Cooling system for liquid immersion cooling of electronic components

Description

[0001] The invention relates to a cooling system for liquid immersion cooling of electronic components according to the preamble of claim 1.

[0002] Liquid immersion cooling systems, such as two-phase immersion cooling systems, are an active cooling solution for electronic components that generate a lot of heat during operation. When the components are immersed in a heat transfer fluid, which usually has a relatively low boiling point, the heat generated by the electronic component can evaporate the surrounding liquid heat transfer fluid, thereby removing heat from the electronic component. A condenser device liquefies the vaporous heat transfer fluid, which is then returned to the reservoir for cooling.

[0003] A two-phase immersion cooling system with a cooling basin is known from US Pat. No. 10,512,192 B2. A condensation chamber, in which the gaseous fluid produced during the cooling process is condensed, communicates with the liquid fluid in the cooling basin. A vapor diversion structure is arranged above the heat-generating electronic components located within the cooling medium in the cooling basin. The vaporized fluid is directed into the condensation chamber for condensation by means of the vapor diversion structure.

[0004] Furthermore, a cooling system for computer components is known from US Pat. No. 1,0477,726 B1. The internal pressure in a pressure-controlled container is reduced to as low as 650 hPa. The container contains a heat-conducting, dielectric heat transfer fluid in liquid and gaseous phases, which has a boiling point below 80 °C at atmospheric pressure. Computer components are arranged in the container and are at least partially immersed in the liquid phase of the fluid. A condenser condenses the dielectric gas-phase fluid, evaporated by the heat generated by the computer components, into a dielectric liquid-phase fluid.

[0005] US 2019 / 0 008 077 A1 describes a liquid immersion cooling system with the features of the preamble of claim 1, comprising a liquid tank for cooling electronic circuits with a cooling device. The cooling device comprises a cooler that cools a gas space between the lid and the liquid level of a coolant in which the electronic circuits are immersed. For heat dissipation, the cooler has an inlet pipe and an outlet pipe for cooling water, which are guided through openings in the wall of the liquid tank. The inlet pipe and outlet pipe are connected to the wall of the liquid tank by means of mounting plates at the openings. Each mounting plate has a disc shape with a central hole through which the inlet pipe or outlet pipe is guided, and bores for screw connections to the wall of the liquid tank.

[0006] The document US 2014 / 0 218 858 A1 also discloses an immersion cooling system in which fluid lines are passed through the wall of a liquid tank for cooling electronic components.

[0007] The invention is based on the object of developing a cooling system for liquid immersion cooling of electronic components with regard to the stability of the container construction.

[0008] The invention is defined by the features of claim 1. The further dependent claims relate to advantageous embodiments and developments of the invention.

[0009] The invention includes a cooling system for liquid immersion cooling of electronic components. The cooling system comprises a container with a container wall, which has a reservoir for liquid heat transfer fluid inside and in which positioning devices for electronic components are arranged, wherein the container has a gas space for gaseous heat transfer fluid.

[0010] In the gas space of the vessel there is a heat exchanger device with heat exchanger tubes for liquefying gaseous heat transfer fluid, wherein the heat exchanger tubes have external fins on their outside.

[0011] The heat exchanger tubes enter the vessel wall at points of penetration or pass through the vessel wall. At these points of penetration, the heat exchanger tubes form a material connection with the vessel wall.

[0012] The gaseous heat transfer fluid in the gas space is in contact with the liquid heat transfer fluid in the reservoir at a phase boundary. The surface of the liquid heat transfer fluid in the reservoir forms the phase boundary with the gaseous heat transfer fluid in the gas space.

[0013] In other words, the heat exchanger tubes can have a smooth exterior or external finning at the points where they enter or pass through the vessel wall. This external finning is enclosed by the material for a material-to-material bond, thus hermetically sealing the passage of gas or liquid. The preferred method is to fuse the outer contour of the tubes, defined by the external finning, into the vessel wall. For a purely material bond, a combination of frictional and positive locking can also be advantageously used.

