US2391244A - Heat exchanger - Google Patents

Description

Dec. 18, 1945. I JJO; JACKSON 4 HEAT EXCHANGER Filed March 21, 1942 s sheets-sha 1 1 W QMM/ Dec. 18, 1945.. J. o. JACKSON HEAT EXCHANGER 3 Sheets-Sheet 2 Filed March 21, 1942 INVENTOR 3 Sheets-Sheet 3 HEAT EXCHANGER J O. JACKSON Filed March 2l, 1942 Dec. 18, 1945.

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HEAT nxcmmcaa James OQJackson, Grafton, Pa, assig'nor to Pittaburgh-Des Moines Company, a corporation of Pennsylvania Application March 21, 1942, Serial No. 435,750

This invention relates to the art of heat transfer, and more particularly to an improved heatv exchanger adapted for use in the liquefaction of natural gas, methane and other liqueflable gases.

Existing heat exchangers, although extensively employed and generally satisfactory, have certain inherent limitations, particularly when such-are employed in carrying out procedures or operations involving high pressures and/or low temperatures. The conventional type of heat exchanger has a flat or straight tube sheet and a flat-or dome-shaped closure at each end. In a heat exchanger of this character, the introduction of a gaseous medium at high pressure, e. g). at 2500 lbs. per square inch absolute, causes the straight tube sheet to flex or toassume a bowed or curved condition with the central portion entirely out of the plane of the peripheral portion. The amount which any particular tube sheet bends depends, of course, on the pressure 5 Claims. (01. 257436) producing a heat exchan er, the interior parts, of which are readily removable as a unit and yet which are so constructed and designed as to.

avoid the imposition of harmful axial stresses on the tube system even at pressures as high as 2500 lbs. per square inch absolute.

A still further object of the invention-is to provide a built-up welded structure which can be made from standard materials and thus which is relatively inexpensive.

A still further object of the invention is to produce a heat exchanger in which the tube shell may be composed of a special metal or alloy resistant to embrittlement and which even attemperatures as low as -260 F. has adequate ductility.

Other and further objects and advantages will be pointed out hereinafter or will be appreciated by those versed in the heat exchanger art.

In the accompanying drawings:

and on the thickness and nature of the material of that tube sheet, but such action unavoidably occurs and when it occurs it brings about undesirable and harmful stresses on the system of tubes extending between such tube sheets and secured to them. The result is that the tubes in the center of thetube system are placed under compression and the tubes around the outer portion of the. tube system are placed under tension, and the damage to the tubes is proportional to theextent of such stressing. In some in stances, this even causes a buckling of the central tubes and rupturing of the outer tubes. An-

other dimculty is that conventional heat exchangers do not stand up under low temperature v conditions because the metal or alloy of which they are made becomes embrittled, thus causing failure. Most heat exchangers are difllcult to disassemble andrepair and, in general, there are a number of disadvantages which are well rec-' ognized by engineers.

It is, accordingly, one object of my present invention to produce -a heat exchanger which, regardless of pressure conditions, does not adversely axially stress the tube system.

Another object of my invention resides in pro Fig. 1 is a vertical sectional view taken through a preferred form of heat exchanger responding to my present invention;

Fig. 1a is an enlarged fragmentary view of certain details of Fig. 1;

Fig. 2 is a cross-sectional view taken through v Fig. 1 along the line 11-11 thereof;

Fig. 3 is a diagrammatical cross-sectional view taken through a group or heat exchanger imits enclosed in a box and insulated to form a compact thermally emclent liquefaction or other ystem;

Fig. 4 is a view similar to Fig. 1 of a modified form of heat exchanger;

Fig. 5. is a cross-section through the heat exchanger of Fig. 4 taken on line' IV-IV thereof;

Fig. 6 is a fragmentary perspective view, partly in section, showing the manner of assembling and connecting certain of the. parts of the modified heat exchanger;

Fig. 7 is a plan view of the right-hand end of the heat exchanger of Fig. 4 but with the heat exchanger shell in horizontal section in order to show further the mode of assembling and connecting certain of the parts; I

Fig. 8 is a-longitudinal vertical sectional view of the box of Fig. .3 at right angles thereto and showing therein in elevation an exemplary group of heat exchanger units such as might be em ployed in a liquefaction system; and

Fig. 9 is a fragmentary view similar to Fig. 8

' of a somewhat modified form of box.

