US2609184A - Heat exchanger - Google Patents

Description

p 2, 1952 M. FRENKEL 2,609,184

HEAT EXCHANGER Filed April 10, 1948 4 Sheets-Sheet 1 Jam m p 1952 M. FRENKEL 2,609,184

HEAT EXCHANGER Filed April 10, 1948 4 Sheets-Sheet 2 p 2, 1952 M. FRENKEL 2,609,184

HEAT EXCHANGER Filed April 10, 1948 4 sheet s-Sheet 5 IN VE/V 7-01? MEKFR FREA/Kz S p 1952 M. FRENKEL 2,609,184

HEAT EXCHANGER Filed April 10, 1948 4 Shets-Sheet 4 er my.

Patented Sept. 2, 1952 HEAT EXCHANGER Meyer Frenkel, London, England Application April10, 1948, Serial No. 20,292 i In Great Britain May 22, 1947 7:

This invention relates to heat "exchangers Among the objectsof the invention are:

1. To p-rovidecons'tructions which ensure that for a heat exchange fluid flowing past the outside of heat exchange elements (e; g.- tubes) the flow-layers should :be so guided that the tem-. perature diiTerence throught he heat transferring wall be kept high substantially all over the sur--' face of the heat transferring walL- so that the mean rate of heat-transfer .per unit area of heat transferring wall-taken over the whole surface should be high, particularly also for cases Where the'fluid' flowing outside the passages' has only'a small; specific heat per unit volume as compared with the fluid flowing inside,-or where fluid flowingoutside the wall is to have only a small temperature-change as compared to the fluid flowing inside, without undue increases in velocity of flow. r

' 2. To provide a construction which will enable a heat exchanger to transfer large quantities-of heat with the fluid flowing outside the heatexchange elements, for example, tubes moving-by virtue of' the natural convection supported by some external moving means (pump, or the like) or where thel fluid moves by virtue of natural convection only; thus dispensing with the external'moving means (pump, blower, or the like) without excessive surface area of heat trans: ferring walls. Under this object would fall, for example, a construction of heat exchanger capable of providing air cooling by means of natural convectionfor large performances, without excessi've surface-areas of heat transferring wall. The following considerations illuminate the ideas underlying this invention; 7

'A' total mean rate of heat transfer per unit area of heat transferring wall, which is indicative of the overall properties of a heat exchanger, depends on; v p

(1) 'On the difierence between the mean temperatures taken over the whole effective surface area of heat transferring wallQbetween the layers of the two fluids flowing in immediate heat exchange proximity to both sides of the heat trans-' ferring wall; a

(2) n the ratio a between the effective surface-area of heat transferring wall and a total area of heat transferring wall, which is obtained by dividing the volume taken up (not enclosed) by the components of theheatexchanger (in cluding essential partsj such (as header tanks, guide-walls, and thelike), by the thickness, of the heat transferring wall. 1 Accordingly, apart from making provision for 19 claims; (01. 257-227) making said mean temperature difference between the flowing fluids large, this invention .also

makes provision for making this factor a as large.

(as near'to unity) aspossible. V a o Further, consider cases in Whichthe fluid flow.-

7 ing outside heat exchange elements: i to' flow due to natural convection I only.\ Let for example, layers of thisifluid .belguided between a row of vertical tubular surfaces and a casingsurrounding the same, forming apassage for said fluid with alarge U/ Aratio, ratio ofawetted cire cumference U to flow-'cross-section;A, as is.neces-.

sary if the layer of fluid is,.-to take effective part in the heat exchange. Then,-. as .proved, the natural convection effect. will .increase the velocity of .the layer only up to .acertain height of passage, while foraa, passage of any greater height the velocity of flow will not increase beyond the value attainedatthat limiting height,

due tolthe. friction lossesin,thepassage; This height, up to which thezvelocity due. to natural.

convection effect still increases, .Idepends .Onthe U/A .ratio, and iinsordercto obtain the benefit, of the. natural convection effect, provision has to. be made to. remove thisfllayer ofcfluid from the heat exchanger pa'ssagecwith the large U/A.,ratio ,at or below this limiting. height, and. to. guide. it into a passage with a smaller Uf/A ratio,-..Where its velocity increases further, .duerito natural convectionefiect. A c g .1

Accordingly, in order to achieve-the objects, this invention provides for means whereby,v at a position along. a flow of a fluid past a heat exchange element in a passage formed, according to this invention,i;between a row of such heat exchange elements and alguide-casing surroundingxsame, layers of said fluid which have attained a required changeof temperature whilejflowing in immediate :heat exchange proximity with said elements are diverted from the heat transferring wall and led. out of said passage, jwhilelayers of thistfluidwhichhave not yet taken part in the heatexchange andthus substantially still have their initial temperature, areguided-into immediate heat exchange proximity,with, continuations of saidheat exchange-elements. ,This is done in order to-avoidth-at further flowof layers which have attained their required, temperature in the immediate heat exchange proximity ofthe element should change the'temp'eratureof, these layers too, far, thus reducing the meantempera: ture, difference through the heat transferring wall, and further, from the point of views of natural convection emotion of the fluid, in order that a layer, of fluid which may have been given side heat exchange elements, thus maintainingthe temperature difference through the heat transferring wall of these elements all along the total surface of heat transferring wall, thereby making high the mean rate of heat transfer per unit area of heat transferring wall, and where this is required, fully exploiting the natural convection effect for moving said fluid.

