HK1140118A

HK1140118A - Thin film cooking devices and methods

Info

Publication number: HK1140118A
Application number: HK10106294.8A
Authority: HK
Inventors: G‧A‧萨斯; M‧卡尔扎达; J‧D‧林达科; J‧S‧迪克逊
Original assignee: 餐饮技术公司
Priority date: 2007-05-08
Filing date: 2008-05-07
Publication date: 2010-10-08

Description

Thin film cooking device and cooking method

Technical Field

The present invention relates to cooking devices and methods that include a disposable flexible non-stick sheet, and more particularly to cooking devices and methods that optimize heat transfer from a heated platen, through a release sheet, to a food product to be cooked.

Background

Disposable flexible non-stick sheets (release sheets) are widely used in direct contact cooking appliances to prevent food from sticking to the hot platen and to facilitate cleaning by providing a disposable or replaceable cooking surface. Typically, one side of a release sheet constructed of Polytetrafluoroethylene (PTFE) or similar low-friction, heat-resistant polymeric material is placed in direct contact with a flat, metal heated platen, while the food product is directly on the opposite side of the release sheet for heating. Such an arrangement results in a thermal resistance between the platen and the food product to be cooked that is significantly higher than that obtained when cooking on a bare platen. As a result, a higher platen temperature is required to cook the food product in a given time. Also, at a given platen temperature, it takes longer to cook food on the release sheet than on a bare platen. In both cases more energy is consumed.

In widely used cooking devices and methods having release sheets, the total thermal resistance between the platen and the food to be cooked is close to the sum of two series thermal resistances, i.e., the sum of the thermal contact resistance between the platen and the release sheet and the thermal conduction resistance through the thickness of the release sheet. A significant portion of the thermal resistance is caused by poor contact between the release sheet and the platen, which results in high contact resistance and contributes to an increase in overall thermal resistance.

Accordingly, there is a need to improve the contact between the hot platen and the release sheet while maintaining the benefits of the release sheet to reduce energy consumption and time in direct contact cooking appliances.

Disclosure of Invention

In accordance with one aspect of the present invention, a commercial method for efficiently cooking a food product includes providing a heated platen and a release sheet, applying a heat transfer enhancing material to the platen and/or the release sheet, securing the release sheet to the platen, and cooking the food product in direct contact with the release sheet. In this manner, improved intimate heat transfer contact is achieved between the release sheet and the platen, thereby providing more efficient heat transfer between the platen and the food product to be cooked.

According to another aspect of the invention, the heat transfer enhancing material comprises heat transfer grease.

According to another aspect of the present invention, the heat transfer enhancing material includes a binder.

In accordance with another aspect of the invention, the release sheet is dry and extremely thin and is in direct contact with the platen, forming a close contact heat transfer interface with the platen surface.

In accordance with another aspect of the invention, the release sheet is secured to the platen by a securing mechanism. For example, the fastening mechanisms may be clips attached to opposite ends of the release sheet. The clip may or may not be attached to the tensioning mechanism. In another example, the fastening mechanism may be a heat transfer adhesive.

In accordance with another aspect of the invention, the release sheet comprises a Polytetrafluoroethylene (PTFE) material. In some embodiments, the PTFE material may be a PTFE impregnated fiberglass sheet.

In accordance with another aspect of the invention, the release sheet has a thickness of about 0.004 inches or less.

In accordance with another aspect of the invention, the release sheet has a thickness of about 0.001 inches or less.

In accordance with another aspect of the invention, improved intimate heat transfer contact is achieved between the release sheet and the platen of a clamshell grill with hinged upper and lower platens.

In accordance with another aspect of the invention, improved intimate heat transfer contact is achieved between the release sheet and the platen of a vertical conveyor oven having a central platen.

Drawings

Fig. 1 shows an embodiment of the device according to the invention.

FIG. 2 shows inner frame 22 nested within outer frame 21 with release sheet 14 compressed between the two frames, and as shown, release sheet 14 is folded over the top side perimeter of inner frame 22.

FIG. 3 shows a front cross-sectional view of the release sheet 14 secured to the upper platen 13 of the clamshell grill device by the dynamic tensioning system 20, taken along line 3-3 of FIG. 1.

Fig. 3A is an enlarged view of the circled portion in fig. 3.

Fig. 4 is a front sectional view of the upper platen 13, the release sheet 14, the food product H, and the lower platen 12, which are stacked in this order, and the direction of heat flow from the upper platen 13 to the food product H is indicated by an arrow denoted by reference character Q ".