[0014] In addition to the external fins, a heat exchanger tube can optionally have an internal structure. The internal structure can be designed in the form of an internally circumferential helix with a predetermined helix angle. If the outside of the heat exchanger tubes has spirally circumferential external fins, the pitch of the circumferential external fins can be the same as, less than, or greater than the pitch of the circumferential helix determined by the helix angle. The two structures can therefore differ in that, for the integral connection of the outside of a heat exchanger tube to the vessel wall, the design of the external fins and the internal structure can be designed independently of each other and thus optimized.

[0015] However, to optimize heat exchange, certain limits are specified for both structures. For example, the ratio of the maximum structural height of the outer fins to the maximum structural height of the inner structure is preferably in the range of 1.25 to 5 for condenser tubes and in the range of 0.5 to 2 for evaporator tubes.

[0016] In addition, the cooling system can advantageously include a control device designed to regulate the operation of the fluid circulation, for example, as a function of the temperature of the heat transfer fluid and the pressure conditions in the vessel. Using sensors, the control device monitors and controls pressure, temperature, conductivity, and all process-relevant parameters.

[0017] The invention is based on the idea that the integral connection of the heat exchanger tubes to the tank wall ensures lasting stability for the entire structure. The direct connection according to the invention eliminates the need for prior art sealing devices such as O-ring seals at the points where the tank wall passes through. The integral, fixed connection of the heat exchanger tubes and the tank wall also makes it possible to reduce the thickness of the tank wall compared to conventional technical solutions, as the heat exchanger tubes essentially act as struts and thus contribute to the dimensional stability of the entire cooling system. In particular, the solution according to the invention also supports the pressure resistance during system operation, both with regard to negative pressure and positive pressure in a hermetically sealed cooling system.

[0018] The arrangement of the heat exchanger tubes in the vessel is virtually freely selectable. This makes it possible to preferably place the heat exchanger tubes in the gas space near the surface of the liquid heat transfer fluid, especially at locations where particularly efficient heat transfer is required. The heat exchanger tubes thus perform multiple functions related to mechanical stability combined with efficient heat transfer. The particular advantage is that the solution according to the invention leads to an optimization in terms of significant material savings, accompanied by a significant increase in performance.

[0019] In the container, the electronic components are arranged in a reservoir of liquid heat transfer fluid in a manner suitable for cooling, which is cooled by evaporation of this liquid fluid. The heat exchanger device of the cooling system can be designed to form liquid heat transfer fluid in the gas space of the container either in the form of advantageously distributed individual tubes or as a tube bundle. In this case, several tube bundles can also be arranged distributed within the gas space of the container, essentially as modules. These each have a material connection to the container wall at the points where they pass through the container wall.

[0020] The heat exchanger tubes are accessible for cleaning from the outside at the points of entry. With suitable connection technology located outside the vessel, the system can continue to operate at reduced cooling capacity even when individual tubes are being cleaned. This allows the cooling medium to be distributed and introduced entirely outside the vessel.

[0021] In a preferred embodiment of the invention, the outer fins can be directly adjacent to the vessel wall or come into contact with it. This occurs in particular when the heat exchanger tubes still have outer fins within the passages where they enter or pass through the vessel wall. The outer fins then remain immediately adjacent to the materially bonded connection between the tubes and the vessel wall. However, even in the case of heat exchanger tubes with unfinned ends, the tube ends are inserted so far into the intended passages for the materially bonded connection that the adjacent outer fins reach directly up to the vessel wall or come into contact with it. This has the particular advantage that the heat exchanger tubes inside the vessel have complete outer fins for efficient heat transfer.

[0022] Advantageously, the material connection can be designed to be gas-tight and pressure-resistant. In addition to providing mechanical stability combined with efficient heat transfer, a hermetic seal is important to prevent fluid exchange with the environment in every operating mode.

[0023] According to the invention, the heat exchanger tubes in the passage points have an inner tube diameter D2 which is larger than the inner tube diameter D1 of the heat exchanger tubes outside the passage points.

