US3214572A

US3214572A - Electrical heater

Info

Publication number: US3214572A
Application number: US204441A
Authority: US
Inventors: Charles J Young
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1962-06-22
Filing date: 1962-06-22
Publication date: 1965-10-26
Anticipated expiration: 1982-10-26

Description

Oct. 26, 1965 c. J. YOUNG 3,214,572

ELECTRICAL HEATER v Filed June 22. 1962 2 Sheetg-Sheet 1 INVEN TOR. CAM/(YES J Yaw/6 ,4 rraemsr Oct. 26, 1965 c. J. YOUNG ELECTRICAL HEATER 2 Sheets-Sheet 2 Filed June 22, 1962 INVENTOR. Z

Arram zy United States. Patent ()ffice 3,214,572 Patented Oct. 26, 1965 ELECTRICAL HEATER Charles J. Young, Princeton, N.J., assignor to Radio Corporation of America, a. corporation of Delaware Filed June 22, 1962, Ser. No. 204,441 3 Claims. (Cl. 219-550) This invention relates generally to improved electrical heating elements and particularly to improved resistive electrical heating elements of the type employing a ribbon of resistive material. 7

In heat exchange systems wherein a flow of air is to be rapidly heated, a ribbon type of resistive electrical heater element is preferred since it provides more surface than a wire of the same cross-section, and therefore more efiicient heat exchange. However, such a ribbon element is mechanically unstable because of thermal expansion and loss of stillness at red heat. This is particularly true wherein the element must be a relatively thin ribbon in order to satisfy fixed requirements of wattage and supply voltage. Ordinarily, a looped or folded thin ribbon of resistive material loosely supported in channels of insulat ing material becomes distorted when heated, causing iineven distribution of heat.

An object of the present invention is to provide an improved electrical heating element. v 7

Another object is to provide a resistive heating element having improved mechanical stability. I

I A further object is to provide a resistive heating element having improved uniformity of heat emission.

Another object is to provide an electrically resistive heating element providing improved and efiicient heat ex: change. I

The foregoing objects and advantages are provided in accordance with the invention which comprises a resistive ribbon type electric heating element including a plurality of convolutions of the ribbon element wherein each convolution mechanically contacts the next adjacent convolutions at a plurality of evenly-spaced points interniediate the ends of the convolutions thereby providing improved mechanical support and stability. I

The several convolutions in contact with the adjacent convolutions may provide diamond-shaped, cnsp shaped or triangular-shaped, or the like, openings therebetween for the passage of air to be heated. Insulation between the contacting portions of the adjacent convolutions may be provided by surface oxidation'of the heating element or by interposed insulating strips. The heating elements may comprise single or multiple pancakes of such convolutions, connected in series or parallel, and with the convolutions arranged either longitudinally, or annularly. The successive convolutions of each resistive element may be supported loosely in channels of cooperating parallel'or concentric insulating supports. V

The invention will be described in greaterdetail by reference to the accompanying drawings in which:

FIG. 1 is an end view of a resistive element with its cooperating channels in insulating supports;

FIG. 2 is a schematic side view representation of a prior art ribbon type heating element;

FIG. 3 is a schematic side view representation of a first embodiment of the invention showing diamondshaped openings'between adjacent heating convolutions;

FIG. 4 is a schematic side view representation of an expanded portion of the heater element of FIG. 3;

FIG. 5 is a schematic side view representation of a modification of the convolution arrangement of FIG. 3 showing a heating element having a larger number of diamond-shaped openings between adjacent convolutions;

FIG. 6 is a schematic side view representation of another embodiment bf the invention showing convolutions having a plurality of cusp-shaped portions contacting similar portions in adjacent convolutions;

\ *FIG. 7 is a 's'tiherriatic side view representation of a thirdenibodirnentofthe invention showing a plurality of zigzag convolutions inter's'pers'ed between straight ribbon portions of the heating element;

FIG. 8'i's "sifn'ilai'"to FIG. -5 with the exception that adjaeentc nvolut'ions "are insulated one from the other by mica 'dr other insulating sheets, indicated by dash lines, looselysupported between said convolutions;

FIG. 9a is asche'matic end view representation of a foiii th embodiment of the invention showing an annular ai'ra g nie'i'itof the resistive'elern'ent of FIG. 3;

FIG. 97; is a modification of the embodiment shown in FIG. 9'a' with the type of resistive element shown in "FIG. 5; and p 7 "FIG; 10 is "a s'eheinatic cross-sectional view taken alongthe sectioii line 10 10 of FIGS. 9a and 9b of a plurality of annular resistive elements in a blower structiire.

