DK177987B1 - Heat exchanger and method and application - Google Patents

Abstract

A heat exchanger (1) comprising at least one first thermosiphon element (2) comprising - a thermosiphon (3) comprising five zones: - 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 crossover zone (8) located between and connecting the two lower siphon zones (4, 6) to the two upper siphon zones (5, 7), and - a hermetically sealed box-shaped profile (9) with two side faces, two edge faces (9a, 9b) and an upper and lower end face and an inner volume, each of the two side faces being divided into four profile zones - a lower, heat absorbing, isothermal profile zone (10), - an upper, heat-emitting, isothermal profile zone (11), - a lower adiabatic profile zone (12), and - and an upper, adiabatic profile zone (13), and wherein the box-shaped profile (9) hermetically encloses the thermosiphon (3) located in the inner volume of the profile (9) so that the lower isothermal profile zone (10) is positioned against the n the lower isothermal siphon zone (4), the upper isothermal profile zone (11) is positioned toward the upper, isothermal siphon zone (5), the lower adiabatic profile zone (12) is positioned toward the lower, adiabatic siphon zone (6), and the upper adiabatic profile zone (13) is positioned against the upper adiabatic siphon zone (6). In addition, the invention comprises processes for producing the heat exchanger (1), as well as using the heat exchanger (1). With the heat exchanger (1) according to the invention, improved cooling is achieved, in particular by electronic components.

Description

Heat exchanger and method and application

The invention relates to a heat exchanger comprising at least one first thermosiphon element comprising: 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 crossover zone, which is located between the upper and lower siphon zones and which connects the two lower siphon zones with the two upper siphon zones.

In addition, the invention relates to processes for producing the heat exchanger.

In addition, the invention relates to the use of the heat exchanger for cooling.

The principle of a thermosiphon ("thermo siphon") has been known since the mid-1800s and includes the fact that a hermetic enclosure is evacuated and then filled with a suitable fluid which is supplied to heat and evaporator in an evaporator part of the thermosiphon. and then condenses into a condenser portion of the thermosiphon, thereby emitting heat. The condensed liquid is returned to the evaporator portion. The heat conduction in this evaporation and condensation process is significantly greater than the thermal conductivity of, for example, metals, and the thermosiphon principle is therefore suitable for heat exchange and cooling purposes.

The fluid in the thermosiphon may consist of a single chemical species, or it may consist of a mixture of several chemical species, for example in the form of an azeotropic or near-azeotropic mixture.

The thermosiphon has an internal geometry comprising an internal, closed loop which enables the aforementioned two-phase circuit process to be run. Since a thermosiphon is a hermetically sealed biphasic system and only pure liquid and gas are represented in the internal hermetic enclosure, the fluid will remain saturated as long as the operating conditions of the thermosiphon are between the triple point of the fluid and its critical point and the thermosiphon will remain to its full extent. isothermal or near isothermal within a very wide range of work.

The thermosiphon is akin to the unit known today as the heatpipe, however, the liquid in the thermosiphon is returned to the evaporator portion only by the effect of gravity, while in the heatpipe it is returned to a capillary structure by capillary forces.

Originally developed for the automotive industry, conventional heat exchangers based on the thermosiphon principle have achieved wide commercial spread for cooling electronics. The principle has the unconditional advantage that the circular process can be operated without the need for moving parts.

This type of heat exchanger is constructed with exchanger sections of a plurality of parallel arranged flat tubes, each extruded in a multiport pattern in which the fluid flows, and equipped with corrugated Louver-type fins for heat exchange with the surroundings. The flat pipes are all connected to a manifold, designated a header, and which hydraulically connect the flat pipes to each other in the parallel structure. The entire structure is typically made of aluminum and can be soldered in a pass-through furnace in one process. Conventional heat exchangers typically consist of two (or more) of such exchanger sections, of which at least one section acts as an evaporator portion and at least one section acts as a condenser portion, and wherein the two or more sections are connected by at least one gas-conducting pipe and at least one liquid-conducting pipe. .

The known technology has several disadvantages: Thermodynamically, the design with an evaporator section and a condenser section means that parts of the heat exchanger are not utilized sufficiently efficiently in both heat absorption and heat dissipation contexts. Thus, especially when cooling hotspots, there is a significant risk that the sectional structure of the heat exchanger results in inappropriate and inefficient cooling, for example because the parts of the heat exchanger which receive the greatest heat flux and thus have the greatest need for cooling are cooled only. bad.

