WO2006010541A1

WO2006010541A1 - Thermosiphon

Info

Publication number: WO2006010541A1
Application number: PCT/EP2005/007883
Authority: WO
Inventors: David Astrain Ulibarrena; José GONZÁLEZ VIAN; José Manuel LAMUELA ROSANO; Salvador Manuel GARCÍA SANTAMARÍA
Original assignee: BSH Bosch und Siemens Hausgeräte GmbH
Priority date: 2004-07-23
Filing date: 2005-07-20
Publication date: 2006-02-02
Also published as: ECSP077186A; DE102004035735A1; EP1774239A1

Abstract

A thermosiphon comprising a tight container (1) containing a heat carrying substance partially as a liquid, partially as vapor, and a heat sink (5) arranged on a first wall (4) of the container (1). Capillary lines are provided on the inner side of a second wall (9) of the container (1), preferably in the form of a porous layer (10).

Description

thermosiphon

The present invention relates to a thermosyphon according to the preamble of claim 1. Such a thermosyphon is known from WO 99/58906.

If a heat sink with a high surface-area power density, such as a Peltier element, is used to cool a heat reservoir, such as the interior of a refrigeration appliance, the problem arises that heat from the reservoir can not flow quickly enough to the surface of the heat sink, so that it is in operation assumes a temperature which is significantly lower than the current temperature of the heat reservoir and also as the target temperature to which the heat reservoir is to be cooled. Achieving this low temperature requires a large amount of energy so that the lower the temperature of the heat sink during operation, the lower the effective efficiency of the refrigeration appliance using such a heat sink. The same problem occurs with an opposite sign to a heat source which releases thermal energy received by the heat sink to a second reservoir, generally the environment.

In order to alleviate these problems, WO 99/58906 has proposed a refrigerator which uses so-called thermosiphons. Such a thermosyphon is a hermetically sealed container which contains a heat transport substance partly as a liquid, partly as a vapor, and in which a high surface area heat sink or source is attached to a first wall of the container and a second wall is provided to be contacted with a heat reservoir.

It is distinguished between positive and negative thermosyphon, depending on whether a heat source or sink is attached to the first wall of the container.

In a positive thermosyphon, the liquid phase of the heat transport substance at the heat source is boiled, whereby the heat is removed from the source with high efficiency, and the vapor condenses on the second wall of the container, which is in thermal contact with a reservoir cooler than the heat source. In a negative heat siphon, the second wall is in thermal contact with a heat reservoir that is warmer than the heat sink, and with the aid of heat-transfer fluid vaporized via the second wall of the walls condenses on a comparatively small surface of the first wall cooled by the heat sink, thereby creating a heat sink Intensified heat flow is achieved at the heat sink.

Due to the phase transitions taking place on the two walls of the container, a significantly larger amount of energy can be transported in the heat siphon than in a container of the same dimensions in which the heat transport substance is present only in a single physical state.

While in a positive thermosyphon the effectiveness with increasing heat output of the heat source continues to increase, as the ratio of vapor to liquid and larger and the vapor becomes denser, so that (even if one considers the convection occurring in the container as independent of temperature), the throughput is always higher heat energy (as long as the heat transfer substance is not completely evaporated), decreases with a negative heat siphon efficiency with increasing cooling capacity of the heat sink, because the vapor density drops and thus less and less heat transfer substance is available in the container, which condense on the heat sink and so can give off heat. In order to obtain an effective negative thermosyphon, it is therefore important to keep the vapor pressure in the thermosyphon always as close as possible to the saturation vapor pressure corresponding to the respective operating temperature of the thermosyphon by means of suitable design measures.

This object is achieved by a thermosyphon having the features of claim 1. While in the conventional negative thermosyphon only the surface of the liquid phase in the container is available to let there evaporate the Wärme¬ transport substance, and heat, which is above the liquid level Wall penetrates into the thermosyphon, essentially contributes only to the heating of the vapor, but not to increase the vapor density, allow the capillary according to the invention, the liquid heat transport substance rise on the inside of the second wall, so that an evaporation of heat transfer fluid substantially on of the entire surface of the second wall is possible and cold saturated steam is created, which allows effective heat transfer to the heat sink.

