GB2284468A - Refrigeration equipment including a eutectic freezing arrangement - Google Patents

Abstract

Refrigeration equipment, particularly for domestic use, comprising one or more freezing chambers having at least one cooling element (10) and an auxiliary quick-freezing device constituted by an eutectic mass housed in a first plate (2) having at least one flat surface (3) is characterized in that a second plate (4), similar to the first plate and also filled with a eutectic mass, is associated with the first plate (2) and can be positioned removably on the first plate so that the two respective flat surfaces (3, 5) fit together. For example, a slice of meat may be located between the surfaces (3, 5). The first and second plates are preferably connected to one another by a hinge (6) fixed to two corresponding edges of the plates. <IMAGE>

Description

REFRIGERATION EQUIPMENT WITH AN IMPROVED FREEZING DEVICE The invention relates to freezing equipment with an improved device for the quick-freezing of foods, the device being disposed within the freezing chamber. The invention relates in particular to refrigerators of all types, particularly domestic refrigerators, which have at least one chamber for freezing foods; the chamber may be cooled either by a forced jet of cold air blown into the chamber (no-frost type) or conventionally, that is, with at least one evaporator which is housed in the chamber and cools the air therein by natural convection.

For greater simplicity, the present description will refer to freezing equipment with only one chamber provided with the invention, and to a method of freezing a slice of meat, which is selected by way of example both because of the great delicacy and value of this type of food and because of its shape which favours its deposition on a flat surface so as to maximize the contact area, but it is intended that the invention may also be extended without restriction to foods of other types and to refrigeration and/or freezing equipment composed of a plurality of freezing chambers.

It is known that the results of a method for the freezing of fresh foods depend greatly on the freezing technique used as well as on the nature of the food; these aspects of freezing techniques, all of which have been studied and analyzed thoroughly, are well known to an expert in the art and are therefore not mentioned.

All efforts in freezing technology for domestic use are therefore devoted to providing, in the easiest, safest and cheapest manner, freezing methods which come closer to the ideal method but which can also be implemented with equipment for domestic use. The basic factor which determines the effectiveness of a freezing method is the speed of the change of state of the item to be frozen, that is, the change of the water contained in the food from the liquid state to the solid state.

In fact, it is known that the faster the change of state takes place in the food, the better will be its subsequent preservation since, the faster the change of state takes place, the less damage is caused to the food cells by the formation of ice crystals which may rupture the cells.

It is well known that one of the methods of accelerating the change of state of foods is the use of a compartment which is previously brought to a very low temperature, and into which the food to be frozen is introduced instantaneously.

In this case, the cooling of the food naturally depends on the temperature difference between the compartment and the food, but also depends on the capacity for the transfer of heat, and conversely cold, between the atmosphere and the food to be frozen.

Since the heat-transfer capacity between the atmosphere and a generic food is quite low, attempts have been made to increase the cooling speed by increasing the temperature difference between the food and the compartment and it is for this reason that freezer compartments may, as is known, reach very low temperatures down to -30 C; however, this technique has limits inherent in the fact that the temperature in the compartment cannot be reduced below a certain limit because of technical difficulties and costs.

The measure of improving the heat-transfer capacity between the two elements has therefore been adopted by the use, at least in part, of a solid, preferably metallic, surface and not the surrounding atmosphere at low temperature, thus considerably increasing the exchange of heat between their sides. This is achieved with the use of plates which contain eutectic masses and upon which the slice of meat to be frozen is placed.

The use of eutectic masses as intermediate freezing elements is known in the art and will not be explained further; it should be remembered simply that the property of these substances is that they freeze at temperatures significantly lower than 0 C and, when cooled to a very low temperature below the freezing point, they therefore remove the heat which corresponds to the change of state at the temperature considerably lower than o C.

Consequently, if a piece of meat is placed on a plate the eutectic mass of which is already frozen, throughout the time taken to freeze the meat, the transfer of heat between the plate and the piece of meat is not modified by a temperature rise induced in the plate by the food, given that this rise would have to pass through the melting point and hence the change of state of the eutectic mass and, as is known, this absorbs a considerable amount of heat because of the change of state; if the heat capacities and temperatures are suitably selected, the eutectic mass therefore remains at a very low temperature throughout the time necessary to freeze the piece of meat whilst providing the necessary coldness to freeze the meat to a sufficiently low temperature, thus correspondingly reducing the time taken to freeze the meat, given that it freezes at an optimal temperature just below -1 C and, ideally, between -1 and -50C.

This solution has a disadvantage, however; in fact, the quick-freezing of a mass of meat by placing it on a eutectic plate at low temperature causes rapid freezing of the region in immediate contact with the plate, but also brings about non-homogeneous freezing in the rest of the mass, since this is cooled over much longer times, approximately similar to the freezing times in a free atmosphere and this non-homogeneous freezing in turn causes unpredictable subsequent preservation.

In addition to this problem, a chance of better and quicker freezing is also lost, given that the possibility of using the upper free surface of the slice of meat which is exposed to the air, in order further to accelerate the freezing thereof, is ignored.

It would therefore be desirable and is the object of the present invention, to provide a domestic refrigerator having an improved device which avoids the disadvantages described without involving structural complications or new technology, but with low production costs.

This and other objects are achieved by a quick-freezing device described in the appended claims. The invention will be explained further by the following description, which is given purely by way of non-limiting example, with reference to the appended drawings, in which: Figure 1 shows schematically the composition of a freezing chamber according to the invention, Figure 2 shows a detail of Figure 1, Figure 3 shows some graphs of the temperature in the food during freezing.

