Rear Wall Condenser For Domestic Refrigerators and Freezers

Abstract

The invention relates to a condenser for refrigerators with gravity-type convection, especially for domestic refrigerators, comprising at least one tape-shaped line (1) which has a width at least twice as large as its thickness, at least two channels (3,4) separated from each other and arranged one adjacent to the other, and, if used in accordance with the invention, is installed on end and largely almost parallel to the bottom edge of the refrigerator. Line sections arranged one behind the other in the direction of flow have the top edge of the preceding line section each offset in parallel in the direction of flow relative to the bottom edge of the succeeding line section. The use of commercial extruded sectional aluminium tubes makes it possible to manufacture a condenser at reasonable cost with excellent heat exchange properties.

Description

The invention relates to a condenser for refrigerating machines with gravity-type convection, especially domestic refrigerators, freezers or combined refrigerators/freezers, which can be manufactured easily and cost-effectively and is characterized by a high efficiency.

Customary refrigerators, freezers or combined refrigerators/freezers are so-called compression-type refrigerators. Refrigerators working according to other refrigerating principles such as absorber refrigerators with their low noise development or thermoelectric refrigerators allowing compact designs have the disadvantage, though offering the mentioned specific beneficial features, of a considerably higher energy consumption and can therefore be used in marginal applications only.

In compression-type refrigerators a compressor compresses a gaseous refrigerant causing the latter to heat up. The refrigerant is passed through a condenser situated on the outside of the refrigerator. The condenser causes the refrigerant to discharge its heat to the environment and thereby to condense. Then the refrigerant flows through a throttle such as an expansion valve or capillary tube, for example, where its pressure is lowered, and into an evaporator situated in the refrigerator interior, in which the refrigerant evaporates and cools down heavily. The evaporator provides for an exchange of heat causing the interior space of the refrigerator to be cooled.

The energy consumption of a compression-type refrigerator depends greatly on the rate at which the condenser can discharge heat to the environment. As energy and electric power prices are constantly on the increase, on the one hand, and the environmental awareness of people is growing, on the other, it is increasingly important to manufacture energy-saving domestic refrigerators.

The condensers used in domestic refrigerators usually comprise a tube bent in meander shape which has wire ribs welded to it for better heat discharge. In order to increase the heat discharge by thermal radiation the tube and the wire ribs are provided with a black paint coat.

Such condensers have the disadvantage, however, that the wire ribs will heat up to the same temperature as the tube only in the area where they are joined to the tube. Due to the comparatively large distances between the tubes and the unfavourable geometry of the wire ribs, namely their great length and small diameter, larger areas of the ribs are weakly heated only. As a result, the efficiency of the ribs is low. This leads to a rather bad heat transfer which in the end causes the power consumption of the refrigerator to rise.

Other known embodiments of condensers have no wire ribs welded to the tube but a metal plate that completely covers the tube. To achieve an efficient thermal interaction between the tube and metal plate it will be necessary however to provide as many welding points as possible between the tube and metal plate. More effectively, the tube may be joined with the metal plate by means of a continuous welding or soldering seam. This concept provides for an improved though still uneven temperature distribution across the heat transfer surface. The mean temperature difference between the refrigerant and the air is thus lower as is the heat transfer rate per unit of area. Another disadvantage consists in the relatively high manufacturing expenditure.

Numerous concepts are known from the state-of-the-art technology, which are aimed at improving the heat discharge and/or reduction of manufacturing cost of condensers for domestic refrigerators.

In EP 0 125 642 A2, for example, a back-wall condenser is proposed which consists only of a tube bent in meander shape with the straight tube sections having an elliptical cross section and the bent sections a circular one. Because tubes with an elliptical cross section have a larger surface area compared with those having a circular cross section, wires or metal plates are not welded to the tubes in this case. Though this leads to a reduction of the manufacturing expenditure it will not improve the efficiency of the heat exchanger.

In EP 0 843 138 A1 a back-wall condenser for domestic refrigerators is described which comprises a tube bent in meander shape and clamped between two metal plates. One of the two metal plates is joined to a third metal plate to form a receptacle which is filled with a liquid of high thermal capacity.

In CN 1616904 A a back-wall condenser is disclosed which consists of two tubes arranged horizontally one on top of the other and connected to one another by a multitude of tubes installed in parallel and in vertical arrangement. The vertical tubes have a diameter of 1 to 3 mm, i.e. they are comparatively thin. The refrigerant is distributed into the vertical tubes by means of the upper horizontal tube and collected again in the bottom tube. To improve the heat discharge, a metal plate may be mounted to the tubes. The use of a multitude of thin tubes or microchannel lines may increase the surface area and ensure an efficient heat exchange. The use of the thin tubes or microchannel lines will however with a view to minimizing pressure loss require the tubes to be connected in parallel which leads to a higher manufacturing expenditure. Another disadvantage results from the fact that the air flows continuously in the longitudinal direction of the tubes or microchannel lines so that comparatively thick laminar boundary layers can build up there which prevent an optimum heat discharge.