The capillary conduits are preferably formed by the inside of the second wall carrying a lining of a porous material.

In particular, this material may be a porous ceramic such as alumina based, silica gel, or a fibrous material such as glass fiber.

In order to ensure effective heat transfer from the second wall to the porous material and the heat transfer fluid rising therein, the lining is preferably materially connected to the second wall. Such a material-locking connection may be made by adhering the porous lining to the inside of the wall, or by making the lining from a material solidified on the inside of the wall.

According to another embodiment, the lining is clamped between the second wall and a perforated intermediate wall, the openings of which allow the entry of heat-transfer fluid to the lining or the escape of steam.

Under normal operating conditions, the capillary tubes should be submerged in the liquid to ensure a constant supply of liquid to be evaporated.

The heat sink is preferably a thermoelectric element such as a Peltier element.

Further features and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying figures. Show it: Figure 1 is a schematic vertical section through a thermosyphon according to the invention along the plane ll of Fig. 2.

Fig. 2 is a horizontal section through the thermosiphon along the plane H-II

Fig. 1;

3 shows a horizontal section analogous to FIG. 2 through a first modification of the thermosyphon;

FIG. 4 shows a horizontal section analogous to FIG. 2 through a second modification of the thermosyphon; FIG. and

Fig. 5 is a horizontal section through a third modification of the thermosyphon.

The thermosyphon shown in Fig. 1 comprises a hermetically sealed housing 1 made of a good heat conducting material such as aluminum with a single, undivided interior 2. An in the interior 2 filled amount of

Heat transport substance such as butane is such that it is in liquid

Condition does not completely fill the interior 2. Under normal operating conditions of the thermosyphon is therefore a supply of liquid heat transfer substance 3 at the bottom of the interior 2, and the rest of the interior space 2 contains the

Heat transport substance in the form of vapor, the pressure of which depends on the temperatures to which the thermosyphon is exposed.

In the upper part of a first wall 4 of the housing 1, above the liquid level, the cold side 5 of a Peltier element is attached as a heat sink. A warm side 6 of the Peltier element is in thermal contact with a heat dissipation aid 7, such as a conventional fin cooler or a positive thermosyphon.

The part of the wall 4 touched by the cold side 5 of the Peltier element forms the coldest part of the housing 1, so that the vaporous heat transport substance preferably condenses here, as indicated by drops 8 on the inside of the wall 4, and the wall 4 down to the liquid reservoir 3 flows. On the inside of a first wall 4 opposite the second wall 9 of the housing 1, a porous layer 10 is attached. The porous layer 10 is here a ceramic layer of aluminum oxide or a mixture on Aluminiumoxidgrund¬ position, which is spun in the form of a suspension together with a suitable binder on the inside of the wall 9 and solidified and adhered thereto by evaporation of the carrier liquid of the suspension. Alternatively comes as a basic component of the porous layer 10 and silica gel into consideration.

In principle, it would also be possible to prefabricate the porous layer 10 separately from the wall 9 and then attach it to the wall with the aid of an adhesive. However, since the layer 10 should be as thin as possible, so as not to slow the flow of heat through the wall 9 into the interior 2, it can be assumed that suitable prefabricated layers 10 with the required porosity will be very sensitive and difficult to handle, so that the direct Generation of the layer 10 on the wall 9 is considered to be the more promising method.

The layer 10 is immersed at its lower end in the stock 3 of liquid heat transport substance. The porosity of the layer 10 is adjusted to allow the heat transfer fluid in the layer 10 to rise above the entire height of the interior space 2, so that the heat flowing in from outside via the wall 9 is largely consumed for the evaporation of the heat transfer fluid. The large surface of the porous layer 10 allows a high evaporation rate, is replaced by the steam condensed on the wall 4 immediately, so that the vapor pressure in the interior 2 does not fall substantially below the saturation vapor pressure of Wärme¬ transport substance at the operating temperature of the thermosyphon.

