EP2006622A2

EP2006622A2 - Refrigerating machine with defrosting unit

Info

Publication number: EP2006622A2
Application number: EP08158472A
Authority: EP
Inventors: Niccolo' Gaggelli; Alessandro Rosi
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-06-19
Filing date: 2008-06-18
Publication date: 2008-12-24
Also published as: ITAR20070030A1; EP2006622A3

Abstract

A refrigerating machine comprising a refrigeration system, a chamber (1) to be refrigerated, a freezing-defrosting subchamber (2), a fan (3) with which the air of the chamber to be refrigerated is pushed and made to circulate through the freezing-defrosting subchamber (2), which is provided with a thermoelectric Peltier-effect refrigerating device (4), whose normally warm part is in contact with evaporator of the refrigeration assembly and whose normally cold part is combined with the freezing-defrosting surface (6), and wherein the electric power source is provided with a switching and adjustment assembly (5) by means of which the surface (6) is switched from cold to warm and its temperature is adjusted.

Description

The invention relates to a refrigerating machine with defrosting unit, aimed at preserving products and adapted to cool a volume to temperatures even below 0°C, provided with a device by means of which the formation of frost in its useful cooled volume is hindered.
Refrigerating machines are known which are used to contain products, particularly food products, to be preserved at a temperature which is lower than the ambient temperature, comprising temperatures below 0°C.
These machines, like refrigerators and freezers, are provided so as to work according to different technical methods. One of them, which works according to the technical method known as "Direct Cooling", comprises a chamber, which is optionally divided into several parts and is delimited by one or more heat-conducting surfaces which act as heat exchangers, and therefore are in contact on one side with the evaporator assembly of the refrigeration system and are in contact on the other side with the air of the volume to be cooled, from which they remove heat. The air inside the chamber to be cooled, in contact with the products therein, becomes humid and warmer and rises, and in this movement it flows over the surfaces that act as heat exchangers, and thus cools, and in the meantime, if the temperature of these surfaces is lower than the dew point, it deposits as frost part of the moisture that is associated with it. Due to this circulation and deposition, the surfaces that act as heat exchangers become coated with a layer of frost which, as it increases, reduces the heat transmission coefficient of the exchanger and therefore reduces the refrigeration capacity of the system associated with the machine.
It is therefore necessary periodically to defrost the machine, with the drawbacks that this entails, due both to the intervention required and to the fall of layers of frost onto the floor, which thus remains wept, and because it is necessary to switch off the system and therefore preserve the contents of the machine outside such machine at ambient temperature, with the danger of damage or deterioration of the products to be preserved, or to temporarily transfer them to another machine.
Another known refrigerating machine, which operates according to a different technical method, normally known as "no frost", comprises a volume which is divided into two chambers, of which the first one is designed to generate cold and has the heat exchangers concentrated therein, and the second one is designed to contain the products to be cooled and does not contain heat exchangers. A suitable fan generates a stream of air, which passes through the two chambers: in the first one, it is cooled by contact with the heat exchange surfaces, which are cooled by the refrigeration system; in the second one, it flows over the products to be preserved and removes heat from them until they are brought to the programmed temperature. The circulating air releases its moisture, in the form of frost, to the heat exchangers that are present only in the first chamber, while the surfaces of the second chamber are preserved from frosting. The first chamber is also provided with a heating assembly, usually an electric resistor, to be activated periodically, when the refrigeration system is deactivated, in order to perform defrosting.
Such machine, for an equal overall volume, has a smaller useful volume, is relatively complicated and therefore more expensive, and entails a higher energy expenditure; moreover, the temperature in the second chamber, despite not being affected by the frost, nonetheless increases during defrosting intervals even in this machine, and therefore the products therein may risk damage.
The aim of the present invention is to provide a refrigerating machine which is constructively simple and in which the moisture of the air gathers in the form of frost in a very small space within the cooled volume, so that the overall refrigeration heat exchange and the temperature inside the machine remain substantially constant over time.
Within this aim, an object of the invention is to provide a refrigerating machine in which defrosting can be performed without altering significantly the temperature in the refrigerated chamber and therefore without requiring, during this step, the extraction of the products accommodated therein from said chamber or the shutdown of the refrigerating machine.
Another object of the invention is to provide a refrigerating machine in which defrosting can be automated and/or programmed by the user.
This aim and these and other objects, which will become better apparent hereinafter, are achieved by a refrigerating machine with defrosting unit, comprising a chamber to be refrigerated and a subchamber, characterized in that the chamber to be refrigerated is delimited at least in one part by the heat exchange surface which is thermally connected to the evaporator assembly, in that the subchamber has a much smaller volume than the chamber to be refrigerated and contains a thermoelectric Peltier-effect refrigerating device, which on one side is connected to the evaporator assembly and on the other side is connected to the freezing-defrosting surface, a fan and a thawing liquid collector, said subchamber comprising a switching assembly with which at least the polarities of the power source of the thermoelectric refrigerating device are exchanged.
Such machine is particularly advantageous, because it is easy to provide and because the introduction of the defrosting assembly does not alter significantly its structure and useful volume.
It is advantageous because the machine, as a refrigeration system, operates continuously and does not require its shutdown in time intervals in which defrosting is performed.
It is advantageous because during defrosting the temperature inside the refrigerated chamber, and therefore the temperature of the products contained therein, remains substantially unchanged.
It is advantageous because the products of defrosting, and particularly the water that derives from the thawing of the frost, can be collected in an external container, without creating problems in terms of cleaning or of wetting the floor on which such machine rests.
It is advantageous because frost forms only on a limited surface inside the machine and thus the heat efficiency of such machine remains substantially constant over time.
It is advantageous because defrosting can be activated with a programmed circuit, in which the defrosting intervals are set and adjusted by the user.
Finally, it is advantageous because it allows to keep the subchamber at an adjustable constant temperature and allows to provide a region inside the chamber which has a different thermal gradient than the chamber itself, and in this manner, for example, the production of ice is allowed even in refrigerating machines which do not have a separate compartment designed as a freezer.
Further characteristics and advantages of the invention will become better apparent from the following detailed description of a preferred but not exclusive embodiment of a refrigerating machine with defrosting unit, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a schematic view of a refrigerating machine provided with an automatic defrosting assembly;
Figure 2 is an enlarged-scale side view of the subchamber for freezing-defrosting;
Figure 3 is an enlarged-scale front view of the heat exchanger associated with the thermoelectric Peltier-effect refrigerating device, shown in the condensation step;
Figure 4 is a front view of the heat exchanger of Figure 3, shown in the step for thawing the frost therein.

