Regenerative heat exchanger

Herein disclosed is a regenerative heat exchanger comprising a cylindrical core casing and a stack body core formed by a plurality of circular mesh plates each having fluid passage holes and stacked on one another to form fluid passageways. The stack body core is housed in the core casing to have a fluid cooling medium introduced into the fluid passageways to carry out heat exchange between the stack body core and the fluid cooling medium. Each of the mesh plates has on its outer periphery a reference mark portion positioned with respect to the fluid passage holes, and the mesh plates collectively form a row of reference mark portions indicative of the form of each of the fluid passageways. The row of reference mark portions enables to easily modify or adjust the shapes of the fluid passageways of the stack body core by relatively rotating the mesh plates with reference to the reference mark portions.

BACKGROUND OF THE INVENTION 
The present invention relates to a regenerative heat exchanger to be 
operated under a high pressure fluid cooling medium, and more particularly 
to a regenerative heat exchanger which is assembled with a reversed 
Stirling refrigerator, a GM(Gifford-McMahon) refrigerator, a pulse tube 
refrigerator and other very low temperature refrigerators. 
Conventionally, there have been provided a wide variety of regenerative 
heat exchangers utilized for very low temperature refrigerators one of 
which is shown in FIG. 11 as comprising a compression cylinder 1, an 
expansion cylinder 2 having an open end portion 2a, a fluid conduit 3 
provided between the compression and expansion cylinders 1 and 2 to have 
the cylinders 1 and 2 held in fluid communication with each other, a 
compression piston 4 housed in the compression cylinder 1 to be 
reciprocally slidable in the compression cylinder 1, an expansion piston 7 
housed in the expansion cylinder 2 to be reciprocally slidable in the 
expansion cylinder 2, a core unit 8 having a plurality of mesh plates 8a 
and a core casing 8b housed in the expansion piston 7 to stack the mesh 
plates 8a in the expansion cylinder 2, a plurality of seal ring members 
4a, 7a, 7b and 7c, and a cooling cover 9 connected to the expansion 
cylinder 2 to close the open end portion 2a of the expansion cylinder 2. 
The above mesh plates number more than 1000 and each called "matrix". 
The compression piston 4 is adapted to define a compression chamber 5 and 
to be reciprocated by a driving means. The core unit 8 is housed in the 
expansion cylinder 2 to define an expansion chamber 6 and to be 
reciprocated by another driving means. The compression chamber 5 and the 
expansion chamber 6 each accommodate a fluid cooling medium consisting of 
a highly pressurized refrigerant gas such as helium, hydrogen and 
nitrogen. The reciprocal motions of the compression and expansion pistons 
4 and 7 cause the compression chamber 5 and the expansion chamber 6 to 
respectively be varied in volume, thereby making it possible to move the 
fluid cooling medium between both chambers 5 and 6. Each of the mesh 
plates 8a of the core unit 8 is formed to be circular and to have a 
plurality of slit-like fluid passage holes. The fluid passage holes 
respectively form a plurality of fluid passageways when the mesh plates 8a 
are stacked on one another to form the core unit 8 in the expansion 
cylinder 2. 
The above refrigerator is operated to perform the reversed Stirling cycle 
by compressing and expanding the fluid cooling medium while the 
compression and expansion pistons 4 and 7 are respectively reciprocated in 
the compression and expansion chambers 5 and 6. 
FIG. 12 shows a solid sine curve "A" and a dot-chain sine curve "B", the 
former of which indicates the locus of the expansion piston 7 during one 
reciprocating motion which provides an isothermal compression stroke (1), 
an isovolumetric heat discharging stroke (2), an isothermal expansion 
stroke (3), and an isovolumetric heat charging stroke (4), and the latter 
of which indicates the locus of the compression piston 4 during one 
reciprocating motion. Each of the marks ".circle-solid." indicates the top 
dead center of the piston 4 or 7, while each of the marks ".largecircle." 
indicates the bottom dead center of the piston 4 or 7. The marks 
".tangle-solidup." shown in FIG. 12 respectively indicate intermediate 
points between the top and bottom dead centers. As shown in this figure, 
the reciprocating cycle of the compression piston 4 is the same as that of 
the expansion piston 7, but the cycle of the compression piston 4 is 
delayed from that of the expansion piston 7 by one fourth of the 
reciprocating cycle of the each piston 4 or 7, i.e., a phase angle of 90 
degrees. 