Referring now to the drawings, itwill be observed that the preferred heat exchanger of Figs.

1 and 2 is provided with a spherical header IE and II at the entrance and exit ends, respectively. Each such header is not only admirably adapted to'withstand high pressures but such spherical form has-the further advantage of having a minimum surface for a given volumetric capacity. The sphericalshape, besides being inherently the strongest structural shape, in addition provides a hemispherical or concavo-convex portion l2 and I3 each of which serves as a curved tube sheet. Such tube-sheet portions are provided with openings of the desired size and spacing for the re ception of the ends of the system or bundle of tubes which extends therebetween and which is made up of a number of copper tubes H which are preferably but not necessarily so arranged as to be equi-distant from one another throughout their length. The ends of such tubes are brazed, welded, galvanized, tinned, soldered or otherwise suitably secured in place in the said curved tube sheets l2 and l3.

At longitudinally spaced intervals, baflies l5 and [6 are provided which are substantially discshaped and provided with openings through which the tubes it pass. The tubes and baflles are suitably secured to each other as by brazing, welding, galvanizing, tinning or soldering. It will be noted that alternate baflies, those numbered I5, extend upwardly into close juxtaposition with the heat exchanger shell I! and that the lower end of each such baflle I5 is appreciably spaced from the bottom of such shell to form a planoconvex passageway. The other set of alternate 'baflles, those numbered 16, is of such nature that they are in close juxtaposition with the-bottom of heat exchanger shell l1 and are appreciably spaced from the top thereof to form a pianoconvex passageway. A pair of end baiiles I6 is provided, as shown, the diameter of which is only slightly less than the internal diameter of shell I! and which effectively limit the longitudinal penetration of the cooling medium within shell 11.

These baflles divide that portion of the shell between ports l8 and is into a series of connecting compartments through which the fluid medium entering inlet port l9 travels to outlet port IS; the fluid medium passing successively through the compartments with a reversal in direction of flow through adjacent compartments of the series.

Located between each pair of spaced baflies l5, l6 and I6 are disposed a plurality of secondary or intermediate baiiies l6" which take the form of plate flns which are arranged in groups or sets, as shown. Each of these plate fins I6" is provided with apertures suitably arranged so as to enable the heat exchanger tubes M to pass therethrough. The plate fins are secured to tubes M in the manner of baflles l5, l6 and I6.

' The plate fins are provided at their top and bottom portions with curved guides or deflectors constituting curved turning vane extremities, it being noted that these are oppositely curved with respect to each such baflle. The structure of batfles I6" is such that theexchange efliciency is greatly improved, the effective exchange area is further increased, channeling" of the coolingmedium is prevented and a uniform distribution or the cooling medium is effected. In-addition.

such group of intermediate baffles '(except the terminal group at each end) the individual baffles are arranged either as a descending or as an ascending series. Referring to Fig. 1, for example, it will be apparent that the intermediate baffles l6" between the main baflles l5 and IS (the first set to the right of inlet 35) are successively lower toward the entrance (right hand) end of the heat exchanger, that between the next main bafiles I6 and I5 each intermediate baffle in the group of tour baflies is disposed successively higher and that the main baffles alternately have their top and bottom portions flush with the tubes H so as not to interfere with the action vided with the deflector portions aforesaid only I as to that portion of each of the intermediate baflies which is remote from each such opening as will be appreciated from Fig. 1. In the former case, the baffles l5 and I6 effectively direct the incoming cooling fluid medium in the desired direction and prevent undesirable spreading or wasting of the cooling medium by retarding its penetration. to that portion of shell H which lies rearwardly of the contiguous end balile IS. The arrangement at outlet opening 18 is the same in principle but oppositestructurally so as to direct the cooling medium to the outlet fitting 34.

