US2611587A - Heat exchanger - Google Patents

Description

P 1952 c. BOLING 2,611,587

HEAT EXCHANGER F e y 27, 1950 I 4,,Sheets-Sheet 1 INVENTOR Ceqil Bali c." BOLING HEAT EXCHANGER Sept. 23, 1952 Filed July 27, 1950 l mi Q J A fin mw. m QN QM... Q h m r hm W'IML mm .wmuw m H q NS. No Q0. I 3 mm. #9 F NR QM Q Q 5 a mm w N m mm 5 I mm R @N l Mw m on v @N $9 m QB In Q l w i Q wm QQ MI HE mm m mm. mm. Q% g QINI QM. w l %Q\ NM. ya w Lu \W n 4. w m0 4N vR 0 ma n C A 6 MM Sept. 23,1952 c. BOLING 2,611587 HEAT'EXCHANGER 7 Filed- July 2'7, 1950 4- Sheets-Sheet;3

INVENTOR C'ecil Balin Sept; 23, 1952' c, BOLlNG 2,611,587

HEAT EXCHANGER Filed July 27, 1950 4-'5 h06tS-$h99t 4 sag N I xi '3 ENVENTOR C'ecLl Bolizy Patented Sept. 23, 1952 UNITED STATES PATENT OFFICE];

.Heat-X-Qha er 00., In 6., Brewster, N. an, a corporation .of ew' York Application 'July -27, 1950, SerialNo. "176,128

"Thisinvention relates :t'orefrigeration :and heat transfer for exchange equipment :such as that which is used in refrigeration systems, with such equipment, and more in particular to improved refrigeration systems and :heat exchange components :such as condensers, 'evaporators land the ilike where one afiuidvis passed into heat exchange relationshi with 'one-ormore otherfluids.

- object of thisdnvention is to provide improved refrigeration systems wherein extremely efficient operation is obtained "with equipment r-which is simple and sturdy in construction, inexpensive to manufacture and maintain, compact, flight inweight and'thoroughly dependable in use, and which :is adaptable "to .meet many problems indifferent fields. Further obj'ectsare to provide improved heat exchange units having certain or all of the above desirable characteristics with particular attention being directed toward providing improved condensers, evaporators and :the "like. Aifnrther objecttis to provide heat exchange equipment which may be of more. or less standardized design and construction and yet which is adaptable for use in solvingmany different'prob :lems which have been encountered in widely diversified fields. A still further object is to provide .for the manufacture of equipment of the above character upon :a mass production basis with the advantages and economies whichmay be obtained thereby. :Ihese and other object will be in part obvious and in part pointed out below.

The invention accordingly consists in the features of construction, combinations of elements, arrangements of :parts and in the several steps and relation and order "of each of the same .to one. or more of the others, all as will be illustra- -tively described herein, and the scope of the application .of which "will :be indicatedin the "following claims.

In :the'drawings: Figure l is a somewhat schematic representation of oneembodirnent of the invention;

v Figure 71,; and,

:5 Claims. (C1. 325F247) 2- ,4 Figure 1051s a section onwthe line [0-40 ,ofaFiE- 'ure 9.

Refrigeration systems generally :include tw-o1or more heat transfer units wherein heat is transferred to. or from :a .streamor streams of the re-- frigeratlng :medium. Examples .of such heat transfer units are: condensers, evaporators and heat changers where one stream of refrigerant is passed in :heat transferrel-ationship with another or where a :liquid or air is cooled or heated by a liquid or .gas. With any particular refrigeration system the performance may be improved "by increasing the rate of heat transfer at the heat transfer units. "Thus, if there is a high-rate of heat transfer .at the condenser, a relatively large amount of refrigerant is condensed with a minimum amount ofrairjor water and-with a relatively small condenser. Similarly, the performance of the system is'im-proved by increasing the rate of heat transfer to the refrigerant in the evaporator, thus, .to promote uniform cooling throughout;the evaporator zone and uniform and completeevaporation of the refrigerant.

