Heat retentive food servingware with temperature self-regulating phase change core

• US 5,954,984 A
• Filed: 07/30/1997
• Issued: 09/21/1999
• Est. Priority Date: 07/31/1996
• Status: Expired due to Term

• Current Assignee: TSI SUB LLC
• Original Assignee: Thermal Solutions Incorporated (Rtx Corporation)
• Inventors: Clothier, Brian L., Ablah, Amil J.
• Primary Examiner(s): Leung, Philip H.
• Application Number:
  US08/902,803
• Time in Patent Office: 783 Days
• Field of Search: 219/620, 219/621, 219/622, 219/624, 219/647, 219/663, 219/649, 219/666, 219/730, 219/759, 219/625, 219/626, 219/665, 219/634, 126/246, 126/375, 126/400, 99/DIG. 14, 99/451
• US Class Current: 219/621
• CPC Class Codes: A47G 23/04 Containers with means for keeping food cool or hot A47G19/027, A47G19/127, A47G19/2288, A47G19/285, A47G23/0313 take precedence; for butter or cheese A47G19/26 ; thermally insulated vessels A47J41/00
• CPC Class Codes: A47J 36/2483 with electrical heating means
• CPC Class Codes: A47J 41/005 comprising heat or cold producing means, i.e. energy transfer from outside the vessel
• CPC Class Codes: H05B 2213/05 Heating plates with pan detection means
• CPC Class Codes: H05B 6/12 Cooking devices
• CPC Class Codes: H05B 6/36 Coil arrangements

Abstract

A heat retentive, temperature self-regulating, food retaining apparatus (10) includes a body (12), heat retentive core (14) and magnetic induction heating element (16). The body (12) includes a substantially rigid, heatable, food-contacting wall (18) defining a cavity (24). The core (14) is positioned in the cavity (24), and in thermal contact with the wall (18) for selective heating of the wall (18). The core (14) includes a solid state phase change material for storing latent heat during a solid-to-solid phase transformation at a phase transformation temperature. A resilient material is in contact with the phase change material to permit expansion of the phase change material during a phase transformation. The heating element (16) is in thermal contact with the core (14) for heating the core (14) to a temperature above the phase transformation temperature to effect a phase transformation in the phase change material. The element (16) includes a ferromagnetic material responsive to a magnetic field for inducing an electric current in the element (16) to heat the element (16). The ferromagnetic material has a Curie temperature between the phase transformation temperature and the melting temperature of the phase change material. A food warming device (42) includes a heater (44) having a holder (46), a magnetic field generator (48), and a no load detector (50), and a food retaining apparatus (10) positioned on the holder (46).

Claims

1. A food warming device comprising:

a magnetic induction heater including a holder, means for generating a magnetic field, and impedance detection means for detecting impedance of a body positioned in the magnetic field generated by said generating means, and for interrupting the magnetic field when the detected impedance drops below a predetermined impedance value; and

a temperature self-regulating device for retaining food and configured to be positioned on said holder and in the generated magnetic field, said food retaining device including a magnetic induction heating element positioned so as to be in thermal contact with food retained by said device for heating said food to a predetermined temperature,

said element including ferromagnetic material responsive to the magnetic field for inducing an electric current in said element to heat said element, said ferromagnetic material having a Curie temperature generally corresponding to said predetermined temperature, and an inherent impedance value when said ferromagnetic material is heated above said Curie temperature, said inherent impedance value being relatively lower than the predetermined impedance value so as to cause said impedance detection means to interrupt the generated magnetic field when said ferromagnetic material of said element is heated above said Curie temperature for regulating the temperature of said food retaining device.

2. The food warming device as set forth in claim 1, said impedance detection means further including means for periodically detecting the impedance of the heating element after interrupting the generated magnetic field for determining when said ferromagnetic material cools below said Curie temperature as represented by the impedance of said element being relatively greater than the predetermined impedance value, and for regenerating the generated magnetic field when said ferromagnetic material cools below said Curie temperature.