Fig. 5 is a front sectional view of the upper platen 13, the heat transfer enhancing material layer 28, the release sheet 14, the food product H, and the lower platen 12, which are stacked in this order, with the direction of heat flow from the upper platen 13 to the food product H being indicated by an arrow denoted by reference character Q ".

Fig. 6 is a front cross-sectional view of a vertical conveyor oven according to the present invention, the oven including a central platen 32 and a conveyor system 34 housed within a cabinet 42.

Detailed Description

Fig. 1-6 illustrate systems for obtaining enhanced intimate heat transfer contact between a release sheet and a heated platen. Specifically, fig. 1 to 5 illustrate a clamshell grill according to the present invention, and fig. 6 illustrates a vertical conveyor oven according to the present invention.

Referring to fig. 1, there is shown a clamshell grill 10 embodying the heat transfer enhancement system of the present invention. A food item H such as a hamburger patty may be positioned on the heated lower platen 12 as shown, and a heated upper platen 13 having a handle 15 may be positioned against the food item H for cooking the food item H on both sides. The release sheet 14 prevents the food H from sticking to the upper platen 13 when the upper platen is raised and at the same time maintains a high heat transfer coefficient between the food H and the upper platen 13.

As shown in fig. 1-3A, release sheet 14 is held in contact with upper platen 13 by a dynamic tensioning system 20 of the release sheet. The dynamic tensioning system 20 is comprised of a tapered outer frame 21, a smaller tapered inner frame 22 nested within the outer frame 21, and a spring mechanism 23, wherein the spring mechanism 23 provides the tensions Tx and Ty on the release sheet in orthogonal directions. One advantage of the dynamic tensioning system 20 having nested frames and providing tension forces Tx and Ty in orthogonal directions is that the tension forces are evenly distributed around the perimeter of the release sheet. This helps to avoid wrinkling or dishing of the release sheet, thereby minimizing air pockets between the platen and the release sheet. Fig. 2 and 3 show the nested relationship between the boxes 21 and 22. As can be seen in FIG. 2, release sheet 14 is placed on top of inner frame 22 and the edges of release sheet 14 are tucked into outer frame 21 as indicated by arrows A, B, C and D. As can be seen in fig. 1, 3 and 3A, the excess edge portion 14' of the release sheet 14 depends downwardly. Fig. 3 is a front cross-sectional view of upper platen 13 showing how release sheet 14 is held between nested frames 21 and 22 and held in tension against upper platen 13 by spring mechanism 23, spring mechanism 23 providing tension between pins 24 located on outer frame 21 and pins 26 located on upper platen 13. The springs used in spring mechanism 23 preferably each provide a constant tension of about 30 pounds to 80 pounds, depending on the yield strength of the release sheet material. The constant tension in the spring mechanism, i.e., the dynamic characteristics of the dynamic tensioning system 20, corresponds to any slack that is created in the release sheet when the release sheet is tightened.

Other fastening assemblies are also suitable for use in the present invention, such as a pair of opposed or multiple spring-tensioned clips or hooks disposed about the periphery of the release sheet. Further, as an alternative to a dynamic tensioning system, release sheet 14 may be held by a heat transfer enhancing adhesive, or in the case of a release sheet that is extremely thin, it may simply be held in a "snug" manner on the surface of upper platen 13. For example, an electrostatic charge can be generated on the release sheet prior to mounting of the release sheet, thereby creating an electrostatic cling force that holds the release sheet in contact with the platen. Although not shown in the figures, the second release sheet may be held in contact with the lower platen 12 in a similar manner by the means described above or other suitable means.

Referring to fig. 4, a front cross-sectional view of the upper platen 13, release sheet 14, food product H, and lower platen 12 is shown. The heat transfer from the upper platen 13 to the food product H is indicated by the arrow denoted Q ". As described above, by reducing the thermal resistance across the interface between upper platen 13 and release sheet 14, the heat transfer Q "is significantly enhanced. Particularly when release sheet 14 is extremely thin, it can adhere well to upper platen 13, thereby achieving enhanced intimate contact and thus low thermal resistance. For example, in a study of a dry, 0.0015 inch thick release sheet of pure PTFE mounted on a stainless steel platen, a release sheet of about 0.0032hr-ft was obtained²Thermal contact resistance-time area product of ° F/BTU. This is greater than the 0.0037hr-ft obtained by impregnating a fiberglass release sheet with a previously known PTFE of 0.0045 inches thick²A15% increase was obtained in- ° F/BTU. As a result, food products, such as meats, may be cooked more efficiently and better, with better browning of proteins and/or caramelization of carbohydrates.

