US3479489A - Heat exchanger construction - Google Patents

Description

Nov. 18, 1969 P. N. RENZI 3,479,489

HEAT EXCHANGER CONSTRUCTION Filed June 28, 1967 b INVENTOR ,0 l2 Peter N. Renzi ATTORNEY United States Patent US. (:1. 219-540 15 Claims ABSTRACT OF THE DISCLOSURE This invention employs, in one of its forms, a heating device having a spirally twisted pair of conductors each constructed of resistance heating wire for electrical applications or of tubes for conducting fluids for fluid thermal applications; and, interleaved between the spiral twists, there are a multitude of radially extending heat conductors which are in thermal contact with the twisted pairs; and the radial conductors serve to dissipate heat.

generated or transmitted by the twisted conductors.

This invention relates to heating devices having improved heat transfer properties. More specifically, this invention relates to electrical heating elements which may be formed by twisted electrical resistance heating cores and having heat transmission elements secured between the twists to dissipate the heat. As an alternative, the heating elements may be formed of twisted tubes for transporting heating fluids and employing heat transmission elements to dissipate or relay the heat conveyed by the heating fluids to the adjoining space.

The configuration of conventional electrical heating elements, for example, is usually fixed within relatively narrow limits as dictated by performance, cost considerations, and specified physical and electrical limits. Some conventional electrical heaters generally employ a metallic outer sheath comprised of an elongated cylindrical tube which surrounds a resistance heating element disposed along the axis of the sheath. The heating element may consist of a straight wire or bar, and it may be supported equi-distantly between the inner walls of the sheath by' an insulating material such as magnesium oxide. To increase the thermal dissipation of the heating element, external radial fins may be added along the length of the outer surface of the sheath. The amount of heat that can be dissipated per unit length of resistance heater wire is a function of the exterior surface area of the sheath and of the difierence in temperature between the surface of the sheath and the surrounding medium.

In accordance with one embodiment of the present invention, an electrical heater is provided which substantially improves upon the heat dissipation from the resistance element. The invention utilizes a longitudinal resistance element comprised of a twisted wire core which includes so-called spine or metal bristles frictionally or otherwise retained between the spirals of the wire core and which transmit the generated or transmitted heat laterally by conduction along the paths of the metal bristles.

The metal bristles serve eflectively to increase the exterior surface area of the resistance heating element to permit an improved dissipation of heat per unit length without materially affecting its electrical properties. The design of the twisted wire core is simple and may be mass produced by automatic machine techniques. Due to its similarity in construction to twisted bristle brushes, it may also be feasible to use many of the same techniques in constructing the heater construction of this invention.

It is therefore a general object according to the present invention to provide a heating device which has improved 3,479,489 Patented'Nov. 18, 1969 ice invention to provide a heating device which is simple.-

in design, easy to manufacture, and reliable in operation.

Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings which disclose various embodiments of the present invention. It should be understood, however, that the drawings of the disclosed embodiments are designed for the purpose of illustration only and not as a definition of the limits of the invention as to which reference should be made in the appended claims.

In the drawings, wherein similar reference characters denote similar elements throughout the several views;

FIG. 1 is a perspective view of a length of a heating device forming a component of the arrangement according to the invention;

FIG. la is a schematic of a cross-sectional view of the heating device component of FIG. 1;

FIG. 12 is a schematic of a cross-sectional view taken along the longitudinal dimension of the electrical heating combination according to this invention;

FIG. 3 is a schematic of a cross-sectional view of the electrical heating device of FIG. 2 taken along the line 33 of FIG. 2; and

FIG. 4 is a schematic of a cross-sectional view taken along the longitudinal dimension of another embodiment of the invention.

Referring to the figures, and particularly FIGS. 1 and 1a, there is shown a component of a heating device according to the invention having an outer sheath 10 consisting of an elongated metal tube. Disposed substantially along the axis of sheath 10 is a wire core comprised of two electrical conductors 11 and 12.

