US2236976A - Method of making heat exchangers - Google Patents

Description

. I C. F. ROSENBLAD Filed July '7, 1958 ATTORNEY.

w INVENlIOdRL( faz April 1, 1941.

METHOD OF MAKING HEAT EXCHANGERS Patented Apr. 1, 1941 s PATENT oFFic METHOD or mmc. HEAT ExcnANGEns Curt Fredrik Resenblad, stneknelm, sweden, ee-

signor, by mesne Reclaiming Corporation,

assignments, to American Heat New York, N. l., a

corporation of New York Application July 7, 1938, Serial No. 217,852

. In Sweden December 16, 1932 This application. is a continuation-impart with respect to my co-pending application Serial No. 730,832, iiled June 15, 1934, and as to common subject matter embodies subject matter divided therefrom. 4

The present invention relates to heat exchange and has particular reference to spiral heat exchangers and methods of manufacture thereof.

Spiral heat exchangers of the kind to which the present invention relates-are constructed of plate structures curved to provide adjacent and uni-directionally spirally curved channels through which iiuid media are adapted to iiow in heat exchange relation and out of direct contact with each other.

In order to provide for highly eiiicient heat transfer and low mechanical loss due to the power required to cause ilow of the heat exchange iiuids through the apparatus, it is important for the channels to have uniformity oi cross-sectional area through the path of flow of the iiuids. It is further important in heat exchange apparatus of this kind which is intended for use with uids which may contain substantial quantities of impurities, .that the construction be such as to cause minimum deposition and accumulation of such. impurities in the Huid channels. Also, the construction should be such as to permit ready removable of accumulated impurities by any suitable mechanical cleaning operations, this latter requirement, if it is to be fulfilled, making it necessary lfor the construction to be such as to render the interiorportions of the uid channels readily accessible for cleaning tools and the like from the exteriorA of the apparatus.

In many instances the desired rate of heat exchange per unit area of surface is such as to make substantially necessary the employment of relatively very thin sheet metal to form the walls of the channels. Such metal has, of course, relatively little resistance to distortion due to difference in internal fluid pressure as between different channels and Where very thin walls are used, bracing is required to positively space adjacent walls vfrom each other if undesired distortlon and resultant change in cross-sectional area of the'channels is to be avoided.

The general object of the present invention is to provide improved heat exchange structure and methods of manufacture thereof which will result in most advantageously and reconomically meeting the various requirements for heat lexchange structures o'f the type under considera- .Cil

tion, some of which requirements have been briefly outlined above. Other and more detailed 'objects of the invention, the manner in which` they are attained, and the advantages to be derlved from use of the invention, all-Will be more clearly apparent from a consideration of the ensuing portion of this specification in which typical apparatus embodying the invention is described by way of example, taken in conjunction with the accompanying drawing illustrative of such apparatus.

In the drawing:

Fig. l is a transverse section of a heat exchanger constructed lin accordance with the present invention;

Fig. 2-is a longitudinal sectiontaken on the line 2- 2 of Fig. 1;

Fig. 3 is a fragmentary section on much larger scale of one form of end sealing construction applicable to a heat .exchanger of the kindshown g in Figs. l and 2.

Fig. 4 is a fragmentary transverse section taken on line'l--Q4 of Fig. 5 illustratingan intermediate stage of manufacture in accordance with the present invention;

Fig. ,5 is a longitudinal section of the structure shown in' Fig. l;

Fig. 6 is a developed view showing an arrangement of spaces in accordance with the invention;

Fig. 7 is a view similar to Fig. 6 showing another arrangement; and A Fig. 8 is a fragmentary view showing another form of spacing means.-

