U.S. patent number 3,800,868 [Application Number 05/243,976] was granted by the patent office on 1974-04-02 for heat exchanger.
This patent grant is currently assigned to Curtis-Wright Corporation. Invention is credited to Murray Berkowitz, Robert C. Davis.
United States Patent |
3,800,868 |
Berkowitz , et al. |
April 2, 1974 |
HEAT EXCHANGER
Abstract
A liquid-to-gas heat exchanger having an internal ribbonlike
flow passage for the liquid, having means in the passage of adding
extended surface and of interrupting, separating, or causing
turbulence in the boundary layer to increase the liquid side film
coefficient of heat transfer. The heat exchanger is of cast
construction, and is provided with external fins for the passage of
air or other gas thereover.
Inventors: |
Berkowitz; Murray (Woodcliff
Lake, NJ), Davis; Robert C. (Ramsey, NJ) |
Assignee: |
Curtis-Wright Corporation
(Wood-Ridge, NJ)
|
Family
ID: |
22920876 |
Appl.
No.: |
05/243,976 |
Filed: |
April 14, 1972 |
Current U.S.
Class: |
165/170;
165/179 |
Current CPC
Class: |
F28F
3/12 (20130101); F28F 3/022 (20130101); F28F
3/04 (20130101); F28D 9/0031 (20130101); F28F
2250/102 (20130101) |
Current International
Class: |
F28F
3/04 (20060101); F28D 9/00 (20060101); F28F
3/00 (20060101); F28F 3/02 (20060101); F28F
3/12 (20060101); F28f 003/04 () |
Field of
Search: |
;165/152,153,170,165,169,17TD |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
806,369 |
|
Jun 1951 |
|
DT |
|
706,350 |
|
Mar 1931 |
|
FR |
|
Primary Examiner: Myhre; Charles J.
Assistant Examiner: Streule, Jr.; Theophil W.
Attorney, Agent or Firm: Wallace; Raymond P.
Claims
What is claimed is:
1. A liquid-to-gas heat exchanger comprising: a. A hollow body
having a ribbonlike liquid passage therethrough undulating in the
liquid flow direction and having a substantially constant
cross-section, the cross-section as viewed in any plane
perpendicular to its flow direction being of elongated form defined
by a pair of relatively long parallel sides joined by a pair of
substantially shorter sides; b. said hollow body having a two-part
rigid die-cast construction with the two parts being bonded
together at a generaly planar junction with the plane of the
junction passing through the liquid passage between and generally
parallel to the long sides of the passage, the undulating form of
the passage being produced by corrugations normal to the general
direction of flow in the passage portion of each body part, the
corrugations of one body part being positioned in a staggered
relation to those of the other body part with the crests of the
corrugations in one part being opposed to the troughs of the
corrugations in the other part to maintain the substantially
constant cross-section of the flow passage, the crests of the
corrugations being sufficiently high to substantially impede a
clear line of sight along the flow direction of the passage;
c. each of the two hollow parts of the body having a plurality of
spaced parallel fins die-cast integral therewith and projecting
outwardly therefrom for coolant gas flow between said fins, the
height of the fins being a plurality of times greater than the
spacing therebetween; and
d. the undulations of the liquid passage directing the liquid flow
alternately against the gas-cooled sides of the hollow body.
2. The combination recited in claim 1, wherein the crests and the
troughs of the corrugations are rounded and the troughs are rounded
on a larger radius than the crests to maintain substantial
parallelism of the flow surfaces and substantially constant
cross-section of the flow passage.
3. The combination recited in claim 1, wherein the crests of the
corrugations of the flow passage do not project beyond the plane of
the junction of the two parts of the hollow body.
4. The combination recited in claim 3, wherein the crests of the
corrugations of the flow passage are approximately flush with the
plane of the junction of the two parts of the hollow body.
5. The combination recited in claim 1, wherein the liquid passage
is serpentined in a plurality of parallel bights in a common plane
through the hollow body.
