METHOD OF MAKING A HEAT EXCHANGER ASSEMBLY WITH INTEGRAL FIN UNITS

Abstract: A heat exchanger assembly (20) of the side-entry cross-fin type includes first and second integral fin units (23, 23a), each comprising a single sheet (43) of material provided with a plurality of aligned apertures (42), the sheet (43) of material being folded in accordian-fashion such that the apertures (42) define a plurality of notches arranged in rows which extend longitudinally of the fin unit (23, 23a). Two of the fin units (23, 23a) are assembled together with a single length of heat exchange tube (22) which threads the notches of the fin units (23, 23a), the tube (22) extending over an oval-shaped helical path through the two fin units (23, 23a). In another embodiment, a single folded fin unit (123) is provided with notches in fins on its upper and lower surface, a single length of tube (122) being wrapped around the single fin unit (123) threading the apertures (142) therein, the tube (122) extending in a generally oval-shaped helix path.

Description: This invention relates to a method of making a heat exchanger assembly of the cross-fin type according to the precharacterising part of claim 1. Such a method is known from FR-A-2 102 193. Cross-fin heat exchangers commonly in use are of two types, namely the plate-fin type and the side-entry type. In the plate-fin type of heat exchangers, the tubing forming the coil portion of the heat exchanger is inserted longitudinally through openings formed in the cross-fins of the heat exchanger in inwardly spaced relation to the marginal edges thereof. In side-entry type heat exchangers, the cross-fins thereof have notches formed in their marginal edge portions. The notches are aligned in rows and the tubing is inserted transversely into the aligned notches from row to row. In known heat exchangers of both types, the fin assemblies comprise a plurality of separate fin strips arranged in an array with the longitudinal openings, or the transverse notches, aligned to receive the tubing. During assembly of such heat exchangers, it is necessary to support the fin assembly in a suitable jig while the tubing is being inserted. Although plate-fin type heat exchangers provide good thermal contact between the cross-fins and the tubing, a shortcoming is that the tubing must be inserted in sections and the sections interconnected at the ends by return bends which are soldered or otherwise connected to the tube sections which define the passes through the fin assemblies. On the other hand, in side-entry type of heat exchangers, the provision of the open-ended notches along the marginal edges of the fin assemblies enables use of a one-piece tube. However, because such heat exchangers have open-ended notches, the cross-fins cannot contact the tubing over its entire outer periphery. The peripheral contact is reduced by at least by the width of the open-end portion of the notch through which the tubing is inserted into the fin assembly. To maximise contact between cross-fins and tubing, it has been common practice in the manufacture of side-entry type heat exchangers to form the notches with an entry portion leading into a body portion, the entry portion being smaller in width than the body portion so that tubing slightly flattened transversely, may be inserted transversely through the entry portion into the body portion and then expanded. Such expansion both interlocks the cross-fin and tubing against removal and enables the tubing to engage the side walls of the body portions along a greater portion thereof. The fin stock used in heat exchanger fin assemblies is typically of a thickness in the range of 0.178mm (0.007 inch) to 0.254mm (0.010 inch). The size of the fin stock as well as the tubing size determine the overall dimensions of the heat exchanger assembly. Heretofore, in exchanger assemblies employing separate fin strips, the need for sufficient structural strength of the fin assembly dictated the size of the fin stock material and thus the overall size of the heat exchanger assembly. That is, the individual fin strips must be of sufficient thickness to allow the tubing to be inserted into the notches of the assembled fin strips without deforming the fin strips. FR-A-2303259 discloses a heat exchanger assembly of the side-entry type having a unitary corrugated heat transfer member with notches formed in its front and back sides. Heat exchange tubing of tortuous form is arranged in these notches. However the heat exchange tubing does not have any complete turns. The heat exchanger is made by fitting the heat transfer member on the preformed tortuous heat exchange tubing. It is therefore an object of the invention to provide a method of making a