In terms of construction or design, the prior art also has the disadvantage that a plurality of headers must be connected to each other by means of pipes to enable the liquid and gas flow in the heat exchanger. These connection pipes, which can typically be both long and curly, reduce the cooling capacity in at least two areas: The connection pipes increase the heat exchanger volume without contributing to the cooling capacity, and further reduce this capacity by limiting the air flow around the heat exchanger.

The increased internal volume also increases the demand for the amount of fluid in the heat exchanger, which has both cost and environmental disadvantages.

The sectional structure of the heat exchanger further has the consequences that a single leakage in the piping system can cause the heat exchanger to cease to function at the same time as a significant amount of fluid may leak to the atmosphere.

From US5286884 a heat exchanger is known, as indicated in the introduction. It comprises at least one thermisophone element which includes consists of a thermophone with zones.

The apparatus comprises a downflow portion containing an indirect heat exchange segment comprising a plurality of heat exchange tubes in fluid communication with the interior of an upright portion in which fluid flows down.

The apparatus comprises an upper isothermal transition segment and a lower transition section which fluidly connect the heat exchange tubes to the rest of the apparatus.

The downstream portion and an adiabatic upstream leg are connected to each other by laterally located U-tubes.

The appliance is designed to take up a lot in terms of its capacity and thus also has environmental disadvantages.

It is therefore an object of the invention to provide a heat exchanger without the above disadvantages.

The object of the invention is met by a heat exchanger of the type specified in the preamble of claim 1, characterized in that the thermosiphon element of the heat exchanger further comprises: a hermetically sealed, box-shaped profile with two side surfaces, two edge faces and an upper and lower end surface and an inner volume , wherein each of the two side surfaces 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 - and an upper, adiabatic profile zone, and where box-shaped profile hermetically encloses the thermosiphon located in the inner volume of the profile such that: - the lower, heat-absorbing, isothermal profile zone is positioned against the lower, isothermal siphon zone, - the upper, heat-emitting, isothermal profile zone is located against the upper, isothermal siphon zone. - the lower adiabatic profile zone is positioned toward the lower adiabatic siphon zone, and - the upper adiabatic profile zone is located toward the upper adiabatic siphon zone.

Thus, with the heat exchanger with the thermosiphon element according to the invention, the thermosiphon is enclosed by a box-shaped profile having a heat-absorbing profile zone and a heat-emitting profile zone and thus is the part of the heat exchanger which exchanges heat with the surroundings. Thus, the heat exchanger with the thermosiphon element constitutes a self-functioning heat exchanger module which does not have the disadvantages mentioned above.

The heat exchanger with the thermosiphon element according to the invention thus allows, with its structure as a self-functioning module, to eliminate the need for the above-mentioned system of connection pipes with consequent reduced volume and reduced fluid volume requirements, and consequently higher specific cooling capacity and reduced environmental impact.

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

The thermosiphon element thermosiphon consists of 5 siphon zones, two of which are isothermal and two are adiabatic. The last siphon zone is called the crossover zone. The upper part of the profile acts as a condenser part while the lower part acts as an evaporator part, and the internal circulation of liquid and gas takes place in the thermosiphon completely independent of both headers and pipes. The thermosiphon itself has an internal geometry that allows circulation. Thus, the geometry comprises the lower isothermal siphon zone where the fluid is evaporated during heat absorption. From here, the evaporated fluid in the form of gas is transported via the upper adiabatic zone to the upper isothermal siphon zone where the gas condenses. From here, the condensed fluid is transported via the lower adiabatic zone, which is a fall channel, under gravity back to the lower isothermal siphon zone. The crossover zone separates the lower evaporator portion from the upper condenser portion, and is designed so that the gas and liquid streams do not run countercurrently and thus do not collide, but are instead directed around each other.

With the heat exchanger with 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 surface. The side surfaces are divided into four profile zones which cooperate with the siphon zones: - a lower heat-absorbing, isothermal profile zone, which is located against the lower, isothermal siphon zone, absorbs heat from the surroundings and conducts this heat to the siphon zone, where evaporation takes place, - an upper adiabatic profile zone which is positioned against the upper adiabatic siphon zone and which does not exchange heat with the surroundings; - an upper, heat-emitting isothermal profile zone located against the upper isothermal siphon zone emits heat to the environment produced; during the condensation process in the siphon zone, and - a lower adiabatic profile zone which is located against the lower adiabatic siphon zone and which does not exchange heat with the surroundings.