The two conductors 11 and 12 may be made of any appropriate materials which, for electrical heating purposes, might be Nichrome, platinum, Chrome-Alumel, etc.; the conductors might be embedded in insulating material 13 such as magnesium oxide, etc.; and the sheath material might be Inconel, stainless steel, etc.

Referring more particularly to FIG. 2, two such sheathed tubes or heating devices 10a and 10b, each encasing a pair of electrical conductors such as 11 and 12, are twisted or wrapped about each other fairly tightly within the physical limits of the materials of the con struction. Interleaved and locked between the spirals or twists of the conductor cores 10a and 10b are a multitude of heat conductors or dissipators 14. Heat conductors 14 are in good physical and thermal contact with the sheaths of the electrical conductor cores 10a and 10b.

As one moves longitudinally along the length of cores 10a and 10b, conductors 14 are seen directed through almost every degree of are along the imaginary envelope of the tips of the conductors or dissipators 14, as shown in FIG. 3. The conductors 14 serve to dissipate heat from the cores 10a and 10b into the adjacent spatial region. The heat conductors 14 may be metallic conductors or rods such as aluminum, copper, etc., and they may even be made of boron nitride.

Twisted core conductors 10a and 10b may also comprise tubes (FIG. 4) which carry a suitable heating or cooling fluid from, for example, an air-conditioner or heat exchange unit. The fins 14 also are employed in similar fashion in this embodiment for heat dissipation purposes. Twisting the tubes or pipes about each other must be performed with care to avoid any rupture of the tubes or pipes.

As already stated, the heat conductors 14 may be constructed of any materials having good heat conduction or dissipation properties, such as aluminum, copper and the like. The heat conductors may, if desired, be composed of appropriate synthetic materials which have good heat conduction properties. The heat conductors 14 obviously need not be metallic. When so designed, then whatever their composition, they can be employed in an electrical conduction system such as that shown in FIG. 2, or in a fluid heat exchanger system such as that shown in FIG. 4, to dissipate the transmitted heat into the adjoining space or room or, in the case wherein a cold fluid is circulated through hollow tubes and 10b as in FIG. 4, to absorb heat from the environment.

The twisted wire core and the heating conducting bristles may be formed separately on automatic machines and assembled into the combination shown in FIGS. 2, 3 and 4.

If conductor cores 10a and 10b are to carry heating or cooling fluids, as indicated in FIG. 4, suitable fluid connections or piping may obviously be provided in any well known manner at the ends of the conductor cores. Similarly, if conductor cores 10m and 10b are to serve as electrical resistance heaters, as in FIG. 2, electrical terminals may obviously be provided in any well known manner at one or both ends of the core constructions according to the invention. As it is readily feasible to sufliciently insulate conductor 11 from conductor 12 in either of the electrical heater cores, it is possible to drive a series electrical current over a return path through the conductors by connecting conductors 11 and 12 together at one end of the core construction. The conductors 11 and 12 may also be connected in parallel by providing electrical terminals at both ends of the heating core element.

It is obvious from the above disclosure that the construction of this invention may embody coaxial cable units each embodying one or more conductors such as 11. And the cable units need not be wrapped or twisted about each other. However, the heat conductors may be either metallic or non-metallic elements having relatively good heat transmission qualities and may be fastened or otherwise aflixed to or between the cable units so as to conduct the electrically generated heat from the cable units to the adjoining space. The sheaths of the cable units need not be metallic. Furthermore, the invention is equally applicable to similar unwrapped or untwisted pipe structures in which a fluid conveyor is transported.

The heat dissipators will relay the heat of the fluid to the outer space or absorb heat from the outerspace and conduct it to a cold fluid in the tubes.

Each twisted core unit, such as 10a, need not be limited to one having but two conductors, but the unit may include any desired number of conductors constructed from fluid tubing or from electrical resistance heating wire, as the case may be. Furthermore, each combination of core units need not be limited to two, as shown in FIGS. 2 and 4, but the combination may embody any desired number of core units wrapped about each other to grip and maintain numerous heat conductors such as 14. The relative tightness of the twists will lock the heat conductors 14 in substantially immovable positions between the core units.