heat exchanger assembly of the side-entry type which is easier to manufacture and assemble than previously available methods of manufacturing heat exchanger assemblies. Another object of the invention is to enable manufacture of a heat exchanger assembly which is more compact and rugged than known heat exchanger assemblies, affording increased efficiency while providing a more compact heat exchanger assembly. According to the present invention there is provided a method of making a heat exchanger assembly as claimed in the ensuing claim 1. Conveniently the transfer means comprises first and second fin units of unitary construction which are assembled together with their rearward sides adjacent to one another with the fin units so oriented so that one of the fin units has its longitudinal axix extending at an angle relative to the longitudinal axis of the other fin unit. Suitably a plurality of apertures is provided in the or each said sheets prior to its folding, the apertures defining said notches when the or each sheet is subsequently folded. Conveniently the diameter of the tube is reduced in a transverse direction to less than the width of the notches prior to wrapping the tube around the or each fin unit and the tube is expanded after it has been wrapped around the or each fin unit and positioned within the notches. The heat transfer members are of a unitary construction with all of the fin portions of each member being formed integrally therewith. Such unitary construction affords a greater degree of rigidity to the heat exchanger assembly, allowing the array to be formed from a sheet of stock material of a thickness in the range of about 0.076mm (0.003 inch) to 0.178mm (0.007 inch). Also, the heat exchange tubing may be formed of a material in the order of 0.305 - 0.508mm (0.012 - 0.020 inch) thick and approximately 6.35 - 12.7mm (0.250 - 0.500 inch) in outside diameter. This results in a smaller more compact heat exchanger assembly than has heretofore been used in heat exchanger assemblies. Because of the dense structure afforded by the use of heat exchanger tubing of smaller size, it has been found, for example, that a heat exchanger assembly reduced in size by up to 1/5 to 1/3 that of a known heat exchanger unit, can achieve equal heat transfer efficiency. Because of the helix shaped serpentine and freedom from having to provide fin support during assembly, more tubes and more fins can be arranged in a smaller volume than was previously possible with the same size tube. For the purpose of facilitating and understanding the invention, there is illustrated in the accompanying drawings preferred embodiments thereof, from an inspection of which, when considered in connection with the following description, the invention, its construction and operation, and many of its advantages will be readily understood and appreciated. Fig. 1 is a top plan view of a heat exchanger assembly made in accordance with the present invention; Fig. 2 is a side elevation view of the heat exchanger assembly of Fig. 2; Fig. 3 is a fragmentary plan view of one embodiment of a fin unit, prior to folding thereof; Fig. 4 is a vertical section view taken along the lines 4-4 in Fig. 2; Fig. 5 is a perspective view of the fin unit in its folded form; Fig. 6 is a plan view of a second embodiment of a fin unit prior to folding; Fig. 6A is a fragmentary view of the fin unit 23'. after folding, showing tube placement, Fig. 7 is a fragmentary side elevation view of a second embodiment of a heat exchanger assembly made in accordance with the present invention; Fig. 8 is a plan view of a third embodiment of a fin unit prior to folding; and Fig. 9 is a fragmentary front elevation view of the heat exchanger assembly shown in Fig. 7. Referring to FIGS. 1 and 2, the heat exchanger assembly 20 includes a one-piece heat exchanger tube 22 and two integrally formed fin units 23 and 23a each of which defines a plurality of rows of aligned notches or slots 25 and 25a, respectively. The single length of tube is threaded in serpentine fashion through the series notches 25,25a provided in respective forward surfaces 26,26a of the fin units 22 and 22a. The fin units 23 and 23a are of the side-entry type and each fin unit 23 and 23a comprises a set of fins formed from a single sheet of metal which is folded back and forth upon itself defining a plurality of fins 24 and 24a for the fin units 23 and 23a. The fins 24,24a of each fin unit are alternately connected together at their tops and bottoms along respective web portions 28 and 28a as shown in FIG. 4. As shown best in FIGS. 1 and 2, the tube 22, which may be formed of any suitable material, such as, for example, aluminium, preferably consists of a unitary