The heat conduction between the isothermal siphon zones and the associated isothermal profile zones is done by metallic heat 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 reference is made to "" upper "and" "lower" zones, respectively, this means 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, ie the corresponding siphon zone or profile zone. This includes that the thermosiphon element can operate vertically, or can operate at an angle so that the "upper" zone is higher than the "lower" zone, but not necessarily vertical above, but so that gravity is sufficient to drive the flow of the thermosiphon element.

It should also be understood that the crossover zone separates '' upper 'zones from' 'lower' zones. Thus, all "upper" zones - ie siphon zones and profile zones - located above the crossover zone and bounded against the '' lower 'zones thereof, while all' 'lower' zones - ie. siphon zones and profile zones - are located below the crossover zone and bounded against its '' upper '' zones.

In the context of the invention, "isothermal" is to be understood as isothermal, i.e. at the same temperature or as near isothermal, i.e. at approximately the same temperature. Similarly, "adiabatic" in the context of the invention is to be understood as adiabatic, i.e. without heat exchange with the surroundings, or near adiabatic, ie. almost without heat exchange with the surroundings.

For the functionality of the thermosiphon element, it is imperative that the gas is cooled as little as possible in the upper adiabatic siphon zone, as condensation at this location will lead to drip formation and the risk of blocking the gas flow.

Similarly, it is essential that the fluid be heated as little as possible in the lower adiabatic siphon zone, as evaporation at this location will lead to gas formation and the risk of fluid flow limitation.

The lower isothermal siphon zone of the thermosiphon and the upper, adiabatic siphon zone of the thermosiphon may advantageously face one edge surface of the profile, while the lower, adiabatic siphon zone and the upper, isothermal siphon zone face the other edge surface of the profile.

With this geometry of the thermosiphon, an appropriate flow of gas and liquid in the thermosiphon is ensured, since the crossover zone can be performed as simple as possible for unobstructed and independent, non-intersecting gas and liquid flow.

The profile isothermal profile zones may be covered by fins, preferably by Louver fins.

With such fins, an efficient heat exchange with the environment is achieved, ie. respectively, an efficient heat absorption from the surroundings of the lower, heat-absorbing, isothermal profile zone and an efficient heat release to the surroundings of the upper, heat-giving, isothermal profile zone.

Louver fins have a high surface area and thus allow a particularly good heat exchange with the surroundings.

Thus, while the profile isothermal profile zones are preferably covered with fins, the profile's adiabatic profile zones are preferably not covered by such fins. This limits the heat exchange with the surroundings from these profile zones.

In an alternative embodiment, the heat exchanger with the thermosiphon element according to the invention is not covered by fins, for example in connection with hot spot cooling.

Thus, the heat exchange with the surroundings can be by conduction, convection, radiation or a combination thereof.

The heat exchanger thermosiphon may be made of an aluminum-based material which is cheap and easy to process.

The heat exchanger thermosiphon can advantageously be made in an Al-Si cladding material which is inexpensive and easy to process, or carried out using sieve flux or composite alloy flux technology.

The profile of the heat exchanger can advantageously be made of aluminum which is cheap and easy to process and which can easily be joined with a corresponding aluminum-based thermosiphon.

The profile of the heat exchanger can also be made in an Al-Si cladding material which is inexpensive and easy to process, or carried out using sieve flux or composite alloy flux technology.

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

Thus, according to this preferred embodiment of the invention, the heat exchanger comprises two or more thermosiphon elements. According to this embodiment of the invention, the heat exchanger is modularly constructed with 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 in a given size.

The heat exchanger according to the invention can advantageously be designed so that the thermosiphon elements are stacked so that a side surface of the first thermosiphon element faces a side surface of the second thermosiphon element.

In this way, a close arrangement of the thermosiphon elements and a resultant high specific cooling capacity for the heat exchanger are obtained. Stacked thermosiphon elements can also be arranged so that two adjacent elements are located with a single founding system in between, so that both neighboring elements can utilize the founding system.

The heat exchanger according to the invention may advantageously further comprise a first header positioned against the two upper or two lower end faces of the first and second thermosiphon elements.

According to the invention, such a header is a continuous band which holds the thermosiphon elements and thus serves only a mounting purpose for the thermosiphon elements. Thus, it is to be understood in the context of the invention that, unlike conventional headers, such a header is devoid of fluid carrying internal volume.

The heat exchanger may comprise a further second header such that the first header is positioned against the two upper end faces of the first and second thermosiphon elements, and the second header is positioned against the two lower end faces of the first and second thermosiphon elements.

