US2789797A - Heat exchanger fin structure - Google Patents

Description

April 23, 1957 c. s. SIMPELAAR HEAT EXCHANGER FIN STRUCTURE Filed Aug. 20, 1955 L LAMINA/esuuyfzv MM f 505 m? WWA 1 7////////////// 6a, 6a 7@ 7a United Seres, Parent HEAT EXCHANGER STRUCTURE Clyde S. Simpelaar, Racine, Wis., assigner to Medine Manufacturing Company, Racine, Wis., a corporation of Wisconsin Application August 20, 1953, Serial No. 375,394

17 Claims. (Cl. 257-245) The invention relates generally to heat exchange structures and more particularly to a iin construction for use therewith.

The present invention is of particular value in connection with high eiciency heat exchangers, as for example, where the nal temperature of uid being acted upon, either cooled or heated, is within ninety-tive to ninety-nine percent of the inlet temperature of the heating or cooling iiuid, and where the density of heat exchange surface is in the approximate range of three hundred or more square feet per cubic foot of volume. Expressed in another way, the invention is of particular use inl exchangers wherein the accomplished temperature change in one fluid divided by the difference in inlet temperatures of the two iiuids exceeds .95.v In certain heat exchange applications, exchangers which cannot meet these requirements are commercially impractical, as for example, in low temperature oxygen plant exchangers wherein it is essentialV that the exchanger volume be at a minimum to reduce exterior heat losses, and where the entire process is commercially. feasible only by virtue of the availability :of high, eiiiciency heatexchangers.

The advantage 'of utilizing interrupted heat transfer surfaces such as thin strips or pins has been heretofore recognized and considerable work has`been done in connection with the utilization of socalled strip or` pin fins. However,l past research work has indicated that while generally it is desirable to. reduce the width of the fin in the direction of iiow, reduction in the width of the ns apparently approached a limiting value .beyond which further reduction failed to produce a corresponding improvement in eiciency. Experiments conducted along the above linesV have appeared toy support such analysis as actual tests. of heat exchange surfaces disclosed a gain in etiiciency as the iin width was reduced down to what appeared to be a critical or limiting factor, beyond which, additionalreduction failed to show a corresponding improvement in eiciency. Normally n de. signs applicable toy strip or pin fins are of necessity repetitious. in pattern, wherein the fins are in line in the direction of flow with other fins, and it has heretofore been expressed that it would appear that all that was necessary with respect to in-line surfaces was that they be separated a few thousandths of an inch.

The present invention is directed to a means of utilizing iins of the strip or pin type which may be constructed'in widths in the direction of flow of considerably less than those heretofore deemed practical to achieve extremely high eiliciency.

Another object of the invention is the production of heat exchange. sur-face having the desired high efficiency which is capable of being commercially produced with present product-ion techniques and available materials.

Many other objects and advantages of the construction herein shown and described will be obvious to those skilledfin Ithe art from the `disclosures herein given.

To'fthis end my invention consists in the novel convn 2,789,797 ,PatentedV Apr. 23,

ice

struction, arrangement and combination of parts herein shown and described, and more particularly pointed out in the claims.

in the drawings, wherein like reference characters indicate like or corresponding parts: y Y

Fig. l is a diagrammatic figure illustrating the present theory in connection with sharp edged iin surfaces;

Fig. 2 is a similar diagrammatic ligure illustrating applicants theory as applied to iin surfaces having a leading edge of finite thickness;

Fig. 3 is a semi-diagrammatic ligure illustrating a cross section of a lin of linite thickness and applicants theory with respect thereto;

Fig. 4 is a diagrammatic figure illustrating applicants theory with respect to laminar layer carry-over between in-line fin surfaces;

Fig. 5 is a diagrammatic figure similar to Fig. 4 illusf trating the application of the present invention thereto;

Fig. 9 is a sectional figure similar to Fig. 6 illustrating a modified form of construction; and p Fig. 1 0 is an end elevational viewof a pair of the iin structures illustrated in Fig. 9. i

rThe boundary layer theory with respect to immersedu bodies, first formulated by Prandtl, brieiiy is that the tluid surrounding a body may be divided into two portions:

(l) a thin layer close to the surface of the body in which the velocity gradient is large enough to produce viscous forces of appreciable magnitude; and

(2) the remaining portions of the fluid outside this boundary layer in which the viscous forces may bey neglected in comparison with the inertia forces, or in other words where the Reynolds number may be assumed to be infinitely large.

The characteristics of laminar flow and turbulent flow were demonstrated by Reynolds and the Reynolds number of course is a dimensionless term involving flow area, and the velocity, density and viscosity of the uid, which defines the limits of laminar and turbulent iiowf. It, in effect, thus involves the characteristics of the iiuid and the operating conditions under which it is employed.

