The invention relates to a heat exchanger, which comprises at least one first thermosiphon element that comprises:

a thermosiphon comprising five zones:

a lower isothermal siphon zone,

an upper isothermal siphon zone,

a lower adiabatic siphon zone,

an upper adiabatic siphon zone, and

- a cross-over zone that is located between the upper and the lower siphon zones and that connects the two lower siphon zones with the two upper siphon zones. ^'

The invention moreover relates to method for manufacturing of the heat exchanger.

In addition the invention relates to the use of the heat exchanger for cooling. The principle of a thermosiphon (English "thermo siphon") has been known since the middle of the eighteen century and comprises that a hermetic compartment is evacuated and thereafter filled with a suitable fluid, which in an evaporator part of the thermosiphon is supplied with heat and evaporates, and afterwards condenses in a condenser part of the thermosiphon and thereby releases heat. The condensed liquid is lead back to the condenser part. The heat conduction of this evaporation and condensation process is significantly higher than the heat conductivity of e.g. metals, and the thermosiphon principle is therefore well suited for heat exchange and cooling purposes. The fluid in thermosiphon can be composed of a single chemical species, or it can be composed of a mixture of several chemical species, e.g. in the form of an azeotrope .or near- azeotrope mixture.

The thermosiphon has an internal geometry comprising an internal closed loop that makes execution of the mentioned two-phased closed process possible. As a thermosiphon is a hermetically closed two-phased system, and only pure liquid and gas are represented in the internal hermetic compartment, the fluid will remain saturated as long as the mode of operation for the thermosiphon is between the triple point of the fluid and its critical point, and the thermosiphon will in its full extent remain isothermal or near isothermal within a very wide working range.

The thermosiphon is related to the unit, which today is known as the heatpipe, however in that the liquid in the thermosiphon is returned to the evaporator part solely under the influence of gravity, while it in the heatpipe is returned in a capillary structure by means of capillary forces.

After originally being developed for the automobile industry, conventionally heat exchangers based on the thermosiphon principle have achieved huge commercial distribution for cooling of electronics. The principle has the unconditional advantage that the loop process can be run without the need for moving parts . This type of heat exchangers is constructed with exchanger sections of a number of parallelly arranged flat tubes, which each is extruded in a multiport-pattern, wherein the fluid flows, and is equipped with corrugated fins of the Louver type for heat exchange with the surroundings. The flat tubes are all connected to a manifold, called a header, and that hydraulically connects the flat tubes with each other in the parallel structure. The entire structure is typically made in aluminium and can be brazed in a continuous furnace in a single process. Conventional heat exchangers typically consist of two (or more) such exchanger sections, of which at least one section functions as evaporator part and at least one section functions as condenser part, and where the two or more sections are connected by means of at least one gas-conducting tube and at least one fluid-conducting tube.

The known technology has several disadvantages: Thermodynamically the construction results in an evaporator section and a condenser section, in that parts of the heat exchanger are not sufficiently utilized in connection with thermal absorption as well as thermal emission. Thus, there is especially when cooling hotspots a significant risk that the sectional structure of the heat exchanger results in an inappropriate and inefficient cooling, e.g. because the parts of the heat exchanger that receive the highest heat flux, and thus has the greatest need for cooling, are only poorly cooled.

Construction-wise or design-wise the know technology has moreover the disadvantage that a plurality of headers have to be connected to each other by means of tubes in order to enable the liquid and gas flow in the heat exchanger. The connection tubes, which typically can be both long and tortuous, reduce the cooling capacity in at least two areas: The connection tubes increases the volume of the heat exchanger without contributing to the cooling capacity, and further reduces this capacity by limiting the air flow-through around the heat exchanger. The increased interior volume moreover increases the demand for the amount of fluid in the heat exchanger, which both has cost-wise and environmental-wise disadvantages.

The section-wise construction of the heat exchanger further has the consequences that a single leak in the tube system results in that the heat exchanger might complete ceases to function concurrent with a significant amount of fluid might leak to the atmosphere. From US5286884 is known a heat exchanger as described in the preamble. It comprises at least one thermosiphon element that among others consists of a thermosiphon having zones.

The apparatus comprises a downstream part that comprises a heat exchange segment comprising a plurality of heat exchange tubes in fluid connection with the interior of an upright part in which fluid flows down.

The apparatus comprises an upper isothermal transition segment and a lower transition section that fluid-wise connects the heat exchange tubes with the rest of the apparatus.

