US3780250A

US3780250A - Apparatus for heating the surface of constructions

Info

Publication number: US3780250A
Application number: US00194966A
Authority: US
Inventors: M Ando
Original assignee: Chisso Corp
Current assignee: JNC Corp
Priority date: 1971-11-02
Filing date: 1971-11-02
Publication date: 1973-12-18
Anticipated expiration: 1990-12-18

Abstract

An economical apparatus is provided for heating the surface of constructions such as a road, floor, wall, etc. which comprises at least two juxtaposed ferromagnetic pipes having a wall thickness of at least twice the skin depth of a.c. flowing therethrough and an insulated electric wire passing in series through each inside of said ferromagnetic pipes, both the ends of which are connected to an alternating current source. When an alternating current is passed through said insulated electric wire, a secondary current is induced along both the inner and outer skin portions of said ferromagnetic pipes and heat is generated therein. Further, the electrically neutral points of the ferromagnetic pipes are connected to each other by an electric conductor and a fault detecting means responsive to a flow of current in the conductor is provided to disconnect the insulated wire from the alternating current source upon occurrence of an electrical fault in the apparatus.

Description

United States Patent [191 IdO Dec. 18, 1973 APPARATUS FOR HEATING THE SURFACE Primary Examiner-A. Bartis OF CONSTRUCTIONS Attorney-Fred C. Philpitt [75] inventor: Masao Ando, Yokohamashi, Japan 73 A Chi C 1 O k .1 [57] ABSTRACT 1 sslgnee' m sa apan An economical apparatus is provided for heating the [22] Filed: Nov. 2, 1971 surface of constructions such as a road, floor, wall,

etc. which comprises at least two juxtaposed ferro- [211 Appl' 194366 magnetic pipes having a wall thickness of at least twice the skin depth of a.c. flowing therethrough and [52] US. Cl 219/l0.49, 219/300, 219/519, an insulated electric wire passing in series through 317/18 D each inside of said ferromagnetic pipes, both the ends [51] lnt.Cl 1105b 9/00, HOS b l/ 02, H02h l/02 of which are connected to an alternating current [58] Field of Search 219/ 10.49, 10.51, source. When an alternating current is passed through 219/300, 301, 514, 519; 317/18 A, 18 D said insulated electric wire, a secondary current is induced along both the inner and outer skin portions of [56] References Cited said ferromagnetic pipes and heat isgenerated therein. UNITED STATES PATENTS Further, the electrically neutral points of the 3,515,837 6/1970 Ando 219/l0.49 erromagnetic pipes are connected to each other by an 3,622,731 ll/197l Ando 219/1049 electric conductor and a fault detecting means 12/1968 Beckius 219/1049 X responsive to a flow of current in the conductor is AI'IdO-i provided to disconnect the insulated wire from the #F' alternating current source upon occurrence of an lce r 3,410,977 11/1968 Ando. 219/10.49 elecmcal'fault m the apparatus 1 Claim, 5 Drawing Figures 9 1 A.C. U CE ,5) I so g PIPES 39 ELECTRICALLYNG INSULATI 38 FAULT DETECTOR PATENTEUBEE 18 ms 3,780,250

sum 1 or 2 FIG. I PRIOR ART APPARATUS FOR HEATING THE SURFACE OF CONSTRUCTIONS The present invention relates to an improvement in the heat-generating pipes utilizing skin effect current, disclosed in U.S. Pat. No. 3,410,977 and U.S. Pat. No. 3,515,837. The inventor and assignee of these patents are the same with those of the'present invention.

Firstly the background of the present invention will be given referring to the accompanying drawings.

FIG. 1 shows the principle of the heat-generating pipe utilizing skin effect current disclosed in the abovementioned U.S. Pat. No. 3,410,977. In this figure, numeral l shows a ferromagnetic pipe such as a steel pipe, and terminals 6 and 6' at both the ends of the pipe are connected to an alternating current source 5 by an electric wire 2 and an insulated electric wire 2 which passes through the inside of .the pipe.

When the resistivity of the material of the ferromagnetic pipe 1 is p cm); the specific permeability thereof is [1,; and the frequency of the alternating current source is f (Hz), the depth of skin of alternating current (a.c.), S (cm), is expressed by the following formula:

If there is a following relationship (2) among the wall thickness t (cm), the inner diameter d (cm) and the length l (cm) of the pipe 1 and the above-mentioned S:

the current 3 supplied from the a.c. source 5 flows concentratedly through the inner skin portion of the ferromagnetic pipe I, and heat is generated only at the inner skin portion. In this case, substantially no voltage appears on the outer surface of the pipe, and hence even if the outer surface is contacted with human beings or animals, they sustain no injury, and also, the heat-generating pipe does not become a cause of fire. Thus, the heat-generating pipe can be utilized as a safe heat-generating pipe for heating e.g. the surface of a road, floor, wall, etc.