In the accompanying drawings, showing some examples:

Fig. 1 is a vertical section through one embodiment of the invention;

Fig. 2 is a plan section along the line II--II of Fig. 1; 3

Fig. 3 is a partial vertical section through a second embodiment;

Figs. 4 and 5 are a sectional front elevation and a part sectional side elevation respectively of a further embodiment, Fig. 4 being taken on line IV--IV of Fig. 5;

Figs. 6 and 7 are a sectional front elevation and a part sectional side elevation respectively of another embodiment, and Fig. 6 being taken on the line VI--VI of Fig. 7.

In said drawings like parts are denoted by like reference characters. y

In the embodiment shownin Fig. 1, I denotes a duct which contains a plurality of rows of heat exchange elements such as tubes 2, bathed externally by a first fluid and traversed internally by a second fluid taking part in the heat ex-, change- Each of these rows is enclosed by a guide casing 3 having an entry [8 at one end and an exit l9 at the other end for said fluid. Each row of tubes 2 also debouches into .two header tanks 4 and '5. which .are individual to each row of tubes 2 and respectively induced into and lead away from said tubes said second heat exchange fluid.

At various positions along each guide casing 3, said casing is provided with entry slots. 6a and exit slots 6b in opposite sidewalls thereof and respectively extending the entire width of the casing, and the upper end of the'casing 3 below each entry slot 6a is bent inwards at l to form an entry-guide vane whilst the lower end of the casing 3 above each exit slot 6b is bent inwards at 8 at the side opposite the inwardly bent guide vane I to form a baflie, the portion 8 constituting a continuation of the guide I, the vane thus formed contacting the respective tubes 2 round their circumferences. The entry guide means 6a and I of each adjacent pair of casings 3 are arranged toface each other whilst the exit guide-means 6b and 8 of each adjacent pair of casings are likewise arranged to face each other.

At the entry end of each alternate space l2b between adjacent casings 3 into which exit guide vanes 8 lead and which is hence denoted an exitspace, baflie plates 9 are disposed. Each bailie plate 9 carries side walls I0 which, together with the plates 9 leave exit-spaces 12b open at their exit ends only. At the outlet end of the other alternate spaces l2a, from which entry guide vanes '1 lead and which are hence called entryspaoes, similar baffle plates H are disposedbeiii alternate pairs of guide-casings 3.

4 tween alternate pairs of guide casings 3, said baflie plates 1 I extending to the walls of the duct l and dividing the space [6a in the duct before entry from space liib after exit.

The aforesaid construction operates as follows:

Assuming that the construction is intended to be used as an air heater, then the entry header tanks 5 will carry a heated liquid, such as hot water, which flows downwards in the tubes 2, and is led out of the heat exchanger by header tanks 4 after having given its heat to the air.

The air flowing in the portion l6a of duct l flows into each guide-casing 3 at its lower open end [8, flowing in contact (immediate proximity) to the outside of the tubes and taking part in the heat exchange, and on reaching guide-vanes I is deflected from the heat transferring wall through slots 6b into exit spaces l2b between In addition the air flows into every other entry-space 12a between alternate pairs of guide-casings 3 from which layers of the air are drawn through slots ea into contact with the outside of the tubes at different positions along the height of the passage, the respective layers being then led out again into exit-spaces [2b. Air coming into the heat exchanger from below is, however, prevented by bafiles 9 and side walls H] from flowing directly into the spaces l2b, in which flows air which has already taken its part in the heat exchange and baffle ll prevents exit of air, which has not yet taken part in the heat exchange, from the entry-spaces I211. into the space I6?) 1 in the duct l, leaving only exit holes for the passages 12b into this space, for air which has been heated. Thus the arrangements of walls Ii!v and bafiles 9 and II prevent air which has not yet been heated from passing from entry-spaces 12a. to exit-spaces l2b, and more generally from spaceifia to space [61) except through spaces bringing it into contact with the heat transferring wall..

Thus this construction is seen to effect that layers of the air which have flowed in contact with the heat exchanger tubes over such, distances that-they have attained their required temperature, are then led away from the heat transferring walls, and replaced on the continuations of the heat transferring walls by fresh layers of air, which still have the initial airtemperature, so that thereby the temperature difference between the air on the outside of the tubes and the hot water inside the tubes is maintained high along the length of the flow, instead of falling too far, as would be the case if the same layer of air remained in contact with the tubes.