Generally, the performance of an air cooled condenser varies over a relative1y wide rang in accordance with the ambient temperature aswell as the load. That is, the rate at which heat is transferred from the condenser drops materially -when the ambient temperature rises, and it has been accepted practice to design air cooled condensers for refrigerationsystems with a relatively high excess load factorat normal o mean ambient temperatures solely to take care of the high loads :at :high ambient temperatures. Proposals have been made to provide both an air-cooled condenser and a water "cooled condenser for a single refrigeration'system or to utilize bothair and water to cool a single condenser unit. With such arrangements most or all of the heatis passed to the air at light loads and at low ambient temperatures, but as the ambient temperature or the load rises, ,heat is passed-to the water. How- 'ever, it has been idifficult to provide for the efficient transfer of heat to both air and \water with condenser structure which is inexpensive to .m n factur and thorou hly -satisfact yii-n-every respect;

3 system cools a building in summer and heating is provided in winter, it is desirable to provide a single heat transfer unit of minimum size and cost in each room which is the heat radiator in winter and the cooling or heat-absorbing unit in summer. In each of the systems referred to above, the present invention contemplates the provision of one or more heat transfer units, each of which is adapted to pass two or more fluids, i. e., liquids or gases, into eiiicient heat transfer relationship with each other or to pass selectivelyor simultaneously two such fluids into heat transfer relationship with air or the like. 7

4 tween the two tubes. In each tube assembly the refrigerant from the compressor passes through the space 32 which acts as a condensing passageway where the gas is cooled thereby to condense it to a liquid.

Cooling water is flowed through the passageway 34 in each inner tube 28j-s'o that cooling of the refrigerant gas is obtained as a result of heat passing through the inner tube wall to the water. The flow of water is controlled by a metering valve 29 which is connected through a pressure tube to the compressed or hot gas line from the Referring particularly to Figure l of the drawings wherein a refrigeration system is shown somewhat schematically, a compressor 2 is driven by a motor 4 and is automatically controlled so that it compresses refrigerant and delivers it through a hot gas line 5 to a primary condenser .6 and thence to a secondary condenser 7. The refrigerant is condensed in the condensers and the liquid refrigerant goes to a receiver 8 and thence through 'a liquid line Ill and an expansion valve l2 to an evaporator [4. The refrigerant, evaporates in the evaporator and flows through a line which has a throttle valve I9 therein which does not interferewith the flow of the refrigerant gas during the refrigeration cycle. The refrigerant then passes through a heat exchange passageway in the secondary condenser I, and a line 16 to the compressor.

During normal operation frost accumulates on evaporator l4 and the evaporator is defrosted by passing hot gas from the compressor directly to the evaporator so that it does not flow through the condensers. Accordingly, the system is provided with a valve II in a bypass line i8, and this valve is opened to connect the hot gas line 5 through line I8 to the inlet of evaporator M; the hot gas heats the evaporator and the ice is melted free. The rise in pressure causes the throttle valve ill to close and throttle the flow of refrigerant as it returns from the evaporator to the compressor throughline l5 to the heat exchange passageway in the secondary condenser I and thence to the compressor through line 16. This causes the refrigerant to condense in the evaporator and it is evaporated in the secondary condenser I so that the secondary condenser is also a re-evaporator.

In the embodiment of Figure 2 the system represented is similar to that of Figure 1 except that: a special evaporator 19 is provided; a condenser 2| of modified form replaces the condensers 6 and 1; and, the bypass line l8 and valves l1 and I9 are omitted. In this embodiment the defrosting operation is carried on by passing a hot liquid through a separate passageway in the evaporator to perform the defrosting operation. Consequently, no hot gas is passed to the evaporator, and it is unnecessary to provide for the i e-evaporation of refrigerant passing to the compressor.

