Internal and internal-external surface heat exchange tubing

Nov. 17, 1959 c. h. kuthe 2,913,009

INTERNAL AND INTERNAL-EXTERNAL SURFACE HEAT EXCHANGE TUBING

Filed July 16. 1956

FIG.I.

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FIG.2.

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United States Patent Office _P, ,. „ ²’®*³’®⁰®

Patented Nov. 17, 1959

2,913,009

INTERNAL AND INTERNAL-EXTERNAL SURFACE HEAT EXCHANGE TUBING

Charles H. Kuthe, Highland Park, Mich., assignor to Calumet &amp; Hecla, Inc., Calumet, Mich., a corporation of Michigan

Application July 16,1956, Serial No. 598,070

Claim. (Cl. 138—38)

This invention relates to heat exchange tubing and refers more particularly to internal and internal-external surface heat exchange tubing.

The tubing in'heat exchange installations is often times provided with an external fin surface to increase the heat transfer characteristics of the tubing. The construction of heat exchange tubing with an external fin surface is done primarily-with prefabricated fins bonded mechanically or metallurgically to a smooth surfaced tube. Other finned tubing is produced with integral fins or corrugations on the .external surface. It has been found, after much experimentation, that heat exchange tubing which is corrugated on the inside, either in addition to or in place of external fins, greatly increases the heat transfer between the .outside and inside fluids.

One object of this invention is to provide heat exchange tubing which is corrugated on the internal surface so as to produce turbulence of the fluid within the tube and promote better heat transfer between the inside and outside fluids.

Another object of the invention is to provide a tube assembly -comprising an outer tube and an inner tube positioned within the outer tube which is corrugated on the inner-surface.

Another object of the invention is to provide a tube assembly comprising an outer tube and an inner tube telescoped within the outer tube in heat exchange relation therewith, the inner tube being corrugated to impart to the inner tribe an undulating configuration in longitudinal section.

Still another object of the invention is to provide a heat exchange tube assembly, as described in the preceding paragraph, in which the outer tube has fins on its outer surface to cooperate with the inner tube in promoting better heat transfer between inside and outside fluids.

Other objects are to provide a tube assembly as described in which the inner tube has a helical corrugation extending over a portion of its length, and in which the inner tube has a plurality of longitudinally spaced circumferentially extending corrugations.

Other objects of the invention will become more apparent as the following description proceeds, especially when taken into consideration with the accompanying drawings, wherein: °

Figure 1 is an elevational view, partly in section, of a heat exchange tube assembly embodying the invention.

Figure 2 is a view similar to Figure 1, illustrating a modification.

Figure 3 illustrates a further modification.

Referring now more particularly to the drawing and especially to Figure 1 thereof, the tube assembly there shown is generally indicated by the reference numeral 10 and comprises an outer tube 12 and an inner tube 14 telescoped within the outer tube in coaxial relationship therewith, these tubes being formed of a suitable material having good heat transfer characteristics. The tube assembly 10 is adapted to be employed in a heat exchange installation.

The outer tube 12 is cylindrical, that is, the radially 5 inner and outer surfaces thereof are of uniform circular cross-section throughout the length of the tube and, therefore, smooth.

The inner tube 14 comprises the plain cylindrical end portions 16 and 18 and the intermediate corrugated por10 tion 20. The intermediate corrugated portion 20 may· be formed in any desired manner and, for example, a· forming disc may be employed with its axis of rotation· arranged obliquely with respect to the axis of the tube and with the periphery of the disc bearing against the. 15 outer surface of the tube to form a helical groove in the tube while at the same time feeding the tube axially and rotating it. However, as pointed out above, the inner tube 14 may be formed by other means.

The corrugated intermediate portion 20 has an un²θ dulating configuration in longitudinal section as illustrated. The intermediate portion has a helical radially inwardly extending corrugation 22, each convolution of the corrugation being indicated at 24. The undulating· configuration also provides, in effect, a helical radially ²⁵ outwardly extending corrugation 26, each convolution of which is indicated at 28.

The crests 30 of the convolutions 28 are of the same' outside diameter and are of the same diameter as the outside diameter of the cylindrical plain end portions 16 ^υ and 18. The crests 32 of the convolutions 24 are of the same inside diameter. It should also be pointed out that the inner tube 14 is of uniform wall thickness from one end to the other.

