U.S. patent application number 12/855762 was filed with the patent office on 2010-12-02 for involute foil regenerator.
This patent application is currently assigned to SUNPOWER, INC.. Invention is credited to David M. Berchowitz, Todd Cale, Neill Lane, James Gary Wood.
Application Number | 20100299924 12/855762 |
Document ID | / |
Family ID | 33298650 |
Filed Date | 2010-12-02 |
United States Patent
Application |
20100299924 |
Kind Code |
A1 |
Berchowitz; David M. ; et
al. |
December 2, 2010 |
Involute Foil Regenerator
Abstract
A regenerator having a plurality of involute foils disposed in
an annular gap between an inner cylindrical tube and an outer
cylindrical tube. The involute shape of the foils provides uniform
spacing throughout the entire regenerator and substantial surface
area for fluid contact.
Inventors: |
Berchowitz; David M.;
(Athens, OH) ; Lane; Neill; (Athens, OH) ;
Cale; Todd; (Coolville, OH) ; Wood; James Gary;
(Albany, OH) |
Correspondence
Address: |
KREMBLAS & FOSTER
7632 SLATE RIDGE BOULEVARD
REYNOLDSBURG
OH
43068
US
|
Assignee: |
SUNPOWER, INC.
Athens
OH
|
Family ID: |
33298650 |
Appl. No.: |
12/855762 |
Filed: |
August 13, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11251045 |
Oct 14, 2005 |
7784184 |
|
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12855762 |
|
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|
10421273 |
Apr 24, 2003 |
6991023 |
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11251045 |
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Current U.S.
Class: |
29/890.034 |
Current CPC
Class: |
Y10T 29/49373 20150115;
F28D 17/02 20130101; Y10T 29/4935 20150115; Y10T 29/49362 20150115;
F28D 19/042 20130101; F25B 2309/003 20130101; Y10T 29/49357
20150115 |
Class at
Publication: |
29/890.034 |
International
Class: |
B21D 53/02 20060101
B21D053/02; B23P 15/26 20060101 B23P015/26 |
Claims
1. A method of making a regenerator through which fluid can flow
for transferring thermal energy into and out of the fluid, the
method comprising: a) forming an inner wall having a radially
outwardly facing cylindrical surface; b) disposing an outer wall
substantially coaxial with the inner wall and spaced radially
outwardly therefrom, forming an annular gap between the inner wall
and the outer wall, said outer wall having a radially inwardly
facing cylindrical surface; c) mounting a plurality of foils in the
annular gap extending along substantial involutes of the radially
outwardly facing cylindrical surface, each foil having an inner
edge at the radially outwardly facing cylindrical surface of the
inner wall at substantially equal circumferentially spaced
intervals and an outer edge spaced from the inner edge, the outer
edge being circumferentially displaced from the inner edge and
extending toward the radially inwardly facing cylindrical surface
of the outer wall; wherein a plurality of longitudinal gaps, each
longitudinal gap being formed between one of the foils and its
respective next adjacent foil, extends from the inner wall to
substantially the outer wall, the longitudinal gaps forming
involute flow passages that extend substantially uninterrupted
between the inner and outer walls.
2. The method in accordance with claim 1, further comprising: a)
disposing a plurality of substantially planar foils substantially
parallel to one another, each of said foils having an inner edge
and an opposing outer edge; b) inserting a spacer between each
foil; c) heating the inner edge of the foils and the spacers until
they are bonded together, thereby forming a wall at the inner edges
of the foils, said wall having first and second opposing edges; and
d) bending the wall and mounting the first wall edge to the second
wall edge, thereby forming said inner wall.
3. The method in accordance with claim 1, further comprising: a)
disposing a plurality of substantially planar foils substantially
parallel to one another, each of said foils having an inner edge
and an opposing outer edge; b) forming at least one aperture in
each foil, and aligning said apertures; c) inserting a ring through
the aligned apertures in the foils; d) forming a wall at the inner
edges of the foils, said wall having first and second opposing
edges; e) bending the wall and mounting the first wall edge to the
second wall edge, thereby forming said inner wall.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/251,045 filed Oct. 14, 2005, which is a divisional of
U.S. patent application Ser. No. 10/421,273 filed Apr. 24, 2003,
now U.S. Pat. No. 6,991,023.
STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH AND
DEVELOPMENT
[0002] Not Applicable
REFERENCE TO AN APPENDIX
[0003] Not Applicable
BACKGROUND OF THE INVENTION
[0004] 1. Field of the Invention
[0005] This invention relates generally to thermal regenerators and
more particularly to a thermal regenerator that uses thin, planar
sheets of material of sufficient thermal conductivity to form the
heat transfer surfaces of the regenerator.
[0006] 2. Description of the Related Art
[0007] Many devices, and Stirling cycle machines in particular,
include a thermal regenerator to which thermal energy is
transferred from a flowing fluid, and from which thermal energy is
transferred to the fluid. Regenerators are normally made with large
surface area structures, such as wool, foils or spheres, made of
metal, such as stainless steel.
[0008] In a Stirling cycle engine, for example, a working gas is
moved between a warmer space and a cooler space by a reciprocating
displacer to drive a reciprocating piston. The gas is heated during
one part of the cycle, and cooled during another part. When the
warm gas is being transported from the warmer space, it flows
through a regenerator, and thermal energy is transferred to the
regenerator by convection, i.e., the impingement of heated gas
molecules on the regenerator's surfaces. The regenerator is warmed
and the gas is cooled when thermal energy is transferred to the
regenerator as the gas flows through the regenerator to the cooler
space.
[0009] Once the gas has been cooled in the cooler space, it is
driven again through the regenerator; ordinarily in the opposite
direction as when the gas was driven from the warmer space. The
cooler gas flowing through the regenerator is warmed by the same
convection mechanism by which the gas warmed the regenerator:
impingement of gas molecules on the regenerator's surfaces.
[0010] Regenerators therefore improve the efficiency of the
Stirling cycle engine because the gas enters the heated end
pre-warmed, and gas enters the cooler end pre-cooled. Of course,
regenerators improve the efficiency of many machines other than
Stirling cycle machines.
[0011] In conventional regenerators, there must be a substantial
amount of contact between the flowing fluid molecules and the
surfaces of the regenerator in order for substantial heat transfer
to occur. One type of regenerator used in Stirling cycle machines
uses a long thin strip of metal, such as stainless steel, that is
wound up in a roll and placed in a chamber through which gas flows
longitudinally of the roll. Each layer of the metal has a space or
gap between it and the next adjacent layer for fluid to pass
through.
[0012] Even though it is desirable to have uniform spacing of the
layers of a regenerator, it is often difficult, in practice, to
achieve such uniformity of spacing. A temperature differential
between the heated end and the cooled end may cause buckling, which
varies the gap sizes. Additionally, the flow of fluid through a
wound regenerator cannot distribute evenly radially, which can
cause areas with substantially more flow to expand or contract the
metal more than areas with less flow. All of these problems result
in high fluid flow rates through larger gaps, and low flow rates
through smaller gaps. Non-uniform flow is disadvantageous, because
large gaps permit some gas flowing through the regenerator to make
poor contact with the surfaces with which thermal transfer should
take place. Furthermore, the pressure drop that is critical to the
class of machines referred to as free-piston machines is often
compromised with conventional regenerators, thereby resulting in
unanticipated dynamic motion of the moving parts.
[0013] There is therefore a need for a regenerator that maintains
substantially uniform spacing throughout the entire region of the
regenerator through which fluid flows.
BRIEF SUMMARY OF THE INVENTION
[0014] The invention is a regenerator through which fluid can flow
for transferring thermal energy into and out of the fluid. The
regenerator comprises an inner wall having a radially outwardly
facing cylindrical surface. An outer wall is spaced radially
outwardly from the inner wall, and is substantially coaxial with
the inner wall. The outer wall has a radially inwardly facing
cylindrical surface. An annular gap is thereby formed between the
inner wall and the outer wall. A plurality of foils is disposed in
the annular gap. The foils extend along substantial involutes of
the radially outwardly facing cylindrical surface of the inner
wall. Each foil has a first edge mounted to one of the cylindrical
surfaces and a second edge spaced from the first edge. The second
edge is near the other of said cylindrical surfaces, and is
circumferentially displaced from the first edge.
[0015] In a preferred embodiment, each foil mounts at its
respective inner edge to the radially outwardly facing cylindrical
surface of the inner wall, and extends toward, and seats against,
the radially inwardly facing cylindrical surface of the outer wall.
