EP0017633B1

EP0017633B1 - Method of defrosting a freezing chamber and arrangement for carrying out the method

Info

Publication number: EP0017633B1
Application number: EP19800850026
Authority: EP
Inventors: Johan Bergseth
Original assignee: Electrolux AB
Current assignee: Electrolux AB
Priority date: 1979-03-20
Filing date: 1980-03-04
Publication date: 1984-01-25
Also published as: AU533466B2; ES489670A0; SE427775B; EP0017633A1; AU5657980A; ES8200468A1; SE7902497L; DE3066231D1

Description

This invention relates to a method of defrosting a freezing chamber in a freezer, preferably in a freezer cabinet, wherein the freezing chamber is emptied and the door closed, and steam is used for heat transfer to frosted parts and surfaces in the chamber. The invention also relates to an arrangement for carrying out the method.
Methods which have until now been used to defrost a household freezer are primitive and far from satisfactory. Usually when defrosting is to be carried out the frozen items are removed from the cabinet and are wrapped in a provisional heat-insulation. The freezer door is left open so that warm ambient air is allowed to act on the frost on the shelves in the cabinet. This takes a long time which may cause the items to be damaged by an increased temperature. Only exceptionally is another freezer available for provisional storing of the items. The defrosting time can be shortened by heat supply, for example a pan with hot water can be put into the cabinet or a hair dryer be placed so as to blow hot air into the cabinet. Also the water formed during defrosting involves great inconveniences. It has been tried to improve the conditions during the collection of water, for example by placing a vessel on the bottom of the cabinet and a funnel-shaped tray of plastics over the vessel. Part of the water will be collected in this way but the majority will escape and flow over the bottom of the cabinet and out in front of it. There are several other proposals for collecting the water but it is still difficult to avoid spreading of water on the floor.
From the United States patent specification No. 3,033,967 a defrosting device for use in a refrigerator is known. The device comprises a water container with a heating element for converting the water to steam. The device is bulky. It is movable and intended to be inserted with water in it into the refrigerator chamber when defrosting is desired.
An object of this invention is to provide a method of defrosting which considerably reduces the time required for the process and at the same time makes it possible in a better way than previously to collect the water formed during defrosting. For this purpose the method according to the invention is generally characterized by the steps defined in the characterizing part of the following claim 1. An arrangement for carrying out the method is characterized by the features defined in the characterizing part of claim 5.
The invention will be described below with reference to an embodiment of a freezer shown in the drawings. Fig. 1 is a front view of the cabinet without door, Fig. 2 is a vertical cross section of the same cabinet (however, with its door) on the line II-II of Fig. 1, Fig. 3 is a top view of a vessel placed in the cabinet, and Fig. 4 is a vertical cross section of the vessel on the line IV-IV of Fig. 3. ¹
Figs. 1 and 2 show a freezer cabinet 10 operated by a compressor 11 and having cooled shelves 12, 13, 14 and a cooling element 15 inside the freezing chamber 17 under the top wall 16 of the cabinet. The cabinet has a door 18, which however is not shown in Fig. 1. A shallow vessel 19 is placed under a shelf 13. The vessel is shown to an enlarged scale in Figs. 3 and 4 and will be described below. In the bottom 20 of the cabinet is provided a drain conduit 21 whose upper opening is covered by a removable plug, not shown, preventing air from flowing through the conduit when the cabinet is in operation. Under the door the cabinet has a vent louvre 22 to an air channel, through which cooling air is supplied to the compressor 11 and to a condensor 23 at the rear side of the cabinet.
The surface of the vessel 19 covers almost the entire cross sectional area of the freezing chamber. A heating element 24 in the form of an electric heating coil is heat-conductively connected to the bottom of the vessel and is fed with current through wires 25, 26 from a control means 27, which as shown in Fig. 1 can be placed under the door 18. This means may be placed in the freezing chamber or somewhere else together with control means for the normal operation of the freezer. The means 27 is fed with current through wires 28 from an electric mains and includes a switch with two contacts 29, 30, one contact 30 being disposed on an arm 31 arranged to snap between two positions. The arm is shown in Fig. 3 with the switch in its off-position. The switch can be caused to close the circuit by depressing a push button 32. Then a lamp 33 lights and indicates that the heating element 24 is active. The control means 27 also includes a thermostat 34 which disconnects the switch. The thermostat 34 has a sensor 35 in heat- conductive contact with the vessel 19 and an impulse conduit 36 therefrom to the control means 27. When vapour is being formed the temperature of the vessel is abt. 100°C nearest the element and lower at a distance from it. When the supply of water ceases, the temperature of the vessel increases rapidly which is used for interruption of the defrosting by the thermost, whose sensor reacts on a temperature which is above the operation temperature in the point in which the sensor is placed.
To make the heating element 24 capable of vaporizing water in the vessel 19 the latter is designed so that not more than a given maximum quantity of water can be collected in the vessel. For this reason holes 37 with flanged edges are made in the bottom of the vessel in the shown embodiment.
Defrosting of the above described freezer cabinet is carried out in the following manner. The refrigerating apparatus of the freezer is disconnected and the cabinet is emptied of items. These are placed outside the cabinet and are shrouded by some insulation or in some other manner protected against temperature increase during the defrosting. The plug in the drain conduit 21 in the bottom 20 of the cabinet is removed and a water collecting vessel 38 is placed under the opening of the drain conduit. The cabinet door is closed and the electric current to the heating element 24 is switched in by depressing the push button 32.
The heat supply to the vessel 19 results in the first hand in that ice and frost on the nearest shelf 13 above the vessel 19 melt so that water drops into the warm vessel 19 and is vapourized. The vapour thus formed goes to the coldest places in the chamber, i.e., those covered by ice. Thus distribution of heat in the entire chamber is obtained in a natural way in spite of the fact that heat is supplied only to a very limited part. The vapour condenses and causes a substantial supply of heat to the desired places. Thereby melting of ice on all cooling coils in the chamber is achieved and fresh melt water drops into the vessel from the shelf 14 higher up and from the cooling element 15 at the top wall 16 of the cabinet. During the whole time of water supply from shelves disposed higher up fresh vapour is formed in the vessel. Should more water be supplied, to the vessel than the quantity which can be vapourized therein, it flows out through the holes 37. The water flows onto the shelves below the vessel and contributes to melting ice thereon. The holes are meant to prevent large quantities of water from collecting at the heating element 24 thereby obstructing or delaying the desired effective vapourization.
When the ice in the chamber has melted and water is no longer supplied to the vessel 19 its temperature will rapidly increase from the vapourizing temperature, abt. 100°C. The result is that the sensor 35 of the thermostat 34 reacts and gives an impulse to the thermostat to disconnect the supply of current to the heating element 24. At the same time the current to the signal lamp 33 is disconnected and the lamp goes out, thereby indicating that defrosting is accomplished. The collecting vessel 38 is removed and emptied of water. It can then be used to store items in the cabinet, which is again started so that the items can be put in. The vessel 38 can also be permanently located in place and an apparatus part which is warm during operation can be used in known manner to evaporate the water collected in the vessel.
When designing a freezer cabinet so that water can be collected during defrosting by a drain conduit 21 in the cabinet bottom 20, the bottom surface should be formed so as to conduct the water flowing down to this drain. It can be suitable to make the front edge and also the upwardly nearest cabinet edge with a slightly marked border which leads the water towards the bottom or prevents water from flowing towards the opening of the cabinet. A smaller water drain can also be placed like a screen on the inside of the door in its lower part to prevent water possibly condensed on the door from flowing straight down to the sealing strip of the door without passing over the bottom of the cabinet.
The embodiment shown and described should not be considered as a limitation of the invention to solely this example, but the invention can be modified within the scope of the following claims. The invention has been described in connection with a freezer cabinet with cooled shelves for example of metal plate or grating with cooling tubes therein. As appears from the above description the vapour formed during defrosting is spread over the entire freezing chamber. Thus also vertical conduits and vertical cooling surfaces inside the chamber can be defrosted in accordance with the proposed method. A condition is, however, that the means for collecting the water with heating element for vapourizing the water can be placed under a surface in the cabinet on which there is such a great quantity of frost that sufficient quantities of water can be delivered to the collecting vessel.

