Offshore wind turbine two-phase immersion cooling system utilizing natural wind-seawater step source cold sink

Abstract

The application discloses a natural wind-seawater step-by-step cold source utilization offshore wind turbine two-phase immersion cooling system and belongs to the technical field of wind power generation converter heat dissipation. The system comprises a sealed immersion cavity, a first air-cooled condenser, a second seawater condenser, a steam pipeline, a descending dry pipe, a liquid return pipeline and an auxiliary circulation assembly. IGBT modules are immersed in liquid insulation coolant, heat absorption boiling generates steam, the steam enters the first air-cooled condenser to utilize offshore natural wind for first-stage condensation, the condensed liquid after first-stage condensation and uncondensed steam enter the second seawater condenser through the descending dry pipe, the second seawater condenser takes seawater as a cold source and is isolated from the insulation cooling working medium to exchange heat, so that the uncondensed steam is secondarily condensed and the liquid is supercooled. The supercooled liquid insulation coolant returns to the sealed immersion cavity through the liquid return pipeline. The application can reduce external power dependence, avoid seawater contact with the loop working medium and improve the reliability of offshore wind turbine converter heat dissipation.

Description

Technical Field

[0001] This invention belongs to the field of heat dissipation technology for wind power converters, specifically involving a two-phase immersion cooling system for offshore wind turbines utilizing natural wind and seawater as a secondary cold source. Background Technology

[0002] As the capacity of offshore wind turbines continues to increase, the current specifications and switching losses of the IGBT modules in wind power converters are also increasing. During operation, the heat generated by the IGBT modules is concentrated in the chip, solder layer, substrate, and base plate areas. When this heat cannot be dissipated in time, the increased junction temperature can cause solder layer fatigue, insulation aging, and thermal cycling failure, affecting the stable operation of the wind power converter.

[0003] Existing wind power converters mostly employ forced air cooling, single-phase liquid cooling, or centralized liquid cooling structures. Forced air cooling structures have lower heat transfer coefficients and are susceptible to salt spray and dust deposition. Single-phase liquid cooling structures require heat transfer through cold plates, thermal interface materials, and liquid circulation loops, resulting in a longer thermal resistance chain and a tendency to generate localized hot spots under high heat flux density conditions. Centralized liquid cooling structures typically rely on pumps, valves, and external heat exchangers for continuous operation, leading to significant auxiliary power consumption and maintenance workload. For offshore wind turbines, the maintenance window is limited by sea state, vessel conditions, and weather conditions; cooling system failures directly amplify downtime losses.

[0004] Two-phase immersion cooling allows IGBT modules to be directly submerged in liquid insulating coolant. The liquid insulating coolant boils on the surface of the IGBT module and utilizes its latent heat of vaporization to dissipate heat, resulting in strong heat exchange capacity and good temperature uniformity. A two-phase immersion cooling system not only requires stable boiling but also continuous condensation and reflux of the vapor generated during boiling. If vapor condensation is insufficient or liquid reflux is unstable, the pressure within the sealed immersion chamber will increase, the liquid level will fluctuate, and both the immersion and boiling states of the IGBT module will be affected.

[0005] Offshore wind turbines utilize both natural wind and seawater cooling sources. Natural wind cooling eliminates the need for seawater extraction, but significant variations in wind speed and temperature can lead to insufficient condensation capacity under conditions of high summer temperatures, low wind speeds, or calm winds. Seawater cooling offers relatively stable temperatures and a large heat capacity, but directly extracting seawater into the nacelle heat exchanger poses risks of corrosion, biofouling, filter maintenance, and leaks. Relying on seawater pumps for long-term operation increases energy consumption and potential failure points. Therefore, the core challenge of two-phase immersion cooling for offshore wind turbines lies in balancing the need to utilize both natural wind and seawater cooling sources with the need to prevent seawater from directly entering the closed working fluid loop, while also minimizing continuous mechanical operation. Summary of the Invention

[0006] The purpose of this invention is to provide a two-phase submerged cooling system for offshore wind turbines that utilizes a natural wind-seawater staged cold source, in order to solve the problems of unstable condensation by single natural wind in existing offshore wind power converter cooling systems, easy corrosion and fouling by direct seawater heat exchange, high energy consumption of continuous mechanical drive, and unstable return flow of two-phase submerged cooling.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] The two-phase immersion cooling system for offshore wind turbines utilizing a natural wind-seawater staged cold source includes a sealed immersion chamber, a primary air-cooled condenser, a secondary seawater condenser, steam piping, downcomer pipes, liquid return piping, and auxiliary circulation components.