[0024] If the heat exchanger tubes still have external fins at the points where they enter or pass through the vessel wall, the process involves expanding the heat exchanger tube, resulting in an increased internal tube diameter D2. This expansion then compresses the external fins at a point of entry. Nevertheless, the integral connection ultimately ensures a stable, hermetic seal.

[0025] Even in the case of heat exchanger tubes with non-finned ends, the tube ends are widened to the point where they pass through to form a materially bonded connection and are additionally stabilized and sealed with a materially bonded joint.

[0026] In an advantageous embodiment of the invention, the heat exchanger tubes can be soldered, glued, or welded into the vessel wall. In addition to the preferred connection types mentioned, other methods can also be used to reliably bond the heat exchanger tubes to the vessel wall.

[0027] In principle, the external finning on the outside of the heat exchanger tubes can preferably run in a circumferential direction or in an axial direction parallel to the tube axis. In an advantageous embodiment of the invention, the outside of the heat exchanger tubes can have spirally circumferential external finning. With spirally circumferential external finning, only the channel surrounding the spirally circumferential external finning needs to be reliably sealed by the integral connection.

[0028] In an advantageous embodiment of the invention, the container can be designed as a pressure vessel that operates under negative pressure and / or positive pressure. The cooling system can be variably adjusted in its operating mode relative to the ambient atmosphere, both with regard to the existing mechanical stability combined with efficient heat transfer under positive pressure and under negative pressure. A typical operating mode in practice is to reduce the internal pressure below atmospheric pressure and above 650 Torr, with the dielectric fluid typically having a boiling point below approximately 80°C.

[0029] Although a suitable, uniform material is generally preferred for the heat exchanger tubes, in an advantageous embodiment of the invention, at least one first heat exchanger tube can be made of a first material and at least one second heat exchanger tube can be made of a second material that differs from the first material. With regard to mechanical stability, steel tubes with particularly high strength can offer a particular advantage. Copper tubes, on the other hand, optimize efficient heat transfer. Other materials, such as titanium, aluminum, aluminum alloys, and copper-nickel alloys, are also possible.

[0030] Advantageously, the first material can be copper and the second material steel. A suitable combination of individual heat exchanger tubes made of these two materials leads to further optimization in terms of existing mechanical stability combined with efficient heat transfer.

[0031] Embodiments of the invention are explained in more detail with reference to the schematic drawings.

[0032] Showing: Fig. 1 schematically shows a front view of a cooling system, Fig. 2 schematically shows a front view of a section of the tank wall with a passage point, and Fig. 3 schematically shows a vertical section of the tank wall in the plane of the passage point of a heat exchanger tube.

[0033] Corresponding parts are provided with the same reference numerals in all figures.

[0034] Fig. 1shows a schematic front view of a cooling system 1 for two-phase liquid immersion cooling of electronic components 2. The cooling system 1 comprises a container 3 and a lock device 9 for exchanging electronic components 2. The electronic components 2 are immersed in the reservoir 4 containing liquid dielectric heat transfer fluid located inside the container 3. The heat exchanger devices 6 are located above the surface 41 of the liquid heat transfer fluid in the gas space 5 of the container 3.

[0035] The cooling system 1 comprises a heat exchanger device 6 with heat exchanger tubes 61 in the gas space 5 of the container 3 for liquefying gaseous heat transfer fluid. The heat exchanger tubes 61 have external fins on the outside, not shown in this figure due to the low structural height. The heat exchanger tubes 61 enter the container wall 31 at passage points or pass through the container wall 31. At these passage points, the heat exchanger tubes 61 have a material connection with the container wall 31. The arrangement of the heat exchanger tubes in the container is, in principle, freely selectable. However, in the container, the heat exchanger tubes 61 are preferably arranged in the form of bundles or in rows at several locations in the gas space 5 in order to achieve mechanical stability combined with efficient heat transfer.