The isothermal compression stroke (1) is performed to have the fluid 
cooling medium in the compression chamber 5 compressed to produce heat in 
the fluid cooling medium, and to have the fluid cooling medium forced out 
of the compression chamber 5 through the fluid conduit 3. The fluid 
cooling medium from the compression chamber 5 is moved to the expansion 
cylinder 2. 
The fluid cooling medium is introduced into the expansion chamber 6 through 
the core unit 8 during the isovolumetric heat discharging stroke (2), and 
cooled by the core unit 8 by performing heat exchange between the mesh 
plates 8a and the fluid cooling medium passing therethrough. 
The isothermal expansion stroke (3) is then performed to have the fluid 
cooling medium in the expansion chamber 6 isothermally expanded as the 
expansion chamber 6 expands. At this time, the fluid cooling medium 
absorbs heat and deprives the cooling cover 9 of heat so as to cool an 
object 10 positioned on the cooling cover 9. The object 10 on the cooling 
cover 9 is therefore cooled by the cooling cover 9. 
In the isovolumetric heat charging stroke (4), the fluid cooling medium is 
discharged from the expansion chamber 6 through the core unit 8 without 
varying its volume. The fluid cooling medium is heated at this time by 
performing the heat-exchange between the mesh plates 8a and the fluid 
cooling medium passing therethrough to a degree that the temperature of 
the fluid cooling medium reaches to the initial temperature. 
The core unit 8 has a high heat-exchange rate enough to cool and 
refrigerate the object 10 on the cooling cover 9 to the very low 
temperature. In addition, the mesh plates 8a are each shaped to be 
circular by means of a blanking die from a mesh screen which is 
preliminarily formed with a number of minute holes. The blanked mesh 
plates 8a are then stacked on one another to form the core unit 8 with a 
plurality of fluid passageways. This makes it possible to produce the core 
unit 8 at a low cost. 
The above prior-art regenerative heat exchanger, however, is liable to 
encounter a drawback that the fluid passage holes of each of the mesh 
plates 8a are slightly different in position from those of another mesh 
plate 8a stacked up in the core casing 8b, and that the actual shapes of 
the fluid passageways are different from their theoretical shapes. The 
actual shapes of the fluid passageways are also varied when the mesh 
plates 8a are stacked up again in different order. This leads to a 
difficulty in forming the fluid passageways to have their accurate shapes. 
In addition, the fluid passageways of the core unit 8 cannot be modified or 
adjusted in their shapes such as diameters, sectional areas, lengths and 
directions of the fluid passageways into other desirable shapes without 
changing the shapes of the mesh plates 8a or the size of the core casing 
8b. This leads to the fact that a number of new mesh plates are required 
to modify the shapes of the fluid passageways and thus raise the 
production cost of the regenerative heat exchanger. 
The present invention contemplates provision of an improved regenerative 
heat exchanger overcoming the drawbacks of the prior-art regenerative heat 
exchanger of the described general natures. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a 
regenerative heat exchanger having a plurality of mesh plates which can be 
adjusted and changed in the shapes of their fluid passageways in spite of 
the fact that the mesh plates have their respective circular shapes. 