Particular attention is directed to the fact that as the cooling medium travels from inlet fitting 35 to outlet fitting 34 its direction of movement is predominantly normal. to the direction or axis of the tubes it. As cooling medium enters shell I1 via inlet fitting 35 it passes directly downwardly between the various bafiles above described, is turned through approximately by the bottom deflector portions of such baiiies, is received by and again turned through 90 by the bottom deflector portions of the next group of intermediate baflies and is thereupon directed upwardly and the stream of cooling fluid is subjected to a number of additional reversals in direction of flow as will be readily understood from Fig. 1 until it is eventually directed out of shell I! via outlet fitting 34. The effectiveness as well as the thermal efllciency of the arrangement described is far beyond that which can be secured by means of prior heat exchangers. In its travel longitudinally of shell I! the cooling fluid is caused to follow an up-and-down tortuous path, the major proportion of which is vertical, either upward or downward, and thus differs markedly from heat exchangers in which the direction oi'flow of the cooling fluid is chiefly longitudinal or parallel to the axis of the shell and its interior. tubes. Since the medium to be cooled is introduced into tubes It'via head tube 26 and leaves by way of tail tube 22 the advantages of the countercurrent principle of heat exchange are also secured.

The tube sheet l3 of spherical header H is welded, as at 20, to an opposed hemispherical member or portion 2l--the header being preferably composed of two substantially equal halveswhich is provided with an opening for the reception of the tail tube 22, one end of which is securely welded as shown at 23" and 24' within such opening. The tail tube 22 extends axially through a stufling box 23 which is on the discharge end of the heat exchanger shell II. The construction of the stufllng box is conventional and reposed hemispherical portion ll having an opencal shape, being made up of a substantially hemispherical portion Ila provided with a central opening in which is'secured as by welding .IIa one end oi a head tube "a, the distal end of which is provided with a flange member Ila welded in position and adapted for connection to the discharge end oi'another unit or to other equipment. The other portion of the head Ila is a concave-convex tube sheet. I2a of relatively ing for the reception of one end of the head tube a, one end of which is welded or otherwise suitably secured in place therein, as at 21, and the other end of which is provided with a flange is welded at to the tube 26 and adapted for con- ,nection to another heat exchanger or to other equipment. The-tube sheet portion I2 of such spherical header II is provided with an apertured flange member extension 3| welded thereto at II which is located between an apertured flange 3| welded at I to and extending at right angle'sirom the heat exchanger tube I1 and an apertured flange 32 secured by welding 32' or otherwise to the hemispherical portion of the header. Members 30, SI and I! are bolted to gether, as shown at 31, andhave opposed,annulaxyflat-bottomed pairs of grooves ll", 3i" and 32" between which are the wire (preferably copper) gaskets g, as will-be understood best from Fig. la. The heat exchanger shell I1 is provided with an outlet nozzle or fitting 34 and an inlet nozzle or fitting 35, which consist oishort tubular members disposed in openings It and I9 provided for that purpose in the shell I1 and welded to the shell and a flange member 38 and 31, respectively, positioned around and welded to the distal end of each such tube member and adapted for connection with similar members of other heat exchanger units or to other equipment.

In any heat exchanger unit which is subjected to low temperatures, and this is usually the case with the third and subsequent units in a liquefaction system, theshell I1 is composed of a material which resists embrittlement and has adequate ductility at the lowest temperature involved. While such shell can be made of copper or aluminum or of an'austenitic steel like 18-8, I prefer to employ nickel steel containing approximately 3%,% 01 nickel, but any amount of nickel between about 3% and about 4% is fully satisfacscope of the term "approximately 3/z% of nickel. In my opinion, any metal or alloy which advantageous depending upon the temperature and other conditions involved in a given installation and thus I have determined that I may em- Charpy impact value. is at least ion. lbs. for a given temperature-unto about 10%.

