Method of producing a tubular distributor of a heat exchanger from juxtaposed porous strips of material

A method for manufacturing a tubular distributor of a heat exchanger in which the distributor is formed by layers of material between which the ends of heat exchange tubes of a matrix are secured in fluid-tight manner. The layers are made of fibers which are juxtaposed between the tube ends of adjacent rows and the layers are deformed by compression so that they each engage around one-half of the associated row of tubes to form an initially porous structure into which a metallic material is injected to integrate the fibers of the layers with one another and with the ends of the tubes in sealed relation.

FIELD OF THE INVENTION 
The invention relates to a method of producing a tubular fluid distributor 
of a heat exchanger from a succession of juxtaposed strips in which the 
ends of heat exchange tubes are mounted in sealed relation. 
DESCRIPTION OF PRIOR ART 
One method of manufacturing a fluid distributor of a heat exchanger is 
known from U.S. Pat. No. 4,597,436 in which a tubular distributor is 
assembled from a plurality of very precisely preformed or preprofiled 
elements corresponding to the number and the desired spacing of the 
profiled heat exchange tubes of a tube matrix. The elements are assembled 
as layers one on the other and the layers are predeformed so that each 
surrounds only one-half of the ends of the heat exchange tubes in 
form-locked manner. 
This arrangement has the disadvantage that, despite relatively precise 
manufacture of the corresponding elements forming the layers, 
manufacturing tolerances must be taken into account, so that the total 
length of the tubular distributor to be produced varies with the sum of 
the thickness tolerances of the elements. In addition to variations in the 
length of the distributor, local offsets of recesses for the tubes with 
respect to the prescribed spacing and arrangement of the tubes is also 
produced. In mass production of the elements, therefore, manufacturing 
tolerances cannot be avoided and can be corrected, if possible, in 
practice only by extremely expensive subsequent machining. 
Any offset of the openings for the tubes and even only slight variations in 
the shape of the openings, make necessary a tedious fine adjustment or 
centering of the corresponding ends of the tubes, particularly as the 
subsequent joinder of the tube ends in the tubular distributor (for 
example, by soldering, welding or brazing), demands an extremely accurate, 
seated fitting of the tube ends in order to minimize local displacements 
of the joining material as much as possible. 
In another known method as disclosed in U.S. Pat. No. 4,698,888, the 
preformed elements are produced by a rolling operation. The assembly of 
the preformed elements suffers from the same disadvantages as noted above. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a method which avoids the 
problems concerning manufacturing tolerances of the layers which make up 
the tubular distributor, and in the location of the openings for receiving 
the ends of the heat exchange tubes. 
A further object of the present invention is to provide a method in which 
the tube ends of a tube matrix of a heat exchanger can be effectively 
secured in integrated fashion in a tubular distributor structure which is 
produced from elements which avoid the use of solid structural parts. 
In accordance with the objects of the invention, there is provided a method 
in which successive layers of strips of fiber material are assembled in 
juxtaposed relation with the ends of rows of heat exchange tubes 
interposed between adjacent strips whereafter compressive forces are 
applied to the strips to squeeze the strips and deform the strips around 
the tubes to form a porous structure in which the tubes are encased. By 
virtue of this method, the need for precision construction of the layers 
with small tolerances as taught by the art is eliminated, and the seating 
of the ends of the tubes in the porous structure is automatically obtained 
by conformance of the strips around the tubes when the strips are 
deformed. 
The porous structure is then filled with a liquid, metallic material to 
integrate the fibers of the strips with one another and with the ends of 
the tubes to form a solid assembly in which the ends of the tubes are 
sealingly secured. 
The invention is characterized in that instead of using annular strips of 
solid material, the strips are made of fiber material. Upon assembly of 
the strips, formed as flat annular layers, on the heat exchanger tubes, 
the fiber material is compressed under the action of axial compressive 
forces and the fiber material completely surrounds the interposed heat 
exchange tubes. The compressing of the fiber material is greatest locally 
where the surfaces of adjacent tubes in the heat exchanger field are at 
the smallest distance from each other. 
The metallic material (metal matrix) acts to fill the hollow spaces in the 
fiber structure and produce a secure, integrated connection between the 
surfaces of the tubes and the surrounding fiber material. 
The formation of the strips of fiber material is effected as follows in 
accordance with the invention. 
The strips are annular in form i.e. cylindrical, oval, rectangular, and in 
the circumferential direction, one portion of the fiber material is 
desirably oriented in order to resist high circumferential forces which 
are developed due to internal pressure in the distributor during operation 
of the heat exchanger. Another portion of the fiber material extends in 
bristle-like manner from the lateral surfaces of each fiber strip so that 
upon assembly, the bristles of adjacent strips interpenetrate one another 
and, after filling by the metallic matrix, provide strength for resisting 
longitudinal forces applied to the distributor. The bristle structure 
furthermore insures that the regions which are least compressed upon 
assembly, particularly at the leading and trailing edges of the heat 
exchange tubes, contain an adequate volume of the fiber material. 