The present theory with respect to the boundary I ayer formed by the iiow of a iiuid over an immersed surface is generally illustrated in Fig. 1, wherein a thin laminar sub-layer adjacent the surface of the object such as'ft'he plate P extends along the area ofthe object. The laminar boundary layer is adjacent the leading edge ofthe plate and a turbulent boundary layer may be produced follow` ing a zone of transition from laminar to turbulent con-v boundary layer, likewise, offers similar resistance but, of course, not to as great an extent as the laminar layer and may be considered as having a transition or buier layer interposed between it and the laminar Vsub-layer, offering intermediate resistance. It is believed that the general theory involving laminar layers and the Prandtl boundary is of suiciently general knowledge inV the rheat transferA art that the above is suicient for the purposes of the present application. It will bepappreciated, however, that as the lankiinar layer acts as an insulating medium if the t theoretical approximation of Fig. 1 is correct, a theoretical fin of the length a would have minimum resistance to heat ow and thus, theoretically, would be the most effective width, but its minute physical proportions would substantially preclude its use in a practical commercial structure. Likewise in such case a theoretical fin of length b would have an average maximum resistance and thus would be the most ineffective width. Furthermore, as there is a transitionfrom the laminar layer to a zone of turbulence or eddying, with proportionately greater eiciency, a tin having a length greater than b would have greater intermediate values of resistance and thus efficiency.

It will be particularly noted that the above analysis involves the utilization ofa fin member wherein a leading edge thereof tapers to a line edge and therefore theoretically has no thickness, whereas practical applications require a n having a thickness of finite order, which from a practical standpoint would approach, or probably be as great as the thickness of the laminar sub-layer. Obviously, where a finite thickness is involved a considerably different action may be produced. Figure 2 illustrates a pos- `sible theoretical analysis with respect to the boundary layers in connection with a tin of finite thickness, in which case it is believed that as a result of the fin thickness,- strong eddying or turbulence would be produced adjacent the leading edge of the fin member, thus` delaying somewhat the formation of the laminar sub-layer as illustrated, and on such theoretical basis a fin having the dimension a would have a minimum resistance and maximum efficiency. The eddying action adjacent the leading edge of the fin probably would also delay the formation of the laminar layer and may even eliminate the formation of such layer as indicatedv in Fig. 2, in which case the distance, equivalent to the distance b of Fig. l, would be-for practical purposes eliminated, and the efficiency theoretically would continuously increase as the fin width is decreased.

v From the above theoretical discussion with respect to the laminar layer it will be appreciated that in connection with `fins having a finite thickness, a fin having a width or dimension in thedirection of flow which is less than the dimension c illustrated in Fig. 2, theoretically, should have exceptionally satisfactory performance, and as a result of experimentation and tests it is believed that the distance approximating dimension c, at normal llowing rates would be equal to approximately one-tenth of an inch to one-eighth of an inch, assuming a fin thickness oli-approximately three thousandths of an inch to .012 inch. In other words, on the basis of the above theoretical analysis it would appear that the heat transfercficiency of the fin would increase as the dimension of the fin in the direction of flow, heretofore referred to as the width, is successively decreased below one-eighth'to onetenth of one inch.

A However, as previously mentioned, research on heat exchange surfaces has indicated that the practical results apparently do not conform to this theory, as corresponding reductions in the fin width have apparently not achieved a corresponding increase in efficiency of the heat exchange structure. p

Strip fins have normally been formed from sheet material by severing the sheet material along spaced parallel lines equal to the fin width, with alternate portions between the lines of severance being offset out of the original plane of the sheet, thus-forming two seriesgof fins each of which are connected at their ends to the sheet, the fins of each series lying in a common plane with the trailing edges of a preceding lin spaced from the leading edge of the next in-line tin by approximately the same distance `as the width of the respective fins. Consequently, as the width of the fin is reduced the spacing between in-line fins is correspondingly reduced; Studies and considerations have apparently not evaluated the in-'line spacing as a factor to be considered in connection with the Overall etliciency of the heat exchange structure and, as previously mentioned, the conclusions of some people in this field have been that such spacing is of relatively little importance and even a few thousandths of an inch would be sufficient to achieve satisfactory results. However, I am of the belief that the in-line spacing of the fins is an important factor which must be considered and that by properly spacing the in-line fins highly efficient resul-ts may be obtained and the full advantages of the use of narrow ns more fullyv realized. This theoretical conclusion has been supported by actual tests on heat exchange structures constructed in accordance with the present invention and compared with tests on structures embodying prior concepts on the subject. For example, in one test a considerable increase in efficiency was obtained merely by removing certain in-line fins to increase the spacing between the remaining in-line fins, the increase showing a gain of from six to fourteen percent.