Referring now more particularly to Figs. 1 and 2 of the drawing, the exchanger illustrated comprises tWo spirally bent plates lil and i2 forming between them unidirectionally spirally curved adjacent channels i6 and i6. The inner ends of plates lil and i2, in the embodiment illustrated, are joined by means of a transverse plate i8 forming a central longitudinally extending partition. As shoWn, the plates are Welded to the side edges of this partition but it will be evident that plates iii and l2 may if desired be formed from one continuous length of plate material, the central portion of .which is bent to form the desired transverse central partition i8. The

central partition i8 provides at either side thereof a chamber extending longitudinally of the structure, the chamber 2i) on one side communicating for example with the spiral channel i4 and the chamber 22 on the other side communicating with the spiral channel I 6. Chambers 20 and 22 communicate at their ends, and prefnal connections 28 and 30, also adapted to either l admit or discharge fluids from the apparatus. The fluids are preferably passed through the Va pparatus in counter flow relation, the peripheral connection for one channel constituting an inlet with the peripheral connection for the other channel constituting an outlet and with one of the axially central connections constituting an inlet while the other constitutes an outlet. The ends of the chambers 20 and 22 are closed by suitable end. plates 32 and 34 at one end of the apparatus and similar plates 36 and 38 at the opposite ends of the apparatus. It will be understood that the desired ones of these end platesv will be suitably apertured to provide for the end connections 24 and 26, one of such apertures 4|! appearing in Figa-4 and 5.

For closing the ends of the spiral channels, various different specific arrangements may be resorted to. Depending upon the relative amount and character of impurities carried by either one or both of the fluids to be passed through the heat exchanger, the channels may be closed at their edges by removable closure means for both spiral edge portions of both channels or at only one edge portion of one or both channels. In the latter case it will be understood that the remaining edge portions oi they of a plurality of small spacing members which advantageously are in the form of separate distance piecesrigidly fixed, at least at one end, to the plate structure. Advantageously, these distance pieces may be of the general form indicated at 52 in Figs. 4 and 5, each welded at one of its ends to one of the spiral plates as indicated by welds 54.

The specific arrangement of the distance pieces I 52 on the plates may be varied as indicated in the developed views of Figs. 6 and "l, but it is particularly to be noted that in accordance with the present invention these distancepieces are Aconfined in their location to the axially central portion or zone of the channels, indicated at a, in

order to leave the edge portions or zones b of at y least those of the channels which are closed by removable spiral strips, free from any fixed obstruction. Preferably, all of the spaced distance pieces are confined to the central portions or zones of the channels.

channels are closed by permanent closure means.

For convenience of illustration, the exchanger illustrated is of the type in which the spiral edge portions of both channels at both ends of the apparatus are adapted to be closed by removable end cover structures which may advantageously be of the kind illustrated on enlarged scale in Fig. 3. With this type of structure a plurality of rigid spiral closure strips 42 are attached to a series of radially extending clamping bars 44 which at their ends are secured, as by means of bolts 46, to suitable brackets 48 fixed to the outer peripheral wall of the exchanger. It will be understood that the curvature of the strips 42 conforms to the curvature of the spiral openings at the edges of the channels, and these spiral strips may advantageously be tapered as shown in Fig.

3 .for ease of entrance into the edge portions of vthe channels. Axiaily inwardly of the strips 42,

the spiral' channels may advantageously be provided with seals against fluid leakage, which seals may be in the form of strips 50 of flexible material, of suitable nature in view of the fluids to be passed through the exchanger. As illustrated, the sealing strips may advantageously be U- shaped in cross-section so as to tend to be forced against the channel walls by internal iluid pressure to provide a fluid tight seal.

Obviously, the specific nature of the removable edge sealing means may be widely varied, but in accordance with one phase of the present invention'it is to be noted that the rigid strips 42 act as spacing members for rigidly holding the spiral wall plates in radially iixedposition relative to each other.

In addition to the spacing of the wall plates effected by the spiral strips 42, the plates are further maintained in desired radially spaced relationship and braced against distortion due to differential internal pressurebetween the adjacent channels by means of fixed spacing means which in accordance with the invention is constituted Instead of employing separate distance pieces welded to the plate structure, the plates may in some instances be indented to provide spacing members 52 integral with the plates as illustrated in Fig. 8. The location of these spacing members 52 is, in accordance with the invention, governed by the same principles as those governing the location of the spacing members which are in the formof separate distance pieces as shown at 52. The spacing members 52' have, like the separate distance pieces 52, small lateral dimensions, particularly in the lateral direction transverse with respect to the direction ofiiuid flow through the channel.

In constructing a heat exchanger in accordance with the present invention, the plates I0 and I2 are secured, as by welding, to the central partition plate if a separate plate is employed, or if a continuous sheet is employed, the sheet is bent to provide a central transverse partition.

