US2908070A - Method of making serpentine tube finned heat exchanger and product - Google Patents

Description

. Oct. 13, 1959' J. B; THOMAS ETAL mmfi v 3 METHOD MAKING SERPENTINE TUBE FIINNED HEAT EXCHANGE IR AND PRODUCT Filed March 5, 196 1: a Sheets-Sheet a.

IN VEN TORS JESSE B.THOMAS EDWIN H WOLFF Oct. 13, 1959 J. B. THOMAS ETAL 2,908,070

' METHOD OF MAKING SERPENTINE TUBE FINNED HEAT EXCHANGER AND PRODUCT Filed March 5, 1954 3 Sheets-Sheet 2 INVENTORS 7 JESSE B.THOMA$ EDWIN H.WOLFF BY I Oct 1959 J. B. THOMAS ET AL 2,908,070

METHOD OF MAKING SERPENTINE TUBE F INNED HEAT EXCHANGER AND PRODUCT Filed March'5, 1954 3 Sheets-Shet a FiglO INVENTORS JESSE B.THOMAS EDWIN H. WOLFF Fig.l2 Q

United TH D OF SERPENT NE FINNED HEAT EXCHANGER AND PROD- UCT Jesse BvTli'onras anwEflwinli's Wolff, Ldnisvill;'Ky;, assignors to-Reynolds;MetalsCompany, I30uisville,-"Ky.,

ar -corporation of-Delaware Application IVIarCIPS 19 54 fiii'iil No. 414M521 7 Claims. 01. 29-1573 The present invention rela'tsto a; finned heat eichfahe r,

'such for exarnple as =afin'ne'd condenser; and to a method of'makingit. Under the Kramer Patent 2,462,511, amulti-layer sefies of separate "rate'planar 'serpentin 'sectiohh one for each layer; each i hr section forms a separate States Patent.

inggs' braiingeor soldhringrareturii-"befid fitting thereto.

It is desirable to make this structure of alumhtnnfl' tubing rbiit this presents 'a vexati'ousproblefim "due tcr the extreme 'difiic'ulty of'prdduoing a good" union" between 'the which it connectslcan be soldered or brazed, but'thisrequires theu eof a :fluxg" which readily" flows into the"'i1iterior ofthiafiubingkwhere it is difiicult' to removex" In a r'efrigerating systern the pfeSence bf=fifix withi1fthe tubing creates eorresivewonditiofis; hence all traces of it -must removed? Aluminum tubing: ean be welded by" the well-knoWhheli'ard process but in'fihe limited"-spade available, it is diflicult to weld completely arounweach joint 'ofi the' retu'm bendfittingfi Whether 'theunioii is made'iby weldingibraiingwrsoldering the heatinvolvd annealstheiilbing so that i-n thesubsequentstegi'of e5;- pairding the tulzv'ingalriy internal pressure,r-rup'ture is' liable tofoccur af the annealed- -areasw It has beeh proposed-'10 make a finned 'condensercoil byb'stringingsfins in spaeedbanks on a-"lorig'tubeif' then bending'that:tubewith the fin's'fllereon to 'for fii straight runs joined serially by return befids. The s'ttucthrthhs produced is not rigid beeause"the banks of fins on each straight i'un: are separateg and'this method is slow; cumbersome'and cOstIyL Otheb proposedr'nethods of constructing a heat exchangen from-= a" single le'ngtli of tubiitg involve disadvantages, and in addition may require bending-under conditions where'a mandrel cannot beeniplbyed; sd'that itis-hdtpbssibleto mak'e smalh-radiusbends This results-in er bulky st'rueture so that the-finsinust be "made larger than necessary; which resnlts in wastemf metal. Ithas beenpropose'dto mak'e'acontinuous-coil nnllti-layer heat exehanger -by bending each vertical return befid on a mandrel in sequence as the horizontal bends are formed 2 v tibllnedfifig straight gun's. However, this n'iethod'is cum; persona andsiitijectt'dh imarie'irofi aiid is not practical where thecoils' ir to'recive fins commas to all the straight p c Pinned air eoeredddn en ers are employed in aircohditioiiers where they are slibje ctto the corrosive action of the atmospliereQ is e'spe'ciallly pronounced in reigitins near" the ocean Where salt sppaygdecursm the air, and ifi'ilidfistrifl areas Where 't'heair is contar rfiriaited by various corrosive Forthis reason the" condense'r' should have good resistance to' corrosionin addition to .good heat exchange roperties.

