BACKGROUND OF THE INVENTION

This invention relates generally to the field of laminated tubing for use in a wide variety of applications, including energy conservation, using concentric pipe including double wall, vented heat exchangers, high strength pipe, corrosion resistant pipe and lightweight pipe.

SUMMARY OF THE INVENTION

Briefly stated, the invention contemplates the provision of a number of concentric tube constructions which will provide both for effective heat interchange, corrosion resistance and increased strength, as well as the effective prevention of fluid and/or gaseous interchange should a leak occur. To this end, the laminated tube is formed as a pair of concentric members of differing materials in intermittent mutual surface contact. The unit is formed by providing a seamless inner member and an outer member which has been longitudinally slit or formed to permit ready positioning about the inner member, leaving a longitudinal narrow gap, which is subsequently welded or brazed. As the welding or brazing material shrinks with cooling, the outer member radially contracts upon the inner member to form a stressed skin. In at least one embodiment, the outer member is provided with internal longitudinally oriented grooves, which collect possible leakage through the wall of the inner member and drain it to a collection point, either in a sealed system or open to the atmosphere. To prevent any fusion between the inner and outer members at the weld or braze area, an elongated flat metal shim is inserted between the inner and outer members to overlie the gap.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing, to which reference will be made in the specification, similar reference characters have been employed to designate corresponding parts throughout the several views.

Figure 1 is a schematic cross-sectional view of a first embodiment of the invention.

Figure 2 is a schematic cross-sectional view of a second embodiment of the invention. Figure 3 is a cross-sectional view of a third embodiment of the invention.

Figure 4 is an isometric view of a laminated tube forming part of any of the first, second and third embodiment.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

In accordance with the first embodiment of the invention, the device, generally indicated by reference character 10, comprises broadly: an inner tube member 11, an outer tube member 12, a heat-shielding shim 26 and a mass of brazing material 14.

The inner tube member 11 is of seamless construction, and is bounded by a smooth inner surface 16 and a smooth outer surface 17.

Typically, it will be formed of thin metal, glass or ceramic, etc.

The outer tubular member 12, may be formed of any weldable metal. It is bounded by an inner surface 20, an outer surface 21 and a pair of longitudinal parallel edges 22 and 23 bordering a gap 24 filled with a welding material 25. Optionally, the outer surface 21 can contain heat-transfer fins 25A (not shown). Also optionally, a thin metal, elongated shim 26 may be positioned at the bottom of the gap 24. This may be formed of a thin strip of desired metallic material.

The embodiment is assembled by providing inner and outer tubular members 11 and 12 of compatible dimensions, and slitting the outer tubular member, which will facilitate the insertion of the inner tubular member therewithin. Since, after slitting, the outer tubular member will possess a degree of radial resiliency, force fitting is not necessary, and relatively long lengths of tubing may be assembled. Following this, the outer tube is welded together in conventional manner. Gas welding will, of course, provide for accurate control, but where the pipes are of substantial diameter, electric welding may be preferred. As the weld cools, normal

shrinkage will occur, which will result in contracting the outer tubular member upon the inner tubular member, the inner tubular member being stressed, so that the outer surface of the inner tubular member and the inner surface of the outer tubular member are placed in intimate contact, permitting excellent heat transmission therebetween. Increased strength results as well because the inner tube 11 will be forced into compression and the outer tube 12 into tension. This prestressed relationship is similar to that used in the manufacture of cannons.

In the second embodiment of the invention, generally indicated by reference character 30, the inner tube member is substituted by a ceramic or glass core 31, and the outer tube member is also metallic, as in the case in the first embodiment. The welding operation is conducted in a similar fashion, care being taken to prevent excess stress which might crack the ceramic or glass core. The thickness of the outer member may be reduced to facilitate this end.

The third embodiment of the invention, generally indicated by reference character 40, is of somewhat more complex construction for use in applications where venting is required in order to prevent contamination and permit leak detection. Referring to Figure 3, the device 40 includes first, second and third concentric members 41, 42, 43, respectively.

The first member 41, as in the first embodiment, is preferably of thin stainless, seamless tubing, and is bounded by an inner surface 46 and an outer surface 47. The second member 42 may be of nonferrous material, such as aluminum, copper or brass. It is bounded by an inner surface 50 and an

outer surface 51, either or both of which are optionally provided with longitudinally extending venting grooves 52.

The third member 43 is, again, preferably of thin-walled stainless steel tubing, including an inner surface 60, an outer surface 61, a longitudinal gap 62 and a heat-shielding shim 63. It is assembled in the same manner as the first and second members, which, when integrated, are slid into the interior of the third member, and a similar welding operation is again conducted. With vent grooves included, the device 40 is an example of multiple wall, vented laminated pipe or tubing. The number of layers of pipe is not limited to the three illustrated in the drawings, but may be of any required number.