The solution devised consists basically of the provision of a second eutectic plate, similar to a first plate which already exists within the freezing chamber, and of the positioning of the second plate above the slice of meat which is already resting on the first plate.

With reference to the drawings, there can be seen a eutectic mass 1 housed in a first horizontal plate 2 having an upper flat surface 3, and a second plate 4 which is similar to the first plate, and which in turn has a lower flat surface 5.

The plates are housed in a freezing chamber also containing a cooling element 10 which may be a conventional evaporator or, possibly, in a "no-frost" type freezer, an evaporator unit outside the chamber, and associated with a fan lOA.

The upper plate is movable and, in particular, can be placed on a slice of meat previously laid on the lower plate.

The slice of meat or, in general, the portion of food interposed between the parallel plates housing respective eutectic masses is thus attacked by the cold from both sides, which considerably reduces the freezing time, practically cancelling out the non-homogeneity of the freezing within the mass to be frozen, particularly if the mass is a slice of meat, as in the imaginary case.

In fact, Figure 3 shows the curve of the fall in temperature detected within a slice of meat as a function of time in the three cases of conventional freezing in air (A), of freezing with the use of only one eutectic plate (B) on which the same mass of meat is placed, and of the freezing of the same mass of meat interposed between two similar eutectic masses (C), all other conditions remaining the same.

It can be noted that, before freezing starts (above the +1"C line), the temperature-fall line (D) is the same in the three cases mentioned above, given that the cooling of the mass of meat has not yet reached freezing temperature and there is therefore no change of state.

During the change of state, the three lines are almost horizontal, given that, at this stage, heat transfer takes place at a constant temperature and, finally, there is a further progressive reduction in temperature due to the progressive transfer of coldness from the surrounding atmosphere (the atmosphere or the eutectic masses).

It can be seen that the times needed to complete the change-of-state stage or, more briefly, the freezing stage, vary as follows: in the case of conventional freezing in air (A), the time taken is indicated Ta and is the longest; in the case of a single plate with a eutectic mass, a considerable reduction in the freezing time, indicated Tb, is achieved. Finally, if a device according to the invention is used, a further significant reduction in the freezing time, now indicated Tc, is achieved.

The advantage gained, which is quantified by the reduction in time Tb - Tc, is the result of the present invention.

A first improvement of the invention consists of an ability to vary the distance between the two plates according to the thickness of the slice of meat, so as to improve the contact between the upper plate and the upper surface of the slice of meat.

This can be achieved either by means of a suitable hinge 6 which is positioned on the corresponding edges of the two plates, and to which these are hinged, or by means of a device, e.g. a slot 12, by means of which the plates are connected and which permits a certain degree of relative movement of the plates. A further improvement of the present invention consists of providing the device connecting the plates with a resilient element, for example, a spring or a torsion bar, which tends to keep the plates permanently closed; the advantage of such a resilient element is due to the fact that it adds an additional clamping force to the force of gravity of the upper plate itself, thus improving the contact between the plate and the interposed food.

Since, however, the pressure of the plates on the meat, together with the effect of the very low temperature, may cause the meat to adhere thereto, an advantageous improvement of the invention consists of the formation of their inner surfaces with non-stick material by one of the many methods and materials offered by the state of the art.

Moreover, another improvement of the invention is represented by the fact that, as an alternative to the resilient clamping element between the plates mentioned above, an adjustable clamping element may be fitted between the plates so that the slice of meat can be gripped by the operation of the clamping element which closes the movable sides 8, 9 of the respective plates 2, 4 according to the dimensions of the slice of meat. This clamping element, e.g. a rotatable spring-loaded handle, can easily be produced by an expert in the art and is not therefore described.

A final improvement of the invention consists of causing one of the plates described above to fit tightly at least partially against the cooling element 10; this permits the maximum transfer of coldness from the cooling element by eliminating the insulation constituted by the air space between the cooling element 10 and the eutectic plates, thus achieving a maximum reduction in the time taken to freeze the foods.

Naturally, each quick-freezing device according to the appended claims can also be produced in forms other than those shown without thereby departing from the scope of protection of the present invention.

Claims (7)

1. Refrigeration equipment, particularly for domestic use, comprising one or more freezing chambers having at least one cooling element (10) and an auxiliary quickfreezing device constituted by a eutectic mass (1) housed in a first plate (2) having at least one flat surface (3), characterized in that a second plate (4), similar to the first plate and also filled with a eutectic mass, is associated with the first plate (2) and can be positioned removably on the first plate so that the two respective flat surfaces (3, 5) fit together.

2. Refrigeration equipment according to Claim 1, characterized in that the distance between the plates can be adjusted so that the respective facing flat surfaces (3, 5) remain substantially parallel when the plates are closed together.

3. Refrigeration equipment according to any one of the preceding claims, characterized in that the plates have a resilient element which keeps the plates in a normally closed position.

4. Refrigeration equipment according to any one of the preceding claims, characterized in that at least one of the facing flat surfaces (3, 5) of the plates is formed of or covered with non-stick material.

5. Refrigeration equipment according to any one of the preceding claims, characterized in that the first and second plates are connected to one another by a hinge (6) fixed to two corresponding edges of the plates.

6. Refrigeration equipment according to Claim 5, characterized in that the movable sides (8, 9) of the plates can be clamped in the closed position by force.

7. Refrigeration equipment according to any one of the preceding claims, characterized in that at least one of the first and second plates is disposed at least partially in contact with the cooling element (10).