According to one aspect of the present invention there is provided a 
regenerative heat exchanger comprising a core casing having first and 
second openings, and a stack body core formed by a plurality of mesh 
plates each having a plurality of fluid passage holes and stacked on one 
another to form a plurality of fluid passageways consisting of the 
plurality of fluid passage holes. The stack body core is housed in the 
core casing to have the fluid passageways held in fluid communication with 
the first and second openings, and is adapted to have a fluid cooling 
medium introduced into the fluid passageways to carry out heat exchange 
between the stack body core and the fluid cooling medium. In the 
regenerative heat exchanger, each of the mesh plates has on its periphery 
a reference mark portion positioned with respect to the fluid passage 
holes around the center axis of the stack body core, and the mesh plates 
collectively form a row of reference mark portions to indicate the form of 
each of the fluid passageways. 
Each of the above fluid passage holes may be formed in the shape of a slit 
elongated in a predetermined elongation direction with respect to the 
reference mark portion. In this case, the stacked mesh plates have the 
fluid passage holes identical with or different from one another in the 
elongation direction. 
Each of the mesh plates may have a flat photo resist layer surrounding the 
openings of the fluid passage holes. 
The reference mark portion may be triangular in shape and may protrude from 
the remaining outer or inner peripheral portion of the mesh plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1 and 2 of the drawings, a preferred embodiment of a 
regenerative heat exchanger embodying the present invention is shown as 
being used for a reversed Stirling refrigerator. The refrigerator roughly 
comprises a compression cylinder unit 20, an expansion cylinder unit 30, 
and a fluid conduit 40 provided between the cylinder units 20 and 30. 
The compression cylinder unit 20 comprises a compression cylinder 21 and a 
compression piston 22 received in the compression cylinder 21 to define in 
the compression cylinder 21 a cylindrical compression chamber 25 which can 
be changed in volume when the compression piston 22 is moved between its 
uppermost and lowermost positions, i.e., the top and bottom dead centers 
by driving means 23. Between the compression cylinder 21 and the 
compression piston 22 is positioned a seal ring 26 which serves to 
hermetically seal the gap formed by the inner surface of the compression 
cylinder 21 and the outer surface of the compression piston 22. 
The expansion cylinder unit 30 comprises an expansion cylinder 31 having 
upper and lower open ends 31a and 31b, an expansion piston 32 received in 
the expansion cylinder 31 and reciprocally movable in a predetermined 
cycle, and a cooling cover 36 covering and closing the upper open end 
portion of the expansion cylinder 31 and encircling the expansion chamber 
35. On the cooling cover 36 is mounted a cooling object 10 which is cooled 
by the fluid cooling medium as will be understood as the description 
proceeds. 
The expansion piston 32 is adapted to define a cylindrical expansion 
chamber 35 in the expansion cylinder 31, and is constituted by a 
cylindrical core casing 33 and a stack body core 34. The core casing 33 
consists of an upper and lower casing members 33a and 33b connected with 
each other by an adhesive. The upper casing member 33a is formed with a 
first opening 33c, while the lower casing member 33b is formed with a 
second opening 33d. On the other hand, the stack body core 34 includes a 
plurality of mesh plates 37 each called a matrix and having a plurality of 
fluid passage holes 37h as best shown in FIGS. 3a, 3b and 3c. The mesh 
plates 37 number for example more than 1000 and are stacked on one another 
to form a plurality of fluid passageways 34h extending along the center 
axis of the stack body core 34 and each consisting of the fluid passage 
holes 37h of the mesh plates 37. The stack body core 34 is housed in the 
core casing 33 to have the fluid passageways 34h held in fluid 
communication with the first and second openings 33c and 33d. This stack 
body core 34 is adapted to have a fluid cooling medium introduced into the 
fluid passageways 34h to carry out heat exchange between the stack body 
core 34 and the fluid cooling medium. The above core casing 33 and the 
stack body core 34 as a whole constitute a regenerative heat exchanger 
unit 50 which is received in and retained by the expansion cylinder 31 
through a plurality of seal rings 39a, 39b and 39c. The seal rings 39a is 
adapted to hermetically seal an annular gap 41 formed between the inner 
surface of the expansion cylinder 31 and the outer surface of the 
expansion piston 32 and to have the expansion chamber 35 separated from 
the annular gap 41, while the seal rings 39b and 39c are adapted to 
hermetically seal the annular gap 41 to reliably introduce the fluid 
cooling medium into the second opening 33d of the core casing 33 from the 
compression chamber 25. 