Further as regards natural convection, this construction ensures that a layer which has flowed in immediate heat exchange proximity with the heat transferring wall in what is, in effect, a passage with a very large U/A ratio of wetted circumference to flow-cross-section, in which beyond a small limiting height its velocity due to natural convection cannot increase any further, is led away from the heat transferring wall into passage [2b whose U/A ratio is much smaller, so'that there the velocity can increase further, the natural convection thus being exploited.

Further, with regard to the uniformity of the heating of the air, layers of air having been heated at the lower end of the tubes where the temperature difference to the already cooled water. is lower, will, in passingjup the passage l2b, flow'past the exits 61) at both sides, from which'emerge layers of air .whichhave been.

heated. athigher and higher temperature differences, so that thus the less heated layers of air are mixed with those layers which haveibeen.

heated to higher. temperature, andthe air emerges from the tops of passages |2bgwith substantially uniform temperature.

1 The arrangement of the tubes 2 in rows, with each row of tubes having header tanks 4 and 5 separately to itself, where the tanks 4 and 5 are staggered for adjacent rows, ensures that the .air fiows into and. out of the spaces between the rows of tubes without substantial change to flow along the tubes in these spaces between the tubes of the same row, so that by this ,arrangement of separate header tanks for eachrow of tubes, which have 'spacesbetween them in the plane normal. to the'flow direction ofthe air, as well as in. the flow-direction, even flow. of the air is provided at all positions round ;the.

circumference ofeach tube, and all tubes of the heat exchange are made subject to air flow at the same velocity.

The embodiment illustrated in Fig. 3 is substantially identical with that illustrated in Figs. land 2, with the following exceptions: The tubes 2 are each traversed by a smaller-diameter tube l3 which is open. at both ends and passes through headers 4 and 5. The water to be cooled thenflows down the annular spaces between the respective tubes 2 and I3, while cooling air also flows upwards through tubes l3. A further feature by which the embodiment of Fig. 3 differs from that of Figs. 1 and 2 is that the duct i does not extend beyond the highest peripheral baffle space, so as to permit free. access of air to'the casings 3 in all directions i. e.'both vertically and horizontally, the bame plates 9 and H. and sidewalls H) of spacer |2b forming a labyrinthine' bafile preventing any direct access of air to the spaces |2b traversed by air which has already taken part in the heat exchange. A further difference between thepresent embodiment and that described with reference to Figs. 1 and 2 is that the duct I terminates in -a chimney ll .of a substantial height depending on requirements, the function of the chimney being to create an updraught and produce extra velocity past the heat transferring walls. -A section is shown between two tubes of a row. indicating air flow there, and a further section through the centre plane of a tube 2, indicating water flow by arrows .in the annular space. between tube 2 and the inner tube l3, carrying cooling air. w i Y Figs. 4 and'5 show another embodiment in which, instead of one row of tubes comprising vertical tubes 2 running from entry header tank 5' for the-hot water at the top to exit header tank 4 at the bottom, there are provided two rows of tubes in the same plane. The top row of tubes is exactly the same as described with reference to Figs. 1 and 2, except that the inner tubel3 in each tube 2 is missing. At the posi- 6 tions where tubes 2 enter their bottom header tankx3 tube stumps. 32 of smaller diameter than; the. tubes 2 are inserted into the mouths of tubes 2,

these stumps 32 continuing through headertanks' 3| to form a row of tubes whichis again surrounded by a; guide-casing3, similar to the upper row of tubes 2. Tubes 32 at their bottom ends debouch into header tanks 33 for the water. The arrangement of the guide-casings 3with their entry and exit slots 6a and 6b and the entry.

and exit passages [2a and [2b formed between them is analogous to that described with reference to Figs. 1 and ,2, with the addition that baiiles and 42. connecting to tank 3| in spaces |2a and |2b respectively cooperate with bafiies and9 respectively to separate spaces containing.

air which has not yet taken part in the heat exchange from spaces containing air which hasv taken part in the heat .exchange.

The aforesaid construction operates as follows: Hot water enters tubes 2 of the top row through header tanks 5 from duct 36 and while. flowing down the tubes 2 the. outer layers of hot water.

in the tubes give up heat to the layers of unheated air which are successively guided into contact with the heat transferring wall by guide-casing 3,.as described with reference to Figs. 1 and 2.

Before the water enters the intermediate header tank 3|, tubestumps 32 separate the inner layers of the flow in each tube, which have substantially retained their original tempera-:

ture,.from the outer layers, which have become cooled, and these outer layers flow into the intermediate header tank 3| and are led from there out of the heat exchanger in duct 34. Meanwhile the still hot-inner layers of water flow down tubes 32,.where they come into heat exchange proximity withunheated layers of air brought to the heat transferring wall by guide-casing 3 as already described, before being led out of the heat exchanger. in header tanks 33, debouching into. collector '35.