3. The food warming device as set forth in claim 1, wherein said heating element is removable from said retaining device.

4. A food retaining apparatus comprising:

food retaining means including a heatable, food-contacting wall;

a first magnetic induction heating element in thermal contact with said wall for heating said wall to a first predetermined temperature, said first element including ferromagnetic material responsive to a magnetic field generated by a magnetic field source for inducing an electric current in said first element to heat said first element to the first predetermined temperature;

a second magnetic induction heating element in thermal contact with said wall for heating said wall to a second predetermined temperature, said second element including ferromagnetic material responsive to the magnetic field generated by the magnetic field source for inducing an electric current in said second element to heat said second element to the second predetermined temperature; and

means for selectively disabling one of said first and second elements so that said wall is heated to the predetermined temperature corresponding to the other of said elements.

5. A method of heating a food retaining device comprising the steps of:

positioning a food retaining device including a food-contacting wall and a magnetic induction heating element in thermal contact with the wall in a magnetic field generated by a magnetic field generating means for inducing a current and a corresponding impedance in the heating element and for raising the temperature of the element;

detecting the value of said corresponding impedance of the element with an impedance detection means;

comparing said detected corresponding impedance value with a predetermined impedance value; and

interrupting the magnetic field when said detected corresponding impedance value of the element is less than said predetermined impedance value.

6. The method as set forth in claim 5, further including the step of regenerating the magnetic field with the magnetic field generating means when said detected corresponding impedance value of the element is greater than said predetermined impedance value.

7. A method of heating a food retaining device comprising the steps of:

providing a magnetic induction heater including generating means for generating a magnetic field, for detecting impedance of a body positioned in the magnetic field, and for interrupting the magnetic field when either the detected impedance drops below a first predetermined impedance value or the absolute value of the rate of change in the impedance exceeds a predetermined rate of change;

providing a device for retaining food including a magnetic induction heating element positioned to be in thermal contact with food retained by the device for heating the wall to a predetermined temperature;

generating a magnetic field using the generating means;

positioning the food retaining device in the magnetic field for inducing current and a corresponding impedance in the element for heating the element;

detecting said corresponding impedance of the element using the detection means;

comparing the detected corresponding impedance with the first predetermined impedance value;

determining the absolute value of the rate of change in the corresponding impedance value;

comparing the absolute value of the rate of change with the predetermined rate of change; and

interrupting the magnetic field when either the detected corresponding impedance value is less than the first predetermined impedance value or the absolute value of the rate of change in the corresponding impedance is greater than the predetermined rate of change.

8. Warming apparatus comprising:

a magnetic induction heater including a magnetic field generator for generating a magnetic field, and an impedance detector for sensing a load impedance parameter of a load magnetically coupled in said magnetic field; and

a temperature self-regulating device in position for magnetic coupling with said magnetic field, said device including a ferromagnetic induction heating element,

said element responsive to said magnetic field for induction heating of said element to a predetermined temperature;

said impedance detector being operable for periodically sensing said load impedance parameter while said device remains in said position, and in response thereto, altering the magnetic field strength of the magnetic field to a different level when said load impedance parameter is above or below a selected value correlated with said predetermined temperature.

9. The apparatus of claim 8, wherein said device can be moved to a position outside of said magnetic field.

10. The apparatus of claim 8, including an adjuster for adjusting the distance between said device and said magnetic field generator to change said predetermined temperature.

11. The apparatus of claim 8, said device including wall structure operable for holding food, said wall structure being in thermal contact with said element.

12. The apparatus of claim 8, said impedance detector being responsive for reducing the magnetic field strength of the magnetic field to a reduced level when said load impedance parameter is below a selected value correlated with said predetermined temperature and increasing the magnetic field strength of said magnetic field when said load impedance parameter is above said selected value.