6. The combination recited in claim 5, wherein the fins extend
across the exterior of the hollow body in a direction generally
transverse to the flow direction of the liquid passage.
7. The combination recited in claim 5, wherein the fins of each of
the two body parts are extended around one edge of the body to the
junction plane, the edges of the fins of the two parts being bonded
together at the junction plane, the outermost edges of the fins
having a sheet cover member bonded thereto continuously along the
edge of each fin to define non-communicating gas passages between
the fins, the fin cover being continuous from one side of the body
around the bonded portions of the fins to the other side of the
body and defining coolant gas passages continuous from one side of
the body to the other, the gas passages being open only at their
ends and having their open ends at the same edge of the body.
Description
BACKGROUND OF THE INVENTION
This invention relates to heat exchangers, and more particularly to
heat exchangers of the type wherein a liquid circulating through a
closed path is passed through a heat exchange relationship with an
externally flowing gas.
Liquid-to-gas heat exchangers are well known wherein the liquid
flows through a plurality of tubes, which may be finned, with gas
passing over the exterior of the tubes. In order to secure good
heat transfer, there must be a large number of such tubes of
relatively small size, with the associated problems of providing
fins for each, since large tubes would not provide a large enough
surface to volume ratio.
In order to increase the heat transfer from the liquid it has been
known to provide flat liquid passages, and a further increase of
flow friction and heat transfer has been obtained by forming such
flat passages in a rippled configuration in the direction of flow,
or by providing them with internal discontinuities such as
turbulators. However, it has heretofore been possible to form such
heat exchangers only of sheet metal, which is a very expensive form
of construction and causes considerable difficulty in the fitting
and mounting of external fins. Further, such sheet metal heat
exchangers cannot be relied on to contain high internal pressure
without danger of leakage and changes in form and dimension. Also,
thermal expansion and distortion of such accordion-like structures
is considerable, whether the heat derives from the liquid or from
the gas.
SUMMARY
The present invention provides a heat exchanger having a hollow
body with a ribbonlike liquid passage therethrough, the exterior of
the hollow body being provided with fins integral therewith for the
passage of air or other gas thereover. The interior of the liquid
passage is provided with extended surface and with means of
disrupting, or preventing the formation of, a continuous boundary
layer along the walls, which would limit the amount of heat
transfer. Such disrupting means include turublators such as
protuberances from the interior surface of the walls or
interruptors in the flow path, or corrugated walls which provide an
undulatory flow path. The terms corrugated and undulatory as used
herein are intended to cover all similar forms such as pleated,
rippled, wavy, serrated, sinusoidal, zigzag, and such generally
crankled configurations, as will be explained in more detail in the
description of a preferred embodiment. The ribbon-like lquid
passage may be of a single pass through the hollow body, or it may
be serpentined in a plurality of bights to secure a longer flow
path within a relatively short space.
The hollow body is formed of two cast members which when joined
together on mating faces define the internal ribbonlike passage,
and which bear integrally cast fins on their exterior sides. This
construction allows the inexpensive production of heat exchangers
with internal boundary layer disrupting means, avoiding the
expensive and time-consuming formation of sheet metal and the
difficult fitting and mounting of fins thereon. The joined halves
of the cast heat exchanger will bear much greater internal pressure
without leakage than a sheet metal one, and the cast exhanger is
much less subject to thermal distortion. Its production cost is
approximately half that of less satisfactory sheet metal exchangers
of the same capacity.
It is therefore an object of this invention to provide a
liquid-to-gas heat exchanger having means for disrupturing the
boundary layer of the liquid.
It is another object to provide such a heat exchanger having high
flow friction for the liquid side and a high film coefficient of
heat transfer on the liquid side.
A further object is to produce such a heat exchanger of cast
construction, at low cost.
Other objects and advantages will become apparent on reading the
following specification in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of the preferred embodiment of the heat
exchanger of the invention, partially broken away, and with no
cover on the fins;
FIG. 2 is a cross-section taken on line 2--2 of FIG. 1;
FIG. 3 is an enlarged fragmentary cross-section similar to FIG.