The fiber material is suitably heat resistant to the operating temperatures 
acting on the structural parts, but it need not necessarily withstand 
oxidation and corrosion. When the fibers are completely immersed in the 
metallic matrix, they are thus protected from exposure to corrosive 
fluids. Therefore, metallic fibers can be used as well as ceramic and 
carbon fibers. 
In the assembly of the heat exchanger, it may further be advantageous, in 
accordance with the invention, to surround the annular fiber strips with 
solid annular strips. The width of the solid strips corresponds to the 
narrowest local spacings of the heat exchange tubes in the heat exchange 
field, so that upon assembly, when the strips are pressed together, the 
solid strips will assure obtaining the required spacings. Since, in such 
arrangement, the solid strips must conform to the undulating shape around 
the heat exchange tubes in the tube matrix in the circumferential 
direction, it is necessary to shape the solid strips before assembly or to 
make the solid strips of deformable material so that they can assume the 
undulating shape during compression of the strips. 
The filling of the fiber material with the metallic matrix material can be 
effected according to the invention as follows: 
1. In vacuum ovens, a shaped injector apparatus is introduced into the 
tubular distributor, and the molten matrix material is injected and fills 
the fiber structure by capillary action whereupon the material solidifies 
and unites with the fibers and the tube surfaces. It may be desirable to 
close the ends of the tubes which extend into the interior of the 
distributor and reopen the tubes after completion of the filling 
operation. 
2. Solid annular elements which may surround the fiber structure on the 
inside and on the outside may be made of a material which is fusible upon 
heating in the oven, i.e. solder material. The fusible material can 
penetrate by capillary action into the fiber structure to fill the matrix 
volume and produce intergrated bonds with the fiber material and the 
tubes. The heat exchange tubes and the fiber material can be subjected to 
a surface pretreatment in order to obtain better wetting and binding with 
the matrix filling material.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 shows a heat exchanger 1 for carrying out heat exchange on a 
cross-counterflow basis between an external fluid G flowing around a 
matrix 2 of heat exchange tubes 3 which convey a second fluid D therein. 
The tubes 3 are formed with U-shaped bends and have straight legs 
connected respectively to a duct 4 in which fluid D is introduced in cold 
state and a duct 5 from which heated fluid is fed at D' to a utilization 
means (not shown). The external fluid G can be hot exhaust gases and the 
fluid D can be compressed air. 
The ducts 4 and 5 are arranged in separated relation in a common 
distributor or manifold 6. The straight legs of tubes 3 extend laterally 
from duct 4 of distributor 6, in parallel relation to one another, up to 
the U-shaped bend regions in which the flow of compressed air is reversed 
by 180.degree. and the compressed air flows in the other straight legs of 
the tubes 3 to the duct 5. The path of flow of the compressed air D in the 
tubes 3 is shown by arrows in FIG. 1. A respective tube matrix 2 is 
disposed at each lateral side of the distributor 6 and both tube matrixes 
are traversed by the hot gases G in a direction perpendicular to a median 
plane disposed between the parallel legs connected to ducts 4 and 5. 
As seen in FIG. 2, the tubes 3 are streamlined in cross-section in the 
direction of flow of the hot gases G. The tubes 3 are arranged in the 
matrix 2 in rows and columns and the tubes in the rows overlap or 
interpenetrate between one another to provide smooth flow paths for the 
gases G. 
Instead of the common distributor or collector tube 6, two or more separate 
distributors or collector tubes can be provided for the respective supply 
of compressed air into the matrix 2 and the removal of heated compressed 
air from the matrix 2. 
The invention is directed to the manufacture of sheet structure 10 of the 
common distributor or collector tube 6 and is also applicable to the 
manufacture of a sheet structure for individual distributors of a heat 
exchanger of the type discussed above. 
In the method described herein, the sheet structure 10 forms the wall of 
distributor 6 and as shown in FIG. 5 comprises an integrated assembly of 
successive layers 11, 12 and 12, 13 of strips of material in which the 
heat exchange tubes 3 are embedded in fluid-tight manner. 
Each of the layers is made of fiber material uniformly distributed in the 
layer. The fibers can be made of metallic material or wires, ceramic 
material, such as partially stabilized zirconium oxide or carbon. 