Condenser 2| is of a special construction which constitutes an important phase of the invention and now will be described more in detail; This condenser is shown in Figures 4 to 8 and comprises a set of six horizontal mult ple-passa eway condenser tube assemblies 20 (Figure 4) rigidly mounted and interconnected at their ends by a pair of header assemblies 22 and 24. Each of the condenser tube assemblies 20 comprises an outer tube 26 and an inner tube 28 (see also Figure 8), having an internal. radially-compressed, fin ascompressor and permits water to flow through the condenser" at a rate sufficient to keep the pressure of the compressed gas within desirable limits.

The header assemblies 22 and 24 (Figure 4) provide rigid support for the condenser tube assemblies and are in turn supported at the bottom (see also Figures 5 and 6) by a pair of sheet metal mounting brackets 33 which are clamped in place on the-base of the machine by bolts (not shown). .The header assemblies provide .fluid connections whereby-the various passageways 32 are connected in series; and, at the sametime, all" of the passageways 34 are connected in series. Accordingly, header assembly 24 is provided at the bottom with a water inlet fitting 35, and at the top with a water outlet fitting 36; andlsee Figure 5) there is at the top a refrigerant inlet fitting 31 and at the bottom a refrigerant outlet fitting 38.

Header assembly 24 is formed by-two interengaged vertical channels 40 and 42 (see Figure 7) and a third enclosing channel 44. Channels 45 and 42 form the header passageways for the inner tubes 28 while channels 42 and 44 form the header passageways for the annular passageways 32 in tubes 26; Accordinglyxchannel 42 is providedwith a set of flanged openings 46 which receive the ends of tubes 28 and channel 44 is provided with concentrically positioned flanged openings 48 which similarly receive the ends of tube 46. Referring to Figured, the space between channels 48 a'nd'42 is divided into four header passageways 50, 52, 54 and 56 by five arch-like transverse walls 58, 60, 62,- B4 and 66 which are positioned as shown in Figure 6 and provide horizontal blocks or walls between the respective header passageways; The header passagewavs 5B and 56 are open respectively to the ends of the top and bottom tubes 28 while each of passageways 52. and 54 is open to the ends of a pair of the centrally positioned tubes 28 (see also Figure 4) Referring to Figure 5, the header passa eways 68. Ill, 12 and 74 between channels 42 and 44 are similarly formed by arch-like transverse walls 16, 18, 80, 82 and 84. The top and bottom passageways 68 and 10 are connected respectively to the annular passageways 32 in the top and bottom tube assemblies while the passageways i0 and 12 are each connected to a pair of the centrally positioned passageways 32.

Referring to the left-hand portion of Figure 4, header 22 is substantially identical in construction with header 24 except that arch-like transverse walls 86 and 88 are positioned to provide: header passageways 90, 92 and 94 which connect the an nular passageways 32 in the lower pair oftubes, the central pair of tubes and the top pair of tubes, respectively; and header passageways 96, 98 and I00 which connect the ends of the lower pair of tubes 28, the central pair of these tubes and the. top pair of these tubes. It is thus seen that the water inlet fitting as is connected to a ater passageway extends through. pasgewayfi s; the lowertube'ze; passageway 96', the

no t tube 28, passagewaysmne next tube as; passage'ay 9a,; the tube 28; passageway 52, the

neat tube as, passa eway! flog the top tubezit-and thence through passageway 50' to the water outvid'ed from the refrigerant inlet fitting 3 1 at the and-through passageways 6'8, 32} 9'4,- 3 2, 10,32, 92, 32', I2, 32", 9t, 32, and 14 to therefrigerant thread d into the to and bottom of these o enin-gs Hi2 and the'othe'r of these openings are closed by a screw cap l-il l thewater' circuit may be readily cleanedby removing these 7 fittings and screw caps, and by inserting a spiral tube cleaner. 7 I v V The various elements of the header assemblies are connected to each other and to tubes 26 and 28 by a soldering operation. Thus, during manufactors the elements are'assembledin a jig, and

the headers are then heated and soldered. Upon cooling the entire unit is held tog'ether as a unitary structure, and the joints and seams are sealed.