[0009] The sealed immersion cavity is installed inside the nacelle of the offshore wind turbine and houses the IGBT module of the wind power converter and the liquid insulating coolant.

[0010] The steam pipeline connects the sealed immersion cavity to the primary air-cooled condenser, allowing the steam generated by the boiling of the liquid insulating coolant to enter the primary air-cooled condenser for natural air condensation.

[0011] The downcomer connects the primary air-cooled condenser to the secondary seawater condenser, allowing the condensate and uncondensed vapor from the primary condenser to enter the secondary seawater condenser.

[0012] The secondary seawater condenser uses seawater as a cold source and is isolated from the insulating cooling medium for heat exchange. It is used to perform secondary condensation on the uncondensed steam and to subcool the condensate. The insulating cooling medium is a general term for the liquid insulating cooling liquid and its steam.

[0013] The liquid return pipeline connects the secondary seawater condenser to the sealed immersion chamber;

[0014] The sealed immersion chamber, the primary air-cooled condenser, the secondary seawater condenser, the steam pipeline, the downcomer, and the liquid return pipeline together form a closed working fluid loop. The thermosiphon head, used to drive the passive circulation of the closed working fluid loop, is generated by the height difference of the offshore wind turbine tower and the density difference between the subcooled pure liquid column in the liquid return pipeline and the vapor-liquid two-phase mixture in the downcomer. The auxiliary circulation component is located in the liquid return pipeline and is used to supplement the circulation head when the circulation flow rate is lower than a preset flow rate threshold.

[0015] As a preferred embodiment of the present invention, the liquid insulating coolant is a hydrofluoroether-based insulating coolant, the atmospheric boiling point of the liquid insulating coolant is at least 40K lower than the maximum allowable junction temperature of the IGBT module, and the saturation pressure of the liquid insulating coolant at a condensation temperature of 28°C to 35°C does not exceed 0.3MPa gauge pressure.

[0016] Furthermore, the substrate surface of the IGBT module is provided with a boiling enhancement structure, which includes a trench structure and a porous metal layer disposed on the surface of the trench structure. Under the design working pressure and static liquid level conditions of the liquid insulating coolant, the boiling enhancement structure ensures that the critical heat flux density corresponding to the IGBT module is not less than 1.8 times the peak heat flux density of the IGBT module.

[0017] The sealed immersion chamber is equipped with a steam space and a mesh-type demister. The steam space is located above the free surface of the liquid insulating coolant, and the mesh-type demister is positioned between the free surface and the steam outlet of the sealed immersion chamber, ensuring that the amount of liquid droplets carried by the steam entering the steam pipeline is less than 1% by mass under rated operating conditions. The sealed immersion chamber is equipped with a liquid level sight glass, and the static liquid level of the liquid insulating coolant is configured to completely immerse the IGBT module and maintain a liquid layer of at least 50 mm above the boiling enhancement structure at the static liquid level.

[0018] As a preferred embodiment of the present invention, the primary air-cooled condenser is installed on the windward side of the top or side of the nacelle of the offshore wind turbine. The primary air-cooled condenser includes an inlet header, an outlet header, and multiple rows of parallel finned tube bundles. The air inlet surface of the fins of the multiple rows of parallel finned tube bundles is passively oriented towards the incoming flow direction as the offshore wind turbine yaws. The outlet header is connected to the downcomer pipe.