FIG. 2 shows the heat-generating pipe utilizing skin effect current disclosed in the above-mentioned U.S. Pat. No. 3,515,837. In this figure,

numerals

7 and 8 show ferromagnetic pipes having the same specified conditions relative to the wall thickness and length as those of the pipe 1 of FIG. 1, the adjacent ends of the two pipes being each connected by a

connecting means

13 or 14 having as low as impedance as possible. Numeral 9 shows an insulated electric wire passing through the insides of the ,two ferromagnetic pipes and connected to the terminals of the a.c. source'12. In this apparatus, thealtemating current 10 passing through the electric wire 9 is a primary current, and the secondary current flows through the inner skin portions 11 of the ferromagnetic pipes to generate heat therein, and substantially no voltage appears on the outer surfaces of the

ferromagnetic pipes

7 and 8, as in the apparatus shown in FIG. 1. Thus, this apparatus can be also utilized as a safe heat-generating pipe. Although the above-mentioned explanation is made referring to single phase circuits, the principle of the polyphase circuit also is same as those of the simple phase circuits.

The advantages of the apparatuses shown in FIG. 1 and FIG. 2 over the MI cable or a plastic materialinsulated cable which are usually used by directly laid under the surface of road, floor or the like, are that the insulated electric wires, which are liable to suffer damages, are protected by ferromagnetic pipes having a considerable mechanical strength; that, even if the in sulated electric wire passing through the inside of the ferromagnetic pipe should suffer damages, they are readily replaced by new wires without digging up the road, floor, wall or the like; and that insulated electric wires of lower heat resistance or thinner electric wires are sufficient for the apparatuses shown in FIG. 1 and 2, because the major part of heat is generated at the inner skin portion of the ferromagnetic pipe, and the ferromagnetic pipe is contacted directly with a substance to be heated to make the transfer of heat easy, and hence the temperature of the insulated electric wire inside the pipe is relatively low.

However, the known heat-generating apparatuses shown in FIG. I and 2 have a drawback in that heat is generated only at the inner skin portion of the ferromagnetic pipe, and the outer skin portion is not utilized. Further, in the apparatus of FIG. I, the larger the surface area to be heated, beneath which the ferromagnetic pipe I is distributed, the greater the number of bend parts to be provided. Thus, it becomes necessary to connect straight pipes with bend pipes by expensive on-the-spot welding. Also in the apparatus of FIG. 2, the connection by welding of the

electric wires

13 and 14 having a low impedance is, as a matter of fact, carried out on the spot, and the cost becomes higher than the material cost of the ferromagnetic pipe such as steel pipe, in some cases.

The object of the present invention is to provide an apparatus for heating the surfaces of constructions such as a road, floor, wall, etc. which does not require expensive on-the-spot working, is safe and utilizes both the inner and outer skinportions of the ferromagnetic pipe as heat-generating portions, whereby about twice the quantity of heat generated by the above-mentioned known heat-generating apparatuses can be obtained.

The present invention resorts to an apparatus for heating the surface of constructions which comprises at least two juxtaposed ferromagnetic pipes having the wall thickness of at least twice the skin depth of a.c. flowing therethrough, and an insulated electric wire passing in series through each inside of said ferromagnetic pipes, both the ends of which are connected to an alternating current source, whereby when an altemating current is passed through said insulated electric wire, a secondary current is induced at both the inner and outer skin portions of said ferromagnetic pipes to generate heat there.

As the insulated electric wire passing through the inside of the pipes, there can be illustrated copper or aluminum wires coated with an insulated material such as organic high molecular weight substances.

As the surface of constructions, there can be illustrated the surfaces of a road, floor, wall, etc.

FIGS. 1 and 2 are schematic cross-sectional views for illustrating the principles of known heat-generating pipes utilizing skin effect current.

FIG. 3 is a schematic view for illustrating the principle of the induction heat-generating pipe of the present invention. 1

FIG. 4 is a schematic plan view of the apparatus of the present invention. v

FIG. 5 is a cross-sectional view of FIG. 4 along the VV line.