The fin assembly 36 is of. the type disclosed in copjendingfl application Serial No. 17,899, filed IS/[arch 30, 1948, and is characterized by being formed'of sheet metal which is somewhat corrugated so that fins are provided extending longiboth tubes, and gives structural advantages.

During construction of the apparatus, the fin assembly 38 and the inner'tube 28 are slid into tube is, and tube 22 is then expanded so that it presses radially outwardly upon the fin assembly 38; Thus, each of the fin portions lliii is com pressed radially so that one edge is pressed at a bendl l against the outer surfaceof tubs-:28 and 'theother edge is pressed at a bend H2 against the inner surface of tube 26. With this constructioiithe fin assembly is expansible so that it is pushed by" the inner tube outwardly against the outer tube, but can not be compressed" to any great extent radially and, thereforeQthe fin assembly is placed under radial compression by the expansion of tube 28. Thus, the fin assembly has good heat transierrelationship with both of the tubes and also witht he refrigerant flowing through the passageway 32 between the tubes. Furthermore, the refrigerant now through this passageway is relatively unobstructed because the fin extend longitudinally of the passageway.

- In Figure} 2 the evaporator I9 is substantially identical-in construction with the condenser 2I,

' except that each of the tube assemblies has onits outer tube '3 a fin assembly [I5 formed by s uare sheet metal II'I. These fins II! are put place on each tube H3 prior" to assembly with its internal fin assembly 36 andits inside. tube 28 and the tube 3 is xpmdd to hold iii) '6 the-final I 1. inplace and. to give good: heat transfer relationship. The: refrigerant passes from the receiver'iithrough line I0 andexp'ansionyalve I2 to the refrigerant inlet fitting 1 UL It; then flows through the series of evaporatorpassaga ways identical with passageways 32 to the re--' *fi-igerant outletfitting I I6 from which it returns through line I5 to the compressor. An inlet fittin'g' I I 8' identical with fitting 35 on the condenser provides an inlet connection for a defrosting liquid which may be an aqueous solution cran other liquid which is heated.

Thus, when frost accumulates on the evaporat tor the refrigeration operation is discontinued.

and heated defrostingliquld is supplied to fitting This liquid flows through the passageway corresponding" to the water passageway in; the

condenser and it is discharged at the bottom of the evaporator, through a fitting I26. The heat from the defrosting liquid passes through the wallsof tubes 28 and thence through the fin assemblies 3b to the outer tubes 26. This heats the outer tubes and the fins so that the accumulated frost or ice is melted free. It is thus seen that the evaporator surfaces arein good heat transfer relationship with the inside tubes 28 and, therefore, the defrosting operation is carried on efiiciently. This good heat transfer relationship exists by virtue of the fin assemblies 30 being held under radial compression so that each fin assembly is in tight contact with the outer surface of its inner tube and the inner surface of its outer tube. j

'Pte'ferring now again to Figure 1, it was stated above that the secondary condenser I is of'speci'al construction and provides a heat transfer passageway for the return refrigerant. Referring to Figure 9; this condenser 1 is in many respects identical with condenser 2i of Figure 2. There are six'tube assemblies I2 I-, each of which 156011! struoted in the same manner as tube'asseinblies of Figure 2 but the outer tube 28 carries a fin assembly I22 formed by fins I23 whichare'identical with the fins "II'l on the evaporaton'of Figure 2. The headers I2 and I are quite similar to the. corresponding headers-22 and 24 of Figure 2 and. differ only in. that certain of the partitions or transverse walls are omitted and the right-hand header l25 is cutaway at the top.

Header I25 is formed by a set of interengaged channels I25, I28 and E32 and thereis a single passageway I32 at the right between channels and I23 which is open. to the right-hand ends ofall of the tubes 28', except for the top tube. There is also a single passageway [34 between channels [23 and I36 which is open totheannular finned passageways 32 between the ooncentrictubes 2s and 28' of the respective tube assemblies. Header 521i is similar to header H25 except that its channels extend to the top of the condenser and provide single passageway Ifili which is open. to the left-hand, ends of all of the tubes 28 and a passage\vay .l38 which: is open to the lefthand ends of all of the passageways 3 2.

