Automatic drain system for maintenance of immersion cooling system

Abstract

The present invention relates to an automatic drainage system for the maintenance of an immersion cooling system. The present invention comprises an immersion tank containing a server and cooling oil, an intake port located near the bottom surface, and a siphon tube having a peak higher than the normal water level. During normal operation, air remains at the peak, keeping the siphon tube in an inactive state; however, if the water level is raised above the peak by inserting an object with volume into the immersion tank or by injecting air into an elastic sealing structure, a siphon phenomenon is triggered, and the cooling oil is discharged into an external recovery tank. Since the intake port is located near the bottom surface, the cooling oil, including sediment, can be discharged without any residue, and the siphon phenomenon automatically stops the moment the water level reaches the height of the intake port. The discharged cooling oil can be purified in a filter within the recovery tank and reused through a re-injection line.

Description

Technology Field

[0001] The present invention relates to maintenance technology for an immersion cooling system for a data center. Specifically, it relates to an automatic drainage and filtering technology that discharges cooling oil by triggering a siphon effect by artificially raising the level of cooling oil in an immersion tank above a trigger threshold point without a separate drainage pump or electric valve, and recovers the discharged cooling oil in a reusable state by filtering it. Background Technology

[0002] Due to the recent surge in high-performance artificial intelligence (AI) and big data computations, the heat generated by high-density servers in data centers is exceeding the cooling limits of conventional air-cooling systems. To address this, liquid immersion cooling technology, which cools servers by directly submerging them in electrically non-conductive insulating cooling fluid, is emerging as a next-generation cooling solution. While liquid immersion cooling can maximize cooling and power efficiency by utilizing a liquid medium with a thermal conductivity tens of times higher than air, it also requires separate consideration for maintenance tasks that occur during the actual operation of the servers.

[0003] In conventional immersion cooling systems, the cooling oil inside the tanks must be emptied in advance to perform maintenance, such as server replacement or inspection. To this end, conventional methods have generally involved installing and operating separate electric drain pumps for each individual tank or having workers manually dismantle piping connected to the bottom of the tanks to drain the cooling oil. However, these methods had structural limitations: not only did they require significant preparation time for drainage, but in emergency situations where power supply to the drain pumps was cut off due to power outages, the electric pumps themselves would not operate, making rapid emergency drainage for fire prevention impossible.

[0004] Furthermore, conventional drainage structures often left sediment and residual cooling oil at the bottom of the tank even after drainage, as the suction point was located at a height separated from the tank bottom or there were no separate structural means to automatically terminate the drainage process. Moreover, despite the insulating cooling oil used in liquid immersion cooling being an expensive special fluid, conventional systems lacked separate recovery mechanisms to purify and reuse the discharged oil, resulting in significant amounts being discarded. This poses problems that lead to increased operating costs and environmental burdens. The problem to be solved

[0005] Conventional immersion cooling systems required the operation of a separate drain pump or the dismantling of lower piping to empty the cooling oil during maintenance. Furthermore, the suction point was often separated from the bottom of the tank, frequently leaving sediment and residual cooling oil, and there were no means provided to recover and reuse the discharged cooling oil in a manageable form. This invention aims to solve these problems through a siphon structure. means of solving the problem

[0006] According to one aspect of the present invention, an automatic drainage system for maintenance of an immersion cooling system may be provided, which automatically discharges cooling oil by initiating a siphon phenomenon using only a water level trigger without a separate drainage pump. The present invention comprises an immersion tank containing a server and cooling oil, a suction port located on or near the bottom surface of the immersion tank, a peak formed at a position higher than the normal water level during normal operation of the immersion tank, and a siphon tube including an outlet for discharging cooling oil toward an external recovery tank. When the water level of the cooling oil is at the normal water level, air remains in the section reaching the peak, thereby keeping the siphon tube in an inactive state, and thus preventing malfunctions in which cooling oil is unintentionally discharged during normal operation.

[0007] According to one aspect of the present invention, a trigger means for activating the siphon tube may be provided. The trigger means comprises an object having a volume inserted into the interior of a liquid immersion tank, or an elastic sealing structure that is immersed and disposed inside the liquid immersion tank and expands as air is injected, thereby activating the siphon phenomenon by raising the level of the cooling oil to an activation level above the highest point and filling the interior of the siphon tube with cooling oil. At this time, the object pushes the cooling oil to raise the level, and after the siphon phenomenon is activated, it may be configured to move in a direction separated from the suction port to avoid physical interference with the suction port while drainage is in progress.

[0008] In this case, when the above-described elastic sealing structure is used, the system may further include a restraining frame that surrounds the elastic sealing structure and is fixedly installed inside the immersion tank. The elastic sealing structure is coupled to the restraining frame so that its vertical position may be restricted so that part or all of it does not float above the surface of the cooling oil even when it expands due to the inflow of air. Additionally, the system may further include an air supply and discharge line connected to the elastic sealing structure to supply or discharge air, and a compressed air supply device connected thereto; when the level of the cooling oil is at a normal level, the air inside the elastic sealing structure may be discharged to maintain a contracted state.

[0009] According to one aspect of the present invention, a self-stopping mechanism may be provided to automatically stop a siphon phenomenon that has been triggered without separate control. The siphon tube may be configured such that when the level of the cooling oil drops to a self-stopping level that matches the height of the suction port while drainage is proceeding due to the triggering, at least a portion of the suction port is exposed outside the surface of the cooling oil, thereby automatically stopping the siphon phenomenon. At this time, by positioning the suction port close to the bottom surface of the immersion tank, the amount of residual cooling oil at the time of self-stopping is minimized to the physical dimension level of the suction port itself, so that substantial total drainage can be achieved.