Next, the present invention will be further illustrated referring to the accompanying drawings.

The schematic view shown in FIG. 3, illustrating the principle of the present invention is the same as that shown in FIG. 2 except that the

low impedance connections

13 and 14 of FIG. 2 are omitted. Thus, in the apparatus of FIG. 3, voltage appears alsoon the outer surfaces 19', 20' of

ferromagnetic pipes

15 and 16. FIG. 3 will be explained further in detail. An insulated electric wire 17 passing through the inside of the ferromagnetic pipe 15,.16, forms a primary circuit together with an a.c. source 21, and an electric current 18 flows therethrough. Secondary electric current is induced in each of the

ferromagnetic pipes

15, 16, and a circuit of the current is formed between the inner skin portion 19 and the outer skin portion 19' in the ferromagnetic pipe 15, while another circuit of the current is formed between the inner skin portion 20 and the outer one 20' in the ferromagneticpipe 16, to generate heat at both'the innerskin portion and the outer one. Such a secondary current is nothing but an eddy current.

In order to make the best use of the present inven tion, it is necessary that the wall thicknesses of the above-mentioned

ferromagnetic pipes

15, 16 are at least twice the skin depth of a.c. flowing therethrough expressed by the formula (1). I

As mentioned above, voltage appears also on the outer surface of the ferromagnetic pipe, in the apparatus of FIG. 3 on which the present invention is based, and hence if the substance to be heated is of a low resistivity, as in' metal, there is a danger that the electric current flows'to the substance to be heated.

However, in the heating of the surface of a road,

floor, wall or the like, the substance surrounding the stance having a similar property, and hence if the voltage appearing on the outer surface of the ferromagallowable in the above-mentioned example, can be extended up to about I00 m.

FIG. 4 shows an embodiment of the present invention. In this figure, numeral 25 shows ferromagnetic pipes corresponding to l5, 16 in FIG. 3, and they are arranged in six parallel rows, the number of which, however, can be varied dependent on the area to be heated. The adjacent ends of these ferromagnetic pipes are connected by

bends

32, 33, 34 made of an insulating material and a connecting box 35 so that the ferromagnetic pipes, the bends and the box can form a serial pipe.

Bends

32, 33, 34 may be made of an electrically conductive material, such as steel, providing that insulating pieces are inserted in between the ferromagnetic pipes and the bends. Numeral 26 shows an insulated electric wire passing through the inside of the abovementioned serial pipe and connected to

electric wires

27, 28 which are connected to an a.c. source 36, at

terminal boxes

30, 31 provided at both the ends of the se.--

rial pipe.

The

bends

32, 33, 34 and connecting box 35, when the heating apparatus is used for preventing the surface of a road from freezing, for melting snow thereon or for the like purposes, are provided on the sides of road or the shoulder of road which is the part where there is not so frequent walking of human being or animals or traffic.

In the apparatus shown in FIG. 4, the left and/or right side ends of ferromagnetic pipes 25 may be accommodated in a duct or ducts allowing the insulated conductor 26 to pass therethrough. In this case, the ends of the ferromagnetic pipes must be electrically isolated from the duct or ducts.

In FIG. 5 showing a. cross-sectional view along the VV line of FIG. 4, the ferromagnetic pipes 25 are surrounded by an'insulating substance or a substance having a similar property 43 which constitutes road, floor, wall or the like, such as asphalt, concrete, etc.

The ferromagnetic pipes may be applied by an insulation coating 44.

As mentioned above, the heating apparatus of the present invention is of a construction in which voltage appears also on the outer surface of the ferromagnetic netic pipe is not so high, concrete, asphalt, etc. func- I tion as an insulating substances which do not give danger to human being or animals. Thus, the apparatus of FIG. 3 can be utilized as by heat-generating apparatus as well as those shown in FIGS. 1 and 2.

The length of each ferromagnetic pipe as required in the heating of the surface of a road, floor, wall or the like, is fortunately about l m to about-2O m. When steel pipes having a length of this extent are used as the ferromagnetic pipe and an alternating current of a commercial frequency of -60 Hz is used as an a.c. source, the voltage appearing on the outer surface of each ferromagnetic pipe is 0.5V to 5V, and hence the apparatus can be fully utilized for the above-mentioned purposes.

