Vented Heat Transfer Tube Assembly

The present invention is concerned with a structure for heat transfer tubes for heat exchangers and the like, and more particularly the present invention relates to a structure for heat transfer tubes for providing venting to the ambient of fluid leaking from a fluid flow enclosure to the other.

Heat exchangers are commonly used for the purpose of transferring heat from a fluid, such as a liquid flowing in an enclosure, to another fluid flowing in an adjacent enclosure without intermixing the fluids. Heat exchangers are in common use in some applications of solar heating devices utilizing a fluid, such as a liquid fluid of high heat absorbing capacity, circulating through a primary fluid flow circuit connected to the solar heat absorber, and where it is desired to transfer the heat from the heated fluid in the primary circuit to another fluid, such as ordinary water or air, circulating in a secondary fluid flow circuit. Heat exchangers are also commonly used in marine and in stationary industrial internal combustion engine installations for absorbing heat from the engine closed cooling system, and in nuclear reactors for cooling the reactor and for utilizing the heat generated by the reactor.

Heat exchangers are often complex devices with many welded or brazed fittings and connections, and they are subject to rapid deterioration, especially when one of the fluids has a corrosive action on the wall of the containing vessels, conduits, and junctions. Conventional heat exchangers are bulky, expensive to fabricate, subject to corrosion and prone to develop leaks.

The invention disclosed in the aforementioned application for Letters Patent remedies the inconveniences of conventional heat exchangers by providing a novel structure for heat transfer tubes for use in heat exchangers, which can be mass-produced in convenient sizes and lengths, and which can be cut from stock to any appropriate lengths for fabricating heat exchanger units of any desired capacity by interconnecting by means of conventional fittings. Heat transfer tubes according to the invention disclosed in said application may be mass-produced at low cost on continuous lines or in batches by means of simple tooling, and consist essentially of an assembly of two conventional tubular elements mounted one within the other and held in spaced apart relationship concentrically to each other by simple wall deformation of the elements, thus requiring no separate holding and connecting members, and no welding, soldering or brazing.

The present invention is an improvement over the invention disclosed in said application, providing a double-walled inner tube formed of a pair of concentrically disposed conduits, the outermost of which is shrunk over the innermost one, one of the conduits or both conduits being peripherally shaped such as to form longitudinally disposed vent or drainage passageways or channels running the whole length of the double-walled inner tube and vented to the ambient, with the result that any fluid which may tend to leak from a fluid flow circuit to the other is trapped in the vent or drainage passageway or channel and exhausted to the ambient, thus preventing intermixing of the two fluids and providing a visual indication, upon inspection, that the inner tube has developed an accidental or useage-induced leak which could not be detected by other means.

The diverse objects and advantages of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawing wherein:

FIG. 1 is an elevation view of a length of vented heat transfer tube according to the present invention;

FIG. 2 is a transverse section along line 2--2 of FIG. 1;

FIG. 3 is a transverse section along line 3--3 of FIG. 1;

FIG. 4 is a view similar to FIG. 3, but showing a modification thereof;

FIGS. 5 and 6 are transverse sections through further modifications of vented inner tubes for vented heat transfer tubes according to the invention;

FIG. 7 is a partial elevational and sectional view through the end of a vented heat transfer tube according to the present invention cut off for mounting on the end thereof appropriate fittings for connection to external circuits;

FIG. 8 is a transverse section along line 8--8 of FIG. 7; and

FIG. 9 is a view similar to FIG. 7, but showing a modification thereof.

Referring now to the drawing, and more particularly to FIGS. 1-3, a heat transfer tube 10 according to the present invention comprises a metallic elongated tubular conduit member or tube 12 having a second elongated tubular conduit member or tube 14 rigidly mounted concentrically within the outer tube 12, such that a generally annular space 16 is formed between the interior wall surface 18 of the outer tube 12 and the peripheral surface 20 of the inner tube 14. The inner tube 14 is held substantially concentric to the outer tube 12 as a result of the outer tube 12 being provided with a plurality of concave indentations of dimples 22 projecting inwardly and radially such as to form a domed surface 24, FIGS. 2 and 3, engaged into a conforming inwardly directed depression or recess 26 formed in the peripheral surface 20 of the inner tube 14. Preferably, a pair of diametrally disposed dimples 22 are formed at regular intervals, the axis of the dimples in each pair being at a right angle to the axis of the next consecutive pair of dimples 22. In this manner, the inner tube 14 is held co-axially within the larger outer tube 12, without requiring any welding, brazing or other assembly arrangement, and an appropriate fluid, such as a liquid, may be longitudinally circulated through the annular space 16, while another fluid may be circulated through the interior 28 of the inner tube 14.

