will simply be called a "loop thermosyphon"
hereafter), the working fluid is evaporated by an external heat,
and the vapor of the working fluid flows toward the condensing
portion where the temperature and the pressure is low to radiate
the heat. For this reason, the loop thermosyphon is allowed to be
operated automatically without requiring any specific power source,
and heat transporting performance thereof is excellent. This
characteristic is useful for the emergency cooling when emergency
or abnormal situation happens in a heating facility or system. For
instance, if the loop thermosyphon is used in the emergency cooling
system for a core or a nuclear fuel storage facility of a nuclear
reactor, a temperature of the nuclear reactor will not be raised
abnormally even if a power is lost.
[0007] Such emergency situation is brought about a loss of power or
cooling water. That is, in the emergency case, the temperature of
the evaporating portion may have been raised abnormally when the
loop thermosyphon is started. In this situation, if the working
fluid is delivered to the evaporating portion, the heat transfer to
the working fluid is disturbed by the afore-mentioned Leidenfrost
phenomenon. Consequently, a cooling operation may be delayed, or
the cooling operation may not be carried out. In order to avoid
such disadvantages, the needlelike protrusion taught by Japanese
Patent Laid-Open No. 7-103679 may be applied to the inner wall of
the evaporating portion. However, although the needlelike
protrusion facilitates the heat transfer to the dew of the working
fluid, it may not solve the Leidenfrost phenomenon completely.
Therefore, the conventional loop thermosyphon has to be improved to
be used in the emergency cooling system for the nuclear
reactor.
DISCLOSURE OF THE INVENTION
[0008] The present invention has been conceived noting the
above-mentioned technical problems, and it is therefore an object
of the present invention is to provide an emergency cooling system
using a loop thermosyphon that has an excellent cooling performance
and that can be started immediately.
[0009] The present invention is applied to an emergency cooling
system comprised of: a loop thermosyphon, in which an evaporating
portion at which heat exchange with a cooling object takes place is
connected with a condensing portion at which a heat radiation takes
place through a vapor pipe and a return pipe in a manner to form a
cyclic conduit; a condensable working fluid that is circulated
within the loop thermosyphon to be evaporated by a heat of the
cooling object at the evaporating portion, and to be condensed at
the condensing portion to radiate the heat conducted from the
cooling object; and a switching valve that is disposed on the
return pipe to selectively allow the working fluid in a liquid
phase to be returned from the condensing portion to the evaporating
portion. In order to achieve the above-mentioned object, according
to the present invention, the emergency cooling system is provided
with a heat transfer pipe, which is arranged in the evaporating
portion and to which the heat of the cooling object is conducted; a
heat transfer protrusion that is formed on an inner wall of the
heat transfer pipe to penetrate through a dew of the working fluid;
and a preheating portion, which is formed within a portion of the
return pipe connected to the heat transfer pipe, and to which the
heat of the cooling object is conducted.
[0010] The preheating portion is formed within the portion of the
return pipe extending inside of the cooling object. Optionally, the
preheating portion may be formed into a meander pipe by bending the
return pipe.
[0011] The condensing portion is situated higher than the
evaporating portion, and the storage tank is connected with a lower
portion of the condensing portion to hold the working fluid in the
liquid phase. In addition, the emergency cooling system according
to the present invention may be used to cool a container holding an
atomic fuel.
[0012] The evaporating portion is comprised of: an upper header
pipe; an lower header pipe; and a plurality of the heat transfer
pipes arranged in parallel with one another while being connected
with the upper header pipe and the lower header pipe. On the other
hand, the condensing portion is comprised of: another upper header
pipe; another lower header pipe; a plurality of a radiating pipes
arranged in parallel with one another while being connected with
said another upper header pipe and said another lower header pipe;
and a plurality of radiator fins mounted on the radiating pipes to
radiate the heat to the air.
[0013] Thus, according to the present invention, the switching
valve is opened to deliver the working fluid in the liquid phase to
the evaporating portion to cool the cooling object in case of
emergency. In addition, the return pipe leading the working fluid
in the liquid phase partially serves as the preheating portion
receiving the heat from the cooling object. In case of emergency, a
temperature of the cooling object is raised significantly.
Therefore, a temperature of the working fluid flowing toward the
evaporating portion is raised almost to the saturation temperature
during passing through the preheating portion. In this situation,
since the evaporating portion has already been heated by the heat
of the cooling object, the liquid phase working fluid is heated
drastically to be turned into dews covered with a vapor film.
However, a plurality of the protrusions are formed on the inner
surface of the heat transfer pipes to penetrate through the dews of
the working fluid. Therefore, the dews of the working fluid is
allowed to be heated from inside through the protrusion. Thus, the
heat can be conducted efficiently to the dews of the working fluid
that has been heated preliminary. For these reasons, the
Leidenfrost phenomenon can be solved to facilitate the heat
conduction to the liquid phase working fluid. That is, the cooling
object can be cooled efficiently through the heat transfer pipes.
