US2125972A

US2125972A - Heat exchanger

Info

Publication number: US2125972A
Application number: US90074A
Authority: US
Inventors: Dustin W Wilson; Stanley J Chute; Robert K Hopkins
Original assignee: MW Kellogg Co
Current assignee: MW Kellogg Co
Priority date: 1936-07-11
Filing date: 1936-07-11
Publication date: 1938-08-09
Anticipated expiration: 1955-08-09

Description

' u 1%. D. w. \NILSON ET AL 2,125,972

HEAT EXG HANGER Filed July 11, 1956 4 Shets-Sheet 1 ATTOR N EY Aug, 9, 1938. D. w. WWWEm 2,125,972

HEAT EXCHANGER v Filed Jui 11, 1936 4 Sheets-Sheet 2 Fly. 4

mvemrons am 11/. MM

ATTO F? N EY Aug. 9, 11938. D. w. WILSON ET AL 2,125,972

" HEAT EXCHANGER Y Filed July 11, 1936 4 Sheets-Sheet 3 lNVENTORS JDM W A TOR NEY Aug. 9, 1938. D. w. WILSON ET AL I 2,125,972

HEAT EXCHANGER Filed July 11, 1956 4 sheets-Sheet 4 F915 54;. AL

Fly/5 Fly/6 DRNVENTORSz M WKM A TORNEY Patented Aug. 9, 1938 UNITED STATES PATENT OFFICE HEAT EXCHANGER of Delaware Application July 11, 1936, Serial No. 90,074

18 Claims.

This invention relates to heat exchangers and particularly to that type of heat exchanger in which one of the heat exchange mediums is passed through a tube, or a series of tubes, in which a nest, or nests, of smaller tubes is disposed to provide passage for the other heat exchange medium, which may be the heat container or the medium to which heat is to be transmitted. Tubular 'heat exchangers as at present constructed include a larger tube, or tubes, in which is housed a nest, or .nests, of smaller tubes. The nest, or nests, of smaller tubes usually has one end fixed against movement relative to the adjacent end of the larger tube and the other end so arranged, by use of various expedients, that it may move axially relative to the other end of the large tube. When a single larger tube houses more than one nest of smaller tubes, the expedi-- ent employed to provide for axial movement of one end of the smaller tubes generally also serves to connect the flow paths of adjacent nests of smaller tubes. When the heat exchanger includes a plurality of larger tubes various crossover elements are employed for connecting the flow paths to render the flow path of each of the heat exchange mediums continuous.

Heat exchangers of the type thus briefly described have numerous inherent disadvantages which the workers of the art have attempted to obviate. The disadvantages while always apparent are magnified when this type of heat exchanger is used in high temperature and high pressure service.

The relation between the available flow area of the larger tube and the available flow area of the smaller tubes, inherent in the construction and design, is the factor responsible for many of the disadvantages of the tubular heat exchangers of .the present practice. In thepresent tubular heat exchangers the available flow area of the larger tube is always many times the available flow area of the smaller tubes with the result that the heat transfer rate is generally low.

The available flow area relation mentioned necessitates comparatively large outside tubes which in high pressure service must be of very heavy construction, with theresult that heat exchangers of this type designed for high pressure service are of great weight and costly. The weight of the heat exchangers necessitates elaborate and costly supporting structures.

To increase the heat transfer rate in tubular heat exchangers it has become the practice to shuttle the medium flowing through the larger tube back and forth across the nest. or nests, of

smaller tubes by the use of suitable baiile arrangements. The turbulent flow thus obtained, while it improves the transfer rate, does not help to solve the basic problem. Furthermore, this expedient introduces a further disadvantage as it renders true countercurrent flow of the heat exchange fluids impossible.

'The expedients now used to provide for the longitudinal movement of one end of the smaller tubes are also responsible for many of the disadvantages of tubular heat exchangers, especially when this type of heat exchanger is used in high pressure service. Some of these expedients render the structure substantially unitary and with them it is almost impossible to either clean, inspect or replace worn parts without cutting the component parts asunder. Others of these expedients are either of expensive construction or do not withstand extreme service conditions suc cessfully.

It is an object of this invention to provide a heat exchanger of the type mentioned which is of simple and rugged construction, is easily demountable for inspection, cleaning and repair and is of low weight and small size for the heat exchange service which it is capable of performing.