[0010] At this time, the opening of the suction port may be positioned on a plane substantially identical to the bottom surface to form a gap through which cooling fluid can flow, or positioned at the lowest point of the bottom surface formed at an angle toward the suction port, or embedded within a sump locally formed in a concave shape on the bottom surface. Additionally, the suction port may be configured to include a plurality of nozzles distributed at different locations on the bottom surface, and a collection header that combines the plurality of nozzles into a single flow path of the siphon tube. At this time, the openings of the plurality of nozzles are positioned at the same absolute height relative to the vertical direction, regardless of the local height of the bottom surface where each nozzle is located, thereby preventing the siphon phenomenon from stopping prematurely by one nozzle being exposed before another nozzle during drainage. Furthermore, the collection header may have a flow path shape that descends or ascends monotonically without any local upward bending section from each nozzle to the point of confluence with the siphon tube, thereby preventing the formation of a section where air remains inside.

[0011] According to one aspect of the present invention, a configuration for recovering and reusing discharged cooling oil may be provided. The system further includes a recovery tank that is fluidically connected to the outlet and receives the discharged cooling oil, and the inside of the recovery tank is equipped with a filter to separate sediment and foreign substances mixed in the discharged cooling oil. At this time, the system may further include a re-injection line that connects the recovery tank and the liquid immersion tank and re-supplies the cooling oil purified through the filter to the liquid immersion tank, thereby enabling a return to a normal operating state after the completion of maintenance work.

[0012] According to one aspect of the present invention, an automatic drainage system (100) for maintenance of a liquid immersion cooling system may be provided. The automatic drainage system comprises: a liquid immersion tank (110) in which a server (120) and a cooling oil (500) are contained; a suction port (210) located on or near the bottom surface of the liquid immersion tank, a peak (220) formed at a position higher than the normal water level during normal operation of the liquid immersion tank, and an outlet (230) for discharging the cooling oil toward an external recovery tank (600), wherein when the water level of the cooling oil (500) is at the normal water level, air remains in the section reaching the peak, thereby maintaining an inactive state; a siphon tube (200). and includes a trigger means for activating a siphon phenomenon by filling the inside of the siphon tube with cooling oil by raising the level of cooling oil in the immersion tank to an activation level (520) above the highest point, by including an object (300) having a volume inserted into the inside of the immersion tank (110) or an elastic sealing structure (400) immersed and disposed inside the immersion tank (110) and expanding as air is injected.

[0013] At this time, when the water level of the siphon tube drops to a self-stopping level that matches the height of the suction port while drainage is proceeding due to the activation, at least a part of the suction port is exposed outside the surface of the cooling oil, so that the siphon phenomenon can be automatically stopped.

[0014] At this time, the automatic drainage system may further include a recovery tank (600) that receives the cooling oil discharged via fluidic communication with the outlet and is equipped with a filter (610) inside to separate sediment and foreign substances mixed in the cooling oil.

[0015] At this time, the automatic drainage system may be configured to move the object in a direction separated from the suction port after the siphon phenomenon is triggered and before the drainage of the cooling oil is completed.

[0016] At this time, the automatic drainage system may further include a restraining frame (430) fixedly installed inside the liquid immersion tank. And the elastic sealing structure may be coupled to the restraining frame so that its vertical position may be restricted so that part or all of the elastic sealing structure does not float above the surface of the cooling oil even when it expands due to the inflow of air.

[0017] At this time, the automatic drainage system may further include an air supply and discharge line (410) connected to the elastic sealing structure to supply or discharge air; and a compressed air supply device (420) connected to the air supply and discharge line. And when the water level of the cooling oil is at the normal water level, the air inside the elastic sealing structure is discharged so that the elastic sealing structure can maintain a contracted state.

[0018] At this time, the bottom surface is formed to be inclined toward the suction port, and the opening of the suction port may be positioned at the lowest point of the inclined bottom surface.

[0019] At this time, a sump (112) is formed locally in a concave shape on the bottom surface, and the opening of the suction port may be embedded within the sump.

[0020] At this time, the suction port may include a plurality of nozzles (113) distributed at different locations on the bottom surface, and a water collection header (114) that combines the plurality of nozzles into a single flow path of the siphon tube.

[0021] At this time, the openings of the plurality of nozzles may be arranged to be located at the same absolute height relative to the vertical direction.

[0022] At this time, the automatic drainage system may further include a re-injection line (620) that connects the recovery tank and the liquid immersion tank and re-supplies the cooling oil purified through the filter to the liquid immersion tank.

[0023] According to another aspect of the present invention, a method for draining a liquid immersion cooling system may be provided using an automatic drainage system comprising: a liquid immersion tank containing a server and a cooling oil; a siphon tube including an intake port located within the liquid immersion tank, a peak formed at a position higher than the normal water level during normal operation of the liquid immersion tank, and an outlet for discharging the cooling oil toward an external recovery tank; and a recovery tank. The drainage method comprises: a trigger step of raising the water level of the cooling oil to an activation level above the peak by inserting an object having volume into the liquid immersion tank or by injecting air into a flexible sealing structure immersed within the liquid immersion tank; a priming step in which, as the water level rises above the peak, air remaining in the section reaching the peak is extruded toward the outlet, and the interior of the siphon tube is filled with cooling oil, thereby triggering a siphon phenomenon; and a drainage step in which the cooling oil inside the liquid immersion tank is discharged to the recovery tank by the difference in water level between the intake port and the outlet while the intake port is submerged in the cooling oil. and a self-stopping step in which the siphon phenomenon is automatically stopped as the level of the cooling oil reaches a self-stopping level that matches the height of the intake port;

[0024] At this time, the automatic drainage system further includes a transfer pump and a re-injection line, and the recovery tank is equipped with a filter for purifying the cooling oil flowing into the recovery tank, and in the drainage step, the cooling oil discharged in the drainage step passes through the filter, thereby separating precipitates and foreign substances mixed in the cooling oil. Furthermore, the drainage method may further include a re-injection step in which, after the self-stopping step, the cooling oil stored in the recovery tank is supplied back to the liquid immersion tank through the transfer pump and the re-injection line. Effects of the invention

[0025] According to the present invention, a siphon can be activated via a water level trigger to drain the cooling oil. Since the intake port is located near the bottom of the tank, the cooling oil, including sediment, is discharged without any residue, and the drainage automatically stops without a separate control signal the moment the intake port is exposed. In addition, the discharged cooling oil can be purified and reused through filtering, thereby reducing both maintenance costs and environmental burden. Brief explanation of the drawing

