A METHOD OF HEATING A PACKAGED FOOD PRODUCT

FIELD OF THE INVENTION

The present invention relates to the food industry, specifically to methods utilizing the heat released in an exothermic chemical reaction for heating a food product prior its use.

BACKGROUND OF THE INVENTION

From the prior art, the various methods of heating a packaged food product with the use of a thermal module are known. A method of heating a packaged food product is known from Pat. FR 2607692, publish. 10.06.1988. According to said method, an exothermic chemical reaction is initiated in the cavity of a thermal module by mixing reagents in solid state and liquid state disposed in the cavity of the thermal module. A heated vapor-gas mixture (generated as a result of the chemical reaction) is first fed out from the thermal module's cavity through the holes in its wall, and then said mixture reacts with the bottom wall of the package with the food product.

The above-described method has the following disadvantages. Firstly, the effective heat supply is provided only to the bottom wall of the package. Secondly, the heat accumulated in solid products of the exothermic chemical reaction is not used.

Another known method of heating a packaged food product is one taken as a prototype and comprising the steps of: disposing a flat thermal module with a reagent in solid state and made with a neck, and a package with a food product, relative to each other, providing thermal contact of the first of the package's two opposite walls with one of two opposite heat- conducting walls of the flat thermal module; initiating an exothermic

chemical reaction in the cavity of the flat thermal module by feeding a reagent in liquid state through the neck (Pat. US 5220909, publish. 22.06.1993).

The main disadvantage of the prototype is that the packaged food product is heated by a one-sided heat energy supply. The consequence of this is irregular distribution of the temperature through the volume of the food product being heated and the rather lengthy process of heating the food product to a temperature not below the predetermined temperature.

DISCLOSURE OF INVENTION

The present invention is focused on solving the technical problem of double-sided heat energy supply to a packaged food product when using only one flat thermal module. However, the achievable technical result consists in improving even distribution of the temperature throughout the volume of the food product being heated, together with simultaneous reduction in the time for heating it up to a temperature not below the predetermined temperature (in other words, together with simultaneous reduction in the duration of the exothermic chemical reaction).

The defined problem is solved by means of a method of heating a packaged food product comprising the following: a flat thermal module with a reagent in solid state and made with a neck, and a package with a food product, are disposed relative to each other, thus providing thermal contact of the first of the package's two opposite walls with the first of two opposite heat-transfer walls of the flat thermal module; an exothermic chemical reaction is initiated in the cavity of the flat thermal module by feeding a reagent in liquid state through the neck to said cavity; a flat thermal module is used, in which the heat-transfer walls are made from flexible, heat-conducting sheet material and hermetically connected to each

other through an open circuit, conjointly forming a cavity for the reagent in solid state and a neck, which communicate with each other, and the length of its neck section is not less than 1.4 times the thickness of the package with the food product; here the heated vapor-gas mixture released under the exothermic chemical reaction and flowing through the neck reacts with the second wall of the package with the food product by means of bending a pre-flattened neck section of the flat thermal module around the side part of the package with the food product.

The advantage of the proposed method of heating a packaged food product over the prototype is that using a flat thermal module of the above- mentioned construction provides (in the course of the exothermic chemical reaction) a simultaneous heat energy supply to opposite sides of the food product package. As a result of more efficient utilization of the heat energy of the vapor-gas mixture released in the exothermic chemical reaction, the heating time of the packaged food product is reduced, with more even distribution of the temperature throughout its volume and a reduction in chemical consumption.

The foregoing description illustrates the preferred embodiment of the invention, which is not limited to this particular configuration.

BRIEF DESCRIPTION OF DRAWINGS Fig. 1 illustrates a package with a food product being heated; Fig .2 illustrates the flat thermal module, front view; Fig. 3 the same, plan view, partial section;

Fig. 4 illustrates the flat thermal module and a package with a food product in thermal contact;

Fig. 5 illustrates the flat thermal module and a package with a food product under exothermic chemical reaction;

Fig. 6 the same, with the use of a cover made from heat-insulating material;

Fig. 7 the same, with the use of a heat-conducting screen.

