DE102011102050A1 - Double-walled vessel e.g. roaster for cooking food at low temperature, has phase change medium stored in cavity, such that phase change of medium is performed from solid into the liquid phase within specific temperature interval - Google Patents

Abstract

The vessel (1) has cavity (2) in which a phase change medium is contained. The phase change of the phase change medium is performed from the solid into the liquid phase within temperature interval between 70-90 [deg] C. A porous and/or cellular metal is provided in cavity in a state contacting with the vessel material, while the phase change medium is provided in free spaces of porous and/or cellular metal.

Description

The invention relates to a vessel for cooking food. Such vessels are often referred to as roast. It can be used for low-temperature cooking of food. In low-temperature cooking, food is cooked for a long time at a temperature below the boiling point. Preferably, a temperature in the range of 80 ° C is used.

Food and in particular meat cooks slowly from outside to inside, the juice contained in the meat remains in it, does not leak out and the meat remains very juicy and tender.

During low-temperature cooking, the formation of unhealthy roasting substances can be avoided or reduced to a minimum. So prepared dishes are therefore much easier to digest and healthier.

However, it is essential to maintain the desired temperature for cooking within a narrow temperature range and to ensure that the correct cooking time is maintained.

The ovens used for cooking usually have insufficiently accurate temperature control and can experience temperature fluctuations of at least ± 10 ° C around an average. A manual control of the temperature is very complex and it is also difficult to measure the temperature of the food.

So far, it is customary to use vessels (roasters), which have a large mass in order to achieve a buffer effect for the desired temperature with the heat capacity achievable thereby. However, this is disadvantageous because of the inertia of the temperature changes and also because of the large mass, which impairs the handling.

The use of phase change medium has hitherto only been used for pure keeping warm or cooling.

It is therefore an object of the invention to achieve compliance with a predetermined temperature when cooking food with little effort and to improve the handling of suitable vessels thereby.

According to the invention this object is achieved with a vessel having the features of claim 1. The claim 9 relates to the use of the vessel. Advantageous embodiments and further developments of the invention can be realized with features described in the subordinate claims.

According to the invention, at least one cavity is present on / in the vessel in which a phase change medium is contained, in which the phase change from the solid to the liquid phase takes place within the temperature interval between 70 ° C and 90 ° C. Preference is given to a phase change temperature of 80 ° C ± 3 K.

This can be exploited that at a higher temperature in the oven, the heat energy initially passes into the heat of fusion of the phase change medium, so that the temperature of the vessel does not increase or only slightly. A temperature increase takes place only when the phase change medium has completely gone over into the liquid phase.

When falling below the melting temperature of the phase change medium heat energy is released during the solidification and the transition to the solid phase. It has been found that a temperature deviation from the desired cooking temperature of 10 K over a period of 15 minutes can be easily compensated. This leads to a significantly safe calculability of the cooking time required in each case and it can be better avoided exceeding a temperature that is critical for the low-temperature cooking. There is no additional control effort, also manually required.

The vessels according to the invention can have a significantly reduced inherent mass compared with conventional ones and are thus easier to handle. The net mass can be reduced compared to those made of cast iron to 30%, with better effectiveness.

Preferably, a mass ratio between the mass of the _vessel material M _vessel and the mass of the phase change medium M _{PCM should be maintained} from 20%: 80% to 95%: 5%.

One or more cavities may be formed in the bottom and / or in lateral wall regions of the vessel wall.

It is particularly advantageous for at least one cavity to contain a porous and / or cellular metal which is in contact with the vessel material. In this case, the phase change medium is contained in the free spaces of the porous and / or cellular metal. It may be a metal foam or an open-cell structure. Through the metal, the heat conduction between the vessel material and the phase change medium can be improved. The metal used for the structure has a higher thermal conductivity than the phase change medium, so that the time constant at the achievable by means of the phase change medium temperature control can be reduced.

In addition, thereby the strength of the vessel in the area or in areas in which cavities are present, can be increased.

Such random metallic structures have an increased surface area compared to other geometrically shaped elements, such as honeycomb structures, so that the surface usable for the heat conduction between the metal of the structure and the phase change medium is increased.

However, these effects can also be achieved with metallic hollow bodies, preferably hollow spheres, which are contained together with the phase change medium in one or more cavities of a vessel. The metallic hollow body should have porous outer walls and phase change medium at least be included in the cavities of the hollow body.

Regardless of whether a metallic structure or metallic hollow bodies are contained in a cavity, a volume fraction of metal volume _metal and volume fraction phase change medium Vol _PCM within a cavity in the range of 75% to 25% to 95% to 5% should be maintained.

The flexibility can be increased if at least one phase change medium-filled cavity is formed in an insert element that can be inserted into the vessel. Thus, a vessel can readily be used in conventional form for cooking or heating food. If it is then used for low-temperature cooking, at least one such insert element can be inserted or inserted into the vessel.

The insert element can contain only phase change medium. However, it is also possible to use an insert element in the invention in which, as described above, a metallic structure or metallic hollow body with the phase change medium is / are included.

The invention will be explained in more detail with reference to examples.

Showing:

1 a partial section through the wall of an example of a vessel according to the invention;

2 a graph of calculated temperature profiles over time at periodic temperature fluctuations for several vessels compared and

3 a graph of calculated temperature curves for several vessels compared, lowering the temperature within a furnace to a temperature of 75 ° C over time.