In a still more preferred embodiment, each foil has at least one
spacer disposed between it and each next adjacent foil. The spacers
can be tabs or regions of the foil deformed toward the next
adjacent foil in the shape of a cup or any other shape.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0016] FIG. 1 is a schematic end view illustrating the preferred
embodiment of the present invention.
[0017] FIG. 2 is an end view in section illustrating the preferred
embodiment of the present invention.
[0018] FIG. 3 is a view in perspective illustrating the present
invention in an intermediate state of manufacture with the foils in
a substantially planar orientation and at substantial right angles
relative to a wall to which they are mounted.
[0019] FIG. 4 is an end view illustrating the present invention in
an intermediate state of manufacture.
[0020] FIG. 5 is a view in perspective illustrating the present
invention in an intermediate state of manufacture.
[0021] FIG. 6 is a schematic end view illustrating an alternative
embodiment of the present invention in an intermediate state of
manufacture.
[0022] FIG. 7 is a view in perspective illustrating an alternative
embodiment of the present invention using rings extending through
apertures in the foils in which thicknesses are exaggerated to
emphasize relative surfaces.
[0023] FIG. 8 is a side view illustrating a foil with one
embodiment of spacers.
[0024] FIG. 9 is a view in perspective illustrating the foil of
FIG. 8 with its spacers in which thicknesses are exaggerated.
[0025] FIG. 10 is an end view illustrating the foil of FIG. 8 in an
operable position relative to other foils in which thicknesses are
exaggerated.
[0026] FIG. 11 is a view in perspective illustrating an alternative
foil and another embodiment of spacers in which thicknesses are
exaggerated.
[0027] FIG. 12 is an end view illustrating the foil of FIG. 11 in
an operable position relative to other similar foils in which
thicknesses are exaggerated.
[0028] FIG. 13 is a schematic side view illustrating the placement
of a regenerator on a Stirling cycle machine.
[0029] In describing the preferred embodiment of the invention
which is illustrated in the drawings, specific terminology will be
resorted to for the sake of clarity. However, it is not intended
that the invention be limited to the specific term so selected and
it is to be understood that each specific term includes all
technical equivalents which operate in a similar manner to
accomplish a similar purpose. For example, the word connected or
term similar thereto are often used. They are not limited to direct
connection, but include connection through other elements where
such connection is recognized as being equivalent by those skilled
in the art.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The preferred embodiment of the regenerator 10 is shown in
FIG. 1, having an inner cylindrical wall 12 and an outer
cylindrical wall 14. The inner wall is, in a preferred embodiment,
a wall within which the displacer 13 of a Stirling cycle machine 15
reciprocates, as shown in FIG. 13. In a preferred embodiment, the
outer wall 14 is coaxial with the inner wall 12, and both the inner
and outer walls are circular cylinders as shown in FIG. 2.
[0031] There is a gap formed between the radially outwardly facing
cylindrical surface 22 of the inner wall 12 and the radially
inwardly facing surface 24 of the outer wall 14. The gap is
preferably annular, and extends a substantial portion, and
preferably essentially the entirety, of the length of the inner and
outer walls 12 and 14. In the contemplated Stirling cycle machine
15, a fluid, such as the working gas, flows through the annular gap
17 in a manner that will be apparent to those skilled in the
Stirling cycle machine art and conventional regenerators.
[0032] There are many foils 16 positioned in the annular gap
between the inner and outer walls 12 and 14. The foils 16 are made
of a material to and from which thermal energy is readily
transferred, but which does not have a high thermal conductivity
that causes it to rapidly conduct the thermal energy to the
surrounding structure. Stainless steel is a preferred material for
the foils 16 used with engines (prime movers), and polyester or a
similar plastic is preferred for coolers (heat pumps). The foils
preferably have a length and width that is substantially greater
than their thickness. For example, a contemplated foil has a length
of 60 mm, a width of 13.67 mm and a thickness of 0.0254 mm. These
dimensions are only exemplary, and it will be understood that the
dimensions can vary significantly. For example, the width of a foil
is determined by the distance across the annular gap, the angle of
the attached edge, and other factors that cause the foil to form an
involute.