DETAILED DESCRIPTION OF THE INVENTION A package 1 with a food product being heated (fig. 1) is made in the shape of pouch with two opposite sides 2 and 3 from gas-water proof material (polyethylene, polypropylene, etc.).

A flat thermal module 4 for embodiment of the claimed invention (fig. 2, fig. 3) is made of two identical sheets (preferably with a rectangular shape) from gas-water proof, heat-conducting material (aluminum foil, lamister, etc.). Said sheets are hermetically connected to each other through an open circuit 5 (by thermo-seam, for example), thus conjointly forming a cavity 6 with two opposite heat-transfer walls 7, 8 and a neck 9 communicating with the cavity, preferably expanding outwards. There is a reagent in solid state, preferably calcium oxide-based, in the cavity 6 of the flat thermal module 4 (preferably in a container 10 made of gas-water- permeable material). The neck section 12 of the flat thermal module 4 has length L, which is greater than thickness H of the package 1 with the food product being heated. Preferably, L=(1.4 - 3.O)H, while the lower limit is chosen to provide the possibility of directing the heated vapor-gas mixture along the surface of the second wall 3 of the package 1. Implementation of the neck section 12 of the flat thermal module 4 with length L more than 3H is inadvisable due to the unreasonable increase in materials consumption of the flat thermal module 4.

In order to provide better utilization of the heat generated as a result of the exothermic chemical reaction, a package 1 with a food product and a flat thermal module 4 are disposed either in the cavity of a cover 13 made

from heat-conducting material (aluminum foil, lamister, etc.), fig. 5, or in the cavity of a cover 14 made from heat-insulating material (permeated paper, cardboard), fig. 6. In the first instance, it is advisable to provide heat insulation of the second heat-transfer wall 8 of the flat thermal module 4 by means of disposing a pad 15 made from heat-insulating material (fig. 5) between said wall 8 and the opposite wall of the cover 13. In the second instance, it is advisable to use a screen 16 made from heat-conducting material, which includes the package 1 with the food product and the flat thermal module 4, thus forming a slot channel 17 between the screen and the second wall 3 of the package 1 with the food product and also a thermal contact between the screen and the second heat-transfer wall 8 of the flat thermal module 4 (fig.7). The screen 16 may be built conjointly with the flat thermal module 4. The heated vapor-gas mixture flowing out the neck 9 is indicated on the figures by dashed arrows 18.

The method of heating a packaged food product is realized in the following manner. A package 1 with a food product (fig.l) and a flat thermal module 4 (fig. 2 and 3) are disposed relative to each other, with thermal contact provided between the first wall 2 (of two opposite walls 2 and 3) of the package 1 with the food product and the first heat-transfer wall 7 (of two opposite heat-transfer walls 7 and 8) of the flat thermal module 4, in other words, close to each other (fig. 4). The flat thermal module 4 that is used has heat-transfer walls 7 and 8 made from flexible, heat-conducting sheet material (aluminum foil, lamister) and hermetically connected to each other through an open circuit 5, thus conjointly forming a cavity 6 and a neck 9 communicating with the cavity (fig. 2), and length L of the neck section 12 is not less than 1.4 times the thickness H of the package 1 with the food product. In the cavity 6 of the flat thermal module 4, an exothermic chemical reaction is initiated between a reagent in solid