Consequently, the working fluid is vaporized and flows toward the
condensing portion. Then, the heat transported by the working fluid
in the vapor phase is radiated from the condensing portion and the
working fluid is condensed again. The working fluid thus condensed
is again delivered to the evaporating portion through the return
pipe to be evaporated while drawing the heat from the cooling
object. Thus, in the emergency cooling system, the heat of the
cooling object is transported and released to outside by the
working fluid circulating in the system while being evaporated and
condensed alternately. In addition, according to the emergency
cooling system of the present invention, the liquid phase working
fluid and the vapor phase working fluid flow through different
routes. Therefore, the liquid phase working fluid and the vapor
phase working fluid will not conflict with each other so that the
working fluid can be returned to the evaporating portion in ample
amounts. For this reason, a heat transporting efficiency and a
cooling performance of the emergency cooling system can be
enhanced. In addition, the emergency cooling system of the present
invention can be operated without requiring an external power.
Therefore, the cooling object can be cooled certainly even if the
electric power is lost.
[0014] As described, according to the present invention, the
condensing portion is situated higher than the evaporating portion,
and the storage tank is connected with the lower portion of the
condensing portion. That is, the working fluid in the liquid phase
is allowed to be returned gravitationally to the evaporating
portion. Therefore, the working fluid is allowed to be returned
certainly to the evaporating portion so that the dry-out of the
evaporating portion can be prevented certainly, and the cooling
object can be cooled certainly.
[0015] The emergency cooling system of the present invention may
also be used to cool a containment of the atomic fuel which may
cause a serious accident.
[0016] In addition, even a large cooling object can be cooled
efficiently by the emergency cooling system of the present
invention using a single loop thermosyphon.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a view schematically showing a preferred example
of the present invention.
[0018] FIG. 2 is a partial cross-sectional view showing a
heat-transfer protrusion according to the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0019] Next, a preferred example of the present invention will be
explained hereinafter. The present invention may be applied to a
heat generating facility that potentially causes an accident under
a situation where a temperature thereof cannot be controlled.
Specifically, the present invention is applied to a facility for
converting thermal energy resulting from an exothermal reaction
into a mechanical power or an electric power. In the preferred
example, the present invention is applied to a fuel container of a
nuclear plant. The loop thermosyphon of the present invention is
entirely formed into a cyclic pathway, and comprised of an
evaporating portion at which a heat of the cooling object is drawn,
and a condensing portion from which the heat is radiated. The
evaporating portion and the condensing portion are connected
through a vapor pipe and a return pipe, and a condensable working
fluid encapsulated therein returns gravitationally from the
condensing portion to the evaporating portion. In order to enhance
a cooling performance, a heat receiving area and a radiating area
may be enlarged. As described, the cooling system according to the
present invention is used for emergencies. Therefore, a switching
valve is disposed in the return pipe to start the system on an
emergency basis. To this end, a fuse closing the valve is unlocked
automatically or broken in case of emergency to open the valve
without requiring external power.
[0020] Referring now to FIG. 1, there is shown the preferred
example of the emergency cooling system applied to a nuclear fuel
container. In order to cool the containment 1 naturally even if the
power is lost, the emergency cooling system is adapted to radiate
heat of the containment 1 without using an external power. To this
end, the emergency cooling system is comprised of a loop
thermosyphon 2 for transporting the heat from the containment 1 to
the air. That is, the loop thermosyphon 2 is a thermoelectric
element (or heat transfer means) adapted to transport the heat in
the form of latent heat of condensable working fluid. Specifically,
the loop thermosyphon 2 is comprised of an evaporating portion 3
where an evaporation of the working fluid takes place, and a
condensing portion 4 where a condensation of the working fluid
takes place. The evaporating portion 3 and the condensing portion 4
are connected through a vapor pipe 5 and a return pipe 6 in a
circular manner.
[0021] The evaporating portion 3 is arranged inside of the
containment 1 in a manner to exchange the heat with the containment
1. According to the preferred example shown in FIG. 1, the
evaporating portion 3 is comprised of a plurality of a heat
transfer pipe 7 arranged in parallel with one another, an upper
header pipe 8, and a lower header pipe 9. An upper end of each heat
transfer pipe 7 is individually connected with the upper header
pipe 8, and a bottom end of each heat transfer pipe 7 is
individually connected with the lower header pipe 9. Such piping
structure provides an enlarged surface area of the evaporating
portion 3. As shown in FIG. 2, a plurality of heat transfer
protrusions 10 adapted to penetrate into dews resulting from the
Leidenfrost phenomenon are formed on inner walls of the heat
transfer pipe 7 and the header pipes 8 and 9. As illustrated in
FIG. 2, the heat transfer protrusion 10 is formed into a needlelike
conical shape so that the protrusion 10 can penetrate into a dew 11
utilizing a strenuous movement of the dew 11 caused by heat.