It is also an object of this invention to provide a heat exchanger of the type mentioned, that .is particularly suited for high pressure service, in which the total flow area of the smaller tubes in each of the larger tubes approaches or equals the available flow area of their respective larger tube whereby high velocity turbulent flow through both the larger and the smaller tubes and a maximum heat transfer rate may be obtained.

, It is a further object of this invention to provide a heat exchanger of the type mentioned, that is particularly suited for true counter-current flow of the heat exchange mediums therethrough, in which the flow path of each of the heat exchange mediums is of substantially constant area throughout its length and the areas of the flow paths approximate one another whereby substantially constant high velocity turbulent flow of both of the heat exchange mediums through the heat exchanger is obtained and the exchange of heat eilected at a maximum heat transfer rate.

It is a still further object of this invention to provide a heat exchanger of the type mentioned that is particularly suited for high pressure service, in which a plurality of pairs of the larger tubes, each of which houses a nest of smaller tubes, are constituted into a unit by novel end arrangements of simple, rugged and easily demountable construction that eliminate all external cross-over connections between the tubes of the unit.

The further objects and advantages of the invention will be readily appreciated from a consideration of the following detailed description of a preferred embodiment thereof taken with the accompanying drawings, in which,

Fig. 1 is a side view of an assembly of several heat exchanger units, portions of the lower units being broken away,

Fig. 2 is an end view of the assembly of heat exchanger units of Fig. 1,

Fig. 3 is an isometric view of a heat exchanger unit with certain parts broken away to better show the internal structure.

Fig. 4 is a side view of the unit of Fig. 3 with the ends of the unit shown in section, the section of the left hand end being taken on line 4a4a of Fig. 6 and the section of the right hand end being taken on line 4b-4b of Fig. 7,

Figs. 5, 6 and 7 are sectional views taken respectively on lines 8-5, 6-8. and 'I-| of Fig. 4.

Fig. 8 is an end view of the heat exchanger unit of Fig. 4,

Fig. 9 is a part sectional plan view of the demountable arrangement employed for connecting the flow paths of adjacent bundles of smaller tubes.

Fig. 10 is a part sectional plan view of another arrangement for connecting the flow paths of adjacent bundles of small tubes.

Figs. 11 and 12 are end and side views respec tively of bearing and sealing plates,

Figs. 13 and 14 are plan and side views respec-- tively of a split ring used in the arrangement of Fig. 9.

Fig. 15 is a sectional view taken on line ll-il of Fig. 4, and

Fig. 16 is a view similar to Fig. 15 illustrating the use of another form of filler rods.

While the invention is applicable to various types of heat exchangers. for the purpose of this specification, it will be disclosed in connection with the transfer line heat exchanger 23 shown in the accompanying drawings. Transfer line heat exchangers in petroleum refineries are usually interposed between the cracking coil and the primary fractionation tower and are used to transfer heat from the cracked products to the feed material on its way to the cracking coil. The service conditions are extremely severe as the temperatures may range to 1100 F., and more. and the pressures to 2000 lbs. per square inch,

and more.

Heat exchanger 28 is composed of heat exchanger units 2Lthat are assembled one above the other as shown in Figs. 1 and 2 on a structural framework that includes channel members 22. Each unit 2| is provided with a plurality of spacer elements 23 distributed between the ends thereof. In Figs. 1 and 3 only two spacer elements 23 are shown on each unit 2i as the intermediate portions of units 2| are broken away. however in the full length of units 2| four or more spacer elements 23 are used. The spacer elements 23 nearest the right hand ends of units 2| are bolted or otherwise fastened to channel members 22 upon which they lie to give the required rigidity to the structure. The remainder of the spacer elements 23 merely rest on their respective channel members 22 so that units 2| may freely expand and contract lengthwise. Heat exchanger while it is preferably arranged as just stated may be arranged otherwise, as for instance, it may be arranged with the component units 2| lying next to one another in a horizontal row or units 2| may be arranged vertically side by side.