2;
FIG. 4 is an enlarged cross-section taken on line 4--4 of FIG.
1;
FIG. 5 is a view taken in the direction of line 5--5 of FIG. 1;
FIG. 6 is a cross-section similar to FIG. 4 of another
embodiment;
FIG. 7 is a similar cross-section of a further embodiment; and
FIG. 8 is a cross-section taken on line 8--8 of FIG. 7.
DESCRIPTION OF A PREFERRED EMBODIMENT
This invention contemplates a plurality of embodiments, all
utilizing the same principle of disrupting and preventing formation
of a stable boundary layer of liquid in a flat ribbonlike passage,
and differing only in the specific physical means by which the
objects are achieved. Some forms of the heat exchanger are slightly
more efficient than others, some are slightly less expensive. On
balance, the one considered preferred is an embodiment, now to be
described, having a ribbonlike liquid passage with the internal
walls thereof corrugated to produce a generally undulatory flow
path therethrough.
In FIG. 1 there is shown a view of the exchanger 11 having the top
plate 12 partially broken away to show the interior of the lower
plate 13. When the two plates 12 and 13 are joined at their mating
inner faces, as by soldering, brazing, or a high temperature
adhesive, they mutually define a flow passage 14 through the heat
exchanger, having an inlet 16 and an outlet 17 for the flow of
liquid. Although the inlet and outlet are shown on the same side of
the exchanger, it will be understood that they may equally well be
on opposite sides, and that the direction of flow may be the
reverse of that shown.
Flow passage 14 is of a flat, generally ribbonlike form, undulating
in the direction of flow, and as viewed in cross-section in a plane
perpendicular to the flow direction (better shown in FIG. 4) it is
defined by a pair of parallel long sides 18 joined by a pair of
substantially shorter sides 19, which may be curved as viewed in
this plane. The long sides 18 of passage 14 are corrugated across
the direction of flow, as seen in FIGS. 1 and 2, providing a flow
path of approximately constant cross-section and generally
undulatory in the direction of flow.
Such a configuration of the flow passage 14 is produced by
corrugations in each of the plates 12 and 13 extending crosswise of
the flow passage between walls 19, the corrugations of one plate
being staggered in spacing with respect to those of the other plate
so that the crests of the corrugations in one plate are opposite
the troughs in the other. The crests of the corrugations in one
plate preferably come to approximately the same plane as the crests
of the corrugations in the other plate, so that there is no clear
line of sight along the flow passage in the direction of flow. This
is readily accomplished by having the crests in each plate come
flush with the mating surfaces, although in the castings they may
be allowed to come a few thousandths of an inch below the faces of
the enclosing walls to allow for flat grinding of the faces if
necessary. If the quality of the castings is good enough not to
require such grinding, a minor sight-through of that magnitude is
of no significance.
The troughs may be as deep as desired, depending on the amplitude
of the undulation it is desired to produce. The shape of te
corrugations as viewed in transverse cross-section, such as that
shown in FIGS. 2 and 3, may be of several related forms. As shown,
the cross-section is generally that of an obtuse isosceles
triangle, with the crests slightly rounded and the troughs rounded
on a larger radius, which maintains good parallelism of the
surfaces of the two sets of corrugations and keeps the
cross-section of the flow passage substantially constant. However,
the altitude of the corrugations can be greater to produce a more
sharply serrated form, or they may be sinusoidal or of any other
simlar conveneint form.
Further, the crests of the corrugations in one or both plates need
not be flush with the mating surfaces. As shown in FIG. 3, the
crests on plate 13 are substantially flush with the plate surface,
but those of plate 12a are on a plane lying below its mating face,
resulting in a certain degree of sight-through of the passage 14a.