The downstream part and an adiabatic upstream leg are connected to each other by laterally located U-tube. The apparatus is constructed so that it take up at lot of space compared to its capacity and thus also has environmental disadvantages . It is thus an object of the invention to provide a heat exchanger without the above-mentioned disadvantages.

The object of the invention is realized by a heat exchanger of the kind mentioned in the preamble of claim 1, which is characterized in that the thermosiphon element of the heat exchanger further comprises:

a hermetically closed box-shaped profile having two side faces, two edge faces and an upper and a lower end face and an interior volume,

where each of the two side faces is divided into four profile zones :

a lower heat absorbing isothermal profile zone,

an upper heat emitting isothermal profile zone,

a lower adiabatic profile zone, and

- an upper adiabatic profile zone,

and where the box-shaped profile hermetically surrounds the thermosiphon, which is located in the interior volume of the profile, so that:

the lower heat absorbing isothermal profile zone is located towards the lower isothermal siphon zone,

the upper heat emitting isothermal profile zone is located towards the upper isothermal siphon zone,

the lower adiabatic profile zone is located towards the lower adiabatic siphon zone, and

- the upper adiabatic profile zone is located towards the upper adiabatic siphon zone. Thus due to the heat exchanger having the thermosiphon element according to the invention, the thermosiphon is surrounded by a box-shaped profile, which has a heat absorbing profile zone and a heat emitting profile zone, and is thus the part of the heat exchanger, which exchanges heat with the surroundings. The heat exchanger with the thermosiphon element thus constitutes a self-functioning heat exchanger module that does not have the above-mentioned disadvantages. By hermetical is in this connection understood that the box- shaped geometry is constructed substantially fluid-tight towards the surrounding space, so that substantially no particles and/or air can penetrate into the thermosiphon itself .

Due to its construction as self-functioning module the heat exchanger having the thermosiphon element according to the invention thus allows eliminating the need for the above- mentioned system of connection tubes with consequently reduced volume and reduced demand for fluid amount, and accordingly increased specific cooling capacity and reduced environmental impact .

Moreover the heat exchanger having the thermosiphon element according to the invention has advantages in form of increased simplicity and increased flexibility in form of better design adaptation for specific cooling purposes, including cooling of hotspots . The heat exchanger can thus be designed with optional height and width.

The thermosiphon of the thermosiphon element consists of 5 siphon zones, of which two are isothermal and two are adiabatic. The last siphon zone is designated the cross-over zone. The upper part of the profile functions as condenser part whereas the lower part functions as evaporator part, and the internal circulation of liquid and gas takes place in the thermosiphon completely independent of both headers and tubes. The thermosiphon itself has an interior geometry that allows the circulation. The geometry thus comprises the lower isothermal siphon zone, where the fluid evaporates during absorption of heat. From here the evaporated fluid, in form of gas, is transported via the upper adiabatic zone to the upper isothermal siphonzone, where the gas condenses. From here the condensed fluid is transported, via the lower adiabatic zone, which is a downtake channel, under the influence of gravity back to the lower isothermal siphonzone. The cross-over zone separates the lower evaporator part from the upper condenser part, and is designed so that the gas and liquid flows do not occur in counterflow and thus do not collide, but instead is lead round each other. By the heat exchanger having the thermosiphon element according to the invention, the thermosiphon is now arranged in a box-shaped profile with two side faces, two edge faces, and an upper and a lower end face. The side faces are divided in four profile zones, which cooperate with the siphon zones:

- a lower heat absorbing isothermal profile zone, which is located towards the lower isothermal siphon zone, absorbs heat from the surroundings and leads this heat to the siphon zone, where the evaporation occurs under consumption of heat,

- an upper adiabatic profile zone, which is located towards the upper adiabatic siphon zone, and which does not exchange heat with the surroundings, an upper heat emitting isothermal profile zone, which is located towards the upper isothermal siphon zone, emits that heat to the surroundings that is produced during the condensation process in the siphon zone, and

a lower adiabatic profile zone, which is located towards the lower adiabatic siphon zone, and which does not exchange heat with the surroundings.

The heat exchange between th isothermal siphon zones and the associated isothermal profil zones takes place by metallic thermal conduction.

The fluid in the heat exchanger according to the invention is preferably hydrocarbons, fluorinated hydrocarbons, water, ammonia, alcohols or acetone, or azeotropic or near-azeotropic mixtures thereof.

