U.S. patent application number 12/763296 was filed with the patent office on 2010-10-28 for ceramics heat exchanger and production method thereof.
This patent application is currently assigned to NGK Insulators, Ltd.. Invention is credited to Hiroshi Mizuno, Michio TAKAHASHI.
Application Number | 20100270011 12/763296 |
Document ID | / |
Family ID | 42357867 |
Filed Date | 2010-10-28 |
United States Patent
Application |
20100270011 |
Kind Code |
A1 |
TAKAHASHI; Michio ; et
al. |
October 28, 2010 |
CERAMICS HEAT EXCHANGER AND PRODUCTION METHOD THEREOF
Abstract
In a heat exchange element 1, first fluid circulation portions 5
having a honeycomb structure having a plurality of cells separated
by ceramic partition walls 4, extending through in an axial
direction from one end face 2 to the other end face 2, and allowing
a heated medium as a first fluid to flow therethrough and second
fluid circulation portions 6 being separated by ceramic partition
walls 4, extending in the direction perpendicular to the axial
direction, allowing a second fluid to flow therethrough,
transferring heat to a medium to be heated as the second fluid are
alternately formed as a unit. The cells 3 on the first fluid
circulation portion 5 side are smaller than the cells 3 on the
second fluid circulation portion 6 side, and the partition walls
have a density of 0.5 to 5 g/cm.sup.3 and a thermal conductivity of
10 to 300 W/mK.
Inventors: |
TAKAHASHI; Michio;
(Nagoya-City, JP) ; Mizuno; Hiroshi;
(Kagamihara-City, JP) |
Correspondence
Address: |
BURR & BROWN
PO BOX 7068
SYRACUSE
NY
13261-7068
US
|
Assignee: |
NGK Insulators, Ltd.
Nagoya-City
JP
|
Family ID: |
42357867 |
Appl. No.: |
12/763296 |
Filed: |
April 20, 2010 |
Current U.S.
Class: |
165/148 ;
29/890.03 |
Current CPC
Class: |
Y10T 29/4935 20150115;
F28F 21/04 20130101; F28D 21/0003 20130101; F28F 7/02 20130101;
F28D 7/0025 20130101; F01N 2240/02 20130101 |
Class at
Publication: |
165/148 ;
29/890.03 |
International
Class: |
F28D 1/00 20060101
F28D001/00; B21D 53/02 20060101 B21D053/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 23, 2009 |
JP |
2009-105246 |
Apr 16, 2010 |
JP |
2010-095149 |
Claims
1. A ceramics heat exchanger comprising: first fluid circulation
portions having a honeycomb structure having a plurality of cells
separated by ceramic partition walls, extending through in an axial
direction from one end face to the other end face, and allowing a
heated medium as a first fluid to flow therethrough, and second
fluid circulation portions being separated by ceramic partition
walls, extending in the direction perpendicular to the axial
direction, being isolated from the first fluid circulation portions
by the partition walls to be capable of heat conduction, allowing a
second fluid to flow therethrough, receiving the heat of the first
fluid circulating in the first fluid circulation portions by means
of the partition walls, and having cells for transferring heat to a
medium to be heated as the second fluid; wherein the first fluid
circulation portions and the second fluid circulation portions are
alternately formed as a unit, the cells on the first fluid
circulation portion side are smaller than the cells on the second
fluid circulation portion side, and the partition walls have a
density of 0.5 to 5 g/cm.sup.3 and a thermal conductivity of 10 to
300 W/mK.
2. The ceramics heat exchanger according to claim 1, wherein each
of the second fluid circulation portions has a slit structure
having no separating partition wall or having 1 to 50 separating
partition walls.
3. The ceramics heat exchanger according to claim 1, wherein a
plurality of the heat exchange elements are bonded together by
means of a bonding material layer of heat resistant cement.
4. The ceramics heat exchanger according to claim 1, wherein SiC is
contained in the ceramics constituting the partition walls.
5. The ceramics heat exchanger according to claim 1, wherein the
ceramics constituting the partition walls is Si-impregnated
SiC.
6. The ceramic heat exchanger according to claim 1, wherein the
first fluid is gas, and the second fluid is liquid.
7. The ceramic heat exchanger according to claim 1, wherein a
catalyst is loaded on wall surfaces of the first fluid circulation
portions.
8. A method for manufacturing a ceramics heat exchanger comprising
the steps of: forming a honeycomb structure having a plurality of
cells separated by ceramic partition walls and extending through in
an axial direction from one end face to the other end face by
extruding a ceramic forming raw material, forming slits with regard
to a part of a plurality of cell lines to extend through the
partition walls forming the cells and the outer peripheral wall of
the honeycomb structure in the direction perpendicular to the axial
direction, and forming plugged portions plugged with a plugging
member on one end face and the other end face of the cells in the
cell lines where slits are formed.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a ceramics heat exchanger
for transferring heat of the first fluid (high temperature side) to
the second fluid (low temperature side).
BACKGROUND OF THE INVENTION
[0002] Generally, driving energy of an automobile is merely about
25% of fuel combustion energy. The rest becomes an energy loss such
as a cooling loss (engine cooling water of 30%), an exhaust gas
loss (exhaust gas of 30%), and the like. After 2010, in the
automobile field, CO.sub.2 reduction has been becoming strict, and
fuel efficiency requirements have been being tightened. Therefore,
many automobile companies work on reduction of the exhaust gas
loss, for example, exhaust heat recovery technology as a measure
for reducing the energy loss to improve automobile gas mileage.
[0003] Patent Document 1 discloses a ceramic heat exchange element
where flow passages for a heated medium are disposed from one end
face to the other end face of a ceramic main body and where flow
passages for a medium to be heated are formed in a direction
perpendicular to the flow passages for the heated medium between
the flow passages for the heated medium.
[0004] Patent Document 2 discloses a ceramic heat exchanger where a
plurality of ceramic heat exchange elements each having flow
passages for a heated fluid and flow passages for a fluid to be
heated formed therein are disposed in a casing with interposing a
cord-shaped sealing material made of unfired ceramic between
bonding faces of heat exchange elements.
[0005] The Patent Document 3 discloses an exhaust system heat
exchanger capable of inhibiting a cooling medium in an external
cylinder from having high temperature. In addition, the Patent
Document 4 discloses an exhaust gas heat recovery unit capable of
relaxing thermal stress with a simple structure. Further, Patent
Document 5 discloses an exhaust gas heat exchanger which is
miniaturized and which can suppress costs with a structure capable
of easy installation.
[Prior Art Document]
[Patent Document]
[0006] [Patent Document 1] JP-A-61-24997
[0007] [Patent Document 2] JP-B-63-60319
[0008] [Patent Document 3] JP-A-2007-285260
[0009] [Patent Document 4] JP-A-2007-332857
[0010] [Patent Document 5] JP-A-2006-284165
[0011] Each of the Patent Documents 1 and 2 shows a structure where
a heated fluid flows thereinto from the flow passages having a slit
structure and where a medium to be heated flows thereinto from
honeycomb structured flow passages to reduce the influence of a
pressure loss of the heated fluid. However, the structure does not
have good efficiency regarding the heat exchange.
[0012] The Patent Document 3 shows a structure where a heat
exchange passage for water cooling is disposed in the periphery of
a heat exchange passage for exhaust gas, it is more difficult to
exchange heat in the central portion of the exhaust gas flow
passages, and the heat exchange rate is low as a whole. In
addition, in the Patent Document 4, the structure is constituted of
an evaporation portion (first heat exchange portion), a
heat-transfer fin, and a condensation portion (second heat exchange
portion) However, since it exchanges heat by means of a
heat-transfer fin without directly exchanging heat, the heat
exchange efficiency is low. On the other hand, in the Patent
Document 5, a heat exchange core portion obtained by laminating a
plurality of flat plates are formed in the route where exhaust gas
passes, and a cooling liquid flow passage extending through in the
thickness direction is formed. However, since exhaust gas flows
through a gap between the flat plates, though the heat exchanger
has high heat exchange efficiency in comparison with those of the
Patent Documents 3 and 4, the contact area is not always large for
heat transfer from the exhaust gas to the flat plates, and
insufficient heat exchange may be caused between the exhaust gas
and the cooling liquid.
[0013] The present invention aims to provide a heat exchanger
having high heat exchange efficiency in comparison with
conventional heat exchange elements, heat exchangers, and the like
and realizing miniaturization, weight saving, and cost reduction
and a production method thereof.