tubular member which may have a diameter of about 9.53 mm (.375 inch) and a wall thickness of about 0.41 mm (.016 inch). The tube with such dimensions affords sufficient mechanical strength to withstand internal pressure without rupturing while being capable of being flattened when subjected to forces on opposite sides of the tube, to facilitate insertion into the fin units. When the tube 22 is assembled with the fin units 23,23a, as shown in FIG. 1, it is formed into a serpentine pattern having an upper row 29 of passes 31 and a lower row 30 of passes 31a spaced apart a distance "s". At the left-hand side (as viewed in FIG. 1) of the assembly, the adjacent passes 31, 31a in each of the upper and lower rows 29 and 30 are interconnected at their ends by return bend portions 32 of the one-piece tube 22, and at the right-hand side of the assembly, the passes 31, 31a in the two rows 29 and 30 are interconnected by return bend portions 33. One of the passes 31 in the upper row 29 extends outwardly beyond the fin unit 23 to afford a fluid inlet 34 for the tube 22, and one of the passes 31a in the lower row 30 extends outwardly from the fin unit 23a to afford a fluid outlet 35 for the tube 32. With this construction, working fluid, such as for example, refrigerant may be fed from a suitable source of supply, such as a compressor, not shown, into the tube 22 through the inlet 34 from which it may flow horizontally through the fin unit 23, forward the left as viewed in FIG. 1, downwardly from pass 31 in the row 29, through the return bend 33 to the pass 31a in the lower row 30, and then horizontally to the right, and then back up through the next pass 31 inwardly and horizontally to the left through upper fin unit 23, etc. The fluid thus passes back and forth through the fin units 23 and 23a through the passes thereof and finally passes through the outlet 35 in the lower row 30. Referring to FIGS. 3-5, each of the fin units, such as fin unit 23 is formed from a flat sheet of fin stock 43 (FIG. 3) such as, for example, a suitable metal, such as aluminum, or the like of a thickness in the order of 0.076 - 0.178 mm (.003 to .007 inch). The sheet stock is provided with a plurality of apertures, of "dog-bone" shape arranged in a rows spaced along the longitudinal extent of the sheet. Each row includes a plurality of apertures eight in the exemplary embodiment, extending transversely in the row. Each aperture 42 has a narrow center portion 42a which extends longitudinally of the sheet and generally circular portions 42b at opposite ends of the center portion 42a. In one heat exchanger assembly which was constructed, the center line-to-center line spacing "y" between adjacent apertures was 19.05 mm (.750 inch). The dimension "y" can be varied between approximately 12.7 mm (1/2") and 25.4 mm (1") or more depending on the outer diameter of the tube. The center line-to-center line longitudinal spacing "z" between aligned apertures in adjacent rows was 27.18 mm (2.07 inches) and the radius of the circular portions 42b was 4.75 mm (.187 inch). Likewise, the dimension "z", can be varied to provide many fin arrangements. The fin assembly was 546.1 mm (21.5 inches) long, 203.2 mm (8 inches) in width and 50.8 mm (2 inches) in height. The apertures 42 are formed in the sheet of material, as by a punching or stamping operation, while the sheet is in a substantially flat condition as shown in FIG. 3. Thereafter, the sheet of material 43 is folded back and forth upon itself in accordian-like fashion along the fold lines 45 and 46, for each row, one fold line 45 bisecting the longitudinal axis of the apertures for that row, the other fold line 46 extending transversely of the longitudinal axis of the sheet and intermediate the apertures of adjacent rows. Fold line 45 may comprise segmented creases formed by the die formed from the apertures 42. When the sheet is folded, providing an accordian-type fold for the fin unit, unapertured portions of the sheet along fold lines 46 define the rearward surfaces 27 and 27a of the units 23 and 23a, the narrow-center portions 42a of the apertures define the open-end portions 51 of the notches at the forward surface of the unit for receiving the tube 22 of the heat exchanger. The generally circular portions 42b of the apertures define the body portions 52 of the notches, located intermediate the rearward surfaces 27 and forward surface 26 of the unit, and in which the tube 22 is received. The tube receiving circular body portions 52 maximize the area of contact between the fins and the periphery of the tube. The notches are disposed in alignment on the forward surface of the fin unit as illustrated in FIG. 5. When the two fin units 23 and 23a are assembled