Figs. 6 and 7 show a further embodiment, the top of which comprises rows of tubes 2 between top header tanks 5 and intermediate header tanks 3|, the rows of tubes being surrounded-by guide-casings 3, similarly as described with reference to Figs. 4. and 5.

The stumps 32 are inserted into the mouths of tubes 2 before these enter their intermediate header tanks 3|, and pass through tanks 3| and lead into a header tank 3'|. From this header tank 31. anew row of tubes 38 begins, the tubes of this row as seen in Fig; '7 not being on the same centre-lines as the tubes-2 of) the row above, but being staggered relatively thereto, the centrelines, however still lying in the same plane. These tubes 38 lead into exit header tanks 33, and are traversed by internal tubes 39 which pass through both header tanks 31 and 33. The row of tubes 38 is surrounded by a guide casing 3, as previ ously described. A baffle 40 is provided between the intermediate header tanks 3| and 31 of a row and baiiles 4| and 42 in spaces |2a and I2!) respectively. operates as follows:

Hot water'coming from duct 36 is led through header tanks 5 into tubes 2 of a top row, and while flowing down tubes 2, the outer layers of the water in the tubes give up heat to the unheated layers of air which are successively guided into contact with the heat transferring. wall by guide-casing 3. as described with reference to Figs. 1 and 2. Tube stump 32 separates the outer layers of the water, which have taken their part The. aforedescribed construction diateheaders 31; whence they-flow out of the heatiexchangerthroughscollector 3 Lv y iThezi'nner layers'fof the :water, whichihair'e substantially. retained their originaltempera'ture. are

led into" intermediate header. tank .31 from where it flows inirthe annular spaces between tiibes'38 and:39.down to header tank. 35. :Air. flows along the :outside of tubes 38, beingl'guided infgiudecasing 3, aspreviously.- rde'scribed xand'rflows through the inner tubes i39,'. to take part in the heat exchange. Battles K ibe'tweengthe intermediate headers 3| and-.31 guide'theair; which has flowed through the inner tubes-39, intothe spaces 12b for; air which hasutakenits part in, the iheat exchange, forming witlribailies .41, '42 and l I, '9 the system of bafiles which, together withrside walls H) of spaces 'l2ciprevents anyair which has notyet taken part in the :heat exchange from enteringssaid spaces l2b.

In both the embodiments described with reference toFigs. 4 'and.5 to Figs; (Sand 7, a duct will surround the assembly, the'functionof the duct being the same as thosezof :the duct described with" reference to Figsl and 2 for a'forced convection heat exchanger, or as described with reference to Fig. 3 for a'natural"convection'iheat exchanger. :Both these embodiments :willbe'suitablefor applications where thezfluid flowing iiII-' side the tubes is to be divided into two separate quantities, each of which "has to experiencea differentv temperature change.v

In the examples described, it will have been noted that the surfaces on whichurespectively are situated the. centre-lines of :the .tubes'ofa row, which surfaces may, according to thisinvention be closed in themselves, as,-:for$ example, cylinders, have'generating lines which are'sub which would arise due to centrifugal forces act-1 ing at changes 'of the flow-direction, and which would reduce the effective'iarea of heat :transferring wall for heat exchange,

'.(3): In "order that, quite generally, theflow-f path of the i'fluid from the entry t9 ith'e 'hea't X: changer to the exit from t heat legchangeri.

should b'e shortest, and v I (4) In order to keep the :cross-sectional a'rea normal to the flow-direction of ithe duct which surrounds the whole. assembly, in lflSLl-Slilfiill !a ratio as possible to the actual total .cross-section of'thisffluidtinto theiispaces between ftherows of tubes (and similarly the ratio betweenwthecross-section for the fluid in the :du'ct after theheat exchanger to the actual totalzexit cross-sections of the fluid from the passages betweenrows of tubes) so that'pressure :losses due to sudden changes of cross sectionaliarea of iflowzarek eptf as low as possible. Y