SUMMARY OF THE INVENTION
[0014] The present inventors found out that the aforementioned
problems can be solved by a ceramics heat exchanger provided with a
heat exchange element where the first fluid circulation portions
for allowing a heated medium as the first fluid to circulate and
the second fluid circulation portions for transferring heat to a
medium to be heated as the second fluid are alternately formed as a
unit. That is, according to the present invention, there are
provided the following ceramics heat exchanger and production
method thereof.
[0015] [1] A ceramics heat exchanger comprising: first fluid
circulation portions having a honeycomb structure having a
plurality of cells partitioned by ceramic partition walls,
extending through in an axial direction from one end face to the
other end face, and allowing a heated medium as a first fluid to
flow therethrough, and second fluid circulation portions being
partitioned by ceramic partition walls, extending in the direction
perpendicular to the axial direction, being isolated from the first
fluid circulation portions by the partition walls to be capable of
heat conduction, allowing a second fluid to flow therethrough,
receiving the heat of the first fluid circulating in the first
fluid circulation portions by means of the partition walls, and
having cells for transferring heat to a medium to be heated as the
second fluid; wherein the first fluid circulation portions and the
second fluid circulation portions are alternately formed as a unit,
the cells on the first fluid circulation portion side are smaller
than the cells on the second fluid circulation portion side, and
the partition walls have a density of 0.5 to 5 g/cm.sup.3 and a
thermal conductivity of 10 to 300 W/mK.
[0016] [2] The ceramics heat exchanger according to the above [1],
wherein each of the second fluid circulation portions has a slit
structure having no separating partition wall or having 1 to 50
separating partition walls.
[0017] [3] The ceramics heat exchanger according to the above [1]
or [2], wherein a plurality of the heat exchangers are bonded
together by means of a bonding material layer of heat resistant
cement.
[0018] [4] The ceramics heat exchanger according to any one of the
above [1] to [3], wherein SiC is contained in the ceramics
constituting the partition walls.
[0019] [5] The ceramics heat exchanger according to any one of the
above [1] to [4], wherein the ceramics constituting the partition
walls is Si-impregnated SiC.
[0020] [6] The ceramic heat exchanger according to any one of the
above [1] to [5], wherein the first fluid is gas, and the second
fluid is liquid.
[0021] [7] The ceramic heat exchanger according to any one of the
above [1] to [6], wherein a catalyst is loaded on wall surfaces of
the first fluid circulation portions.
[0022] [8] A method for manufacturing a ceramics heat exchanger
comprising the steps of: forming a honeycomb structure having a
plurality of cells separated by ceramic partition walls and
extending through in an axial direction from one end face to the
other end face by extruding a ceramic forming raw material, forming
slits with regard to a part of a plurality of cell lines to extend
through the partition walls forming the cells and the outer
peripheral wall of the honeycomb structure in the direction
perpendicular to the axial direction, and forming plugged portions
plugged with a plugging member on one end face and the other end
face of the cells in the cell lines where slits are formed.
[0023] In a ceramics heat exchanger of the present invention,
attention is paid to heat and a heat exchange element which
exchanges heat in exhaust heat recovery technology, and the heat
exchanger realizes high heat exchange efficiency, miniaturization,
weight saving, and cost reduction in comparison with a conventional
heat exchange element (heat exchanger or its device).
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a perspective view showing an embodiment of a heat
exchange element of the present invention.
[0025] FIG. 2A is a view showing an embodiment of an end face in
the axial direction of a heat exchange element of the present
invention.
[0026] FIG. 2B is a view showing another embodiment of an end face
in the axial direction of a heat exchange element of the present
invention.
[0027] FIG. 3A is a view showing an embodiment viewed from the
outer peripheral wall side where slits are formed.
[0028] FIG. 3B is a view showing another embodiment viewed from the
outer peripheral wall side where slits are formed.
[0029] FIG. 4 is a view showing an embodiment where a plurality of
heat exchange elements are bonded together.
[0030] FIG. 5 is a view showing an embodiment of a ceramics heat
exchanger of the present invention where a heat exchange element is
disposed therein.
[0031] FIG. 6 is a view showing an embodiment of a heat exchange
element where some of the partition walls have different
thickness.
[0032] FIG. 7A is a view from the inlet side of the first fluid,
showing an embodiment where an end face in the axial direction of
partition walls of a heat exchange element is a tapered face.
[0033] FIG. 7B is a cross-sectional view taken along a face in
parallel with the axial direction, showing an embodiment where an
end face in the axial direction of partition walls of a heat
exchange element is a tapered face.
[0034] FIG. 8A is a view showing an embodiment of a heat exchange
element where cells having different sizes are formed.
[0035] FIG. 8B is a decomposition perspective view of the
embodiment of FIG. 8A.
[0036] FIG. 8C is a decomposition perspective view showing an
embodiment of a circular columnar heat exchange element where cells
having different sizes are formed.
[0037] FIG. 8D is a view showing an embodiment of a heat exchange
element where the size of the cells is changed.
[0038] FIG. 8E is a view showing an embodiment of heat exchange
element where the thickness of the partition walls is changed.
[0039] FIG. 9A is a view showing an embodiment of a heat exchange
element where the thickness of the partition walls is increased
from the inlet side of the first fluid toward the outlet side.
[0040] FIG. 9B is a view showing an embodiment of a heat exchange
element 1 where the first fluid circulation portion is gradually
narrowed from the inlet side toward the outlet side of the first
fluid.
[0041] FIG. 10A is a view showing an embodiment where the cells of
a heat exchange element has a hexagonal shape.
[0042] FIG. 10B is a view showing an embodiment where the cells of
a heat exchange element has an octagonal shape.
[0043] FIG. 11 is a view showing an embodiment of a heat exchange
element where R portions are formed at the corners of the
cells.
[0044] FIG. 12A is a view showing an embodiment of a heat exchange
element having protruding fins in a cell.
[0045] FIG. 12B is a view showing another embodiment of a heat
exchange element having fins in a cell.
[0046] FIG. 13A is a view showing an embodiment of a heat exchange
element where a part of the cell structure is densified.
[0047] FIG. 13B is a decomposition perspective view of the
embodiment of FIG. 13A.
[0048] FIG. 13C is a decomposition perspective view showing an
embodiment of a circular columnar heat exchange element where cells
having different sizes are formed.
[0049] FIG. 13D is a view showing an embodiment of a heat exchange
element where the cell density is gradually changed.
[0050] FIG. 13E is a view showing an embodiment of a heat exchange
element where the cell structure is changed by changing the wall
thickness.
[0051] FIG. 14A is a view showing an embodiment of a heat exchanger
where the direction of the partition walls is offset between the
front part heat exchange element and the rear part heat exchange
element.
[0052] FIG. 14B is a view showing an embodiment of a heat exchanger
where the position of the partition walls is offset between the
front part heat exchange element and the rear part heat exchange
element.
[0053] FIG. 15 is a view showing an embodiment of a heat exchanger
where the cell density of the rear part heat exchange element is
higher than that of the front part heat exchange element.
[0054] FIG. 16 is a view showing an embodiment of a heat exchanger
having a constitution where the cell density of the front part heat
exchange element is high on the inside and low on the outer
periphery side and where the cell density of the rear part heat
exchange element is low on the inside and high on the outer
periphery side.
[0055] FIG. 17A is a view showing an embodiment of a heat exchanger
where a plurality of heat exchange elements are disposed, each of
the heat exchange elements has two semicircular regions having
different cell densities, the heat exchange elements are disposed
so that the cell density distribution is different between the
front part heat exchange element and the rear part exchange
element.
[0056] FIG. 17B is a decomposition perspective view of the
embodiment of FIG. 17A.
[0057] FIG. 17C is a view showing an embodiment of a heat exchange
element having two prismatic columnar regions having different cell
densities.
[0058] FIG. 18A is a view showing an embodiment of a heat exchanger
having a constitution where the front part heat exchange element is
plugged on the outer periphery side and where the rear part heat
exchange element is plugged on the inside.
[0059] FIG. 18B is a view showing an embodiment of a heat exchanger
obtained by disposing heat exchange elements where plugged
prismatic column and unplugged prismatic column are combined in the
front part position and the rear part position.
[0060] FIG. 19A is a view showing an embodiment of a heat exchange
element where the inlet and the outlet of the first fluid
circulation portion are alternately plugged.
[0061] FIG. 19B is an A-A cross section in FIG. 19A.
[0062] FIG. 20 is a cross section of the first fluid circulation
portion, showing an embodiment where porous partition walls are
formed in the first fluid circulation portion.
[0063] FIG. 21 is a view showing an embodiment of a heat exchange
element where the thickness of the partition walls forming the
first fluid circulation portion is gradually increased from the
center toward the outer periphery in a cross section perpendicular
to the axial direction.