Claims

1. Method of defrosting a freezing chamber in a freezer, preferably in a freezer cabinet, wherein the freezing chamber (17) is emptied and the door closed, and steam is used for heat transfer to frosted parts and surfaces in the chamber, characterized by the following steps: to use a water collecting means (19) disposed under and close to a cooled surface (13), having ice and frost thereon, to supply heat by electric heating means (24) to the collecting means so as to first melt ice and frost present on the cooled surface immediately above the collecting means, to collect water thus obtained, to vapourize part of this water so as to form steam for further defrosting, to drain off excessive water from the water collecting means, to evacuate this water and the water obtained during defrosting through a bottom outlet in the chamber (17), and to discontinue the supply of heat to the collecting means after the defrosting has been completed.

2. Method according to claim 1, characterized in that the water is collected in the means (19), having the shape of a vessel, to a height defined by an overflow.

3. Method according to claim 2, characterized in that the temperature increase of the vessel (19) after the supply of water has ceased is used to discontinue to the supply of energy to the heating element (24).

4. Method according to claim 3, characterized in that defrosting is discontinued automatically by a thermostat (34) coupled to a wire (25, 26) to the heating element (24), the thermostat having a sensor (35), disposed near the vessel (19), which disconnects the supply of current to the element (24) when the temperature of the vessel (19) rises above a given value.

5. Arrangement in a freezing chamber in a freezer, preferably in a freezer cabinet, for carrying out the method of claim 1, characterized by a means (19) arranged under and close to a cooled surface (13) to collect water flowing down, the means (19) having an electric heating element (24), which when energized, melts ice and frost present on the cooled surface (13) and vapourizes part of the water thus obtained which is collected in the collecting means (19), the collecting means comprising means for evacuating therefrom excessive water, which together with defrost water from other surfaces is evacuated through a bottom outlet.

6. Arrangement according to claim 5, characterized in that the means (19) is a vessel having an overflow in the form of several holes (37) with flanged edges.

7. Arrangement according to claim 5, characterized in that a thermostat (34) is connected in a conduit (25, 26) to the heating element (24) in the vessel (19), the sensor (35) of the thermostat being disposed near the vessel and having a disconnecting temperature which is some degrees above the operation temperature at the same location.