Thus, in-embodiments of ithe inventionthefluid flowing outside the passages (tubes) :willvbe guided by guide-walls ,andaguide-vanes fin'snch a way,;-that for the periods that layers of- ,thisfluid' 8 are actua'lly taking direct part in'the heat exchange, i. 'e. are in contact with the-'heat'transferring wall, :the centres of gravity of .these'layers anywhere along their flow in contact with he'at transferring .ivall} are on substantially straight lines I I In order to provide for layers being led away' from the heat transferring'wall when they have taken their part in the heatexchange, and other layers, which have not yet been in contact with heat transferring wall, being led into contact with heat transferring Wall, each row of tubes is provided with a guide-wall substantially surrounding it, and openat either end to allowlentry and exit for the fluid flowing outside the tubes. Theseguidewa'lls, at difierent positions along the flow'of the fiuidlayers in contact with a heat transferring wall, 'will'have slots running normally to this flow direction, or other suitable openings, to provide exits and respectively'em tries for-suchlayers. 'In preferred embodiments, using the same guide-vane to lead layers of fluid away from a heat transferring wall with its one side and otherlayers .into contact with a con- I tinuatlon of heat transferring wall with'its other side, the exits forthe fluid layers whichhave takentheir partinthe heat-exchange are arranged-to one side of this row ofltubes, while the entries for the fluid layers which have not yet'taken part 'in the heat exchange are arranged onthe other side of this row ofit'ubes.

The rows oftubes making up a heat exchanger,v

with their surrounding guide-casings, will in preferred embodiments be so arranged relatively to one another, that the entries for adjacent rows of tubes face one" anoth'erzacross aspace between the guide-walls of these rows, andosimilarly the exit slots ofa'cljacent rows of tubes face one another across another such space between two guidewalls. Accordingly, every second space between adjacent rows of tubes will-have fluid flowing in. it which has not yet :been in contact with'a heat transferring'wall, which is being :led off inlalyers to therows of heat exchange, elev mentszateitherjside' to come into contact with-a heatztransierrin'g wall at different positions along the fiowiiof such layers, while every :other second spacew'ill have fluid-flowing in it which has already taken its part in the heat e hansa. h v ing been guided into said space from both rowsof tubes atidifierent positions. The walls forming the spaces carrying fluid which has already't'aken its part the-heat exchange :will be so closed,

that nolayers 'of fluid whichha've 'not been in 1 contact :with a :heat transferring wall can enter into:siichwspacessi I .In::-:prfefer'red embodiments of this invention, the generating linesaof :the: centre-line surfaces of adjacent-wows 10f? tubes will ,be somewhat inclinedto 'oneuanctheryso that passages between rows of tubes which c'arryxfiuid which. has not yet taken :;part :inithe'rheat exchange and is led away alongthetlengtliof the passages .get narrower in the flow-direction: while the passages carrying change get wider in the flow direction;

' In construction of the heat exchangers in accordance with the ;invention, \difiere nt positions on the-heat transferring wall or walls along the flow- .of. the; fluid :flowin'g outside the passages or tubes, are :brought :into contact with different layers'of thisfluid, *WhiChfhtlVB notyet taken part in the heat-exchange, and in this way; one and the same ."volume ofv thei fluid flowing inside the passages 01' tubes; will .in "its passage through the attain tubes, come into heat exchange proximity in consecutive intervals of time with layers of the outside fluid, which have not yet taken part in the heat exchange and thussubstantially still have their initial temperature, so that in this way the temperature difference through the heat transferring wall is kept high particularly for special cases where in the fluid inside the tubes has the 7 high specific heat per unit volume, while the outside fluid has a low specific heat per unit volume, without velocities being increased, and in this losses of the fluid flowing outside the tubes; from the pointof view of bringing about effective heat exchange between a liquidof high specific heat per unit volume inside the tubes'an'd air oranother gas fiowing outside the tubes, where this gas has a very much smaller specific heat per unit volume (for'the'cases of water inside and air outside the tubes, the'ratio of the specific heats per unit volume may be'about 3000-to 1) and finally from the point of view of efiicient 'exploitationof the natural convection as moving agent for the cooling air, leading e. g. toeconomical designs of coolers of large capacity without fan-draught for the cooling air, and making'atmospheric air applicable as cooling agent instead of water for certain-applications.

It will be understood that the embodiments of my invention described in the foregoing are by way of example only, and that many other examples and modifications of the invention are possible within the scope of the appended claims.

1. In and for a heat exchanger the combina tion of a row of heat exchange elements respectively bathed externally by a first fluid and traversed internally by a second fluid taking part in the heat exchange, of a guide-casing for'said first'fluid around said ro'w of heat exchange elements with an entry for said first fluid at one end and an exit for said first'fluid at its other end, and

of an entry guide means and an exit guide-means in-the walls of said guide-casing situated between the entry and exit ends of said guide-casing, at a position along the length of at least one of the heat exchange elements of said row, for diverting at least a layer of said first fluid which has flowed in immediate heat exchange proximity with only a part of said one element and has taken its part in the heat exchange, away from said element to outside said casing, and for guiding a layer of said first fluid, which'has flowed outside said guide-casing and has not'yet been in contact with a heat exchange element into immediate heat exchange proximity at least with said one heat-exchange element of said row on its continuation to flow therealong in the same direction in which flowed the layer which has been diverted from'said element.

2. In and for a heat exchanger, the combination as claimed in claim 1, in which said entry and exit guide-means are in direct contact with at least said one heat exchange element of said row.

