US20080010999A1

US20080010999A1 - Device for cooling food

Info

Publication number: US20080010999A1
Application number: US11/728,918
Authority: US
Inventors: Gerrit Sonnenrein
Original assignee: SGL Carbon SE
Current assignee: SGL Carbon SE
Priority date: 2004-09-27
Filing date: 2007-03-27
Publication date: 2008-01-17
Also published as: JP2008514892A; EP1797382A1; DE102005014742A1; NZ554149A; WO2006034829A1; BRPI0516133A; CA2585464A1; EP1797382B1; DE502005008503D1; NO20072207L; HK1108732A1; ATE448455T1; AU2005289132A1

Abstract

An apparatus for cooling food, in particular water-based beverages, includes a cold accumulator (6) that contains a phase transition material. A conduit (8) for a water-based liquid that is to be chilled is guided through the cold accumulator (6). Also provided is a device (2) for dissipating heat from the cold accumulator (6). In order to make such an apparatus less expensive, easier to produce, and more effective, the cold accumulator (6) is made from a composite material containing expanded graphite and a phase transition material that undergoes a solid-liquid phase transition at or above 273 K.

Description

The invention relates to an apparatus for cooling foods, in particular water-based drinks, which is described in the preamble of claim 1.
Such an apparatus is disclosed by DE 198 56 214. In one embodiment of the known apparatus, a cold accumulator is provided in the form of an ice bank which is cooled via a coolant by the cold side of a Peltier plate module. The drink to be cooled is passed round or through the ice bank. The thermal conductivity of the ice water and therefore the heat transfer properties of the ice bank can be improved by distributing a good conductor, such as, for example copper wool or copper pieces, in its volume. The cooling of foods and drinks by ice is current practice, but has critical disadvantages. A main disadvantage is the low thermal conductivity of ice. The addition of copper material is firstly expensive and secondly involves the risk that, for example, copper pieces, under the influence of gravity, and with partial melting of the ice bank, collect in the lower region and are depleted in the upper region. A further disadvantage of ice which, however, has hitherto always been accepted, is the unfavorable phase change temperature of ice to water, with to date there always being the risk, which had to be avoided by complex control technology, that also water-based drinks froze. Although in this publication the use of a eutectic salt or an aluminum block is mentioned as cold accumulator, the special choice of the eutectic salt, in particular according to its solid-liquid phase change temperature, is not described however.
For industrial applications as tubular or plate heat exchanger, EP 914 399 B1 discloses a composite material in which pressed expanded graphite is impregnated with a phase change material. The graphite acts as heat conductor which in addition is able to take up the most varied phase change materials. As phase change material, use can be made of paraffin, but preferably likewise water/ice.
In industrial and commercial applications, generally use is made of compression or absorption refrigeration units, the relatively large dimensions of which and also high production costs, oppose use in the domestic sector, however. For this reason, for the provision of cooled drinking water in the lower price segment, in particular in the field of small domestic units, Peltier elements suggest themselves, in which, by applying an electric field to two different electric conductors, one side heats up and the other cools down.
Periodic provision of cooled drinking water for application in the domestic sector, owing to the low thermal efficiencies of Peltier elements, make effective storage of, for example during night phases, a critical criterion for the capacity of a continuous flow Peltier cooling.
The simplest form of such a cooling is disclosed, for example, in DE 299 10 820, in which a closed water reservoir is cooled down to the desired temperature by Peltier elements and replenishing water replaces a corresponding fraction of the cooled water. Since for storage of cold in this case only the specific heat capacity of the water in the reservoir is available, large volumes are required even for small capacities.
U.S. Pat. No. 5,544,489 discloses in this respect an improvement in capacity by utilization of the melting enthalpy of the water to be cooled. For this, on the cold side of the Peltier element, ice is generated within a water reservoir, as a result of which the energy density of the cold accumulator is markedly increased.
However, both said apparatuses are opposed by the expected high microbial loading due to stagnant water in a reservoir with respect to approval under drinking water law.
EP 0 777 090 provides an aid in this respect with the essential difference from U.S. Pat. No. 5,544,489 that the drinking water to be cooled is passed through the ice-cooled reservoir in a pipe coil and direct contact is therefore avoided. A problem in this regard of the spatial dimensions of such an apparatus is that the space filled by ice is no longer available for the drinking water coil.
A fundamental problem of all known continuous-flow Peltier-based chillers is the low efficiency of Peltier elements which is predominantly determined by the temperature difference between the cold and warm sides. Whereas the warm side, by use of corresponding cooling bodies and aeration fans, is problem-free in principle and technically solved, the cold side is a problem which has not yet been solved to date. Owing to the low specific thermal conductivity of the cold accumulator medium used [λ_waterapproximately 0.57 W/(mK), λ_iceapproximately 2.2 W/(mK)], there is an increase in the temperature difference and thus an impairment of the efficiency.
