Multi-pass heat exchanger circuit

A concept for reducing the number of parts in, and for simplifying the assembly of, a plate and fin type heat exchanger in which a fluid makes plural passes at least at one level of the heat exchanger. A single layer of a secondary heat transfer material replaces multiple detail parts of the prior art and is appropriately configured in conjunction with flow divider members to assure continuous fluid flow to and between fluid passes.

BACKGROUND OF THE INVENTION 
In plate and fin heat exchangers, a "fin" layer of a relatively ductile 
sheet or strip material, crimped to a corrugated configuration, is placed 
between overlying and underlying plates where it acts as a secondary heat 
transfer surface. In some instances, particularly in the case of compact, 
high performance heat exchangers, it is possible or desirable, or both, to 
conduct at least one of the fluids admitted to the heat exchanger in a 
serpentine or reversing flow path between adjacent plates. This poses a 
problem in respect of the "fin" layer since flow in a serpentine path has 
components of transverse movement which cannot obviously be accommodated 
by the as-formed corrugated "fin" material. In the known prior art, this 
problem has been dealt with by using a "fin" layer comprised of multiple 
"fin" segments including a connecting segment in which the corrugations 
orient at right angles to the corrugations of connected segments. The 
segments are configured to achieve miter joints at turn-around locations. 
This practice satisfactorily solves the problem of impeded flow but is a 
relatively costly solution. Multiple "fin" segments of different 
configuration must be provided, and separately and selectively laid in 
place in assembling each level of a plate and fin heat exchanger. The 
advantages of a multi-pass heat exchanger accordingly have heretofore been 
possible only by an expenditure of relatively high materials and labor 
costs. 
SUMMARY OF THE INVENTION 
A multi-pass plate and fin heat exchanger of the instant invention retains 
basic structural and operational details of the prior art. In lieu of a 
segmental, mitered "fin" layer, however, it substitutes a single, 
one-piece layer of material which can be constructed and assembled in the 
heat exchanger in substantially the same manner as would be done in 
constructing a single pass heat exchanger. The problem of impeded flow is 
obviated by giving the fin corrugations a slitted, or lanced, 
configuration enabling fluid flow to take place through the corrugations 
in a sense laterally or transversely thereof. The slited or lanced 
configuration may appear throughout the length of the corrugations, or may 
be limited to locations where the flowing fluid is required to move in a 
sense transversely of the fin corrugations. In an optional practice of the 
invention, the fin layer is configured with transverse slots at locations 
of transverse flow, and these may be used instead of or in addition to a 
slit or lanced fin configuration. 
An object of the invention is to provide a multi-pass heat exchanger 
circuit substantially as set forth in the foregoing.

Referring to the drawings, a plate and fin heat exchanger core in 
accordance with an illustrated embodiment of the invention may assume a 
form substantially as is indicated in partly diagrammatic form in FIG. 1. 
The structure there illustrated is adapted to place separate, 
non-communicating fluids in a heat transfer relation through a series of 
vertically spaced apart plates 10. The plates 10 are held in a 
superposing, spaced apart relation by means including side bars or 
"nose-pieces" 11 and 12, end bars or nose-pieces 13 and channel shaped 
members 14. The core device is in the illustrated instance generally 
rectangular in configuration. Channel members 14 position between an 
adjacent pair of plates 10 and at opposite ends thereof. They confine 
between them a secondary heat transfer material in the form of a 
corrugated fin means 15 oriented so that the corrugations thereof extend 
in a direction laterally or transversely of the length of the heat 
exchanger core. A pair of oppositely positioning channel members 14 is in 
an alternating relation to an arrangement of marginal nose-pieces 11, 12 
and 13 which effectively close three sides of the core at levels above and 
below the level at which channel members 14 position. Within a flow area 
bounded by the nose-pieces 11, 12 and 13 is a layer of fin material 16, to 
be more particularly considered hereinafter, and a divider member 17. The 
latter locates intermediately of the nose-pieces 11 and 12 and lies in a 
parallel relation thereto. At its one end, the divider member 17 
terminates substantially at one end of the core or at an end coincident 
with an end of the fin layer 16. At its opposite end, divider member 17 
terminates within the described flow area or short of end nose-piece 13, 
the latter marking the opposite terminus of the fin layer 16. 
