US2256993A

US2256993A - Heat exchange structure

Info

Publication number: US2256993A
Application number: US346118A
Authority: US
Inventors: James G Van Vleet
Original assignee: Linde Air Products Co
Current assignee: Linde Air Products Co
Priority date: 1940-07-18
Filing date: 1940-07-18
Publication date: 1941-09-23
Anticipated expiration: 1958-09-23

Description

p 1941. J. G. VAN VLEET HEAT EXCHANGE STRUCTURE Filed July 18, 1940 2 Sheets-Sheet l lNV ENTOR JAMES G. VAN VLEET ATTORNEY p 1941- J. G. VAN VLEET 2,256,993

- HEAT EXCHANGE STRUCTURE Filed July 18, 1940 2 Sheets-:Sheet 2 INVENTOR JAMES G. VAN VLEET ATTORNEY Patented Sept. 23, 1941 UNITED STATES PATENT OFFICE,

nrza'r nxcmoa STRUCTURE James G. Van Vleet, Kenmore, N. Y, assignor to The Linde Air Products Company, a corporation of Ohio Aiml cation July 18, 1940, Serial No. 346,118

Ciaims.

employed for the transfer of heat between bodies of fluid flowing in heat exchanging relationship, if the transfer of heat is effected through the agency of finned tubes, one of the fluids ordinarily flows inside the tubes while another fluid is passed or repassed transversely across the tube in a direction generally parallel to the surfaces of the fins. Where more than one fluid is passed, or the same fluid is repassed, across a tube, or a bank oftubes, it is important to control, with more or less precision, the direction of flow of fluid across the tubes, to conflne the fluid to a desired zone and to prevent leakage or escape of fluid from one zoneto another, all as required according to a number offactors. For this purpose, baflies or partitions extending transversely of the tubes have 'been commonly employed. Furthermore, it is essential that tubes of substantial length be supported between their ends to avoid sagging, and in certain types of uses excessive vibration.

Heretofore the use of transverse baiiles with helically finned tubing has been found impracticable or attended with disadvantages and ob- Jections. Methods for the fabrication of struc-.

' are: the provision of improved structures comprising helically finned tubes or tubing in combination with plates or sheets extending transversely of such tubing and serving as bailles or supports for the tubing; and the provision of improved heat exchangers employing helically finned tubes.

H Still another object is to provide a heat exchange vessel of improved structure and efflciency which is particularly adapted for the countercurrent exchange of heat between high pressure air and one of the constituents of air in processes for the rectification of air involving compression and liquefaction.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in conjunction with the accompanying drawings,

in which:

Figure l is a side elevational view, partly in section, of a shell and tube heat exchanging structure embodying the principles of the invention;

Figure 2 is a section taken along the line 2-2 of Figure l, the tubes not being shown;

Figure 3 is an enlarged detailed view showing the arrangement of helically finned tubing with a transversely extending baflie or support, the view being partly in section along the line 3-4 of Figure 4.

Figure 4 is an enlarged detailed view, partially in section, showing one arrangement of a plurality of tubes extending through a battle or pp Figure 5 is a side elevational view showing a modified form of heat exchange structure embodying the principles of the invention.

Figures 6, 7, 8, 9, and 10 are details of modifications of the invention described hereinafter.

Figure 11 is an elevation of an arrangement modified from that shown in Figure 5.

Referring to Figures 1 and 2, the form of apparatus shown therein is a heat exchange vessel E of the shell and tube type, comprising a shell H, helically finned tubes l2, and tube sheets l3, ii. The shell II is provided with an inlet M and an outlet I5 for fluid flowing through the shell in heat exchanging relationship with the exterior surfaces of the tubes l2. Headers l6,

l1 are for the purpose of distributing fluid for flow through the tubes l2, and for collecting the fluid after it has traversed the tubes.

Within the shell I l are provided a number of flanged sheets or flanged plates l8 which serve both as supports for the tubes l2 and as baflies for directing the flow of fluid through the shell ll. As shown in Figure 3, the tubes H are provided with helical flns I! for substantially the entire length of the tubes within the shell. The helical flns of the finned tubes may be formed of ribbons or narrow strips of'metal which are attached in good thermal contact to the walls of the tube, as by welding, soldering, brazing and the like, or the fins may be formed integral with the tubes.

