US3249154A - Heat exchanger - Google Patents

Description

May 3, 1966 P. LEGRAND 3,249,154

HEAT EXCHANGER Filed Nov. 3, 1961 2 Sheets-Sheet l H 'ma 1 10o 470 May 3, i966 P. LEGRAND 3,249,154

HEAT EXCHANGER Filed Nov. :5. 1961 2 Sheets-Sheet 2 United States Patent O 3,249,154 HEAT EXCHANGER Pierre Legrand, 98 Rue de Rennes, Paris 6, France Filed Nov. 3, 1961, Ser. No. 149,928 Claims priority, application France, Nov. 23, 1960, 844,720; June 7, 1961, 864,173 1 Claim. (Ci. 165-164) This invention relates essentially to heat exchangers and notably to heat exchangers of the type comprising a nest of parallel longitudinally aligned Itubes adapted Ifor eecting heat transfer ibetween Ia heat exchanging medium passing through the interior of said tubes and an external iluid tilowing in a generally longitudinal direction through said nest along the external surf-aces of said tubes.

A primary object of this invention is to promote the efficiency of =a heat exchanger of the type referred to by creating a secondary transverse movement vof the external fluid, namely, by introducing between adjacent -tubes helically wound strip means adapted to impart a gyratory motion to said tiuid.

It is lanother object of this invention to promote the efficiency of a heat exchanger of the type referred to by forming on the tube integral iin means extending substantially transversely thereof, with a view to increase the area of said tubes in contact with said fluid, and t-o promote and maintain said gyratory motion.

It is a further object of this invention t-o provide a heat exchanger `of the type referred to, having a compact 'and reliable structure.

The heat exchanger according to lthis invention comprises a nest of longitudinally extending parallel tubes .adapted for the passage therethrough of the heat exchange medium to effect heat ytransfer between said medium and an external -uid circulating in a -generally longitudinal direction through said nest alon-g the external surfaces of said tubes. The outer surfaces of said tubes are peripherally grooved to Ifor-m on said surfaces integral tn means extending substantially transversely of said tubes. The tubes are arranged in an yarray of rows and columns such that `the axes of said tubes respectively detine a regular triangular lmesh pattern in which a tube in :any one row forms a regular triangle with -two adjacent tubes, -at least one `of which lies in an adjacent row. vOn the outer surface of selected tubes are provide-d helically wound strip means, Iwhile the remainder f the tubes are bare or plain. The tubes with the strip means are selected such that each plain tube is surrounded by tubes with strip -means thereon and in each row there is alternately disposed a plain tube .and Itwo tubes Vwith strip means thereon. Moreover, the strip means are helically wound in opposite directions on adjacent tubes, each strip means contacting the outer surface of an `adjacent tube such .that each tube with strip means thereon is disposed between a bare tube and a tube with strip means thereon which is Wound in an opposite direction, while each bare tube is disposed between two tubes with strip means thereon which are wound in opposite directions.

Further objects and features of the invention will become apparent from the following description taken with reference to the attached drawing in which:

FIGURE 1 illustrates diagrammatically in cross section one portion of a nest of heat exchange tubes according to the invention,

FIGURE 2 is a diagramrnatical side elevational view showing one row of tubes as taken along arrows II-II in FIG. 1,

FIGURE 3 is a detail view, with parts shown in axial section, of one end .of the nest illustrated in FIGS. 1 and 2, and

4.adapted to impart a gyratory motion to the iluid.

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FIGURE 4 is a cross-section taken along line lV-IV of FIG. 3.