It will be evident that a heat exchanger core substantially as shown in 
FIG. 1 is constructed by a stacking of parts to assume substantially the 
relationship illustrated. Thus, a bottom or base plate 10 has a pair of 
channel members 14 placed thereon and between the channel members 14 is 
placed a strip of corrugated secondary heat transfer material 15. These 
parts are followed by another plate 10 and on this plate is placed side 
bars or nose-pieces 11 and 12 and an end nose-piece 13. Within the area 
bounded by these parts there is placed a layer of a secondary heat 
transfer surface material 16 and a divider member 17. This is followed by 
another plate 10 and by additional channel members 14 and secondary 
surface material 15, and by another plate 10 and so on until a heat 
exchanger core of the desired number of vertical layers or flow passes has 
been assembled. The parts are appropriately held in an assembled relation 
in a jig, fixture or the like and while so held are subjected to a 
metallurgical joining operation, as for example brazing. In this 
connection, the parts may, prior to assembly, be coated with a braze alloy 
so that when the assembly is complete and upon the assembled core being 
subjected to an appropriate heating and cooling operation, the braze alloy 
will flow and harden to establish a seal and a bond between contacting 
parts. The secondary heat transfer surface or fin material 15 and 16 has 
the peaks and valleys thereof in contact with overlying and underlying 
plates 10. As a part of the brazing operation, the fin material 
accordingly is joined to the plates and by being bonded thereto establish 
ties between adjacent plates strongly reinforcing the heat exchanger core 
against disruptive effects of fluid pressure. At the same time, since the 
peaks and valleys of the fin material are in contacting, sealed relation 
to adjacent plates, an intercommunication of flowing fluid between 
adjacent fin corrugations over and under the peaks and valleys thereof is 
impossible. 
As is evident from the illustration of FIG. 1, the described construction 
forms flow passes for the different fluids which are substantially at 
right angles to one another. By appropriate manifolding, ducting or the 
like, a first fluid is brought to one or the other sides of the heat 
exchanger core and admitted to passages occupied by fin material 15 and 
defined by channel members 14. This fluid flows in a single pass through 
such passages, entering on one side of the core and exiting at the other. 
Simultaneously, a second fluid is brought to what may be regarded as an 
open end of the heat exchanger core, or that end opposite the end occupied 
by nose-pieces 13. Again, suitable manifolding or ducting means is 
provided. In the illustrated instance, the presence of a mainfold 18 is 
indicated which provides a separate chamber 19 and a chamber 21 in 
communication respectively with end portions of the heat exchanger core 
which lie to opposite sides of divider members 17. Through respective 
ports 22 and 23, the chambers 19 and 21 communicate with a line flowing 
the described second fluid, and the ports 22 and 23 may function 
alternatively as the inlet and the outlet for the second fluid. In the 
case of the second fluid, therefore, it is admitted to the heat exchanger 
core by way of port 22 and chamber 19, for example, and flows 
longitudinally within a flow area defined by side nose-piece 11 and 
divider member 17 in the direction of end nose-piece 13. After passing 
beyond the inner end of divider member 17, the fluid is able to flow 
transversely or toward side nose-piece 12 (in a manner to be discussed 
more particularly hereinafter) and then moves in a sense reversely of its 
former flow back in the direction of manifold 18 where it enters chamber 
21 and discharges by way of outlet 23. Within the heat exchanger core, 
therefore, the described first and second fluids are in a heat transfer 
relation through separating plates 10, with fin material 15 and 16 
providing secondary heat transfer surface promoting a better and more 
efficient transfer of heat between the separated fluids. In the 
illustrated instance, the described first fluid has a single pass through 
the heat exchanger core whereas the described second fluid is constrained 
to move in a serpentine or reversing flow path. The arrangement is 
generally one of cross flow fluid movement, with components of counterflow 
in those portions of the heat exchanger core in which the described second 
fluid makes a turn around the inner free end of the divider members 17. 
Referring more particularly to FIGS. 2 and 3, the fin layer 16 is seen to 
be a one-piece, lanced article, formed with an elongated slot 24 
positioned to accommodate the divider member 17. The slot 24 accordingly 
opens through one end of the fin layer 16 and terminates well short of the 
opposite end. The fin layer is comprised of individual corrugations 25, 
each being "lanced" or cut along its length to provide offset portions 25a 
and open area 25b. Throughout their length, therefore, individual flow 
paths as defined by individual fin corrugations are in an 
intercommunicating relation with adjacent, like flow paths. Further, the 
open area 25b provides a route by which fluid may move in a sense 
transversely of the fin layer, as across a portion of the fin layer 
occupied by multiple corrugations. Referring again to FIG. 1, therefore, 
and to the flow circuit described in connection with the described second 
fluid, a fluid admitted to manifold chamber 19 and admitted to the flow 
passes occupied by fin layer 16 can move longitudinally along the several 
communicating corrugations 25 until it passes beyond a point of 
confinement as represented by the inner free end of divider member 17. 
Continued flow then is in a sense transversely of the fin layer and takes 
place through open area 25b. As the transversely flowing fluid reaches 
corrugations 25 positioning on the opposite side of divider member 17, it 
is enabled again to move in a sense longitudinally of the layer 16 and 
flows this time in a reverse direction back toward the manifold 18 and 
into manifold chamber 21 to be discharged by outlet 23. The described 
second fluid accordingly completes plural passes through the heat 
exchanger core, which passes are interconnected by components of lateral 
or transverse flow enabled by the lanced fin construction. 