[0036] In the cooling system 1, a Fig. 1An automatic assembly system (not shown) can be arranged in the container 3, with which the electronic components 2 can be transported from the lock device 9 to the operating position 31 in the reservoir 4 containing liquid heat transfer fluid for replacement. The electronic components 2 can be transported by robot gripper arms or linear transport systems, which automatically pick up the electronic components 2 to be replaced from the operating position in the positioning device 8. In reverse order, the ready-to-use electronic components 2 to be installed are transferred by the assembly system to the operating position in the positioning device 8.

[0037] Fig. 2shows a schematic front view of a section of the container wall 31 with passage 32. At the passage 32, the recess in the container wall 31 is preferably just large enough to allow a heat exchanger tube to be inserted and bonded there. Adhesive and soldered joints can be made at the passage 32 across the entire wall thickness. Welded joints can be arranged on the outside and / or inside. With favorable melt flow, a welded joint extending through the entire wall thickness can be created at the passage 32 even with one-sided welding from the outside or inside of the container.

[0038] Fig. 3 shows schematically a vertical section of the container wall 31 along the section line AA from Figure 2in the plane of the passage point of a heat exchanger tube 61. The illustrated heat exchanger tube 61 has external ribbing 62 on its outside. The heat exchanger tube 61 passes through the vessel wall 31 at the passage point 32. At this passage point, the heat exchanger tube 61 has continuous external ribbing 62 and a material-to-material connection 7 in the form of a continuous weld seam with the vessel wall 31. Depending on the material combination of the vessel wall 31 and the heat exchanger tube 61, advantageous new intermetallic phase formations can occur in the molten pool at the weld point. Laser welding, for example, is a suitable method for producing a material-to-material connection with a locally limited melt flow. List of reference symbols

[0039] 1 Cooling system 2 Electronic component 3 Vessel 31 Vessel wall 32 Passage point 4 Reservoir for liquid heat transfer fluid 41 Surface of the liquid heat transfer fluid 5 Gas space for gaseous heat transfer fluid 6 Heat exchanger device 61 Heat exchanger tube 62 External finning 7 Material connection 8 Positioning device 9 Lock device A-A Section line

Claims

1. Cooling system (1) for the liquid immersion cooling of electronic components (2), comprising - a container (2) which has container walls (31) and which has at the inner side a tank (4) for liquid heat transfer fluid and in which positioning devices (8) for electronic components (2) are arranged, wherein the container (3) has a gas compartment (5) for gaseous heat transfer fluid, - a heat exchange device (6) having heat exchange pipes (61) in the gas compartment (5) of the container (3) for liquefying gaseous heat transfer fluid, wherein the heat exchange pipes (61) have at the outer side thereof an outer ribbing (62) and enter the container walls (31) at passage locations (32) or pass through the container walls (31), characterised in that - the heat exchange pipes (61) have in the passage locations (32) a pipe inner diameter D2 which is greater than the pipe inner diameter D1 of the heat exchange pipes (61) outside the passage locations (32), and - in that at these passage locations (32) the heat exchange pipes (61) have a materially engaging connection (7) to the container walls (31).

2. Cooling system (1) according to claim 1, characterised in that the outer ribbing (62) at these passage locations (32) directly adjoins the container walls (31) or comes into contact with them.

3. Cooling system (1) according to claim 1 or 2, characterised in that the materially engaging connection (7) is constructed to be gas-tight and pressure-resistant.

4. Cooling system (1) according to any one of claims 1 to 3, characterised in that the heat exchange pipes (61) are soldered, adhesively bonded or welded into the container walls (31).

5. Cooling system (1) according to any one of claims 1 to 4, characterised in that the outer side of the heat exchange pipes (61) has a helically circumferential outer ribbing (62).

6. Cooling system (1) according to any one of claims 1 to 5, characterised in that the container (3) is in the form of a pressure container which functions at a reduced pressure and / or excess pressure.

7. Cooling system (1) according to any one of claims 1 to 6, characterised in that at least a first heat exchange pipe (61) comprises a first material and at least a second heat exchange pipe (61) comprises a second material which is different from the first material.

8. Cooling system (1) according to claim 7, characterised in that the first material is copper and the second material is steel.