[0019] As a preferred embodiment of the present invention, the downcomer pipe is laid downward along the inner wall of the offshore wind turbine tower. The downcomer pipe is inclined downward along the flow direction of the condensate and uncondensed steam after the first stage of condensation, with an angle of not less than 5° with the horizontal plane, so that the condensate and uncondensed steam can flow smoothly downward under the action of gravity and avoid liquid accumulation. A gas-liquid separation buffer chamber is provided between the downcomer pipe and the second-stage seawater condenser. The gas-liquid separation buffer chamber has an inlet, a steam outlet, and a condensate outlet. The inlet is connected to the downcomer pipe. The second-stage seawater condenser is divided into a condensation section and a subcooling section along the flow direction of the working fluid. The condensation section is located upstream and is used to condense the uncondensed steam. The subcooling section is located downstream and is used to subcool the condensate. The outlet of the condensation section is connected to the subcooling section, so that the liquid formed by the condensation of the uncondensed steam in the condensation section enters the subcooling section. The steam outlet is connected to the condensation section, and the condensate outlet is connected to the subcooling section.

[0020] As a preferred embodiment of the present invention, when the offshore wind turbine adopts a monopile foundation, the secondary seawater condenser includes a serpentine tube bundle submerged in seawater. The serpentine tube bundle is fixed to the outer wall of the underwater section of the monopile foundation by a segmented, assembled arc-shaped jacket. A heat-conducting filling layer is provided between the segmented, assembled arc-shaped jacket and the outer wall of the underwater section of the monopile foundation. The interior of the serpentine tube bundle is connected to the closed working fluid loop, and the exterior of the serpentine tube bundle is in contact with seawater.

[0021] As a preferred technical solution of the present invention, when the offshore wind turbine adopts a jacket foundation or a floating foundation, the secondary seawater condenser includes a shell-and-tube heat exchanger, the tube side of the shell-and-tube heat exchanger is connected to the closed working fluid loop, the shell side of the shell-and-tube heat exchanger is connected to seawater, the seawater inlet and outlet of the shell side is provided with Venturi guide pipes, and a turbulence vortex generator is provided inside the shell side.

[0022] Furthermore, the thermosiphon pressure head satisfies the following relationship:

[0023]

[0024] in, The effective vertical height difference between the outlet of the secondary seawater condenser and the free liquid surface within the sealed submerged cavity. The average density of the subcooled pure liquid column in the liquid reflux pipeline. The average density of the vapor-liquid two-phase mixture in the downcomer pipe. It is the acceleration due to gravity. The total pressure drop of the closed working fluid loop under the design heat load is denoted as .

[0025] As a preferred embodiment of the present invention, the auxiliary circulation assembly includes a shielded magnetically driven circulation pump, a one-way bypass valve, and isolation valves disposed at both ends of the shielded magnetically driven circulation pump. The one-way bypass valve is connected in parallel with the shielded magnetically driven circulation pump. The one-way bypass valve only allows the liquid insulating coolant to flow from the secondary seawater condenser to the sealed immersion chamber. When the shielded magnetically driven circulation pump stops working, the liquid insulating coolant flows back through the one-way bypass valve. When the shielded magnetically driven circulation pump starts, it provides additional pressure head to the liquid return pipeline.

[0026] As a preferred embodiment of the present invention, a bellows compensator is provided in parallel via a bypass pipe on the sealed submerged cavity or on the steam pipeline; the bellows compensator is connected to the steam space of the sealed submerged cavity via the bypass pipe, or connected to the steam pipeline via the bypass pipe; the bellows compensator has a pre-charge pressure and a variable volume, the variable volume being used to absorb the volume expansion of the liquid insulating coolant during temperature changes; a pressure relief valve is provided at the top of the sealed submerged cavity, and the exhaust port of the pressure relief valve is led to a safe location outside the nacelle of the offshore wind turbine via a discharge pipe.

[0027] As a preferred embodiment of the present invention, it further includes a monitoring and control unit, which is connected to a pressure sensor, a liquid level sensor, a flow sensor, an IGBT module temperature sensor, a natural wind speed sensor, and a seawater temperature sensor, respectively. The monitoring and control unit is used to start the shielded magnetic drive circulation pump when the circulating flow rate is lower than a preset flow rate threshold and the pressure in the sealed immersion chamber is higher than a preset auxiliary start-up pressure threshold, and to output a load reduction command to the wind power converter when the liquid level is lower than the minimum safe immersion level or the pressure in the sealed immersion chamber is higher than a preset pressure over-limit threshold; the preset pressure over-limit threshold is higher than the preset auxiliary start-up pressure threshold.