Heat exchanger unit 2| includes ends 24 and 25, end 24, may conveniently be called the stationary end and end 25 the floating end. Stationary end 24 is made up of a stationary end cover plate 26, a stationary end tube sheet 21 and a stationary end shell flange 28. Floating end 25 is made up of a floating end shell flange 29 and a bonnet 30. The elements of stationary end 24 are held together in fluid tight engagement by studs 3| and nuts 32. Studs 3| screw into suitably tapped holes evenly distributed adjacent the periphery of stationary end shell flange 28. Studs 3| pass through stationary end cover plate 26 and are so disposed that they clear stationary end tube sheet 21. If

desired tube sheet 21 may be of a diameter approximating that of cover plate 2 6 and studs 3| passed through appropriate holes in it. The elements of floating end 25 are held together in fluid tight engagement by studs 33 and nuts 34. Studs 33 screw into suitably tapped holes evenly distributed adjacent the periphery of bonnet 80 and pass through holes in floating end shell flange 29.

Stationary end tube sheet 21 is grooved on one side to accommodate the tongue 36 formed on the inside face of stationary end shell flange 28 and grooved on the other side to accommodate the tongue 36 formed on the inside face of stationary end cover plate 26. Gaskets 31 are interposed between

tongues

35 and 36 and the bottoms of their respective grooves to facilitate the obtaining of a fluid tight seal. The configuration of tongue 35 and its groove is best shown in Fig. 7. As shown in Figs. 3, 4 and 7. tongue 35 together with its groove and gasket 31 divides the interfacial space between stationary end tube sheet and stationary end shell flange 28 into three non-communicating compartments. The configuration of tongue 36 and its groove is best shown in Fig. 8. As shown in Figs. 3, 4 and 8, tongue 36 together with its groove and gasket 31 divides the interfacial space between stationary end cover plate 26 and stationary end tube sheet .21 into three noncommunicating compartments.

Four nests of small tubes 38 are fastened into stationary end tubes sheet 21 with their ends in communication with the interfacial space between stationary end tube sheet 21 and stationary end cover plate 26. or otherwise expanded into tube sheet 21, as in the usual practice, as the rolling or other expanding operation requires such center to center spacing of tubes 38 that some of the highly advantageous results of this invention could not be obtained. In accordance with this invention tubes 38 are spaced on center to center distances much smaller than those required for rolling and the tubes are inserted in appropriate holes in tube sheet 21 to fit snugly therein and their ends then welded to tube sheet 21 by depositing welds 38. Tubes 38 may be fastened to tube sheet 21 in other ways. thus the ends of tubes 38 may be threaded and tubes 38 screwed into tapped holes in tube sheet 21 and the threaded joint sealed by welding; these modes of fastening tubes 38 in tube sheet 21 allow the employment of the minimum center to center distances and make it possible to produce a nest of tubes 38 whose flow area will closely approach or equal the available- Tubes 38 are not rolled for any particular unit 2| will depend on various factors such as the relation of thevolumes of the mediums to be passed through until 2| during a period of time, the size of tubes 38, and the amount of metal of tube sheet 21 required between tubes 38 for strength, the pressure heads available, etc. However, in every case the center to center distance chosen will be the smallest possible so that the one to one ratio will be obtained or closely approximated, as with this ratio the size and thickness of tubes 40 as well as the size and thickness of the elements of ends 24 and 25 will be a minimum. The one to one' ratio furthermore assures the maximum heat transfer rate as with it the mass velocity of the heat exchange mediums may be maintained equal or approximately equal, and turbulent flow of both mediums obtained without the use of any 1 means such as bailies for promoting turbulent flow. Since with the one to one ratio, or an approximation thereof, a maximum transfer rate may be obtained without the use of baifies, a true countercurrent flow of the mediums may be obtained. When the volumes of the heat exchange mediums to be handled per unit of time are unequal, a'departure from the one to one ratio may be necessary but such departure should be kept small in order to obtain the novel results of the invention. At present it has been found that ratios ranging from the preferred one to one ratio to a one to one and one half'ratio are satisfactory.