'I'he portions of the plates adjacent tothe central partition are then bent around the end plates :i2- 38, which plates, as appears more clearly from Fig. 3, project respectively as at 32a and 34a somewhat beyond the longitudinal edges of the central partition at the opposite sides thereof. The projecting portions of these end plates serve to space the respective spiral walls from each other to form the desired spiral channels.

A The plates i0 and i2 are then progressively bent around each other but before this bending operation is performed the fixed spacing members are provided on the plates. Preferably the spacing members for one channel are provided on one plate and the spacing members for the other channel are provided on the other plate. It will y be understood, however, that the spacing members for both channels may alternatively be provided on one of the plates, on the opposite surfaces thereof, the remaining plate not being provided with any fixed distance members.

Particularly when forming'an exchanger of -very thin metal, great care must be exercised in shaping the plates to their spiral form in order to prevent their being distorted during the fabricating operation and to avoid forming channels of varying cross-section due to such distortion. Preferably, in accordance with the present Iinvention, `the plates, provided with the xing spacing members distributed over their axially central portion, are bent around spiral forming members 56 which serve as rigid guides between the edge portions of the plates at each end ofthe apparatus for bending them to smoothly4 curved form.

of clearness in the drawing.

operation, and experience in practical manufacture with thin plate structures -has shown that if the height of the xed spacing members centrally of the structure is the same as that of the'spiral forming members, the fixed spacing members may in some instances produce dents or local distortions in the plates.- In accordancev with one phase of the present method, this diicultyis overcome by making the height of the spiral forming members, which act as the primary bending guides, slightly greater than that of the intermediate xed spacing members. This -difference in height is very small, vpreferably being lless in proportion to the depth of the channels than vshown on the accompanying drawing, in which` the difference in height has been exaggerated somewhat, proportionally, for the sake As will be clearly evident from Figs. 4 and 5, the difference in height between the spiral end pieces 56 and the distance pieces 52, provides a very small clearance c between one yend of each distance piece and the adjacentl plate, which clearance is suiiicient to insure prevention of the distance piece from denting the plate as the plate is bent into shape. i y

Apparatus of the character under considera'- tion is ordinarily subjected to variations in temperature in normal operation and the difference between -the' temperature of the apparatus under normal working conditions and when the apparatus lis not in use is frequently of substantial vaiue.

urally result in expansion and contraction of the pansion and contraction which stress might be l sutlicient to be of a damaging nature. This freepermanently closed, as forlexample, when it is.v known that the exchanger is to be utilized to effect heat exchange between fluids .at least one of which is clean," for instancawhenl clean feed 1 water is heated or when a liquid isheatedby a vapor which does not carry impurities. In such instances, one or more of the spiral forming members 56 used as guides for bending the spiral platesmay be retained in the organization and permanently ilxed to the plates as by welding, such members being used in conjunction with the removablel strips 42 providing access to those channels which in normal service would require f vperiodic cleaning.

In a spiral heat exchanger of the type to which the present invention relates, the spiral llow of the fluids results in the applicationnf centrifugal Vforce to any impurities carried thereby,r tending to cause the -impurities vto concentrate in the'y outer portions of the channels. Consequently,

- in this type of device, cleaning of the channels These temperature differences natwhen certain types of impurities are carried by the fluid or uids is highly important. Any deposits of impurities will obviously adversely af fect the heat transfer per unit area of the apparatus and since in many applications the appa'- ratus may be placed with the longitudinal axis `in ya vertical position, it is 'highly important that" the edge zones, particularly the lower or bottom edge zone of a channel carryingla lfluid with a high percentage of impurities; be readily accessible and free from obstruction in orderto permit both rapid and effectivel cleaning. This is accomplished in the present structureby confining the distance pieces to the axially central zone of the apparatus so that when -such spiral end strips asmay bemade removable are removed,

dom of relative movement of various parts ofthe y I through the apparatus, it is furthei-.obviouslydeinternal structure relative to each other is also aided in a desirable fashion by the provision of the slight clearance between the distance pieces and the plates'if this clearance is maintained after fabrication'is completed. y

In order to accomplish. the principal object of the clearance provided during the fabrication,

it is not essential that this clearance be maintained in the'completed structure, since experience has shown that if the spiral forming members 56 are withdrawn after the bending oper-y ation has been completed, the completed spiral structure may thereafter be subjected to a slight additional torque o f a nature causing'the bent plates to wrap themselves rmly against the distance pieces, andl that tthis additional wrapping ofthestructure to take up the clearance can b'e I accomplished without causingthe distance pieces plane state to their spiral shape.