The fluid conduit 40 is connected at its one end to the upper end portion 
of the compression cylinder 21 and has an inner passageway 40a held in 
fluid communication with the compression chamber 25. The fluid conduit 40 
is connected at its the other end to the lower end portion of the 
expansion cylinder 31 to have the inner passageway 40a held in fluid 
communication with the second opening 33d of the core casing 33 through 
the annular gap 41 formed between the expansion cylinder 31 and the 
expansion piston 32. The compression chamber 25, the inner passageway 40a 
of the fluid conduit 40, the annular gap 41, the first and second openings 
33c and 33d of the core casing 33, the fluid passageways 34h of the stack 
body core 34, and the expansion chamber 35 are filled with a high pressure 
fluid cooling medium such as helium, hydrogen and nitrogen. 
The expansion chamber 35 is held in fluid communication with the 
compression chamber 25 through the first and second openings 33c and 33d, 
the fluid passageways 34h of the stack body core 34, and the fluid 
passageway 40a of the fluid conduit 40. The expansion piston 32 is adapted 
to reciprocally be moved by driving means 38 between its lowermost and 
uppermost positions, i.e., the top and bottom dead centers to compress and 
expand the fluid cooling medium in the expansion chamber 35. 
As best shown in FIGS. 3a and 3b, each of the mesh plates 37 has on its 
outer periphery 37a a pair of reference mark portions 51 and 52 each 
positioned with respect to the fluid passage holes 37h around the center 
axis of the stack body core 34. The mesh plates 37 collectively forms two 
rows of reference mark portions 51 and 52 both of which indicate the form 
of each of the fluid passageways 34h. The present embodiment is 
exemplified in FIG. 3b as having the reference mark portions 51 and 52 
each shaped to be triangular and to protrude from the outer peripheral 
portion 37a of the mesh plate 37. The reference mark portions 51 and 52 
may be rounded, dented or painted to be distinguishable from the remaining 
portions of the mesh plate 37 according to the present invention. Each of 
the mesh plates 37 comprises a base metal plate not shown in the drawings 
and at least one flat photo resist layer 37b laid on the base metal plate 
to surround the openings of the fluid passage holes 37h. The photo resist 
layer 37b is patterned to have a plurality of holes coincident with the 
shapes of the fluid passage holes 37h to etch the fluid passage holes 37h 
in the mesh plates 37. The fluid passage holes 37h of the mesh plate 37 
may be formed by a known lithography technology or the like. 
As shown in FIG. 3c, each of the fluid passage holes 37h is formed in the 
shape of a slit elongated in a predetermined elongation direction with 
respect to the reference mark portions 51 and 52, and has a length "L" set 
at 1 mm and a slit width "W" of 50 .mu.m with a spacing distance "D" set 
at 50 .mu.m between two adjacent fluid passage holes 37h. 
The first embodiment of the stacked mesh plates 37 forming part of the 
regenerative heat exchanger is particularly exemplified in FIG. 4 as 
having the fluid passage holes 37h of the mesh plates 37 arranged to be 
identical with one another in the elongation direction. 
The refrigerator constructed as above is so operated as to complete one 
cycle of the reversed Stirling cycle consisting of an isothermal 
compression stroke, an isovolumeric (or isochronic) heat discharging 
stroke, an isothermal expansion stroke, and an isovolumeric heat absorbing 
stroke. The reciprocating motion cycle of the compression piston 22 is in 
coincidence with that of the expansion piston 32, while the cycle of the 
compression piston 22 is delayed from that of the expansion piston 32 by 
one fourth cycle, i.e., a phase angle of 90 degrees. 