It is not always possible to obtain or approximate the one to one ratio merely by the close spacing of tubes 38 as in some cases, even if tubes 8|) and tubes 38 of proper relative size are chosen, more metal of tube sheet 21 and tube sheets 88 is required for strength between tubes 38 than the one to one ratio, or an approximation thereof, will allow. In such cases the one to one ratio may be obtained or approximated by using filler rods, or bars, 88. Filler rods 88 may be of circular cross section as shown in Figs. 3, 4 and 15, and either solid or hollow; also as shown in Fig. 16 filler rods 88 may be of triangular or rectangular cross section so as to occupy a greater amount of the area of tubes 88. Filler rods 88 may be spaced between all of the tubes or only some of them. To render the inside surfaces of the nests of tubes 38 more readily available for inspection and cleaning, the filler rod 88 at the center of the nest of tubes 88 may be omitted. Filler rods 88 may be positioned in various ways, thus they may be tack welded in place as shown, or dowels may be'welded or screwed into tube sheets 21! and 88 and the ends of rods 88 made hollow so that they can be slipped over the dowels and permanently positioned by tack welding one end to its dowel. It is to be noted however that even when filler rods 88 are used the tubes 88 are spaced on the allowable minimum center to center distances so that the'size and weight of the parts of unit 8i may be kept down.

The nests of tubes 88 are preferably arranged as shown in Figs. 4, 6 and 7 so that a pair of with which it communicates. To assure proper communication between tubes 38 and tubular members 4| and 42 tapered recesses 45 are provided. While the flow area of recesses 45 is greater than the flow area of tubular members 4| and 42 and the flow area of their respective nests of tubes 38, recesses 45 do not materially afiect the flow velocity of the heat exchange mediums or provide pockets for deposition of solids because of their shallowness and location. The flanges of tubular members 4|! and 42 are provided with holes 46 therein to accommodate connecting bolts 81.

The inside face of stationary end cover plate 28 is also recessed as shown in Fig. 4 to provide a crossover passageway 48 between the ends of the nests of tubes 88 that open in the larger of the compartments. The flow area of crossover passageway 88 is substantially equal to the flow area of each of the nests of tubes 88.

The larger tubes 88 are arranged on the same pattern as the nests of tubes 38 with each of the larger tubes 88 concentric with its nests of tubes 38. Each of the larger tubes 88 extends into a hole provided in stationary end shell flange 28 and is fixed to stationary end shell flange 88 by welds 88.

Tubes are spaced on substantially the minimum center to center distances that will provide suflicient metal between tubes 88 to withstand the stresses set up in service so that unit 2i will be as compact as possible and the weight of the component parts of its ends 88 and 28'will be minimum. Holes 88 and 88 into which open flanged tubular connectors 88 and 53, respectively, are also provided in stationary end shell flange 88. Tubular connectors 88 and 53 are connected to stationary end shell flange 28 by welds 88. Tubular connectors 88 and 88 each have a flow area that is substantiallyequal to the available flow area of a tube 88. Recesses are provided in the inner face of stationary end shell flange 28 at the ends of tubes 88. The recess in one of the smaller of the compartments between tube sheet 88 and stationary end shell flange 28 is connected by a passageway 88 to hole 88. The recess in the other of the smaller of the compartments is connected by a passageway 88 to hole 88. The recesses in the larger of the compartments are connected to each other by a passageway 88. These recesses and passageways 88, 88 and 88 are of a flow area substantially equal to the available flow area of tubes 88 so that a constant velocity of the heat exchange medium flowing through these passages and recesses and tubes 88 may be ob-- tained. It is to be noted that hole 88 directs the heat exchange medium flowing through it on to the face of tube sheet 8'8 so that tube sheet 28 in effect becomes an impingement bame. Tubular connectors 88 and 88 are provided with holes 58 therein to accommodate connecting bolts 89. I

The other ends of tubes 88 fit into holes provided in floating end shell flange 88. These ends of tubes 88 are connected to floating end shell flange 89 by welds 68. The face of floating end shell flange 29 that is adjacent bonnet 88 is recessed to providecrossover passageways 8i and 62. The flow area of each crossover passageway Bi and 62 is substantially equal to the available flow area of E tube 48. Each of crossover passageways GI and 62 connects the flow paths of a pair of tubes 40.

