US3295599A - Heat transfer fin heat exchanging tube - Google Patents

Description

Jan- 3, 1967 YOSHIZO OKAMOTO ETAL 3,295,599

HEAT TRANSFER FIN HEAT EXCHANGING TUBE Filed April 5, 1963 Fig.

ATTORNEY.

United States Patent 3,295,599 HEAT TRANSFER FIN HEAT EXCHANGING TUBE Yoshizo Okamoto, Tokai-mura, Naka-gun, Ibaragl-ken, Shinichi Negoya, Hitachi-shi, Ibaragi-ken, and Ken Namatame and Miyoshi Ohuchi, Tokai-mura, Nak agun, Ibaragi-ken, Japan, assignors to Nil on Genshiryoku Kenkyujo, Tokyo, Japan, a corporation of Japan Filed Apr. 5, 1963, Ser. No. 270,860 Claims priority, application Japan, Apr. 23, 1962, 37/ 15,650 1 Claim. (Cl. 165-484) The present invention relates, to improvements in the heat dissipating fins of heat exchanging tubes, as for in stance, a fin in a cladding tube enclosing a fuel element of a nuclear reactor, where a number of longitudinal fins are usually provided.

Generally, longitudinal fins providing heat transfer surfaces are, as compared with other kinds of fins, more advantageous that any other kinds of fins by reason of the fact that they can furnish a high heat transfer rate without increasing pressure loss and that they have a much greater operative heat transfer area in the cooling passage. As a consequence, the pressure loss thereby incurred is five or six times as large as that of the heat transfer surface of a cylindrical tube, whereas heat transfer rate may be increased up to ten to fifteen times that in the same tube. However, longitudinal fins have other disadvantages. If the number of fins is increased in order to obtain a high efiiciency of heat transmission, it follows that the space between adjacent fins will become narrow and therefore the flow is turbulent between the closely spaced fins. This will cause lowering of flow velocity to one third of the outside flow, and the effective heat transfer coefficient will be reduced accordingly as, for instance, when the number of fins is of the order of several scores, the heat transfer area becomes thirty times as large as the original tube, but the effective heat transfer rate will remain at an approximate value of seven to ten times as large. Also, under high temperature, non-uniformity of temperature on the surface of fins often gives rise to be repeated stress, thermal deformation, bending, and excessive local heating of fins, which may limit the possibility of good design for the heat transfer surface of a fin.

The present invention is such that a number of helical grooves are defined between the adjacent ends of axially aligned radially extending fin elements formed on the external surface of a cylindrical tube, thus to improve the heat transfer characteristics of fins by diagonally extending turned-over projections formed during the cutting of the diagonal or helical grooves in the longitudinal fins to form the fin elements.

The present invention will be described, by way of example, with reference to the accompanying drawing, in which:

FIGURE 1 is a perspective view of a part of a cooling tube having heat transmission fins.

FIGURE 2 is a transverse section of FIGURE 1.

FIGURE 3 is an enlarged fragmentary front view show- 3,295,599 Patented Jan. 3, 1967 ing the arrangement of fin elements on the tube of present invention.

FIGURE 4 represents a fragmentary perspective view showing a single fin element.

FIGURE 5 is a perspective view of a modified heat exchanger having helical guide strips extending radially outwardly of the fin elements.

FIGURE 6 is a transverse section of FIG. 5.

The embodiment shown in the drawing is explained in more detail. In FIGURES l and 2, 1 is a tube having a heating source inside as, for instance, a nuclear fuel element (not shown). On the outer surface of the tube, there are provided integrally formed fin elements 2 aligned axially of the tube. However, between the confronting ends of adjacent fin elements 2, there are a series of diagonally cut grooves 3 defining parallel interrupted helical slots 4 extending circumferentially around the tube 1. This is best shown in FIGURE 3, where a number of interrupted helical slots, extending as indicated by the arrow A, are defined by the. grooves 3. Due to a turning over of the metal during the cutting of the diagonal grooves 3, there are produced convergent laterally projecting edges 2a, 2b on both ends of each fin element 2. (Refer to FIGURE 4.) Coolant gas therefore flows between laterally adjacent longitudinal rows of fin elements 2 and then runs through the diagonal grooves 3, being deflected by the convergent projecting edge portions 2b, 2a of each lower and upper end. For example, the coolant gas flows along dotted lines in FIGURE 3. Therefore, each fin element 2 will have much larger effective heattransfer area than that of conventional continuous longitudinal fins.

FIGURES 5 and 6 show a modified embodiment where the fin elements 2 are combined with several helical guide members 4 for guiding the coolant gas. The guide memhere are positioned in the helical slots defined by diagonal grooves 3 between longitudinally adjacent fin elements 2, the cooling effect of each fin element 2 between guide members 4 being the same as FIGS. 1 to 4.

While we have shown and described what we believe to be the best embodiments of our invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined in the appended claim. 4

What we claim is:

A heat exchanger comprising: an elongated tube; a series of spaced fin elements formed on the external surface of said tube, each of said fin elements extending radially outwardly from said external surface and 'being elongated axially of said tube, said fin elements being aligned in regularly circumferentially spaced axially ex tending rows, the ends of adjacent fin elements in each row being spaced to define a groove therebetween the bottom of which extends along said external surface diagonally with reference to the axis of said tube, said grooves in each row being staggered with respect to the grooves in both adjacent rows to define regularly axially spaced series of interrupted helical slots extending circumferentially completely around said tube, each of said fin elements having a convergent laterally projecting edge portion formed at each end thereof, said edge portions projecting in one direction at one end of every fin element and on the opposite direction at the opposite end of every fin element, said edge portions extending in opposite directions at opposite sides of each helical slot, whereby cooling fluid flowing longitudinally of said tube in either direction is deflected laterally through said helical slots.

References Cited by the Examiner UNITED STATES PATENTS 10/1952 Newlin 165184 1/ 1954 Chapman 165-184 9/1954 Legatski 165181 X 3/1961 Latharn 165--184 X 5/1961 Fairhurst 165183 8/1963 Nihlen et a1 29157.3

FOREIGN PATENTS 8/ 1955 Belgium. 9/ 1959 Great Britain.

FREDERICK L. MA'ITESON, I R., Primary Examiner.

CHARLES SUKALO, Examiner.

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