The invention consists of a refrigerating machine, such as for example a refrigerator or freezer of the type for family use or for shops or points of sale of products to be preserved at a temperature which is in any case lower than the ambient temperature, including the temperature around the dew point in which the defrosting operation, i.e., the removal of the frost that has formed inside it by condensation of the moisture of the air that is present in the refrigerated chamber, occurs automatically or under the command of the operator.
The machine comprises a chamber 1 to be refrigerated, a small subchamber 2, within which the formation of frost, i.e., the freezing of the moisture that is present in the air that has entered such chamber to be refrigerated during its opening and introduction of the products to be kept at the chosen temperature, which is lower than the ambient temperature. Both the chamber 1 to be refrigerated and the subchamber 2 have heat exchange surfaces which are connected, directly or by means of a eutectic fluid, to an evaporator assembly 10 of the refrigeration system with which the machine is equipped.
The subchamber 2, whose volume is normally much smaller than the volume of the chamber 1 to be refrigerated, on the order of one hundredth or even less than the volume of the chamber 1 to be refrigerated, contains a Peltier-effect thermoelectric refrigerating device 4, which on one side is connected directly to the evaporator assembly 10 or connected thereto by means of a eutectic mass, in the vicinity of its initial portion, where the temperature is substantially constant, and on the other side is combined with a freezing-defrosting surface 6. A suitable small fan 3 conveys thereon a stream of air which is drawn from the chamber 1 to be refrigerated, where it is then returned after skimming the surface 6 associated with the thermoelectric refrigerating device 4.
Inside the subchamber 2 for freezing-defrosting there is also a collector 7 for defrosting liquids, which is provided with a duct 9 by means of which they are conveyed outside.
The Peltier effect is the thermoelectric phenomenon by which an electric current that flows between two different metals or semiconductors arranged in contact (Peltier junction) produces a transfer of heat, i.e., the opposite of the better-known Seebeck effect.
The Peltier cell therefore should be considered as a solid-state heat pump, having the appearance of a thermoelectric circuit which has a pair of electrodes, a "warm" electrode and a "cold" electrode, which are mutually connected by a pair of laminas: one lamina absorbs heat, while the heat is emitted by the other lamina. The direction in which the heat is transferred depends on the direction of the applied current.
In practice, the thermoelectric refrigerator 4 comprises a circuit which is constituted by two bars made of different semiconductors, for example antimony and bismuth, which are welded at their ends. A generator is inserted between the two semiconductors, which are connected by means of a pair of copper laminas which are mutually parallel, so that such current can circulate. In this manner, a pair of electrodes is formed which are referenced as "warm" and "cold" because if a positive voltage is applied to one electrode and a negative voltage is applied to the other electrode, the result is that one lamina becomes cool and the other one becomes warm.
By reversing the voltage, the heat energy displacement is also reversed.
The thermoelectric refrigerating device 4 is therefore, on the side that is normally warm, in thermal contact with a portion, preferably the initial portion at a substantially constant temperature, of the evaporator assembly 10 of the refrigeration system, or with a eutectic mass which is refrigerated by the evaporator assembly 10, with which the machine is equipped, which drives and keeps substantially constant its operating temperature. The other side of the thermoelectric refrigerating device 4, the one that is normally cold, is instead connected to the heat exchanger with the large surface 6, acting as a condensation surface during the freezing step and as a liquefaction surface in the defrosting step. This heat exchanger is normally a structure made of metal or otherwise a material which has a high thermal conductivity. It normally has a finned configuration with a surface which is suitable for the frost to be collected therein during normal operation and is designed to be skimmed by the air stream that is pushed into the subchamber 2 by the fan 3. During the normal operation of the machine, the warm side of the thermoelectric refrigerator 4 is therefore substantially at the temperature of the initial portion of the evaporator assembly 10 with which it is in contact. Its cold side, and the freezing surface 6 with it, is at a temperature which is approximately 10°C and lower than the warm side and is in any case lower than the dew point.
The moisture that is present in the air that skims it undergoes a sudden cooling and freezes therein in the form of frost 8. The average moisture diffused in the air inside the chamber 1 to be refrigerated of the machine is thus reduced, hindering or in any case reducing in this manner the formation of frost outside the subchamber 2, even if the temperature of the surfaces outside the subchamber 2, at least part of which act as refrigerating surfaces, reaches temperatures lower than the dew point.