The inner tube 14 is made of welded-seam or, preferably, seamless metallic tube such as copper tubing and the like, providing good heat transfer from the interior 28 of the inner tube 14 through its wall to the annular space 16 surrounding its peripheral surface 20. The outer tube 12 is also made of metallic seamless or welded-seam tubing, preferably of the same material as the inner tube 14 to prevent electrolytic corrosion of the wetted surface, especially where the surfaces are proximate or in firm contact with each other, for example where the domed surface 24 of the dimples 22 formed in the outer tube 12 engages the surface of the recess 26 formed in the peripheral surface 20 of the inner tube 14. Disposing the dimples 22 in diametrally opposed pairs with the axis of each pair at substantially a right angle to the axis of the adjoining diametrally opposed pairs of dimples tends to divert the flow of fluid through the annular space 16 and creates turbulence which facilitate the heat exchange between the fluid circulating in the annular space 16 and the fluid circulating through the interior 28 of the inner tube 14. The recesses 26 are formed by deformation of the wall of the inner tube 14 such as to cause on the interior 28 of the tube diametrally opposed pairs of convex projections 30 which, without causing undue restriction to the flow of fluid through the interior 28 of the inner tube 14, tend to agitate and cause turbulence of the fluid circulating through the interior 28 of the inner tube 14.

The inner tube 14 is double-walled, as illustrated, i.e. made of an inner tubular conduit 32 disposed within an outer tubular conduit 34, the outer conduit 34 being shrunk by rolling or, preferably, passage through a sizing die for reducing its diameter while simultaneously reducing slightly the diameter of the inner conduit 32. In the example of structure of FIGS. 1-3 and as best shown at FIGS. 2 and 3, the outer conduit 34 is formed with longitudinally extending, radially projecting, upwardly bulging wall portions 36 regularly disposed about the periphery of the outer conduit 34, such that when the outer conduit 34 is shrunk over the inner conduit 32, the outer surface of the inner conduit 32 is intimately in contact with the inner surface of the outer conduit 34, as illustrated at 38, and other portions corresponding to each of the longitudinal bulges 36 formed in the wall of the outer conduit 34 are spaced apart such as to form longitudinal venting passageways or channels 40 extending the whole length of the double-walled inner tube 14. The size of the diverse elements and their arrangement are such that, in the structure illustrated, there are four such venting passageways or channels 40 each disposed between the portions of the inner conduit 32 and of the outer conduit 34 in intimate surface contact, as is shown at 38, and the dimples 22 are formed at locations where the inner tubular conduit 32 engages with the outer tubular conduit 34, such as not to interfere with the venting passageways or channels 40.

The venting passageways or channels 40 act as evacuation conduits for any fluid attempt leak from the interior 28 of the double-walled inner tube 14 to the annular space 16 or for fluid attempting to leak from the annular space 16 through the double wall of the inner tube 14, in the event that the wall of the inner conduit 32 or the wall of the outer conduit 34, respectively, experiences a crack or a rupture while in service. The venting passageways or channels 40 are vented to the ambient, such that any contamination of one of the fluids by the other is prevented as the leaking fluid is evacuated to the ambient. The venting passageways or channels 40 may be left empty or, in the alternative, if so desired they may be filled during manufacturing of the heat transfer tube 10 with a material preferably in the form of a gel which provides relatively good transfer of heat from the wall of the inner conduit 32 to the wall of the outer conduit 34 through the space formed by the passageways or channels 40 by convection through the material filling the space in the venting passageways or channels. Ethylene glycol aqueous solutions in the form of a gel by addition of sodium silicate or the like, and silicone resins have been found convenient as materials for filling the venting passageways or channels 40. Other materials may be used to fill the passageways or channels 40 such as crystaline materials or salts soluble in the liquid fluids used in the heat exchanger system. The leaking fluid captured in the venting passageways or channels 40 tends to dissolve or displace, as the case may be, the crystaline materials, the salts or the gel contained in the passageways or channels through the venting aperture to the ambient such that, in addition to the fluids themselves being vented to the ambient, the gel, crystaline materials or salts seeping through the venting aperture provides an indication of a leakage having occurred.

