Electric heating – Metal heating – Of cylinders
Patent
1991-05-22
1993-01-19
Leung, Philip H.
Electric heating
Metal heating
Of cylinders
219 1055A, 219 1055E, H05B 672
Patent
active
051808951
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention concerns microwave-powered heating devices, and in particular heating apparatus for heating foodstuffs, more particularly for defrosting and heating to a serving temperature frozen pre-cooked foodstuffs.
Background to the Invention
With the increasing demand for quick, hot snacks and so-called "fast food", there is an increasing requirement to be able to process frozen pre-cooked foodstuffs ready for consumption. In particular, it is necessary to be able to heat up from the frozen condition a pre-cooked foodstuff to a serving temperature in the shortest possible time, and typically a temperature change from -17.degree. C. to +74.degree. C. must be achieved. Preferably the time should be as short as possible and ideally should be well under one minute.
Conventional microwave ovens are not particularly well suited to this function, and it has been proposed to concentrate the available energy by providing concave or other appropriately-shaped reflecting surface within a chamber into which microwave energy is transmitted so that the latter is focused generally into the region of the chamber in which the foodstuff is located. In this way the energy is concentrated into the foodstuff and the latter is raised in temperature at the maximum possible rate.
It is an object of the present invention to provide a more uniform heating of a foodstuff within a chamber in which microwave energy is intentionally reflected and thereby focussed onto the foodstuff.
SUMMARY OF THE INVENTION
According to the present invention there is provided heating apparatus comprising a heating chamber in which a foodstuff is to be heated using microwave energy which is focussed onto the foodstuff by means of appropriate reflecting surfaces within the chamber, and at least two independent microwave sources for supplying microwave energy to the chamber so as to reduce the risk of standing waves being set up within the chamber thereby resulting in a more uniform heating-through of the foodstuff, the microwave energy being directed through wave guides whose cross sections increase from relatively small circular or rectangular cross section inputs to two or more outlets which cooperate together to describe a complete annulus, the outer diameter of which annulus corresponds to the diameter of the reflecting surfaces within the chamber and the inner diameter of which annulus corresponds to the diameter of (or comprises the walls of) a circular platform on which the foodstuff is to be located.
Alternatively, a concentration of standing waves may be achieved, centred around and in the foodstuff being heated within the chamber.
The design of the focussing elements and the arrangements within the cavity are preferably matched to the shape and structure and composition of the foodstuff. This matching may be achieved by empirical means, or by computer or mathematical modelling of the E-field within the cavity.
According to a preferred feature of the invention, the apparatus is such that microwave energy entering the chamber does not impinge directly on the foodstuff but can only reach the foodstuff after being reflected at least once.
According to a further preferred feature of the invention, the interior of the chamber is formed at least in part with a concave microwave energy reflecting surface, typically in the form of a dome. The microwave energy from the plurality of microwave sources is directed towards perimeter region of the concave surface to be reflected therefrom and generally focused towards the centre of the chamber where the foodstuff is to be located, so that it is in fact prevented from reaching the foodstuff other than by first being reflected by the perimeter regions of the concave reflector either directly onto the foodstuff or onto a microwave reflecting surface situated below the foodstuff so that microwave energy incident thereon is reflected up onto the underside of the foodstuff.
By locating the foodstuff on a microwave transparent platform, above the microwave reflecting surface, so mi
REFERENCES:
patent: 2820127 (1958-01-01), Argento et al.
patent: 2856497 (1958-10-01), Rudenberg
patent: 2956144 (1960-10-01), Woodman
patent: 4752663 (1988-06-01), Meisel
Briggs David H.
Freeman Richard F.
Leung Philip H.
Unilever Patent Holdings B.V.
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