Heat-generating Pipe Utilizing Skin Effect Current Controlled Locally In Heat Generation By Short-circuiting Bridges

Abstract

In a heat-generating pipe comprising a highly ferromagnetic pipe and an insulated conductor line inserted therein and having such a connection that AC flowing through the insulated conductor line is equal in intensity and opposite in direction to the AC flowing concentratedly through the inner wall portion of the pipe due to the skin effect of AC, the heat-generating pipe is characterized in that a certain section of the inner surface of the pipe is brought to short circuit state by a conductor line optionally including a thermostatic or other switch and having an impedance which is selected according to the requirement for decreasing or elimination of heat generation in said section, to control the heat generated in said section.

Description

This invention relates to heat-generating pipe utilizing a skin effect of AC flowing through the inner wall portion of a ferromagnetic pipe such as a steel pipe, which enables to control heat-generation in a certain section of the inner surface of the pipe.

When the skin effect is pronounced, the depth of the skin S(cm) which is an index showing the range of flow of current in a conductor is represented by a following formula,

S = 5030 .rho./.mu.f (1)

Wherein .rho.(.OMEGA.cm) is resistivity, .mu. is specific permeability and f is frequency of current per second.

Such a skin effect caused in a ferromagnetic pipe, such as a steel pipe, will be hereinafter explained by referring to an attached drawing.

In FIG. 1, an insulated conductor line 1 passes through the inside of a ferromagnetic pipe 3. One end of the conductor line is connected to one terminal of AC source 2 and the other end thereof is connected to one end 4 of the ferromagnetic pipe 3. The other end 5 of the ferromagnetic pipe 3 is connected to the other terminal of the AC source 2 by a conductor line 6.

If a relationship represented by the following formula:

T > 2S, D>>S and l>>D (2)

wherein D(cm) is an inner diameter of the steel pipe, l(cm) is its length, and t(cm) is its thickness, exists between l, D and S, the current is concentrated on the inner surface of the ferromagnetic pipe having a large specific permeability, and does not appear onto the outer surface of the pipe, and such an apparatus can be utilized as a heat-generating body. This is a publicly known fact disclosed in Japanese Pat. No. 460,224 (Patent Publication No. 12128/1965) whose counterparts in U.S.A. and Canada are U.S. Pat. No. 3,293,407 and Canadian Pat. No. 760,556.

In such a heat-generating pipe, it is impossible to decrease or stop heat generation in at least one section of the pipe, for example, between X and Y as indicated in FIG. 1.

An object of the present invention is to provide a heat-generating pipe in which the above-mentioned drawback is overcome, namely, a heat-generating pipe capable of controlling heat generation in an optional section of the pipe made of a highly ferromagnetic steel or the like.

Now, it has been found that the above-mentioned object can be attained by the apparatus of the present invention.

This invention consists in a heat-generating pipe comprising a highly ferromagnetic pipe and an insulated electric line inserted therein and passing therethrough and having such a connection that AC flowing through the insulated conductor line is equal in intensity and opposite in direction to the AC flowing only through the inner wall portion of the pipe due to the skin effect of AC which is characterized in that a section or plural sections of the inner surface of the pipe are brought in short circuit state by a wire or wires having an impedance which varies according to the requirement for decrease or stoppage of heat generation in said section or sections, in order to control the heat generated in said section or sections.

In addition, it is also possible to use with great deal of advantage the apparatus of the present invention in which a switchgear is interposed at an arbitrary position within the above short circuit to realize its on-off cycles, which may be activated automatically by a thermostat.

The present invention will hereinafter be illustrated with reference to the attached drawings.

FIG. 1 shows a schematic view of a publicly known heat-generating pipe utilizing skin effect current, which is given as a reference, to enable persons skilled in the art to understand the principle and the construction of the present apparatus.

FIG. 2 shows a schematic, cross-sectional view of a heat-generating pipe having a short circuit apparatus in a section thereof, according to the present invention.

FIG. 3 shows a schematic, cross-sectional view of a further embodiment of the present invention.

In FIG. 2, an insulated conductor line 1 is inserted in and passes through the inside of a ferromagnetic pipe 3, One end of the conductor line is connected to one terminal of an AC source 2 and the other end thereof is connected to one end 4 of the ferromagnetic pipe 3. The other end 5 of the ferromagnetic pipe 3 and the AC source are connected by a conductor line 6.

Terminals 7 and 8 are provided at both the ends of a section where heat generation is to be stopped, or controlled, and the section between both the terminals is shorted by a conductor line 9 having an impedance much lower than that of the inner surface of the section of the ferromagnetic pipe. (The section between both the terminals corresponds to the section between X and Y in FIG. 1.) Flanges 10 and 12 and covers 11 and 13 are installed for the convenience of connecting both the ends of the conductor line 9 to the terminals 7 and 8.