The thermal contact resistance between the platen and the release sheet can be calculated by measuring the total thermal resistance between the platen and the surface of the food product and subtracting the conductive resistance of the release sheet from the total. In particular, the total thermal resistance-time area product (R) between the platen and the food product can be measured in this way "_{General assembly}Measurement unit hr-ft²- ° F/BTU): 1) measuring the Fahrenheit temperature of the surface of the platen and the surface of the food product contacting the release sheet; 2) the average heat flux per unit area (Q', in BTU/hr-ft) transferred from the platen to the food product is measured²) (ii) a 3) The temperature difference (Δ T) between the platen and the food product is divided by the average heat flux per unit area according to the following equation:

R”_{general assembly}＝ΔT/Q”

Next, the product of conductive thermal resistance-time area (R) of the release sheet "_Sheet) By using release sheet thickness (inches, t)_Sheet) Divided by the thermal conductivity of the release sheet material (in BTU-in/hr-ft)²- ° F) as follows:

R”_sheet＝t_Sheet/k_Sheet

Finally, the product of thermal contact resistance-time area (R) between the platen and the release plate "_{Contact interface}) Calculated by subtracting the conductive thermal resistance-time area product of the release sheet from the total thermal resistance-time area product, as follows:

R”_{contact interface}＝R”_{General assembly}-R”_Sheet

Referring to FIG. 5, a close-contact liquid or fluid heat transfer enhancement system is shown that includes an interfacial heat transfer enhancement material (for ease of reference, the term "wet" is used to illustrate that the inventive system includes a heat transfer enhancement material. As shown, heat flux Q' is directed from platen 13 through heat transfer enhancing material layer 28 and release sheet 14 to food H. The heat transfer enhancing material 28 may be applied directly to the platen and/or release sheet before the release sheet is attached to the platen. While not wishing to be bound by this insight, it is believed that the heat transfer enhancing material, in either a fluid or liquid state, forms an enhanced intimate contact heat transfer interface by filling in voids that would otherwise be filled with air, thereby reducing the gap thermal resistance due to surface imperfections and other gaps that may exist between the platen and the release sheet.

Referring to fig. 6, a vertical conveyor contact oven 30 including the heat transfer enhancement system of the present invention is shown. As shown, release sheet 14 is draped over central platen 32 so that bun tip BC and bun base BH can be baked in direct contact with release sheet 14 on either or both sides of central platen 32. Alternatively, release sheet 14 may be held by a heat transfer enhancing adhesive, clips, or similar fastening mechanism, or when it is thin, it may "cling" to the surface of central platen 32. The release sheet 14 promotes sliding contact with the top and bottom of the bread loaves as they are conveyed by the conveyor in the feed direction FD, while maintaining a high heat transfer coefficient between the top and bottom of the bread loaves and the central platen 32. By way of example and not limitation, conveyor 34 may be comprised of an endless belt 36, rollers 38, and guides 40. The rollers 38 provide a feed rotation FR to continuously convey the endless belt 36 past the guide members 40. In this manner, guide 40 defines the feed direction FD and provides pressure that holds the bun base BH and bun apex BC against release sheet 14 and center platen 32. The central platen 32, release sheet 14, and conveyor 34 may be contained within a magazine 42. In accordance with the present invention, enhanced intimate heat transfer contact between central platen 32 and release sheet 14 can be achieved by using an extremely thin release sheet that can be tightly affixed to central platen 32; or by applying a fairly uniform layer of heat transfer enhancing material to the central platen and/or release sheet, thereby creating an enhanced intimate heat transfer contact interface.

The release sheet according to the present invention may be made of a low friction, non-stick, high temperature resistant material, preferably a polymeric material, such as pure or doped PTFE, with or without a coating. The very thin release sheet used in the dry system of the present invention preferably has a thickness of no greater than 0.002 inches, more preferably no greater than 0.001 inches, and most preferably no greater than 0.0005 inches, so that it can be tightly adhered to the platen, minimizing the presence of air pockets at the interface between the platen and the release sheet. This preferably results in a thermal contact resistance-time area product between the platen and the release sheet of less than about 0.0037hr-ft²- ° F/BTU, more preferably less than 0.0033hr-ft²- ° F/BTU. More preferably, the release sheet 14 is made of a material that is additionally gas permeable (i.e., allows the passage of gases including vapors) but liquid impermeable, such as a semipermeable membrane of dispersed polymer or an expanded PTFE membrane as is well known in the art. Such materials prevent air pockets from being trapped between the release sheet and the platen, while it is possible to maintain a liquid heat transfer enhancing composition between the release sheet and the platen, thereby achieving improved intimate heat transfer contact.