[0064] FIG. 22 is a view showing an embodiment of a heat exchange
element using a honeycomb structure where the external shape is an
ellipse and where partition walls on one side is formed thick.
[0065] FIG. 23 is a view showing an embodiment where the outer
peripheral wall of a honeycomb structure forming the heat exchange
element is thicker than the partition walls forming the cells.
[0066] FIG. 24 is a view showing an embodiment where the external
shape of the honeycomb structure forming the heat exchange element
is flattened.
[0067] FIG. 25A is a perspective view showing an embodiment where
the end face on the inlet side of the first fluid is inclined.
[0068] FIG. 25B is a perspective view showing another embodiment
where the end face on the inlet side of the first fluid is
inclined.
[0069] FIG. 25C is a perspective view showing still another
embodiment where the end face on the inlet side of the first fluid
is inclined.
[0070] FIG. 26 is a view showing an embodiment where the end face
on the inlet side of the first fluid of the honeycomb structure
forming a heat exchange element is formed to have a depressed face
shape.
[0071] FIG. 27 is a view showing an embodiment of a heat exchanger
where an adiabatic plate have the same shape as the cells forming
the first fluid circulation portion is disposed on the inlet side
of the first fluid of a heat exchange element.
DETAILED DESCRIPTION OF THE INVENTION
[0072] Hereinbelow, embodiments of the present invention will be
described with referring to drawings. The present invention is not
limited to the following embodiments, and changes, modifications,
and improvements may be made as long as they do not deviate from
the scope of the invention.
[0073] FIG. 1 is a perspective view of a heat exchange element 1
with which a ceramics heat exchanger 10 of the present invention is
provided. In the heat exchange element 1, the first fluid
circulation portions 5 (high temperature side) each having a
honeycomb structure having a plurality of cells separated by
ceramic partition walls 4, extending through in the axial direction
from one end face 2 to the other end face 2, and allowing a heated
medium as the first fluid to flow therethrough and the second fluid
circulation portions 6 (low temperature side) each being separated
by porous partition walls 4, extending through in the direction
perpendicular to the axial direction, allowing the second fluid to
be circulated, and transferring heat to a medium to be heated as
the second fluid are alternately formed as a unit. The cells 3 on
the first fluid circulation portion 5 side are smaller than the
cells 3 on the second fluid circulation portion 6 side (In the
embodiment of FIG. 1, the cells 3 on the second fluid circulation
portion 6 side are slits.), and the partition walls 4 have a
density of 0.5 to 5 g/cm.sup.3 and a thermal conductivity of 10 to
300 W/mK. Making the cells 3 on the first fluid circulation portion
5 side smaller than the cells 3 on the second fluid circulation
portion 6 side is superior to making it larger in terms of heat
exchange efficiency. This is because heat can be transferred to the
partition walls 4 more easily when the cells 3 for the first fluid
(high temperature side) are small, and the size relation of the
cells 3 serves as an important element for heat transfer. That is,
by constituting the cells 3 on the first fluid circulation portion
5 side to be smaller than those on the second fluid circulation
portion 6 side, heat exchange efficiency can be improved.
[0074] Each of the first fluid circulation portions 5 preferably
has a honeycomb structure having a plurality of cells 3 separated
by ceramic partition walls 4 and extending through in the axial
direction.
[0075] It is preferable that each of the second fluid circulation
portions 6 has a slit structure having no separating partition wall
4 (partition wall 14 between slits (see FIG. 3B)) or having small
number of (1 to 50) separating partition walls. The second fluid
circulation portion 6 is isolated from the first fluid circulation
portion 5 by a partition wall 4 to be able to transferring heat,
and the second fluid circulates in it and receives heat of the
first fluid circulating in the first fluid circulation portions 5
by means of the partition walls 4, thereby heat is transferred to
the circulating medium to be heated, which is the second fluid.
[0076] In the case of honeycomb structure, when the fluid passes
through a cell 3, the fluid cannot flow into another cell 3 due to
the partition walls 4 and proceeds linearly from the inlet to the
outlet. On the other hand, in the case of a slit structure, for
example, the interior of the two slits as shown in FIG. 3B has no
partition wall 4, and slits in the same line are connected to each
other to allow a fluid to pass through to the slit outlet different
from the inlet of the fluid. That is, the slits in the same line
are connected to one another in the inside. However, in slits in
different lines, fluid cannot pass through because of the partition
wall 4.
[0077] The heat exchange element 1 of the present invention is
constituted by segments each having the first fluid circulation
portion 5 (high temperature side) of a honeycomb structure where
the first fluid (heated medium) circulates and the second fluid
circulation portion 6 (low temperature side) where the second fluid
(medium to be heated) for transferring heat circulates are formed.
For efficient heat exchange, it is more preferable that the first
fluid circulation portion 5 has a honeycomb structure. In the
honeycomb structure, a plurality of cells 3 functioning as fluid
passages are partitioned and formed by the partition walls 4, and,
for the cell shape, a desired shape may suitably be selected from a
circle, an ellipse, a triangle, a quadrangle, other polygons, and
the like. Incidentally, when a large-sized heat exchange element 1
is desired, a module structure where a plurality of segments are
bonded together can be employed. On the other hand, the second
fluid circulation portion 6 (low temperature side) where the second
fluid (medium to be heated) circulates preferably has a slit shape
(one or some in one line), and the shape of the second fluid
circulation portion 6 is not particularly limited.
[0078] Though the shape of the segment of the heat exchange element
1 of the present invention is a quadrangular prism, the shape is
not limited to this and may be another shape such as a circular
cylindrical shape.
[0079] There is no particular limitation on the cell density (i.e.,
number of cells per unit cross-sectional area) of the segment,
which is a heat exchange element 1 of the present invention, and
design may be performed suitably in accordance with the purpose.
However, it is preferably in the range from 25 to 2000 cells/sq.
in. (4 to 320 cells/cm.sup.2). When the cell density is below 25
cells/sq. in., the strength of the partition walls 4, eventually,
the strength of the heat exchange element 1 itself, and effective
GSA (geometrical surface area) may be insufficient. On the other
hand, when the cell density is above 2000 cells/sq. in., a pressure
loss when a heat medium flows therethrough may increase.
[0080] There is no particular limitation on the thickness of the
partition walls 4 (wall thickness) of the cells 3 of the honeycomb
segment, which is a heat exchange element 1 of the present
invention, and it may suitably be designed in accordance with the
purpose. The wall thickness is preferably 50 .mu.m to 2 mm, and
more preferably 60 to 500 .mu.m. When the wall thickness is smaller
than 50 .mu.m, the mechanical strength is decreased, and breakage
may be caused by an impact or thermal stress. On the other hand,
when it is larger than 2 mm, the rate of the cell capacity on the
honeycomb structure side is lowered, and a defect of deterioration
in heat exchange rate of permeation of a heating medium may be
caused.
[0081] FIG. 2A is a view from an end face 2 in the axial direction
of a segment, which is a heat exchange element 1 of an embodiment.
As shown in FIG. 2A, the heat exchange element 1 has a plurality of
cells 3 partitioned by ceramic partition walls 4 and functioning as
fluid passages, and an end face 2 on one side in the axial
direction is plugged in every other line. In addition, in the other
end face 2, the same cells 3 as in the end face 2 on the one side
are plugged in the same manner as FIG. 2A. Inside the plugged cells
3, partition walls 4 isolating the plugged cells 3 from one another
are removed to form a slit shape (see FIG. 3A). That is, in the
second fluid circulation portion 6, the end faces 2 in the axial
direction are plugged with a plugging material to form plugged
portions 13.
[0082] FIG. 2B is a view from an end face 2 on one side in the
axial direction of a heat exchange element 1 of another embodiment.
As shown in FIG. 2B, the heat exchange element 1 has a plurality of
cells 3 partitioned by ceramic partition walls 4 and functioning as
fluid passages, and an end face 2 on one side in the axial
direction is plugged in every other line. In addition, in the other
end face 2, the same cells 3 as in the end face 2 on the one side
are plugged in the same manner as FIG. 2A. Inside the plugged cells
3, partition walls 4 isolating the plugged cells 3 from one another
are removed to form a slit shape (see FIG. 3A). In the unplugged
cells 3, some of the partition walls 4 isolating the cells 3 from
one another are removed to form large-sized cells 3. In other
words, the unplugged line is formed to have a honeycomb structure
where at least one partition wall 4 is present. The constitution as
in FIG. 2B is effective for a segment having a long flow passage
because pressure loss of a fluid is smaller. That is, a large
amount of the first fluid can be allowed to flow.