In the modified form of heat exchanger iuus- 'trated in Big. 4 et seq.. the'construction is generally 'gimilarto that or l 'lgt l with certain noted exceptions. This inlet header Ila at the entrance end orthe heat exchanger is of modifled spheri large radius in which one end of each of tubes Ila is fixed and provided with a flange extension.

"a which is bolted at 33a or otherwise suitably secured to and between a flange 32a welded to the edge of hemispherical member'ila and a flange tIa welded on the outside oi. the heat exchanger tube Ila. Copper wire gaskets may be provided as shown in Figs. 1 and 1a.

The header Ila atthe other end oi the heat exchanger is-likewise not a true sphere, as compared with the construction otlig. 1. In Fig. 4, I build up the header IIa from a short cylinder or tube 3| 0: less diameter than shell Ila one end oi' 'which is provided with a concavo-convex tube sheet portion Ila suitably welded at 20a to the contiguous end oi the cylinder and the other end of which is provided with a concavoconvex member Zia similar in shape to the tube sheet portion Ila and welded at 20a to the other end of the cylinder 18 but provided with a central opening in which is secured, by welding 23a or the like, one end 01' a tail tube 22a. the Y Y distal end of which is provided with a welded-on tall tube flange 24a which is small enough to pass through shell Ila during disassembling of the heat exchanger.

Another distinction between the structure 0! Fig. 4 and that shown in Fig. 1 resides in the employment of the side vanes 30 which are thin strips of suitable metal or alloy such as copper tory and is intendedto be included within the and are usually made oi the same material as the tubes Ila but I wish it distinctly understood that suchvanes may also be, and in many cases are, employed in the Fig. 1 form 01' the. invention. As will be especially noted from Figs. 4-7, vanes 39 reduce the effective fluid-carrying capacity oi the tubular shell Ila to a predetermined value so that there can be readily obtained thedesired or requisite ratio between the net fluid-carrying capacity of the shell and that of the tubes. In this way it is possible to employ a standard pipe size for the shell Ila and to adjust 'or alter its fluid-carrying capacity by means of the said vanes. This is both desirable and highly advantageous.

In the structure of Fig. 4 et seq., the bailies Ila are disposed in the same manner as thebailles ploy nickel 'inyany-smount from a fraction of .iqt-i. e1. 'the=minimum amount at which the II in Fig. 1, but the babies IIa have straight sides, as will be apparent from Fig. 5, instead of being substantially disc-shaped as shown in Fig. 2. The nature of bailles Ita will be equally apparent. The vanes 39 are preferably continuous and suitable connections are made between such varies and th'elbailles, such as by the use of the angle brackets shown at III, but it is to be understood that other'modes oi connection or any suitable connecting instrumentality may equally well lie-employed. In this form of the invention. it will be noted that piano-convex passageways lI' are left between thevanes and the sides of the shell Ila. These are inactive spaces and since the vanes ll extend substantially from tube sheet to tube sheet. and since the outlet "a for the cooling medium is connected into shell 'I la rearwardly of the forward ends J oi thevanes, it will be apparent that such cool- 4iing medium does not-enter the said spaces II and, therefore, that the desired proportion is maintained between the reduced cross-sectional area of the shell and the cross-sectional area the tubes of the tube system.

Intermediate or secondary baflles "a" are provided between the main or primary baffles and are similar to batlles I6", above described, except that theyare not provided with the curved or deflecting end portions characteristic of bailles IS". The bailie structure of Fig. 1 way. however, be employed equally well here and the arrangement and functioning of baiiies IBa" will be understood from what has preceded. The path of the cooling medium is likewise predominantly normal to'the axis of the tubes Ila and such cooling medium follows an up-and-down tortuous path between the inlet 35a and the outlet 34a. The general direction of travel of the cooling medium is also counter-current to the medium to be cooled which enters via head tube 26a and leaves via tail tube 22a.

