GB2278668A

GB2278668A - Defrosting using microwaves

Info

Publication number: GB2278668A
Application number: GB9410685A
Authority: GB
Inventors: Reginald Edward Gray
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-06-03
Filing date: 1994-05-27
Publication date: 1994-12-07
Anticipated expiration: 2014-05-27
Also published as: GB2278668B; GB9311516D0; GB9410685D0

Abstract

An evaporator (2) of a refrigerator may be defrosted by using microwave energy in conjunction with a screen (6) resistant to the passage of microwave energy. The screen is interposed between the microwave source (5) and the cold contents of the refrigerator, eliminating the need to remove the contents of the cold compartment (1) of the refrigerator during the defrosting process. The refrigerator may also include a freezer compartment (3), and a drip tray (4). The screen (6) may be removable, and stored outside the refrigerator when defrosting is not required. The screen may be perforated or solid. <IMAGE>

Description

REFRIGERATOR DEFROSTING.

Refrigerators, as used typically but not exclusively in the home and also in industry and in catering, are subject to the internal build of ice due to the freezing and deposition of the water content of air spuriously introduced into the storage compartment of the refrigerator for instance when the access door is opened.

From time to time it is necessary to remove this "atmospheric ice" to secure the continued efficient functioning of the refrigerator, and also in extreme cases to avoid loss of storage space within the refrigerator.

The process of removing this atmospheric ice is known as "defrosting", and will be referred to as such in this patent application.

This conventional defrosting process is particularly inconvenient in the case of large refrigerators, such as those used in catering and in industry.

The invention simplifies and minimises the inconvenience of the defrosting process by the use of microwave energy, and the invention is equally applicable to very low temperature refrigerators, usually referred to as "freezers".

Figures 1 and 2 show the main components of a typical refrigerator. The cooling element 2 is typically situated inside the top of the main storage compartment 1 of the refrigerator. If a so-called freezing compartment 3 is present, this freezing compartment is usually immediately under the cooling element 2. If a freezing compartment is present, drip tray 4 is usually situated under the freezing compartment. The function of the said drip tray is to collect the water resulting from the melting of the atmospheric ice during the defrosting process. If a freezing compartment is not present, then the drip tray 4 will be in a similar location under the cooling element 2.

In the case of a freezer, no drip tray is present, and the melted atmospheric ice falls to the lowest point in the freezer, from which point it is collected and removed.

The spurious deposition of atmospheric ice can only take place in the areas of the refrigerator where the temperature is below the freezing point of water, and therefore the deposition of atmospheric ice largely occurs on and close to the cooling element 2 of the refrigerator, inside the top of the main storage compartment 1, and on the inside and /continued.

/continued.

outside walls of the freezer compartment 3, if present. The conventional defrosting process is time consuming and inconvenient, and is typically effected by temporarily removing all the contents of the refrigerator from the storage compartment 1 and the freezing compartment 3 of the refrigerator, preferably to an alternative cold location, melting the deposited ice by allowing the temperature of the inside of the refrigerator to rise above freezing point by de-energising the cooling element 2, optionally leaving the access door open and optionally warming the internal compartments of the refrigerator, then removing the water resulting from the melting of the deposited ice which has collected in the drip tray 4 and elsewhere.The refrigerator is then restored to normal operation by closing the access door, re-energising the cooling element 2 and replacing the contents from the alternative cold location into the storage compartment 1 and freezing compartment 3 of the refrigerator after the said storage compartment and said freezing compartment of the refrigerator have regained appropriate low temperatures.

The invention offers a means of easily removing the "atmospheric ice" from the refrigerator, while at the same time avoiding the complexities and inconvenience of the conventional defrosting process. This simplification and improvement in the defrosting process is realised by the introduction of a switched source of radio frequency energy into the refrigerator. This auxiliary source of radio frequency energy is preferably a microwave source and will be referred to as such in this specification, and is shown as component 5 in figures 3 and 4. The radio frequency energy source may take any appropriate form, and in the case of a microwave source is preferably of substantially the same type as that used in domestic and other microwave ovens.The said switched source of radio frequency energy, which may be a microwave source may be contained within the refrigerator or may be in another convenient close location.

For a domestic refrigerator the available energy from the microwave source 5 would typically but not necessarily be less than that normally associated with domestic microwave ovens.