The object of the present invention is to provide an apparatus for cooling foods, in particular water-based drinks, which is simple and inexpensive to produce and has a high cooling capacity.
The object is achieved by the features specified in claim 1.
By means of the design according to the invention, for the first time an apparatus for cooling foods, in particular water-based drinks, is provided which represents a high-grade solution for small equipment, in particular in the household or restaurant. By means of the cold accumulator used according to the invention and made of expanded graphite and a phase change material which passes through its solid-liquid phase change at or above 273 K, that is the freezing temperature of water, preferably a few ° C. (up to 10° C.) above the freezing point of water, a very effective cold accumulator is provided which firstly, as a result of the graphite, has a high thermal conductivity, and thereby ensures relatively rapid shock-like cooling, and which secondly comprises a phase change material which, even without complicated control technology, does not involve the risk that water-based drinks freeze and form an ice block. In addition, firstly the size of the cold accumulator required for good performance is decreased, and secondly the space and costs of comprehensive control are saved.
Both measures lead to optimum matching of the apparatus according to the invention to the requirements in the chilling of foods, in particular water-based drinks.
Advantageous developments may be found in the subclaims.
To remove the heat taken up by the cold accumulator, preferably a Peltier element is provided which further has the advantage that the liquid flowing through the line can be heated for disinfection by reversing the polarity of the voltage supply of the Peltier element. Peltier elements are very cheap. The comparatively low thermal efficiencies of a Peltier element are of less importance owing to the very effective storage material having expanded graphite, in particular when there is the possibility of being able to “charge” the cold accumulator in idle times of the apparatus, for example during the night.
However, instead of a Peltier element, conventional refrigerator technology can also be used, for example the absorber or compressor technique for “charging” the cold accumulator. Thus it is conceivable, for example, to integrate the cold accumulator into a conventional refrigerator and there, either for equipping the refrigerator for active and effective shock cooling, for example to use it in the area of the freezer compartment, or to use it for dispensing a drink, for example water, from a central water supply, in or on the refrigerator, in the course of a shock-like continuous-flow cooling.
In principle, however, the invention may also be used advantageously wherever a high cooling capacity with periodic load or fluctuating cooling power requirement must be provided inexpensively with small spatial dimensions.
In order that the entire container is available for the drinking water-bearing pipe geometry, in the invention use is made of a material as cold accumulator medium which passes through a phase change at, or a few ° C. above, the freezing point of water, for which in principle salt hydrates, eutectic mixtures and also paraffins are suitable.
To increase the efficiency of the Peltier element, the cold accumulator medium is admixed with expanded graphite, as a result of which the thermal conductivity can be increased by up to a factor of 150.
The invention is in addition suitable for construction of a cooling container, wherein the cold accumulator can be integrated into an insulated wall of the cooling container, or into the interior, wherein the interior can also be completely filled by the cold accumulator. By means of the apparatus according to the invention, for example inexpensively available commercially conventional refrigerators can be refitted in this manner.
The invention can, for example, also be used as a shock-cooling unit for dispensing drinking water into a cooling container. The invention is also particularly suitable for dispensing units, wherein, in the interior of a housing, a drink source, for example a beer keg, can be received and the cold accumulator is active both in the interior and in the dispense line.
Examples of the invention will be described in more detail hereinafter with reference to the drawings. In the drawings:
FIG. 1 shows a diagrammatic representation of a first example of an apparatus according to the invention,
FIG. 2 shows the plan view onto FIG. 1,
FIG. 3 shows a diagrammatic representation of a further example of an apparatus according to the invention,
FIG. 4 shows the depiction of the section A-A from FIG. 3 for a first arrangement of the line,
FIG. 5 shows the sectional view A-A from FIG. 3 for a second arrangement of the line,
FIG. 6 shows a diagrammatic representation of an apparatus according to the invention using refrigerator technology.
FIG. 1 shows a device according to the invention for chilling foods having a cylindrical container 1 which has an introduced line in the form of a pipe coil 8 through which passes a water-based liquid to be cooled from an inlet 5 to an outlet 4. The liquid to be cooled can be either the drink to be cooled, preferably water with or without gas admixture (carbon dioxide and/or oxygen) which originates from a water source, preferably the central local water supply. Or, however, the liquid can be a coolant, which is, however, preferably likewise water and originates from the central water supply, but serves for cooling foods or drinks at another point.
The container 1 is filled by a cold accumulator 6 which comprises a composite material made of expanded graphite and also a material which passes through a phase change at or above 273 K, the phase change preferably being a few ° C. (up to 10° C., preferably 3° to 5° C.) above the freezing point of water.
