AU427406B2 - An improvement for partially increasing heat tobe generated ina heat-generating pipe system utilizing skin effect current - Google Patents

Description

18.8 5 9/70 The present invention relates to an improvement for

partially increasing the amount of heat to be generated, in

a heat-generating pipe system utilizing skin effect current.

The heat-generating pipe system utilizing skin effect current referred to herein is a heat-generating pipe composed

of a ferromagnetic pipe or pipes and an insulated wire passing

therethrough, and having such a circuit that a.c. can flow

concentratedly only on the inner skin portion of the ferro-

magnetic pipe.

Some of the examples are such an apparatus as that

described in the specification of Japanese Patent No.

460,224 (Patent Publication No. 12128/1965) entitled "Method

for transporting viscous liquid or liquid.needing temperature maintenance, and transporting pipe equipment thereof",

(corresponding to United States Patent Application No.

3,293,407), or in the specification of Japanese Patent

Application No. 20427/1966 entitled "Heat-generating pipe

apparatus utilizing skin effect current" (corresponding to

United States Patent No. 3,515,837).

Figures la and lb of the accompanying drawings illustrate the principle of the heat-generating pipe system described in

the specification of said Japanese Patent No. 460,224 (United States Patent No. 3,293,407).

In these Figures, numeral 1 shows a ferromagnetic pipe such as a steel pipe, and numeral 2 shows an insulated wire

passing through the inside of the ferromagnetic pipe, one end of which is connected to one terminal of an a.c. power source

3 and the other end of which is connected to one end 5 of the

ferromagnetic pipe 1 remote from the power source.

The other end 4 of the ferromagnetic pipe 1 nearer

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18.8 5 9 no to the power source, is connected to the other terminal of

the power source 3 by a wire, whereby alternating currenits

6 and 6' flow as showrn by arrows, and alternating current

6' flowing through the ferromagnetic pipe I is concentrated

only in the inner surface skin portion. Figures 2a and 2b illustrate the principle of the heat-generating pipe/described in the specification of

said Japanese Patent No. 20427/1966 (United States Patent

No. 3,515,837). In this Figure, numerals 7 and 7' show two

ferromagnetic pipes such as a steel pipe, both the ends there-

of being mutually connected together by conductors 8 and 8'.

Numeral 9 shows an insulated wire passing through the inside

of the ferromagnetic pipes, both the ends thereof being con-

nected to an a.c. source 10. In this case, induction cur-

rents 11 and 11' flow through the ferromagnetic pipes 7 and

7' and conductors 8 and and alternating current 11 flow-

ing through the ferromagnetic pipes 7 and.7' is concentrated

only in the inner surface skin prtion thereof. In these heat-generating/P-es the region where

the alternating current flows on .the surface portion of the

ferromagnetic pipe is called the skin depth of alternating

current. The skin depth of alternating current, S (cm) is

given by the following formula,

S 5030 JO J~f (1)

wherein Resistivity of a ferromagnetic

pipe (t cm)

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18.8 5 9 no Permeability of the same

f Frequency of the alternating

Current. (Hz).

If the above-mentioned ferromagnetic pipe has a thickness of t a length of, (cm) and an inner diameter of d and among them, there is a relationship

of

t>2s, d (2) alternating currents 6' and 11 flow concentratedly only

on the inner skin portion of the ferromagnetic pipe, and

almost no voltoage appears on the outer surface. According-

ly, even if the outer surface of the ferromagnetic pipe is

short-circuited by a wire having a low impedance, almost no current leas:s out, and safety is maintained even in contact with any object to be heated, and hence such appaeatue can be utilized as a safe heat-generating/ijpe Thus such a heat-generating/ippe can be utilized as an economical means

for heating or temperature-maintenance of a transporting pipe

of a fluid, surfaceaof roads, floors or walls of buildings,

and the like.

In the utilization of the heat-generatina/pi4pe

there is often encountered a case where a partial increase

of heat to be given to an object such as the above-mentioned

transporting pipe, is required. -Por example, when said

transporting pipe is supported by stanchions, heat escapes

through the stanchions, and the temperature on these parts

of the transporting pipe is more reduced than on other parts

thereof. Thus, in case of transporting a viscous liquid,

there sometimes occurs such a disadvantage as plugging in

these parts. While, in case of a condensible gas, there

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is a fear of such a disadvantage that condensation occurs in

these parts.