The floating ends of each nest of the smaller I6 tubes 38 are welded into a tube'sheet member 63 as best shown in Figs. 4 and 9. Tube sheet members 63 are of such size that they will readily pass through tubes 40 and the holes in floating end shell flange 29. The center to center distance between tubes 38 in members 63 is the same as that in tube sheets 21. Members 63 are surrounded by a combined sealing and bearing plate 64 that is fastened to floating end shell flange 29 by bolts 65. Sealing plate 64 as shown in Figs. 11 and 12 is preferably in two parts which parts when positioned are separated by the dividing plate 66 that is welded to bonnet 30. Dividing plate 66 contacts floating end shell flange 29 and thus divides bonnet into two substantially non-communicating compartments. The separating function of dividing plate 66 may be enhanced by the use of a suitable gasket. The bearings of bearing plate 64 contact with member 63 and assure the alignment oi member 63 and tubes 38 during the axial movement due to expansion and contraction of tubes 38. While some of the heating medium in crossover passageways 6| and 62 may flow between bearing plate 64 and members 63 into bonnet 30, no harm is done since it cannot leave bonnet 30 but can only flow back into the tube 40 of the next pass.

A crossover device 61 connects members 63 of adjacent passes. Crossover device 61 includes a pair of hollow yokes 68 each of which is adapted to encircle a member 63. Yokes 68 have shoulders at each end thereof. 14 at the end adjacent to member 63 is adapted to engage a split ring 69 that fits in a groove in member 63. The shoulder at the other end of member 68 is adapted to coact with a plate 10 that carries bolts H therein. Bolts ll exert pressure on connector 12 and thereby hold connector 12 in fluid tight relation on the end of member 63. Suitable gaskets 13 are provided between connector 12 and members 63 to assure the fluid tight joint.

The crossover device is assembled in the following manner. Yokes 68 are slipped over the ends of members 63. A connector 12 is then positioned on the ends of a pair of members ders ll engage rings 69. Plates 10 are then positloned and bolts 1| tightened until connector I! is tight on its seat. To disassemble crossover device 61, bolts II are loosened and plates 18 removed. After this, members 68 may be moved down to allow removal of split 'rings 69.

While the crossover device 61 just described is at present preferred, the invention is not limited to the use of this particular form of crossover device but other crossover devices such as crossover device 15 shown in Fig. 10 may be employed.

Crossover device 15 includes tubular bend 16 having shouldered ends over which threaded members II pass. By screwing members 11 on to the threaded ends of tube sheets 63 a fluid tight connection may be obtained.

. In either case the cross sectional area of the member that connects the flow path of adja- The shoulder cent nests of tubes 38, connector 12 or bend 16, is made' with a cross sectional area substantially equal to the flow area 01' a nest of tubes 38.

As above stated some of the medium flowing through tubes 40 may flnd its way into bonnet 30. Drain plugs 18 are provided for evacuation of bonnet 30 prior to the removal of bonnet 38 from contact with floating end shell flange 29.

It is to be particularly noted that the construction of heat exchanger unit H is such that a true countercurrent flow of the heat exchange mediums is obtained.

The component parts of unit 2| are easily accessible for inspection, cleaning and repair. Thusby merely removing bonnet 30, crossover devices 61 may be gotten at and by removing crossover devices 61, tubes 38 are made accessible. By removing bonnet 30, crossover devices 61 and stationary end cover plate 26, tube sheet 21 and tubes 38 may be removed so that the outside of tubes 38, or the inside of tubes 40 may be cleaned or repaired. When

necessary tubes

38 or 40 may be replaced easily and quickly by removing the weld metal that attaches them, substituting a new tube or tubes and attaching the new tube or tubes by new weld metal.

We claim:

1. A heat exchanger adapted for high pressure service including a plurality of larger tubes each of which houses a nest of smaller tubes, said smaller tubes being of substantially constant cross section, said larger tubes being connected to provide a continuous flow path of substantially constant flow area for one heat exchange medium, and said smaller tubes being connected to provide a continuous flow path of substantially constant flow area for another heat exchange medium, the flow area of said second flow path approximating or being substantially equal to the flow area of said first flow path.

2. A heat exchanger of the character described including a plurality of larger tubes connected to provide a continuous flow path for one heat exchange medium, a plurality of smaller tubes in each of said larger tubes, means to which said smaller tubes are attached supporting said smaller tubes in said larger tubes, each tube of each of said plurality of smaller tubes being spaced from adjacent smaller tubes on center to'center distances which are substantially the minimum compatible with safety and strength in the intended service, said pluralities of smaller tubes being connected to provide a continuous flow path for another heat exchange medium, the flow area of each of said plurality of smaller tubes being substantially equal to or approximating the available flow area of its respective larger tube.

