Evaporator for a refrigeration device

The present invention relates to an evaporator for a refrigerator. The surface of such an evaporator, when supplied with refrigerant, reaches temperatures below 0 ° C. Humidity from the interior of the refrigeration unit can therefore condense and freeze on the surface of the evaporator. A thin, uniformly distributed frost layer is formed on the surface of the evaporator and, if it is not defrosted in the meantime, reaches an increasingly greater thickness during the operation of the refrigeration apparatus and finally grows to form a solid, rigid ice layer. Since the temperature of the evaporator varies with time, depending on whether it is supplied with refrigerant or not, this ice layer expands periodically with time and contracts again. This causes stresses to build up between the ice layer and the underlying evaporator, which ultimately lead to a slipping of the ice layer. The resulting crackling noises are perceived as disturbing. One solution to this problem by using a hydrophobic coating is disclosed in EP 0485801 A.

Such a coating is effective to delay the formation of first ice crystals on an ice-free evaporator and thus lengthen the time required for an ice quantity to accumulate on the evaporator after a defrosting operation. That is strong enough to cause cracking noises. Another effect of the hydrophobic layer is that it prevents the formation of a homogeneous frost layer on the surface of the evaporator. Instead, the icing begins on a small number of non-avoidable germs on the surface of the evaporator. The ice beads forming there grow more or less uniformly on their entire surface and thus reach a considerable thickness before they begin to grow together. That is, a large quantity of ice compared to a non-hydrophobic evaporator can collect on the evaporator according to the invention before a coherent layer is formed which is capable of producing cracking noises.

A further advantage of the islander growth of the ice layer is that surface areas of the evaporator remain relatively free of ice-free and allow an effective heat exchange between the refrigerant and the environment of the evaporator even if a considerable amount of ice has already collected at other regions of the evaporator surface. The time interval between two defrosting phases can therefore be selected to be longer than for a non-hydrophobic evaporator, which for the user of a refrigeration appliance equipped with an evaporator according to the invention entails a gain in comfort and a reduction in the energy consumption of the refrigeration unit and thus its operating costs.

The hydrophobic coating may preferably contain a silicone which acts as a hydrophobizing component.

The object of the invention is to achieve a further improvement in the coating.

The coating is applied as an oil layer. The oil layer has the particular advantage that, since it does not solidify in itself, it promotes the displaceability of the forming ice beads on the surface of the evaporator, so that even when the evaporator is completely iced with a layer thickness which, in a conventional evaporator, Generation of cracking noises, these are reduced in the evaporator according to the invention because no high thermal stresses have to be built up for shifting the ice crust with respect to the evaporator, which are discharged in loud cracking noises but a considerably lower tension is sufficient to relate the ice layer To slip onto the evaporator or even to cause a continuous sliding movement of the ice layer on the evaporator.

The evaporator according to the invention is preferably constructed as a lamellar evaporator suitable for use in a circulating air cooling or freezing unit.

The enclosed figure shows a schematic view of a partially iced-up section of a slat evaporator 4 according to the invention. The slat evaporator 4 comprises a tube 1, which is flowed through during operation of refrigerant. Around the outer surface of the tube 1, a lamella 2 is helically wound. The lamella 2 and the outer surface of the tube 1, on which the lamella 2 is mounted, form the heat-exchangeable surface of the lamella evaporator and are provided with a hydrophobic coating of a silicone oil.

Due to the hydrophobicity of the coating, much energy is required to wet the surface of the lamellar evaporator 4, and this energy must be released when moisture freezes on the surface. This is a major obstacle to the formation of ice crystals on the surface. A considerable proportion of the moisture of a stream of air pasting the lamellar evaporator therefore does not condense on the lamellar evaporator 4 even if the air stream is saturated with moisture, simply because the moisture does not hit a surface on which freezing would be energetically favorable. The lamellar evaporator 4 therefore has only a slight drying of the air in the interior of the refrigerator when it is used in a forced-air or no-frost cooling device, which is quite desirable for the storage of sensitive foods such as fresh vegetables.

In order for the air to condense on the lamellar evaporator 4, there must be surface areas on which the condensation is energetically favorable. Such sites are usually condensation nuclei in the form of dust particles, surface discontinuities or the like, which are unavoidably present on the surface of the lamellar evaporator, but only make up a very small part of it. As shown in FIG. 1, a large number of compact ice beads 3 are formed on these condensation nuclei during operation of the lamellar evaporator 3. On the surface of these ice beads 3, further moisture condenses preferentially from the air surrounding the lamellar evaporator 4 so that the beads 3, While the areas of the surface of the lamellar evaporator 4 lying between the beads remain free of ice for a long time and enable an efficient heat exchange between the refrigerant circulating in the lamellar evaporator 4 and the surrounding air.