[0033] Each of the foils 16 is mounted to the radially outwardly
facing surface 22 at its inner edge at spaced intervals of equal
width, and each extends along a path that is a substantial involute
of the surface 22 to contact the inwardly facing surface 24. The
outer edges of the foils can be welded, adhered or otherwise seated
against the surface 24, but this is not required. The outer edges
can be left free so that they seat against the inwardly facing
surface 24 and cause slight compression of the foil regenerator
structure. In this configuration, the regenerator conforms to
accommodate the differential expansions that occur when using
different materials for the foils and the walls 12 and 14, such as
plastic foils and metal walls.
[0034] By lying along an involute of the radially outwardly facing
surface 22, and being spaced at equal intervals around the
cylindrical surface 22, each foil 16 maintains a constant spacing
relative to its nearest neighbor along the entire length and width
of each foil. Thus, there is a uniform spacing between each of the
foils 16 at all radial and longitudinal positions, so that gas
flowing through the annular gap does not have any larger pathways
to flow preferentially through. This uniform flow prevents "hot
spots", and, likewise, "cold spots", from reducing the effect of
the regenerator 10 on the efficiency of the machine to which it is
mounted.
[0035] The regenerator 10 can be manufactured by one of several
methods. In a preferred method, a substantially planar wall 32 has
a plurality of substantially parallel planar foils 36, each of
which is attached at a foil edge along the wall's 32 major surface
42, preferably by welding, brazing or soldering when using metal
foils and walls, or hot-melting, solvent bonding, ultrasonic
welding or other plastic bonding technique when the materials are
plastic. Each foil's edge is mounted substantially perpendicular to
the wall 32 equally spaced from each adjacent foil by, for example,
0.115 mm for foils that are 0.0254 mm thick. Once all of the foils
are attached, the structure has the appearance of a book when
viewed along the planes of the foils 36 and the wall 32 as shown in
FIG. 3. Each of the foils is a "page" of the "book", and the
"spine" is the wall 32.
[0036] Once the foils 36 are all mounted to the wall 32, the wall
32 is deformed, preferably by bending it around (away from the
foils 36) to form a circular cylinder as shown in FIG. 4. The wall
could be bent into a rectangular cylinder or any other shape
desired. The opposite edges of the wall 32 are connected together,
such as by welding, to retain the previously planar wall 32 in the
circular cylindrical shape to which it is bent. Each of the foils
36 retains its substantially planar shape, and is oriented radially
of the wall 32.
[0037] The space between each of the foils 36 in the configuration
shown in FIG. 4 is pie-shaped, because it increases in width as a
function of the radial distance from the wall 32. If the
regenerator were to be assembled in this configuration, the
non-uniform gaps would permit most of the gas to flow through the
widest regions of the gaps between the foils 36, at the greatest
radial distance from the wall 32, because the resistance to fluid
flow is least there.
[0038] Instead of assembling the regenerator when the foils are in
the FIG. 4 configuration, the entire structure is next placed in a
diameter-reducing device, such as a person's hand, a funnel-shaped
tube or another device, while at the same time rotating the wall 32
in one direction. The outer edges of the foils 36 seat against the
surface of the diameter-reducing device during the rotation of the
wall 32, and due to frictional resistance at the tips of the foils,
all of the foils 36 bend in one circumferential direction, such as
clockwise as the radially innermost edges rotate with the wall 32
and the radially outermost edges stay seated against the device
used to reduce the diameter of the foil 36 and wall 32 combination.
As all of the foils bend in the same circumferential direction and
the diameter of the diameter-reducing device decreases, the foils
begin to form substantial involutes of the wall 32. When this
occurs, the outer edges of the foils 36 are closer to the wall 32,
which permits the combination of the wall 32 and the foils 36 to be
inserted into an outer cylindrical wall against which the outer
edges of the bent foils seat. The outer wall into which the wall 32
and foils 36 is inserted has an inwardly facing cylindrical surface
that is closer to the radially outwardly facing surface 42 than the
outer edges of the foils 36 prior to bending. The final structure
is structurally identical to that shown schematically in FIG.
1.
[0039] It also is possible to form a regenerator according to the
present invention by first attaching a plurality of parallel foils
to a wall at an angle to the wall that approaches zero degrees. The
wall is then bent in the direction opposite that shown in FIG. 4 to
form a cylindrical outer wall, so that the foils extend inwardly of
the wall. Then a tube is inserted within the outer wall after the
foils are all rotated in the same circumferential direction and
their inner edges are attached to the tube, which serves as the
inner wall to form a regenerator. In this embodiment, the foils are
attached at substantial right angles to the inner wall and curve
outwardly along involutes toward the outer wall, intersecting the
outer wall at the angle at which they were attached.