[0083] FIG. 3A show an embodiment viewed from the outer peripheral
wall 7 side where slits are formed. As shown in FIG. 3A, in the
heat exchange element 1, slits extending through from one end face
12 in the direction perpendicular to the axial direction of the
outer peripheral wall 7 to the other end face 12 are formed, and
the slits function as the second fluid circulation portions 6. Each
of the slits is formed by removing the partition walls 4 of the
cells 3 plugged in one end face 2 and the other end face 2 in the
axial direction. That is, the slits are formed in the same
direction as the direction of the cell lines of the plugged cells
3. The cells 3 unplugged in the end faces 2 are in the state that
the partition walls 4 are formed as shown in FIG. 2A.
Alternatively, as shown in FIG. 2B, there may be employed a
constitution where the outer peripheral wall 7 is left and where
the partition walls 4 isolating the unplugged cells 3 from one
another are removed.
[0084] FIG. 3B shows another embodiment viewed from the outer
peripheral wall 7 side where slits are formed. As shown in FIG. 3B,
in the heat exchange element 1, slits extending through from one
end face 12 in the direction perpendicular to the axial direction
of the outer peripheral wall 7 to the other end face 12 are formed,
and an inter-slit partition wall 14 separating the slits is formed
in the center in the axial direction. Incidentally, the inside of
the inter-slit partition wall 14 has a shape where partition walls
of the cells 3 remain. This makes the structure of the heat
exchange element 1 itself strong. Therefore, the heat exchange
element 1 hardly breaks. When the slits are long, strength is
reduced, and breakage may be caused. However, by forming the
inter-slit partition wall 14, in other words, by leaving the cell
wall faces, increase in strength can be planned. The slits are
formed by removing the partition walls 4 of the cells 3 plugged in
one end face 2 on one side and the other end face 2 on the other
side in the axial direction, and the cells 3 unplugged in the end
faces 2 are as shown in FIGS. 2A and 2B like the aforementioned
embodiment.
[0085] It is preferable that the segment, which is a heat exchange
element 1, employs ceramics excellent in thermal resistance, in
particular, silicon carbide in consideration of conductivity.
However, it is not always necessary that the entire segment of the
heat exchange element 1 is constituted of silicon carbide as long
as silicon carbide is contained in the main body. That is, it is
preferable that the heat exchange element 1 of the present
invention is of conductive ceramics containing silicon carbide. As
a property of a segment of the heat exchange element 1, the thermal
conductivity at room temperature is preferably 10 W/mK or high, and
300 W/mK or low. However, it is not limited to the range. It is
possible to use a corrosion resistant metal material such as a
Fe--Cr--Al base alloy in place of the conductive ceramics.
[0086] The density of the partition walls 4 of the cells 3 of the
heat exchange element 1 is preferably 0.5 to 5 g/cm.sup.3. In the
case that it is below 0.5 g/cm.sup.3, the partition walls 4 have
insufficient strength and may break due to pressure when the first
fluid passes through the flow passages. In addition, when it is
above 5 g/cm.sup.3, the heat exchange element 1 itself becomes
heavy, and the characteristic of weight saving may be impaired. By
the density in the aforementioned range, the heat exchange element
1 can be made strong. In addition, the effect in improving the
thermal conductivity can be obtained.
[0087] In order that the heat exchange element 1 of a ceramics heat
exchanger 10 of the present invention may obtain high heat exchange
rate, it is preferable to use a material containing silicon carbide
having high thermal conductivity as the material for the segment.
However, since high thermal conductivity cannot be obtained in the
case of a porous body even by silicon carbide, it is more
preferable to obtain a dense body structure by impregnating the
segment as the heat exchange element 1 with silicon in the process
of producing the segment. By the dense body structure, high thermal
conductivity can be obtained. For example, in the case of porous
body of silicon carbide, it is about 20 W/mK. However, by the dense
body, it can be made about 150 W/mK.
[0088] That is, though Si-impregnated SiC, Si.sub.3N.sub.4, SiC, or
the like may be employed as the ceramic material, it is
particularly desirable to employ Si-impregnated SiC in order to
obtain a dense body structure for obtaining high heat exchange
rate. Since the Si-impregnated SiC has a structure where a
coagulation of metal silicon melt surrounds the surfaces of the SiC
particles and where SiC particles are unitarily bonded together by
means of metal silicon, silicon carbide is blocked from the
atmosphere containing oxygen to be inhibited from being oxidized.
Further, though SiC has the characteristics of high thermal
conductivity and easy heat release, Si-impregnated SiC is formed
densely with showing high thermal conductivity and heat resistance
and shows sufficient strength as a heat transfer member. That is,
the heat exchange element 1 of a Si--SiC based (Si-impregnated SiC)
material shows high thermal conductivity as well as properties
excellent in corrosion resistance against acid and alkali besides
thermal resistance, thermal shock resistance, and oxidation
resistance.
[0089] More specifically, in the case that the heat exchange
element 1 contains a Si-impregnated SiC composite material as the
main component, when the Si content specified by Si/(Si+SiC) is too
small, the bonding material becomes insufficient. Therefore,
bonding of adjacent SiC particles by the Si phase becomes
insufficient to lower the thermal conductivity and to have a
difficulty in obtaining strength capable of maintaining the thin
wall structure such as a honeycomb structure. Inversely, when the
Si content is too large, the heat exchange element 1 is excessively
contracted by firing due to the presence of metal silicate in the
amount where the SiC particles can suitably be bonded or more to
cause negative effects such as decrease in porosity and reduction
in average pore diameter, which is not preferable. Therefore, the
Si content is preferably 5 to 50 mass %, more preferably 10 to 40
mass %.
[0090] In such Si-impregnated SiC, pores are filled with metal
silicon, and there is a case that the porosity is 0 or nearly 0. It
is excellent in oxidation resistance and durability and can be used
for a long period of time in a high temperature atmosphere. Once it
is oxidized, since an oxidation protection film is formed,
oxidation deterioration is not caused. In addition, since it has
high strength from ordinary temperature to high temperature, a thin
and light weight structure can be formed. Further, it has high
thermal conductivity which is about the same as that of copper or
aluminum metal, high far-infrared emissivity, and electrical
conductivity, thereby hardly having static electricity.
[0091] In the case that the first fluid (high temperature side)
allowed to circulate in a ceramics heat exchanger 10 of the present
invention is exhaust gas, it is preferable that a catalyst is
loaded on the wall surfaces inside the cells 3 of the heat exchange
element 1 where the first fluid (high temperature side) passes.
This is because it can exchange also reaction heat (exothermic
reaction) generating upon exhaust gas purification in addition to
the role of exhaust gas purification. The catalyst preferably
contains at least one element selected from the group consisting of
noble metals (platinum, rhodium, palladium, ruthenium, indium,
silver, and gold), aluminum, nickel, zirconium, titanium, cerium,
cobalt, manganese, zinc, copper, zinc, tin, iron, niobium,
magnesium, lanthanum, samarium, bismuth, and barium. These may be
metals, oxides, and other compounds. The amount of the catalyst
(catalyst metal and carrier) loaded on the first fluid circulation
portion 5 of the heat exchange element 1 where the first fluid
(high temperature side) passes is preferably 10 to 400 g/L. In the
case of a noble metal, the amount is further preferably 0.1 to 5
g/L. When the amount of the catalyst (catalyst metal and carrier)
is below 10 g/L, it may be difficult to exhibit the catalyst
function. On the other hand, when the amount is above 400 g/L,
pressure loss increases, and the production costs may increase. As
necessary, a catalyst is loaded on the partition walls 4 of the
cells 3 of the heat exchange element 1. In the case of loading the
catalyst, a mask is applied on the segment, which is a heat
exchange element 1, to allow the catalyst to be loaded on the heat
exchange element 1. After a ceramic powder functioning as carrier
microparticles is impregnated with an aqueous solution containing a
catalyst component in advance, drying and firing are performed to
obtain catalyst-coated microparticles. To the catalyst-coated
microparticles are added a dispersion medium (water or the like)
and other additives to prepare a coating liquid (slurry), and,
after the slurry is coated on the partition walls 4 of the heat
exchange element 1, drying and firing are performed to load the
catalyst on the partition walls 4 of the cells 3 of the heat
exchange element 1. Incidentally, upon firing, the mask of the heat
exchange element 1 is peeled off.
[0092] As shown in FIG. 4, a ceramics heat exchanger 10 of the
present invention may have a structure where a plurality of
segments functioning as heat exchange elements 1 are bonded
together with a bonding material layer 8 of heat resistant cement.