The amount of separation between the planes of the crests may be
divided between the two plates rather than produced only in one as
shown, but in any case it is preferable that it should not be too
great, for instance not more than about one-third of the distance
between apposed crests and troughs. If the distance were greater
than that there is the possibility that the liquid would simply
travel through the clear sight passage without much rippling, with
dead volumes of liquid in the troughs.
It is also contemplated that in certain cases the crests of the
corrugations may project beyond the plane of junction of the mating
surfaces, in one or both plates. This may be done where the crests
on opposite sides come to approximately the same level, or even
when there is a separation between opposite crests, but it is
particularly useful when it is desired that the crests of one side
shall be re-entrant within the troughs of he other side, in order
to produce a more sharply rippled flow pattern.
The heat exchanger may be so formed as to have an undulatory flow
passage traveling straight through the exchanger, with the inlet at
one side and outlet at the other, but for high efficiency and
economy of space it may be formed as shown in FIG. 1 with the flow
passage serpentined in a plurality of bights between a plurality of
walls 19. The interior walls 19 project from alternate side walls
to a distance short of the opposite side wall equal to the width of
passage 14, so that the liquid flows in alternate directions from
side to side in its path through the exchanger. The interior walls
19 are congruent in the two plates, with surfaces flush with the
joining plane so that they form part of the mating surface which is
bonded together. The corrugations of passage 14 at each turn may go
around the corner, radiating from the end of wall 19, so that the
flow path is always transverse to the corrugations. However, for
convenience of fabrication the corrguations may continue parallel
to each other, as shown, out to the side walls, without substantial
loss of efficiency.
The heat transfer effect of a passage of this undulatory
configuration is in part due to its extended length, that is, it
has a length as if the undulations were pulled out straight into a
flat ribbonlike passage. However, this is a minor effect as
compared with that of the corrugations in disrupting and preventing
the build-up of a continuous boundary layer. At each undulation in
the passage the fluid turning in its flow impinges strongly on the
walls of the passage with increased contact pressure and high flow
friction, resulting in disruption and separation of such boundary
layer as may have formed within each half-undulation, and
preventing build-up of the boundary layer to a constant thickness.
The heat transfer effect due to this boundary layer disruption is
many times that of increased flow length.
Each of the two plates 12 and 13 bears integral cast
heat-dissipating fins 21 on the exterior thereof, over which the
gas of the heat exchange relationship flows. The fins may be
disposed either parallel or transverse to the direction of the
internal flow path, but when the exchanger is constructed with a
plurality of serpentine bights in the flow passage it is preferable
that the fins should be disposed transverse to the internal walls
19. Such an exchanger has a considerable plate area subject to
internal pressure. The walls 19, being bonded together on their
mating surfaces, provide stiffness against such pressure in one
direction, and transverse fins provide stiffness in the other
direction.
When the exchanger is used in an environment where there is a
strong current of air or other gas across it, the fins may be left
exposed and will dissipate enough heat from the liquid to be
serviceable for some uses. However, where such a free gas is not
avaiable, or when the direction of heat exchange is from the gas to
the liquid, the fins are covered and a gas stream ducted to
them.
The fins 21 have a jacket or cover 22 of thin plastic, sheet metal,
or foil bonded to their external edges, again by soldering,
brazing, or a high temperature adhesive. High temperature epoxy is
suitable for such bonding, or other adhesives capable of
withstanding the expected temperature. The cover over the fins
confines the gas flow to the spaces between the fins, and may
comprise a separate cover on each side of the exchanger for two
separate gas flows. The exchanger may also be formed as shown in
FIG. 5, wherein the fins 21 of each plate are carried halfway
around one end of the exchanger with curved outer edges, and bonded
together at their mating edges at the juncture plane at that end.
In such a case the cover 22 is curved around the continuous fins at
that end and brought back along the other side. This forms a
continuous cover with the gas passages between fins open only at
one end, on opposite sides. The gas is therefore introduced at the
open end on one side, passes entirely around the exchanger, and
returns to discharge adjacent the entry.