In a first stage of manufacture, layers 11', 12', 13' are disposed in 
spaced relation around the rows of tubes 3 as shown in FIG. 3 so that the 
tubes 3 are interposed between adjacent, juxtaposed layers. As shown in 
FIG. 6 for layer 12, the layers are annular and the ends of the tubes 3 
extend through the layers into the interior of the distributor 6. An axial 
compressive force is applied to the end layers at P, P' to squeeze the 
strips and cause them to deform around the tubes such that each strip 
accomodates itself to one-half the cross-section of the tubes of each row 
while its fibers interconnect with the fibers of the adjacent strips. In 
this way, a porous structure is formed in which the tubes are encased. 
A molten metallic material is then introduced into the porous structure as 
a matrix material to integrate the fibers of the layers to one another and 
to the ends of the tubes as a solid assembly in which the ends of the 
tubes are sealingly integrated. 
As shown in FIG. 4, each layer, for example, layer 12' is formed from 
interwoven fiber plies or sublayers having main fibers 14 extending in the 
circumferential direction of the distributor and secondary fibers 15 
extending transverse thereto. Upon the compressing and the deforming of 
the layers from the state shown in FIG. 4, the secondary fibers 15 
interengage one another in the regions outside the tubes. 
In the plane 16 where the adjacent juxtaposed strips come into contact with 
one another as shown in FIG. 5, the secondary fibers 15 of each strip 
intimately engage one another by interpenetration of the fiber bristles 
with one another. In this way an interbraiding of the fibers is obtained 
without formation of gaps even at the oval, streamlined ends of the tubes. 
The planes of contact 16 are aligned in the longitudinal planes of 
symmetry E (FIG. 5) of each row of tubes. 
As seen in FIGS. 7 and 8, cover elements 18, 19 can be respectively mounted 
on the outer and inner surfaces of the distributor 6 to cover the layers 
11, 12, 13 formed from the fiber material. The layers 11, 12, 13 can be 
covered in whole or in part by the cover elements 18, 19. 
The cover elements are composed of solid metallic ring elements and as seen 
in FIG. 7 for cover element 18, the ring elements are shown at 17 and are 
formed as undulating members which collectively surround the tubes. The 
ring elements 17 can serve to stiffen the structure of the distributor and 
to protect the layers of fiber material from environmental and temperature 
influences. 
The ring elements 17 can also assist in the filling operation of the matrix 
material by preventing outflow of the injected molten material. 
If, for example, the filling of the fiber layers with molten metallic 
material is effected from the outside of the distributor into the fiber 
material, then the ring elements 17 are arranged exclusively at the inner 
surface of the distributor to prevent outflow of the metallic material. 
After the filling operation is completed the ring elements 17 can be 
removed. 
In a further development of the method of the invention, the metallic ring 
elements 17 are made of deformable material and when the layers 12',13' 
are deformed under compressive forces, the ring elements 17 are also 
deformed to undulated shape while assuring the necessary spacing of the 
tubes 3 in the distributor 6. 
Instead of compressing the fiber layers and the ring elements concurrently, 
it is also possible for the metallic ring elements 17 to be initially 
undulated or preformed in accordance with the final shape and to be placed 
on the tubes at the inner and outer surfaces of the distributor 6 over the 
fiber layers 11, 12, 13 before filling with the metallic material. 
In accordance with another advantageous variation of the invention, the 
metallic ring elements 17 can be made of the material which is to fill the 
porous structure. In this case, the ring elements 17 are placed on the 
tubes at the inner and outer surfaces of the porous structure and the ring 
elements 17 are of undulating shape to conform with the deformed layers. 
An extremely practical manner of effecting the filling operation is to make 
the metallic ring elements 17 of a meltable matrix material and to heat 
the assembly in an oven to melt the matrix material and achieve filling of 
the porous material. 
When no ring elements are used, a metallic composite material (matrix) can 
be injected in molten form, within a vacuum furnace, at the inner and 
outer surfaces of the distributor through oval shaped injectors which move 
over the undulated deformed layers of the porous structure (FIG. 5). 
In a further development of the method of the invention, the ends of the 
profiled tubes 3 of the matrix which are open at the interior of the 
distributor can be closed by a metallic filling operation from within the 
distributor and after filling of the porous structure, the tube ends can 
be reopened by machining. 
The metallic material which fills the porous structure as a matrix metal, 
can be an aluminum alloy. 
The distributor 6 has been shown as a cylindrical element in FIGS. 1, 6 and 
8, however, it can have any tubular shape and, for example, it can be 
square or rectangular. The process of filling the porous structure with 
the matrix metal can be carried out continuously over the entire 
circumference of the porous distributor structure. 
Instead of making the ring elements 17 of metal, they can be made of a 
fiber-reinforced plastic material or of ceramic material. 
Although the invention has been disclosed in connection with specific 
embodiments thereof, it will become apparent to those skilled in the art 
that numerous modifications and variations can be made within the scope 
and spirit of the invention as defined in the attached claims.