When in the context of the invention is referred to "upper" and "lower" zones, respectively, this comprises that an "upper" zone of a given type, e.g. an upper siphon zone or profile zone, is located at a higher level than the corresponding "lower" zone, i.e. the corresponding siphon zone or profile zone. This comprises that the thermosiphon element can operate upright, or can operate anglular at an angle, so that the "upper" zone is located higher than the "lower" zone, but not necessary vertically above it, although so that the gravity is sufficient to drive the flow in the thermosiphon element .

It must also be understood, that the cross-over zone separates "upper" zones from "lower" zones. All "upper" zones - i.e. siphon zones and profile zones - are thus located above the cross-over zone and is delimited towards "lower" zones hereof, whereas all "lower" zones, i.e. siphon zones and profile zones are located below the cross-over zone and is delimited against "upper" zones thereof.

In the context of the invention "isothermal" must be understood as isothermal, i.e. at the same temperature, or as near-isothermal, i.e. at approximately same temperature. Correspondingly, in the context of the invention, "adiabatic" must understood as adiabatic, i.e. without heat exchange with the surroundings, or near-adiabatic, i.e. approximately without heat exchange with the surroundings .

It is decisive for the functionality of the thermosiphon element that the gas is cooled at little as possible in the upper adiabatic siphon zone, as condensation at this location will cause formation of drops and risk of blocking of the gas flow.

The lower isothermal siphon zone of the thermosiphon and the upper adiabatic siphon zone of the thermosiphon can advantageously face towards an end face of the profile, whereas the lower adiabatic siphon zone of the thermosiphon and the upper isothermal siphon zone of the thermosiphon face towards the other edge face of the profile.

By this geometry of the thermosiphon an expedient flow of gas and liquid is ensured in the thermosiphon, in that the crossover zone can be made as simple as possible for unhindered and independent non-crossing gas and liquid flow. The isothermal profile zones of the profile can be covered by fins, preferably by Louver fins.

By such fins are achieved an efficient heat exchange with the surroundings, i.e. an effective heat absorption from the surroundings in the lower heat absorbing isothermal profile zone, and an efficient heat emission to the surroundings in the upper heat emitting isothermal profile zone, respectively. Louver fins have a high surface and accordingly enables a particular good heat exchange with the surroundings.

Whereas the isothermal profile zones of the profile thus preferably are covered by fins, the adiabatic profile zones of the profile are not covered by such fins. Thereby the heat exchange with the surroundings from these profile zones is reduced.

In an alternative embodiment, the heat exchanger having the thermosiphon element according to the invention is not covered by fins, e.g. in connection with hotspot cooling.

The heat exchange with the surroundings can thus take place by conduction, convection, radiation or a combination thereof.

The thermosiphon of the heat exchanger can be made of an aluminium-based material, which is inexpensive and easily worked. The thermosiphon of the heat exchanger can advantageously be made of a Al-Si-cladding material, which is inexpensive and easily worked, or be made by means of sil flux or composite alloy flux technology.

The profile of the heat exchanger can advantageously be made in aluminium, which is inexpensive and easily worked, and which easily can be joined to a corresponding aluminium-based thermosiphon.

The profile of the heat exchanger can similarly be made in a Al-Si-cladding material, which is inexpensive and easily worked, or be made by means of sil flux or composite alloy flux technology.

The heat exchanger according to the invention can advantageously comprise at least one other thermosiphon element .

According to this preferred embodiment of the invention the heat exchanger thus comprises two or more thermosiphon elements. The heat exchanger has according to this embodiment of the invention a modular design of a plurality of modules, and in this way it can be designed freely according to specific cooling requirements and dimension requirements by using a given number of modules of a given size.

The heat exchanger according to the invention can advantageously be made such that the thermosiphon elements are stacked, so that a side face from the first siphon element faces towards a side face from the other thermosiphon element.

In this way is achieved a tight arrangement of thermosiphon elements, and as a consequence thereof a high specific cooling capacity of the heat exchanger. Stacked thermosiphon elements can furthermore be arranged, so that two adjacent elements are located with a single fin system between them, so that both adjacent elements can utilize the fin system.

The heat exchanger according to the invention can advantageously further comprise a first header, which is located towards the two upper or the two lower end faces of the first and the second thermosiphon element.

According to the invention, such a header is a continuous band, which secures the thermosiphon elements and thus solely serves an assembly purpose for the termosiphon elements. Thus, in the context of the invention it must be understood that compared to conventional headers such a header is without fluid-guiding interior volume.

The heat exchanger can further comprise a second header, such that the first header is located towards the two upper end faces of the first and the second thermosiphon element, and the second header is located towards the two lower end faces of the first and the second thermosiphon element.