Example 1:

In a double-walled vessel 1 , with wall thickness of the two vessel walls 1' each 0.5 mm stainless steel, was in the between the vessel walls 1' trained cavity 2 filled with Paraffin Rubitherm RT 82. The phase change from the solid to the liquid phase takes place in this phase change medium at a temperature of 81 ° C. There were comparative studies with two vessels according to the invention 1 and a conventional vessel with a constant wall thickness of 3 mm, without cavity 2 and phase change medium. The one vessel according to the invention 1 had in the area of between the vessel walls 1' trained cavity 2 a distance of 2 mm and the other a distance of 6 mm, so that correspondingly different sized cavities 2 , which were filled with the phase change medium with the appropriate volume, resulted.

The calculations show how out 2 It can be seen, the different temperature curves with periodic temperature fluctuations of ± 10 K within a furnace. It becomes clear that the vessel 1 in which the distance between the vessel walls 1' 6 mm, after a preheating time, the temperature during cooking varies by less than 1 K. The fluctuation of the temperature but can already with the second vessel according to the invention 1 in which by the smaller distance of the vessel walls 1' also less phase change medium in the cavity 2 was reduced compared to the conventional vessel made of stainless steel material. The conventional vessel shows a temperature profile which follows the course of the furnace temperature out of phase and thereby the bandwidth of the temperature variation of the furnace are reduced by only a few degrees Kelvin.

From the in 3 The diagram shows the temporal temperature behavior for these three vessels, starting from an oven temperature of 80 ° C, which was reduced to 70 ° C, recognizable. The container 1 with the greater distance between the vessel walls 1' was able to hold the temperature of 80 ° C for more than 5 minutes before cooling down. A temperature of 75 ° C was reached only after 18 min. In comparison, the temperature is reduced of the conventional vessel at 75 ° C already after 4 min.

A comparison of the net mass of the vessels with the same content volume also results in significant advantages of the invention. So is the net mass of a vessel according to the invention 1 , with the specified wall thicknesses and distances of the vessel walls 1' , with a mass of approx. 1.4 kg. By contrast, a conventional cast iron vessel with a wall thickness of 5 mm has a mass of approx. 6.2 kg, which is more than three times heavier.

Example 2

Here is an inventive vessel 1 in his cavity 2 , in which the paraffin is also contained as a phase change medium, additionally provided with a metal foam structure. This has a porosity of 90%. The free spaces of the structure are filled with the paraffin and the metallic structure is in touching contact with the vessel walls 1' in the area of the cavity 2 , The metal used was an iron-copper alloy with a thermal conductivity of 15 W / mK. Due to the porosity, the thermal conductivity was reduced to 0.8 W / mK. The net mass of the vessel 1 was only increased by a maximum of 0.7 kg. In contrast, the response could be improved and a shortening of the time constant in the event of temperature fluctuations can be achieved.

Example 3

The vessel according to the invention 1 for this example, in principle, the structure, as in Example 1 on. It's just the cavity 2 filled with a bed of metallic hollow balls, which are also filled with the paraffin as a phase change medium in addition to the space between the metallic hollow spheres. The metallic hollow spheres were prepared so that a fluidized bed coating of expandable polystyrene beads with a metal powder of stainless steel 1.4404, with a mean particle size d ₅₀ of 6 microns, an organic binder and binder aid was performed. The organic components were removed by pyrolytic heat treatment. This was followed by sintering at a temperature of 1200 ° C. One possibility for the production of these metallic hollow spheres is in the DE 199 29 760 A1 described.

The metallic hollow spheres thus obtained, with their porous walls, were heated with the paraffin and, at a pressure well below atmospheric ambient pressure, melted the paraffin and thus infiltrated the metallic hollow spheres with the paraffin.

After cleaning the outer surfaces, the paraffin-filled hollow spheres could be electroplated with a coating of nickel. The coating can then form a seal which can prevent leakage of the phase change medium.

The metallic hollow spheres can then be further paraffin into a cavity 2 a vessel 1 filled and the cavity then sealed.

Even with such a vessel, the effect of the phase change medium and the better thermal conductivity of the metallic hollow spheres can be used advantageously combined and possibly occurring during cooking temperature fluctuations better and in less time, so that almost constant temperatures can be maintained even with fluctuating furnace temperature ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19929760 A1 [0033]

Claims (9)

Food cooking vessel, characterized in that on / in the vessel ( 1 ) at least one cavity ( 2 ) is present, in which a phase change medium is contained, in which the phase change from the solid to the liquid phase within the temperature interval between 70 ° C and 90 ° C takes place. A vessel according to claim 1, characterized in that a mass ratio between the mass of the vessel material M _vessel and the mass of the phase change _medium M _PCM of 20%: 80% to 95%: 5% is maintained. A vessel according to claim 1 or 2, characterized in that the cavity (s) ( 2 ) in the bottom and / or in lateral wall regions of the vessel wall ( 1' ) is / are formed. Container according to one of the preceding claims, characterized in that in at least one cavity ( 2 ) is a porous and / or cellular metal, which is in contact with the vessel material in contact and in the free spaces of the porous and / or cellular metal, the phase change medium is contained. Vessel according to one of the preceding claims, characterized in that the at least one cavity ( 2 ) or more cavities filled with metallic hollow bodies and the phase change medium is / are. Container according to claim 5, characterized in that the metallic hollow body have porous outer walls and phase change medium is contained in the cavities of the hollow body. Vessel according to one of claims 4 to 6, characterized in that a volume fraction of metal Vol _metal and volume fraction phase change medium Vol _PCM within a cavity ( 2 ) in the range 75% to 25% to 95% to 5%. Container according to one of the preceding claims, characterized in that at least one filled with phase change medium cavity ( 2 ) in an insert element that enters the vessel ( 1 ) is used, is formed. Use of a vessel according to one of the preceding claims for the low-temperature cooking of food.

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