In order to intensify the heat flow into the thermosyphon via the second wall 9, this can, as shown in Fig. 2, be provided on its outer side with ribs or fins 11.

Slats 12 may also be provided on the inside of the wall 9. Thus, Fig. 3 shows a structure with inside vertical slats 12, which are lower than the thickness of the porous layer 10, on the one hand in the interstices 13 between the slats to provide a sufficient line cross-section for the rise of the liquid 3 and on the other hand, via the lamellae 12, to guide the heat effectively into a region of the layer 10 close to the surface, and to evaporate the heat transfer fluid so quickly and efficiently.

On the other hand, as shown in Fig. 4, lamellae 14 may also be provided which are higher than the thickness of the layer 10 and whose effect is simply an enlargement of the wall surface covered with the porous material.

Another alternative embodiment of the cross section of the thermosyphon is shown in FIG. Here, the porous layer 10 is not fully attached to the wall 9, but clamped between the wall and an intermediate wall 15, in which a plurality of large holes 16 is broken, so that the intermediate wall 15 does not escape the escape of vaporized heat transport substance from the porous layer 10 significantly impeded.

For attachment of the intermediate wall 15 may, as shown in the upper part of Fig. 5, a formed on a side wall of the housing 1 vertical rib 17 serve, to which the intermediate wall 15 is pressed by the slightly elastic compressed material of the porous layer 10. At the same time, the intermediate wall 15 thus keeps the porous layer pressed against the wall 9 and thus ensures efficient heat transfer from the wall 9 into the layer 10 and the liquid ascending therein.

Alternatively, as shown in the lower part of the figure, threaded pins 18 on the wall

9, on which the porous layer 10 is impaled and on which the intermediate wall 15 is held pressed by a nut 19. This variant has the advantage that it provides a continuous adjustment of the compression of the porous layer

10 allows. That is, the compression can be increased to increase the capillary effect in the layer 10 if it turns out to be insufficient to provide sufficient liquid to evaporate the entire surface of the wall 9, or it can be reduced if the material is too compacted to ensure adequate fluid supply.

As a flexible material for the porous layer 10, glass wool is particularly suitable in this embodiment, wherein the fiber orientation is preferably vertical. Others too Fiber materials such as natural textile fibers or plastic fibers resistant to the transport substance used can be used.

Claims

claims

1. thermosyphon with a dense, a heat transport substance partly as a liquid, partly as a vapor-containing container (1) and on a first wall (4) of the container (1) mounted heat sink (5), characterized in that on the inside a second wall (9) of the container (1)

Capillary lines are formed.

2. Thermosyphon according to claim 1, characterized in that the Kapillarleitungen on the inside of the second wall (9) are formed by a lining of a porous material (10).

3. thermosyphon according to claim 2, characterized in that the lining (10) is an alumina-based ceramic.

4. Thermosyphon according to claim 2, characterized in that the lining (10) contains silica gel.

5. thermosyphon according to claim 2, characterized in that the lining (10) comprises a fiber material.

6. thermosiphon according to claim 5, characterized in that the fiber material is glass fiber.

7. thermosyphon according to one of claims 2 to 6, characterized in that the lining (10) is materially connected to the second wall (9).

8. thermosyphon according to claim 7, characterized in that the lining (10) is glued.

9. thermosyphon according to claim 7, characterized in that the lining (10) is made of a material solidified on the inside of the second wall.

10. Thermosyphon according to one of claims 2 to 6, characterized in that the lining (10) is clamped between the second wall and a perforated intermediate wall (15).

11. Thermosyphon according to one of the preceding claims, characterized in that the capillary under normal operating conditions in the liquid (3) dive.

12. Thermosyphon according to one of the preceding claims, characterized in that the heat sink (5) is a thermoelectric element.