A large size can be obtained by modularization by bonding segments
functioning as the heat exchange elements 1 of the present
invention. The segments are bonded by the use of heat resistant
cement. The heat resistant cement plays a role of an adhesive and
is applied to the periphery of the face where the inflow port and
the outflow port of the second inflow circulation portion 6 are
formed of the outer peripheral walls 7 of the segments to bond
segments together. In this case, the bonding material is applied
lest the second fluid circulation portion 6 should be closed by the
heat resistant cement.
[0093] As shown in FIG. 5, a ceramics heat exchanger 10 of the
present invention includes a heat exchange element 1 and a heat
exchange element-holding container 11 having the heat exchange
element 1 therein. Though the material of the heat exchange
element-holding container 11 is not particularly limited, the
container is preferably constituted of a metal having good
workability (e.g. stainless steel). The material for the
constitution including a connection pipe is not particularly
limited.
[0094] FIG. 6 shows another embodiment of a heat exchange element 1
and is a view from the end face 2 on the one side, which is the
first fluid inlet side of a heat exchange element 1. As shown in
FIG. 6, the heat exchange element 1 has a plurality of cells 3
separated by ceramic partition walls 4, extending through in the
axial direction from one end face 2 on one side to the end face 2
on the other side (see FIG. 1), and allowing the heating element
functioning as the first fluid to circulate therethrough. Some of
the partition walls 4 forming the cells 3 have different thickness
(wall thickness). That is, the heat exchange element 1 of FIG. 1 is
an embodiment where the partition walls 4 have thick portions and
thin portions. The constitution other than the thickness of the
partition walls 4 is the same as the heat exchange element 1 of
FIG. 1 and is formed in such a manner that the second fluid
circulates perpendicularly to the first fluid. By such a difference
in wall thickness, pressure loss can be reduced. Incidentally, the
thick portions and the thin portions of the walls may be disposed
regularly or at random as shown in FIG. 6, and similar effects can
be obtained.
[0095] FIG. 7A shows an embodiment where an end face 2 of the
partition wall 4 of the heat exchange element 1 is a tapered face
2t and is a view of the end face 2 on one side of the heat exchange
element 1 from the first fluid inlet side. FIG. 7B shows an
embodiment where an end face 2 of the partition wall 4 of the heat
exchange element 1 is a tapered face 2t and is a cross sectional
view taken along the face in parallel with the axial direction. As
shown in FIGS. 7A and 7B, the heat exchange element 1 has a
plurality of cells 3 partitioned by ceramic partition walls 4 and
extending through in the axial direction from one end face 2 to the
other end face 2 (see FIG. 1), and allowing a heated medium
functioning as the first fluid to circulate therethrough with the
end face 2 being a tapered face 2t. By making the end portion of
the partition wall 4 of the inlet of the first fluid have a tapered
face 2t, the inflow resistance of the fluid is decreased to reduce
pressure loss.
[0096] FIG. 8A is a view of the end face 2 viewed from the first
fluid inlet side of the heat exchange element 1, showing an
embodiment where the cells 3 having different sizes are formed.
FIG. 8B is a decomposition perspective view of the embodiment of
FIG. 8A. Since the first fluid flowing the central portion has a
high flow rate, the temperature is high, the volume is large, and
the pressure loss is large. Therefore, by making the cells 3 in the
central portion large, the pressure loss can be reduced. In the
embodiments shown in FIGS. 8A and 8B, a honeycomb structure having
large-sized cells 3 partially including plugged portions 13 is
disposed in the central portion, and the outer peripheral wall is
provided with a fluid sealing material 19 in the end portion
thereof. Four honeycomb structures 4 having small-sized cells
partially including plugged portions 13 are provided to surround
the outer periphery of the honeycomb structure in the central
portion. It allows the second fluid to flow from the second fluid
circulation portion 6 of the outside honeycomb structure to the
second fluid circulation portion 6 of the inside (central portion)
honeycomb structure by the fluid sealing material 19.
[0097] FIG. 8C is a decomposition perspective view showing an
embodiment of a circular cylindrical heat exchange element 1 having
the cells 3 having different sizes and partially including plugged
portions 13. Each of the inside circular columnar honeycomb
structure and the outside circular honeycomb structure has the
first fluid circulation portion 5 and the second fluid circulation
portion 6 formed therein (Cells 3 are plugged similarly to, for
example, FIG. 2A, and each circulation portion is formed.), and a
fluid sealing material 19 is unitarily provided between the inside
circular cylindrical honeycomb structure and the outside
cylindrical honeycomb structure. (FIG. 8C shows the inside
honeycomb structure and the outside honeycomb structure in the
decomposed state.) The fluid sealing member 19 enables the second
fluid to flow from the second fluid circulation portion 6 of the
outside honeycomb structure to the second fluid circulation portion
6 of the inside honeycomb structure.
[0098] FIG. 8D shows an embodiment where the cells 3 have different
sizes and is a view of an end face 2 from the inlet side of the
first fluid. The embodiment is formed so that the size of the cells
3 gradually increases from the right side to the left side of the
figure. The right side of the figure is the inlet side of the
second fluid, and the cells 3 are small on the inlet side of the
second fluid inlet side while the cells 3 are large on the outlet
side. In the heat exchanger 10 shown in FIG. 5, when the first
fluid circulation portion is formed as FIG. 8D with sending the
second fluid from the right side to the left side of FIG. 8D, since
the temperature of the second fluid is high in the downstream side
(left side of FIG. 8D) of the second fluid, the temperature of the
first fluid flowing on the down stream side of the second fluid
becomes high, and pressure loss is large. However, by enlarging the
cells 3 on the down stream side of the second fluid, pressure loss
can be reduced. FIG. 8E shows an embodiment where the thickness of
the partition walls 4 of the cells 3 is changed and is a view of
the end face 2 on the inlet side of the first fluid. The partition
walls 4 are formed so that the thickness gradually reduces from the
right side to the left side of the figure. The right side of the
figure is the inlet side of the second fluid, and, by thinning the
partition walls 4 of the cells 3 on the downstream side of the
second fluid, the pressure loss can be decreased like the case of
FIG. 8D.
[0099] FIG. 9A is a cross-sectional view taken along a cross
section in parallel with the axial direction, showing an embodiment
of a heat exchange element 1 where the thickness of the partition
walls 4 is increased from the inlet side of the first fluid toward
the outlet side (from the upstream side to the downstream side). In
addition, FIG. 9B shows an embodiment of a heat exchange element 1
where the first fluid circulation portions 5 are gradually narrowed
from the inlet side of the first fluid toward the outlet side (from
the upstream side to the downstream side). In the first fluid
circulation portions 5, temperature of the first fluid falls, and
heat transfer is reduced by the volume contraction of the first
fluid as it flows toward the downstream side. By narrowing the
first fluid circulation portions 5, contact is improved, and heat
transfer between the first fluid and the wall faces of the
partition walls can be increased.
[0100] In a heat exchange element 1 shown in FIG. 1, the shape of
the cells 3 functioning as the first fluid circulation portion 5
may be made hexagonal as shown in FIG. 10A. In addition, as shown
in FIG. 10B, the shape of the cells 3 of the first fluid
circulation portion 5 may be made octagonal. By such a shape, since
the angle of the corners is widened, stagnation or the like of the
fluid is reduced, and boundary film thickness (temperature boundary
layer thickness of the first fluid) can be reduced to raise the
heat transfer coefficient between the first fluid and the wall
faces of the partition walls.
[0101] In addition, in a heat exchange element 1 shown in FIG. 1,
as shown in FIG. 11, the R portion 3r may be formed by making the
corner portion of the cell 3 functioning as the first fluid
circulation portion 5 have an R shape. By such a shape, since the
angle of the corners is widened, stagnation or the like of the
fluid is reduced, and boundary film thickness can be reduced to
raise the heat transfer coefficient between the first fluid and the
wall faces of the partition walls.
[0102] Further, in the heat exchange element 1 shown in FIG. 1, as
shown in FIGS. 12A and 12B, there may be employed a fin structure
having fins 3f protruding in the cells 3 functioning as the first
fluid circulation portion 5. The fins 3f are formed so as to extend
in the axial direction (direction where the first fluid flows) on
wall faces of partition walls 4 forming the cell 3, and the shape
of each fin 3f may be a plate-like shape, a semispherical shape, a
triangle, a polygon, or the like. This enables not only to increase
the conductive area, but also thin the boundary film by
disarranging the flow to raise the heat transfer coefficient
between the first fluid and the wall faces of the partition walls.
Incidentally, the fins 3f may be formed only in unplugged cells 3
or in plugged cells 3.