Although the cover sheet 22 is shown of substantial thickness in
the drawings for convenience of illustration, for cost saving
reasons it should be as thin as possible consistent with
convenience in fabrication and handling. In an environment wherein
the exchanger is not subject to any impact or puncture, a foil of
0.005 inch thickness has been found satisfactory.
The heat exchanger is provided with appropriate lugs 23 for
mounting, positioned as required. In the embodiment shown the two
plates are also provided with lugs 24 having holes for self-tapping
screws 26, which provide registry of the two plates and pressure
during bonding. Any other convenient means of registry and pressure
may be used.
The two plates of the heat exchanger described above may be
conveniently and inexpensively formed by die casting, permanent
mold casting, low pressure casting, or any other similar technique
which is adapted to rapid production and which holds close
tolerances. Each of the two plates is cast with all its fins, lugs,
mounting holes, inlet and outlet apertures, etc. produced in the
mold. The mating surfaces of the two plates are generally flat
enough for bonding without any dressing, but when necessary a
simple flatting operation on a sander may be performed. Suitable
metals are those having good thermal conductivity, such as copper
or aluminum or their alloys.
FIG. 6 is a cross-section, in a plan perpendicular to the flow
direction, of another embodiment having a flow passage 14b
employing other means of providing extended surface and disruption
of the boundary layer. Protuberances 27, integral with plates 12b
and 13b, project into the passage 14b. The protuberances as shown
are generally cylindrical studs having their free ends rounded and
their bases filleted to the passage wall. However, protuberances 27
may be of other shapes, such as rectangular finlike members,
generally airfoil-shaped members disposed at such angles as to
direct the flow in a tortuous path, or other members causing
turbulence in the flow.
Such protuberances extend the internal surface of passage 14b
without extending its length, providing additional heat transfer
between the liquid and the fins exposed to gas flow. They also
cause turbulence which disrupts such boundary layer as may form for
short distances, and prevent the build-up of a continuous layer.
The protuberances 27 are preferably staggered in the passage, both
across the passage and longitudinally thereof, for maximum effect.
As in the previously described embodiment, they may project
approximately to the juncture plane in both plates, or beyond or
below it in one or both, and they may be re-entrant into the spaces
between the protuberances of the opposite plate.
FIGS. 7 and 8 show a further embodiment in which extension of
surface and disruption of the boundary layer are provided by
another type of turbulator member. FIG. 7 is a cross-section
similar to FIG. 6, showing a passage 14c having flat, smooth walls.
A strip of wire screen 28 is positioned in passage 14c in contact
with both the flat walls of the passage, the screen being contoured
in such a manner as to present a series of successive meshes to the
flow of the liquid and to constrain the liquid to pass through the
meshes. Such a contour of the screen is produced by providing it
with corrugations extending across the width of the passage, giving
it an undulated shape in the direction of flow. In order to insure
good contact of the screen with the passage walls and consequent
heat transfer, the overall height of the corrugations from crest to
trough is somewhat greater than the height of the passage, as shown
in FIG. 8. At assembly when the two plates 12c and 13c are bonded
together along their mating faces the corrugations of the screen
are squeezed so that their crests are in firm contact with the
passage walls.
The secreen is formed with an open mesh so that it will not act as
a filter, and extends across the width of the passage 14c and along
its full length. If such an exchanger is made with a plurality of
serpentine bights it is not necessary that the screen should extend
around the turns, and a separate screen 28 is positioned in each
bight. Such a screen requires the liquid to flow successively
through a plurality of meshes, and provides the desired turbulence
of flow and disruption of boundary layer, and increased
surface.
The body plates of the exchangers of this invention are formed as
thin as consistent with the pressure conditions expected, and their
actual thickness may be quite minimal in view of the stiffness
imparted by the external fins and the transverse internal walls.
Heat exchangers fabricated according to any of the embodiments of
this invention are far less expensive than exchangers made of sheet
metal, since they avoid the time-consuming operations of forming
and assembly of the prior art.
* * * * *