[0026] FIG. 1 is an overall schematic diagram of a rapid automatic drainage and filtering system for maintenance provided according to one embodiment of the present invention. FIG. 2 is a cross-sectional view showing a siphon tube maintaining an inactive state during normal operation where oil discharge is unnecessary, provided according to one embodiment of the present invention. FIG. 3 is a cross-sectional view showing a state in which the water level rises above the highest point of the siphon tube and the siphon is activated (primed) by the insertion of a dummy block, provided according to one embodiment of the present invention. FIG. 4 is a cross-sectional view showing a state in which a siphon is activated by the water level rising above the highest point of the siphon tube due to the expansion of an elastic bladder provided according to another embodiment of the present invention. FIG. 5 is a cross-sectional view showing a state provided according to an embodiment of the present invention in which drainage proceeds after siphon activation and then self-stops when the water level reaches the height of the suction port. FIG. 6 is a diagram of an external recovery tank that recovers and filters discharged cooling oil and reinjects it, provided according to one embodiment of the present invention. FIG. 7 is a partial detail view showing a multi-point suction structure provided according to one embodiment of the present invention, wherein the suction port is configured to include a plurality of nozzles and a water collection header. Specific details for implementing the invention

[0027] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be implemented in various other forms. The terms used in this specification are intended to aid in understanding the embodiments and are not intended to limit the scope of the present invention. Furthermore, singular forms used below include plural forms unless the phrases clearly indicate otherwise.

[0028] FIG. 1 is an overall schematic diagram of a rapid automatic drainage and filtering system (100) for maintenance provided according to one embodiment of the present invention.

[0029] A system (100) according to one embodiment of the present invention has a trigger siphon structure that remains in an inactive state normally and operates only when necessary, in order to eliminate the operational inconvenience of having to drive a separate drain pump or manually dismantle the lower piping to drain the cooling oil for maintenance in a conventional immersion cooling system.

[0030] To this end, the system (100) may include three components: an immersion tank (110) that immerses and accommodates a server (120) in a cooling oil (500); a siphon pipe (200) that connects the immersion tank (110) and a recovery tank (600) that is independently positioned outside, only when necessary; and a trigger means that determines whether the siphon pipe (200) is activated.

[0031] The liquid immersion tank (110) accommodates a heat-generating server (120) inside and is designed so that the entire or heat-generating part of the server (120) is submerged in a non-conductive insulating cooling oil (500).

[0032] In one embodiment, the immersion tank (110) may be operated independently as a single tank, and in another modified embodiment, the immersion tank (110) may be any one of a plurality of immersion tanks included in a multi-stage immersion cooling system.

[0033] The destination of the cooling oil (500) transported by the siphon tube (200) of the present invention may be a recovery tank (600) rather than another circulation stage or another immersion tank inside the system (100).

[0034] The above siphon tube (200) can be defined by dividing it into three major geometric points.

[0035] First, the suction port (210) is positioned so as to be located on or near the bottom surface (111) of the liquid immersion tank (110). This arrangement is intended to structurally support the effect of draining the entire amount of cooling oil that the present invention aims to achieve. If the suction port (210) is positioned at any height spaced apart from the bottom of the tank, the residual cooling oil (500) at the point where the siphon phenomenon self-stops will remain below the height of the suction port (210), and thus the effect of draining the entire amount of cooling oil cannot be achieved. By positioning the suction port (210) close to the bottom surface (111), the point at which the self-stopping mechanism described later operates coincides almost exactly with the point at which the tank is substantially emptied. Furthermore, thanks to this structure, even the sediment (sludge) settled at the bottom can be sucked in together.

[0036] Second, the highest point (220) corresponds to the physically highest position within the entire section of the siphon tube (200). The highest point (220) may be located inside or outside the liquid immersion tank (110). The height of the highest point (220) is designed to be higher than the maximum water level during normal operation, which will be described later, and this height relationship acts as a principle that allows the siphon tube (200) of the present invention to remain in an inactive state during normal operation.

[0037] Third, the outlet (230) extends downward from the highest point (220) and forms the final path of the fluid discharged when the siphon is activated, by discharging the cooling oil (500) in the direction of the external recovery tank (600).

[0038] In addition, the system (100) according to the present invention may further include a trigger means for intentionally activating a siphon tube (200), which is normally in an inactive state, at a time when maintenance is required. The trigger means may perform the function of artificially raising the level of the cooling oil (500) inside the liquid immersion tank (110) so that the level reaches a height above the highest point (220). Such a trigger means may be embodied in various embodiments according to the specific implementation method, for example, a method of pushing up the level by the volume of an object inserted into the liquid immersion tank (110) and a method of forcibly raising the level by applying air pressure to the internal space of the liquid immersion tank (110) are each described in detail through the embodiments of FIGS. 3 and FIGS. 4 described later.

[0039] The present invention allows cooling oil to be discharged only when necessary through a trigger such as a change in water level, without the need for a separate drainage pump or a normally open valve.

[0040] In the present invention, the automatic drainage and filtering system (100) may also be referred to as the automatic drainage system (100).

[0041] FIG. 2 is a cross-sectional view showing the siphon tube (200) maintaining an inactive state in a normal operating state where oil discharge is not required, provided according to one embodiment of the present invention.

[0042] For stable cooling of the server (120), the entire server (120) or the heat-generating part must be immersed in the cooling oil (500). Therefore, during normal operation, the water level of the cooling oil (500) in the immersion tank (110) can be maintained at a level that satisfies the immersion submersion condition and is below the normal maximum water level (510).

[0043] The system (100) according to the present invention is designed so that the highest point (220) of the siphon tube (200) is formed at a position higher than the normal maximum water level (510), thereby allowing the siphon tube (200) to remain in an inactive state where it is not activated within the normal operating range for cooling the server (120).

[0044] This height relationship corresponds to a design margin adopted by the present invention to prevent unintended malfunctions, namely, an accident in which the cooling oil (500) is arbitrarily discharged during normal operation that does not require maintenance.