[0103] FIG. 13A shows an embodiment of a heat exchange element 1
where a part of the cell structure is dense. FIG. 13B is a
decomposition perspective view of the embodiment of FIG. 13A. The
first fluid flowing in the cells 3 in the central portion of the
heat exchange element 1 has high temperature because of a high flow
rate. It is preferable to narrow the cells in the central portion
of the heat exchange element 1 and to widen the cells 3 in the
external side portion of the heat exchange element 1. In the
embodiment shown in FIGS. 13A and 13B, a honeycomb structure having
small-sized cells 3 partially including plugged portions 13 is
disposed in the central portion, fluid sealing materials 19 are
provided in the end portions of the outer peripheral walls, and
four honeycomb structures 4 having large-sized cells 3 partially
including plugged portions 13 are provided so as to surround the
outer periphery of the honeycomb structure in the central portion.
The fluid sealing materials 19 enable the second fluid to flow from
the second fluid circulation portion 6 of the outside honeycomb
structure to the second fluid circulation portion 6 of the inside
(central portion) honeycomb structure.
[0104] FIG. 13C is a decomposition perspective view showing an
embodiment of a circular cylindrical heat exchange element where
cells 3 partially including plugged portions 13 and having
different sizes. Each of the inside circular columnar honeycomb
structure and the outside circular honeycomb structure has the
first fluid circulation portion 5 and the second fluid circulation
portion 6 formed therein (Cells 3 are plugged similarly to, for
example, FIG. 2A, and each circulation portion is formed.), and a
fluid sealing material 19 is unitarily provided between the inside
circular cylindrical honeycomb structure and the outside
cylindrical honeycomb structure. (FIG. 13C shows the inside
honeycomb structure and the outside honeycomb structure in the
decomposed state.) The fluid sealing member 19 enables the second
fluid to flow from the second fluid circulation portion 6 of the
outside honeycomb structure to the second fluid circulation portion
6 of the inside honeycomb structure.
[0105] FIG. 13D is an embodiment where a part of the cell structure
is densely formed, viewed form the end face 2 on the inlet side of
the first fluid. The structure is formed so that cell density may
gradually increase from the right side of the figure to the left
side. In the cells 3 functioning as the first fluid circulation
portion 5, the cell density on the second fluid inlet side is low,
and the cell density on the outlet side is high. In addition, FIG.
13E shows an embodiment of a heat exchange element 1 where the cell
structure is changed by changing the thickness (wall thickness) of
the partition walls 4. The cells 3 functioning as the first fluid
circulation portions 5 have low cell density on the inlet side of
the second fluid on the right side of the figure and high cell
density of the outlet side on the left side of the figure. In the
heat exchange element 1 shown in FIG. 5, by forming the first fluid
circulation portion 5 as in FIG. 13D (or FIG. 13E) to allow the
second fluid to flow from the right side to the left side of FIG.
13D (or FIG. 13E), the first fluid flowing on the second fluid
downstream side (left side of FIG. 13D (or FIG. 13E)) has high
temperature because the second fluid has high temperature and has
high pressure loss. However, by raising the cell density on the
downstream side of the second fluid of the cells 3 of the first
fluid circulation portion 5, the conductive area can be increased.
In addition, by increasing the thickness of the partition walls 4,
the total heat transfer amount can be increased.
[0106] FIG. 14A shows an embodiment of a heat exchanger 10 where a
plurality of heat exchange elements 1 are disposed in series in the
direction where the first fluid flows and where the direction of
the partition walls 4 forming the cells 3 of the front part
(upstream side) heat exchange element 1 and the direction of the
partition walls 4 forming the cells 3 of the rear part (downstream
side) heat exchange element 1 are offset. In the present
embodiment, cells 3 are plugged similarly to the case of, for
example, FIG. 2A with each circulation portion being formed. FIG.
14B shows an embodiment of a heat exchanger 10 with the positions
of the partition walls 4 being offset. Thus, by allowing the heat
exchanger 10 to have a structure where the directions, positions,
and the like of partition walls 4 of a plurality of the heat
exchange elements 1 are offset, the flow of the fluid can be
disarranged at the sites where the positions of the walls are
offset, and boundary film thickness can be reduced to raise the
heat transfer coefficient between the first fluid and the wall
faces of the partition walls.
[0107] FIG. 15 shows an embodiment of a heat exchanger 10 having a
constitution where a plurality of heat exchange elements 1 are
disposed in series in the direction where the first fluid flows and
where the cell density of the rear part (downstream side) heat
exchange element 1 is higher than that of the front part (upstream
side) heat exchange element 1. In the present embodiment, cells 3
are plugged similarly to the case of, for example, FIG. 2A with
each circulation portion being formed. In the first fluid
circulating in the first fluid circulation portion 5, temperature
falls as it flows downstream, and heat transfer is reduced by
volume contraction of the first fluid. In the present embodiment,
by the disposition where the rear part (downstream) heat exchange
element 1 has higher cell density, conductive area is increased to
improve heat transfer between the first fluid and the wall faces of
the partition walls 4.
[0108] FIG. 16 shows an embodiment of a heat exchanger 10 where a
plurality of heat exchange elements 1 having regions having
different cell density distributions are disposed in series in a
direction where the first fluid flows. Each of the heat exchange
elements 1 has a constitution shown by any of FIGS. 8C and 13C.
Specifically, the embodiment has a constitution where two regions
of the inside (center side) and the outer periphery side in a
peripheral direction are formed and where the cell density of the
front part (upstream) heat exchange element 1 is high in the inside
and low in the outer periphery side while the cell density of the
rear part (downstream) heat exchange element 1 is low in the inside
and high in the outer periphery side. By allowing the fluid flow to
be disarranged by the cell structure where the cell density
distribution is changed between the front part and the rear part,
boundary film thickness can be reduced to raise the heat transfer
coefficient between the first fluid and the wall faces of the
partition walls 4. Incidentally, the number of regions having
different cell densities is not limited to two and may be three or
more.
[0109] FIG. 17A shows an embodiment of a heat exchanger 10 where a
plurality of heat exchange elements 1 each having regions partially
including plugged portions 13 and having different cell density
distributions formed therein are disposed in series in the
direction where the first fluid flows. FIG. 17B is a decomposition
perspective view of the embodiment of FIG. 17A. In the present
embodiment, cells 3 in each region are plugged similarly to, for
example, the case of FIG. 2A with each circulation portion being
formed. Specifically, two semicircular regions are formed, and,
upon disposing honeycomb structures as the heat exchange elements 1
in series, the cell density distributions are changed between the
left and the right (or the top and the bottom) of the front part
(upstream) and rear part (downstream) honeycomb structures. The
embodiment has a constitution where the cell density of the front
part heat exchange element 1 is high on one side (right side in the
figure) and low in the other side (left side in the figure), and
the cell density of the rear part heat exchange element 1 is high
on the other side (left side in the figure) and low in the one side
(right side in the figure). That is, since the cell density in the
corresponding portions is different between the front part heat
exchange element and the rear part heat exchange element, in other
words, because of a cell structure where the cell density
distribution is changed between the front part one and the rear
part one, the fluid flow can be disarranged, and boundary film
thickness can be reduced to raise the heat transfer coefficient
between the first fluid and the wall faces of the partition walls
4. As shown in FIG. 17C, there may be employed a heat exchange
element 1 having a honeycomb structure where quadrangular two
regions are formed. By the constitution where the cell density
distribution is changed between the left and the right (or the top
and the bottom) of the front part (upstream) and rear part
(downstream) honeycomb structures upon distributing the heat
exchange elements 1 shown in FIG. 17C in series as in FIG. 17A, the
fluid flow can be disarranged, and the heat transfer coefficient
can be raised.
[0110] FIG. 18A shows an embodiment of a heat exchanger 10 having a
constitution where a plurality of heat exchange elements 1 are
disposed in series in the direction where the first fluid flows and
where the flow passages of the first fluid are changed between the
front part one and the rear part one. Specifically, two regions of
the inside (center side) and the outer periphery side are formed in
a peripheral direction, the front part heat, exchange element 1 is
entirely plugged in the outer periphery side and partially plugged
in the inside (Cells 3 in the inside are plugged similarly to, for
example, the case of FIG. 2A with each circulation portion being
formed.), and the rear part heat exchange element 1 is entirely
plugged in the inside and partially plugged in the outer periphery
side (Cells 3 in the outer periphery side are plugged similarly to,
for example, the case of FIG. 2A with each circulation portion
being formed.) By such constitution, the fluid low can be
disarranged, and boundary film thickness can be reduced to raise
the heat transfer coefficient between the first fluid and the wall
faces of the partition walls. FIG. 18B is a view showing an
embodiment of a heat exchanger where heat exchange elements 1 each
obtained by combining an entirely plugged prismatic column and a
partially unplugged prismatic column are disposed in the front part
and rear part portions. The bottom region of the front part is
completely plugged, and the upper region of the rear part is
completely plugged. The constitution enables the flow of the first
fluid to change.