As shown at FIG. 4, instead of providing the outer conduit 34 with longitudinally bulging wall portions, the outer conduit 34 forming part of the inner tube 14 may be formed substantially cylindrical and the inner conduit 32 provided with longitudinally extending inwardly directed bulges 42 forming longitudinally extending venting passageways or channels 40 or, in the alternative, both inner conduit 32 and outer conduit 34 may be provided with regularly disposed longitudinally extending bulges 36 and 42, respectively, such that the longitudinally extending venting passageways or channels 40 are disposed therebetween, as shown at FIG. 5.

Any number of shapes of double-walled inner tubes 14 may be devised within the purview of the present invention as for example the generally octagonal, in transverse section, shape of FIG. 6 wherein the inner conduit 32 is, for example, in the shape of a regular octagon with rounded corners and the outer conduits 34 is in the form of an octagon, in section, having longer sides 44 alternating with shorter sides 46 such that between each shorter side 46 of the outer conduit 38 and the corresponding side of the inner conduit 32 the venting passageways or channels 40 are thus formed, the longer side 44 of the outer conduit 34 being in tight engagement, as shown at 38, with the corresponding side of the inner conduit 32.

The heat transfer tubes of the invention are preferably manufactured on a continuous line, or by batches, the assembly of the double-walled inner tube 14 within the outer tube 12 being effected by the roll apparatus described in detail in co-pending application Serial No. 112,393, the only difference being that manufacture of the double-walled vented heat transfer tube of the present invention requires substantial accurate alignment of the inner tube 14 relative to the dimple forming mechanism at the start of an assembly operation such that the dimples 22 will be formed at the location where the inner conduit 32 and the outer conduit 34 are in firm engagement with each other, and the venting passageways or channels 40 are disposed between rows of dimples. Alternatively, the dimples may be formed by means of a die and forming-punch apparatus.

In use, the heat transfer tubes 10 of the invention are cut to an appropriate length, first by effecting a cut through both the peripheral or outer tube 12 and the inner tube 14, and subsequently effecting a cut only through the wall of the outer tube 12, as shown at 62 at FIGS. 7 and 9, thus leaving on the end, a projecting end portion 64 of the inner tube 14 beyond the cut end 62 of the outer tube 12. A T-shaped connector 66, for example, has an end 68 fitted over the cut end 62 of the outer tube 12 and soldered or brazed in position. The connector 66 has another end 70 of reduced diameter fitting the outer conduit 34 of the double-walled inner tube 14 at its end projecting portion 64, soldered or brazed thereto. A connector 72 is soldered or brazed in the end of the inner tube 14 for forming a junction with an inlet, or outlet, conduit (not shown) for the fluid circulating through the inner tube 14. The other end 74 of the T-shaped connector 66 may be connected to a fluid inlet or outlet, as the case may be, or connected in the same manner to another length of heat transfer tube 10, either in series or in parallel, as desired for fabricating heat exchanger units of greater capacity than provided by a single length of heat transfer tube.

As best shown at FIG. 8, the cut end of the double-walled inner tube 14 provides open ends for the venting passageways or channels 40 directly to the ambient, such that any leakage of fluid into the venting passageways or channels 40 may be evacuated to the ambient. As a further precaution to ensure that each passageway or channel 40 is actually open to the ambient, in the event that dirt, solder or brazing alloy obturate the open ends of the passageway or channel 40 during soldering or brazing in position of the connectors and more particularly the connector 72, a slit 76, as shown at FIG. 9, is provided by effecting a saw cut through the wall of the outer conduit 34 at each longitudinal bulge 36 thereof forming a passageway or channel 40 between the bulge inner surface and the corresponding outer surface of the inner conduit 32 and the exposed end of the double-walled inner tube 14 beyond the end 70 of the T-shaped connector 66. In this manner, fluid leaking to the venting passageways or channels 40 is directly evacuated through the saw cuts or slits 76 to the ambient, or is caused to displace the gel or other material filling the passageways or channels 40 through the saw cuts 76, even though the end of the passageway or channel 40 at the cut end of the double-walled inner tubing 14 may be clogged by dirt, solder or brazing material.

Having thus described the present invention by way of structural examples thereof, modifications whereof will be apparent to those skilled in the art.