3. In and for a heat exchanger, the combination as claimed in claim 1, in which said entry and exit guide-means in the walls of said guideleasing arerespectively disposedalong the entire "width of said guide-casing on opposite side-walls thereof. 7 V 4. In and for a heat exchanger, the combination "as claimed in claim 1, in which said entry and exit guide-means comprise slots in opposite sidewalls of said casing, said slots extending respectively the entire width of said guide-casing, and a vane connecting one edge of the entry-slot with 10 the other edge'of the exit-slot in a gradual transition, said guidevvane gradually di-verting with Lone side-surface layers of fluid, which have flowed in immediate heatexchange proximity substan- {tially along saidheat exchange elements or said row and have taken their part in the heat exchangeto outside said guide-casing'on one side,

and said guide-vane with its opposite side-sur- Lfacefgui ding layers of fluid, which have flowed ,o'utsidesaid guide-casing on its other side and have not yet been in heat exchange proximity with a heat exchange element into immediate heat exchange proximity with said elements of said row on'the'ir respective continuations.

' 5. In and for a heat exchanger, the combination of a'plurality of rows of heat exchange eler'nents, which arerespectively bathed externally by a first fluid and traversed internally bye. second fluid taking part in the heat exchange, of

a plurality of guide-casings for said first fluid, each arranged around a row of said elements, and having each an entry for said first fluid at one end and an'exit for said first fluid at its other end, and ofat least one entry guide-means and exit guide-means for said first fluid in opposite sidewalls and situated between the entry and exit end of said casing at a position along the length of said heat exchange elements of said row, for diver-ting layers of said first fluid which have flowed in immediate heat exchange proximity substantially along the elements of said row and have taken their part in the heat exchange away from said'elements'out of said casing to one side thereof, and for guiding layers of said first fluid which have flowed outside said guide-casing on itso'ther side and have not yet flowed in heat exchange proximity with a heat exchange element into immediate heat exchange proximity with said elements of said row on their respective continuationsto flow therealong in the same direction in which flowed the layers which have been diverted from said elements, said rows of heat exchange elements with their guide-casings being spaced adjacent one another so that for adjacentrows said entry and respectively exit guidemeans face one another across alternate spaces between guide-casings of adjacent rows of elements, each alternate space between two guidecasings into which face exit guide-means thus forming an exit-space and containing said first fiuid'iwhich. has already taken part in the heat exchange, and every other alternate space between two such guide-casings into which face entry guide-means thus forming an entry-space and containing said first fluid which has not yet taken part in the heat exchange, the said combination further comprising side-walls at least for said exit-spaces, which side-walls extend between adjacent guide-casings, and baflles situated substantially at one end of said space for at least said exit-spaces, for separating said exitspaces from said entry-spaces.

6. In and for a heat exchanger, the combination as claimed in claim 5, in which said heat eX- change elements have entry and exit header tanks respectively common to each row for said 11 second fluid flowing internally through said heat exchange elements and taking part in the; heat exchange. I 7. In and for a heat exchanger, the combinationas claimed in; claim 5 in which said heat exchange elements, are tubes having entry and exit header tanks respectively common. to each; row

rality-of, rows of heat'exchang e elements. within said duct, said elements being respectivelybathed externally by-a first fluiditraversingsaid duct and traversed internally'bya; second fluid taking part in-the heatexchange; 'apluralityof guide casings for said first fluid each-arranged around a rowof said elements and having each an entry forsaid first fluid at one end: and an exit for saidflrst fluid at its other end, andat least one entryguide-means and exit, guide-means; for said first fluid in opposite side-walls andsituated between the entry and-exit ends of; said casing at a position along the length ofsa-idheat exchange'elements of said r0w,--for, divertinglayers-of said first fluid which have flowed in' immediateheat exchange proximity substantially along the elements of said row' and have taken their part in the heat'cxchange away from said elements out of said casing to one side thereof, and for guiding layers of saidifirst fluid which have flowed outside said guide-casing onits other side and have not yet flowed. inheat exchange proximity with a heat exchange element into immediate heat exchange proximity with said -elements of said row on their respective continuations, to flow. therealcng in the same directionin which flowed the layers which have been diverted from said elements, said' rows of heat exchange elementszwith-their guide-'casingsbeing spaced adjacent to one another so that for adiacentrows said entry and respectively 5 exit guide-means face one another across alternate spaces between guide-casings of adjacent rows of elements, each alternate space between two guide-casings, into which face exit guide-means thus forming-Jan exit-space and containing, first fluid which has already taken part in the heat exchange; and every other alternate space between two-such guide-casings, into which face entry guide-means, thus'forming an entry-space containing first fluid which has not yet takenpartin the heat-ex change, the said heat exchanger further comprisi ing the side-walls at-least for said exit-spaces, which side-walls extendbetween adjacent guidecasings, and baffles. situated substantially at at least one. end of said exit and entry spaces,- the said bafiies at the ends of said entry-spaces extending to the wall of said duct, for separating space in said duct which contains said first fluid before it has taken part in the heat exchange from spacein said duct which containssaid first fluid after it has taken part in the heatexchange.