Each flanged sheet or plate i8 serving as a baflle or support for the tubes is provided with a tube receiving aperture or apertures 2|, which in each sheet correspond to the tubes in number. The aperture 2| includes a circular part 22 slightly in excess of the outside or external radius of the finned tubes. By root diameter of the finned tube is here meant the outside diameter of the tubing itself. The circular part 22 of the opening 2| should be slightly larger than the root diameter of the finned tubes but preferably I only to the extent that may be necessary for convenience in assembling the structure. 0n the other hand, it is desirablethat the finned tube fit as snugly as possible in the aperture 2| for the purpose of more firmly supporting the tubing by the plate and to minimize leakage between the plate and the tube. In any event, however, the tube receiving aperture 3| in the plate l8 should be smaller than the transverse section of the finned tubing. By transverse section of the finned tubingis meant the area to the outside 'diameter of the tube including the fin, taken transversely of the longitudinal axis.

The thickness of the sheet or plate, or at least that part thereof, immediately adjacent the aperture 2|, is so limited that the plate may be accommodated or positioned between adjacent turns of the fins. The slot 23 should be of such a width between the edges thereof as to accommodate the pitch .of the fln with the edges of the slot substantially in contact with the fin to minimize leakage between e fln and the sheet. If desired, the edges of the slot may be bent or flared slightly in the direction of the pitch to permit the use of a narrower slot, or the walls of the slot may be helical. A modification of the invention in which the edges 54 of the slot 53 are bent -or flared is illustrated in Figures 6, 1 and 8. Another modification of the invention in which the walls 64 of the slot 83 are helical is shown in Figures 9 and 10.

Thus it is seen "that the helically finned tubes I! may be screwed and secured into plates or sheets l8 provided with apertures-2|. In order to be able to screw the finned tubes l2 into a number of plates or baiiles as shown in Figure 1, it is essential that the centers of the circular part 22 of the apertures 2| for a given tube be substantially in alignment with the longitudinal axis of that tube for all such plates.

In assembling the shell and tube type structure, the sheets l8 may first be placed within the shell II and properly positioned and spaced by spacers 24. with the apertures 2| in substantial alignment, the tubes may be screwed through the bames' and longitudinally positioned within the shell I! beginning at either end of the shell. The shell may then be closed in the usual fashion by the tube sheets l3, l3. The connections between the headers |8 and I1 and the tubes l2 may also be made in the customary manner after the tubes II have been mounted tially the same as the inside diameter of the shell 'I l, are so positioned relatively to one anthe fins. Spacers 24'and tie bolts 25 extending axially of the shell 4| additionally assist in spacing and supporting sheets or plates i8. The- I tie bolts also assist in holding the tube sheets l3 against the ends of theshell ll. 4 Additional reinforcement of the tube sheets I3 may be provided by the tubes it, the unflnned ends of which may be sealedto the tube sheets as by welding, soldering, brazing and the like, or by 1 expanding. the tubes into tube sheet.

A wide variety ofpatterns and arrangements of helically finned tubing in combination with sheets and plates serving as baiiies and supports can'be employed in accordance with the principles of the invention to suit particular requirements. Such heat exchangers are not only more rugged in structure but also more efficient. Leakage through the baflies atthe openings where the finned tubes pass therethrough unusually small.

Referring to Figure 5, the form of apparatus shown therein comprises a heat exchange structure of the so-called. surface cooler type embodying the principles of the invention. It comprises helically finned tubes 3|, 32, 33, 34 and the openings in the 35 in combination with substantially parallel] sheets 38, 31 and 38,- which plates serve as supportsfor thetubes and may also serve as guiding elements or baflles for fluid flowing trans- 'versely across the finned tubes.

an angle of about 180 degrees relatively to the longitudinal axis of the remaining finned part of the tube; each reversely bent end is bent to such a radius that it is adapted to serve as a return bend in an assembly of finned tubes forming a heat exchangeistructure. End sheets 36 and 38, and intermediately positioned sheet 31-, are each provided with apertures of the type shown in Figures 3 and 4. The apertures in the several sheets are so aligned with respect to one another that tubes'3l, 32, 33, 34 and 35 can be screwed through the sheets to provide the structure illustrated in Figure 5.. Tube 33 which is a terminal tube without a reversely bent end, may be screwed into the plates beginning at either end plate 36 or 38. Tubes 3| and 33 are screwed into the sheets beginning at end sheet 36, and tubes 32. and 34 are screwed into the 43 and 44 are adjusted to bring them into alignment with the longitudinal axes of tubes 32, 33,

34 and 33, respectively. I

Because the reversely bent ends of' tubes 3|, 32, 33, and 34 are bent to such a radius as adapts them to serve as retum bends, as described above, (or, conversely, the aligned openings spaced from one another according to the radius of the return bends) each reversely-bent end maybe brought into substantial proximity and alignment withthe straight or unb'ent end 2,256,993 of an adjacent tube by turning the corresponding tubes in a clockwise or counterclockwise direction. The final adjustment may be made by cutting, trimming or building up the ends of the tubes, if necessary, and the tubes joined, as by welding, brazing, soldering and the like,

to form a continuous path for fiow of fluid therethrough.