According to a preferred embodiment of the invention as illustrated in the drawing, a heat exchanger comprises a triangular mesh nest. iln this respect the nest is considered to be comprised of bare tubes lil arranged in an .array of rows and columns such that the axes of the tubes 10 respectively dene a regular triangular mesh pattern in which a tube in Iany row for-ms a regular triangle with two adjacent tubes, at least one of which lies in an adjacent row. A iluid medium circulates externally of the tubes in a generally longitudinal direction, for example -from top :to bot-tom, and contacts the walls of the tubes which are formed with relatively shall-0W peripheral grooves extending transversely. In order to improve the efliciency of Ithe heat exchanger a rotary motion is imparted to the circulating duid in each stream formed between adjacent tubes 1@ by interposing between the tubes further tubes similar to those of tubes 10 but having wound and secured thereon a fiat, spiral-forming strip In the embodiment illustrated in FIGURE l there is interposed between adjacent tubes 10 tube 11 similar to tubes 1t) but having wound and secured thereon, for example by spot welding, a dat forming strip 12. This strip `12 extends preferably normally to the surface of the tube on ywhich it is wound and secured. From FIGURE 1, it will be seen that the width of strip 12 is such that its outer edge engages the wall of the tubes 10. In the mesh consisting of the two tubes 10 located respectively in the lower left-hand corner and in the center of IFIG. 1 and of the tube 10 of which only one half is visible in the middle of the lower border of the tigure, there is disposed another tube 114 having wound thereon a spiral-forming strip 1S of which the pitch is opposite to .that of spiral 12. With this arrangement, the tluid streams circulating from top to bottom will obviously be forced along a transverse lgyratory path shown by the arrows of FIG- URE 1 and 2. Since the pitches of the spiral strips have opposite directions on adjacent tubes such as 11 .and 14 or 14 and 16, it is possible as shown in FIG. -2 to imbri- `cate the strips associated with these tubes and to bring the strips in contact with the outer walls of the adjacent tubes, `whether these tubes themselves are provided with strips or not. Thus, a compact tubular nest is obtained, wherein the tubes bear against one another and are thus protected against vibration. As shown in FIGURE l, `the num-ber and cross-sectional area of vertical by-pass passages through ywhich the fluid might flow directly without producing the necessary heat exchanges are relatively low.

The heat exchanger structure as hereinabove described could be considered as well in terms of an array of tubes. Indeed, any one of the tubes shown in FIG. \1 pertains to three angularly equidistant rows of tubes, such as the row along line II--II shown in elevational view in FIG. l2. In each row a bare tube, such as -tube ,10, is located between two tubes such as tubes 11-17, `14, 19 or `1li-18, provided :with iin-like strip means wound helically thereon according to Iopposite pitches respectively. Similarly, tube 11 is disposed between a bare tube 10 and a tube provided with opposite pitch helical strip means, such as tubes 14 or '18, according .to the row being considered.

The heat exchanger structure as shown could be fur- .ther described by yconsidering tha-t any one of the tubes shown in lFIG. 1 is surrounded by six adjacent tubes, and that these seven tubes constitute a unit mesh of ,the heat exchanger nest.

From a mere consideration of the figure, it will clearly appear that in each such mesh, the central tube, whether it is bare or provided with left-hand or right-hand helical strip means, is surrounded by six tubes in a particular arrangement. 'By way of example, the bare tube 10 located centrally of FIG. l is surrounded by - tubes 11, 16 and v19, provided with lefthand wound helical strip means 12 and by tubes .14, 17 and .18 provided .with right-hand wound fhelical strip means 15, Whereas each tube with a strip means thereon is surrounded by alternating bare tubes and tubes with strip means thereon in which the latter are all wound in opposite direction with respect to the strip means on the central tube.

FIGURES 3 and 4 illustrate the manner in which Ithe seven tubes 10, 11, 14 land 16-19 constituting a central hexagonal mesh in FIG. l are interconnected at their upper and/or lower ends in the case of a vertical heat exchanger, the tube end portions being left plain after the formation of the ns, splines, ribs, grooves or low-pitch threads therein. The central 4tube -10 has six circular ports formed Itherein, these ports being disposed as shown by `diarnetrally opposite pairs in three superposed planes intersecting the tube axis at 60-degree intervals, the necks of the bent ends of tubes |11, y1&1, 16, 17, 18 and 19 being welded on the wall of the central tube `10, as shown.