The isothermal compression stroke is carried out by the compression piston 
22 to have the fluid cooling medium compressed in the compression chamber 
25 to produce heat in the compression chamber 25. The compressed fluid 
cooling medium in the compression chambers 25 is discharged from the 
compression chamber 25 through the fluid conduit 40. 
The isovolumeric heat discharging stroke is then performed to transfer the 
compressed fluid cooling medium to the expansion chamber 35 through the 
fluid passageways 34h of the stack body core 34 by downwardly moving the 
expansion piston 32 and upwardly moving the compression piston 22 -between 
their top dead centers and the intermediate points. At this time, the 
regenerative heat exchanger unit 50 is operated to deprive heat of the 
compressed fluid cooling medium to cool the fluid cooling medium to be 
transferred to the expansion chamber 35. 
The isothermal expansion stroke is then carried out to have the fluid 
cooling medium in the expansion chamber 35 expanded in its volume under 
the isothermal state. At this time, the fluid cooling medium absorbs heat 
from the surroundings, especially from the cooling cover 36. This leads to 
the fact that the cooling cover 36 and the cooling object 10 can be 
sufficiently cooled by the fluid cooling medium. 
The isovolumeric heat absorbing stroke is then performed to have the fluid 
cooling medium transferred to the compression chamber 25 from the 
expansion chamber 35 while the compression piston 22 is downwardly moved 
and the expansion piston 32 is downwardly moved between their intermediate 
points and bottom dead centers. When the cool fluid cooling medium is 
being transferred from the expansion chamber 35 to the compression chamber 
25, heat exchange is performed between the fluid cooling medium held at a 
relatively low temperature and the regenerative heat exchanger unit 50 
maintained at a relatively high temperature after the former isovolumeric 
heat discharging stroke is performed. This results in the fact that the 
regenerative heat exchanger unit 50 is cooled by the fluid cooling medium. 
The above four strokes cause heat exchange to be performed while the fluid 
cooling medium is transferred back and forth between the compression and 
expansion chambers 25 and 35 by the regenerative heat exchanger unit 50. 
The four strokes are repeated with the compression and expansion pistons 
22 and 32 reciprocated, which results in the fact that the cooling object 
10 is sufficiently cooled and refrigerated by the fluid cooling medium. 
Under these conditions, heat transmission is retarded between each pair of 
adjacent mesh plates 37 by the photo resist layer 37b having its heat 
conductivity smaller than that of the base metal plates of the mesh plates 
37, thereby making it possible to perform desirable strokes of the 
reversed Stirling cycle in the refrigerator to improve the efficiency of 
the regenerative heat exchanger unit 50. 
If, on the other hand, the shapes of the fluid passageways 34h are required 
to be changed in response to the cooling condition or the properties of 
the refrigerator, the arrangement of the mesh plates 37 is changed. In 
this instance, the reference mark portions 51 and 52 provided on the 
periphery 37a of the mesh plates 37 enable to modify and adjust the shapes 
such as diameters, sectional areas, lengths and axial directions of the 
fluid passageways 34h into other desirable shapes by relatively rotating 
the mesh plates 37 with reference to the reference mark portions 51 and 
52. This means that the fluid passageways 34h can be easily adjusted and 
changed in shape without changing the shapes of the mesh plates 37 or the 
size of the core casing 33 in spite of the fact that the mesh plates 37 
have their identical circular shapes. New mesh plates are unnecessary for 
adjusting and modifying the shapes of the fluid passageways 34h of the 
stack body core 34. 
The second embodiment of the stacked mesh plates forming part of the 
regenerative heat exchanger is exemplified in FIG. 5 as comprising a stack 
body core 54 in which the fluid passage holes 37h are arranged to have 
their elongation directions different from one another. The stack body 
core 54 includes first and second mesh plates 57A and 57B having two 
different elongation directions of the fluid passage holes 37h, and held 
in contact with each other to have their reference mark portions 51 and 52 
lined up in three lines. In this case, each of the fluid passageways 
becomes to be minimum in cross sectional area where the fluid passage 
holes of the first and second mesh plates 57A and 57B cross each other. 