9. A heat exchangeras claimed in claim 8,.in which the surfaces containing the middle-lines of the heat exchange elements of saidrowshave substantially vertically directed generating lines,

and in which said duct surrounding the assemoly ends in a chimney, the said first fluid flowin through the said heat exchanger by virtue of natural convection only.

10. A heat exchanger asclaimed in claim 8, in which said heat exchange elements are tubes having entry and, exit header tanks respectively common to each row of tubes for said second fluid flowing. internally through said tubes and taking ,part in theheat exchange, said. entry and respectively exit header tanks for every adjacent pair ofrows being. disposed in staggered relationship to. one another, and the-surfaces containing the middle-lines of the heat exchanger-tubes of said rows having substantially vertically directed generating lines, andsaid duct surrounding the assembly ending in a chimney, the said firstfluid flowing through the heat exchangerby virtue of natural convection only.

11. A heat exchanger comprising at least two sets of rows of heat exchange elements, 1 each forming a heat exchanger as claimed in claim 8, arranged one. after theother inthe flow.- direction of said flrst'fluid withsaid-duct' common toboth, the saidheat-exchange elements being tubes ofstep-wise increasing diameters "for consecuti-ve rows of tubes of'the said sets, a'header tank disposed betweenjand common toeach two such consecutive rows of tubes, the tubes of the rows of larger'diameter' tubes debouching thereinto and the smaller, diameter tubes of the consecutive row passing therethrough into the mouths of the larger-diameter tubes of said firstmentioned row, said header tanks serving to'lead away out of the heat exchanger the outer layers of the second fluid flowing inside said tubes of said consecutive rows from said larger'diameter tubes tosaid smaller diameter tubes, while the inner layers of said fluid continue to flow inthe smaller diameter tubes of'the consecutive row.

12. A heat exchanger comprising two sets of rows of heat exchange elements, each'forming a heat exchanger as claimed in claim 8', arranged one after the other in the flow direction of said first fluid with the said. duct common to both, the said heat exchange elements of each row bemg tubes having entry and exit header tanks respectively common to each row of tubesfor said second fluid flowing internally therethrough, said heat exchanger further comprising smaller diameter tube-stumps passing from the mouths of; the tub-es of a row through the exit header tanks of this row into the entry header tanks of the consecutive row of tubes, the outer layers of the flow of saidsecond fluid in the tubes of'said first-mentioned row flowingoutside said" tubestumps into the exit header tank of this row, which leads them out of the heat exchanger, while the inner layers of flow of the second fluid in the respective tubes flow through said tubestumps into the entry header tank of the consecutiverow of tubes, the tubes of said consecutlVe' row being on centre-lines different from those of the tubes of the first row and'being provided with smaller diameter inner tubes which pass through the entry and exit header tanks of this row, the annular spaces between said tubes and said inner tubes of said row being traversed by said second fluid taking part in the heat exchange, while the inner tubes themselves are traversed by said first fluid which also bathes externally the tubes of all rows, said heat ex changer further comprising bafiies' between the exit header tank of one row of tubes and the entry header tanks of the consecutive row of tubes, for guiding layers of said first fluid which have flowed through said smaller diameter inner tubes of a row into the exit space formed between the guide-casing of this and of a laterallv ad acent row, said bafiles further serving to sepa ratesuch exit-spaces, in which flows fluid which" "'13 has taken part in theheat exchange from entry spaces which contain first fluid which has not yet taken partin the heat exchange. 1 3

1 3 A heat exchanger comprising a duct, a row of. heat exchange elements respectively bathed externally by first fluid traversing said duct and traversed internally by a second fluid taking part in the heat exchange, a guide-casing'for said first fluid around said 'roW'of' heat exchange elements with an entry for said first fluidsa-t'bne end and an exit for saidfirst fluid at itsfother end, andan entry guide-meansand an exityguidemeans in the walls of said guide-casing and situated between the entry and exit ends thereof, at a position along the length of at least one of said heat exchange elements of said row, for diverting at least a layer of said first fluid which has flowed in immediate heat exchange proximity with only a part of said one element and has taken its part in the heat exchange, away from said element to outside said guide-casing, and for guiding a layer of said first fluid which has flowed outside said guide-casing and has not yet been in contact with a heat exchange element into immediate heat exchange proximity at least with said one heat exchange element of said row on its continuation, to flow therealong in the same direction in which flowed the layer which has been diverted from said element, the said heat exchanger further comprising baiiles connecting said guide-casing and the wall of said duct for separating space in said duct and outside said guide-casing which contains first fluid before it has taken part in the heat exchange from space in said duct and outside said guide-casingwhich contains first fluid which has not yet taken part in the heat exchange.