As previously pointed out, some of the edges of the spiral channels may in'some instances be 4to' this end by introducingfa certain lanilint of the adjacent end zone is' free from any fixed obstruction and through this free and unobstructed 'I end zone comparatively Tready access is obtained for cleaning not only such adjacent 'end zone but.

also the central zone in which the spacing members are located, which central zone is furthermore readily cleanable because of its relative small area as compared with the total' area of the channel. v,

Where iiuids carrying impuritiesjgare. passed` sirable to reduce'as faras possible the deposition and adherence of. Asuch impurities to the surfaces of the plates andthe distance pieces contribute disturbance or'iturbulenfce' in theow ofjgiluid,A sutlicient to breaklup the.sc -calledlaningf of' the uid which if .undisturbed would tendfto in;-

crease the rapidityv of deposits ofimpurltiesand L which would further tend ,t reduce the rateof heat transfer through.` the spiral `walls asrcompared with that effected by slightly turbulent flow operating to bring different portionsof the .iluid body into 'direct contact-'With the'walls of the channels. 'With' spacing. members* having small lateral dimensions,'particularly transversely of the directionv of ilow thro'ugh`the '.channels, sufficient turbulence to break up undesirable Ilan'- ing of the uids maybe effected without introducin'g suicient resistance to ilowbfI fluid` to materially increase the pressure drop through the apparatus due to such resistance( While for purposes of illustrating the invention, only one kind of spiral heat. exchangeor-I ganization has been shown 'by way4 of' example;`

it will be evident that the principlesy of the invention are equally applicable to othei kinds ci.

spiral exchangers in which. fluids are passed changers, that -improvement which consists in' providing spacing members on a plate section at spaced places distributed through the axially central zone of the section and thereafter bend- 3. In the manufacture of a spirial heat exchanger, that improvement which includes the steps of welding distance pieces having small lateral dimensions to the axially central zone of one surface of each of two plate sections, therel after bending said sections around spiral shaping ing said section and another plate section around spiral forming members located between the edge portions of the sections, whereby to form spiral convolutions having a spiral channel therebetween in which said spacing members are located, the height of said spiral forming members being slightly greater than the height of said spacing members whereby to insure sucient clearance between the ends of the spacing members and the adjacent plate section to prevent distortion of the plate sections as they are bent because of bending contact with the ends of the spacing members during the forming operation.

2. In the manufacture of spiral heat exchangers, that improvement which includes the steps of welding distance pieces having small lateral dimensions at spaced places distributed over the axially central zone of a plate section and thereafter bending said plate section and another plate section over spiral forming members located between the edges of the plate sec-v tions to form from said sections adjacent spiral convolutions providing av spiral channel therebetween, said spiral forming members having slightly greater height than said distance pieces whereby to prevent the distance pieces from distorting the plate sections during the bending operation. Y l

members located between the edges of the adjacent plate sectlons to forrnfrom said sections spiral convolutions having spiral channels therebetween with said distance pieces located in said channels, the height of said forming members being somewhat greater than the height of said distance piece to prevent distortion-oi the plate section by the distance pieces during the bending operation.

. `4. In the manufacture of spiral heat exchangers, that improvement -which includes the steps of providinga plate section with a plurality of spacing members located in the axially central zone .of the section, bending said section and another plate lsection over spiral forming members located between the edge portions of the sections to form from said sections spiral convolutions having a spiral channel therebetween in which said spacing members are located, said spiral forming members having some@ what greater height than said spacing membersy whereby to provide a slight clearance between the tops of the spacing members and the adjacent plate as the plates are bent, removing the spiral forming members from between the edge portions of the plate sections after they have been bent substantially to final shape and thereafter subjecting the spiral plates to torque to induce a nal wrapping action of the plates relative to each other to eliminate the clearance l between the tops of the spacing members and 'the adjacent plate.

CURT FREDRIKROSENBLAD.

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