It is an object of'the present invention to provide a methocl' for constructing" a" r'i'iulti-layer heat eirc lialig'fer frdni fll 'siligl cb "qu's'lilglfii tubing; which is readily shaped as mas' 'prauction 'metheds;

Anotherobj'ect is" to been a con inuous length of tunin into ai'munrisyetheat exchanger by' a novel method which involves reratiwy little handling; and lit'tl'e'liabilit'y tuhing 'djurihgmanutacture.

eliminates the j necessity of making joints between the layisgafidwhich'is easy-to v Afnotherobjject isth'e' provision of aniethod fofi forming a-com acrm" "'-layer"h"eat exchangef inwhich all layers and "all retnnr bends, including these which @611- neetone la er to another; are" reformed before the fin assernby operation. 7 y p Amether object is to'niale a rigid finned heatexeh'afi er, comprising a 'cdntinnousl'engnr 'of tuhingbe t into siiiilous layers integrally 'jo ined wi'tlic'iuf separate fittings; anovel methodwhichenables all layers to be assent ed as a onacommdh fin a's'senibly' in 'afi asy mariner:

Another object is the provision of a heat ei'rcha'iiigr comprising a contintlous' length of tubing' bent in't'o sinuous'laye'rs, which 'ar'e' integrallyjoinedfr'ont' end to "end without sepzirate' 'fittings'; and which are mounted QhTa commonfinassenibly:

A further object is the rovision; of a"coi1"deiisr' or heat iexchanger' of aluminum tithing-which carries 'a' corr'osion"resistant coating" of good heat cenducting pm ert-ies."

The heat exchanger of are present inventio'h made eliminates entirely "the making'ofjoints between" layers and provides a compact, ri gid' structure. Where a slight constriction of the tube pass'age at the bends not-objectionable, or the radii of the bends are large, the'be'nds may be 'forme'dwithouta mandrel; However, for corn- ;paetne ss, b'ends'ofsrnall' radiu's are desirable and attempts tofmake such bendsv'vithout a mandrel generally result intoo'great a constriction of the .passag'e'at' thebend. The" method of the present invention is esp'e'cially' applicable for producing multi-layer shapes after all return bends have been made, and therefore the rethrn bends maybe made withor without'a mandrel as desired.

Inaccordance Witlr'the method of the present inventionga' single continuous length of tubing; long enou h tojform-a desired nurnbcr of layers, is sinuously'b'ent to form a serpentine having straight runs extending loing'itudi'nally betweefi itsfr'ont andrear ends and connected by return bends at-each' erid; and, during or aft'e {the formation-oftheserpentinqeach; of we o'r'more selected runs of the tubing, is separately tv'listed about 'itsiilon'g axis to rotate the succeeding tubin'g'on on'e side'fofzs'aid run as'a tinit relatively to the preceding tubing oii' the other side ofsaid run.

If we assume that a planar serpentine, such as is shown in Figure 1, is made long enough to embrace a two layer condenser, then it may be processed to form two layers by twisting the last straight run of one section, which is to form the first layer, about the long axis of that last run so as to rotate 'both the next following or layerconnecting return bend and the second section through a first angle, of desired magnitude ranging from 45' to 135, and then twisting the adjacent or first straight run of the next section about the long axis of that first run so as to rotate the second section in the same direction through a second angle equal to 180 less the value of said first angle. For example, if the first twisting operation rotates both, the adjacent layer-connecting return bend and the remaining tubing, 90 about the axis of the last straight run of the first section, then the first section will extend at right angles to the remaining tubing. Now if we move from the last straight run of the first section to the first straight run of the second section and twist that I first run in the same direction 90 about its axis, the second section will rotate into spaced face-to-face relationship with the first section while the interposed layer-connecting return bend extends at right angles to both 'sections or layers. Inother words, by twisting successive last and first straight runs in the same direction through 90 angles, the second section may be made to overlie or underlie the first section and be spaced from it a distance equal to the span or pitch of the layer-connecting return bend. Obviously any desired number of layers may be made by providing a flat serpentine of sufficient length to embrace a desired number of sections and suitably twisting the adjacent last and first runs of successive sections. v