By an arrangement of headers in both ends of the thermosiphon elements these can be secured in a more stable construction, which offers a further freedom of design of the heat exchanger according to the invention.

In a further expedient embodiment according to the invention the heat exchanger comprises that the distance between the interior walls of the box-shaped profile and the delimited outer circumference of the thermosiphon is 0 - 10 mm. Preferably 0 - 5 mm.

The heat exchanger is constructed so that there is contact between the interior faces on the upper and lower end faces of the box-shaped profile and the outer circumference of the thermosiphon in these areas, whereas there can be a certain distance between the edge faces and side faces of the box- shaped and the outer circumference of the thermosiphon in these areas.

By delimited outer circumference is understood the plane faces that are created when the most projecting elements of the outer walls of the thermosiphon are connected to each other by means of right lines/plane faces. Hereby is ensured good thermal contact between the box-shaped profile and the thermosiphon.

In a further appropriate embodiment according to the invention the heat exchanger comprises that the cross-over zone comprises a first connection port, which fluid-tightly connects the lower isothermal siphon zone with the upper adiabatic siphon zone, which first connection port is distanced from a second connection port that connects the upper isothermal zone fluid-tightly with the lower adiabatic siphon zone.

In a further expedient embodiment according to the invention the heat exchanger comprises that the first connection port and the second connection port of the cross-over zone are integral with the thermosiphon. By integral with is in this connection understood that the ports are not made as separate components, but constitute a part of the constructed thermosiphons. In a further expedient embodiment according to the invention the heat exchanger comprises an upper header and a lower header, which upper header is located towards one end face/end faces of the thermosiphon element/thermosiphon elements, and which lower header is located towards the end face/end faces situated opposite the one end face/end faces.

The volume of the final heat exchanger is hereby reduced. In the context of the invention is must thus be understood that such a header contrary to conventional headers is without fluid-guiding interior volume.

A second aspect of the invention comprises a method for manufacturing of the heat exchanger according to the invention, wherein the thermosiphon is manufactured in one processing, preferably by a punching process.

The thermosiphon itself can thus advantageously be made in a plate material, typically thin-walled, and be produced in a tool, preferably by a punch process, so that all zones of the thermosiphon are produced in a single processing.

The method for manufacture of the heat exchanger can comprise that the thermosiphon and the box-shaped profile are joined by a joining technique from the group of joining techniques comprising Al-Si-cladding, sil flux and composite alloy flux. All these techniques are based on that aluminium having a certain, modest content of silicium, has a somewhat lower melting point than the pure aluminium, and that aluminium- based elements having a low content of silicium in or on the surface thus can be joined by means of a brazing process at a temperature, which is at little lower than the melting point of the elements themselves. The process can hereby be carried out in one processing, e.g. in a continuous furnace.

In aluminium-silicium cladding the elements are made in a multi-layer composite material, where the core has a lower silicium content than the surface layers. The melting temperature of the outermost layer is typically in the range 577-610°C, whereas the melting point of the core material typically is in the range between 630-660°C. The object is that the outermost layer melts and in this way functions as brazing material, whereas the core material remains in solid form. Before the components are brazed together in a furnace the oxide layer of the materials can be removed ("stripped") e.g. by sprinkling with a flux.

Sil flux is, in contrast to Al-Si Cladding, a silicium- containing paste, which is applied at least one of the construction elements that are joined by pressing the elements together before they are brazed in a continuous furnace. This method has the advantage that the use of material can be limited to application solely on the areas of the elements that are to be joined, because the stripping flux is integral with the sil flux paste. Composite alloy flux has a corresponding mode of operation. The method for manufacturing of the heat exchanger can moreover comprise that the box-shaped profile is joined with at least one header by a joining technique from the group of joining techniques comprising Al-Si-cladding, sil flux and composite alloy flux.

According to this embodiment all elements of the heat exchanger according to the invention, including one or more headers that typically are aluminium-based, can thus be joined in one processing using joining techniques as described above.

A third aspect of the invention comprises use of the heat exchanger according to the invention for cooling, preferably for cooling of electronic components.

The invention will now be explained further with reference to the drawings, in which:

Fig. 1 shows a heat exchanger according to the invention.

Fig. 2 shows a thermo siphon in the heat exchanger according to the invention.

Fig. 3 shows a heat exchanger with two stacked thermosiphon elements according to the invention.

Fig. 4, comprising fig. 4a and fig. 4b, shows a use of a heat- exchanger from the known technology and a heat exchanger according to the invention.

