Electric heating – Inductive heating – With heat exchange
Patent
1994-06-14
1995-10-03
Leung, Philip H.
Electric heating
Inductive heating
With heat exchange
219634, 219670, H05B 610
Patent
active
054554020
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an induction heater wherein material is heated by contact with an inductively heated heating element.
Bulk or continuous flow heaters are employed as driers or calciners. Typically, a heating member contacts material to be heated so that heat is efficiently transferred from the heating element to the material to be heated. Some degree of mixing action to improve contact can also be incorporated with the heating action of the heating element. This can for example be provided by the heating element with fin members. As a result, contact between the heating element and the material to be heated is enhanced. However, it is preferable to provide substantial uniform heating of the material to be heated. Consequently means are required to supply heat uniformly to the heating member and the fin members thereof.
The supply of heat to the heating element is particularly problematical where fin members are included. Known driers incorporate heating by means of gas jets or hot fluid. Consequently, in order to heat such fin members complicated supply tubing must be engineered into the fin member. It is also known to adapt the fin member to enhance the mixing resulting from movement of the heating element. This only serves to further complicate the design of the fin member. Particular problems are encountered with rotary drum driers and calciners since it is necessary to incoporate rotary couplings for supply of the hot fluid or gases. Consequently, there are a number of drawbacks for heating the heating element of known bulk continuous flow heaters.
GB 2163930 discloses an induction heater having an alternating current carrying conductor extending along an axis. A core means substantially encircles the axis to guide magnetic flux resulting from an alternating current in the conductor. The heating element is an electrically heating closed loop which encircles the magnetic flux in the core means and so is heated by electrical current induced therein.
Two of the embodiments disclosed in GB 2163930 are shown in FIGS. 1 and 2. In the embodiment of FIG. 1, the conductor 1 forms an axis about which is provided a ferromagnetic core 4. The core 4 is enclosed within a metal skin formed from concentrically aligned inner cylinder 5 and outer cylinder 7 and end plates 6 and 9. In this way, the skin forms a closed electrically conducting loop about the core 4. Alternating current set up in the conductor 1 by a toroidally wound transformer 8 set up an alternating magnetic flux which is guided by the core 4. In turn, the alternating flux in core 4 induces currents to flow around the above-mentioned electrically conducting closed loop. The material to be heated is placed within the inner cylinder 5 and is heated by the energy produced in the cylinder by the induced currents. The structure comprising the cylinders 5 and 7 and core 4 can be rotated in the direction of the arrow A. In this way the material to be heated is moved into and out of contact with the cylinder 5 to allow uniform transfer of the heat from the cylinder to the material to be heated.
FIG. 2 shows a continuous flow induction heater. A motor 21 rotates a screw structure 22 in the direction of the arrow A. The screw structure 22 comprises an outer wall 23 which has a spiral slot cut in it to receive screw flight 24. The structure 22 also has an inner wall 25. A toroidal ferromagnetic core 26 is sandwiched between the inner and outer walls 23, 25. An electrically conducting conductor 1, corresponding to that shown in FIG. 1, runs along the axis of the structure 22. As in the embodiment of FIG. 1, a magnetic flux is induced in the core 26 by an alternating current in the conductor 1; this magnetic flux, in turn, induces electrical currents to flow in the walls 23, 25 and the screw flight 24 of the structure 22. The structure 22 is located within a can 28 having an inlet 29 and outlet 30 as shown. Consequently material entering at 29 contacts the structure 22 and is urged towards outlet 30 by the screw flight 24 as the structure 22 is rotated. The
REFERENCES:
patent: 4366356 (1982-12-01), Ando
patent: 4678881 (1987-07-01), Griffith
patent: 5274207 (1993-12-01), Griffith
EA Technology Ltd.
Leung Philip H.
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