It will be understood that the return bends along one end of the original flat serpentine are flattened preferably before the layers are formed so that, after the layers are formed, the flattened end of each layer of the tube assembly may be inserted through the openings of the fin assembly to form what may be termed a loose condenser assembly. Now, by applying internal fluid pressure to the tube assembly, all straight runs of each layer in the tube assembly are simultaneously expanded into firm contact with all fins in the fin assembly so as to produce a rigid structure having good heat transfer contact while all flattened return bends are simultaneously expanded to eliminate their flattened areas and thus restore them to their orlginal shape. Preferably the outer surfaceof the entire finished rigid assembly is coated to protect it from corrosion, by treatment in a bath comprising chromic acid and fluoride ions with or without an alkali metal com- .plex heavy metal cyanide.

bends at the opposite end. While such location of the inter-layer return bends is not essential, it is preferred because it permits the fins to be madewith slot-like openings in-rows corresponding to layers without requiring the fins to have any layer-connecting slots to accommodate any Inter-layer or layer-connecting return bends. Fins of this character, having one or more rows of slots, may be stamped and blanked by the same die.

The invention will be described in greater detail in connection with the accompanying drawing illustrating a preferred method by way of example and wherein:

Figure 1 is a plan view of a serpentine coil formed in one plane;

, Figure 2 is a plan view showing a flattened bend; Figm'e 3 is an end view of Figure 2;" 7 '7 V W i Figure-4 is a diagrammatic view of a serpentine after a 90 twisting operation, guide lines being used to make the illustration clearer;

Figure 5 is a view of the serpentine coi], shown. in

Figure 4 after it has'been turned to a different position and subjected to a second 90 twisting operation;

Figure 6 is an end viewof the coil after athird 90. twisting operation;

Figure 7 is an end view of the completed coil;

Figure 8 is an obverse view of Figure 7 on a larger scale;

Figure 9 is an end elevational view showing the end plate at one end of a bank of fins;

Figure 10 is a plan view of a completed finned condenser, the fins being shown diagrammatically;

Figure 11 is an enlarged section taken on line XIXI through the left end of one slot on the end plate shown in Figure9, this section omitting the right half of the same slot and being identical to a corresponding section through a fin; and V Figure 12 is an end elevational view of a multi-layer finned condenser of the type wherein each layer contains two rows of tubes with the straight runs of one row staggered relatively to the straight runs of the other row in the same layer; p Y

Referring to the drawing, Figure 1, the serpentine coil A has an inlet end B, an outlet end C, and a plurality of straight runs'joined serially by return or reverse bends. As shown in Figure 1, the straight runs are numbered consecutively from 1 to 36, and the return bends are similarly numbered with a primed number. straight runs and return bends lie in a common plane. They are formed from a single length of tubing bent into shape preferably over a mandrel to form short radius reverse bends. The methods of forming such planar coils are known to the art and need not be. described here. In Figure 1 only certain coils and bends are indicated by reference numbers, the omitted portion indicated by dash and dot lines being duplications. Thus, the first straight run at'the inlet end B is number 1, the first return bend, which connects it to the next adjacent straight run 2, is 1', the second straight run is 2, the next return bend is 2', and so on up to the last straight run 36, which terminates in outlet end C. In other words, there are 18 hair-pin 0r U-shaped tubesthe first comprising straight runs 1 v and 2 connected together by return bend 1' and the last comprising straight runs 35 and 36 connected together by return bend 35and these hair-pin or U-shaped tubes are connected in series by the evenlynumbered return bends 2' etc.

Where it is desired to string fins uponthe finished coil, the return bends at one end of the coil A areflattened. Thus, as illustrated in Figures 2 and 3, a portion of the return bend on apex 1' of. the first U.-shaped hair-pin tube, is flattened to form a narrow or flat tubular portion 37 joined to the straight runs 1 and 2 by fillets 38, 38' and 39, 39 respectively.

In processing the flat planar serpentine of Figure 1 to form, say a 3 layer condenser, the first step, after the flattening operation, is to bend it to the form shown in Figure 4. In so'doing, clamps 41 and 42. are applied to the end portion of the last straight run 24 of the second section or layer, to grip that run firmly. These clamps are then rotated relatively to each other, as by holding clamp 41 fixed and rotating clamp 42, in the counter clockwise direction indicated by the arrow, to the position shown in Figure 4. In other words, run 24istwisted between the clamps to rotate return bend 24' and the tubes of the third section or layer until they areinf a plane which extends substantially at a right angle to the plane of runs 1 to 24 forming the first and second sections or 1 The coiljA is next processed to the form shown" in Figure 5. In so doing clamps 41 and "42 are similarly applied to the first 11m 13 of thesecond section and one of 7 these clamps is rotated to twist run. 13 so as to rotate the first section (runs 12-1 and return bends 121') until the first section extends in a plane at a right angle to the All the P n of e e d se t on. unsll t ndbends 1 35:

24). The form of the coil thus produced is substantial.- -Y s ape nd {it egbserr d-tha r-the ret rnse l'au 4fl e a ed t. ha endctt ie coih cm which inlet B and outlet C extend.