The invention utilises the inherent electrical, mechanical and constructional characteristics of both the refrigerator and the microwave energy source.

The principal features of the invention are shown in figures 3 and 4.

/continued.

The invention will be described by reference to figures 3 and 4, showing the construction of a refrigerator incorporating a microwave energy source 5 preferably, but not essentially, in proximity to the cooling element 2 of the refrigerator adjacent to which most of the "atmospheric ice" is deposited. The said cooling element of the refrigerator is usually but not necessarily situated at the top of the cold compartment.

The essential features of the invention are the combination of; (i) A microwave energy source 5, and (ii) A screen 6 which separates the refrigerator into two compartments, one of which is made up of the cooling element 2, the microwave source 5, the freezing compartment 3 if present, and the drip tray 4; the other compartment consists of the main cold compartment 1 of the refrigerator.

For the satisfactory functioning of the defrosting process incorporating a microwave source, the internal surfaces of the storage and cold compartments, and the internal surface of the access door of the refrigerator should be electrically conducting, in order to minimise the transfer of microwave energy from the inside of the refrigerator to the outside world, and may either be of sheet metal or other electrically conducting material or lined with metallic foil or with other electrically conducting material. In addition, the freezing compartment 4 should preferably be constructed so that the interior of the said freezing compartment is illuminated by the microwave radiation from the microwave source 5. By way of example, the wall of the said freezing compartment 4 closest and/or facing the microwave source, or part of the said wall, may consist of material transparent to microwave radiation.

In all embodiments of the invention the defrosting of the refrigerator is carried out with the refrigerator access door closed.

In one embodiment of the invention, the screen 6 is permanently fixed in position below the drip tray 4, and consists of a material which minimises the transfer of microwave energy from the microwave source 5 to the contents of the refrigerator. The said screen 6 is constructed so that during normal operation of the refrigerator air can pass from the cooling element 2 through or past the said screen 6 to circulate throughout the storage compartment 1 /continued.

/continued.

of the refrigerator. The said screen 6 may be perforated or slotted, or may be of any construction permitting the circulation of air through or past it, while as already said being of a material and construction minimising the transfer of microwave energy through it.

In an alternative embodiment of the invention the screen 6 is again of a material and construction minimising the transfer of microwave energy from the microwave source 5 to the contents of the refrigerator in the main storage compartment 1, and may be perforated or solid. In this alternative embodiment, the screen 6 is movable, and may either be rigid, and stored outside the refrigerator when defrosting is not proceeding, or rigid and may be for instance slid or hinged into and out of position as required. The screen 6 may alternatively be flexible, facilitating the easy movement of the said flexible screen between the stored and operational positions.

This movable screen 6 divides the refrigerator into two compartments only during the defrosting process, and is of a material and construction such that the transfer of energy from the microwave source 5 to the main storage compartment 1 of the refrigerator is minimised, but in this embodiment the screen 6 does not necessarily allow the circulation of air through or past it.

During the normal operation of the refrigerator, by the physical process of convection, cold air sinks through the fixed screen 6 described above in the first embodiment of the invention, but during the defrosting process, when the microwave source 5 is energised, air warmed by the microwave source is largely confined above the said fixed screen 6, the warm air being less dense than the cold air in the storage compartment 1 of the refrigerator.

In the case of the second embodiment of the screen 6, in which the said screen is movable, then the screen is positioned below the drip tray of the refrigerator only during the defrosting process, and the function of the screen 6 in this embodiment is to minimise the transfer of microwave energy from the part of the refrigerator containing the microwave source 5, the cooling element 2, the freezer compartment 3 and the atmospheric ice, to the storage compartment 1 containing the cold contents of the refrigerator, and any movement of air through or past the screen 6 in this second embodiment is incidental to the defrosting process.

/continued.

The process of microwave heating is largely by transfer of energy from the microwave source 5 to water molecules, and in the case of defrosting, to the water molecules making up the "atmospheric ice". Thus in the case of the refrigerator defrosting process the utilisation of a microwave energy source 5 is particularly appropriate, because the "atmospheric ice" is preferentially heated and therefore melted, with minimum energy transfer to, and therefore spurious warming of, the air within the refrigerator. In conjunction with the either of the two embodiments of the screen 6 described above this ensures minimum spurious transfer of microwave energy to, and therefore spurious warming of, the contents of the storage compartment 1 of the refrigerator.