An object of the present invention is to provide an

improvement for partially increasing the amiount of heat to be

generated in a heat-generating pipe system utilizing skin

effect current, in order to overcome such drawbacks. Such

an object has been found to be attained by the present

invention.

The present invention resorts, in the abovementioned heat-

generating pipe system utilizing tkin effect current, to such

a method that the ferromagnetic pipe is cut and divided into

two portions, within a section where increase of heat to be

generated is required, and the two locations on the outer

surfaces of the divided ferrornaqnetic pipe portions at both

ends of the section are connected by a conductor, whereby,

within the section, a.c. flows also on the outer skin portion of the ferromagnetic pipe, and the amount of heat to be

generated within the section is increased.

The present invention will be further illustrated referring

to the accompanying drawings.

Figures la, lb, 2a anC 2b 4iJ.1ustrate the princinles of

publicly known heat-generating pipe systems utilizing skin

effect current, as alreadNy mentioned above, and Fiqures la an12 2a show a cross-sectional view in the longitudinal direction,

while Figures lb and 2b show a lateral cross-sectional view

along lines I-I' and II-II' in Figures la and 2a, resnectively. Figures 3a and 3b illustrate the principle of thc

present invention, and Figure 3a shows a cross-sectional view

in the lonqitudinal direction, while Figure 3b shows a cross-

sectional view along line III-Ill' in Figure 3a.

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Figures 4a and 4b illustrate an embodiment of

the present invention, and Figure 4a shows a cross-sectional

view in the longitudinal direction, while Figure 4b shows

a cross-sectional view along line IV-IV' in Figure 4a.

Figures 5a and 5b illustrate another embodiment

of the present invention, and Figure 5a shows a cross-section-

al view in the longitudinal direction, while Figure 5b shows

a cross-sectional view along line V-V' in Figure

In Figures 3a and 3b, numeral 12 shows a trans- porting pipe of fluid, and an increase of heat within a section between X and Y is contemplated. In these Figures, an insulated wire 13 corresponds to the wire 2 of Figures a and 1b or the wire 9 of Figures 2a and 2b. Alternating current 14 flows through this wire 13, and currents 16 and 16' corresponding respectively to a.c. 6' of Figure la and a.c. 1 of Figure 2a flow

Now, the pipes 15 and 15' are not continuous

and hence different from the ferromagnetic pipes 1 of Figures

la, lb and 7, 7' of Figures 2a, 2b. Namely, they are cut

and divided into two portions at.the part 17 of Figure 3a,

and the points 18 and 18 on the outer surface of said ferro-

magnetic pipes at both the ends of the section between X and

Y are connected by a conductor 19. When the transporting

pipe 12 is made of steel, its outer surface portion can func-

tion as a conductor by welding it to pipes 15 and 15' at both

points 18 and 18'. Due to such dividing, the current flowing

through the pipes 15 and 15', flows through both the inner

and outer surfaces of the pipes 15 and 15' within the section between X and Y to form a circuit, as shown in this Figure,

Nanely, the current 16' flowing concentratedly through the

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inner skin portion of the pipe 15', passes from the inner

skin portion to the outer skin portion at the cut end of

the pipe, further passes through a connecting point 18, a

conductor 19 and a connecting point 18 to the pipe 15, flows

through the outer skin portion of this pipe 15, passes from

the outer skin portion to the inner skin portion at the cut

end thereof, and flows therethrough as an inner skin current 16.

Thus, in each part of the ferromagnetic pipes

between X and Y, an equal amount of current flows on both

the inner and outer surfaces, and since the heat gen-ration

of the heat-generating pipe utilizing skin effect current is

generally caused mainly by the current flowing through the

ferromagnetic pipe, it will be understood that an increase

in the amount of heat to be generated resuilts between X and Y. In order to improve the conduction of the increas-

ed heat, a substance which has an electrically inferior but

thermally good conductivity, can be filled in the clearance

part between the ferromagnetic pipes 15, 15' and the object

to be heated 12. As such a substance, a heat-conductive

cement composed mainly of graphite can be illustrated. Figure 4 illustrates another embodiment of the