Figs. 3, 4, and 5 roughly illustrate the concept involved in connection with the spacing of in-line fins. Fig. .3 generally illustrates the boundary layer flow of fluid along the fin surface which, for the purposes of explanation may be compared with a generally sticky or viscous material which is frictionally retarded at the fin surface and thus has a tendency to build up into a low velocity mass which is increasing in thickness toward the trailing edge of the fin. However, as illustrated in Fig. 4, it is believed that the flow following the trailing edge would tend to revert into its original state prior to engagement with the first fin surface, so that the mass tends to taper off as illustrated in Fig. 3, which will hereafter be termed the boundary layer carryover. If, however, before the same can be completely dissipated the next in-line fin is reached, the result is an additional build-up of a relatively low velocity, high resistance mass, the latter probably increasing in thickness over that formed on the first tin. This action is continued with each succeeding in-line fin, and as a consequence thereof the fins are in effect enveloped in a high resistance boundary layer or mass, resulting in a reduction in the heat transfer efficiency of the structure.

I am therefore of the belief that if the distance between the trailing edge of a precedingfin and the leading edge of the next following in-line fin is suitably spaced as illustrated in Fig. 5, substantially complete dissipation of the high resistance uid mass may be achieved before the following in-line fin is reached, eliminating a carryover and possible additional build-up on such following fin and resulting in substantially uniform heat transfer between the fluid and each fin of the exchanger structure. It is my conclusion that by properly correlating the spacing between in-line fins with the fin width, the width of the fins may be reduced to any desired practical value and at the same time fully utilize the increase in efficiency resulting from the decrease in fin width, whereby an exchanger of high efliciency and large heat transfer surface area per cubic foot of volume may be produced.

Figs. 6 to 10 illustrate typical fin structures employing the present invention, and while I'have shown n structures of the nested channel type, these structures are merely by way of example and it is believed that the present invention may be readily applied by those skilled in the art`to other forms of fin structures, as for example, serpentine structures and the like.

Referring to'Figs. 6 and 7; the reference numeral 1 indicates generally a channel shaped fin structure, two of which are illustrated in the drawings, which are constructed to be positioned in nested relation with a sufficient number of channel members being employed to extend across the uid pass in which they are assembled, the channels extending parallel to the direction of flow through' the pass. Each channel member 1 comprises a pair of side wallsor' portions 2, each of which are 0E- set outwardly as indicated'at 3. The walls 2 are connected adjacent their upper edgesl as viewed in Fig. 7

einen??? .s by @plurality ef strinans .,f 4b. esenti 4d In nnnnel a' s fbf the 1nv nithe. thielsnes's ef, material. aan ns the Inernber 1. is ni .feiilike thickness, rangingv fr in approXimatelyv .003 lto, $01,?r inch, the metal employed rnbly 'beine Conner,y aluminum er other Suitable maf ...nai having' satisfactory heat transfer eharnetefistes. fscleaily' illustrated in Fig. `7, the` offset 3 is substantially equal tol the thicknessI of the metal employed, wheres' lily, the distance between the inner faces of the offset portions lisr substantially equal to the outer dimension between the portions abovethe offset, Vso'that the channel rnmbers may be nested or interloc'lted as illustrated in E 7. The strip tins 4 are formed byseveririg the metal al. nsf sna'eed raaliei lines which extend frein one side wallto the opposite sidewall and deforming orolsettingthe 'mateiial'interniediate the respective slits to form the tinfistt.