[0045] In particular, according to one embodiment of the present invention, the suction port (210) is positioned near the bottom surface (111) of the liquid immersion tank (110), so that the suction port (210) may already be submerged in the cooling oil (500) even in a normal operating state. Even in this case, in the system (100) according to the present invention, regardless of whether the suction port (210) is submerged, air remains in at least a portion of the section from the suction port (210) to the highest point (220) inside the siphon tube (200).

[0046] The reason for this phenomenon is as follows. As the intake port (210) is immersed, the cooling oil (500) flowing into the siphon tube (200) rises only to a height equal to the current level of the cooling oil (500), that is, a height where the external atmospheric pressure balances the pressure pressing the cooling oil (500) inside the liquid immersion tank (110), and then stops in that state. Inside the siphon tube (200), an air layer remains between the top of the risen cooling oil (500) and the highest point (220) located higher than it. In other words, since the condition of the intake port (210) being immersed in the cooling oil (500) alone does not provide the force to push the cooling oil (500) inside the siphon tube (200) up to the highest point (220) and form a continuous column of liquid to the opposite side, the siphon tube (200) remains in a stagnant state with only the cooling oil (500) partially filled.

[0047] Ultimately, whether the siphon tube (200) according to the present invention is activated is determined by the relative height relationship between the level of the cooling oil (500) in the liquid immersion tank (110) and the highest point (220). Therefore, even if the suction port (210) is immersed in the cooling oil (500), if the level of the cooling oil (500) is maintained at a lower level than the highest point (220), the siphon tube (200) can be maintained in an inactive state.

[0048] FIG. 3 is a cross-sectional view showing a state in which the siphon is activated (primed) by the insertion of a dummy block (300) according to one embodiment of the present invention, so that the water level rises above the highest point (220) of the siphon tube (200).

[0049] FIG. 3(a) shows a state in which the dummy block (300) does not encroach upon the space of the cooling oil (500), and FIG. 3(b) shows a state in which the dummy block (300) descends and encroaches upon the space of the cooling oil (500), causing the level of the cooling oil (500) to rise. In this specification, the dummy block (300) may also be referred to as an object (300) having volume.

[0050] When maintenance is required for the immersion tank (110), the present invention can initiate a drainage trigger using a siphon tube (200) simply by pushing a dummy block (300) having volume into the cooling oil (500) without driving a separate drainage pump or electric valve. When the dummy block (300) is inserted into the cooling oil (500), according to Archimedes' principle of volume exclusion, the cooling oil (500) of the same volume as the volume occupied by the dummy block (300) is pushed out, causing the entire surface of the cooling oil (500) in the immersion tank (110) to rise.

[0051] In order for drainage through the siphon tube (200) to be triggered by such a rise in water level, the water level rise resulting from the insertion of the dummy block (300) must be designed to reach an activation water level (520) that is greater than or equal to the height of the highest point (220) of the siphon tube (200). This is because, as described above, the condition determining whether the siphon phenomenon is activated is the relative positional relationship between the water level of the cooling oil (500) in the immersion tank (110) and the highest point (220). Therefore, the volume of the dummy block (300) immersed in the cooling oil (500) must be calculated based on the horizontal cross-sectional area of ​​the immersion tank (110) and the height difference from the normal maximum water level (510) to the highest point (220). Furthermore, it is desirable to design it to secure a margin that clearly exceeds the height of the highest point (220) by taking into account water level fluctuations or local deviations that may occur during the insertion process.

[0052] At the moment the water level reaches the activation level (520) and substantially exceeds the peak (220), the air that had been stagnating in the peak (220) section and preventing the activation of the siphon tube (200) can be extruded toward the outlet (230) by the rising cooling oil (500). Through this process, priming is completed in which the entire section from the intake port (210) to the outlet (230) of the siphon tube (200) is completely filled with a continuous column of liquid cooling oil (500) without interruption, thereby activating the siphon phenomenon caused by the difference in water level between the intake port (210) and the outlet (230).

[0053] Meanwhile, the specific lifting method for inserting and retrieving the dummy block (300) inside the liquid immersion tank (110) can be implemented in various ways depending on the environment in which the system (100) is installed and the required level of automation.

[0054] First, a buoyancy-based automatic lifting method may be employed by providing an air chamber and a valve for opening and closing the dummy block (300) inside the dummy block (300), thereby varying the average density of the dummy block (300) itself through the control of opening and closing the valve, so that it rises and sinks on its own without a separate external mechanical device. This method is advantageous for combining with remote control or a scheduled automated maintenance schedule.

[0055] Second, a sliding guide and locking method may be employed in which a sliding rail is formed on the side wall of the liquid immersion tank (110), and a dummy block (300) is inserted and withdrawn along the sliding rail by manual or motor drive, and fixed with a locking device at the inserted position. This method allows the insertion position of the dummy block (300) to be mechanically fixed, resulting in excellent positional reproducibility.

[0056] Third, a ceiling wire hoist method may be adopted in which a wire hoist is installed on the ceiling of the liquid immersion tank (110) and the dummy block (300) is lifted upward or lowered downward using the wire hoist. This method is advantageous for minimizing flow resistance or heat exchange interference during normal operation, as the dummy block (300) can be kept in a space outside the liquid above the liquid immersion tank (110) during normal operation.

[0057] Fourth, a rotating block method may be employed in which a cam is formed fixed to the side wall of the liquid immersion tank (110), and the dummy block (300) itself rotates in conjunction with the rotational drive of the cam, moving between a volume exclusion position and a standby position.

[0058] Fifth, instead of a solid-shaped dummy block (300), a separate compartment separated from the liquid immersion tank (110) by a partition wall may be provided, and by opening and closing a gate between the compartment and the liquid immersion tank (110), the fluid within the compartment is moved toward the liquid immersion tank (110) to achieve an equivalent water level rise effect, thereby eliminating interference associated with directly inserting a solid object into the internal space of the liquid immersion tank (110) where servers (120) are densely arranged.