[0111] FIG. 19A shows an embodiment of a heat exchange element 1
where the inlets and the outlets of the first fluid circulation
portions 5 are alternately plugged. FIG. 19B is an A-A
cross-sectional view in FIG. 19A. The material for the partition
walls 4 is varied depending on the place of the partition walls 4,
and the constitution is made so that the first fluid flowing in
from the inlet passes the partition walls 4 and flows out from the
outlet. By the constitution, heat collection of the first fluid is
performed not on the wall face but inside the porous partition
walls 4. Since heat can be collected not by the two-dimensional
surface but three-dimensionally, the conductive area can be
increased.
[0112] FIG. 20 shows an embodiment where porous walls 17 are formed
in the first fluid circulation portion 5 as the first fluid
passage. FIG. 20 is a cross-sectional view of the first fluid
circulation portion 5. The porosity of the porous walls in the
first fluid circulation portion 5 is higher than that of the
partition walls 4 between the first fluid circulation portion 5 and
the second fluid circulation portion 6. Therefore, in the present
embodiment, the first fluid passes through the porous walls 17 and
is discharged from the outlet. Since heat can be collected not by
the two-dimensional surface but three-dimensionally, the conductive
area can be increased even in the same volume. Alternatively, the
heat exchange element 1 can be miniaturized.
[0113] FIG. 21 shows an embodiment of a heat exchange element 1
where the thickness (wall thickness) of the partition walls 4
forming the first fluid circulation portion 5 is gradually
increased from the center toward the outer periphery in a cross
section perpendicular to the axial direction. In the case of the
heat exchange elements having the same size, the thicker the wall
is, the higher the fin efficiency is. By thickening the path for
transferring heat collected from the cell central portion, heat
conduction inside the wall can be increased.
[0114] FIG. 22 shows an embodiment of a heat exchange element 1
employing a honeycomb structure having an external shape of an
ellipse. In the present embodiment, the partition walls 4 extending
in the short axial direction is formed to be thick. Since the fin
efficiency is high as the partition walls 4 became thick, thick
walls are disposed on the side perpendicular to the second fluid so
that the heat of the first fluid can be transferred to the second
fluid to raise the entire thermal conduction. In addition, pressure
loss can be reduced in comparison with increase of the thickness in
the entire portions. The shape of the heat exchange element 1 may
be rectangle.
[0115] FIG. 23 shows an embodiment where the outer peripheral wall
7 of a honeycomb structure forming the heat exchange element 1 is
thicker than the partition walls 4 forming the cells 3. By making
the outer peripheral wall 7 thicker than the cells 3 in the central
portion, strength of the structure can be enhanced. In the present
embodiment, the cells 3 are plugged similarly to, for example, the
case of FIG. 2A with each circulation portion being formed.
[0116] FIG. 24 shows an embodiment where the external shape of the
honeycomb structure forming the heat exchange element is flattened.
The conductive path can be made short in the short axial portion in
comparison with a circle, and it has small waterway pressure loss
in comparison with the case of making the external shape of the
honeycomb structure a corner structure.
[0117] FIGS. 25A to 25C show an embodiment where end faces 2 on the
inlet side of the first fluid of the honeycomb structure are
inclined. By inclining the inlet, the area where the high
temperature portion of the first fluid is brought into contact
becomes wider to increase the entire conductive area. It is also
possible to make the end faces on the outlet side inclined, and, in
this case, the pressure loss can be reduced.
[0118] FIG. 26 shows an embodiment where the end face 2 on the
inlet side of the first fluid of the honeycomb structure forming a
heat exchange element 1 is formed to have a depressed face shape.
By making the inlet of the first fluid depressed, the high
temperature portion of the first fluid is extended backward to
raise the heat exchange efficiency of the honeycomb backward
portion with the second fluid. In addition, by making the
depression, the thermal stress at the surface can be made a
compression stress to be able to maintain high rupture
strength.
[0119] FIG. 27 shows an embodiment of a heat exchanger 10 where an
adiabatic plate 18 has the same shape as the cells 3 forming the
first fluid circulation portion 5 is disposed on the inlet side of
the first fluid of a heat exchange element 1. Since the opening
ratio of the inlet on the first fluid side is small, in the case of
disposing no adiabatic plate, when the first fluid is brought into
contact with the end face on the inlet side, heat is lost at the
inlet wall face. Disposing an adiabatic plate having the same shape
in accordance with the inlet allows the first fluid to flow into
the honeycomb with maintaining the heat to prevent the heat of the
first fluid from being lost. In the present embodiment, cells 3 are
plugged similarly to, for example, the case of FIG. 2A with each
circulation portion being formed.
[0120] There is no particular limitation on the heated medium as
the first fluid being circulated in a ceramics heat exchanger 10 of
the present invention having a constitution as described above as
long as it is a medium having heat, such as gas or liquid. An
example of gas is automobile exhaust gas. In addition, regarding
the medium to be heated as the second fluid which take heat from
(exchange heat with) the heated medium, there is no particular
limitation on the medium as long as the temperature is lower than
that of the heated medium, such as gas or liquid. Though water is
preferable in consideration of handling, it is not particularly
limited to water.
[0121] As described above, since the heat exchange element 1 has
high heat conductivity, and there is a plurality of sites
functioning as fluid passages by the partition walls 4, high heat
exchange rate can be obtained. Therefore, the entire heat exchange
element 1 can be miniaturized, and it can be mounted on an
automobile. In addition, pressure loss is small with respect to the
first fluid (high temperature side) and the second fluid (low
temperature side).
[0122] Next, a method for manufacturing a ceramics heat exchanger
10 of the present invention is described. In the first place, a
ceramic forming raw material is extruded to form a honeycomb
structure where a plurality of cells 3 partitioned by ceramic
partition walls 4 and extending through in an axial direction from
one end face 2 to the other end face 2 are partitioned and formed.
Then, regarding a part of the cell lines, slits are formed so as to
extend through the partition walls 4 forming the cells 3 and the
outer peripheral wall 7 of the honeycomb structure in the direction
perpendicular to the axial direction, and plugged portions 13
plugged with plugging members are formed on one end face 2 each of
and the other end face 2 of each of the cells 3 in the cell lines
where the slits are formed to manufacture a heat exchange element
1.
[0123] Specifically, the manufacturing can be performed as follows.
After kneaded clay containing a ceramic powder is extruded into a
desired shape, drying and firing are performed to obtain a
honeycomb structure segment. By this, there can be obtained a
honeycomb structure segment (rectangular parallelepiped) where a
plurality of cells 3 functioning as gas flow passages are
partitioned and formed by the partition walls 4.
[0124] Though the aforementioned ceramics can be employed as the
material for the heat exchange element 1, for example, in the case
of manufacturing a segment containing Si-impregnated SiC composite
material as the main component, in the first place, predetermined
amounts of a C powder, a SiC powder, a binder, and water or an
organic solvent are kneaded and formed to obtain a formed article
having a desired shape. Next, the formed article is put in
pressure-reduced inert gas or vacuum in a metal Si atmosphere to
impregnate the formed article with metal Si.
[0125] Incidentally, also, in the case of employing
Si.sub.3N.sub.4, SiC, and the like, kneaded clay of a forming
material is formed, and the kneaded clay is subjected to extrusion
forming in a forming step to form a honeycomb-shaped formed article
having a plurality of cells 3 partitioned by partition walls 4 and
functioning as exhaust gas passages. The article is dried and fired
to obtain a heat exchange element 1 of a segment formed as a
honeycomb structure (honeycomb structure segment).
[0126] Next, the honeycomb structure segment manufactured above is
cut out to form slits in every other cell line on the side of the
honeycomb structure segment. Then, with respect to the cut-out face
(end face 2) on the honeycomb structure side, plugging on each cell
line having a slit is performed. The plugging material preferably
has the same composition as that of the honeycomb structure
segment. When the segment is of silicon carbide (SiC), the plugging
material is preferably of silicon carbide. Then, the plugged
honeycomb structure (segment) is fired in a hydrogen atmosphere to
manufacture a segment as a heat exchange element 1.
[0127] As described above, a side face (outer peripheral wall 7) of
the honeycomb-structured segment manufactured by extrusion forming
as described above is subjected to slit-working to form the second
fluid circulation portions 6, and the first fluid circulation
portions 5 are subjected to plugging for manufacturing at low
costs. When the size of the heat exchange element 1 is increased,
modularization is easy.