14. A heat exchanger as claimed in claim 13, in which said entry and exit guide-means comprise slots in opposite side-walls of said guidecasing, said slots extending respectively the entire width of said guide-casing, and a vane connecting one edge of the entry-slot with the other edge of the exit-slot in a gradual transition, said guide-vane gradually diverting with one side-surface layers of fluid, which have flowed in immediate heat exchange proximity substantially along said heat exchange elements of said row and have taken their part in the heat exchange, to outside said guide-casing on one side, and said guide-vane with its other side-surface guiding layers of fluid which have flowed outside this guide-casing on its other side and have not yet been in proximity with a heat exchange element into immediate heat exchange proximity with said elements of said row on their respective continuations.

15. A heat exchanger comprising a duct, a plurality of rows of heat exchange elements within said duct, said elements being respectively bathed externally by a first fluid traversing said duct, and traversed internally by a second fluid taking part in the heat exchange, a plurality of guide-casings for said first fluid, each arranged around a row of said elements and having each an entry for said first fluid at one end and an exit for said first fluid at its other end, and at least one entry-guide-means and an exit guidemeans for said first fluid in opposite side-walls and situated between the entry and exit ends of said casing at a position along the length of said heat exchange elements of said row, for diverting layers of said first fluid which have flowed in immediate heat exchange proximity substantially along the elements of said row and have taken their part in the heat exchange away from said elements out of said casing to one side thereof, and for guiding'layers *of said first fluid which have flowed outside said guide-casing "on its other side and 'havenot yet flowed'irl heat exchange proximity with a heat exchange 'ele meiitl'*into immediate' heat exchange proximity with said elements of said row on their respective continuations, to flow therealong in the same direction in which flowed the layers which have been diverted from said elements, said rows of heat exchange elements with their guide-casings being spaced adjacent to one another so that for adjacent rows said entry and respectively exit guide-means face one another across alternate spaces between guide-casings of adjacent rows of elements, each alternate space between two guide-casings into which face exit guide-means thus forming an exit-space and containing first fluid which has already taken part in the heat exchange, and every other alternate space between two such guide-casings into which face entry guide-means thus forming an entry-space containing first fluid which has not yet taken part in the heat exchange, the said guide-casings extending up to the walls of said duct, and the said heat exchanger further comprising baffies situated substantilly at at least one end of each of said spaces and extending between adjacent guide-casings and up to the wall of said duct, for separating space in said duct which contains first fluid before it has taken part in the heat exchange from space in said duct which contains first fluid after it has taken part in the heat exchange.

16. A heat exchanger as claimed in claim 15, in which the surfaces containing the middle-lines of the heat exchange elements of said rows have substantially vertically directed generating lines, and in which said duct surrounding the assembly ends in a chimney, the said first fluid flowing through the heat exchanger by virtue of natural convection only.

1'7. A heat exchanger as claimed in claim 15, in which said heat exchange elements are tubes having entry and exit header tanks respectively common to each row of tubes for said second fluid flowing internally through said tubes and taking part in the heat exchange, said entry and respectively exit header tanks for every adjacent pair of rows being disposed in staggered relationship to one another; in which the surfaces containing the middle-lines of the heat exchanger elements of said rows have substantially vertically directed generating lines, and in which said duct surrounding the assembly ends in a chimney, the said first fluid flowing through the heat exchanger by virtue of natural convection only.

18. A heat exchanger as claimed in claim 15, in which said heat exchange elements are tubes having entry and exit header tanks respectively common to each row of tubes for said second fluid flowing internally through said tubes and taking part in the heat exchange, said entry and respectively exit header tanks for every adjacent pair of rows being disposed in staggered relationship to one another.

19. A heat exchanger as claimed in claim 15, in which said heat exchange elements are tubes having entry and exit header tanks respectively common to each row of tubes, said tubes being traversed by smaller diameter tubes passing through the header tanks of said row of tubes,

15 said header tanks serving: the annular spaces between said: outer and innertubes with said second fluid taking part ,in-the-heatr. exchange, said first; fluid taking part in the heat exchange also flowing through said'smaller diameter, inner 5 tubes. MEYER FRENKEL.

, REFERENCES; CITED "The following references are of record. in the 10 file of this patent: I

Number Number UNITED STATES PATENTS Name I Date McGregor Mar. 25, 1924 Smith Dec. 1'7, 1929 Jacocks Feb. 2% 1931 FOREIGN PATENTS Country Date Great Britain Oct. 28, 1926 Great Britain June 29, 1933 Germany Oct. 10, 1917 Germany' Mar. 23, 1935

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