The process of defrosting using the invention will now be described; If the refrigerator has a freezing compartment 3, then the contents of this freezing compartment are removed to an alternative cold location, for instance to the cold compartment of a domestic or other freezer.

Alternatively, because the refrigerator defrosting process which is the subject of the invention is rapid, the contents of the freezer compartment may be wrapped in thermally insulating material or contained in a thermally insulating box and stored in the main cold compartment of the refrigerator during the defrosting process.

The cooling element 2 is preferably energised by electricity, but may equally use any other source of energy, for instance gas supplied either from mains or from a container.

The defrosting process is carried out by switching off or otherwise de-energising the cooling element 2 of the refrigerator, and in the case of the implementation of the invention with the fixed screen 6, switching on the microwave energy source 5.

In the case of the implementation of the invention with the movable screen 6, the said movable screen 6 is moved to its position below the drip tray 4. The refrigerator access door is then closed and the microwave source energised.

An interlock switching mechanism should preferably be provided to prevent the microwave source 5 being energised with the refrigerator door open. This ensures the safety of persons and animals near the microwave source, by reducing /continued.

/continued.

the emission of spurious radiation from the refrigerator system when the microwave source is energised.

After a time sufficient for the melting of the atmospheric ice in the refrigerator, the microwave source is deenergised, and the water resulting from the melting of the ice, most of which has collected in the drip tray 4, is removed from the refrigerator. In the case of the second implementation of the invention with the movable screen 6, the said screen is removed from its position below the drip tray after the defrosting process, either before of after removing the melted ice from the refrigerator. The cooling element 2 is then re-energised and the contents of the freezer compartment of the refrigerator are restored to the freezer compartment when the said freezer compartment has reached an appropriately low temperature.

Thus the atmospheric ice is removed without disturbing the contents of the main storage compartment 1 of the refrigerator.

In a further embodiment of the invention an interlock is introduced preventing the simultaneous energising of the microwave source 5 and the cooling element 2 of the refrigerator.

An interlock may also be introduced in the case of the second embodiment of the screen 6 in which the said screen is movable, whereby the microwave source 5 cannot be energised unless the said screen is interposed between the microwave source and the storage compartment 1 of the refrigerator.

Either, both or neither of the above interlocks may be introduced as considered appropriate.

In a further embodiment of the invention, the system may incorporate visible, audible or other signals to indicate the energised or non-energised state of the microwave source 5, and/or the position of the movable screen in the case of the second embodiment of the screen, and/or the energised or non-energised state of the cooling element 2 of the refrigerator, and/or the temperature(s) within the various compartments of the refrigerator during the defrost cycle, and/or the stage of the defrosting cycle which has been reached, and/or an indication of the completion of the defrosting process.

In a further embodiment of the invention the refrigerator is defrosted by any of the above sequences, the said defrosting /continued.

/continued.

sequence being initiated by an operator, and then progressing without further intervention. The sequence and timing of the switching operations by which the defrosting sequence is progressed are controlled by a timer, or by reference to a temperature measuring instrument or instruments placed in appropriate positions in the refrigerator, or by a combination of timing and temperature control, or by signals applied to the refrigerator system from an external source, which may, by way of example be a microprocessor, which said microprocessor may be controlled by a timer or by reference to a temperature measuring instrument or instruments placed in appropriate positions in the refrigerator or by a combination of timing and temperature control.

This automatic defrost facility is applicable principally, but not exclusively, to the embodiment of the invention in which the screen 6 is fixed in position, but may be extended to the second embodiment of the invention with a movable screen by the addition of visible, audible or other signals instructing the operator to position the movable screen appropriately, according to the part of the defrost cycle which is being automatically implemented.

In all cases the system may include interlock features preventing undesirable combinations of energising and deenergising of the microwave source 5, energising and deenergising of the cooling element 2, the opening and closing of the access door, and in the case of the second embodiment of the invention, the positioning of the movable screen 6.

Claims

CLAINS.

1. Defrosting apparatus by means of microwave energy.

2. A refrigerator or freezer including defrosting apparatus according to Claim 1.

3. A refrigerator or freezer according to Claim 2 including a source of microwave energy and a screen which resists the passage of the said microwave energy.