[0028] This invention also discloses a two-phase immersion cooling control method for offshore wind turbines utilizing a natural wind-seawater staged cold source, applied to the two-phase immersion cooling system for offshore wind turbines utilizing the natural wind-seawater staged cold source as described above. The control method includes:

[0029] The IGBT module is immersed in the liquid insulating coolant in the sealed immersion cavity, and the liquid insulating coolant absorbs the heat of the IGBT module and boils to generate steam.

[0030] The steam is introduced into the primary air-cooled condenser through the steam pipeline, and the steam is condensed in the primary stage using natural sea winds.

[0031] The condensate and uncondensed vapor after primary condensation are introduced into the gas-liquid separation buffer chamber through the downcomer. In the gas-liquid separation buffer chamber, the uncondensed vapor and the condensate are separated, so that the uncondensed vapor enters the condensation section of the secondary seawater condenser and the condensate enters the subcooling section of the secondary seawater condenser.

[0032] The uncondensed vapor is condensed in the condensation section using seawater as a cold source, and the condensed liquid is then subcooled in the subcooling section.

[0033] The supercooled liquid insulating coolant is returned to the sealed immersion cavity via the liquid return pipeline;

[0034] The thermosiphon pressure head formed by the density difference between the subcooled pure liquid column in the liquid reflux pipeline and the vapor-liquid two-phase mixture in the downcomer pipe, as well as the height difference of the tower, drives the closed working fluid loop to perform passive circulation.

[0035] The system collects data on circulating flow rate, sealed immersion chamber pressure, liquid level, and IGBT module temperature. When the circulating flow rate is lower than the preset flow rate threshold and the sealed immersion chamber pressure is higher than the preset auxiliary start-up pressure threshold, the auxiliary circulation component is activated. The system stops when the circulating flow rate recovers to above the preset flow rate threshold and the sealed immersion chamber pressure is lower than the preset auxiliary start-up pressure threshold. When the liquid level is lower than the minimum safe immersion level or the sealed immersion chamber pressure is higher than the preset pressure over-limit threshold, the load on the wind power converter is reduced.

[0036] Furthermore, the present invention also discloses an offshore wind turbine generator set, including a tower, a nacelle, a wind power converter, and an offshore wind turbine two-phase submerged cooling system utilizing a natural wind-seawater staged cold source as described above. The sealed submerged cavity is disposed inside the nacelle, the primary air-cooled condenser is disposed outside the nacelle, the secondary seawater condenser is disposed in the underwater section of the foundation structure of the offshore wind turbine generator set or at the connection point of the foundation structure, and the IGBT module of the wind power converter is disposed inside the sealed submerged cavity and cooled by the offshore wind turbine two-phase submerged cooling system utilizing a natural wind-seawater staged cold source.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] This invention utilizes natural wind cooling and seawater cooling in series according to condensation stages. The primary air-cooled condenser handles normal steam condensation, while the secondary seawater condenser handles secondary condensation of non-condensed steam and liquid subcooling. The system can adapt to fluctuations in natural wind speed and ambient temperature. A thermosiphon pressure head is established using the tower height difference and working fluid density difference of the offshore wind turbine, enabling the closed working fluid loop to primarily operate in a passive circulation mode. Compared to continuous pump-driven circulation, the system has lower auxiliary energy consumption and shorter operating time for rotating components. The insulating cooling working fluid circulates within the closed working fluid loop and exchanges heat with seawater through the secondary seawater condenser, preventing seawater from entering the closed working fluid loop and causing corrosion, biofouling, and coolant contamination.

[0039] Furthermore, this invention uses the gas-liquid separation buffer chamber to separate the uncondensed steam and condensate after the first-stage condensation, allowing the uncondensed steam to enter the condensation section and the condensate to enter the subcooling section, thus making the condensation and subcooling processes of the second-stage seawater condenser more stable. The auxiliary circulation assembly forms an intermittent auxiliary circulation structure, which can replenish the circulation head under extreme conditions and maintain passive reflux under normal conditions. The steam space, mesh-type demister, bellows compensator, pressure relief valve, liquid level monitoring, and load reduction control create a safety boundary, suitable for long-term operation of offshore wind turbines. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0041] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0042] Figure 2 This is a diagram of the overall system architecture described in this invention.