As shown in FIGS. l and "2 the main portion of each tube has tted therein a cylindrical core such as a, Illa, s17a, etc. in a cylindrical or tubular core such `as 11a, 10a, 17a closed at top and bottom by a streamlined, water-tight or nearly water-tight tip portion as shown at 11b, 1Gb and 17b in FdG. 3. Thus, the cross-sectional area of the annular space formed between the tubes 1/1 and 11a, 10 and 10a, 17 and 17a corresponds substantially to that of the tapered and -bent end portions of these tubes which connect the latter to the central tube 10.

With this arrangement the six mesh-forming tubes can be connected to the central tube by means of slightly tapered end portions without restricting the cross-sectional area available for the passage of the inner tluid. This arrangement is particularly valuable in the case of nuclear reactors wherein the number of welds should be as small as possible.

IFor properly wedging the central ltubular core in the tubes and improving the heat exchange, it is advantageous to provide a tube, braid or spiral-wound strip of a width of thickness substantially equal to the radial dimension `of the annular space left between the outer surface of .the core and the inner surface of the tube. The provision of this spiral or coil-wound distance-piece ensures a proper stabilization in case of a vertical heat exchanger in which the water reheat followed by the water vaporization and rlinally the superheating of the steam thus produced are accomplished sequentially at different levels. By providing a non-sealed central tubular core, that is, a tubular core more or less open at its ends, this specic operation is improved since it is possible to constitute within this core a make-up reserve of water which, during the operation of the heat exchanger, has a temperature increasing gradually from bottom to top up to vaporization temperature.

The construction of the device just described is particularly convenient if tubes 4having end portions are used with a view to form the tapered tips mentioned hereinabove to permit the proper connection of the tube constituting one mesh with the main or central tube.

FIGURE 4 illustra-tes by Way `of example this hexagonal distribution of the six tubes 11, 14, 161, 17, 118 and 19 about the central tube 10.1

Of course, this invention is also concerned with a tubular nest having a square pattern.

Although the present invention has been described in conjunction with a preferred embodiment, it is to be understood that modilcationsy and variations may be resorted to without departing from the spirit and scope of Ithe invention, as those skilled in the art will readily understand. Such modications and variations are considered to be within the purview and scopeof the invention if defined by .the appended claim.

What I claim is:

A heat exchanger comprising a plurality of longitudinally extending parallel tubes adapted for the passage therethrough of a heat exchange medium, said tubes being arranged in an array of rows and columns such that the axes of said tubes in any lone row forms a regular triangle with two adjacent tubes at least one of which lies -in an adjacent row, said tubes being adapted for the passage along .the external surfaces thereof of a second heat exchange medium, said tubes having peripheral transverse grooves in the .outer surfaces thereof, said grooves extending substantially perpendicular to the longitudinal direction of the tubes, helically wound strip means on the outer surface of selected tubes, the remainder being plain, said tubes with the strip means being selected such that each plain tube is surrounded by tubes with strip means thereon and in each row there are alternately disposed a plain tube and two tubes with strip means thereon, said strip means being helically Wound in opposite directions on adjacent tubes each strip means contacting the outer surface of an adjacent tube, such that each tube with strip means thereon is disposed between a plain tube and a tube with strip means thereon which is wound in an opposite direction, While each plain tube is disposed between .two tubes with strip means thereon which are wound in cpposi-te directions.

References Cited bythe Examiner UNITED STATES PATENTS 2,406,121 8/1946 Young 165-74 2,998,228 5/1961` Huet 16S-'177 3,030,292 4/ 19162 Ritz 11615-18@ 3,030,293 4/ 1962 Wyatt 165-184 3,111,168 11/1963 Huet 1615-183 X FOREIGN PATENTS 3,980 4/f1-90'1 Austria. 27,6184 l11/1910 Great Britain. 308,651 10/ 1955 Switzerland.

ROBERT A. OLEARY, Primary Examiner.

`CHARLES SUKALO, FREDERICK L. MAT'IESON, JR., T. W. STR-EULE, Examiners.

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