Release sheets used in wet systems need not conform so closely to the shape of the platen and thus can be thicker than the very thin release sheets used in dry systems, but preferably have a thickness of no greater than about 0.004 inches, and more preferably have a thickness of no greater than about 0.0005 to 0.002 inchesAnd (4) thickness. Less than about 0.003hr-ft may be achieved due to the filling of the voids in the contact interface with the heat transfer enhancing material 28²- ° F/BTU and more preferably less than about 0.002hr-ft²Thermal contact resistance-time area product between platen 12 and release sheet 14 (over the entire contact interface) at ° F/BTU.

The heat transfer enhancing material of the present invention may be a heat transfer grease, liquid or adhesive, which is described in more detail below. The grease, liquid or adhesive is preferably safe in case of occasional contact with food; effective and safe at cooking temperatures of, for example, 425 ° F or higher and even up to 475 ° F or higher; and in the case of liquids, can wet the platen and release sheet. Preferably, the adhesive according to the invention allows the release sheet to be easily removed from the platen, and the adhesive to be easily cleaned from the platen.

The heat transfer grease according to the invention may be, for example, a silicone fluid thickened by a metal oxide filler, such as Dow Corning340 heat sink compound ("DC-340"), available from dow corning corporation. DC-340 is stable at high temperatures and has a BTU-in/hr-ft of about 4.1²Thermal conductivity of DEG F.

The heat transfer liquid according to the present invention may be, for example, a liquid paraffin such as Duratherm F G, available from Duratherm Extended Life liquids ("Duratherm"). Duratherm FG, based on materials available from Duratherm, meets the united states department of agriculture requirements for occasional food contact (H1), meets the standards of 21c.f.r. § 178.3570, and is registered with NSF. Duratherm FG is available at temperatures up to 620 ° F and has a BTU-in/hr-ft of 0.92 at a temperature of 425 ° F²Thermal conductivity of DEG F

The heat transfer adhesive according to the present invention may be, for example, a Room Temperature Vulcanizing (RTV) adhesive rubber of silicone developed for heat dissipation applications, such as SS35RTV silicone ("SS 35 adhesive"), available from Moreau marking&Obtained from Sales inc. SThe S35 adhesive may be used at operating temperatures up to 500 DEG F and has a BTU-in/hr-ft of 2.0 at room temperature²Thermal conductivity of DEG F.

The platens of the present invention are preferably substantially flat, metal platens widely used in contact grills and ovens such as clamshell grills or vertical conveyor ovens commonly used in the food industry. The platens are typically stainless steel.

While certain preferred embodiments of the present invention have been described herein, it will be appreciated by those skilled in the art that the invention is susceptible to numerous variations, modifications and rearrangements. Such changes, modifications, and rearrangements are intended to be covered by the appended claims.

Claims

1. A cooking device, comprising:

a) at least one platen;

b) a flexible, non-stick release sheet releasably attached to the platen; and

c) a heat transfer enhancing material forming a close contact heat transfer interface between the platen and the release sheet.

2. The cooking device of claim 1, wherein the heat transfer enhancing material is selected from the group consisting of heat transfer grease, liquid, and adhesive.

3. The cooking device of claim 1, wherein the release sheet has a thickness of about 0.004 inches or less.

4. The cooking device of claim 1, wherein the release sheet has a thickness of about 0.0005 inches to about 0.002 inches.

5. The cooking device of claim 1, wherein the cooking device is an opposed dual platen cooking device.

6. The cooking device of claim 1, wherein the cooking device is a conveyor equipped cooking device comprising:

a) a housing having at least one inlet and at least one outlet; and

b) a conveyor system adapted to convey the food product from the inlet to the outlet while maintaining the food product in close proximity to the release sheet.

7. The cooking device of claim 6, wherein the cooking device is a vertical conveyor oven.

8. The cooking device of claim 6, wherein the cooking device is a vertical conveyor grill.

9. The cooking device of claim 1, wherein the thermal contact resistance-area-over-time product between the platen and the release sheet is less than about 0.003hr-ft²-°F/BTU。

10. The cooking device of claim 1, wherein the release sheet is gas permeable and liquid impermeable.

11. The cooking device of claim 1, wherein the thermal contact resistance-area-time product between the platen and the release sheet is less than about 0.002hr-ft²-°F/BTU。

12. A cooking device, comprising:

a) at least one platen;

b) a flexible, non-stick, very thin release sheet detachably attached to and conforming to the platen, thereby obtaining intimate heat transfer contact with the platen,

wherein the thermal contact resistance-area-over-time product between the platen and the release sheet is less than about 0.0037hr-ft²-°F/BTU。

13. The cooking device of claim 12, wherein said very thin release sheet has a thickness of about 0.001 or less.

14. The cooking device of claim 12, wherein said very thin release sheet has a thickness of about 0.0005 or less.

15. The cooking device of claim 12, wherein the cooking device is an opposed dual platen cooking device.

16. The cooking device of claim 12, wherein said release sheet is breathable and liquid impermeable.

17. The cooking device of claim 12, wherein the cooking device is a conveyor equipped cooking device comprising:

a) a tank having at least one inlet and at least one outlet; and

b) a conveyor system adapted to convey the food product from the inlet to the outlet while maintaining the food product adjacent to the release sheet.