In Fig. 11 there is shown a heat-exchange structure of the so-called surface cooler type very similar to the structure of Fig. in its fundamentals. For greater efiiciency of heat exchange, however, the finned tubes I2 in Fig; 5 are spaced so closely together, and the helical fins have such an outside diameter that the tips of the fins of adjacent tubes barely clear one another, thus substantially eliminating the open flow area between adjacent tubes found in ordinary structures.

It is not essential that the aligned openings for a number of tubes of a heat exchange structure be so spaced, relative to one another, that the tubes positioned therein are parallel. aligned openings for the tubes may be so spaced that the tubes areInon-parallel. In a heat exchange structure having tubes which are substantially horizontal or at a small angle to the hori-,

zontal, a non-parallel arrangement of tubes in series flow is of advantage where it is desired to provide a pitch to the tubes for the fall of fiuid flowing therethrough.

It is not essential that the slots for the fins be cut at the bottom of the circular part of the aperture, as shown in Figure 2 for instance. In structures in which the tubes extend substantially horizontally, it may be advantageous to cut the slot for the fin at a place above the bottom of the circular part of the opening in order to provide the best support for the tubes and to insure that the weight of the tube is not carried on the corners of the slot in on the edge of the fin.

The form of heat exchange structure illustrated in Figure 1 is particularly suited for the countercurrent exchange of heat between warm high pressure air and cool nitrogen gas in processes for the separation of air into two or more of its constituents. In such processes the high pressure air may be admitted to one of the warm high pressure air heaters, say I! in Figure l and, as it flows through the tubes or conduits I2, it is cooled by countercurrent heat exchange with cold nitrogen which may be admitted to the shell H through the inlet l4 'and be discharged from the shell at the outlet l5. Although the passes of nitrogenacross the tubes l2 in the passages defined by the plates l8 are essentially cross flow rather than counter fiow, nevertheless, the over all result very closely approximates a true countercurrent heat exchange relationship by the use of an appropriate number of baflies and passes.

One important reason for thehigh efliciency which it is possible to attain with heat exchange structures made in accordance with the present invention is that the finned tubes (I! in Figure 1 or 12 in Figure ll) can be placed more closely together than would be the case if the openings 22 were made as large as the outside diameter of the fins. In the latter case, adjacent tubes would .ordinarily be spaced so far apart that an If desired, the

open fiow space or area outside the fins would resuit. Thus, in accordance with the present invention a greater heat transfer surface can be provided per unit space while at the same time leaving ample metal in the baflie or plate to provide adequate strength for support even with very close spacing of the apertures. It has been found that a very desirable arrangement is one in which the tubes are so closely spaced that the tips of the fins of one tube barely clear the tips of the fins of an adjacent tube or tubes.

The forms of invention here described and illustrated in the accompanying drawings by ,way of examples are disclosed to indicate how .the invention may be applied. Other forms which may difi'er more or less in detail without difiering in principle, however, will suggest themselves to thoseskilled in the art.

I claim: I

1. An apparatus comprising, in combination, a helically finned tube and a sheet extending transversely of saidtube and being positioned intermediately of adjacent turns of the fin of said tube; said sheet being provided with an aperture for said tube smaller than the transverse section of such finned tube, said aperture including a circular part having a diameter at least as great as the root diameter of the finned tube and a radially extending slot having a length in a radial direction such that the radius of said circular part plus the length of said'slot is at least as great as the external radius of the finned tube; and said sheet being of a thickness, at least in the area immediately adjacent said aperture, to be accommodated between said adjacent turns of the fin.

2. An apparatus as defined in claim 1 wherein the slot is of such a width as to barely accommodate the fin therebetween, with the edges of said slot substantially in contact with the surfaces oi. said fin, whereby to minimize leakage between said fin and said sheet.

3. An apparatusas defined in claim 1 wherein the edges of said slot are bent or flared in the direction of the pitch of the fin.

4. An apparatus as defined in claim 1 wherein the walls of said slot are helical, conforming substantially .to the pitch of said fin.

5. An apparatus comprising in combination a plurality of helically finned tubes and a sheet extending transversely of said tubes and being positioned intermediately of adjacent turns of the fins of each ofsaid tubes; said sheet being provided with apertures for said tubes-smaller than the transverse section of such finned tubes, each. of said apertures including a circular part having a diameter at least as great as the root diameter of the finned tubes and a radially extending slot having a length in a radial direction such that the radius of such circular part plus the length of said slot is at least as great as the external radius of the finned tubes: said apertures being so closely spaced relative to one another that the tips of the fins of adjacent tubes barely clear one another; and said sheet being of a thickness, at least in the areas immediately adjacent said apertures, to be accommodated between said adjacent turns of the fins.

JAMES owmvmn'rp