[0040] Another method of making the regenerator according to the
present invention is to align a plurality of foils 46 parallel to
one another in a "stack." The spacers 48, which are preferably made
of a similar or identical material to the foils, but much shorter
than the foils 46, are interposed between each pair of foils 46
near the inner edges of the foils 46. Next the stack of foils 46 is
packed together in a tight relationship with the spacers 48 all
aligned near the inner edge of the foils 46. Heat is then applied
to the inner edge of the foils 46 and the spacers 48. The spacers
48 and foils 46 become hot enough to melt slightly at the inner
edge, and then they are cooled, causing solidification, which forms
a thin wall 42 at the inner edge as shown in FIG. 6. The heat can
be applied along parallel lines perpendicular to the foils, and may
be accompanied by a meltable rod, so as to weld the foils and
spacers together. Once the thin wall 42 is formed, it is then bent
into a cylinder, or bent around and attached to a cylinder, the
foils 46 are rotated circumferentially in the same direction and
the entire device is placed in a cylindrical outer wall as in the
method described in association with FIGS. 3 and 4.
[0041] Another alternative method of making a regenerator according
to the present invention is to insert one or more rings such as the
stainless steel ring 50 shown in FIG. 7, through a plurality of
aligned apertures formed near one edge of each of the foils 56. The
ring 50 has overlapping ends to prevent foils from sliding off the
ring 50. Spacers, such as shorter foils, can also be placed on the
rings to space the foils. Once all of the foils 56 are placed on
the ring 50 by spreading the ends of the ring, the ring 50 springs
closed and a circular cylinder shaped tube is inserted within the
ring 50 until the inwardly facing edges of the foils 56 seat
against the radially outwardly facing surface of the tube wall.
Then the foils can be attached to the tube, bent circumferentially
in the same direction, and then the entire structure is inserted
into a second tube. Alternatively, the foils and spacers can be
heated to form a wall as in the embodiment described in association
with FIG. 6.
[0042] Each of the foils of the regenerator of the instant
invention can have a spacer structure that mechanically maintains
its spacing relative to each next adjacent foil. In one embodiment
shown in FIG. 8, a foil 106 has tabs 110 that serve as spacers.
Each tab 110 is formed by cutting the foil 106 along a U-shaped
curve, and then pushing the free end of the portion of the foil 106
that is within the U-shaped curve to one side along a path
transverse to the plane that contains the foil 106 as shown in
FIGS. 9 and 10. In FIG. 10, the foil 106 is shown with its tabs 110
functioning as spacers by seating against a next adjacent foil 104.
The foil 108 has tabs 118 seating against the foil 106.
[0043] In an alternative embodiment shown in FIGS. 11 and 12, the
spacers are bumps 120 formed in the foil 126. The bumps 120 can be
formed by plastically deforming the foil 126, such as by forcing
the foil into a recess with a molded instrument, thereby stretching
the foil locally. The tips of each of the bumps 120 seat against
the next adjacent foil 128, and the bumps 134 of the other adjacent
foil 124 seat against the foil 126.
[0044] A regenerator made according to the instant invention may be
placed in an environment where a fluid, such as a liquid or a gas,
flows through it longitudinally in one direction during one part of
a cycle, and then flows through it longitudinally in an opposite
direction during another part of the cycle. In a preferred
embodiment, the regenerator is mounted in a Stirling cycle machine
with its inner and outer cylindrical walls tack welded or otherwise
rigidly connected to adjacent cylindrical structures as shown in
FIG. 13. The longitudinal ends of each foil are supported against
longitudinal and circumferential movement by tack welding or by
compressing metal wool (in the case of engines) or plastic foam (in
the case of heat pumps) between the longitudinal ends of the foils
and the adjacent structure. The wool or foam restricts the foils,
and thereby resists any movement of the regenerator or its
components as the fluid is displaced rapidly first in one direction
and then in the opposite direction. The wool or foam can serve some
regenerating purpose, but most importantly acts as a mechanical
stop to prevent circumferential movement of the foils or
longitudinal movement of the entire structure or any component
parts.
[0045] While certain preferred embodiments of the present invention
have been disclosed in detail, it is to be understood that various
modifications may be adopted without departing from the spirit of
the invention or scope of the following claims.
* * * * *