The current from one terminal of an AC source 2 passes through the insulated conductor line 1 and flows through the inner surface of the ferromagnetic pipe 3 from one end 4 of the ferromagnetic pipe 3 to the terminal 5 while generating heat, but it passes mostly through the conductor line 9 during the part from the terminal 8 to the terminal 7 and flows only through the inner surface of the pipe 3 again from the terminal 7 to the other end 5 of the pipe 3 while generating heat again; and returns to AC source 2 through the conductor line 6.

In this case, the current flowing through the insulated conductor line 1 is almost equal in intensity, and opposite in the direction of flow, to the current flowing through the conductor line 9, and there is hardly any skin current occurred in the section of the pipe between the terminals 8 and 7. Thus, heat generation hardly occurs in this part.

If the impedance of the conductor line 9 is made larger than that in the case where the above-mentioned heat generation is almost stopped, the intensity of the current flowing through the conductor line 9 becomes smaller than that flowing through the insulated conductor line 1. In this case, some extent of skin current occurs in the section of the ferromagnetic pipe between the terminals 8 and 7, and hence some extent of heat generation occurs there.

Thus, in accordance with the variation of the impedance of the conductor line 9 from an extremely low value to a very higher one, the heat generation in the short-circuited section of the pipe may be controlled from almost no heat generation to the value attained without such short circuiting.

FIG. 3 is a schematic representation in which a switchgear is interposed at a position within the short circuit described above. In this FIG., the short circuit, as set forth, is made by shunting the section X-Y by at least one insulated conductor line 9 in the inside of pipe 3, and the conductor line 9 is drawn out from said pipe so as to connect with a switchgear 15 in series. When the switch 15 is open, the shunting effect is eliminated; therefore, heat is generated to the extent of full capacity. On the other hand, when the switch 13 is closed, the heat generation will be restrained in the shunted section from generating heat because a greater amount of the current is shunted by the line 9. Thus, actuation of the switch in on-off cycles can adjust the heat generation. It goes without saying that the control of on-off cycles may be done by an attached thermostat.

When the impedance is made much higher, the heat generation in the section becomes almost the same with that of other sections of the ferromagnetic pipe 3 where no short circuit is made.

The above-mentioned explanation has been given in case of the control of heat generation in one section of a heat generating pipe utilizing skin effect based upon such a circuit as in FIG. 2. In cases of any number of plural section, it is also possible to control heat generation in each section so as to make it take the same or a different value in each of the sections.

Further, this invention can be also applied to a circuit other than the above-mentioned ones, for example, such a circuit as described in Japanese Pat. Application No. 20427/1966, entitled "Heat-generating Pipe Utilizing Skin Effect Current," whose counterparts are U.S. Ser. No. 627,086, Canadian Pat. Application No. 986,431, West German Pat. Application No. P 1615192.1, British Pat. Application No. 23142/68 and French PV 154842.

The above-mentioned Japanese patent application relates to a heat generating pipe having an arrangement including a primary circuit of an electric conductor line connected to a source of AC supply and inserted within at least one pipe of ferromagnetic metal throughout the entire length thereof in electrically insulated relation from the inner wall portion of said pipe and a secondary circuit consisting of said at least one pipe of ferromagnetic metal and at least one conductor having an impedance as low as possible and connecting the ends of said pipe, the secondary alternating current induced in the secondary circuit by the primary current being concentrated on the inner wall portion of said pipe on account of the skin effect while satisfying the relations expressed by equations (1) and (2).

The apparatus of the present invention can be applied with great commercial advantage in various cases. For example it can be applied to booster pumps, valves or the like installed in the liquid transportation pipe described in Japanese Patent No. 460,224.

Claims

I claim:

1. In the known type of heat generating apparatus comprising a length of ferromagnetic pipe, a first length of an electrical conductor line disposed within said ferromagnetic pipe but insulated therefrom, and electrical and power connections so that upon the passage of alternating voltage through said first length of electrical conductor line there is a concentrated flow of current along the inner skin of the ferromagnetic pipe to thereby generate heat in said ferromagnetic pipe, the improvement which comprises:

a. at least one additional length of electrical conductor line disposed within said length of ferromagnetic pipe,

b. said additional length of electrical conductor line being shorter than said first length of electrical conductor line and arranged generally parallel to at least a portion of said first length of electrical conductor line,

c. said additional length of conductor line being connected to said ferromagnetic pipe at two spaced apart points whereby the concentrated flow of current along the inner skin of the ferromagnetic pipe is at least partially short circuited along the inner surface thereof between said two spaced apart points to an extent dependent upon the impedance of said additional length of conductor line between said two spaced apart points.

2. A heat-generating pipe according to claim 1 wherein at least one switchgear is interposed at a position within the short circuit shunting said inner surface so as to control the heat generation within said section of said heat generating pipe on an on-off basis.