In fig. 1 the heat exchanger according to the invention is designated with 1. The heat exchanger 1 comprises a thermosiphon element 2, which comprises a thermosiphon 3 comprising a lower isothermal siphon zone 4, an upper isothermal siphon zone 5, a lower adiabatic siphon zone 6, an upper adiabatic siphon zone 7, and a cross-over zone 8, which is located between the upper siphon zones 5 and 7 and the lower siphon zones 4 and 6, and which connects the two lower siphon zones 4 and 6 with the two upper siphon zones 5 and 7.

The thermosiphon element moreover comprises a hermetically closed box-shaped profile 9 (here shown cut-through) having two side faces, to edge faces (9a, 9b) and an upper and a lower end face and an interior volume, where each of the two side faces is divided in four profile zones comprising a lower heat absorbing isothermal profile zone 10, an upper heat emitting isothermal profile zone (not shown) , a lower adiabatic profile zone 12, and an upper adiabatic profile zone (not shown) .

The box-shaped profile 9 hermetically envelops the thermosiphon 3, which is located in the interior volume of the profile, so that the lower heat absorbing isothermal profile zone 10 is located towards the lower isothermal siphon zone 4, the upper heat emitting isothermal siphon zone (not shown) is located towards the upper isothermal siphon zone 5, the lower adiabatic profile zone 12 is located towards the lower adiabatic siphon zone 6, and the upper adiabatic profile zone (not shown) is located towards the upper adiabatic siphon zone 7. The distance between the interior walls of the box-shaped profile 9 and the delimiting outer circumference of the thermosiphon 3 is 0 - 10 mm, preferably 0 - 5 mm. Moreover, the figure shows two headers 14 and 14a for holding the thermosiphon elements 2 together. The refrigerant in the termosiphon element 2 is a fluorinated hydrocarbon . Fig. 2 shows the thermosiphon 3 in the heat exchanger 1 according to the invention. The thermosiphon 3 is punched in one processing in one piece of aluminium-silicium-cladding plate, and comprises thermosiphon 3 comprising a lower isothermal siphon zone 4 where the evaporation occurs, an upper isothermal siphon zone 5 where the condensation occurs, a lower adiabatic siphon zone 6, and an upper adiabatic siphon zone 7, both of which are transport zones for liquid and gas, respectively, and a cross-over zone 8 that is located between the upper siphon zones 5 and 7 and the lower siphon zones 4 and 6, and that connects the two lower siphon zones 4 and 6 to the two upper siphon zones 5 and 7, and that is formed so that the gas flow and the liquid flow are separated. The cross-over zone 8 comprises a first connection port 8a, . which fluid- tightly connects the lower isothermal siphon zone 4 with the upper adiabatic siphon zone 7. First connection port 8a is distanced from a second connection port 8b, which connects the upper isothermal siphon zone 5 fluid-tightly with the lower adiabatic siphon zone 6. The first connection port 8a and second connection port 8b of the cross-over zone 8 are integral with the thermosiphon 3, whereby is understood that separate tubes for connection are not present, but that the ports 8a, 8b or the channels are a part of the very construction of the thermosiphon 3. Fig. 3 shows the heat exchanger 1 having two stacked thermosiphon elements 2 according to the invention. In the figure is shown how the lower heat absorbing isothermal profile zone 10 is provided with heat absorbing Louver fins 15 for heat absorbing from the surroundings, and how the upper heat emitting isothermal profile zone 11 in the same way is provided with heat emitting Louver fins 16 for heat emission to the surroundings. The figure also shows that neither the lower adiabatic profile zone 12 nor the upper adiabatic profile zone 13 is provided with fins.

Fig. 4 shows in fig. 4a how a conventional ^' heat exchanger 21 is located in a flow channel 22, where the heat exchanger 21 that has an extensive tube system 23 occupies a large part of the cross-section of the flow channel 22, and thereby reduces the air flow. In fig. 4b is shown how the heat exchanger 1 according to the invention, here consisting of three thermosiphon elements 2 and having same cooling capacity as the heat exchanger 21, occupies far less of the cross-section of the flow channel 22 and thereby ensures a better air flow. It is characteristic, among others, that it comprises an upper header and a lower header, where the upper header is located towards one of the end face/ end faces of the thermosiphon element/thermosiphon elements. The lower header is located towards the end face/end faces situated opposite the said one end face/end faces. In the context of the invention it must thus be understood that in contrast to conventional headers such a header is without fluid-guiding interior volume.