'the embodiment illustrated in Figs. 6 andl 7, the nist'srrip in aan at fae'nignest elevaron as viewed in rigs. e and' 7, ineen 4c at the next elevation, the an 4b at the next elevation and the fin 4d at the lowest elevation. This staggered pattern then repeats itself, the nent fin 4g being positioned at the highest elevation and successively followed by tins 4b, 4c and 4a', so that all the tins 4a are aligned inthe direction of flow and in like manner all corresponding fins 4b, 4c, and 4d are respectively in alignment. Thus in lthe embodiment 'illustratedI each in-line fin is separated from the preceding or fol# lowingin-line 'iin by a distance equivalent to they width of threefin's, It will be appreciated that when `a relatively large number of channel members A1 are nested together theresulting s tructurecontains a plurality of series of fins positioned in sequential arrangementl with respect to the direction of flow. Thus the lirst row of fins 4a ex-v tending across the fluid pass transversely to the4 direction of ilowforms the first series, the f'ns`4b the second seriesr the fins lo thethird and thev fins 4d the'fourth. As the pattern repeats` the second transversely exteridfug rowv ffins 4c form the fourth series and so on throughout the length of the channel member, s o that the structure may bec nsidnered as clomprisinga plurality of groups of series', th fins in cach series being similarly arranged and the respective series being similarly'arranged in their respective; sronps- The transverse spacing between the planes of the tins 4a, 4b, 4c and 4d, corresponding to the spacing between the respective tins illustrated in Fig. '7, isi substantially uniform andthe oliset 3 in the side walls is so positioned that the fin 4a of the adjacent channel memberis spaced alike distance from the tins 4d of the first or upper channel member, so that all of the respective fins lie in parallel planes which are substantially uniformly spaced. Thespacing of in-,line fins and the transverse spacing betweenA the respective planes above referred to are de t'ermincd in accordance with the theoretical explanation heretofore set forth, whereby the spacing between in-line fins is greater than the so-called boundary layer carryover-from the preceding in-line tins, and the transverse spacing is greater than the combined thicknesses of the boundary layers of adjacent fins along any point in the direction of flow, so that each iin functions substantially independently of the other ins and without interference between the boundary layers and boundary layer carryover of the respective tins.

`In the bulk of applications of the present invention the iin spacing will normally range from ten to sixteen per inch, such dimension taken from the center line distance between strips normal to the direction of flow. liikewise in the bull; of the` applications of theI present invention the transverse distance between the trailing edges 'and leading edges ef edie'eent fins ei' the distniiee betweenthe` planes of respective in-line fins will range frein'fnpnnexiineteir 015 te 04%. The Width of enen ind dis-'ei iinin'tiife difeetie ef. new Will` nerineliy rn' 'entretiens three y-seesnss. to; Qn,

et' anineit. and the distance from the: -trailinsetigeci ne nn' o. 'the ieading'edgs @eine next. infuus nnwir. run from approximately three-sixteenths to three-quarters of an inch. As previously mentioned, normal iin'thiels'-l nesscorresponding to thethickness of the material form; ing lthe channel member will range from approximately .003 to.0l2"inch.` W it will, be appreciated that in forming the tin structitres in. 'the manner illustrated in Fiss-''nd 7. from thin stok, and' offsetting the respective fins 4a, 4b, 4c and rv4d different amounts, the transverse lengths of the fins bef tween the walls` 2 will vary, the tins 4a and 4d being slightly longer than the fins 4b and 4c. vIn this type of iinstructure the fins preferably may be formedina suit.I able die or the like,t he fins being offset above e below a center line` cf whiehnaybeconsidered as passe.v ing through the juncture's of the respective 'fins with thek sidewalls 2. Thus lthe tins 421 and V4al"m'ay. be equally'. offset above and below thecenter'line, and in like man,- ner the tins 4c and 4b may be respectively offset equal distances above and below such center line. The metal forming the channel members 1 usually'is of copper, aluminum or Vother comparatively soft metal which is, capable of owing a sufficient amount to compensate for they diiference in lengths of the respective fins. Thusy in forming the fins, the metal comprising the ns 4a and 4d would ow outwardlypthereby effecting a stretching action and increasing the effective lengthv of the fin to compensate for the dilerence in length thereof. Likewise, some compressive action may be produced in the other tins, depending on the particular method of production employed. i

Fig. 8 illustrates diagrammatically a iin pattern gen-` erally `similar to that illustrated in'Fig. 6 involving a l clorresponding spacing between irl-liney surfaces of three times the width of the individual iin so that the fin pat, tern repeats in series of fours. ln the pattern illustrated in Fig. 8 tins 6a extend parallel to thedirection of flow as do the ns 6c, while the fins 6b and 6d are slightly tilted or twisted angularly with respect to the direction of flow to increase the transverse distance between the. trailing edges of the ns of one series and the leading edges 'of the tins of the immediate following series. A small twist to the tins as illustrated serves to increase such transverse spacing without materially aiecting the eiiiciency of the structure and thereby enables the transf verse center lines of the fins to be positioned closer than in the construction illustrated in Figs. 6A4 and 7, whereby` a greater area of heat transfer surface per cubic foot of heat exchanger volume may be obtained. The construction illustrated in Fig. S also illustrates the use of a iin pattern wherein each successive fin is at a lower elevation than the preceding lin before the pattern repeats itself, whereas Fig. 6 illustrates a staggered arrangement.

Fig. 9 illustrates the utilization of a lin pattern wherein the spacing between in-line fins is twice the iin width, whereby the pattern repeats itself in groups. of three.