[0128] Since a heat exchange element 1 of the present invention has
a cross-flow structure of the first fluid (high temperature side)
and the second fluid (low temperature side) and shows high heat
exchange efficiency between the first fluid (high temperature side)
and the second fluid (low temperature side) in comparison with
conventional ones, the heat exchanger 10 itself can be
miniaturized. Further, since manufacturing from a unitary type by
extrusion forming is possible, costs can be reduced. The heat
exchange element 1 can suitably be used in the case that the first
fluid is gas and that the second fluid is liquid. For example, it
can suitably be used for exhaust heat recovery or the like to
improve automobile gas mileage.
EXAMPLE
[0129] Hereinbelow, the present invention will be described in more
detail on the basis of Examples. However, the present invention is
by no means limited to these Examples.
[0130] (Manufacturing of Segment of Heat Exchange Element)
[0131] After the kneaded clay containing a ceramic powder was
extruded to have a desired shape, it was dried and fired to
manufacture a heat exchange element 1 of silicon carbide segment
having a main body size of 33.times.33.times.60 mm.
Examples 1 to 5
Comparative Examples 1 to 3
[0132] The structures of the segments of the heat exchange elements
1 of Examples 1 to 5 and Comparative Examples 1 to 3 are as in
Table 1. Incidentally, no catalyst was loaded on any of the
Examples and Comparative Examples. In addition, the "number of the
partition walls" of the first fluid circulation portion 6 shows the
number of the partition walls in one line (For example, the numbers
of the partition walls are "6" in FIG. 2A and "2" in FIG. 2B.).
[0133] (Heat Exchange Element-Holding Container)
[0134] As the outside container for the heat exchange element 1, a
stainless steel heat exchange element-holding container 11 was
used. Pipes are provided on the heat exchange element-holding
container 11 in accordance with the cross-flow structure of the
heat exchange element 1. Incidentally, the two routes are
completely partitioned lest the first fluid and the second fluid
should be mixed together.
[0135] (First Fluid and Second Fluid)
[0136] The inlet temperature and the flow rate of the first fluid
and the second fluid were entirely the same. As the first fluid,
nitrogen gas (N.sub.2) at 350.degree. C. was used. As the second
fluid, water was used.
[0137] (Test Method)
[0138] The nitrogen gas had a SV (space velocity) of 50,000
h.sup.-1 with respect to the heat exchange element 1. Model gas was
allowed to flow into the first fluid circulation portions 5 of the
heat exchange element 1, and (cooled) water was sent into the
second fluid circulation portions 6. The (cooled) water had a flow
rate of 5 L/min. Though the heat exchanger 10 of Comparative
Example 1 has a structure different from those of the heat
exchangers 10 of Examples 1 to 3, the test conditions such as flow
rate of the first fluid and the second fluid were entirely the
same. Incidentally, the pipe capacity (portion of the heat exchange
element 1) of Comparative Example 1 was the same as the main body
capacity (33 cc) of the segments of heat exchange elements 1 of
Examples 1 to 3. Comparative Example 1 had pipes having a dual
structure where the second fluid flow passage is present in the
outer peripheral portion of the pipe functioning as the first fluid
flow passage. That is, it had a structure where the second fluid
flows outside the pipe for the first fluid. It had a structure
where the (cooling) water flows outside (gap of 5 mm) the pipe. The
pipe capacity of Comparative Example 1 means capacity of the pipe
functioning as the first fluid flow passage.
[0139] (Test Result)
[0140] Table 1 shows heat exchange rate. The heat exchange rate (%)
was obtained by calculating each energy amount from the
.DELTA.T.degree. C. (outlet temperature of heat exchange
element-inlet temperature) of each of the first fluid (nitrogen
gas) and the second fluid (water) with the formula 1.
Heat exchange rate(%)=temperature rise energy amount of medium to
be heated (second fluid)/temperature fall energy amount of heated
medium (first fluid) (formula 1)
TABLE-US-00001 TABLE 1 Heat exchange element Partition wall First
fluid circulation Second fluid Partition wall thermal Heat exchange
portion (number of circulation density conductivity efficiency
Material Shape partition walls) portion Route (g/cm.sup.3) (W/mK)
(%) Example 1 Silicon carbide Segment Honeycomb structure Slit
structure Cross flow 0.5 10 85 (6 partition walls) structure
Example 2 Silicon carbide Segment Honeycomb structure Slit
structure Cross flow 1.5 23 88 (6 partition walls) structure
Example 3 Silicon carbide Segment Honeycomb structure Slit
structure Cross flow 1.5 23 84 (2 partition walls) structure
Example 4 Silicon carbide Segment Honeycomb structure Slit
structure Cross flow 3.0 150 92 (densification by (6 partition
walls) structure Si impregnation) Example 5 Silicon carbide Segment
Honeycomb structure Slit structure Cross flow 5.0 300 96
(densification by (6 partition walls) structure Si impregnation)
Comp. Ex. 1 SUS304 Piping structure Outside of Outer periphery 7.5
15 79 structure flow structure Comp. Ex. 2 Silicon carbide Segment
Honeycomb structure Slit structure Cross flow 0.3 8 Broken during
(6 partition walls) structure test Comp. Ex. 3 Silicon cargide
Segment Honeycomb structure Slit structure Cross flow 5.1 320
Broken during (densification by (6 partition walls) structure
production Si impregnation)
Comparison of Examples 1 to 3 with Comparative Example 1
[0141] As shown in Table 1, Example 1 showed high heat exchange
efficiency in comparison with Comparative Example 1. This seems to
be because, in the case of Comparative Example 1, though heat
exchange with the first fluid (nitrogen gas) was easy on the side
close to (cooling) water, sufficient heat exchange was hard in the
central portion of the pipe, and thereby the thermal exchange rate
was low as a whole. On the other hand, since the present invention
has a honeycomb structure, the wall area where the first fluid
(nitrogen gas) is brought into contact with (cooling) water is
large in comparison with Comparative Example 1, and this seems to
be the cause of high heat exchange efficiency.
Comparison of Example 2 with Example 3
[0142] As shown in Table 1, Example 2 had high heat exchange
efficiency in comparison with Example 3. This shows that a
honeycomb structure having more partition walls (Example 2) is more
excellent in heat exchange than a honeycomb structure having less
partition walls, and this seems to be because the wall area where
the first fluid is brought into contact increases by a honeycomb
structure having more partition walls.
Comparison of Examples 1 to 3 with Examples 4 and 5
[0143] As shown in Table 1, Examples 4 and 5 had high heat exchange
efficiency in comparison with Examples 1 to 3. This seems to be
because Examples 4 and 5 became dense bodies by impregnation of the
segment of the heat exchange element 1 with Si to raise thermal
conductivity. This shows that performing Si impregnation is more
preferable.
Comparison of Example 1 with Comparative Example 2
[0144] As shown in Table 1, Example 1 had no breakage of partition
walls during the test evaluation in comparison with Comparative
Example 2. This seems to be because, since Comparative Example 2
had small partition wall density, strength was insufficient, and
partition walls had a breakage during the test by the internal
pressure of the fluid. From this, the partition wall density is
more preferably 0.5 g/cm.sup.3 or more.
Comparison of Example 5 with Comparative Example 3
[0145] As shown in Table 1, Example 5 had no breakage of the main
body during the production of the heat exchange element 1 in
comparison with Comparative Example 3. This seems to be because,
though Comparison Example 3 had high strength due to high partition
wall density, it was prone to break inversely, and thereby breakage
was caused during the production of the heat exchange element 1.
From this, in consideration of production of the heat exchange
element 1, the partition wall density is more preferably 5
g/cm.sup.3 or less.
INDUSTRIAL APPLICABILITY
[0146] The use of heat exchange element of the present invention is
not particularly limited in either the automobile field or the
industrial field as long as heat exchange is performed between a
heated medium (high temperature side) and a medium to be heated
(low temperature side). In the case of using the heat exchange
element for exhaust heat recovery from exhaust gas in the
automobile field, it can be used to improve gas mileage of
automobiles.
DESCRIPTION OF REFERENCE NUMERALS
[0147] 1: heat exchange element, 2: end face (in the axial
direction), 3: cells, 4: partition wall, 5: first fluid circulation
portion, 6: second fluid circulation portion, 7: outer peripheral
wall, 8: bonding material layer, 10: heat exchanger, 11: heat
exchange element-holding container, 12: end face, 13: plugged
portion, 14: inter-slit partition wall, 19: fluid sealing
material
* * * * *