Furthermore, condensers for refrigerators with forced convection are known in which extruded sectional lines of aluminium are used with the lines being of tape shape and comprising several parallel channels. Accordingly, EP 1 557 622 A2, US 2006/0144076 A1 and DE 10 2004 024 825 A1 describe condensers for forced convection with headers, and US 2005/0076506 A1 and JP 06317363 condensers of this type without headers.

Due to their construction these condensers are not suitable as back-wall condensers for refrigerators with gravity-type convection. Even if the condensers would be installed on end and air would be allowed to flow through them by gravity from bottom to top, they would have an extremely bad efficiency because firstly the horizontal sectional lines would produce a high flow resistance and they could secondly discharge little heat to the environment by radiation due to their orientation. Condensers with gravity-type convection do however, unlike those with forced convection, discharge up to 45% of the heat by radiation.

It is the purpose of the invention to eliminate the disadvantages of the state-of-the-art technology described before. In particular, it is the objective to provide a condenser for domestic refrigerators with gravity-type convection which has a high efficiency and can be manufactured easily and at low cost.

This problem is solved in accordance with the invention by the characterizing features of Claim 1; useful embodiments of the invention are described in Claims 2 to 15.

According to the invention, the condenser for refrigerators with gravity-type convection comprises at least a line for the refrigerant which is formed like a tape, whose width is at least double the size of its thickness and which incorporates at least two channels separated from each other and running adjacent to one another. In the application according to the intended use the line is installed on end and largely in parallel to the bottom edge of the refrigerator.

The air flows through the lines by gravity, i.e. from bottom to top, and thus hits the narrow edges of the lines.

In line sections arranged one behind the other in the direction of flow, with the line sections being either sections of one and the same line or sections of different lines of the condenser, the top edge of the preceding line section is offset in parallel in the direction of flow relative to the succeeding line section. In this way the air flow will newly start at each line section and the insulating laminar boundary layer at the line sections will thus be minimized in thickness. This may increase the efficiency of the condenser by up to 15%.

The parallel displacement of the top and bottom edges is achieved by either arranging the line sections at an offset position in parallel in the direction of flow or tilting them. In terms of flow conditions, effective angles of tilt should be in the range between 0° and 45° only. It is also possible to both offset and tilt the line sections which will however not result in a particular advantage.

In an embodiment of the condenser according to the invention, which is characterized by the refrigerant side being subject to a particularly low flow resistance, the condenser comprises a vertically positioned header at the inlet and outlet of the refrigerant. The two headers may have a round, namely circular, semicircular, elliptical and oval, or angular, namely triangular, square or rectangular flow cross section. The header at the inlet may incorporate a distributor.

The headers are connected primarily in parallel by a multitude of lines for the refrigerant arranged horizontally at different vertical levels and in parallel to one another. The headers may however also incorporate built-in elements to allow all lines or several parallel lines to be connected in series so that the refrigerant flows through the condenser in meander mode from top to bottom. The lines are installed in a straight line between the headers or are bent in wave or meander shape in horizontal direction.

It is intended to have several lines placed at a horizontal level one beside the other and usually spaced in parallel. Preferably, the lines should be installed with spacers such as metal plates, for example, which provides for a secondary heat exchange surface at the same time.

In another embodiment of the condenser, which is characterized by a particularly simple construction, the line for the refrigerant is of bent shape and placed in at least one layer formed as a plane of spiral, helicoidal, helical or three-dimensional meander contour. Headers are not used in this concept.

The preferred three-dimensional meander-shaped layout of the line means that it is meander-shaped in its side view and in addition offers spatial depth. Typically, such a line is characterized in its space by a helicoidal or helical behaviour though it does not have circular or elliptical cross-sectional surfaces as are usually found with screws/helixes but a cross section (in top view) that is either shaped as an oblong rectangle with rounded corners or contoured like an “eight” of oblong shape.

A layer formed as a plane is understood to be a level arrangement of the line such as a three-dimensional meander, for example, which is characterized by spatial depth. According to the nature of the invention, also several layers of this type may be arranged one behind the other.

For common-type domestic refrigerators it is sufficient for this embodiment to make use of only one line for the condenser, which is preferably bent in three-dimensional meander shape. Such a condenser is particularly easy to manufacture and ensures a sufficiently good heat exchange between the refrigerant and the ambient air. Special applications can however also be set up by means of several separate lines installed with spacers, if applicable, or lines arranged in several layers placed one on top of the other.

It is also possible to use lines installed by means of connectors such as sleeves, for example. Lines of this construction may be effective in terms of cost if standardized lengths of lines can be used.

To achieve large surface areas for the heat transfer, on the one hand, and to avoid larger pressure drops because of too small flow cross sections, on the other, line cross-section section areas from 3 to 30 mm² are used for both the version with and the version without headers with the hydraulic diameters of the channels being in the range from 0.1 to 3 mm.