[0022] The condensing portion 4 is situated in the air above the
level of the evaporating portion 3. Specifically, the condensing
portion 4 is comprised of a plurality of a radiating pipes 13
arranged in parallel with one another, an upper header pipe 14, and
a lower header pipe 15. In order to enlarge a radiation area, a
plurality of radiator fins 12 are mounted to each radiating pipe
13, and an upper end of each radiating pipe 13 is connected
individually with the upper header pipe 14 and a bottom end of each
radiating pipe 13 is connected individually with the lower header
pipe 15.
[0023] The upper header pipe 8 of the evaporating portion 3 is
connected with the upper header pipe 13 of the condensing portion 4
through the vapor pipe 5, and the lower header pipe 9 of the
evaporating portion 3 is connected with the lower header pipe 15 of
the condensing portion 4 through the return pipe 6. Accordingly,
the loop thermosyphon 2 is entirely formed into a circuit conduit.
Here, a diameter of the vapor pipe 5 is larger than that of the
return pipe 6. In the loop thermosyphon 2 thus structured,
condensable working fluid such as water or alcohol is encapsulated.
In order to allow the working fluid to circulate smoothly within
the loop thermosyphon 2, and to expedite an evaporation of the
working fluid, it is preferable to evacuate incondensable gas such
as the air from the loop thermosyphon 2.
[0024] A portion of the return pipe 6 within a predetermined length
from the evaporating portion 3 serves as a preheating portion 16.
Therefore, a temperature of the liquid phase working fluid flowing
through the preheating portion 16 can be heated preliminary by
exchanging heat with containment 1. To this end, one of the end
portions of the return pipe 6 within a predetermined length from
the evaporating portion 3 extends through the containment 1.
Optionally, the preheating portion 16 may be formed by partially
bending the preheating portion 16 to form a meander pipe so that
the containment 1 may also be cooled by the preheating portion
16.
[0025] In order to block the flow of the working fluid in the
liquid phase, a switching valve 17 is disposed on a predetermined
portion of the return pipe 6 between the condensing portion 4 and
the preheating portion 16. The switching valve 17 is opened in case
of emergency without requiring external power such as electricity.
For this purpose, the switching valve 17 is closed by a fuse or a
locking mechanism under the normal condition, and the fuse or the
locking mechanism is melted or broken to open the switching valve
17 in case of emergency so as to cool the containment 1
urgently.
[0026] A storage tank 18 for holding the working fluid in the
liquid phase is connected with a lower portion of the condensing
portion 4, more specifically, to the lower header pipe 15. Given
that the switching valve 17 is closed, the working fluid condensed
into the liquid phase at the condensing portion 4 flows gradually
into the storage tank 18. Since the storage tank 18 is connected to
the cyclic conduit, the incondensable gas such as the air is also
evacuated from the storage tank 18 so that only the working fluid
is allowed to enter into the storage tank 18.
[0027] Next, an action of the emergency cooling system thus
structured will be explained hereinafter. Provided that the
containment 1 is in the normal condition, the temperature of the
containment 1 is not especially high and the cooling operation of
the loop thermosyphon 2 will not be carry out. Therefore, the
switching valve 17 is closed. In this situation, the working fluid
is not delivered to the evaporating portion 3 so that the
evaporating portion 3 is dried out. Therefore, the heat
transportation utilizing the evaporation and the condensation of
the working fluid is not caused. By contrast, if the power is lost
accidentally thereby causing a cessation of an electric cooling
system, the temperature of the containment 1 is raised excessively
by a heat resulting from a collapse of the fuel rod. The switching
valve 17 is opened in response to such an emergency thereby
allowing the working fluid in the condensing portion 4 and the
storage tank 18 to flow down through the return pipe 6
gravitationally (i.e., by a hydraulic head pressure).
[0028] As described, the portion of the return pipe 6 within a
predetermined length from the evaporating portion 3 serves as the
preheating portion 16. Therefore, the working fluid in liquid phase
is heated at the preheating portion 16 so that the temperature of
the working fluid is raised and the working fluid is evaporated
partially. In this situation, the Leidenfrost phenomenon can be
inhibited to facilitate the heat transportation to the liquid phase
working fluid by forming the heat transfer protrusions 10 shown in
FIG. 2 on the inner wall of the preheating portion 16.
Consequently, the working fluid preliminary heated almost to the
saturation temperature is delivered to the evaporating portion 3.
According to the example shown in FIG. 1, the working fluid is
delivered initially to the lower header pipe 9, and the heat
transfer pipes 7 are gradually filled with the working fluid. That
is, the fluid level in the heat transfer pipe 7 rises with an
increase in quantity of the working fluid delivered to the lower
header pipe 15.
