WO1987005093A1

WO1987005093A1 - Microwave water heater

Info

Publication number: WO1987005093A1
Application number: PCT/GB1987/000123
Authority: WO
Inventors: William Nevil Heaton Johnson; Noel Robertson Mckenzie
Original assignee: Applied Agricultural Research Limited
Priority date: 1986-02-20
Filing date: 1987-02-19
Publication date: 1987-08-27
Also published as: AU7030787A; GB8604243D0

Abstract

A water heater comprises a water-containing vessel (1) of heat-resistant glass or plastics, having a cylindrical outer wall and a cylindrical cavity, coaxial with the outer wall, extending upwardly from a circular aperture in the bottom vessel and closed by a top wall (8) so that the interior of the cavity is sealed off from the water-containing interior of the vessel but is in communication with the surroundings. A magnetron (2) is mounted in the cavity and emits microwave radiation to pass substantially radially into the water-containing space through the cylindrical wall (6) of the cavity, into the water to heat the water. Within the water-containing space, a co-axial cylindrical shield, open at top and bottom, surrounds the cylindrical wall of the cavity co-axially and serves to reflect and contain the microwave radiation. Water heated in the annular space between the cavity wall and the shield rises into the main part of the water-containing space to be replaced by colder water from below, producing a continuous thermosyphon circulation.

Description

DESCRIPTION OF INVENTION

Title: "Microwave water heater"

THIS INVENTION relates to a water heater and it is an object of the present invention to provide a water heater, such as a domestic water heater, capable of utilising the advantages of heating by microwave electromagnetic radiation.

According to the invention there is provided apparatus for heating water, comprising an emitter of microwave electromagnetic radiation, and a vessel for containing water, a wall of material which is transmissive to electromagnetic radiation being interposed between the microwave emitter and the interior of said vessel.

An embodiment of the invention is described below by way of example with reference to the accompanying drawing which is a schematic view in vertical section of a domestic water heater embodying the invention.

Referring to the drawing, a water heater comprises a vessel or tank 1 for containing water to be heated and which is made of a material which is transmissive to microwave radiation, for example heat-resistant glass such as sold under the Registered Trade Mark "Pyrex" or melamine plastics. The vessel 1 has a cylindrical outer wall and, located coaxially within the outer wall, an inner cylindrical wall 6 the lower edge of which is connected with the lower edge of the outer wall of vessel 1 by a annular bottom wall 7, whereby the inner wall 6 defines a central chamber extending into the vessel from the opening defined in the bottom of the vessel at the junction of the lower edge of wall 6 with the inner edge of the annular wall 7. This central chamber is closed at its upper end by an end wall 8. There is thus defined between the inner wall 6 and the outer wall 1 an annular water space which is continuous with the substantially cylindrical water space immediately above the chamber 8, this water space being appropriately sealed with respect to the exterior. Mounted within the central chamber is an emitter 2 of microwave electromagnetic radiation, such as a magnetron, the emitter 2 being arranged to emit its microwave radiation substantially radially outwardly therefrom relative to the vertical central axis of the vessel 1, to pass through the inner wall 6.

Mounted within the water space is a cylindrical tubular shield 3 open at its upper and lower end, the shield 3 being coaxial with the inner and outer walls of the vessel and being spaced radially inwardly of the outer wall and radially outwardly of the inner wall to define, with the inner wall, a space 4 which is annular in horizontal section. The lower end of the shield 3 is spaced upwardly from the bottom wall 7 whilst the upper end of the shield 3 is spaced substantially below the top of the vessel. In operation, microwave radiation from the emitter 2, passing through the inner wall 6, heats the water within space 4. Microwave energy is reflected by and contained by shield 3 so that the molecular excitation produced by the microwave radiation is concentrated within the space 4 thus producing rapid heating of the water within space 4. The rapidly heated water within space 4 rises within the shield 3 by convection to pass into the major part of the water space within the vessel, whilst cooler water from the bottom of the tank enters the space 4 by way of the lower end of the shield 3 to replace the water thus heated, such cooler water being similarly heated in its turn producing a continuous thermosyphon circulation distributing the heat throughout the water within the water space. Residual excitation within the mixing masses assists in general temperature rise through¬ out the tank.

Claims

1. Apparatus for heating water, comprising an emitter of microwave electromagnetic radiation, and a vessel for containing water, a wall of material which is transmissive to electromagnetic radiation being interposed between the microwave emitter and the interior of said vessel.

2. Apparatus according to claim 1 wherein the vessel has a chamber extending into the vessel from an opening in an outer wall of the vessel, said vessel defining a water space which surrounds said chamber but which is sealed off from said chamber by the wall of said chamber, the wall of said chamber being integral with, or sealingly connected with said outer wall around said opening, at least part of the wall of said chamber being transmissive to microwave radiation, and wherein said microwave emitter is housed within said chamber and arranged for emission of its microwave radiation through said transmissive portion of the wall of said chamber.

3. Apparatus according to claim 2 including, within said water space, and surrounding said chamber wall at a distance therefrom, a shield, reflective to microwave radiation, the shield being adapted to intercept microwave radiation from said emitter after it has crossed the limited space between the trans¬ missive wall of said chamber and said shield, the configuration of the shield being such as to allow cool water from the remainder of the water space within said vessel to enter said limited space, and water, after heating by microwave radiation to leave said limited space.

4. Apparatus according to claim 3 wherein the transmissive wall of said chamber is arranged to extend substantially vertically from said opening, and wherein said shield is in the form of a tube, open at its upper and lower ends, and extending around said chamber.

5. Apparatus for heating water, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.