The thermoelectric refrigerator 4 is combined with its own electric power supply. Its input electric terminals, during normal operation, have the polarity that gives its inner side, i.e., the side in thermal contact with the evaporator assembly 10 of the machine, a "warm" temperature. It is further combined with a switching-adjustment assembly A-C 5, by means of which the polarity of the electric source that supplies it is switched, so that once such switching has been performed its inner side becomes the "cold" one and therefore its outer side becomes the "warm" one, i.e., reaches a temperature higher than 0°C and in any case sufficient to thaw the frost 8 in contact with the surface 6, which in this step acts as a defrosting surface. The temperature of the surface 6 is changed by means of a suitable adjustment of the absorbed electric current, such current being adjusted as a function of the refrigerating machine in which the invention is applied.
In one embodiment, the heating of the surface 6 in the defrosting steps is achieved by combining such surface with an electrical resistor which is activated, and therefore heated, in the intervals in which defrosting is performed.
In another embodiment, such heating of the defrosting surface 6 is achieved by the combined effect of an electric resistor which is crossed by a current and by the reversal of the current in the thermoelectric refrigerator 4.
The dripping caused by the thawing of the frost and optionally the sliding of the part of frost that has remained solid, under the action of its own weight, are directed into the defrosting liquid collector 7.
In these conditions, the frost 8, at least the frost in direct contact with the surface 6 which, when heated, becomes the defrosting surface, thaws and slides into the defrosting liquid collector 7 and at least its liquid part is conveyed outside the machine through the suitable duct 9.
The switching assembly 5 can have manual activation or can be combined with a programmed timing assembly, which is adapted to drive for a definite time and at programmed intervals the reversal of the polarity of the power supply of the thermoelectric refrigerating device 4 in defrosting intervals.
Normally, reversal of the polarities of the power supply source of the thermoelectric refrigerating device 4 also causes an interruption in the power supply of the fan 3, so that in the defrosting steps in the subchamber 2 the air is stationary, thus facilitating such defrosting.
Due to the great difference between the volumes of the chamber 1 to be refrigerated and of the freezing-defrosting subchamber 2, during the defrosting step the temperature in the chamber 1 to be refrigerated remains substantially unchanged, and the products inside it therefore do not detect the transition of the operation of the machine from the freezing step to the defrosting step.
The surface 6 is normally of the type with fins, so that for an equal occupied volume it is large and therefore, in the freezing step, facilitates contact with the air to be dehumidified. This set of fins, or in any case its contour, when heated, therefore in the defrosting step, is further such as to also facilitate the sliding of the frost and of the drops toward the collector 7.
The liquid produced in the defrosting step is guided outward and normally conveyed into an open container 11, which is arranged above a compressor assembly 12, from which it receives heat to facilitate the evaporation of such liquid, so that it is made to mix with the air of the enclosed space in which the refrigerating machine is accommodated.
Advantageously, the subchamber 2 can have a constant temperature which can be adjusted by the user.
For this purpose, there is a suitably programmed thermoelectric control circuit, by means of which the temperature of the subchamber 2 is adjusted by controlling the current that is sent to the Peltier cell of the thermoelectric refrigerating device 4, such control being performed by means of a device for measuring the temperature of the subchamber 2 and a current regulator.
In particular, the thermoelectric control circuit is programmed to vary the current that passes through the Peltier module (and therefore the delta T between the two faces of such module), depending on the measurements of the temperature measurement device.
Advantageously, in order to produce ice it is possible to connect to the freezing-defrosting surface 6 a container for liquids, for example an ice holder tray, so that if such container is filled with water it is possible to obtain ice inside it during the freezing step. By placing the "cold" electrode at the temperature for liquid-solid state transition (or below) and the "warm" electrode at the temperature provided in the chamber 1, it is in fact always possible to generate ice even when the chamber 1 is adjusted to operate at temperatures above zero and in the refrigerating machine there is no separate freezing compartment or freezer.
In another embodiment, such defrosting unit is shaped like a container for liquid.
Finally, it is also possible to apply in series to the thermoelectric refrigerating device 4 at least one more Peltier cell, which is accommodated within the subchamber 2, so as to obtain, by adding each thermal delta of each Peltier cell, an important high temperature gradient between the subchamber 2 and the chamber 1.
Each one of these cells must have both electrodes connected to a power supply provided with adjustment and reversal means for the electric current in order to obtain the freezing or defrosting effects.
The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.
All the details may further be replaced with other technically equivalent elements.
In practice, the materials used, as well as the dimensions, may be any according to requirements without thereby abandoning the scope of the protection of the appended claims.
The disclosures in Italian Patent Application No. AR2007A000030 from which this application claims priority are incorporated herein by reference.
Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

