Electric heating – Microwave heating – Tunnel furnace
Reexamination Certificate
1999-01-11
2002-10-08
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
Tunnel furnace
C219S701000, C219S699000, C219S746000, C219S748000, C219S756000, C219S739000, C219S741000
Reexamination Certificate
active
06462320
ABSTRACT:
THIS INVENTION relates to a dielectric heating device. More particularly it relates to a dielectric heating device which employs microwave heating , suitable. for heating or cooking foodstuffs and suitable for, but not restricted to, use as a domestic or institutional microwave oven.
According to the invention there is provided a dielectric heating device which comprises:
a plurality of electrically conductive side walls which are electrically interconnected and arranged in series to define a heating cavity, at least one pair of adjacent side walls being inclined to each other at a corner having an included angle selected from the group consisting of acute angles and obtuse angles; and
at least one electromagnetic power source capable of emitting electromagnetic radiation suitable for dielectric heating and arranged to feed such radiation into the cavity at a frequency which varies with time and which causes the heating cavity to act as a multimode resonant heating cavity.
The selected angle will not be a right angle, the included angle being less than 180° but not equal to 90°, and being either an acute angle or an obtuse angle.
Preferably, adjacent side edges of each adjacent pair of side walls physically abut, electrically to interconnect the pair of side walls. Instead, each adjacent pair of side walls may be electrically connected together along their adjacent side edges. Naturally, the dimensions of the cavity should be large enough, bearing in mind the wavelength of the radiation emitted by the power source, to ensure multimode resonant operation in the cavity.
The device may be in the form of an oven defining the heating cavity, the cavity being tubular in shape and the side walls extending from one end of the cavity to the other end of the cavity, the cavity having an outline in cross-section which is polygonal and which has a plurality of sides arranged in a peripherally extending series, the sides of each adjacent pair of which define between each other a corner of the cavity.
The cavity may have an outline in cross-section which has an odd number of sides, being eg that of a regular polygon, the polygon having sides all of the same length and the number of sides being selected from the values of three, five, seven, nine and eleven, preferably five or seven and more preferably five. The polygon may be a regular pentagon having five sides of equal length, the sides of each adjacent pair of which are inclined to each other at an obtuse included angle of 108°, each said side wall being a panel which is flat and planar in shape, and of rectangular outline. Instead, however, at least two sides may have lengths of different magnitudes. The outline in cross-section of the cavity will thus have sides which are substantially straight and, accordingly, each side wall panel will be substantially planar, eg rectangular in form, and all the sides of the outline will be of equal length, with all the included angles being equal in size, namely said 108°.
The ends of the cavity may be open, said open ends respectively defining an inlet to the cavity and an outlet from the cavity to permit continuous heating of a profile which is moved lengthwise through the oven. In this case, each end of the cavity may be provided with a choke having an opening therein for receiving, with a working clearance, a profile which is moved lengthwise through the cavity, each said clearance being selected to suppress emission of electromagnetic radiation, in use, from the cavity via the opening of the choke and around the profile.
When the ends of the tubular cavity are open, thereby defining an inlet and an outlet which is spaced from the inlet, so that the oven is suitable for continuous throughput from the inlet to the outlet of solids, such as an object or substance to be heated, the oven will, for example, be suitable for heating continuously extruded profiles, or the like, the choke at each end being constructed and/or configured to suppress or reduce emission of electromagnetic radiation from the cavity via said end in use.
The cavity may thus be elongated so that it is vertically elongated when it is upright to permit downward movement of an extrusion therethrough. The cavity may be provided with a plurality of microwave sources, at least some of which are adjustable as regards their microwave output, and which sources may be both vertically and circumferentially spaced from each other around a central zone in the cavity intended for receiving the moving extrusion, eg down which, in use, the extrusion can pass, when the cavity is upright.
The microwave sources may be arranged in the cavity, in said circumferentially and/or longitudinally spaced relationship, around a central path in the cavity down which the profile passes, the sources being arranged to direct microwave radiation at a said profile in said path. The microwave cavity may thus be provided by a vertically extending microwave oven having an outlet at its lower end and an extruder for extruding a profile, or an inlet, at its upper end, as the case may be.
Instead, the oven may have a pair of end walls which close opposite ends of the cavity, at least one of the walls of the oven forming at least part of a door into the cavity, to permit batch operation in the heating of at least one object placed in the oven. In this case, one of the end walls may form a floor for the cavity, the other end wall being spaced above the floor and forming a roof for the cavity, the oven having at least five side walls which are panels, each side wall panel being flat and planar in shape, and being rectangular in outline, and the door cooperating with a closable door opening leading into the cavity, the door opening being larger in area than the area of each side wall panel. The door may form at least one side wall panel of the oven, the door forming less than two side wall panels of the oven. The door may be selected, on the one hand, from a single door panel, hinged at one side of the door opening and, on the other hand, from a pair of door panels arranged side by side and hinged respectively at opposite sides of the door opening, the door having at least one hinge and each hinge extending in a direction from the one end wall of the oven towards the other end wall thereof.
When the ends of the cavity are closed, the cavity may be foreshortened in length, its length between its ends being less than its cross-sectional width, although, naturally, the length can be greater than the width.
In the usual way, as indicated above, the floor, roof and side wall panels will typically be electrically conductive and electrically interconnected, and the oven may have one or more door panels which close the door opening and which are similarly electrically conducting and electrically connected to said floor, roof and side wall panels. Conveniently, the floor is a flat floor panel optionally having a turntable mounted on its upper surface for rotating contents of the oven while they are being subjected to microwave heating, and the roof may similarly be a flat panel and may have a ventilation opening provided with a grid, and the roof panel may be parallel to the floor panel, the side wall panels being normal to the floor panel and to the roof panel.
In a particular construction, when the oven is regular-polygonal in horizontal cross-section, it may have a single microwave power source, such as a magnetron, klystron or the like, the oven including a waveguide for guiding microwave radiation from said source to microwave feed openings in the side wall panels for feeding microwave radiation from the waveguide into the interior of the cavity. The waveguide may extend, in the form of a hollow partial belt or collar, horizontally partially around the oven on the outer surfaces of the wall panels spaced, eg midway, between the floor and the roof of the oven. In this regard it will be appreciated that the side wall panels will be constituted, at least in part, by the door panel or panels but, typically, said door panel or panels will not have microwave feed openings therethro
Fuls Paul Fritz
Joubert Andre Keith
le Roux Johann Daniel
Rossouw Mathys Johannes
Leung Philip H.
Technology Finance Corporation (Proprietary) Limited
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