Although the heat transmission elements 14 have been shown and described as radial elements, naturally these elements 14 may be positioned or held at any desired angle or orientation with respect the longitudinal path of the elements 10a and 10b. The angle or orientation may be perpendicular to the general path of the elements 10a and 10b, or positioned at any other angle or orientation, such as 80, 100 etc. Furthermore, the elements 14 may be closely spaced or widely spaced from each other; indeed, they may even be crowded together and hence virtually in close or intimate contact with each other. Also, they may be long elements or short elements, and each element may have any desired cross-sectional configuration, such as circular, elliptical or square. They may be flexible or inflexible. All of these physical factdrs would be considered in arriving at a desired design of a heat transfer device for a particular installation or operation and these factors would be considered in connection with the number of twisted core elements and their physical and thermal characteristics for the installation or operation.

While only a few embodiments of the present invention have been shown and described, it will be understood that many other changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

What is claimed is: I

1. A heat transfer apparatus comprising; two longitudinal electrical current-carrying conductor cores electrically insulated from each other and helically twisted about each other, and a multitude of linear heat transmission elements held and secured between the twists of said conductor cores.

2. The apparatus as recited in claim 1, wherein each of said twisted cores comprises at least one electrical re.- sistance wire.

3. The apparatus as recited in claim 1, in which each of said cores comprises a plurality of electrical resistance wires mounted within a sheath and the space between the wires and between the wires and the sheath is filled with an insulating material.

4. The apparatus as recited in claim 3, wherein each of said heat transmission elements is made of heat conducting material.

5. The apparatus as recited in claim 2, said electrical resistance wires are connected in series.

6. The apparatus as recited in claim, 2, said electrical resistance wires are connected in parallel.

7. The combination of a pair of electrical currentcarrying core members helically twisted about each other over a generally linear path, and a plurality of linear fins interposed between and held by the core members for supplying heat derived from the core members into the surrounding space.

8. A claim according to claim 7, in which each electrical core member includes a material having a substantial resistance per unit of length and generates and transmits heat in substantial amount when current flows through.

9. A claim according to claim 8 in which each resistance material is enclosed within a sheath which is filled with a powder having substantial insulating capability.

10. A heat transfer device for a pair of linear cores helically twisted about each other and electrically insulated from each other and which carry heating electrical current, comprising a plurality of linear heat transmitting fins positioned in physical contact with said linear cores throughout the length of the cores, said fins being held between and maintained substantially perpendicular to said linear cores and dissipating heat developed by said linear cores.

11. A heat transfer device according to claim 10, in

which the fins are made of a material which is classifiable both as a good electrical insulator and as a good heat transmitter.

12. A heat dissipator according to claim 10, in which the fins are composed of boron nitride.

13. A heat transfer device according to claim 10, in which the transmitting fins are bilateral heat conducting media which will transfer heat from the surrounding space to the linear cores when the surrounding space is at a higher temperature than those of the linear cores and will transfer heat from the linear cores to the surrounding 5 space when the temperature of the cores exceeds that of the surrounding space.

14. A heat transfer device for maintaining a spatial region within predetermined temperature limits, comprising two linearly arranged electrical core elements electrically insulated from each other and helically twisted about each other, a plurality of linear fins having good heat transmitting properties, and means for fastening said fins between said core elements to hold and maintain said fins substantially perpendicular to said core elements so that said fins may transfer heat between said core elements and the spatial region.

15. A heat transfer device according to claim 14, in which the fins are made of heat conducting metals.

References Cited UNITED STATES PATENTS 4/1928 Hicks et al. 219-540 7/1937 Soverhill 219-540 X 6/1941 Novak 165-185 X 4/1944 Clancy 165-177 X 11/1959 MacCracken 219-530 X FOREIGN PATENTS 9/ 1963 Japan.

VOLODYMYR Y. MAYEWSKY, Primary Examiner US. Cl. X.R.

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