together with the tube 22, as shown in FIG. 4, the fin unit 23 is offset a distance "x" relative to the longitudinal axis of the fin unit 23a as shown in FIG. 1. In one heat exchanger assembly which was constructed, the length of the fin unit was 546.1 mm (21.5 inches) and the offset length was 25.4 mm (1 inch). Thus, the tube 22 when assembled with the fin units 23 and 23a extends is an oval-shaped helical path from the fluid inlet 34 at the upper right-hand corner (FIG. 1) of the heat exchanger assembly 20 to the fluid outlet 35 at the lower right-hand corner of the heat exchanger assembly. As shown in FIG. 2, the passes 31 in the upper row 29 and the lower row 30 are spaced apart from one another by a distance "s" which in one assembly which was constructed was 15.9 mm (5/8 inch). When the tube 22 is assembled with the fin units 23 and 23a, the tube is located in the enlarged generally cylindrical body portions 52 of the notches 42 as shown in FIG. 4. During insertion of the tube, the tube may be flattened slightly to enable it to pass through the narrow throat portion 51 of the notches, the tube being expanded, such as by introduction of fluid under pressure into the tube 22, when assembly is complete. Referring to FIG. 6, there is illustrated a further embodiment for a fin unit 23' which is generally similar to fin unit 23, but which includes generally oval-shaped apertures 42' and which includes a cut out portion 61, generally rectangular in shape, in alternate row positions which define openings at the ends of alternate rows to provide wider channels for the passage of air such as when the heat exchanger is used in a low temperature refrigeration unit provided with a defrosting cycle. As shown in FIG. 6, after folding, the slot shape allows variations of tube placement from row to row within each coil so as to maximize coil efficiency. Referring to FIGS. 7-9, a further embodiment of a heat exchanger assembly 120 includes a single fin unit 123 upon which is wrapped a one-piece heat exchanger tube 122 which threads aligned notches 152 and 152a provided in fins on the upper and lower surfaces of the fin unit 123. The fin unit 123 is the same as the fin units 23, 23a except that two sets of apertures 142 and 142a are provided for defining the notches 152a on the lower surface of the fin unit 123 as well as notches 152 on the upper surface of the fin unit. Briefly, fin unit 123 is formed from a flat sheet 143 of fin stock (FIG. 8) of aluminum or the like having a thickness in the order of 0.076 - 0.178 mm (.003 to .007 inch). A first plurality of sets "A" of aligned apertures 142 provided in the sheet 143 are arranged in rows extending transversely of the sheet. By way of example, each set "A" of apertures may include eight apertures. Each of the apertures 142 is oval-shaped, and its major axis extends parallel to the longitudinal axis of the sheet 143. The apertures 142 in each are aligned along a fold line 145 and spaced apart from adjacent apertures in the same row by a distance "y" which is in the order of 19 mm (.750 inch). Similarly, a second plurality of sets "B" of aligned apertures 142a provided in the sheet 143 are arranged in rows extending transversely of the sheet, with, for example, eight apertures per set. Each of the apertures 142a is oval-shaped, and its major axis extends parallel to the longitudinal axis of the sheet. The apertures 142a are aligned along a fold line 145, offset a distance "y"/2 relative to the apertures 142. Thus, after the sheet 143 has been folded in accordian-like fashion, as shown in FIG. 9, to define the fins on its upper and lower surfaces, the sheet 143 being folded over along fold lines 145 and 146 through its apertured portions, the sets of apertures 142a, which define the notches 152a on the lower surface of the fin unit 123 are located midway between vertical plane bisecting the notches 152 defined by apertures 142 in the upper surface of the fin unit 123. When the heat exchanger tube 123 is wrapped on the folded fin unit, the upper notches 152 are threaded by the upper passes 131 of the tube and the lower notches 152a are threaded by the lower passes 131a of the tube, the upper and lower passes being joined by return bend portions 132 so that the heat exchanger tube 123 defines a generally oval-shaped helical path through the fin unit 123. In manufacturing of the heat exchanger assembly 20, with reference to FIG. 3, first the two fin units 23, 23a are produced from separate sheets of fin stock. Each sheet of fin stock material 43 is provided with a plurality of apertures 42 in a punching or stamping operation. Each sheet is then folded along fold lines 45 and 46, providing an accordian-like fold for the fin