state 11 disposed there and a reagent in liquid state (water). In the embodiment of the claimed invention, a uniform mix of calcium oxide and anhydrous silica gel with an anhydrous silica gel content of 1 part in 3.0- 6.0 weight parts of calcium oxide is used as the reagent in solid state. The reagent in liquid state is fed through the neck 9 to the cavity 6 of the flat thermal module 4 (on fig.4, the solid arrow shows the water feed direction). Afterwards, the hole size of the neck section 12 is decreased to the minimum possible value by means of forces applied to its walls and directed towards each other. Then, the flattened neck section 12 of the flat thermal module 4 is bent around the side part of the package 1 with the food product, pressing it wherever possible to the external surface of the package (fig. 5 - 7). Heat generated under the exothermic chemical reaction is first transferred through the first heat-transfer wall 7 of the flat thermal module 4, and then through the first wall 2 of the package 1 to the food product disposed in it. A heated vapor-gas mixture is formed under the exothermic chemical reaction. Under action of the pressure of said mixture, a neck in the shape of a slot channel is formed in the bent, flattened neck section 12. This hereby promotes the action of the heated vapor-gas mixture 18 feeding out through the neck on the second wall 3 of the package 1 with the food product. On contact of the heated vapor-gas mixture 18 with the second wall 3, which has a lower temperature, a heat transfer process accompanied by the intensive condensation of water vapor takes place.

Thus, the use of only one flat thermal module 4 provides a simultaneous heat supply to both opposite walls 2 and 3 of a package 1 with a food product. This makes it possible to decrease the irregular temperature distribution throughout the volume of a food product being

heated, and also to reduce the time for heating the product up to a temperature not below the predetermined temperature.

For better utilization of the heat energy generated as a result of the exothermic chemical reaction (which includes a decrease in heat loss to the surrounding space), a package 1 with a food product and a flat thermal module 4 are disposed either in a cover 13 made from heat-conducting material (fig. 5), or in a cover 14 made from heat-insulating material (fig. 6, fig. 7). In fact, as a result of a slot channel forming either between the second wall 3 of the package 1 with a food product and the wall of the covers 13 and 14, respectively (fig. 5, fig. 6), or the slot channel 17 (fig.7), contact of the heated vapor-gas mixture flowing out the neck is provided along the whole length of the package 1 with a food product. In other words, the surface area over which heat transfer takes place is increased. The implementation of the neck 9 expanding outward also leads to an increase in area of said surface. It should be noted that the heat emission accompanying the intensive condensation of water vapor makes it possible to substantially decrease the pressure inside the covers 13 and 14. The consequence of the above-stated is a substantial reduction of the requirements for mechanical strength characteristics of these covers.

The advantages of the claimed method were experimentally confirmed by means of heating two identical 220-gram packages 1 with a food product (pilaf) with the use of two identical flat thermal modules 4 with reagent 11 in solid state in the form of uniform mix of 5Og of calcium oxide and 1Og of anhydrous silica gel of "MCKM" grade. In both instances, an exothermic chemical reaction was initiated by feeding 50 ml of water into the cavity 6 of each flat thermal module thorough a neck 9. The difference is that in the first instance, the neck part 12 of the flat thermal module 4, after flattening, was bent as illustrated in fig. 5, and in the

second instance, it was not. The temperature of the first wall 2 and the second wall 3 of each package 1 was measured during the exothermic chemical reaction. The time dependency of the temperature of the first wall 2 of the first package 1 differed slightly from the time dependency of the temperature of the first wall of the second package 1 (not more than 3 %).

As for the time dependency of the temperature of the second wall 3 of the first package, it differed significantly from the time dependency of the temperature of the second wall 3 of the second package. Thus, within 2 minutes after the experiment started, the temperature of the second wall of the first package differed by 17 ⁰ C from the temperature of the second wall of the second package. Within 5 minutes after the experiment started, this difference was 29 ⁰ C. Within 10 minutes after the experiment started, the temperature of the first and the second walls of the first package was equal to 81 ⁰ C and 79 ⁰ C, respectively, and the temperature of the first and the second walls of the second package was equal to 79 ⁰ C and 58 ⁰ C, respectively.

INDUSTRIAL APPLICABILITY

Industrial applicability of the proposed invention is supported by the possibility of its realization using popular materials.