It has been. pointed out above that (see also Figure '.i) the compressed gas fiows from the compressor to the primary condenser 6 which, in actual construction, is mounted. at the side of the secondary condenser l and asingle fan passes air through the two condensers. The

refrigerant from the primary condenser passes through two tubes M9 and. I42 to the upper por- ;tion of passageway I38 at the left-hand end of the secondary condenser and, aswindicated, this 'to the intake port of the compressor.

-passageway is open to the left-hand end of all of the annular finned passageways 32 in the various tube assemblies. The bottom of this passageway I38 is connected through a line 144 to the receiver and, therefore, the condensed refrigerant from the primary condenser flows through the lines I40 and I42 into passageway I38 and down this passageway and through line I44 to the receiver with minimum resistance to flow. However, any refrigerant gas which is not condensed in the primary condenser 6 separates from the liquid refrigerant in passageway I38 and fiows into the various passageways 32 where heat is passed from it by the internal fin assemblies 38 and also by contact with the outer tubes 26.

The internal fin assemblies 38 are compressed as a result of the expansion of the internal tubes action is performed by the secondary condenser.

The secondary condenser is also a re-evaporator and the refrigerant returns through it from the evaporator to the compressor. This return i e-evaporator passageway is formed by the inside tubes 28 and the interconnecting passageways I32 and I36. Line i is connected to the bottom passageway I32 at the right-hand side of the unit and the top tube 28 has its righthand end connected to line #8 which extends As indicated above, passageway I32 is connected to the right-hand end of all of tubes 28 except the top one and the left-hand passageway I35 is connected to all of the tubes 28. Thus, the refrigerant flowing from line I5 into passageway I32 flows freely to the left through the five lower tubes 28 and into passageway 138. From passageway I36 the refrigerant fiows to the right through the top tube 28 which is of sufficient size to carry the refrigerant without objectionable pressure drop. Thus, the refrigerant returning from the evaporator to the compressor during the refrigeration cycle is passed into heat exchange relationship with refrigerant on the high side. This not only insures that no drops or slugs" of liquid refrigerant will reach the compressor in the return line but it also improves the performance of the system.

During the defrosting cycle the fiow from the evaporator to the compressor is unchanged and, as indicated, hot gas fiows through line I8 directly to the evaporator where it melts ice or frost free. During this operation refrigerant is condensed in the evaporator and this fiows through line I5 and valve I9, which then provides a pressure drop to passageway I32 and thence through the lower five tubes 28 to passageway I36. The liquid refrigerant tends to 'fiow through the lower tubes while the upper "tubes 26 and the external fins I23. Therefore, heat is absorbed by the fins I23 and passed by the internal fin assemblies to the refrigerant in the inner tubes 28. The unit therefore acts as an efficient re-evaporator and insures the evaporation of all liquid refrigerant which flows from the evaporator. The five tubes 28 operate in parallel and, as indicated, they ofier minimum resistance to the refrigerant flow. The top tube 28 prevents slopping over which might occur under some conditions of operation if line I6 were connected to passageway I36. Under some circumstances there may be one or more additional tubes connected in parallel with the top tube or a more extended series arrangement may be provided so that the refrigerant follows a longer path.

In the embodiment of Figure 3 an arrangement is shown schematically wherein a single heat transfer unit I43 acts as an evaporator in. the summer to cool the air in a room, for example, and acts as a heat radiator in the winter to heat the room. The unit I43 is identical with evaporator l9 of Figure 2 and the parts are correspondingly numbered. However, when the unit is acting as an evaporator its surface temperature'is above freezing and therefore frost does not form and it is unnecessary to defrost it.