'Sii'nilarreference*haractei's are applied to similar elerrieiits throughout the drawings.

R erring to FIGS. 1 and 2 of the drawing, a prior art "resrsti'vetypefelectric heater element 1 includes successiveloops of Nic hrome ribbon loosely supported in channels :3, '5 of

insulating supports

7, 9, respectively. The ins'u ting supports may comprise any insulating ceramic material eapable of withstanding the heat generated by the element 1. As shown by the dash lines 1l,fwhen"the"'heatingelement 1 is heated to a bright red temperature, the suec'essive'convolutions become distorteid, "thereby providing haphazard electrical contact therebetween and uneven heat distribution along the length of the leile'infent 1. Furthermore, the rounded portions l3fwithin the ehannels' 3, 5 have a substantial area which is out ofthe circulation path of air blown through the heating element as indicated by the arrow 15 in FIG. 1.

Y FIG. 3 shows an embodiment of the invention wherein element. The ends '17 of the convolutions form angles which are loosely "supported within the

channels

3, 5 in the ceramic insulating supports 7, 9, respectively. The angles 171211 the ends of the successive convolutions provide a minimum area of the element 1 outside of the direct airflow through the heating element. The

diamond-shaped convolutions are uniformly arranged to provide an 'even'nii'rnber of contacting points 19 between adjacent eonvolutions. The ends of the heating element are terminated in any desired manner in suitable terininals 21. Thedesired number of convolutions of the heating elements are squeezed together in firm contact with each next adjacent convolution by ceramic plugs 23.

Prior 'to thefinal'assembly, the successive convolutions are stretched apart as shown at the right in FIG. 4 and heated to a bright red temperature to form an oxidized coating thereon which'vvill prevent electrical contact between successive convolutions at the points 19 when the heating element is finally compressed as shown in FIG. 3. "If desired, an oxidizing atmosphere will assist in forming the oxidized layer on the heating element. If on assembly one or more bright spots are found at contacting points 19, the oxidation process is repeated until this condition is overcome.

A heater element as shown in FIG. 3, having a crosssectional area of only 1 x 9 inches, has been tested for hundreds of hours of operation with substantially no which supports the center ceramic support deformation of the convolutions thereof and-no shorting H volutions of the heater elements of FIGS. 3 and 5 can be extended to any desired width, but the intersectingpoints between one convolution and the two adjacent convolutions will always be even in number.

FIG. 6 shows another embodiment of a ribbon heater element in accordance with the invention wherein instead of preformed zig-zag convolutions, each convolution includes a number of arcuate or cusp-shaped portions eachcontacting the center of similar arcs or cusps at the points 20, and wherein, as in FIGS. 3 and 5, there are an even number of such contacting points between adjacent convolutions.

FIG. 7 shows another embodiment of the zig-zag convolutions having a straight convolution 21 interspersed between alternate zig-zag convolutions 23. This arrange-.

ment also provides an even number of contacting points 25 between adjacent convolutions.

heattransfer characteristics thereof are quite similar.

While in FIGS. 3, 5, 6 and 7 insulation of the surface of the resistive element is provided by oxidation thereof.

to prevent electrical contact at the successive mechanically contacting points between successive convolutions, FIG. 8 shows an alternative arrangement, having convolutions shaped similarto FIG. 5, but wherein the insulation between successive convolutions is provided by thin mica,

or other insulating, sheets indicated by the dash lines 27. The insulating sheets 27 may be loosely supported between adjacent convolutions merely by the pressure exerted thereon to squeeze them together in the final assembly of the heater element.

FIG. 9a shows an annular type of diamond-shapedv heater element wherein the zig-zag convolutions are sup- -ported in concentric channels 31, 33 in concentrically disposed ceramic cylinders 35, 37, respectively. The ends of the heater element 29 are terminated in

suitable terminals

39, 41 and are. physically separated by a radial ceramic insulator 43.