Referring to Figs. 9 and l0, this structure also is illustrated in a'chann'el type of iin structure similar to that illustrated in Figs. 6 and 7, the channel member 1 have` ing side walls 2 provided with olset portions 3 whereby the lower offset portions 5 of ythe side walls are adapted to receive a similar channel member nested therein. In this construction the iins 7a of the first series are posi,-VA tioned parallel to the direction of ow similar to the construction` illustrated in Fig. 6, while the second and third iins 7b and 7c are angled in substantially the same manner as the tins 6b and 6rd illustrated in Fig. 8. Like' wise as in the case of the construction illustrated in Fig. 8,'the tins 7a, 7b and 7c are' arranged in symmetrical Order 0n the channel member with sneeessivetins nvins less elevation than the preceding, iin of the'partieular pattern group. This ennstrnetien may be fabricatedin..

substantially 'the saine manner es deseribed. inu Fiss.. v6. and 7, the ns 7b approximately falling on the center;

Wiebke# lineconnecting thel junctures of the tins at the opposite slightly or may have the metal thereof slightly cornv pressed, while the metal forming the fins 7a and 7c ows or is slightlyl stretched` to accommodate the difference in lengths.

Fig. ll illustrates one application of the present invention to a heat exchange structure illustrated in the present instance as including a pair of Huid passes 8 formed by outer plates 9 and an intermediate separated plate 10, the side edges of the passes being bounded by side wall members 11, the channel members of each respective pass being nested together to form in effect a fin slab withthe respective elements being suitably bonded together to form a unitary structure. Suitable means may be provided at the respective ends of the structure for providing inlet and outlet means for the fluids into their respective uid passes. This construction is similar to that illustrated in my prior Patent No. 2,606,007 issued August 5, 1952.

It will be appreciated that the present invention is adapted for use in any heat transfer structure utilizing strip tins, pin fins and the like, irrespective of the particular physical construction of the uid passes, etc., and could readily be employed in structures where the entire heat transfer tin surface is constructed from a single sheet of material which is of corrugated or serpentine shape and from which the individual fins are struck up or otherwise formed.

It will be appreciated from the above description that I have provided a novel heat transfer structure and method of arranging the fins thereof to achieve maximum efliciency together with a high heat transfer surface area per cubic foot of heat exchanger volume and which permits the utilization of narrow fins of high eciency without interference between in-line iin surfaces.

It might be mentioned that where I have referred to the boundary layer, this term is intended to mean the layer ofrelatively low velocity Huid adjacent the fin surface, a carryover of which from one iin to another will produce a material decrease in heat transfer ethciency.

Having thus described my invention, it is obvious that various immaterial modicationsmay be made in the same without departing from the spirit of my invention; hence, I do not wish to be understood as limiting myself to the exact form, construction, arrangement and combination of parts herein shown and described, or uses mentioned.

What I claim as new and desire to secure by Letters Patent is:

l. In av uid pass for heat exchangers, the combination of an elongated relatively thin uid pass structure, and a plurality of elongated strip tins having their ends operatively connected to the opposite sides of the uid pass structure in heat transfer relation therewith, the thickness of the respective fins being less than the width thereof in the direction of uid flow through the pass structure, said ns being of substantially uniform width and arranged in a plurality of series, each of which extends across the fluid pass transversely to the direction of iiow therethrough, and to the individual fins, said series being positioned in repeated sequential arrangement with respect to such direction of flow, the fins of each seriesbcing positioned out of line in relation to the direction of flow with respect to the iins of the next followingseries, the spacing transverse to the direction of flow between the trailing edges of the ns of one series and the leading edges of the next series adjacent thereto being approximately from three to ve times the thickness of said fins, and the spacing in the direction of ow betweenanyfins of corresponding series in line in such diflov'vdirection.`

2. In `a fiuid pass for heat exchangers, the eombina-1 tion of an elongated relatively' thin fluid pass structure; and a plurality of relatively narrow tins'having their ends operatively connected to the opposite sides of the iiuid pass structure in heat transfer relation therewith,l the respective fins extending transversely in thin longitudinal direction with respect to the direction of fluid iiow through the pass structure, said fins being arranged in a plurality of series, each of which extends across the fluid pass transversely to the direction of iiow therethrough, and to the individual tins, said series being positioned in repeating sequential arrangement with respect to such direction of flow, the tins of each series being positioned out of line in relation to the direction of ilow with respect to the tins of the next following series, the spacing transverse to the direction of ow between the fins of one series and the ns of series adjacent thereto being greater than the thickness of the boundary layers along said tins, and the spacing in the direction of flow between any ns of different series which arc in line in such direction being greater than the iin width and the boundary layer carryover in the flow direction from the adjacent preceding in line tin, under the particular operation conditions and uid characteristics involved.