With an arrangement of headers at both ends of the thermosiphon elements, these can be retained in a further stable structure which offers a further freedom of design for the heat exchanger according to the invention.

Another aspect of the invention comprises a method of producing the heat exchanger of the invention, wherein the thermosiphon is produced in one process, preferably by a punching process.

Thus, the thermosiphon itself can advantageously be formed in a, typically thin-walled, sheet material and produced in a tool, preferably by a punching process, so that all the zones of the thermosiphon are produced in a single process.

The method of producing the heat exchanger may comprise joining the thermosiphon and box-shaped profile by a joining technique from the group of joining techniques comprising Al-Si cladding, strain flux and composite alloy flux.

All of these techniques are based on the fact that aluminum with a certain, modest content of silicon has a slightly lower melting point than pure aluminum, and that aluminum-based elements with a small content of silicon in or on the surface can thus be joined by a soldering process at a temperature slightly lower than the melting point of the element itself. The process can thereby be carried out in one process, for example in a through oven.

With aluminum-silicon cladding, the elements are made of a multilayer composite material, the core having a lower silicon content than the surface layers. The melting temperature of the outermost layer is typically in the level of 577-610 ° C, while the melting point of the core material is typically in the level between 630-660 ° C. The outer layer is intended to melt and in this way act as solder while the core material remains in solid form. Before the components are soldered together in an oven, the oxide layers of the materials can be removed ('' stripped '') for example by spraying with a flux.

Silflux, unlike Al-Si Cladding, is a silicon-containing paste that is applied to at least one of the structural members joined by compressing the elements before soldering in a pass-through furnace.

This method has the advantage that the material use can be limited to application only in the areas of the elements to be joined, the stripping flux being integrated into the sieve flux paste. Composite alloy flux has a similar mode of operation.

The method of producing the heat exchanger may further comprise the box-shaped profile being joined to at least one header by a joining technique from the group of joining techniques comprising Al-Si cladding, strain flux and composite alloy flux.

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

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

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

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

FIG. 2 shows a thermosiphon 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 an application of a heat exchanger of the prior art and a heat exchanger according to the invention.

In FIG. 1 is denoted by 1 the heat exchanger according to the invention. The heat exchanger 1 comprises a thermosiphon element 2 comprising 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 crossover zone 8 located between the two. upper siphon zones 5 and 7 and the lower siphon zones 4 and 6, which connect the two lower siphon zones 4 and 6 with the two upper siphon zones 5 and 7. The thermosiphon element further comprises a hermetically sealed box-shaped profile 9 (shown here cut through) with two side faces , two edge faces (9a, 9b) and an upper and a lower end face and an inner volume, each of the two side faces being divided into 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 encloses the thermosiphon 3, which is located in the inner volume of the profile, so that the lower, heat-absorbing, isothermal profile zone 10 is positioned against the lower, isothermal siphon zone 4, the upper, heat-emitting, isothermal profile zone (not shown). toward the upper, isothermal siphon zone 5, the lower adiabatic profile zone 12 is positioned toward the lower, adiabatic siphon zone 6, and the upper, adiabatic profile zone (not shown) is positioned toward the upper, adiabatic siphon zone 7. In addition, the figure shows two headers 14 and 14a for comparing the thermosiphon elements 2.

The refrigerant in the thermosiphon 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 die cut in one process in one piece of aluminum-silicon cladding plate, and comprises thermosiphon 3 comprising a lower isothermal siphon zone 4 where the evaporation takes place, an upper isothermal siphon zone 5 where the condensation takes place, a lower adiabatic siphon zone 6 and an upper adiabatic siphon zone 7, both of which are liquid and gas transport zones, respectively, and a crossover zone 8 located between the upper siphon zones 5 and 7 and the lower siphon zones 4 and 6, which connect the two lower siphon zones 4 and 6 with the two upper siphon zones 5 and 7, which are configured to separate the gas stream and the liquid stream.

FIG. 3 shows the heat exchanger 1 with two stacked thermosiphon elements 2 in accordance with the invention. The figure shows how the lower, heat-absorbing, isothermal profile zone 10 is provided with heat-absorbing Louver fins 15 for heat absorption from ambient, and how the upper, heat-emitting, isothermal profile zone 11 is also provided with heat-emitting Louverfins 16 for heat-emitting to the surroundings. The figure also shows that neither the lower adiabatic profile zone 12 nor the upper adiabatic profile zone 13 are provided with fins.