4. A refrigerator or freezer according to Claims 2 and 3 in which the source of microwave energy and the cooling element of the refrigerator are separately energised.

5. A refrigerator or freezer according to to Claims 1, 2 and 3 in which the microwave energy has substantially the same frequency as the microwave energy in microwave ovens.

6. A refrigerator or freezer according to Claims 1,2 and 3 in which the source of microwave energy is of substantially the same construction as the source of microwave energy in microwave ovens.

7. A refrigerator or freezer according any of the Claims 2 to 6 in which the microwave energy is contained substantially within the refrigerator.

8. A refrigerator or freezer according any of the Claims 3 to 7 in which the screen permits the passage of air through the said screen and is positioned so as to restrict the passage of microwave energy from the microwave source to the main cold compartment of the refrigerator.

9. A refrigerator or freezer according to any of the Claims 3 to 7 in which the screen is substantially rigid.

10. A refrigerator or freezer according to any of the Claims 3 to 7 in which the screen is flexible.

11. A refrigerator or freezer according to Claim 10. in which the screen may be folded, rolled or compressed.

12. A refrigerator or freezer according to any of the Claims 9 to 11 in which the screen is moveable and is stored either outside or inside the refrigerator, and during storage has no effect on the operation of the refrigerator. The said screen is interposed between the microwave energy source and the contents of the main cold compartment only during the defrosting operation.

/continued.

/continued.

13. A refrigerator or freezer according to any of the Claims 9 to 12 in which the screen is of a construction permitting the passage of air through the said screen.

14. A refrigerator or freezer according to Claim 3 in which an interlock prevents the simultaneous energising of the cooling element of the refrigerator and the microwave energy source.

15. A refrigerator or freezer according to Claims 3 and 12 in which an interlock prevents the energising of the microwave energy source unless the movable screen is interposed between the radio frequency source and the main cold compartment of the refrigerator.

16. A refrigerator or freezer according to Claims 14 and 15 in which the interlock is at least in part mechanical.

17. A refrigerator or freezer according to Claims 14 and 15 in which the interlock is at least in part electrical.

18. A refrigerator or freezer according to Claims 14 and 15 in which the interlock is at least in part electronic.

19. A refrigerator or freezer according to Claim 4 in which an indicator shows when the cooling element is energised.

20. A refrigerator or freezer according to Claim 4 in which an indicator shows when the microwave energy source is energised.

21. A refrigerator or freezer according to Claim 12 in which an indicator shows when the screen is interposed between the microwave energy source and the main cold compartment of the refrigerator.

22. A refrigerator or freezer according to any of the Claims 1 to 22 in which an indicator or indicators are provided controlled from a sensor or sensors measuring the temperature(s) of appropriate part(s) of the refrigerator and/or elapsed time, or a combination of temperature(s) and elapsed time.

/continued.

/continued.

23. A refrigerator or freezer according to any of the Claims 2 to 8 in which the defrosting process is started manually and proceeds automatically under the control of a microprocessor and optionally a timing device, and which uses information from sensors measuring the temperature(s) of appropriate part(s) of the refrigerator, the said microprocessor utilising the information from the said sensors and the said optional timing device to switch on and off the cooling element and the microwave energy source at appropriate times.

24. A refrigerator or freezer according to any of the Claims 2 to 7 and Claims 9, 10 and 23 in which the defrosting process is started manually and proceeds automatically under the control of a microprocessor and optionally a timing device, and which uses information from sensors measuring the temperature(s) of appropriate part(s) of the refrigerator, the said microprocessor utilising the information from the said sensors and the said optional timing device to switch on and off the cooling element and the microwave energy source at appropriate times, and which includes an indicator or indicators showing when to insert and when to remove the movable screen.

26. A refrigerator or freezer according to any of the Claims 19 to 24 in which the said indicator or indicators consist at least in part of visible, audible or tactile elements.

27. An apparatus for defrosting a refrigerator or freezer substantially as herein described with reference to the accompanying drawings.

28. A refrigerator or freezer including a defrosting apparatus substantially as herein described with reference to the accompanying drawings.

29. A method of defrosting a refrigerator or freezer substantially as herein described with reference to the accompanying drawings.