GB2217824A

GB2217824A - Drying apparatus

Info

Publication number: GB2217824A
Application number: GB8810013A
Authority: GB
Inventors: Nicholas Parsons
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-04-27
Filing date: 1988-04-27
Publication date: 1989-11-01
Also published as: GB8810013D0

Abstract

Drying apparatus such as a tumble drier has a microwave source (60) for directing microwaves into a rotating drum (10) to dry clothes and the like contained therein. <IMAGE>

Description

DRYING APPARATUS This invention relates to drying apparatus for drying articles such as clothes.

In a conventional domestic tumble drier, the clothes are agitated in a rotating drum whilst air heated by an electric heating element is passed through the drum, gradually removing moisture from the clothes. The disadvantage of such systems is that they consume a relatively large amount of electrical energy and are therefore expensive to run. Moreover, the temperature of the clothing may increase to such an extent that delicate materials may be damaged during the drying process.

Also, the time taken to dry clothing in such machines can, in some circumstances, be unacceptably long.

A need exists therefore for a drying apparatus which completes the drying process quickly and efficiently without damaging delicate materials.

According to one aspect of this invention, there is provided drying apparatus for drying articles, e.g. clothes, said apparatus including container means for containing said articles, agitating means for agitating said articles, microwave irradiation means for irradiating said articles with microwave radiation and ventilation means for causing a gas to pass through said container means.

The invention will now be described by way of non-limiting example with reference to the accompanying drawings in which: Figure 1 is a schematic top plan view of a tumble drier according to an embodiment of the invention; Figure 2 is a front view of the drum of the tumble drier of Figure 1; Figure 3 is a rear view of the drum of the tumble drier of Figure 1; and Figure 4 is a block diagram of the control system for the tumble drier.

Referring to the drawings, the tumble drier illustrated is intended for domestic or light industrial use (for example in a launderette).

The tumble drier comprises a rotatable drum 10 which is connected to a drive shaft 12 which is rotatably mounted in a bearing 14 fixed with respect to the chassis of the tumble drier. The shaft is connected to the drum adjacent a central air outlet 16 by means of a spider connector 18 (see Figure 3). The drum 10 is cylindrical including front and rear end walls 20 and 22 respectively and a cylindrical wall 24.

The major portions of the end walls 20 and 22 and the cylindrical wall are made of a metal plated with material which reflects microwave radiation and which is covered by a microwave transparent protective coating. The end walls however also each include an annular window 26 of material which is transparent to microwaves (e.g. a rigid plastics material) and typically about 3 to 5 mm thick. The windows 26 are concentric with the drive shaft 12. The front end wall 20 includes a central circular loading aperture 28 (see Figure 2) which is covered during the drying process by a door 30 which is hinged to the casing of the tumble drier and which is formed of a material which is opaque to microwave radiation. The door seals to the end wall 20 about the circular loading aperture 28.

Surrounding the loading aperture is a series of inlet apertures 27 which pass air into the drum 10. A cylindrical outer casing 33 is spaced from the end wall 20 and the cylindrical wall 24 to define a duct through which air is drawn before it passes into the drum 10. This provides pre-heating of the inlet air. Associated with the door are a "door closed" sensor 29 and an electromechanical lock 31.

A cuff 32 surrounds the air outlet 16 and is sealed to the end 34 of an outlet duct 36 by a suitable sealing arrangement which allows rotation of the cuff 32 relative to the duct. The duct 36 is of generally J shape, delivering air from the drum outlet 16 to an exhaust 38. The inner surface of the duct 36 is coated with a black, non-transmitting microwave absorbent material. Both the inlet end and the outlet end are cranked through 900 to provide a microwave trap.

The duct includes heat exchange 37 elements located therein to extract heat from gas passing therethrough. In one arrangement (not shown) the heat extracted by heat exchange elements 37 may be used to pre-heat air before it enters the drum 10 through the door 30. It will be appreciated that the route of the gas between the outlet 16 of the drum and the exhaust 38 may be modified from that shown to allow optimum heat exchange between the inlet air and the outlet air. The outlet duct includes a moisture sensor 40 of known design for measuring the moisture content of the air passing along the duct.