_3g The tubes 12 and 14 are assembled together by insert.° ing the inner tube within the outer tube and then sinking the outer tube on the inner tube. A mechanical or metallurgical contact of the two tubes is thereby achieved with the crests 30 of the convolutions 28 of the inner tube contacting the smooth internal surface of the· outer tube. Preferably, the crests 30 have a full and continuous contact with the smooth internal surface of the outer tube throughout the full extent of the-corrugated portion. The external surfaces of the plain end portions45 ^and 1® ^{are a}^^so brought into full and continuous surface-to-surface contact with the smooth internal surface of the outer tube by the sinking operation.

As a result of this construction, a heat exchange tube assembly is provided having a substantial helical corruga50 tion on the inside and producing turbulence in a fluid moving through the corrugated portion of the inner tube, and, hence, promoting better heat transfer with a fluid on the outer side of the tube assembly. The continuous and uninterrupted contact between the crests 30 of the 55 inner tube and the smooth inner surface of the outer tube also promotes heat transfer. The degree of turbulence may be controlled by varying the shape of the convolutions of the corrugation on the inner tube.

Figure 2 illustrates a modification in which correspond60 P^arts are designated by the same reference numerals. The inner tube 114 is exactly like the inner tube 14 described in the first embodiment. The outer tube 112 differs from the outer tube 12 previously described in that it has an integral fin 115 formed on the external surge face, the fin extending helically and continuously about the outer surface of the tube. The crests 130 of the corrugations on the inner tube have a continuous and iminterrupted contact with the smooth inner cylindrical surface of the outer tube 112, thus achieving a mechani70 cal or metallurgical contact between the tubes which may be accomplished in any suitable manner.

The fin 115 is shown as being formed integrally on

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the outer tube although it will be understood that the fin may be prefabricated and bonded mechanically or metallurgically to the outer surface of a smooth cylindrical tube such as the tube 12.

By varying height and linear spacing of the convolutions of tire fin on the outer tube, and also by varying the shape of the corrugation on the inner tube, the desired inside-outside surface ratio may be obtained for optimum heat transfer.

Figure 3 illustrates a further modification in which corresponding parts are designed by the same reference numerals. The outer tube 212 is exactly like the outer tube 112. The inner tube 214 differs from the inner tubes 14 and 114 only in the shape of the corrugated portion 220. The corrugated portion 220 is formed of a plurality of circumferentially extending longitudinally spaced radially inward corrugations 224 which are disposed in a plane at right angles to the tube axis. The corrugations 224 are similar to the convolutions 24 shown in the previous embodiments except that whereas the convolutions 24 extend helically and connect end to end into adjacent convolutions to provide a continuous helical corrugation, the corrugations 224 are separate and spaced from each other. The undulating configuration of the corrugated portion 220 also provides, in effect, radially outwardly extending corrugations 228 between adjacent corrugations 224, the corrugations 228 being disposed in planes at right angles to the tube axis.

The crests 230 of the corrugations 228 are of the same outside diameter and are of the same diameter as the outside diameter of the cylindrical plain end portions of the inner tube. The crests 232 of the corrugations 224 are of the same inside diameter and the tube 214 is of uniform wall thickness from one end to the other.

The tubes 212 and 214 are assembled together in any suitable manner so that a mechanical or metallurgical contact of the two tubes is achieved with the crests 230 of the corrugations 228 contacting the smooth internal surface of the outer tube. Preferably, the crests 230 have a full and continuous contact with the smooth internal surface of the outer tube. The external surfaces of the plane end portions of the tube also have a full and continuous surface-to-surface contact with the smooth internal surface of the outer tube.

It will be readily apparent that in the Figure 3 embodiment, the plain tube 12 might be substituted for the ⁴ finned tube 212, in which event the crests 230 and external surfaces of the ends of the inner tube would have a full continuous and uninterrupted surface-to-surface contact with the smooth inner surface of the outer tube 12.

The drawings and the foregoing specification constitute a description of the improved internal and internal-external surface heat exchange tubing in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claim.