The remaining parts of the heat exchanger of Fig. 4 are generally similar to those of Fig. 1

as will be appreciated from the numerals employed. In Fig. 4, however, .it should be particularly noted that the stumng box 23a is of an alternate type as compared with that of Fig. 1 and whereas in the latter construction the stufiing box 23 is relatively small and cooperates with tail tube 22 in the former the stufling box is substantially of the same diameter and size as the tube shell IIa itself. Thus, stufling box 23a cooperates directly with the tubular portion 38 of the spherical type header I Ia. Contraction and expansion can take place readily through this enlarged stufling box 23a and therefore avoids the necessity of a screwed connection between fiange 24a and tube 22a and permits welding or otherwise permanently securing the two parts together. Moreover, the headers of Fig. 4, although not true spheres, partake of spherical nature and the advantages of the spherical form The significance of such will be appreciated by those skilled in this art.

In Figs. 3 and 8 I have illustrated, somewhat diagrammatically, a set of heat exchanger units I, which may be of any suitable or desired construction such as either that of Fig. 1 or Fig. 4 and as shown a set or system of heat exchangers has been grouped together within an enclosing metal box 2. Within the box the units are maintained equi-distant from one another or in any desired relative positioning by means of transverse spacers 3, which, while preferably made of wood, may be composed of any suitable material which is a poor conductor of heat. Spacers 3 are located alongthe length of the box and units at intervals, as will be noted from Fig. 8, and these intervals are suitably selected so as to maintain the units in properly positioned and supported condition, but preferably in such manner as to avoid the imparting of bending or other undesirable stresses to the said units. The unoccupied spaces within the box are filled with a suitable heat-insulating material. which may, for example, be granulated cork but which may be oi any other thermally effectiv material.

From Fig. 8 it will be observed that the box 2 is made in three parts, namely, a body portion and a pair of end closures 5. Such closures are detachably bolted or secured to the body portion oi the box as by means of the angle brackets 6 bolted together at 'I. Each end closure is also provided with an eye" I by means of which it may be removed by a hook or the like operated by a crane or winch (not shown). Each end closure member 5 is filled with a granular heat-insulating medium such as cork which has been mixed with a suitable binder and molded-in in such form or configuration as to cooperate properly with the projecting ends, couplings, etc., of the various heat exchanger units. In other words, the molded insulating material designated a 9 has recesses to receive the portions of the heat exchanger units which extend beyond the body portion of the box 2. In Fig. 9 the arrangement is modified to the extent that each end closure 5a is provided with an opening 5a by means of which granular cork or other suitable heat-insulating material may be introduced into the said end closures after the same have been assembled withthe body portion of the box. In this form of the invention enough granular insulating material is introduced to fill the end closures and this automatically positions itself around the heat exchanger parts which project thereinto. In such case also no binder is employed so that when the end closures are removed the granular insulating material runs out but it can be'readily collected and reused.

It will be appreciated that by removing either of the end closures 5 accesscan be readily obtained to the ends and/or connections of the various heat exchanger units. Various connections can also be made and likewise the connections can be changed in any desired manner. In addition. when the appropriate end closure 5 has been removed, that spherical or spherical type header which is detachably connected to the entrance end of a given heat exchanger can be disconnected and the bundle of tubes with its bafiles and associated parts can be readily withdrawn from the shell of the header as an integral unit for any desired or required purpose.

The arrangement is further such that a continuous path is or can be provided for the coolin or heat exchanging medium and not only is there provided generally countercurrent flow of cooling or heat exchanging medium with relation to the medium to be cooled for each individual heat exchanger unit but the group of units as a whole or any sub-group within the enclosing box likewise has the cooling or heat exchanging medium flowing in countercurrent relationship with the medium tobe cooled. While as above stated the heat exchanger units I can be inter-connected in various ways, as shown in Fig. 8 the medium to be cooled enters at the arrow A, travelsfr'om right to left of that particular heat exchanger unit and then may pass directly to the next lower unit I in which it travelsfrom left to right and so on until it is discharged at the arrow B in the condition desired, for example, asa liquified gas, or, since it will be understood that a plurality of vertical rows of units I are-or may be employed, the medium to be cooled may alternatively pass horizontally or laterally to another row or rows eventually returning to the appropriate unit visible in Fig. 8. Similarly, the cooling or heat exchanging medium enters the system at the arrow C, travels from right to left of the lowermost unit I and, as in the. case of the medium to be cooled, eventually works its way up to the topmost unit I where it is discharged atthe arrow D. It is not essential that a direct path be provided from C to D, nor does'the arrangement illustrated fully show such but it is to be understood that, in the manner explained in connection with the medium to be cooled, the cooling or heat exchanging medium may travel laterally or horizontally to another row or rows depending upon the'particular installation and the results to beachieved.