A refrigerating machine with defrosting unit, comprising a chamber (1) to be refrigerated and a subchamber (2), characterized in that the chamber (1) to be refrigerated is delimited at least in one part by the heat exchange surface which is thermally connected to the evaporator assembly (10), in that the subchamber (2) has a much smaller volume than the chamber (1) to be refrigerated and contains a thermoelectric Peltier-effect refrigerating device (4), which on one side is connected to the evaporator assembly (10) and on the other side is connected to the freezing-defrosting surface (6), a fan (3) and a thawing liquid collector (7), said subchamber (2) comprising a switching assembly (5) with which at least the polarities of the power source of the thermoelectric refrigerating device (4) are exchanged.
The refrigerating machine according to claim 1, characterized in that the thermoelectric refrigerating device (4) on one side is thermally connected to the evaporator assembly (10) of the machine and on the other side is combined with a heat exchanger with high thermal conductivity and a large surface (6), which acts as a freezing surface to be skimmed with the air moved by the fan assembly (3).
The refrigerating machine according to claim 1, characterized in that the thermoelectric assembly (4) on one side is connected thermally to the initial portion of the evaporator assembly (10) directly and/or by means of a eutectic mass.
The refrigerating machine according to claim 1, characterized in that the thermoelectric refrigerating device (4) is combined with an electric power supply and with a switching assembly (5), by means of which the polarities of the electric source that powers it are exchanged.
The refrigerating machine according to claim 1, characterized in that the thermoelectric refrigerating device (4) is powered with an adjustable electric current.
The refrigerating machine according to claim 1, characterized in that the thermoelectric refrigerating device (4) is combined with a programmed timer assembly which reverses the power supply polarities in the defrosting steps for specified time intervals and periods.
The refrigerating machine according to claim 1, characterized in that the surface (6) is of the type with fins.
The refrigerating machine according to claim 1, characterized in that the surface (6) is contoured so as to facilitate, when it is heated, the sliding of the frost (8) toward the collector (7).
The refrigerating machine according to claim 1, characterized in that the heating of the surface (6), when defrosting is performed, is achieved by the combined effect of an electric resistor which is crossed by a current and by the reversal of the current in the thermoelectric refrigerating device (4).
The refrigerating machine according to claim 1, characterized in that said subchamber (2) is at an adjustable constant temperature.
The refrigerating machine according to claim 10, characterized in that it comprises a programmed thermoelectric control circuit and a device for measuring the temperature of said subchamber (2) which is connected to said thermoelectric control circuit in order to keep constant the temperature in said subchamber (2) depending on the measurement detected by said temperature measurement device.
The refrigerating machine according to claim 1, characterized in that it comprises a container for liquids (7) which is connected to said freezing-defrosting surface (6), said liquids being freezable during the freezing step of said subchamber (2).
The refrigerating machine according to claim 1, characterized in that said defrosting unit is shaped like a container for liquids.
The refrigerating machine according to claim 1, characterized in that it comprises at least one other Peltier cell which is accommodated within said subchamber (2), in series with said thermoelectric refrigerating device (4), and is provided with electrodes which are connected to a power supply which is provided with adjustment and reversing means for the electric current.