For convenience of disclosure the invention has been shown in FIGS. 1 to 3 
as comprised in a multi-pass heat exchanger in which the described second 
fluid completes its flow through the heat exchanger core in two passes or 
in what may be considered a single reversing path. It will be obvious that 
the serpentine or reversing movement of the fluid may include more than 
one turn around portion to provide an extended flow path of multiple 
reversing passes. 
By way of example there is shown in FIG. 4 a modified multi-pass heat 
exchanger core in which plates 26 are separated in the one instance by 
channel members 27 and fin material 28 and in the other instance by 
nose-piece means 29 and 31, the arrangement insofar as the flow of the 
described first and second fluids is concerned being the same as described 
in connection with the embodiment of FIG. 1. Nose-piece means 29 is in 
this instance a one-piece part of U-shaped configuration and corresponds 
substantially to the side bars 11 and 12 and end member 13 of the first 
considered embodiment. Nose-piece means 31 is likewise of U-shaped 
configuration and has a telescopic reception within nose-piece means 29, 
in a reverse orientation. The inwardly projecting legs of U-shaped 
nose-piece means 31 form divider members 32 and 33. The nose-piece 
assembly is completed by a divider member 34 based in the closed end of 
nose-piece means 29 and projecting between the legs 32 and 33 toward but 
short of the closed end of nose-piece means 31. The open end of nose-piece 
29, in conjunction with the closed end of nose-piece means 31, defines 
entrance and exit ends of a circuitous flow path for the described second 
fluid. A manifold 35 has a port 36 opening thereinto and provides a 
chamber 37 communicating with what may be regarded as the start of the 
circuitous flow path or that longitudinal portion lying between leg 32 and 
the adjacent leg of nose-piece means 29. A manifold 38 has a ported 
opening 39 and provides a chamber 41 communicating with what may be 
regarded as the exit end of the circuitous flow path, or that portion of 
the flow path lying between leg 33 and the adjacent leg of nose-piece 
means 29. At ends of the legs 32-33 and at the end of divider member 34, 
are turn-around portions of the circuitous flow path, or locations of 
transverse fluid flow. The area bounded by nose-piece means 29 is occupied 
by a one-piece layer of fin material 42 which may be a corrugated, lanced 
material essentially the same as the fin layer 16 of FIGS. 1 to 3. In this 
instance, however, the fin layer 42 is preformed with a plurality of slots 
of longitudinal extent respectively accommodating flow divider members 
32-34. As in the case of the FIGS. 1-3 embodiment, the lanced 
configuration of the fin material provides for components of transverse or 
lateral flow at the turn-around locations beyond extremities of the legs 
32-33 and member 34. 
It will be understood that parts comprised in the embodiment of FIG. 4 are 
assembled and united into an integrated structure substantially in the 
same manner described in connection with the FIG. 1 embodiment. 
In the illustrated instances of FIGS. 1 and 4, the described second fluid 
is required to move transversely in turn-around locations through means 
providing for a relatively tortuous passage of the fluid, namely the fin 
open area 25b. It may be desirable to facilitate transverse flow with 
reduced resistance at the turn-around locations and to this end there is 
shown in FIG. 5 a modified form of fin layer, indicated at 42a therein. 
The fin layer is in an illustrated environment corresponding to that of 
FIG. 4 and like parts are given the same reference numeral identification 
in FIG. 5 as they have in FIG. 4, with the addition of the letter "a." Fin 
layer 42a may be made to a lanced configuration, as in the case of fin 
layers 16 and 42 or may be made to other, known configurations, as for 
example one in which the individual corrugations are straight and 
unapertured. In either event, the fin layer is further provided with a 
longitudinal series of transverse slots 43, 44 and 45 at each turn-around 
location. The slots 43-45 bridge the inner free end of each adjacent 
divider member 32-34 and intersect a selected number of corrugations in 
the fin layer. The slots 43-45 provide relatively low resistance flow 
paths whereby the described second fluid at the end of each longitudinal 
pass through the heat exchanger core may with greater ease and facility 
move transversely to the next following longitudinal pass segment. Low 
resistance passage means as represented by the slots 43-45 herein may be 
provided in whatever number and configuration may be found appropriate, 
having regard to involved fluid flow rates and heat transfer requirements. 
In the illustrated instance, slot 43 is relatively narrow and has 
divergent ends. Slot 44 is made without divergent ends and is relatively 
shorter than slot 43 but is somewhat wider. Slot 45 is relatively broad 
but short in length. In conjunction with one another, they provide for an 
intersection of all corrugations of adjacent flow passes. 
In the illustrated instances of FIGS. 4 and 5, all successive portions of 
the circuitous flow path are occupied by a single, one-piece fin layer 42 
or 42a. It will be understood that, if found necessary or desirable, there 
may be interposed at any location in such path a circuit component of the 
prior art, that is, one of relatively low flow resistance making use of 
multiple fin parts assembled in a miter joint. 
The invention has been disclosed as comprised in certain illustrated 
embodiments, and modifications have been discussed. It will be evident 
that these and other modifications and embodiments, which will be obvious 
to persons skilled in the art, are fully comprised in the intent and 
concept of the invention.