[0043] Figure 3 This is a flowchart illustrating the cooling cycle principle of the present invention.

[0044] Attached reference numerals: 101 Tower, 102 Nacelle, 103 Monopile Foundation, 104 Primary Air-Cooled Condenser, 105 Secondary Seawater Condenser, 106 Steam Pipeline. Detailed Implementation

[0045] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0046] The following is in conjunction with the appendix Figures 1-3 The embodiments of the present invention will be described in detail below.

[0047] Example 1: This example provides a two-phase submerged cooling system for an offshore wind turbine using a natural wind-seawater staged cold source for a monopile foundation 103. The offshore wind turbine includes a tower 101, a nacelle 102, a monopile foundation 103, and a wind power converter. The wind power converter, which includes an IGBT module, is located within the nacelle 102. The cooling system includes a sealed submerged cavity, a primary air-cooled condenser 104, a secondary seawater condenser 105, a steam pipeline 106, a downcomer, a liquid return pipeline, and auxiliary circulation components.

[0048] The sealed immersion cavity is fixed to a support frame within the cabin 102 and has a shell, cover, seals, and flange interface capable of withstanding saturated vapor pressure. The cavity is filled with a hydrofluoroether-based liquid insulating coolant. Preferably, the atmospheric boiling point of the liquid insulating coolant is at least 40K lower than the maximum permissible junction temperature of the IGBT module, and the corresponding saturation pressure at a condensation temperature of 28°C to 35°C does not exceed 0.3 MPa gauge pressure, ensuring that the liquid insulating coolant boils within a safe junction temperature range while the system pressure remains within an engineeringly achievable range.

[0049] The IGBT module is fixed in the sealed immersion cavity by insulating supports and is completely immersed in the liquid insulating coolant. Its electrical connection terminals are led out through a sealed electrical connection structure. A boiling enhancement structure is provided on the substrate surface, including a trench structure processed on the substrate surface and a porous metal layer covering the trench structure surface. The trench structure forms a liquid supply channel, and the porous metal layer provides vaporization nucleation sites. Under the design operating pressure and static liquid level conditions, the boiling enhancement structure ensures that the critical heat flux density is not less than 1.8 times the peak heat flux density, guaranteeing that it remains within the safe range of nucleation boiling under peak heat load.

[0050] The sealed immersion chamber contains a steam space and a mesh-type demister. A free surface is formed on the upper surface of the liquid insulating coolant within the chamber. The steam space is located above this free surface, accommodating and buffering the steam generated during boiling. The mesh-type demister is positioned between the free surface and the top steam outlet. As steam passes through the mesh-type demister, it carries droplets that coalesce and fall back, ensuring that the amount of droplets carried by the steam entering the steam pipe 106 under rated operating conditions is less than 1% by mass. A liquid level sight glass is installed on the side wall. After filling, the static liquid level ensures the IGBT module is completely submerged, and a liquid layer of at least 50 mm is maintained above the boiling enhancement structure at the static liquid level.

[0051] The top steam outlet is connected to steam pipe 106, which extends out of the outer cover of engine room 102 and connects to the steam inlet header of the first-stage air-cooled condenser 104. An insulation layer is installed on the outside of steam pipe 106 to prevent the formation of liquid accumulation low points.

[0052] The primary air-cooled condenser 104 is installed on the windward side of the top or side of the nacelle 102 outer casing, and includes an inlet header, an outlet header, and multiple rows of parallel finned tube bundles. The finned inlet surface is passively oriented towards the incoming flow direction by yaw of the nacelle 102, maintaining windward heat exchange through yaw action. The multiple-row parallel structure reduces flow resistance and increases the heat exchange area.