13. The apparatus of claim 12, said reduced level of said magnetic field strength being zero.

14. The apparatus of claim 12, said impedance detector operable for maintaining the magnetic field strength of the magnetic field at said reduced level so long as said load impedance parameter is below said selected value.

15. The apparatus of claim 12, said load impedance parameter being the absolute value of the rate of change of an induction heater circuit parameter that depends upon the load impedance, said impedance detector being operable for periodically determining the absolute value of the rate of change of the load impedance of said element and comparing said absolute value with a predetermined rate of change of said circuit parameter and comparing said absolute value with said selected value, and reducing said magnetic field strength to said reduced level when said absolute value is greater than said selected value.

16. The apparatus of claim 8, said load impedance parameter being an induction heater circuit parameter that depends upon the load impedance.

17. The apparatus of claim 8, said load impedance parameter being the magnitude of the induction heating coil current.

18. The apparatus of claim 8, said load impedance parameter being the absolute value of the rate of change of an induction heater circuit parameter that depends upon said load impedance.

19. The apparatus of claim 8, said load impedance parameter being the absolute value of the rate of change of the magnitude of the induction heating coil current.

20. The apparatus of claim 8, said device including solid state phase change heat retentive material in thermal contact with said element.

21. The apparatus of claim 20, including a flexible binder in contact with said material.

22. The apparatus of claim 8, said predetermined temperature being above the Curie temperature of said element.

23. The apparatus of claim 8, said element formed of nickel-copper alloy.

24. The apparatus of claim 8, said selected value being adjustable for changing said predetermined temperature.

25. A method of controlling the temperature of a warming device comprising the steps of:

placing said device in a position for magnetic coupling of said device and a magnetic field generated by a magnetic induction heater, said heater having a magnetic field generator for generating said magnetic field and an impedance detector for sensing a load impedance parameter of a load magnetically coupled in said magnetic field,

said device including a ferromagnetic induction heating element responsive to said magnetic field for induction heating of said element to a predetermined temperature; and

operating said impedance detector to sense periodically said load impedance parameter while said device remains in said position, and in response thereto, altering the magnetic field strength of the magnetic field to a different level when the load impedance parameter is above or below a selected value correlated with said predetermined temperature.

26. The method of claim 25, including the step of adjusting the distance between said device and said magnetic field generator to change said predetermined temperature.

27. The method of claim 25, including the step of adjusting said selected value to change said predetermined temperature.

28. The method of claim 25, said device including wall structure operable for holding food, said wall structure being in thermal contact with said element.

29. The method of claim 25, including the step of reducing the magnetic field strength of the magnetic field to a reduced level when the load impedance parameter is below a selected value correlated with said predetermined temperature, and increasing the magnetic field strength of the magnetic field when said load impedance parameter is above said selected value.

30. The method of claim 29, including the step of reducing said magnetic field strength to zero as said reduced level.

31. The method of claim 29, said load impedance parameter being the absolute value of the rate of change of an induction heater circuit parameter that depends upon the load impedance, said impedance detector being operable for periodically determining the absolute value of the rate of change of said circuit parameter and comparing said absolute value with said selected value, and reducing said magnetic field strength to said reduced level when said absolute value is greater than said predetermined rate of change.

32. The method of claim 29, including the step of maintaining the magnetic field strength of the magnetic field at said reduced level so long as said load impedance is below said selected value.

33. The method of claim 25, said predetermined temperature being above the Curie temperature of said element.

34. The method of claim 25, said load impedance parameter being the magnitude of the induction heating coil current.

35. The method of claim 25, said load impedance parameter being the absolute value of the rate of change of an induction heating parameter that depends upon the load impedance.

36. The method of claim 25, said load impedance parameter being the absolute value of the rate of change of the magnitude of the induction heating coil current.

37. The method of claim 25, said device including solid state phase change heat retentive material in thermal contact with said element.

38. The method of claim 37, including a flexible binder in contact with said material.

39. The method of claim 25, said element formed of nickel-copper alloy.