Electric heating – Inductive heating – Specific heating application
Reexamination Certificate
1998-08-31
2001-10-30
Walberg, Teresa (Department: 3742)
Electric heating
Inductive heating
Specific heating application
C219S628000, C392S441000, C392S469000
Reexamination Certificate
active
06310334
ABSTRACT:
This application is based on Japanese Patent Application No. 9-239901 filed on Sep. 4, 1997, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present application relates in general to a surface current heating apparatus, and more particularly to such a heating apparatus suitable for small-scale heating applications.
2. Discussion of the Related Art
A known surface current heating apparatus includes a heat generating tube made of a ferromagnetic material, and an electrically conductive wire extending through the heat generating tube such that the conductive wire is electrically insulated. In operation, an alternating current is applied from an AC power source to the conductive wire, so that a surface current flows near the inner circumferential surface of the heat: generating tube, causing the heat generating tube to generate heat. The heat generating tube is a tubular member made of a steel or other ferromagnetic material. Generally, the conductive wire is electrically insulated at its surface with an organic or inorganic insulator.
The surface current heating apparatus was originally developed for heating a pipe line, and has been used for various applications, as snow-melting or anti-freezing heating devices, industrial heat sources, and heaters such as panel heaters, as disclosed in Japanese Patent Applications laid-open for opposition purpose as Publication Nos. 43-16931 and 52-14854. The snow-melting or anti-freezing heating devices include those for roadways, floors and walls. The industrial heat sources include those for boilers, hot water supplies and plating baths.
Conventionally, the surface current heating apparatus of the type mentioned above uses a heat generating tube which is as long as possible for a particular application of the apparatus. That is, commercially available steel tubes of various nominal lengths are used where the specific heating apparatus allows the use of a steel tube of a particular nominal length. Where the heating apparatus does not permit the use of any of such steel tubes of nominal lengths, due to a limited length of installation space for the steel tube in the apparatus, a steel tube of an appropriate nominal length is cut to a desired length suitable for use in the apparatus.
However, the present inventors discovered that the use of a long heat generating tube or tubes is not necessarily advantageous, and that the use of a relatively large number of heat generating tubes each having a comparatively small length is more advantageous in most cases of small-scale heating or heat generating applications. The inventors recognized potential advantages of a surface current heating apparatus which uses a heat generating member or members in the form of a plate, block or slab having through-holes through which an electrically conductive wire extends.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a surface current heating apparatus or a combination of a plurality of such surface current heating apparatuses, which is suitable for small-scale heating applications.
The above object may be achieved according to any one of the following modes or forms of the present invention. Like the appended claims, these modes of the invention are numbered, and each mode refers to the number or numbers of the other mode or modes, where appropriate, to indicate possible combinations of features or elements of the two or more modes of the invention described below.
(1) A surface current heating apparatus comprising: a plurality of hollow heat generating members each made of a ferromagnetic material and having a through-hole, the hollow heat generating members being spaced apart from each other so as to provide at least one array of the hollow heat generating members; and an electrically conductive wire electrically insulated and extending through the through-hole of each hollow heat generating member, an alternating current from a power source being applied to the electrically conductive wire, to cause a surface current to flow through a skin layer of each hollow heat generating member which is located near an inner surface of the through-hole, whereby heat is generated from the skin layer.
As described below in detail, the hallow heat generating members may be heat generating tubes each having a comparatively small axial length, or plates or blocks each having a through-hole. In essence, each hollow heat generating member is required to be made of a ferromagnetic material and have a through-hole through which the electrically conductive wire extends, and a comparatively large transverse cross sectional area which provides a closed magnetic path.
Upon application of an electric current to the electrically conductive wire, a magnetic field is produced around the conductive wire. In the presence of the hollow ferromagnetic heat generating members each having a closed magnetic path around the conductive wire, lines of magnetic force produced by application of the electric current to the conductive wire tend to be concentrated within each hollow ferromagnetic heat generating member. Further, the lines of magnetic forces tend to gather and to be concentrated in the skin layer of the heat generating member near the inner surface of the through-hole. Where an alternating current is applied to the conductive wire, the magnetic flux density periodically changes, and there arise a voltage and a current in the hollow heat generating member, so as to disturb the periodic change of the magnetic flux density. As a result, a surface current flows through the skin layer of the hollow heat generating member near its through-hole, in a direction perpendicular to the lines of magnetic force, so that the skin layer near the inner surface of the through-hole is concentratively heated. If the two or more hollow heat generating members are arranged in mutually spaced-apart relationship with each other, there is provided a relatively large surface area for heat radiation, than where only an electrically conductive or resistive wire is used to generate heat. The present heating apparatus is capable of generating a large amount of heat while restricting the temperature rise at the highest-temperature portion of the apparatus.
The present invention provides various advantages which will be described in detail with respect to preferred modes, forms or arrangements of the invention. Each of the features described below need not be provided or is not essential for each of the arrays of the hollow heat generating members. Heat generating members which do not have such a feature or features may be provided in the present heating apparatus. For instance, the conductive wire may be disposed to extend through a long heat generating tube as used in the prior art, under a specific environment, for example, where the conductive wire should be completely protected, or where the heat generating tube has a particularly high property of heat radiation.
(2) A surface current heating apparatus according to the above mode (1), wherein the at least one array of the hollow heat generating members includes at least one array consisting of a plurality of heat generating tubes each of which has an axial length no more than 20 times an outside diameter thereof.
Where the plurality of heat generating tubes are arranged along a curve, the array of these heat generating tubes may extend along either a plurality of circular arcs or curves or a plurality of straight lines. When the heat generating tubes have comparatively small lengths, these heat generating tubes may be arranged along two or more curved lines which cooperate to define a desired curve along which the array of the heat generating tubes extends. The heat generating tubes may be formed such that the centerline of each tube is curved along a circular arc or such that the centerlines of the tubes are curved along respective different circular arcs. These curved heat generating tubes may be readily arranged along a desired curve. In this case, the le
Nagasawa Shinichi
Niwa Kunio
Fuqua Shawntina T.
NA Corporation
Oliff & Berridg,e PLC
Walberg Teresa
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