-In processing the coil of Figure 5 to the form shown in F g erfie hede tls raiaht m idfiiinathedirsesection is twisted to makelhat section oyerlie thesecond section as these sections appear inFigure '5: Similarly, in procs -t e SWGQ B? hQWl1..i Fi l @25-d the form. s o n in F u and}. the .Ufirst. s ra ght. 25 mtherzthird e n s-; st d she: t tqretamehet e irdzsection de hee sec ion. as:'.- he.se ee a ppe r in F u e hus. .w .be obser edethati the Pl nam eil of ur srtecessedthrQug athef s 1 howmin u e .1 11 1 thats nwn'iurFiaures-7 z8 by twis ns hehst -uu ,.0t the first. sec on-laud e fi strun .1 t e-i ce d' seqticnaudby twist uerthe hr nrz s ond ect on and thewfirstmncliiac t eth rdt ecsn noadqinathe. r turube da i. is rotatedfifit to become the connection for the first and second layers while return bend 24 is rotated 90 to become the interlayer connection for the second and third sections.

By rotating these return bends (12' and 24) 90, the layers are spaced a center-to-center distance equal to the pitch of these return bends. Naturally this spacing can beincreased or decreased by increasing or decreasing the pitch of these bends. This spacing may also be increased by selecting, for twisting purposes, more widely spaced straight runs such as runs 11 or 10 of the first section and run 13 of the second. The spacing may be decreased by twisting, say run 13, more or less than 90 but it will not normally be practical to twist one tube less than 45 or the other tube more than 135 for layer spacing purposes. In either of these cases, the sum of both twists must equal 180 if the layers are to be in parallel relationship.

For simplicity of illustration the flattened bends of the coil are not shown in Figures 1 and 4 to 7. It will be noted that in showing the coil in its various states of manufacture, the position has been transposed but this is not essential. In the method illustrated for making a three layer coil the middle layer is formed first, but the order in which the layers are formed may be varied as desired.

Figure 9 may be considered as an end elevational view of either an end plate alone or of an assembly of end plates and fins ready to receive the coil of Figure 8, since both views are identical. Viewing Figure 9 as a front end elevational view of an assembly of end plates and fins and Figure 8 as a front end elevational view of a three layer condenser coil, the finished structure shown in Figure 10 is produced by shoving the front or flattenedend of the condenser coil of Figure 8 through the rear end of the assembly of Figure 9 until the front end of the Figure 8 condenser coil projects through the front end of the Figure 9 assembly.

This assembly comprises rear and front end plates 45, 46 and a plurality of intermediate fins 47 common to all the runs. Each end plate and fin is provided with a plurality of apertures 48 of the general outline of a dumbbell, comprising circular portions 49, and a connecting slot 52, which may be formed by stamping or punching a sheet of suitable size. The circular portions 49 are of a size to provide a close fit around the straight runs of the coil, and the narrow slot 52 is of a width to pass the flattened portions 37 of the return bends. Because in the form of coil shown in Figure 8 the flattened return bends 37 in the various layers are in vertical alignment, the apertures 48 in the fins also are arranged in vertical columns.

Referring to Figure 11, which may be viewed as a detail of either an end plate or a fin, it will be seen. that the circular end portion 49 of the slot-like aperture 48, is surrounded by a collar or flange 53. suitably formed thereon. It acts as a spacer to hold the fins and end platesaseparated. To. assemble. thewfins. .omthe coil, the finsare i laeed in position: on -a suitable jig and theacoil isinserted,. flattened. end zgfi-tfit t through the apertures 48. The inleaand outlet ends of the ,coihthentare-connect'edzto a; suitable. source ofipressureatouinflate ;or-; restore the flattened bends, ,the .pressure;empl oyed preferably being. greataenough. .to; expand; or, stretchther.diameterof ;-the straight; runsaintocontactrwith- -the;eol la1;s. S3 and thus provide for good rigidity and heat transfer Thecoil then is, disconneeted-ifromthe Pifissure source. Itwilb be obsepvedthabby having the layerconnecting-,return-bends all at; oneaendrofathe; coil. opposite-the flattened- -end,- it becomesqunnecessary ;.to,. provide vertical; slots inthezfins or end plates. Because .ofithis: arrangement, the=sarne die may ,be used tostamp out onearow of slots inronefin o'rutwo5o1-rnore. -rows an the. same fin as-desireda Wherethewondenser .-is.-constr.uoted?of. :aluminurn pipe or-. .tuhing yvith aluminum. :fins,,. ,we-impart impr oved .;cor.- rosion resistancenth'ereto byimmersingit for-ashort time, fonexamplaeone.todiveminutes .at-atemperature =ofa'ahout" 70-tw90 F ina bathieontaining chromic aoidg. a fluorine compound producing fluorine ions in solution, and with or without the presence of an alkali metal cyanide complex. The following bath illustrates a preferred composition.