[0059] In addition, it is preferable that the dummy block (300) has a structure that rises or retreats away from the vicinity of the suction port (210) after priming is completed and drainage begins, regardless of which lifting method described above is employed. This is because if the dummy block (300) remains in a state adjacent to the location of the suction port (210) positioned close to the bottom surface (111) of the liquid immersion tank (110), there is a risk that the dummy block (300) itself may physically block the opening of the suction port (210) or reduce the flow cross-sectional area around it, thereby reducing the drainage speed or blocking the suction path, during the process of drainage proceeding and the water level dropping. That is, when designing the lifting structure of the dummy block (300), it is preferable to actively move the dummy block (300) away from the vicinity of the suction port (210) after priming is activated.

[0060] FIG. 4 is a cross-sectional view showing a state in which a siphon is activated by the water level rising above the highest point of the siphon tube due to the expansion of an elastic bladder provided according to another embodiment of the present invention.

[0061] FIG. 4(a) shows a state in which the volume of the bladder (400) is small because no air is injected into the bladder (400), and FIG. 4(b) shows a state in which air is injected into the bladder (400) and the volume of the bladder (400) expands, and this expanded part encroaches on the space occupied by the cooling oil (500), resulting in the water level of the cooling oil (500) rising.

[0062] The dummy block method described in FIG. 3 above was configured to raise the water level according to the volume exclusion principle by inserting a solid object with volume into the liquid immersion tank (110) from the outside or lifting it from the inside when maintenance is required. This embodiment utilizes the same volume exclusion principle as the embodiment of FIG. 3, but is characterized by replacing the specific means of securing the volume with the expansion and contraction of a bladder (400) made of a flexible material that expands or contracts on its own through the variation of the internal air volume, rather than the mechanical insertion and withdrawal of a solid object. The bladder (400) may be formed of a flexible sealing membrane such as oil-resistant rubber or a thermoplastic polyurethane (TPU) film, and may be placed in an immersed state in the internal space of the liquid immersion tank (110), preferably at a location spaced apart from the suction port (210). The internal space of the bladder (400) is fluidly connected to an externally installed compressed air supply device (420) and an air supply and discharge line (410), and the injection of air into the bladder (400) and the discharge of air from the bladder (400) can be selectively controlled by opening and closing a valve provided on the air supply and discharge line (410).

[0063] In normal operating conditions, as described in FIG. 2, the siphon tube (200) must stably maintain an inactive state, so the bladder (400) according to the present embodiment is maintained in a contracted state of minimum volume with the internal air discharged as much as possible through the air supply and discharge line (410). In this state, the bladder (400) occupies only a negligible volume within the liquid immersion tank (110), so it does not substantially affect the formation of the normal maximum water level (510) or the cooling performance of the server (120).

[0064] When maintenance is required, the compressed air supply device (420) injects compressed air into the bladder (400) through the air supply and discharge line (410), causing the bladder (400), which is an elastic sealing membrane, to gradually expand and increase its external volume. As the bladder (400) expands, the water level in the immersion tank (110) rises by the volume of cooling oil (500) that is excluded. This rise in water level is designed to exceed the normal maximum water level (510) and reach the activation water level (520), which is above the highest point (220) of the siphon tube (200), as described in detail in FIG. 3. At this time, the volume of the bladder (400) at maximum expansion is calculated based on the horizontal cross-sectional area of ​​the immersion tank (110) and the height difference from the normal maximum water level (510) to the highest point (220), and it is preferable that the volume be designed to exceed the activation water level (520) in a fully expanded state. The priming and siphon activation mechanism at the moment when the water level reaches the activation level (520) and substantially exceeds the highest point (220) is the same as described in FIG. 3.

[0065] The bladder (400) is configured to penetrate the wall of the liquid immersion tank (110), and since its expansion and contraction can be controlled using only a relatively thin passage such as the air supply and discharge line (410), it is advantageous in terms of securing airtightness and simplifying the structure compared to lifting means that require a relatively large opening or mechanical penetration structure in the tank wall, such as the sliding rail or ceiling wire hoist of FIG. 3.

[0066] However, since the bladder (400) is made of a flexible sealing membrane that cannot maintain its shape on its own, there is a risk that if there is no separate restraining structure, the bladder (400) may be deflected upward toward the liquid immersion tank (110) by buoyancy during the expansion process, or that a portion of the upper side of the bladder (400) may penetrate the surface of the cooling oil (500) and be exposed to the atmosphere. If the upper surface of the bladder (400) is exposed above the water surface in this way, the expansion volume of the exposed portion no longer contributes to pushing out the cooling oil (500) and becomes an expansion that simply occupies volume in the air, so a discrepancy may occur between the target exclusion volume calculated during the design phase and the effective exclusion volume that actually contributes to the rise in the water level of the cooling oil (500), thereby reducing the predictability and reproducibility of reaching the activation level (520).

[0067] To prevent this, the system (100) according to the present embodiment may further include a restraining frame (430) made of a rigid material that surrounds the bladder (400) and is fixedly installed inside the liquid immersion tank (110). The restraining frame (430) is designed so that its upper end is positioned at a height lower than the normal maximum water level (510) by a predetermined margin, thereby physically restricting the upper surface of the bladder (400) from exceeding the upper height of the restraining frame (430) even when the bladder (400) expands to its maximum. With this configuration, the expansion direction of the bladder (400) is limited to the internal space defined by the restraining frame (430), that is, the underwater area that is always submerged in the cooling oil (500). As a result, the entire volume excluded by expansion contributes to the rise in the water level of the cooling oil (500), thereby ensuring that the cooling oil (500) reaches the triggering water level (520).

[0068] The restraining frame (430) may be formed as a rigid frame structure in the form of a grid or porous structure so as not to hinder the free flow of the cooling oil (500), thereby allowing the surrounding cooling oil (500) to freely enter and exit through the opening of the restraining frame (430) during the expansion and contraction process of the bladder (400). In addition, the restraining frame (430) may also serve a position fixing function by fixing the bladder (400) at a specific location within the liquid immersion tank (110), thereby preventing the bladder (400) from arbitrarily rising or flowing and moving to the vicinity of the intake port (210) or server (120) due to buoyancy.