The structure of FIG. 9b is similar to that of FIG. 9a with the exception that each successive convolution includes a larger number of contacting points 19, as in the structure of FIG. 5. It should be understood that the shape of the convolutions may alternatively be according to the teachings of FIGS. 6 or 7 or the like, and that if desired the insulating spacers 27 of FIG. 8 may be substituted for the oxidized surface on the heater element to prevent electrical contact between successive convolutions.

FIG. shows an arrangement wherein a plurality of

annular heaters

51, 53 as in FIGS. 9a or 9b are arranged in parallel pancakes, supported in concentric-slots 55-, 57 of

ceramic supports

59, 61, respectively. The

heater elements

51, 53 may be electrically connected in series or in shunt as desired. An air stream indicated by the arrows 63 is provided by a blower fan 65 driven by a motor 67 However, the struc-. ture of FIG. 7 does not provide as great mechanical stability as the structures of FIGS. 3, 5 and 6 although the 59. The mo- -tor is supported within the outer ceramic support by radial legs 69. It will be seen that the fan 65 cools the motor 67 prior to projecting the air stream 63 through the

successive heaters

53, 51.

What is claimed is:

1. An electrical heating element comprising a single continuous ribbon of electrically resistive material formed into a pattern of a plurality of successive complementary convolutions, the ends of each convolution forming an angle with the next adjacent convolution, cooperating in sulating supports for said ends channeled to receive said ends in slidable contact, alternate ones of said convolu-" tions having a zig-zag conformation to contact a next adjacent substantially straight convolution at regularlyspaced points intermediate said ends thereof to increase the rigidity of said ribbon element, means for insulating said ribbon element at said contact points, and means for connecting said ribbon to a source of electrical energy.

2. An electrical heating element comprising a single continuous ribbon of electrically resistive material formed into a pattern of a plurality of successive complementary convolutions, the ends of each convolution forming an.

angle with the next adjacent convolution, cooperating insulating supports for said ends being channeled to receive said ends in slidable contact, each of saidconvolu-. tions having a zig-Zag conformation to contact the next adjacent convolutions at an even number of regulraly spaced points intermediatesaid ends thereof to increase the rigidity of said ribbon element, means comprising anoxide layer on the surface of said material for insulating said ribbon element at said contact points, and means for connecting said ribbon to a source of electrical energy.

3. An electrical heating element comprising a single continuous ribbon of electrically resistive material formed into a pattern of a plurality of successive complementaryconvolutions, the ends of'each convolution forming an' angle with the next adjacent convolution, insulating supports for said ends being channeled to receive said ends in slidable contact, each of said convolutions having a zig zag conformation to contact the next adjacent convolu tions at a number of regularly-spaced points intermediate said ends thereof to increase the rigidity of said ribbon element, means comprising an oxide layer on the surface of said material for insulating said ribbon element at said contact points, and means for connecting said ribbon to a source of electrical energy.

References Cited by the Examiner UNITED STATES PATENTS RICHARD M. WOOD, Primary Examiner.

Claims

3. AN ELECTRICAL HEATING ELEMENT COMPRISING A SINGLE CONTINUOUS RIBBON OF ELECTRICALLY RESISTIVE MATERIAL FORMED INTO A PATTERN OF A PLURALITY OF SUCCESSIVE COMPLEMENTARY CONVOLUTIONS, THE ENDS OF EACH CONVOLUTION FORMING AN ANGLE WITH THE NEXT ADJACENT CONVOLUTION, INSULATING SUPPORTS FOR SAID ENDS BEING CHANNELED TO RECEIVE SAID ENDS IN SLIDABLE CONTACT, EACH OF SAID CONVOLUTIONS HAVING A ZIGZAG CONFORMATION TO CONTACT THE NEXT ADJACENT CONVOLUTIONS AT A NUMBER OF REGULARLY-SPACED POINTS INTERMEDIATE SAID ENDS THEREOF TO INCREASE THE RIGIDITY OF SAID RIBBON ELEMENT, MEANS COMPRISING AN OXIDE LAYER ON THE SURFACE OF SAID MATERIAL FOR INSULATING SAID RIBBON ELEMENT AT SAID CONTACT POINTS, AND MEANS FOR CONNECTING SAID RIBBON TO A SOURCE OF ELECTRICAL ENERGY.