18. The cooking device of claim 17, wherein the cooking device is a vertical conveyor oven.

19. The cooking device of claim 17, wherein the cooking device is a vertical conveyor grill.

20. The cooking device of claim 12, wherein the thermal contact resistance-area-time product between the platen and the release sheet is less than about 0.0035hr-ft²-°F/BTU。

21. The cooking device of claim 12, wherein the thermal contact resistance-area-time product between the platen and the release sheet is less than about 0.0033hr-ft²-°F/BTU。

22. A method of cooking comprising the steps of:

a) providing a cooking device comprising at least one platen;

b) providing a flexible, non-stick release sheet;

c) applying a heat transfer enhancing material on at least one of the platen or release sheet;

d) detachably attaching the release sheet to the platen such that the heat transfer enhancing material provides a intimate heat transfer contact interface between the platen and the release sheet; and

e) heating the food product in direct contact with the release sheet;

wherein the heat transfer enhancing material is selected from the group consisting of heat transfer grease, liquid, and binder.

23. The cooking method of claim 22, wherein the heat transfer enhancing material is selected from the group consisting of heat transfer grease, liquid, and adhesive.

24. The cooking method of claim 22, wherein the release sheet has a thickness of about 0.004 inches or less.

25. The cooking method of claim 22 wherein the release sheet has a thickness of about 0.0005 inches to about 0.002 inches.

26. The cooking method of claim 22 wherein the release sheet is breathable and liquid impermeable.

27. The cooking method of claim 22 wherein the cooking device is an opposed dual platen cooking device.

28. The cooking method according to claim 22, further comprising the steps of:

a) providing a housing having at least one inlet and at least one outlet;

b) providing a delivery system adapted to deliver food product from the inlet to the outlet while maintaining food product in contact with the release sheet; and

c) adding a food product to the inlet;

during the transfer from the inlet to the outlet, the food product is cooked.

29. The cooking method of claim 28, wherein the cooking device is a vertical conveyor oven.

30. The cooking method of claim 28, wherein the cooking device is a vertical conveyor grill.

31. The cooking method of claim 22 wherein the cooking is performed at the stationThe thermal contact resistance-area-over-time product between the sheet and the release sheet has a thermal contact resistance of less than about 0.003hr-ft²-°F/BTU。

32. The cooking method of claim 22 wherein the thermal contact resistance-area-time product between the platen and the release sheet has a thermal contact resistance of less than about 0.002hr-ft²-°F/BTU。

33. A method of cooking comprising the steps of:

a) providing a cooking device comprising at least one platen;

b) providing a flexible, non-stick, very thin release sheet;

c) detachably attaching the release sheet to the platen; and

d) heating the food product in direct contact with the release sheet;

wherein the release sheet conforms to the surface of the platen to provide intimate heat transfer contact between the platen and the release sheet.

34. The cooking method of claim 33, wherein the very thin release sheet has a thickness of about 0.001 inches or less.

35. The cooking method of claim 33, wherein said very thin release sheet has a thickness of about 0.0005 inches to about 0.002 inches.

36. The cooking method of claim 33 wherein the release sheet is breathable and liquid impermeable.

37. The cooking method of claim 33 wherein the cooking device is an opposed dual platen cooking device.

38. The cooking method according to claim 33, further comprising the steps of:

a) providing a housing having at least one inlet and at least one outlet;

c) adding a food product to the inlet;

during the transfer from the inlet to the outlet, the food product is cooked.

39. The cooking method of claim 38, wherein the cooking device is a vertical conveyor oven.

40. The cooking method of claim 38, wherein the cooking device is a vertical conveyor grill.

41. The cooking method of claim 33 wherein the thermal contact resistance-area-time product between the platen and the release sheet is less than about 0.0037hr-ft²-°F/BTU。

42. The cooking device of claim 33, wherein the thermal contact resistance-area-time product between the platen and the release sheet is less than about 0.0033hr-ft²-°F/BTU。