present invention. Numeral 12' shows a transporting pipe

of steel, numerals 13, J416 and 17 are of the same as in

Figure 5, and numerals 15 and 15' show steel pipes. An

external box 20 made of plate of ferromagnetic matcrial such

as steel is welded to the steel pipes 15, 15' and the trans-

porting pipe 12'. Numeral 21 shows a stanchion. As shown

in this Figure, the current 16' passes from the imnner skin

portion to the outer one of the steel pipe 15' at the cut end

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18,8 59

of the pipe, flovs through the skin portions of the trans-

porting pipe 12' and the 'ex::ternal box 20, then flows through the outer skin portion of the steel pipc 15, passes to the inner skin portion at the cut end of the pipe 15, and flows therethrough as an inner skin current 1.6. In this apparatus, if the external box 20 and the transporting pipe 12' have each a sufficient thickness, i.e. a thickness more than twice the depth of the s.:in effect current, practically no current

appears on their outer surfaces, and thus safety is maintain- ed. Also, the external box 20 protects the part of the

vire 13 exposed at the gap 17 from any abrasion coming from

the outside. In the apparatus of Figures 4a and 4b, the amount of heat to be generated between X and Y is slightly

less than twice those of other parts. The amount will be explained as follows:

The resistance per cm run of the inner skin portions of the ferromagnetic (steel) pipes 15, 15' inside of the external box 20, R, (fl- is expressed using

the equation as follows:

TV do 50307Ld while the resistance R 2 (A/cm) per cm run of the outer skin

portions, R2 is expressed as follows:.

R 16SH 2 5030 1 D (4)

wherein D (cm) is the outer diameter.

Since D d 2t

Rr R2 (6) results, and therefore the resistance per cm run of the skin

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portions including both the outer and inner ones of the steel pipes 15, 15' between X and Y, R (fl/cm), has the following relation: R R1 R2 Z. 1 The amount of heat to be generated is generally in proportion to the circuit, hence the amount of heat to be generated between X and Y is slightly less than twice that of the other part. In order that the equations are per- fectly held, one of the conditions among the relations, i.e. t> 2s, must become such an extent that the condition t >4S (8) is also held. Since the steel pipes 15, 15' are usually welded to the transporting pipe 12' in order to make the heat con- duction easy, the temperature difference between the steel pipes and the transporting pi-e is very small. However, since the parts between X and Y, of the steel pipes 15, are welded to the external box 2U only at their piercing parts, and they cannot be welded, to other parts of the box nor to the transporting pipe 12', the temperatures of these parts under such a situation may rise above tihe allowable range. In such a case, a heat-conductive cement 22 composed

mainly of graphite as mentioned above which has an electric- ally inferior but thermally good conductivity, is filled within the box. Thus, an abnormal rise of teimperature in these parts, i.e. the section between X and Y, of the steel pipes 15, 15' can be avoided. Figure 5 illustrates concretely a method for further increasing the amount of heat to be generated, within

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the Goction between X and Y, wherein ferroagnrctic rings are .st-ru11y; on tht3 hr'roinagnotic pines within the section between X and Y, as shown in Pi--ure 3. In this Figure 5, numeral 12' shows a transport- ing iJc of steel, otnd numerals 13, 14, 16 and 17 are of the sari3 meaing a±s in F igure 3. Steel pipes 15, 1 5' are welded to said trana-'ortlrng piue 12', at each point 18 and 18' on their outer surfaces located at both the ends of the asection betw~een X and Y. IThueral 23 shows ferromnagnetic rings such as steel ones. 1,u .ral 25 shows a stanchion welded to the trunsporting pipe of' steel, throug;h which heat escapes. An edd.7' current 24. is induced on the above-mentioned rings 23, by the current flo,.-in.g through the outer skin portion of the ferromagnetic pipes onto which rings are strung and by the current flow,,ing through a conductor connecting the outer sur- face points 1S and 18' at both the ends of the section be- tw-een X and Y of the above-mentioned ferromagnetic pipes (in thiis Fiigure 5, the section betwleen X and Y, of the, transport- ing steel pipe corresponds to the conductor 19 in Fvigurwe 3), vhereby heat-generation occurs in the rings 23. The thick- neas T of the section of' the6 rings is preferred to be T> 2s. If' the rings are made of steel and the current floviing throuh the fe±'romiagnctic pipes has a commercial frequency, 3 mm or more of the above-mentioned thickness T may be sufficient. The number of the rings cam be increased according to the required increase of heat to be genertted. As to the cross- sectional shape of the ring,,s, a circular one is illustrated in 7i.gure 5, but any one of.G retanular, trapezoidal ones, or the like can be selected. The hoat generated on these rings i, Trrefer;,'lY cconducter'l to the transporting pipe 12'