3. A fin structure for heat exchange uid passes comprising a sheet of thin metal of a thickness of approximately .003 to .012" formed to provide a pair of body portions connected by an intermediate portion, the body portions providing means for securing the fin structure to opposite side walls of a heat exchange uid pass, the. intermediate portion of said fin structure being cut along parallel lines uniformly spaced in the direction of tlow to form a plurality of individual substantially at strip iins which extend transversely between the two body portions and have their ends operatively connected to the respective body portions, the width of said ns in the direction of flow being substantially uniform and from approximately /g" to M4, the fin structure being adapted to be positioned in a iiuid pass with such intermediate portion extending in the same direction as the fluid flow through such a pass, each of said strip fins being laterally offset with respect to the adjacent strip tins, said strip fins being offset in a predetermined pattern and sequence which repeats itself whereby each strip iin is substantially aligned in the direction of ilow with other strip ns, the pattern being such that the strip tins substantially in line are spaced apart in the direction of flow a distance offrom approximately to the offset distance between trailing and leading edges of adjacent strip fins being from approximately .015 to .040", with alternate tins being positioned in planes extending substantially parallel to the direction of flow and intermediate fins being positioned in parallel planes extending angularly with respect to the direction of liow.

4. A tin structure for heat exchange fluid passes comprising a sheet of thin4 metal of a thickness of approximately .003" to .012" formed to provide a pair of body portions connected to an intermediate portion, the body portions providing means for securing the tin structure to opposite side walls of a heat exchange fluid pass, the intermediate portion of said tin structure being cut along parallel lines uniformly spaced in the direction of ow to form a plurality of individual substantially flat strip fins which extend transversely between the two body portions and have their ends operatively connected to the respective body portions, the width of said iins in the direction of iiow being substantially uniform and from approximately g" to 1A", the n structure being adapt-l ed to be positioned in a lluid pass with such intermediate portion extending in the same direction as the uid ow through such a pass, each of said strip fins being laterallyl os'et` with respect to the adjacent strip tins, saidstrip.' tins being offset in a predetermined patternandsequencet. which repeats itself whereby each strip iin is substantiaily laligned in tbe, dir-editen et tisnuwith 4:aber @tric hns, tbe, pattern beingJ auch that the.; Siria ns substantially in lineare erased apart in the direction of new? distance of from approximately da", to 1%", the, oiset distance between trailing and leading edges of adjacent strip iins being from approximately .015," Ato .040, with certain corresponding fins extending substantially parallel to the direction of flow andl other corresponding fins eX- tending angularly to the direction of flow.

l A yn structure for heat exchange fluid passes comprising a sheet of thin` metal of a thickness of approximately .003 to. .'012` formed to. provide a pair of body portions connected to an intermediate portion, the body portions providing means for securing the lin structure; to, opposite side walls of ar heat, exchange fluid pass, the interrnefdiate` portion of said structure being cut along parallel lines uniformly spaced in the direction of ow to form a plurality of individual substantiallyl at strip fins which extend transversely between the two body portions and have their endsl operatively connected to the respective body portions, the width of said fins in the` direction of owbeing substantiallyv uniform and from approximately :'ggf to 1/t the lin structure being adapted to be positioned in a uid pass with such intermediate portion extending in the same direction as the iuidr ow through suchl pass, each of said strip tins being laterally oiset with respect to the. adjacent strip tins, said strip tins being offset in a predetermined pattern and sequence which repeats itself' whereby each Strip iin is substantially aligned in. the direction et now with other strip fins, the pattern beingl such, that the strip ns substantially in line are spaced apart in the direction of llow a distance of fromV approximately die to 2A, the` offset distance between trailing and leading edges of adiaeent strip` tine. beine ,from approximately .015 te .040, with each fin oi the structure being similarly positioned with reSpect to the third n therefrom in the 'direction of HOW'.

6 A iin structure for heat exchange fluid passes comprising a sheet of metal formed to provide a pair of body portions connected by an intermediate portion, the body portions providing means for securing the iin structure to opposite side walls of a heat exchange uid pass, the intermediate portion of said n structure being cut to form Plurdliiy Q. individual tinsI which extend transversely between the two body portions and have their ends operatively Connected to the respective body portions, the lin structure being adapted to be positioned in a iluid pass with such intermediate` portion 'extending generally in the same direction as the fluid flow through such a pass, each of said tins being laterally offset with respect to the adjacent fins, said lins'being olset in a predetermined pattern and sequence which repeats itselfwhereby each n issubstantally aligned in-'the direction of flow with other ns, the patternbeing such that the tins substantiallyin line are spaced apart in the direction of ow a distance at least twice the width of the hns in such direction, the offset distance between adjacent ns being greater than the corresponding dimensions of the boundary layers along said tins, andthe distance between in-line ns being g1; Vr. than they boundary carryover from aprecedin'g ii; t. the direction of ow, under the particular operating'conditions and fluid characteristics involved in the particular Huid pass, with alternate fins being positioned in planes extending sub- Stantiauy Parallel to the direction of ow andiintermediate ins being positioned in parallel planes extending angularly with respect to the direction of llow.