3. A heat exchanger of the character described including a plurality of larger tubes assembled into a unit and connected to provide a' continuous flow path for one heat exchange medium through the heat exchanger, a plurality oi! smaller tubes 01' substantially constant cross section in each of said larger tubes, means to which said smaller tubes are attached supporting said smaller tubes in said larger tubes, said larger tubes and said smaller tubes being of such size and said smaller tubes 01 each plurality of smaller tubes being so spaced from each other in their respective larger tubes that the flow area through each plurality of smaller tubes approaches the flow area through its respective larger tube, and means in said larger tubes occupying such a portion 01' the are. thereof that the available flow area oi each of said larger tubes equals or approximates the flow area of its respective plurality of smaller tubes, said pluralities of smaller tubes being connected to provide a continuous flow path for another heat exchange medium through the heat exchanger.

4. A heat exchanger adapted for high pressure service comprising a plurality of larger tubes assembled into a unit and connected to provide a continuous flow path for one heat exchange medium through the heat exchanger, a plurality of smaller tubes in each of said larger tubes, a tube sheet into which one end of all of said smaller tubes is attached, a plurality of tube sheets into each of which the other" ends of the' smaller tubes in one of said larger tubes are attached, said smaller tubes being connected to provide a continuous flow path for another heat exchange medium through the heat exchanger, said smaller tubes being of such size and being so closely spaced in said larger tubes that the flow area of said smaller tubes approximates or substantially equals the available flow area oi said larger tubes.

5. A heat exchanger adapted for high pressure service comprising a plurality of larger tubes assembled into a unit and connected to provide a continuous flow path for one heat exchange medium through the heat exchanger, a plurality oi smaller tubes in each of said larger tubes, a tube sheet into which one end of all oi said smaller tubes is attached, a plurality of tube sheets into each of which the other ends of the smaller tubes in one of said larger tubes are attached, said smaller tubes being connected to provide a continuous flow path for another heat exchange medium through the heat exchanger, said smaller tubes being so closely spaced in said larger tubes that the flow area of the flow patch through each plurality of smaller tubes approaches the how area of its larger tube, and means in said larger tubes further reducing the flow area thereof whereby the available flow area through the larger tubes substantially equals the flow area of its respective plurality of smaller tubes.

6. A heat exchanger adapted for high pressure service which comprises a pair of spaced tube support members, a plurality of larger tubes between said support members and fastened thereto, said support members being formed to provide communication with the passageways of said larger tubes, a nest of smaller tubes in each oi said larger tubes, means positioned adjacent one of said support members carrying attached thereto one end of each of said nests of smaller tubes, said positioned means substantially fixing the ends of said smaller tubes attached thereto relative to said one supporting member and being formed to provide communication withthe passageways in said smaller tubes, a plurality of supporting means each of which has attached thereto the other ends of one of said nests of smaller tubes and is movably positioned adjacent the other end of the respective larger tube,

means connecting said larger tubes into a continuous flow path for one heat exchange medium, and means connecting the nests of smaller tubes into a continuous flow path for another heat exchange medium, '7. In a heat exchanger adapted for high pressure service, a plurality of pairs of larger tubes each of which houses a nest of smaller tubes;

inlet means for one heat exchange medium; outlet means for said one heat exchange medium;

a, support into which are fastened said inlet means, said outlet means and one end or each of said larger tubes; said Support having recesses therein; one of said recesses connecting said inlet means with one of said larger tubes, another of said recesses connecting said outlet means with another of said larger tubes and the remainder of said recesses connecting pairs of said larger tubes, a tube sheet to which is fastened one end of each oi said smaller tubes, adapted to be positioned against said support to close said recesses, said tube sheet having nests of holes therein that form continuations of said smaller tubes;

inlet means for another heat exchange medium;

outlet means for said other heat exchange medium; a cover member adapted to be positioned against said tube sheet into which are fastened said inlet means and said outlet means for said other medium; said cover member having recesses therein and being adapted to register with said nest of holes and to be closed by said tube sheet, one oi said recesses connecting said inlet means for said other medium with one of said nest of holes, another of said recesses connecting said inlet means for said other medium with another oi said nest of holes and the remainder of said recesses connecting pairs of said nests of holes, means adapted to hold said support said tube sheet and said cover member in fluid tight engagement, means connecting the other ends of said larger tubes in pairs, and means connecting the other ends oi said nests of smaller tubes in pairs.