The drive shaft 12 extends through the wall of the duct 36 and carries a drive pulley 42 which is connected by a drive belt .43 to a drum drive pulley 44 which is secured to the output shaft of an electric motor 46. A cylindrical outer shaft 48 surrounds the drum drive shaft 12 and carries at one end fan blades 50 adjacent the outlet 16 of the drum. The outer shaft 48 is sealed to the wall of the duct 36 by suitable means (not shown) and carries at its other end a drive pulley 52. The pulley 52 is connected by a drive belt 54 to a fan drive pulley 56 which is mounted on the output shaft of the electric motor 46, concentric with the drum drive pulley 44. The motor drives the drum at a relatively low speed and the fan at a relatively high speed. The fan draws air out of the drum outlet 16.A removable lint filter 58 is detachably mounted within the drum, covering the outlet 16 so that air leaving the drum is filtered before entering the duct 36.

At the periphery of the drum is provided a microwave emitter 60 which remains stationary whilst the drum rotates and which introduces microwave radiation into a resonant cavity defined between a semisilvered reflector 62 and a reflector 64 which lie to either side of the drum, adjacent the annular windows 12. The semi-silvered reflector 62 may be sensitive to the polarisation of the radiation so that it passes radiation emitted by said emitter 60, but not radiation reflected by said reflector 64. In a typical example, the microwave emitter may be rated at 600 watts and emit radiation of wavelength in the range from 10#2m and 10-lm.

A microwave sensor 66 of known design is located adjacent the reflector 62 to provide a signal representing the sensed intensity of the microwave radiation.

The resonant chamber defined between the reflector 62 and the semi-silvered reflector 64 may typically be of dimension (n x > ) where)2 is the wavelength of the radiation and n is an integer in the range 3 < n < 6.

Referring now to Figure 5, the control system includes a controller 68 which controls the functions and safety of the tumble drier.

Specifically the controller is supplied with signals from the door closed sensor 29, the moisture sensor 40, the microwave sensor 56 and a timer circuit 70. The controller processes these signals in accordance with a preset program to control the door lock 31 and the power level of the microwave emitter 60 and switching of the motor 46. The program ensures that the radiation level in the drum remains substantially constant throughout the drying process. It will be understood that the moisture in the clothes damps the resonance of the chamber by absorbing microwave energy and that as the moisture is removed from within the drum, less radiation is required to keep the radiation in the drum constant. There is a relationship between the amount of moisture in the drum and the microwave energy required to remove that moisture. The system works on a feedback process whereby the moisture content of the clothes is determined by the residual level of radiation. Thus as the clothes dry, less radiation needs to be introduced by the emitter 60 and consequently the power consumed drops as the moisture in the clothes decreases. The door 30 is locked during the drying process by lock 31.

The user may key in the particular drying requirements via a keyboard or switchpad 62; for example, the length of cycle, the moisture content (as measured by sensor 40) at which the cycle should stop and so on may be programmed.

In the described embodiment, the microwave radiation heats the water in the clothes. By the nature of microwave radiation, dry clothes remain cool and only the water in the clothes is directly heated by the microwave radiation, not the clothes themselves.

Initial studies conducted by the applicant have shown that power consumption of the illustrated embodiment is expected to be about 50% less than that of conventional tumble driers which use electric heating elements. The peak start-up current will be about 5-6 Amps which will reduce to about 1 to 2 Amps for a fully dried load. The time taken to dry will be about 30% to 50% of conventional driers given an overall efficiently of about 3 to 5 times that of a conventional type electrically heated drier.

Claims

1. Drying apparatus for drying articles, e.g. clothes, said apparatus including container means for containing said articles, agitating means for agitating said articles, microwave irradiation means for irradiating said articles with microwave radiation and ventilation means for causing a gas to pass through said container means.

2. Drying apparatus according to claim 1, wherein said container means comprises a drum rotatable in use about a generally horizontal axis thereby agitating articles contained in said drum.

3. Drying apparatus according to claim 1 or claim 2, wherein said microwave irradiation means is located outside said container means and is oriented to direct radiation into said container through a generally transmissive window portion of said chamber.

4. Drying apparatus according to claim 3, wherein opposed regions of said container means are provided with window means and reflector means defining a resonant cavity for the microwave radiation are provided outside the container adjacent a respective window portion and said microwave irradiation means is arranged to introduce radiation into said resonant cavity.

5. Drying apparatus according to any one of the preceding claims which includes sensor means for determining the intensity of radiation within said chamber and control means for controlling said microwave irradiation means in response to the output of said sensor means to maintain the intensity of radiation within said chamber at a predetermined level.

6. Drying apparatus according to any one of the preceding claims, wherein heat exchange means are provided to transfer heat from gas leaving said container to gas entering or about to enter said container.

7. Drying apparatus substantially as hereinbefore described with reference to, and as illustrated in, any of the accompanying drawings.

8. Any and all novel features and combinations and subcombinations thereof, substantially as disclosed herein.