7. A lin structure for heat exchange fluid passes comprising a sheet of metal formed to provide a pair of body portions connected by an intermediate portion, the body portions providing means for securing the n structure to opposite side walls of a heat exchange uid pass, the intermediate portion of said iin structure being cut to fer-1nA a. plurality et individual tins which extend; tiene# rersftly between the. two, body portions` and; have; their endsy operatively connected to the respective body-y ptn?-AA tibns, the iinv Structure being adapted to be nositpned in a duid pass with such intermediate portion 'exten generally in the same direction as the fluid flow th ugh, s uch a pass, each of saidr fins being laterally offse respect to the adjacent fins, said fins, being ois'et predetermined pattern and sequence which repeatsitsel whereby each iin is substantially aligned inA the direction` of flow with other fins, the pattern being such` that he, ns substantially in line are spaced apart in the dire t tion of flow a distance at least twice the width of lins in such direction, the olset distance betweenV aid. jacent tins being greater than the corresponding dim l, sions of the boundary layers along said tins, and the; di tance between in-line ns being greater than the behind?1 ary carryover from a preceding fin in the dirrectionv g flow, under the particular operating conditions and ilu characteristics involved in the particular iiuid pass, certain corresponding ns extending substantially par allel to the direction of flow and other corresponding ns extending angularly to the direction of dow.

V3,. A iin structure for heat exchange fluid passes com;

, prising a sheet of metal formed to provide a pair of body;

portions connected by an intermediate portion, the body portions providing means for securing the strntrire to opposite side walls of a heat exchange fluid pass, the, intermediate portion of said fin structure being cut to form a plurality of individual tins which extend transversely between the two body portions and have their ends operatively connected to the respective bodyI por tions, the iin structure being adapted to be positioned in,` a ilni'd pass with such intermediateV POltrion extending` generally in the same direction es. the, duid. flew thrnusby such a pass; each of said tins being laterally 'offset withl respect 'to the adjacent dus, Said tins, being Offset in a predetermined pattern and sequence which repeats itselfk whereby each llin is substantially aligned in the direction of iow with other ns, the pattern being such that the. fins substantially in line are spaced apart in the direc-1, tion of flow a distance at least twice the width of 'the fins in such direction, the offset distance between adjaf cent` tins being greater than the corresponding dimenf sions of the boundary layers along said tins, and vthe, distance between ineline iins being greater than the bound-V ary carryover from a preceding iin in 'the direction of llow, onder the particular operating conditions and'lluid characteristics involved in the particular uid pass,k with each tin of the structure being similarly positioned with respect to the third tin therefrom in the direction of flow.

9 In a huid pass for heat exchangers, the combina? tion of an elongated relatively thin fluid pass structure, of a plurality of relatively narrow tins each, having at least one end thereof operatively connected to the Huid; pass strnctnre in heat transfer relation therewith, the respective fins extending transversely in their longitudi-h nai direction with respect to the direction of iluid flow through the pass structure, said ns being arranged in a plurality of series, efachofwhich extends acrossthe iluid pass transversely to the direction of flow therethrough, and to the indiyidual tins, said series being positioned in repeating sequential arrangement with respect to such direction of how, the ns of each yseries being positioned out of line in relation to the direction of iiow with re-v spent to the fins of the next following series, the Spacing transverse t0 tbe direction. of 110W between the fins of one series and the ns of series adjacent thereto being greater than the thickness of the boundary layers along said iins, and the spacing in the direction of ow between any fins of different series which are in line in such direction being greater than the n width and the boundary layer carryover in the ow direction from the adjacent preceding in line fin, under the particular operation conditions and fluid characteristics involved.

11 v'.' In a fluid pass for heat exchangers, the combinationv of an elongated relatively thin fluid pass structure, of a plurality of relatively narrow fins having their ends operatively connected to the opposite sides of the fluid pass structure in heat transfer relation therewith, the respective fins extending in their longitudinal direction transversely with respect to the direction of fluid ow through the pass structure, said hns being arranged in a plurality of series, each of which extends across the fluid pass transversely to the direction of flow therethrough, and to the individual fins, said series being positioned in groups sequentially arranged with respect to such direction of flow, corresponding series of the respective groups being similarly arranged and the fins of each series of a group being positioned out of line in the direction of ow relative to the ns of the other series of such group and in line with respect to the fins of the corresponding series of the next following group, the spacing transverse to the direction of owv between the trailing edges of fins of each series and leading edges of fins of the following adjacent series being greater than the thickness of the boundary layers along said fins, and the spacing in the direction of ow between consecutive in line fins of corresponding series of adjacent groups being greater than the fin width and the boundary layer carryover in the flow direction from the adjacent preceding in line fin, under the particular operation conditions and fluid characteristics involved.