Suitable phase change materials are preferably salts and also paraffins known for their phase change properties. In the example shown, the graphite is present as free-flowing granules and is impregnated with the phase change material. The heat taken up from the liquid in the pipe coil 8 is taken off from the cold accumulator 6 again by a suitable unit. The unit in the example shown is a Peltier element 2 which is in intimate contact with the cold accumulator 6 by its cold side. The hot side of the Peltier element 2 is provided with an apparatus 3 for transporting away the heat. The apparatus 3 can be any suitable apparatus and is in particular a fan as is customarily used with Peltier elements. In addition, measures can be taken to reverse the polarity of the Peltier element 2 so that if appropriate the liquid flowing through the line 8 can be heated for disinfection.
To improve the thermal conductivity, the point of the container 1 at which the Peltier element 2 is mounted is made of a readily-conducting material, in particular a metallic material.
Finally, a plurality of Peltier elements can be provided.
In FIGS. 3 to 5, further examples of the apparatus according to the invention for cooling foods are shown which differ from the example according to FIGS. 1 and 2 only by the details described hereinafter. The apparatus according to FIG. 3 also comprises a container 1 which in this example, however, is rectangular, but can equally be cylindrical, as in the first example. In the container 1, a cold accumulator 6 is accommodated which this time consists of plate-type, expanded graphite which was impregnated with the same phase change material which has already been described with reference to FIG. 1. The cold accumulator has a layer structure, with plates of the graphite material alternating with a layer-type arrangement 7 of suitably shaped and laid lines which, however, again extend from the container 1 by the water outlet 4 and the water inlet 5. The layer-type arrangement 7 can contain, for example, a meander-like line geometry 9 of FIG. 4 or a spiral-type line geometry 10 of FIG. 5. Each line layer 7 is connected by inlet and outlet in a manner which is not shown to the adjacent line layers, with the first and last line layers being connected to the water outlet 4 and the water inlet 5, respectively.
The line layers can either be laid as pipes, or in the shape of profiled plates, wherein preferably two plates are provided in a mirror image fashion with corresponding embossings of the size of the half cross section of the line, and the plates are subsequently laid one upon the other and are fastened to one another, so that the embossings supplement each other to give continuous channels which are closed on the periphery side. Not only the pipes but also the profile plates consist of readily heat-conducting material, for example metal. The lines 8, 9 or 10 preferably have a diameter between 3 and 11 mm, in particular 4-10 mm, since, with this diameter, in combination with a water pressure as is supplied on average by a water pipe grid (1.5-4.5 bar) which, if appropriate, can be set by a pump or a pressure-reducing valve to a constant insignificantly varying pressure (±0.5 bar), a strong flow counteracting microbial infestation forms.
The layer-like arrangement according to FIGS. 3 to 5 is preferably produced by compressing the line layers having the graphite plates, which leads to a particularly intimate, heat-transferring contact between the layers.
In this example also, the system for “charging” the cold accumulator 6 preferably contains the Peltier element 2 already described, wherein the Peltier element 2 is arranged in such a manner that the surface normal to the graphite plates is oriented in parallel to the surface of the Peltier element 2.
The examples corresponding to FIGS. 1 to 5 are preferably constructed in the form of a cold battery, that is to say a handleable unit. In this form, the apparatus according to the invention can be installed anywhere where it is required, if appropriate even retrospectively. It is only necessary that measures are taken to connect the water inlet and outlet 4, 5 to a water source, for example the local drinking water supply. However, if appropriate, it is also possible to construct the apparatus according to the invention as a cold battery without the Peltier element and to use another technology for “charging” the cold accumulator.
This can be, for example, the cooling unit of a conventional refrigerator, for example an absorber or compressor refrigerator. This case is illustrated in FIG. 6. FIG. 6 shows a conventional refrigerator 11 which is provided with its own cooling unit 12. In the refrigerator 11 a cold accumulator 6 of the invention is installed which is constructed as a cold battery. The cold accumulator 6 can, as shown in FIG. 6, be accommodated anywhere in the interior 13 of the refrigerator 11, if appropriate also retrospectively. In the example shown, it is accommodated in the rear region opposite a door 14. The cold accumulator 6, however, can also be accommodated anywhere in a wall 15 (including base and upper cover or door 14) or in an intermediate base or the like.
The cold accumulator 6 is provided with the line 8 through which a water-based liquid is passed. The water inlet 5 is connected to a drinking water grid which is preferably detachable via a valve 5 a, for example a conventional water tap. The water outlet 4 can be passed to a dispense point which is not shown.
The function of the Peltier element, here, however, is met by the cooling unit 12 of the refrigerator 11. The cold accumulator 6 can, as shown, be provided only in one part of the interior 13, but can also fill the entire interior 13.
The latter version leads to an apparatus for cooling drinks which can be manufactured particularly inexpensively, the line being passed through the entire interior filled with cold accumulator 6.