For purposes of heating in winter the inner tubes 28 of unit I43 are connected to a heating medium, illustratively, steam supplied from a remote boiler I41. The condensing unit of Figure 3 is identical with that of Figure 2 except that a water cooled condenser I45 is provided which is identical in structure with evaporators I9 and I43. In condenser I45 the inner tube circuit, formed by tubes 28 connected in series, acts as a water circuit for the condenser cooling water the same as in Figure 1 and therefore water is supplied to this inner tube circuit through a valve I44 identical with valve 29 of Figure 2. However, each of the condenser tube assemblies is provided with external fins as in Figure l, and under low load, conditions and at low ambient temperatures, the cooling effect of the fins is sufiicient to condense all of the refrigerant. Under such circumstances, valve I44 remains closed and there is no water flow because the pressure of the hot gas does not rise. However, at high loads and when the ambient temperature rises the high side pressure rises indicating that the condenser is not condensing the refrigerant; this opens valve I44 and permits water to fiow through the condenser so that there is auxiliary cooling. With this arrangement it has been found that the unit can be designed for normal operation as a solely air cooled unit; and yet peak and abnormal loads need not be taken into consideration insofar as the air cooling surface is concerned because such loads are handled with the assistance of water cooling. This arrangement is of particular advantage under circumstances where the free use of water is objectionable and where maximum efficiency is important.

With the embodiment of Figure 3 the refrigeration system operates to cool the air during warm weather in accordance with the normal refrigeration cycle of operation. During such operation the inner tubes carry no heating or cooling medium. However, they perform the function referred to previously of providing the high heat transfer relationship between the fin structures and the outer tubes and thence with the air. When cooling is no longer required the refrigeration system is turned off and, if desirable, heating may be effected immediately by merely supplying the heating medium such as steam to aoiiss i the f-ihner tube circuit. "The steam or other heating mediurn such ashot'w'ater flows through the inner tube circuit and the heat is transferred through the walls of tubes 28 and thence through the-internal fin assemblies to the outer tubes 26 where it is transferred to the air. -'It is thus seen that the refrigeration system-and the heat:

ing system utilize the sameheattransfer st um tures and yet the cooling fiuid andheating fluid circuits are not interconnected. in Figure 3 the to provide a high rate of heat transfer with theairas well as with the water. Similarly, in the heat transfer-unit 43 high heat transfer is provided-between-the refrigerant and the air in the summer and also between the steam and the air in the winter-. Thus,- a single heat transfer unit of ininimumsize maybe provided with a single air. circulating and mounting structure. Under some circumstances hot water or other hot nuid may be used as the heating medium and the fins may be omitted if the external surface is suihcientotherwise ;Geherally, transfer units-of the type herein disclosed are provided withfans when there is to bee heat transfer relationship with-air.- Thus, in the embodiments shown, fans are used whenever the tube assemblies are provided with external fins.

With the various heat transfer units herein disclosed it will be appreciated that the header structures may be modified to obtain either full parallel or full series flow, or there may be combined parallel and series flow. For example, with a condenser the inner tubes may be connected to operate with adjacent pairs in parallel or all of them may be in parallel. Similarly, the passageways 32 may be connected so that two or three are in parallel. The particular internal fin structure gives minimum pressure drop through the passageways 32 even though there is rapid flow. The pressure drop is, of course, reduced if parallel flow is provided, although under some circumstances, it is desirable to provide an extended'series flow.

The arrangement of providing the internal fin structures with U-bends of greater mean radius at the outer tubes than at the inner tubes is an important feature of construction. This the heat a characteristic of the fin structures is obtained by corrugating sheet metal with alternate wide and narrow U-bends. Thus, in actual production, a strip of sheet metal having a width or transverse dimension which is exactly that desired as the length of the fin assembly is placed in a fin-forming machine. This fin-forming machine has a sheet holder adjacent a forming zone at which the sheet is clamped originally with a leading edge projecting into the zone. Two forming strips of diiferent widths are positioned on the opposite sides of the projecting leading edge of the sheet and they are moved edgewise into engagement with the opposite sides of the sheet. The engagement of the two forming strips is along zones spaced slightly from each other and the movement of the forming strips is continued so that the sheet is formed into two corrugations. One of the corrugations is narrower than the other because its forming strip-is narrower and one whom! isalso harerower than the other;