In the apparatus of FIG. 3, an insulation coating can be further applied on the outer surface of the ferromagnetic pipe. As the insulation coating, there can be illustrated coating with paint, coaltar, or'the like, lining with polyvinyl chloride, polyethylene, or the like, or winding of insulating tape around the pipe. By applying such'an insulation coating, thelength of the steel pipe pipe, and hence if a fault should occur on the insulated electric wire, there is a possibility that the outer surface of the ferromagnetic pipe has a potential close to the voltage of the a.c. source dependent on the place of the fault. 1 i i V Since the voltageof the a.c. source is far greater than that appearing on the outer surfaces of the respective pipes, such fault could lead to more serious accidents in the vicinity of the fault point unless it is detected so that any countermeasure can be taken. For this reason, some device capable of detecting faults should be incorporated into the heating pipe arrangement in the present application. For the purpose of providing such a device, a voltage detector is connected in the pipe arrangement as shown in FIG. 4.

As a method for preventing troubles from occurring from the above-mentioned accident, each one point, preferably each one electrically neutral point, on the outer surface of each ferromagnetic pipe is connected to each other by an electrical conductor which is further connected to a voltage-detector. One example thereof is illustrated in FIG. 4, where each ferromagnetic'pipe is connected to each other byan electric wire 39, at each one electrically neutral point 42 on the outer surface of each pipe, that is, each one point on the outer surface of the middle part in the longitudinal direction, of each steel pipe, and the electric wire 39 is further connected by an electric wire 40 to one terminal of a voltage-detector 38, another terminal of the detector being connected by an electric wire 41 to a specific point of voltage at an ac. source 36. When the heating apparatus of the present invention is under normal operation, no voltage occurs in the electric wire 39 or no current flows therein, and hence the detector 38 for detecting a fault does not operate.

However, if a fault should occur in the insulated electric wire 26 in one of the ferromagnetic pipes 25, the potential of the ferromagnetic pipe is elevated to generate an electric current in the electrical conductor 39 connected to the pipe, followed by actuating the detector 38, and breaking the connection with the ac. source by means of a breaker 37.

Although such a fault in the electric wire 26 can be detected by a known fault-detector and circuit, the detection by way of such a conventional detecting circuit becomes difficult or expensive if the ferromagnetic pipes are surrounded by a substantially insulating material such as concrete or asphalt. However, according to the above-mentioned method of the present invention, an easy and highly sensitive detection is possible.

As mentioned above, it is preferable that each one point on the outer surface of each ferromagnetic pipe 25, to be connected by the connecting conductor 39, is at the neutral point of the pipe or near this point. The reason will be explained asfollows referring to FIG. 3.

When the connection 22 carried out at each neutral point of the

ferromagnetic pipes

15, 16 or near this point, is compared withthe connection 22 carried out at each one adjacent end of the pipe, the potential difference between the other adjacent ends 23 and 24 in the former case becomes half that of the latter case.

What is claimed is:

1. An apparatus for heating the surface of constructions of an electrically insulating nature which comprises, at least two juxtaposed ferromagnetic pipes each having a length ranging from about one meter to about twenty meters and wall thickness of at least twice the skin depth of the alternating current flowing therethrough, an insulated electric conductor passing in series through the inside of each of said ferromagnetic pipes, the ends of said conductor being connected to the opposite terminals of an alternating current source, said pipes being electrically separated from each other, the respective electrically-neutral points .of the outer surfaces of said ferromagnetic pipes being connected to each other by a further electric conductor, and voltage detecting means responsive to'a flow of current in said further conductor to detect a fault in said insulated electric conductor and disconnect said insulated conductor from said alternating current source, whereby when an alternating current from the source is passed through said insulated electric conductor a secondary current is induced in both the inner and outer skin portions of said ferromagnetic pipes to generate heat there.

Claims

1. An apparatus for heating the surface of constructions of an electrically insulating nature which comprises, at least two juxtaposed ferromagnetic pipes each having a length ranging from about one meter to about twenty meters and wall thickness of at least twice the skin depth of the alternating current flowing therethrough, an insulated electric conductor passing in series through the inside of each of said ferromagnetic pipes, the ends of said conductor being connected to the opposite terminals of an alternating current source, said pipes being electrically separated from each other, the respective electrically-neutral points of the outer surfaces of said ferromagnetic pipes being connected to each other by a further electric conductor, and voltage detecting means responsive to a flow of current in said further conductor to detect a fault in said insulated electric conductor and disconnect said insulated conductor from said alternating current source, whereby when an alternating current from the source is passed through said insulated electric conductor a secondary current is induced in both the inner and outer skin portions of said ferromagnetic pipes to generate heat there.