The third embodiment of the stacked mesh plates forming part of the 
regenerative heat exchanger is exemplified in FIG. 6 as comprising a stack 
body core 64 which includes a plurality of mesh plates 67 each having an 
elongation directions of the fluid passage holes different from that of 
another mesh plate 67 and held in contact with one another to have their 
reference mark portions 61, 62 arranged in two spiral lines. The 
difference of the elongation directions of the fluid passage holes between 
each adjacent pair of mesh plates 37 is set at .alpha..degree. that is 
exaggeratedly shown in FIG. 6. 
The fourth embodiment of the stacked mesh plates forming part of the 
regenerative heat exchanger is exemplified in FIG. 7 as comprising a stack 
body core 74 which includes first and second groups of mesh plates 77A and 
77B. The mesh plates 77A and 77B have different indexing angles and are 
held in 35 contact with each other to have first reference mark portions 
71A, 72A arranged in two straight lines and second reference mark portions 
71B, 72B arranged in two spiral lines. The first group of mesh plates 77A 
have a single elongation direction of the fluid passage holes such as for 
example 0.degree., whilst the second group of mesh plates 77B have 
respective elongation directions of the fluid passage holes different from 
one another by an angle .beta..degree. between each adjacent pair of the 
second group of mesh plates 77B. 
The fifth embodiment of the stacked mesh plates forming part of the 
regenerative heat exchanger is exemplified in FIG. 8 as comprising a stack 
body core 34' having on its periphery a plurality of specified form 
portions 51' and 52'. The specified form portions 51' and 52' are 
respectively shaped by chamfering or cutting the reference mark portions 
51 and 52 of the stack body core 34 to have their specified indications 
distinguishable from the remaining outer peripheral portions of the stack 
body core 34'. The specified form portions 51' and 52' of the stack body 
core 34' can facilitate to insert the stack body core 34' in the core 
casing 33. Other reference mark portions of the above replaceable stack 
body cores may also be chamfered or almost cut away from the stack body 
core. 
The sixth embodiment of the stacked mesh plates forming part of the 
regenerative heat exchanger is exemplified in FIG. 9 as comprising a stack 
body core 84 including a plurality of annular mesh plates 87 each of which 
has outer and inner peripheral portions 87a and 87b and a pair of 
reference mark portions 91 and 92 inwardly protruding from the inner 
surface portion 87b of the mesh plate 87. As shown in FIG. 10, each of the 
mesh plates 87 has a plurality of fluid passage holes 87h each formed in 
the shape of a slit elongated in a predetermined elongation direction with 
respect to the reference mark portions 91 and 92. The fluid passage holes 
87h of the mesh plates 87 collectively form a plurality of fluid 
passageways 84h of the stack body core 84 when the mesh plates 87 are 
stacked on one another to form the stack body core 84. The fluid passage 
holes 87h may be arranged to be different from or to be identical to one 
another in the elongation direction with the rows of reference mark 
portions 91 and 92. The stack body core 84 of this regenerative heat 
exchanger can be received in an outer tube 101 which forms a hollow 
cylindrical passageway 103 in combination with an inner tube 102 to have 
the fluid cooling medium pass through the fluid passageways 84h each held 
in fluid communication with the hollow cylindrical passageway 103. 
If the shapes of the fluid passageways are required to be changed in 
response to the cooling condition or the properties of the refrigerator, 
the fluid passageways of the stack body core 84 can be easily adjusted and 
changed in shape in spite of the fact that the mesh plates 87 have their 
respective circular shapes. Therefore, the shapes of the fluid passageways 
of the stack body core 84 can be modified and adjusted into other 
desirable shapes by relatively rotating the mesh plates 87 with reference 
to the reference mark portions 91 and 92. 
The present invention has thus been shown and described with reference to 
specific embodiments, however, it should be noted that the present 
invention is not limited to the details of the illustrated structures but 
changes and modifications may be made without departing from the scope of 
the appended claims.