[0029] Before the power was lost accidentally, the evaporating
portion 3 has been kept in the dry condition so that the
temperatures of the lower header pipe 9 and the heat transfer pipes
7 have been raised considerably. Therefore, the working fluid
delivered to the lower header pipe 9 is contacted sequentially with
the inner walls of the lower header pipe 9 and the heat transfer
pipe 7 and evaporated rapidly. As a result, the dews 11 covered
with the vapor of the working fluid are created. That is, the
Leidenfrost phenomenon occurs at least locally. However, a
plurality of the heat transfer protrusions 10 shown in FIG. 2 are
formed on the inner walls of the lower header pipe 9 and the heat
transfer pipe 7. Those protrusions 10 penetrate into the dews 11 of
the working fluid so that the dews 11 are heated by the protrusions
10 from the inside. If the surface of the dew 11 is covered with
the vapor film, the dew 11 is prevented from being contacted with
the inner walls of the lower header pipe 9 and the heat transfer
pipes 7, and this makes difficult to transfer the heat to the to
the dews 11. However, the heat can be conducted efficiently to the
dews 11 by the heat transfer protrusions 10.
[0030] The liquid phase working fluid flowing through the return
pipe 6 has already been heated to almost the saturation temperature
by the preheating portion 16 on the way to the evaporating portion
3. Therefore, the working fluid is immediately evaporated when
reaches the evaporating portion 3. However, the temperature of the
evaporating potion 3 has been raised considerably after the
occurrence of emergency. For this reason, even if the working fluid
in the liquid phase has already been heated nearly to the
saturation temperature, the Leidenfrost phenomenon may be caused in
this situation. According to the preferred example, however, the
heat is conducted efficiently to the dews 11 of the working fluid
resulting from the Leidenfrost phenomenon from inside by the
protrusions 10. Therefore, the heat transfer to the working fluid
can be facilitated to vaporize the working fluid rapidly in large
quantity by thus preliminary heating the working fluid almost to
the saturation temperature while solving film boiling.
[0031] The vapor thus generated by the heat transfer pipes 7
ascends to the upper header pipe 8, and then migrates to the
condensing portion 4 exposed to the air to be cooled. Therefore,
the heat of the vaporized working fluid is radiated through the
radiating pipes 13 and the radiating fins 12. Thus, the heat of the
containment 1 is conveyed in the form of latent heat and radiated
to the air so that the containment 1 is cooled naturally
indirectly. After radiating the heat, the temperature of the
working fluid is lowered so that the working fluid is condensed to
be brought into the liquid phase, and falls to the lower header
pipe 15. As described, the condensing portion 4 is situated higher
than the evaporating portion 3 so that the working fluid thus
brought into liquid phase is allowed to be returned gravitationally
(i.e., by a hydraulic head pressure) to the evaporating portion 3
through the return pipe 6. The working fluid thus delivered again
to the evaporating portion 3 is evaporated by the heat of the
containment 1. In this situation, the temperature of the inner
walls of the lower header pipe 9 and the heat transfer pipes 7 has
been lowered to some extent by the working fluid delivered thereto
previously. Therefore, the evaporation of the working fluid can be
facilitated by thus heating the liquid phase working fluid to some
extent by the preheating portion 16 while preventing the occurrence
of the Leidenfrolst phenomenon. Here, even if the Leidenfrost
phenomenon occurs, the heat is transmitted swiftly to the dews 11
of the working fluid by the heat transfer protrusions 10 formed on
the inner walls of the lower header pipe 9 or the heat transfer
pipes 7 forming the evaporating portion 3. Therefore, the
evaporation of the working fluid can be facilitated in case of
Leidenfrost phenomenon.
[0032] Thus, according to the emergency cooling system of the
present invention, the working fluid is delivered automatically to
the cooling object by opening the switching valve 17, and the heat
can be transported by the working fluid continuously to the air.
Therefore, even if the power is lost, the temperature of the
cooling object such as the containment 1 can be maintained to be
lower than a temperature which might destroy the cooling object 1.
Especially, even if the temperature of the cooling object or the
evaporating portion 3 is abnormally high in the beginning of the
emergency cooling, the preheating portion 16 and the heat transfer
protrusions 10 prevent an occurring of the Leidenfrost phenomenon
so that the heat transmission to the working fluid and the
evaporation of the working fluid can be facilitated. Therefore, the
cooling object can be cooled immediately and certainly in the
begging of emergency situation.
[0033] Here, although the emergency cooling system is applied to
the containment 1 holding the atomic fuel in the preferred example,
the emergency cooling system of the present invention may also be
applied to other facilities necessary to be cooled in the emergency
situation.
* * * * *