Claims

1-12. (canceled)

13. An apparatus for cooling foods, comprising:

a cold accumulator containing expanded graphite and a phase change material configured to pass through a solid-liquid phase change at or above 273 K;

a line for conducting a water-based liquid to be cooled through said cold accumulator; and

a device for removing heat from said cold accumulator.

14. The apparatus according to claim 13, configured to cool water-based beverages.

15. The apparatus according to claim 13, wherein said cold accumulator contains a loose bed of graphite granules impregnated with said phase change material.

16. The apparatus according to claim 13, wherein said phase change material has a phase change temperature not above 10° C.

17. The apparatus according to claim 13, wherein said phase change material has phase change temperature above 0° C. and not above 10° C.

18. The apparatus according to claim 13, wherein said device for removing heat contains a Peltier element.

19. The apparatus according to claim 18, wherein said Peltier element is connected to a reversible voltage supply and the liquid flowing through said line is heatable for disinfection by reversing a polarity of the voltage supply of said Peltier element.

20. The apparatus according to claim 13, wherein said device for removing heat includes an absorber and/or evaporator refrigeration unit.

21. The apparatus according to claim 13, configured as a cold battery having at least one cold accumulator as a portable unit.

22. The apparatus according to claim 21, wherein said portable unit includes said device for removing heat.

23. The apparatus according to claim 13, wherein said line is connected to a drink source and leads to a dispensing system.

24. The apparatus according to claim 13, wherein said line is connectible to a central water supply.

25. The apparatus according to claim 13 configured as a cooling container, which comprises a housing with an insulated wall and said cold accumulator and said line integrated in said wall and/or disposed in an interior of said housing.