A particularly cost-effective embodiment of the condenser is achieved if an extruded sectional tube is used for the lines. For the further improvement of the heat transfer properties a rib structure may be formed on the outside of the sectional tube.

To provide a simple way of connection of the line to the domestic refrigerator it is provided according to the invention that the line is formed with connectors at the inlet and outlet of the refrigerant with the outlet advantageously incorporating a filter drier.

The lines are usually manufactured from aluminium because this has a good thermal conductivity, is reasonable in cost and can be easily bent. A coating with a high coefficient of emission applied to the lines will result in an improved heat discharge by radiation to the ambient air.

In accordance with the nature of the invention, compact condensers for refrigerators with forced convection could be made from extruded sectional tubes which are bent so that several layers are formed in stacks arranged one behind the other in the direction of flow with line sections placed one behind the other being offset relative to each other.

In condensers with forced convection the offset arrangement could also lead to an up to 10% higher efficiency. Another advantage results from the fact that the arrangement in several layers makes it possible compared with conventional single-layer configurations to arrive at a better utilization of the available space.

The invention will hereinafter be described in greater detail by reference to two embodiments of condensers with gravity-type convection; wherein:

FIG. 1 schematically depicts a cross section of the line of the condenser;

FIG. 2 is a diagram of a condenser with headers in a side view;

FIG. 3 is a diagram of a condenser with headers in a top view;

FIG. 4 is a diagram of a condenser (without headers) with a line bent in three-dimensional meander shape.

The line 1 according to FIG. 1 consists of extruded sectional aluminium tubes with a width of 2.54 cm and a thickness of 2.1 mm. The sides 5 of the sectional tubes 1 are rounded at a radius of 1 mm, for example. To improve the heat transfer properties, the sections are coated with black paint. The sectional tubes 1 are made from standardized material and can thus be provided at reasonable cost.

The line 1 has thirteen channels 3,4 through which the refrigerant 2 will pass. The channels 3 have a square cross-section with rounded corners and an edge length of approx. 1.5 mm. The two outside channels 4 are of approximately rectangular shape with the outward-facing side being rounded. In the present embodiment the channels 4 have a length of 1.5 mm and a width of 0.5 mm.

As is evident from FIG. 2, in the condenser with header tubes 9 the latter are connected by several pairs of lines 1 arranged in parallel one on top of the other with the pairs each placed on a horizontal plane and being separated by spacers 8 (see FIG. 3). The pairs of lines 1 arranged on adjacent levels are offset relative to one another in the direction of flow (not shown).

In the condenser with headers it is practically impossible that pressure losses can affect the efficiency because each level has 26 channels 2 running in parallel so that a very large flow cross section is provided for the refrigerant.

In the condenser without headers (see FIG. 4) the line 1 is bent in three-dimensional meander shape with the bending radii being approx. 1.5 cm. The lines 1 placed in parallel are spaced relative to each other at approx. 3 to 8 cm which means that they are arranged comparatively densely (see FIG. 4). The great number of parallel channels provides a large flow cross section for the refrigerant so that the pressure loss of the refrigerant is minimized also with a great length of the line 1.

Also in this embodiment, the line sections constituting the windings of the meander arranged on top of each other are offset in the direction of flow. The condenser is particularly easy and cost-effectively to manufacture because there is no need for welding any components.

In either embodiment the planar, tape-like shape of the lines 1 and their dense, parallel and meander-shaped arrangement ensures a large surface area of the condenser. The offset arrangement of the sectional tubes 1 causes the air flow to start anew on the longitudinal sides of all sections. As a result, the insulating laminar boundary layer at that position is minimized in thickness with an effective heat transfer being ensured.

The surface area of the condenser may be increased with the same tube length by using sectional tubes 1 with ribbed structure.

The densely placed channels 3,4 and the good thermal conductivity of the aluminium will cause the total surface area of the condensers to take on the same temperature during operation in a very short time.

The condensers can be manufactured easily and cost-effectively because with the extruded sectional aluminium tubes low-cost standard components may be used. The condensers may be easily cleaned, a factor that contributes considerably to their constant performance characteristics.

Both versions of condensers can with the surface area being the same achieve an up to 15% higher heat discharge as against conventional condensers. On the other hand, the surface area of the condensers could with the same heat transfer rate be decreased by approx. 15%.

LIST OF REFERENCE NUMBERS USED

1. line/sectional tube

2. refrigerant

3. inside channel

4. outside channel

5. rounded side

6. inlet

7. outlet

8. spacer

9. header

Claims

1. A condenser for domestic refrigerators with gravity-type convection comprising at least one line for the refrigerant wherein the line is tape-shaped, has a width at least twice as large as its thickness, comprises at least two channels (3,4) separated from each other and arranged one adjacent to the other characterized by the line (1), if used in accordance with the intended purpose, being installed on end and largely almost parallel to the bottom edge of the refrigerator with the top edge of the line sections of the same or of different lines being each offset in parallel relative to the bottom edge of the succeeding line section.

2-15. (canceled)