11. A fin structure for heat exchange fluid passes cornprising a sheet of thin metal formed to provide a pair of body portions connected by an intermediate portion, the body portions providing means for securing the fin structure to opposite side walls of a heat exchange fluid pass, the intermediate portion of said fin structure being cut along parallel lines spaced in the direction of flow to form a plurality of individual substantially at strip fins which extend transversely between the two body portions and have their ends operatively connected to the respective body portions, the fin structure being adapted to be positioned in a fluid pass with such intermediate portion extending generally in the same direction as the fluid flow` through such a pass, each of said strip fins being laterally offset with respect to the adjacent strip fins, said strip fins being offset in a predetermined pattern and sequence which repeats itself whereby each strip fin is substantially aligned in the direction of flow with other strip fins, the pattern being such that the strip fins substantially in line are spaced apart in the direction of flow a distance at least twice the width of the strip fins in such direction, the offset distance between adjacent strip fins, transverse to the direction of flow being greater than the corresponding dimensions of the boundary layers along said fins, and the distance between immediately adjacent in-line fins being -greater than the boundary layer vcarryover from a preceding fin in the direction of ow under the particular operating conditions and fluid characteristics involved in the particular fiuid pass.

12. A fin structure for heat exchange fluid passes comprising a sheet of thin metal of a thickness of approximately .003 to .012 formed to provide a pair of body portions connected by an intermediate portion, the body portions providing means for securing the fin structure to opposite side walls of a heat exchange fluid pass, the intermediate portion of said fin structure being cut along parallel lines uniformly spaced in the direction of flow to` form a plurality of individual substantially flat strip ns which extend transversely between the two body portions and have their ends operatively connected to the respective body portions, the width of said fins in the direction of flow beingA substantially uniform and from approximately g to Mz", the n structure being adapted to be positioned in a fluid pass with such intermediate portion extending in the same direction as the fluid flow through such a pass, each of said strip fins being laterally offset with respect to the adjacent strip fins, said strip fins being offset in a predetermined pattern and sequence which repeats itself whereby each strip fin is substantially aligned in the direction of flow with other strip fins, the pattern being such that immediately adjacent strip fins substantially in line are spaced apart in the direction of ow a distance of from approximately 3A6" to the offset distance between trailing and leading edges of adjacent strip fins being from approximately .015" to .040".

13. A fin structure as defined in claim l2 wherein the fins are positioned in planes extending substantially par allel to the direction of flow.

14. A fin structure as defined in claim 12 wherein each fin of the structure is similarly positioned with respect to the fourth fin therefrom in the direction of flow.

15. A fin structure for heat exchange uid passes comprising a sheet of metal formed to provide a pair of body portions connected by an intermediate portion, the body portions providing means for securing Athe fin structure to opposite side walls of a heat exchange fluid pass, the intermediate portion of said fin structure being cut to form a plurality of individual fins which extend transversely between the two body portions and have their ends operatively connected to the respective body portions, the fin structure being adapted to be positioned in a fluid pass with such intermediate portion extending generally in the same direction as the fluid flow through suchA a pass, each of said ns being laterally offset with respect to the adjacent fins, said fins being offset in a predetermined pattern and sequence which repeats itself whereby each fin is substantially aligned in the direction of flow with other fins, the pattern being such that the fins substantially inline are spaced apart in the direction of flow a distance at least twice the width of the fins in such direction, the offset distance between adjacent fins being greater than the corresponding dimensions of the boundary layers along said fins, and the distance between immediately adjacent in-line fins being greater than the boundary carryover from the immediately preceding fin in the'direction of flow, under the particular operating conditions and fluid characteristics involved in the particular uid pass.

16. A fin structure as defined in claim 15 wherein the fins are positioned in planes extending substantially parallel to the direction of ow.

17. Afin structure as defined in claim 15 whereineach n of the structure is similarly positioned with respect to the fourth fin therefrom in the direction of ow.

References Cited in the file of this patent UNITED STATES PATENTS 2,360,123 Gerstung etal Oct. 10, 1944 2,549,466 Hoheisel Apr. 17, 1951 2,606,007 Simpelaar Aug. 5, 1952 FOREIGN PATENTS 915,093y France July 8, 1946 1,018,691 France. Oct. l5, 1952

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