The arrangement of heat exchanger units within the box is thus not only susceptible to many variations but a group of heat exchanger units assembled in a box provides a flexible and a versaheat exchange operations which take place during.

liquefaction it is to be understood that the present arrangement is not restricted or limited thereto and that the particular illustration and description is intended to be purely exemplary.

It will be appreciated from the structures above described and from the underlying conception upon which the present invention is based that curved tube sheets are not subject to the defects and disadvantages pointed out above in connection. with flat or straight tube sheets. The fact that the curved tube sheet is a part of a header which is either spherical or of near spherical shape not only produces a much stronger construction and one in which the high pressure fluid is advantageously confined to relatively small headers and tubes but tube sheet movement is practically nil and any very slight amount of movement, which might occur under high pressure is not of such character as to bring about undesirable bending stresses on the tube system. The construction is also unusually free from temperature stresses due to contraction and expansion. If any slight stresses are imparted to the tubes, such will be of negligible amount. Conditions thus do not arise which would cause buckling of the central tubes or rupturing of the peripheral'tubes. Such an arrangement, particularly in conjunction with the ready removability of the internal parts of the heat exchanger as a unit, constitutes important parts of this invention. Removal of those internal parts as a unit is accomplished, as will be appreciated, by detaching (unscrewing) the tail tube flange (Fig. 1 only) and unbolting the flanges on the forward tube sheet, whereupon the unit may be slid out after loosening up on the stufling boxes.

The foregoing is intended as illustrative and not as limitative and within the scope and principleshereof other and further additions, omi s sions, substitutions and modifications may be made. The invention is rather that defined by 5 the subioined claims. The expression spherical type header" is employed in the claims in a ge-' neric manner to designate both headers in accordance with Fig. 1 which are true or substantially true spheres as well as spheroidal or near spherical headers such as those illustrated in Fig. 4 in which the headers partake of the nature of spherical headers and have similar advantages.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A heat exchanger comprising a tubular shell having longitudinally spaced inlet and outlet ports, a bundle of tubes extending longitudinally of the shell, a series of parallel baflles carried by said tube bundle, extending at right angles to the major axis of the shell and dividing the shell between said ports into a'series of. connectingcompartments so constructed and arranged as to cause the fluid entering the inlet port to reverse its direction of travel through adjacent compartments of the series, and a series of plate fins car-- ried by the tube bundle between said baflies, arranged'in parallel relation thereto and each having oppositely curved fluid directing terminal portions; the construction and arrangement being such that fluid entering said inlet fiOWs successively through said compartments, is separated by said plate fins into relatively thin parallel layers, and friction in the fluid entering and leaving the compartments is minimized by the oppositely curved fluid directing terminal portions of said plateflns.

2. A structure according to claim 1 .in which the plate flns in each compartment have their curved terminal portions located within the space between the tube bundle and the shell and positioned at .diflerent distances from the major axis of the tube bundle.

3. A structure according to claim 1 in which the plate fins-in line with the inlet and outlet ports have curved terminal portions only at their ends remote from such ports; said terminal portions curving toward the opposite port.

4. A structure according to claim 1, in which the terminal portions of corresponding plate fins in adjacent compartments are curved in opposite directions.

5. A- structure according to claim 1, in which the distance between the major axis of the tube bundle and the curved terminal portions of the flns at the inlet end of each compartment increases from the inlet port side of the compartment to the opposite side thereof, and at the outlet end of each compartment increases from the outlet port side thereof to the opposite side.

JAMES O. JACKSON.

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