[0069] Additionally, after priming is completed and drainage begins, the bladder (400) can contract by releasing the internal air again through the air supply and discharge line (410), thereby eliminating the volume it occupied around the suction port (210) in the same manner as the separation and retraction structure of the dummy block (300) described in FIG. 3, and thus preventing physical interference with the suction port (210) during drainage. In this case, it is desirable to design the placement location of the bladder (400) at a point sufficiently separated from the suction port (210) so that it does not encroach upon the flow cross-sectional area around the suction port (210) even in the expanded state.

[0070] FIG. 5 is a cross-sectional view showing the process of drainage after siphon activation and the state in which the siphon phenomenon self-stops when the water level reaches the height of the suction port, provided according to one embodiment of the present invention.

[0071] Hereinafter, with reference to FIG. 5, the process of drainage proceeding after the siphon is activated and the phenomenon in which the siphon phenomenon stops on its own when the water level reaches the height of the suction port (210) will be explained.

[0072] As previously described in FIGS. 3 and 4, once the water level reaches the activation level (520) by means of a trigger means and priming is completed, the subsequent drainage process itself no longer requires external active intervention such as a dummy block (300) or air pressure. That is, the siphon tube (200) according to the present invention, once the entire section from the intake port (210) to the outlet port (230) is filled with a continuous column of liquid, continues to flow on its own solely by the difference in water level between the intake port (210) and the outlet port (230) as long as the intake port (210) is submerged in the cooling oil (500), and continues to discharge the cooling oil (500) inside the liquid immersion tank (110) to the outside of the liquid immersion tank (110).

[0073] In order to substantially and completely drain the cooling oil (500) inside the liquid immersion tank (110), the geometric arrangement of the suction port (210) can be configured in various ways described below.

[0074] First, a flush arrangement method may be adopted in which the opening of the intake port (210) is placed on substantially the same plane as the inner bottom surface (111) of the tank. At this time, a minimum gap must be secured between the lower end of the opening of the intake port (210) and the inner bottom surface (111) of the tank so that the cooling oil (500) can flow in toward the intake port (210). Although this is the simplest structure, due to the height of the gap and the physical thickness and opening shape of the intake port (210) itself, the cooling oil (500) inside the liquid immersion tank (110) may not be completely discharged during the discharge process by the siphon phenomenon, and a small residual amount may structurally remain.

[0075] Second, a structure may be used in which the entire bottom surface (111) of the liquid immersion tank (110) is formed to slope gently toward the suction port (210), and the suction port (210) is positioned at the lowest point of the slope. In this method, the cooling oil (500) and sediment are naturally guided toward the suction port (210) by gravity, thereby minimizing the actual amount of residue at the end of drainage. FIG. 5 (a) shows an example in which the entire bottom surface (111) of the liquid immersion tank (110) is formed to slope gently toward the suction port (210).

[0076] Third, a multi-point suction nozzle method may be employed in which multiple low-position suction nozzles are distributed across the entire bottom surface (111). In this case, the suction port of each nozzle must be combined with the aforementioned flat bottom surface arrangement or sloped bottom water collection method in order to achieve the purpose of suctioning sediment across the entire bottom surface. At this time, the suction port (210) may be configured to include multiple nozzles distributed at different locations on the bottom surface (111), and a water collection header that combines the multiple nozzles into a single flow path of the siphon pipe (200).

[0077] Fourth, a recessed sump trap method may be adopted in which a portion of the bottom surface (111) is processed downwardly to form a separate recessed sump (112) and an intake port (210) is embedded inside the sump (112). This corresponds to an embodiment that can increase both the suction efficiency and the filtering efficiency of sediment by forming a localized pool structure where sediment naturally accumulates. Here, the sump (112) refers to a portion formed in the shape of a localized pool where cooling oil (500) naturally gathers at a position lower than the surrounding bottom surface (111) by locally processing a portion of the bottom surface (111) of the liquid immersion tank (110) downwardly to form a concave area. FIG. 5 (b) shows an example in which a portion of the bottom surface (111) is processed downwardly to form a separate recessed sump (112).

[0078] As the suction port (210) is located at the lowest point near the bottom surface (111), the sediment (sludge) that had settled at the bottom of the liquid immersion tank (110) during drainage is naturally transported toward the suction port (210) along with the cooling oil (500) and can be discharged through the outlet (230). This is based on the phenomenon in which the flow velocity increases locally near the suction port (210) while the siphon flow continues, and the fluid traction force formed accordingly draws sediment particles that had stagnated on the bottom surface (111) into the suction path. This is organically combined with the configuration of the external recovery tank (600) and filter (610) of FIG. 6 described later, providing a maintenance effect that not only discharges the cooling oil (500) but also removes the sediment.

[0079] As drainage continues, the water level inside the immersion tank (110) gradually decreases, and since the intake port (210) is located at the bottom surface (111) or the sump (112) nearby, this drainage can continue without interruption until the water level approaches the height of the bottom surface (111). And at the moment the water level reaches a self-stopping water level (530) corresponding to the physical location of the intake port (210), the system (100) according to the present invention is equipped with a structural safety device that terminates the drainage on its own without a separate control signal or valve operation. Specifically, when the water level reaches a limit where it can no longer decrease below the self-stopping water level (530), at least a portion of the intake port (210) begins to be exposed outside the surface of the cooling oil (500), and external air is introduced into the interior of the siphon tube (200) through this exposed opening. The incoming air interrupts the continuity of the liquid column that had been continuous from the intake port (210) to the outlet port (230) until then, and as a result, the hydrodynamic suction force is immediately eliminated, causing the siphon phenomenon to structurally stop immediately.