unit such as fin unit 23 shown in FIG. 5, with the apertured portions of the sheet defining notches 42 in the aligned rows which extend along the longitudinal axis of the unit in a plurality of columns. The two fin units 23 and 23a, thus produced, are positioned with their back surfaces 27, 27a adjacent to one another, others in contact with one another, or in a spaced relation as shown in FIG. 4, and with the upper most unit 23 extending at a slight angle (FIG. 1) relative to the lower unit 23a to be offset by an amount "x" relative to the side edge of fin unit 23a. Then, the one-piece tube 22 is wrapped around the thus arranged fin units 23 and 23a and is threaded through the notches 42 in the individual fin units 23 and 23a so that the fins 26, 26a establish a series of cooling fins which extend across the width of the fin units and bridge the straight pass sections 31 of the tubing 22. The enlarged body portions 52 of the notches 42 to accommodate the tube 22 (FIG. 4) and the narrow entrance throat portions 51 facilitate admission of the tube 22 into the notches 42, the tube being in slightly flattened form. Because of the relatively thin size of the fin stock, lubrication of the tube 22 outer surface is not required during assembly of the tube with the fin units. After the tube has been wrapped around the fin units and is positioned in the notches 42, the outlet end 35 of the tube 22 is closed and internal pressure is applied to the tube 22 through its inlet 34 to expand the tube back to its original cylindrical shape. This causes the outer wall of the tube 22 mechanically to engage the edges of the enlarged body portions 52 of the notches 42. Heat exchanger assembly 120 is manufactured in a manner similar to that for heat exchanger assembly 20 except that a single fin unit is employed and its fin stock is provided with two sets of apertures "A" and "B" (FIG. 8) to define the notches for the upper surface and the lower surface respectively of the folded fin unit. Also, the heat exchanger tube is wrapped around the single fin unit. The assembled tubing and fin units constitute a basic heat exchanger assembly 20 which may be operatively installed or mounted in a wide variety of installation by means of suitable mounting or support hardware (not shown). The free ends of the tubing which define the inlet 34 and outlet 35 are located on the same side of the unit, the right-hand side as illustrated in FIG. 1.

Claims: A method of making a heat exchanger assembly (20) comprising the steps of providing a heat transfer array from at least one fin unit (23, 23a), the or each fin unit being formed by folding a first sheet of a heat conductive material (43) back and forth on itself to provide accordionlike folds which define a plurality of corrugations (24) having a plurality of first web portions (28) on a forward side and a plurality of second web portions (28a) on a rearward side, each of said first web portions having a plurality of notches (25) formed therein, and threading a one-piece heat exchange tube (22) through said notches (25) to define forward pass portions (31 ) extending parallel to each other along the front of the array, rearward pass portions (31a) extending generally parallel to each other along the back of the array and interconnecting return bend portions (32, 32a), characterised in that the heat exchange tube (22) is threaded through said notches (25) by helically wrapping the tube around the at least one fin unit with each return bend portion (32, 32a) interconnecting next following forward and rearward pass portions. A method according to claim 1, characterised in that said transfer means comprises first and second fin units (23, 23a) of unitary constructions which are assembled together with their rearward sides adjacent to one another with the fin units so oriented that one of the fin units has its longitudinal axis extending at an angle relative to the longitudinal axis of the other fin unit. A method according to claim 1 or 2, characterised in that a plurality of apertures (42) is provided in the or each of said sheets (43) prior to its folding, the apertures (42) defining said notches (25) when the or each sheet is subsequently folded. A method according to any one of claims 1 to 3, characterised in that the diameter of the tube is reduced in a transverse direction to less than the width of the notches prior to wrapping the tube around the or each fin unit and in that the tube is expanded after it has been wrapped around the or each fin unit and positioned within the notches.

Inventors: PAULMAN, ROGER, WOHRSTEIN, FRANZ X.
Applicants: PEERLESS OF AMERICA, INCORPORATED
Application year: 1987
Main classification: F28F1
IPC codes: F28F1, F28D1