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18.8 5 9

through a cement 26 which has an electrically inferior but

thermally good conductivity. The reason why the cement 26

should have an electrically inferior conductivity is that an electrical short-circuit among the transporting pipe 12',

ferromagnetic pipes 15, 15' aind the rings 23 must be prevent- ed. In the usual constructions, since the potential dif-

ference among them is within the range of several volts, even

such a heat-conductive cement as composed mainly of graphite

can be sufficiently used. If a box composed of a ferro-

magnetic material as shown in Figure 4-ao4

above rnto.e d 16eel -ipc5s 45, rng is provided in such a way as to accommodate the above mentioned steel

pipes 15, 15' and rings 25, safety is maintained without

any current leaking outward, and the part of the wire 13

exposed in the gap 17 can be protected from abrasion coming

from the outside.

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Claims (1)

18.8 59 no

The Claims defining the invention are as follows:-

1. In a heat-generating pipe system utilizing

skin effect current, composed of a ferromagnetic pipe or

pipes and an insulated wire passing through the inside there

and having such a circuit that when an alternating current

is passed through the insulated wire, a current flows throug

said ferromagnetic pipe by way of the insulated wire, or by induction of the a.c. current passed therethrough

forming a concentrated flow only on the inner skin portion

of said ferromagnetic pipe(s), an improvement for partially increasing the amount of heat to be generated in said heat-

generating pipe utilizing skin effect current which comprisei

said ferromagnetic pipe or at least one of said pipes being

cut and divided into two portions, within the section where

increase of heat to be generated is desired, and an electric

conductor connecting two locations spaced on the outer sur-

faces of the divided pipe portions at either end of the

section whereby, within the section, the current flows

through not only the inner skin portions but also the outer

skin portions of the pipe portions within the section.

2. heat generating pipe system according to

claim 1, wherein a substance which has an electrically inf-

erior but thermally good conductivity, is filled in a clear-

ance space between the ferromagnetic pipe portions and an

object to be heated, within said section to improve the heat conductivity therebetween.

3. heat generating pipe system according to claim 2, wherein said substance which has an electrically

12 427.406

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inferior but thermally good conductivity is a heat-conductive

cement composed mainly of graphite. 4. The improvement in a heat generating pipe system

according to claim 1, wherein the electrical conductor

connecting the two locations is a box composed of a plate

or plates of ferromagnetic material having each a thickness

more than twice the depth of the skin effect current and

containing therein the ferromagnetic pipe portions within

the section.

The improvement in a heat generating pipe system according

to claim 1, wherein one or more rings of a ferromagnetic mat-

erial are strung on the ferromagnetic pipe portions or on

either portion within said section.

6. The improvement in a heat generating pipe systen

according to claim 5, wherein a substance which has an

electrically inferior but thermally good conductivity, is

filled in a clearance space among said ferromagnetic pipe

sections, said rings and the object to be heated, within said

section to improve the heat conductivity among the object to

be heated and each of the ferromagnetic pipe portions or

rings.

7. The improvement in a heat generating pipe system

according to claim 6, wherein said substance which has an

electrically inferior but thermally good conductivity is a

heat conductive cement composed mainly of graphite.

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19. Th!-c i'nrovient in a heat generating pipe system

3ccording to claim 5, wherein the electrical conductor

cornnectinax the two locations on the outar surfaces of the

(dij~ded oire portions at the both ends of the section, is a

box cornosedc of ainlatc or plates of a ferronagnetic material

having a thickness more than twice the depth of the skin effect

current xtnO accoraiodating therein the ferromagnetic pipe vortions rnd the rings within the section.

DATED this 24th day of July, 1972. CHISSO CORPORATION

EDWD.WATERS &SONS Russell Street MELBOURNE. VIC.

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FI G. Ia FIG. lb Prior Art Prior. Art

FIG. 2a FIG. 2b Prior Art Prior Art

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FIG.3a FIG.3b

FIG.4a FIG. 4b

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FIG. 5a FIG.

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