10 to 15 g./l. chromic anhydride 3 to 6 g./l. ammonium fluosilicate 2 g./l. up to limit of solubility potassium ferricyanide Upon removing the condenser from the bath it is washed and dried.

In the above example, other fluoride activator ion compounds may be employed as for example, sodium fluoborate, ammonium bifluoride, or complex fluorides and the like, and potassium ferricyanide or the complex cyanides of copper, manganese or chromium may be used in place of potassium ferricyanide. Or if desired, complex cyanides may be omitted from the bath.

This invention is not limited to aluminum tubing but may be employed with tubing composed of copper and other metals. While the manufacture of a three layer condenser, with all three layers in series, is illustrated, this invention may be used to make multi-layer condensers with the layers in series or in parallel or with one or more layers connected in one way to form one set and one or more other layers connected in the same way or diiferent way to form another set with each set intended .to be devoted to the same use or to independent uses.

Furthermore, the invention contemplates the manufacture of condensers or heat exchangers of the type having one or more layers wherein each layer is formed of a double row of tubes, such as is illustrated in 'Figure 12. Here the straight runs in one row of one layer are staggered from the straight runs in the second row of the same layer and practically every tube is twisted to rotate the next return bend to the position required by the next straight run.

Having described our invention, we claim:

1. In the method of making a heat exchanger or the like from a serpentine tubing having a series of straight runs extending longitudinally between its front and rear ends and connected serially at said ends by return bends, the steps comprising: gripping a selected straight run of the tubing in a pair of clamps spaced apart along said straight run while leaving the return bends at the opposite ends of said straight run free to move; and turning one clamp about the longitudinal axis of said straight run relative to said other clamp to twist said straight run and swing the tubing portions located on the opposite sides of said straight run relative to each other about said axis while confining said twist-to the portion of said straight run located between said clamps. v

2. The method of claim 1 wherein: before twisting said selected run, said tubing lies substantially in a common the tubing on opposite sides thereof lie respectively in separate planes which extend at an angle to each other.

3. The method of claim 2 including: selecting a second straight run in one of said tubing portions and repeating said clamp gripping and turning steps on it to twist it and swing a part of said one tubing portion substantially into parallelism with the'other tubing portion. 7

4. The method of claim 3 wherein: said second straight run is connected to said first straight run by a single return bend. I

5. The method of claim 4 wherein: said part of said one tubing portion is swung about said second straight run into spaced face-to-face relationship to said other tubing portion to provide a pair of spaced parallel facing sections of tubing connected by a return bend.

' 6. The method of claim 5 including: flattening the return bends at the front end of said tubing; inserting said tubing with said flattened return bends foremost into a bank of fins having aligned slots shaped to receive said flattened return bends until said bank of fins lies on the straight runs of said tubing; and applying internal pressure to said tubing to distend said flattened return bends to 8 substantially their original shapes prior to being flattened and toexpand the straight runs into firm contaetwith idfi NH. 7..

- 7. The method'ofc ,m 6 wherein: theflatteningof the return bendsis performed prior to the twisting of said tubing. '5 7 s V References Cited the file of this patent 11mm)" STATES PATENTS 718,035 Jan. 6, 1903 Tindel -2 1,788,068 Scott=' Jan. 6, 1931 1,921,198 'Marsl1 Aug. 23,1933 1,943,557 Ruthenburg Jan. 16, 1934 2,338,847 I-Iansen Jan. 11, 1944 2,354,131 -Larkin July 18, 1944 2,450,876 Blumensaadt Oct. 12,1948 2,462,511 Kramer Feb. 22, 19.49 2,507,956- Bruno et al. May 16, 1950 2,632,482 Lincoln Mar. 24,- 1953 2,747,258 Kramer May 29, 1956

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