The forming strips are then withdrawn and then the sheet is advanced and the operation is then repeated until there is a 'sufiici'ent number of corrugations tor a 'fin assembly 30-. The an assembly is then curved i'r'i'to annular formand edges are interlocked-as shown. inner tube as and a assembly 8c is then inserted into a tube =26 and in this embodiment the inner tube 2'8 is expanded. Theexpansion is sufii'cient ressxthe an assembly 30 outwardly'again s t the inner 'wail or tube 26 and: each corrugation or fin ortion is placed. under compression. Under some circumstances the outer tube may be us forrhed to a smallersize to obtain this com :rhe internal assembly i's 'd'eformable so that its mean radius 7 pressed condition bi -the nns.

may be changed readily or it may even be do formed toa shape so as to conform to the exact radial dimensionsor the space tim vided'ifor it. such deforming changes the totaii angles of the various ubends but the radially extending 'iinportions are hot bent materially;

Thus, the an assembly will, still withstand sub; stantial radial compression which, in any event,

of the mechanical features of the above invention and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinabove set forth, or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In heat exchange apparatus of the type wherein a fluid is subjected to a heat transfer operation, the combination of, a pair of concentrically positioned rigid members defining a sub-. stantially annular chamber for the how of the fluid to be subjected to a heat transfer operation, and an annular metallic fin assembly within said chamber and comprising sheet metal corrugations each of which is substantially straight and is non-distortable and extends longitudinally of said chamber bridging the space between said rigid members and is connected to the next adjacent corrugation by a trough-like connecting portion which presents a straight portion in contact with a surface of one of said members, said trough-like connecting'portions providing the heat transfer contacts with the surfaces of said rigid members at the inner and outer peripheries of said annular chamber, said trough-like connecting portions at said outer periphery beingof substantially greater radius than those at said inner periphery, the distance between said rigid members being such that each of said trough-like connecting portions is dismembers.

2. In heat exchange apparatus of the type wherein a fluid is subjected to a heat transferop is substantially straight and is non-distortable and extends longitudinally of said chamber bridging the space between said rigid members and is connected to the next adjacent corruga- V tion by a trough-like connecting portion which presents a straight portion in contact with a surface of one of said members, the trough-like connecting portions which contact the larger radius member being of substantially greater radius than the trough-like connecting portions contacting the lesser-radius member, the distance between said rigid cylindrical members being such that each of said trough-like connecting portions is distorted and each of said trough-like connecting portions is subjected to substantial compressive forces which are applied at the inner and outer peripheries of said fin assembly by said rigid members.

3. Apparatus as described in claim 2 wherein said cylindrical members comprise inner and outer tubes, and a fin assembly positioned upon the outer surface of said outer tube.

. 4. Heat exchange apparatus as described in claim 3 which includes, a pair of headers positioned at the respective ends of said tubes and each providing separate fluid connections to said inner tube and said annular chamber.

5. Apparatus as described in claim 2 whereinsaid cylindrical members comprise inner and outer metal tubes concentrically positioned and with theinner tube being of greater length than the outer tube, and a heater assembly mounting said tubes and comprising separate header means providing support and providing for the flow of separate fluids through the two chambers.

CECIL BOLING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 660,202 Durr Oct. 23, 1900 890,526 Numan June 9, 1908 907,084 McKenzie Dec. 15, 1908 1,584,772 Hyde May 18, 1926 1,585,671 Harms May 25, 1926 1,794,692 Hyde Mar. 3, 1931 2,003,122 Schwartz May 20, 1935 2,085,677 Thayer June 29, 1937 2,117,830 Van Der Beyl May 17, 1938 2,206,826 Hopper July 2, 1940 2,415,865 Booth Feb. 18, 1947 2,526,032 La Porte Oct. 7. 1950 2,534,031 Kollsman Dec. 12,1950 2,589,262

Keith Mar. 18, 1952

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