US 3154141 A
Description (OCR text may contain errors)
Oct. 27, 1964 A. HUET noucumusn HEAT mccmucm was Filed April 26. 1960 United States Patent 3,154,141 ROUGHENED HEAT EXCHANGER TUBE Andi- Huet, 43 Avenue du President Wilson, Paris, France Filed Apr. 26, 1960, Ser. No. 24,760 Claims priority, application France, Apr. 28, 1959, 793,350 3 Claims. (Cl. 165133) It has already been proposed to form grooves of small depth or striations in the surface of tubes intended for heat exchangers, thereby forming, in the said surface, hollows and raised portions of the order of one or a few millimeters, with a view to increasing the surface of the tube for the exchange of heat. These grooves can be formed either in the longitudinal direction parallel to the axis of the tube, or in the transverse direction, or in both directions at once so as to form a chequer-work pattern on the tube. The tube can be either of circular section or it can have diametral or tangential fins, or it can be of any desired section, for example, of double-convex section. Grooves of this type are always uniform (and produce regularly-disposed raised portions.
The present invention has for its object a tube intended for the exchange of heat, the surface of said tube having rough excrescences and indentations or depressions of various shapes and orientations, arranged irregularly and symmetrically or asymmetrically. These rough excres cences or depressions can in particular be given the shape of points, or more exactly small cone frustums, either raised or hollow, the dimensions of which can be of the order of a tenth of a millimeter or larger, and are selected as a function of the nature and the conditions of temperature and pressure of the fluids with which the tube is in contact, either externally or internally. These points can be combined with channels or grooves of all shapes and orientations, or raised portions of any shapes and orientations.
Instead of resulting from the formation of raised portions on a cylindrical surface, this rough surface of the tube can be obtained by depressions formed in the initially smooth surface of the tube. To this end, in the case of a metallic tube which has passed through rollers in the course of its manufacture, rough excrescences are formed on the said rollers so as to produce holes or grooves of any desired shape in the surface of the tube. If the tube has a deformed section, for example a doubleconvex section, obtained by passing a tube of circular section between a roller-train designed to deform the section, these latter rollers will in this case be provided with rough excrescences. Alternatively, sand is introduced between the surface of the tube and the smooth or roughened rollers between which the said tube passes, so as to obtain a rough surface having concave points or grooves having various shapes and arrangements. If the tube is manufactured by extrusion, for example in the case of a tube having diametral or tangential fins, or if the tube is produced by drawing, a die is employed which is provided with combs which oscillate or come into periodic contact with the surface of the extruded tube so as to obtain in the longitudinal direction depressions in the form of grooves formed in the surface of the tube. In order to obtain depressions transverse to the axis of the tube, the tube can be subjected to cold or hot die-forming or to hammering of its surface, preferably by means of pneumatic hammers striking punches in which raised points are formed.
Various forms of embodiment of the tubes which form the object of the present invention have been shown in 3,154,141 Patented Oct. 27, 1964 perspective in FIGS. 1 to 4 of the accompanying drawings.
In the form of embodiment of FIG. 1, points or small craters b have ben stamped asymmetrically so as to form hollows, and alternating with channels or grooves c. The depth of these channels is of the order of one millimeter to one tenth of a millimeter.
In FIG. 2, the tube a is only provided with channels or grooves c which are distributed, as can be seen in the drawing, in asymmetric and irregular manner over the surface of the tube.
In FIG. 3, there is in this case a tube d, having tangential fins e and the grooves f are distributed in an irregular manner, both over the surface of the tube proper and over the surfaces of the fins. It would also be possible to form points.
On the tube g of FIG. 4, the hollow points h have a density or depth which varies betwen one extremity of the tube and the other, the points it being, for example, of greater density at the entrance than at the outlet.
The tube can be mounted in heat exchangers of all types, with parallel flow or cross-flow. In particular, it is an advantage to employ them in combination with tubes so arranged that the passages formed between tubes in the exchanger for the circulation of the external fluid vary both in section and direction. For example, in an exchanger between two fluids circulating in cross-flow, tubes having double-convex sections with faces of unequal curvature, and in which hollowed and raised portions have been formed in accordance with the present invention, will be disposed quincuncially or in a staggered pattern, and the transverse passages thus formed between the tubes will be provided in known manner, with variations of section and of direction of the flow of the external fluid.
These tubes can also be employed in heat exchangers having deflecting undulated walls disposed between the rows of tubes so as to channel and modify the flow of the fluid outside the tubes. They can also be employed with sheath envelopes placed co-axially to the tubes and having a profile which is either symmetrically or asymmetrically corrugated, the period or pitch of the corrugations of the envelope being variable from one end to the other of the tube or along certain portions of the said tube, in combination or otherwise with a variation of the density or of the height of the depressions and raised portions formed in the surface of the tube itself.
The present invention does not necessarily apply to meballic tubes, but can also apply to tubes of any other nature, for example of ceramic material, in which the depressions or raised portions which are irregularly disposed, can be even more easily produced and applied especially to the surfaces of fuel elements of nuclear reactors, either to their sheathings or to the surface proper of the fuel cores when they are of ceramic material.
What I claim is:
l. A heat-exchanger tube defined by a tube wall having an outer surface provided with integral rough, discontinuous excrescences in relief disposed spaced from each other axially and circumferentially on said tube, said ex crescences being limited in axial and circumferential extent so that a plurality are accommodated circumferentially of said tube and axially of said tube, said excrescences each having a height of about of a millimeter to about one millimeter with respect to the surface of said tube, said excrescences varying in height over the length of said tube, and said excrescences being formed wholly from the material of said tube wall.
2. A heat-exchanger tube defined by a tube Wall having an outer surface provided with integral rough, discontinuous excrescences in relief disposed spaced from each other irregularly axially and circumferentially on said tube, said excrescences being limited in axial and citrcumferential extent so that a plurality are accommodated circumferentially of said tube and axially of said tube, said excrescences each having a height of about V of a millimeter to about one millimeter with respect to the surface of said tube, said excrescences varying in number and in height over the length of said tube, and said excrescences being formed wholly from the material of said tube wall.
3. A heat-exchanger tube defined by a tube wall having an outer surface provided with integral rough, discontinuous, excrescences in relief disposed spaced from each other axially and circumferentially on said tube, said excrescences being limited in axial and circumferential extent so that a plurality are accommodated circumferentially of said tube and axially of said tube, said excrescences each having a height of about A of a millimeter to about one millimeter with respect to the surface of said tube, said excrescences varying in number per unit length and in height over the length of said tube, said excrescences being formed Wholly from the material of said tube Wall, said tube outer surface comprising discontinuous, irregularly shaped indentations intermediate at least some of said excrescences and disposed spaced circumferenti ally and axially on said tube, and said indentations having a depth of about A of a millimeter to about one millimeter.
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