[0080] This self-stopping mechanism provides a termination mechanism corresponding to the priming mechanism described above in FIGS. 3 and 4. That is, while the initiation of drainage requires intentional intervention in the form of an active trigger from the outside (insertion of a dummy block or application of air pressure), the termination of drainage is automatically completed solely by static structural conditions, such as the geometric position of the intake port (210), without requiring any such active intervention. This provides operational convenience in that maintenance workers do not need to separately monitor the time of drainage termination or manually apply a stop signal, and at the same time, it functions as a safety device to prevent accident situations in which the immersion tank (110) is exposed to the air due to excessive drainage caused by valve malfunction or delay in control signals.

[0081] In addition, due to the configurational feature of FIG. 1 in which the intake port (210) is positioned close to the bottom surface (111), the amount of residual cooling oil (500) at the time of self-stopping can be minimized to the level of the physical dimensions of the intake port (210) itself, that is, the opening height of the intake port (210) and the extremely shallow puddle formed around it. This is a result that contrasts with the case where the intake port (210) is located at an arbitrary height separated from the bottom surface (111), in which a significant amount of the separated height remains undischarged.

[0082] FIG. 6 is a layout diagram showing the configuration of an external recovery tank (600) that recovers and filters cooling oil (500) discharged through a siphon tube (200) and reuses it, provided according to one embodiment of the present invention.

[0083] Since the insulating cooling oil (500) used for liquid immersion cooling is typically an expensive special fluid, it is necessary to recycle it instead of discarding it during maintenance. To recycle the cooling oil (500), an external recovery tank (600) fluidically connected to the outlet (230) of the siphon tube (200) is provided, and the discharged cooling oil (500) can be guided to this external recovery tank (600).

[0084] The external recovery tank (600) is a storage container installed independently below or adjacent to the liquid immersion tank (110), and is designed to have a volume capable of receiving the cooling oil (500) discharged from the outlet (230) via a drop or piping path. During the drainage process caused by the siphon activation, the cooling oil (500) flowing into the external recovery tank (600) may contain a significant amount of sediment (sludge) and other foreign substances that had settled on the bottom surface (111) or sump (112) of the liquid immersion tank (110) as described above. Accordingly, a filter (610) is provided inside the external recovery tank (600) according to the present invention, and the filter (610) is positioned on the path of the cooling oil (500) flowing into the external recovery tank (600) so that sediment and foreign substances are separated and collected as the incoming fluid passes through the filter (610). The above filter (610) can be designed in various ways, taking into account the filtration precision, material, and placement position of the cooling oil (500), the particle size of the expected precipitate, and the required level of purification, and multiple filters (610) having different filtration grades can be arranged in series or in parallel as needed.

[0085] In this way, the cooling oil (500), from which sediment and foreign substances have been removed by passing through the filter (610) within the external recovery tank (600), is stored inside the external recovery tank (600) in a purified state. After the replacement, inspection, or other maintenance work of the server (120) is completed, the system (100) according to the present invention can quickly restore the system (100) to its normal operating state prior to maintenance by supplying the stored and purified cooling oil (500) back to the liquid immersion tank (110) through the re-injection line (620). The re-injection line (620) is a separate piping path connecting the external recovery tank (600) and the liquid immersion tank (110), and can be implemented as either a natural gravity flow method using gravity drop or a forced pumping method using a separate transfer pump (301). Additionally, a separate water level detection means may be combined to check whether the water level has reached a target level during the re-injection process.

[0086] Through such a circulating configuration of recovery, filtering, and re-injection, the system (100) according to the present invention can minimize the amount of cooling oil (500) lost during each maintenance, while completing the entire maintenance process as a single closed-loop procedure.

[0087] FIG. 7 is a partial detail view showing a multi-point suction structure provided according to one embodiment of the present invention, wherein the suction port (210) is configured to include a plurality of nozzles (113) and a water collection header (114).

[0088] Figure 7 is a view looking down from above.

[0089] In the embodiment described above, if the suction port (210) is formed as a single opening, even if sediment is concentrated in a specific corner of the bottom surface (111) of the liquid immersion tank (110), the suction efficiency may be reduced if that point is spaced away from the suction port (210). To compensate for this, the suction port (210) according to the present embodiment is not a single opening, but is composed of a combination of a plurality of nozzles (1131, 1132, 1133, 1134, 1135) extending radially toward different locations on the bottom surface (111), and a collection header (114) that combines the cooling oil (500) and sediment sucked from the plurality of nozzles (113) into a single flow path.

[0090] Specifically, the plurality of nozzles (1131 to 1135) are formed in the form of a plurality of tubular arms extending radially from a central hub, and a loop-shaped opening for the inflow of cooling oil (500) and sediment may be provided at the end of each arm. As shown in FIG. 7, the plurality of nozzles (113) may have a multi-directional dispersion structure, thereby allowing sediment to be sucked in simultaneously across multiple areas of the bottom surface (111), unlike a suction port concentrated at a single point. A collection header (114) extends from the central hub where the plurality of nozzles (113) merge, and the collection header (114) performs the function of collecting the cooling oil (500) introduced through the plurality of nozzles (113) into a single flow path and delivering it to the siphon pipe (200).

[0091] Meanwhile, in a structure in which multiple nozzles (113) are connected in parallel to a single siphon tube (200) through a collection header (114), it is necessary to note that the continuous column of liquid extending from the intake port (210) to the outlet port (230) is a single path shared by all of the multiple nozzles (113). That is, if any of the openings of the multiple nozzles (113) are exposed first outside the surface of the cooling oil (500) and air is introduced, the entire siphon phenomenon can be stopped immediately, even if the remaining nozzles (113) are still submerged in the cooling oil (500). To prevent such premature cessation, it is preferable that the multiple nozzles (113) according to the present embodiment be positioned at substantially the same height from the bottom surface (111), thereby preventing the drainage of the entire system from ending prematurely by ensuring that a specific nozzle is exposed ahead of other nozzles while drainage is in progress.

[0092] In addition, it is desirable that the opening cross-sectional area of ​​each nozzle (113) be designed to a level that suppresses the phenomenon of air being sucked in before the liquid surface reaches the actual nozzle height due to a vortex that may occur near the opening while drainage is in progress. Furthermore, the water collection header (114) has a flow path shape that descends or ascends monotonically so that a local upward bending section is not formed from each of the plurality of nozzles (113) to the point of confluence with the siphon pipe (200), thereby preventing the formation of a separate air retention section or a local airlock inside the water collection header (114).