8. In a heat exchanger adapted for high pressure service, a plurality of pairs of larger tubes each of which houses a nest of smaller tubes; a tube sheethaving a plurality of nests of holes therein into which are fastened one end of each of saidnests of smaller tubes; an inlet connector and an outlet connector for one heat exchange medium; a support member adapted to be positioned in fluid tight relation against one side of said tube sheet having holes therein into which are fastened said connectors and one end of said larger tubes; said inlet connector and said larger tubes entering their respective holes from the same side oi said support member; said support member having recesses therein; one of said recesses connecting said inlet connector to one of said larger tubes, another of said recesses connecting said outlet connector with another of said larger tubes and the remainder of said re cesses connecting the remainder of said larger tubes in pairs; said recesses being closed by said tube sheet whereby said tube sheet serves as an impingement and distribution bame for the me dium entering said larger tubes.

9. A heat exchanger as defined in claim 8 in which said inlet and outlet connectors, said holes exchange medium; a support member adapted to v be positioned in fluid tight relation against one side of said tube sheet having holes therein into which are fastened said connectors and one end of said larger tubes; said support member having recesses therein; one of. said recesses connecting said inlet connector to one or said larger 75 tubes, another of said recesses connecting said outlet connector with another of said larger tubes and the remainder of said recesses connecting the remainder of said larger tubes in pairs; an inlet connector and an outlet connector for another heat exchange medium; an end member adapted to be positioned in fluid tight relation against the other side of said tube sheet having holestherein in which are fastened said inlet and outlet connector for said other heat exchange medium; said end member having recesses therein in line with said nests of holes; one of said end member recesses connecting said inlet connector to one nest of holes, another connecting another nest of holes with said outlet connector, and the remainder connecting the remainder of said nest of holes in pairs.

11. A heat exchanger as defined in claim 10 in which said inlet and outlet connectors for said one heat exchange medium, and said holes and said recesses in said support member each have an eflective flow area substantially equal to the available flow area of each of said larger tubes, and said inlet and outlet connectors for said other heat exchange medium, and said holes and recesses in said end member each have an efiective flow area substantially equal to the flow area of each of said nests of smaller tubes.

12. In a heat exchanger adapted for high pressure service, a plurality of pairs of larger tubes each of which houses a nest of smaller tubes; a tube sheet having a plurality of nests of holes therein into which is fastened one end of said smaller tubes; a supporting member in which one end of each of said larger tubes is attached positioned against one side of said tube sheet; in let and outlet connectors for a heat exchange medium; an end cover member having holes therein in which said inlet and outlet connectors are attached adapted to be positioned in fluid tight relation against the other side of said tube sheet; said cover member having recesses therein which are adapted to register with said nests of holes and to be closed by said tube sheet, one of said recesses connecting one of said nests of holes with said inlet connector; another of said recesses connecting another of said nests of holes with said outlet connector, and the remainder of said recesses connecting the remainder of said nests of holes together in pairs; and removable means for holding said supporting member, said tube sheet and said end cover member in fluid tight engagement.

13. In a heat exchanger adapted for high pressure service, a plurality of pairs of larger tubes each of which houses a nest of smaller tubes; means supporting one end of each of said larger tubes and one end of each of said smaller tube nests in substantially fixed relation; a support member having holes therein into'which the other ends of said larger tubes are attached; said support member having recesses opening in the face of said support member opposite that into which said larger tubes enter, connecting said other ends of said larger tubes in pairs; a plurality of tube sheets having holes therein into which are attached the other ends of said nests of smaller tubes; one tube sheet being provided for each nest of smaller tubes and being of a size to pass through said recesses and said larger tubes; means adapted to support said tube sheets and to close the recesses; and demountable means connecting said tube sheets in pairs.