FIG. 4 shows in FIG. 4a, how a conventional heat exchanger 21 is located in a flow duct 22, wherein the heat exchanger 21 with an extensive pipe system 23 occupies a large portion of the cross-section of the flow duct 22, thereby reducing the air flow.

In FIG. 4b shows how the heat exchanger 1 according to the invention, here consisting of three thermosiphon elements 2 and with the same cooling capacity as the heat exchanger 21, takes up much less of the cross-section of the flow duct 22 and thus ensures a better air flow.

Claims (14)

A heat exchanger (1) comprising at least one first thermosiphon element (2) comprising: a thermosiphon (3) comprising five zones: - a lower isothermal siphon zone (4), - an upper, isothermal siphon zone (5) - a lower , an adiabatic siphon zone (6), - an upper, adiabatic siphon zone (7), and - a crossover zone (8) located between the upper (5, 7) and the lower siphon zones (4, 6) and connecting the two lower siphon zones (4, 6) with the two upper siphon zones (5, 7), characterized in that the thermosiphon element (2) further comprises: a hermetically sealed box-shaped profile (9) with two side faces, two edge faces (9a, 9b) and an upper and a lower end surface and an inner volume, each of the two side surfaces being divided into four profile zones: - a lower, heat absorbing, isothermal profile zone (10), - an upper, heat-emitting, isothermal profile zone (11), - a lower , adiabatic profile zone (12), and - and an upper adiabatic profile zone (13), and wherein the box-shaped profile (9) hermetically encloses thermos the casing (3) located in the inner volume of the profile (9) so that: - the lower, heat absorbing, isothermal profile zone (10) is positioned against the lower, isothermal siphon zone (4), - the upper, heat-emitting, isothermal profile zone (11) is positioned toward the upper isothermal siphon zone (5), - the lower adiabatic profile zone (12) is positioned toward the lower adiabatic siphon zone (6), and - the upper adiabatic profile zone (13) is positioned toward the upper adiabatic siphon zone (6). Heat exchanger (1) according to claim 1, characterized in that the lower, isothermal siphon zone (4) of the thermosiphon and the upper, adiabatic siphon zone (6) face one edge surface (9a) of the profile, while the lower, adiabatic siphon zone (7) and the thermosiphon upper isothermal siphon zone (5) faces the second edge surface (9b) of the profile. Heat exchanger (1) according to claim 1 or 2, characterized in that the isothermal profile zones (10, 11) of the profile (9) are covered by fins (15, 16), preferably by Louver fins. Heat exchanger (1) according to one or more of claims 1 to 3, characterized in that the thermosiphon (3) is made of an aluminum-based material. Heat exchanger (1) according to claim 4, characterized in that the thermosiphon (3) is made of an Al-Si cladding material. Heat exchanger (1) according to one or more of claims 1-5, characterized in that the profile (9) is made of aluminum. Heat exchanger (1) according to one or more of claims 1 to 6, characterized in that the heat exchanger (1) further comprises at least one other thermosiphon element (2). Heat exchanger (1) according to claim 7, characterized in that the thermosiphon elements (2) are stacked so that a side surface of the first thermosiphon element (2) faces a side surface of the second thermosiphon element (2). Heat exchanger (1) according to claim 8, characterized in that the heat exchanger (1) further comprises a first header (14) which is positioned against the two upper or two lower end faces of the first and second thermosiphon elements (2). Heat exchanger (1) according to claim 9, characterized in that the heat exchanger (1) further comprises a second header (14a) such that the first header (14) is positioned against the two upper end faces of the first and second thermosiphon elements (2). ), and the second header (14a) is positioned against the two lower end faces of the first and second thermosiphon elements (2). Process for producing the heat exchanger (1) according to one or more of claims 1 to 10, characterized in that the thermosiphon (3) is manufactured in one process, preferably by a punching process. Method for producing the heat exchanger (1) according to one or more of claims 1-11, characterized in that the thermosiphon (3) and the box-shaped profile (9) are joined together by a joining technique from the group of joining techniques comprising Al-Si cladding, sieve flux and composite alloy flux. Process for producing the heat exchanger (1) according to claim 9 or 10, characterized in that the box-shaped profile (9) is joined by at least one header (14, 14a) by a joining technique from the group of joining techniques comprising Al-Si cladding, silflux and composite alloy flux. Use of the heat exchanger (1) according to one or more of claims 1 to 13 for cooling, preferably for cooling of electronic components.