[0093] The combined structure of such multi-point suction nozzles (113) and water collection headers (114) can be applied in combination with the previously described floor surface coplanar arrangement, sloped floor water collection, or recessed sump (112) method. For example, the opening of each of the plurality of nozzles (113) may be formed on the same plane as the floor surface (111). Alternatively, a plurality of small sumps may be formed on the floor surface (111), and each nozzle (113) may be embedded within each small sump.

[0094] The embodiments described above do not require a separate drainage pump for draining the cooling oil (500) from the immersion tank (110), and therefore do not require a separate driving power for driving the drainage pump.

[0095] Using the embodiments of the present invention described above, those skilled in the art will be able to easily make various changes and modifications within the scope of the essential characteristics of the present invention. The content of each claim of the patent claims may be combined with other claims that are not related by reference within the scope of what can be understood from this specification.

Claims

Claim 1 An automatic drainage system (100) for maintenance of a liquid immersion cooling system, comprising: a liquid immersion tank (110) in which a server (120) and cooling oil (500) are contained; a suction port (210) located on or near the bottom surface of the liquid immersion tank, a peak (220) formed at a position higher than the normal water level during normal operation of the liquid immersion tank, and an outlet (230) for discharging cooling oil toward an external recovery tank (600), wherein when the water level of the cooling oil (500) is at the normal water level, air remains in the section reaching the peak to maintain an inactive state. An automatic drainage system comprising: an object (300) having a volume inserted into the interior of the liquid immersion tank (110), or a flexible sealing structure (400) that is immersed and disposed inside the liquid immersion tank (110) and expands as air is injected, and a trigger means for activating a siphon phenomenon by filling the interior of the siphon tube with cooling oil by raising the water level of the cooling oil in the liquid immersion tank to an activation water level (520) above the highest point. Claim 2 An automatic drainage system according to claim 1, wherein the siphon tube is characterized in that when the water level drops to a self-stopping water level that matches the height of the suction port while drainage is proceeding due to the activation, at least a part of the suction port is exposed outside the surface of the cooling oil, thereby automatically stopping the siphon phenomenon. Claim 3 An automatic drainage system according to claim 1, further comprising: a recovery tank (600) that receives cooling oil discharged in fluidic communication with the outlet and is equipped with a filter (610) inside to separate sediment and foreign substances mixed in the cooling oil. Claim 4 An automatic drainage system according to claim 1, configured to move the object in a direction separated from the suction port after the siphon phenomenon is triggered and before the drainage of the cooling oil is completed. Claim 5 An automatic drainage system according to claim 1, further comprising a restraining frame (430) fixedly installed inside the liquid immersion tank, wherein the elastic sealing structure is coupled to the restraining frame and its vertical position is restricted so that even when expanded by the inflow of air, part or all of the elastic sealing structure does not float above the surface of the cooling oil. Claim 6 An automatic drainage system according to claim 5, further comprising: an air supply and discharge line (410) connected to the elastic sealing structure to supply or discharge air; and a compressed air supply device (420) connected to the air supply and discharge line, wherein when the water level of the cooling oil is at the normal water level, the air inside the elastic sealing structure is discharged so that the elastic sealing structure maintains a contracted state. Claim 7 An automatic drainage system according to paragraph 2, wherein the bottom surface is formed to be inclined toward the suction port, and the opening of the suction port is positioned at the lowest point of the inclined bottom surface. Claim 8 An automatic drainage system according to paragraph 2, characterized in that a sump (112) is formed locally concavely on the bottom surface, and the opening of the suction port is embedded within the sump. Claim 9 An automatic drainage system according to paragraph 2, wherein the suction port comprises a plurality of nozzles (113) distributed at different locations on the bottom surface and a collection header (114) that combines the plurality of nozzles into a single flow path of the siphon tube. Claim 10 An automatic drainage system according to claim 9, characterized in that the openings of the plurality of nozzles are arranged to be located at the same absolute height relative to each other with respect to the vertical direction. Claim 11 An automatic drainage system further comprising, in paragraph 3, a re-injection line (620) connecting the recovery tank and the liquid immersion tank and re-supplying the cooling oil purified through the filter to the liquid immersion tank. Claim 12 A method for draining a liquid immersion cooling system using an automatic drainage system comprising: a liquid immersion tank containing a server and cooling oil; a siphon tube including an intake port located within the liquid immersion tank, a peak formed at a position higher than the normal water level during normal operation of the liquid immersion tank, and an outlet for discharging cooling oil toward an external recovery tank; and a recovery tank; wherein the method comprises: a trigger step of raising the water level of the cooling oil to an activation water level above the peak by inserting an object having volume into the liquid immersion tank or by injecting air into a flexible sealing structure immersed within the liquid immersion tank; a priming step in which, as the water level rises above the peak, air remaining in the section reaching the peak is extruded toward the outlet port and the interior of the siphon tube is filled with cooling oil, thereby activating a siphon phenomenon; and a drainage step in which the cooling oil inside the liquid immersion tank is discharged to the recovery tank by the difference in water level between the intake port and the outlet port while the intake port is submerged in cooling oil. A drainage method for an immersion cooling system comprising: a self-stopping step in which the siphon phenomenon is automatically stopped as the water level of the cooling oil reaches a self-stopping water level that matches the height of the suction port. Claim 13 A method for draining a liquid immersion cooling system according to claim 12, wherein the automatic drainage system further comprises a transfer pump and a re-injection line, the recovery tank is equipped with a filter for purifying the cooling oil flowing into the recovery tank, and in the drainage step, the cooling oil discharged in the drainage step passes through the filter to separate precipitates and foreign substances mixed in the cooling oil, and after the self-stopping step, the method further comprises a re-injection step of supplying the cooling oil stored in the recovery tank back to the liquid immersion tank through the transfer pump and the re-injection line.

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