14. In a heat exchanger adapted for high pressure service, a plurality of pairs of larger tubes each of which houses a nest of smaller tubes; means supporting one end of each of said larger tubes and one end of each of said smaller tube nests in substantially fixed relation; a support member having holes therein into which the other ends of said larger tubes are attached; said support member having recesses therein opening in the face of said support member opposite that into which said larger tubes enter and connecting said other ends 01' said larger tubes in pairs; a plurality of tube sheets having holes therein into which are attached the other ends of said nests of smaller tubes; one tube sheet being provided for each nest of smaller tubes and being of a size to pass through said recesses and said larger tubes; bearing means supporting said tube sheets and closing said recesses; demountable means connecting said tube sheets in pairs; and a bonnet member removably positioned against said support member in fluid tight relation enclosing the outside face of said support member and said demountable means.

15. In a heat exchanger adapted for high pres sure service, a plurality of pairs of larger tubes each of which houses a nest of smaller tubes; means supporting one end of each of said larger tubes and one end of each of said smaller tube nests in substantially fixed relation; a support member having holes therein into which the other ends of said larger tubes are attached; said support member having recesses in the face thereof opposite to the face into which said lar er tubes enter connecting said larger tubes in pairs; the effective flow area of each of said recesses being substantially equal to the effective flow area of each of said larger tubes; a tube sheet of a size to pass through said recesses and said larger tubes for each of said nests of smaller tubes having a nest 01 holes therein into which are attached the other ends of said smaller tubes; bearing members attached to said support member adapted to support said tube sheets and to close said recesses; demountable means connecting said tube sheets in pairs; the effective flow area of said tube sheets and said demountable means being substantially equal to the flow area of each of the nests of smaller tubes; and a bonnet member removably positioned against said support member in fluid tight relation to enclose said demountable connecting means and said bearing means.

16. In a heat exchanger of the character described including a plurality of larger tubes each of which houses a nest of smaller tubes, said smaller tubes and said larger tubes being arranged to provide separate flow paths for heat exchange mediums, means for connecting adjacent ends of said nests of smaller tubes together in pairs at one end of said exchanger comprising, a tube sheet for each of said nests of tubes, said tube sheets having a nest of holes therein into which are attachedthe ends of the smaller tubes; a circumferential groove in the outside of each of said tube sheets; split rings adapted to flt in said groove and extend outwardly therefrom to provide a shoulder around each of said tube sheets; a hollow encircling member around each of said tube sheets having a shoulder at each end, the bottom shoulder of said hollow member being adapted to engage said split ring; cross-over members adapted to be positioned on pairs of said tube sheets to connect the flow paths of the tube sheets of said pairs; and pressure applying means adapted to engage the top shoulder 'of said hollow members and the top of said cross-over members cooperating with each pair of said hollow members, whereby said crossover members may be pressed in fluid tight relation on said tube sheets; said hollow. members having a portion of their sides cutaway to allow said cross-over members, said split rings and said pressure applying means to be operably posicombined sealing and bearing means through which said tube sheets extend adapted to support said tube sheets and to substantially seal said passageways, a bonnet member adapted to be held in fluid tight engagement against said support member to enclose said tube sheets, cross-over devices and said sealing means and dividing means attached to said bonnet member adapted to divide the space enclosed by said bonnet into a plurality of substantially fluid tight compartments each of which houses one of said cross-over devices and its pair of tube sheets.

18. In a heat exchanger of the character described including two pairs of larger tubes each of which houses a nest of smaller tubes, a floating end comprising a support member into which one end of the larger tubes is attached and having passageways therein through which extend said nests of smaller tubes, a tube sheet for each of said nests of smaller tubes, cross-over devices connecting said tube sheets together in pairs, 9. pair of combined sealing and bearing plates attached to the face of said support member through which said nests of smaller tubes extend, each of said plates supporting a pair of said tube sheets and substantially sealing the passageways through which they extend, a bonnet adapted to be held in fluid tight engagement against said face of said support member enclosing said tube sheets, said cross-over devices and said plates, and a dividing plate attached tc said bonnet'and adapted to coast with said face to divide the space enclosed by said bonnet intc a pair of substantially fluid tight compartment:

each of which houses one or said plates, its pai1 of tube sheets, and its cross-over member.

DUSTIN W. WILSON. STANLEY J. CHUTE. ROBERT K. HOPKINS.