[0053] During operation, the IGBT module generates heat, and the liquid insulating coolant boils on the surface of the boiling enhancement structure to produce steam. The steam passes through the mesh-pad demister and steam pipeline 106 into the primary air-cooled condenser 104, where it undergoes primary condensation using natural sea winds. The condensate and uncondensed steam after primary condensation mix and flow into the downcomer.

[0054] The downcomer pipe is laid downwards along the inner wall of tower 101, inclined downwards in the direction of condensate and uncondensed vapor flow, with an angle of not less than 5° to the horizontal plane, to ensure that condensate and uncondensed vapor flow smoothly downwards under gravity and avoid liquid accumulation. The pipe diameter is determined according to the vapor-liquid flow rate under the design heat load, so that the vapor-liquid flow in the pipe is in a continuous drainage state. A sealable liquid collection and drain outlet is provided at the lowest point.

[0055] A gas-liquid separation buffer chamber is provided between the downcomer and the secondary seawater condenser 105, having an inlet, a steam outlet, and a condensate outlet. The inlet is connected to the downcomer. The secondary seawater condenser 105 is divided into a condensation section and a subcooling section along the working fluid flow direction. The condensation section is located upstream, and the subcooling section is located downstream. The outlet of the condensation section is connected to the subcooling section. The steam outlet is connected to the condensation section, and the condensate outlet is connected to the subcooling section. After the condensate and uncondensed steam enter the gas-liquid separation buffer chamber, the condensate enters the subcooling section through the condensate outlet, and the uncondensed steam enters the condensation section through the steam outlet, thus achieving flow separation.

[0056] In the embodiment of the monopile foundation 103, the secondary seawater condenser 105 is a serpentine tube bundle submerged in seawater, arranged circumferentially along the outer wall of the underwater section of the monopile foundation 103, and fixed by a segmented, assembled arc-shaped jacket. A thermally conductive filling layer is provided between the jacket and the outer wall of the foundation, using thermally conductive putty, thermally conductive silicone grease, or a flexible thermally conductive material with thermally conductive gap-filling function. The outer wall of the foundation serves as an installation support structure and can assist in heat conduction. The interior of the serpentine tube bundle is connected to the closed working fluid loop, while the exterior is in contact with seawater. The insulating cooling working fluid and seawater exchange heat through the tube wall.

[0057] The condensing section receives uncondensed steam and condenses it inside the pipe. The condensate and the condensate from the gas-liquid separation buffer chamber enter the subcooling section together and continue to release heat to the seawater, forming a subcooled liquid insulating coolant.

[0058] The liquid return pipeline connects the outlet of the secondary seawater condenser 105 to the sealed submerged cavity, and extends upwards along the inner wall of the tower 101 to the return chamber 102. An external insulation layer is installed, and the outlet connects to the return port below the static liquid level. The downcomer contains a vapor-liquid two-phase mixture, while the liquid return pipeline contains a subcooled pure liquid column. The latter has a higher average density than the former. Combined with the effective vertical height difference between the outlet of the secondary seawater condenser 105 and the free liquid surface, a thermosiphon pressure head is formed, satisfying the relationship described above. During the design, the installation height, free liquid surface height, and pipe diameter are determined to ensure that the thermosiphon pressure head overcomes the total pressure drop of the entire loop under the design heat load.

[0059] An auxiliary circulation assembly is installed in the liquid return pipeline, including a shielded magnetically driven circulation pump, a one-way bypass valve, and an isolation valve. The one-way bypass valve only allows liquid insulating coolant to flow from the secondary seawater condenser 105 to the sealed submerged chamber. When the shielded magnetically driven circulation pump stops, the working fluid passively returns via the one-way bypass valve; during startup, it provides additional pressure head.

[0060] A bellows compensator is connected in parallel to the sealed submerged cavity or steam pipeline 106 via a bypass pipeline, which is connected to the steam space or steam pipeline 106 to absorb the volume expansion caused by temperature changes through variable volume. A pressure relief valve is installed at the top of the sealed submerged cavity, and the exhaust port is led to the outside of the engine room 102 through an exhaust pipeline.

[0061] The monitoring and control unit is located inside the engine compartment 102 and connected to all sensors. The preset flow rate threshold is determined based on the minimum liquid return flow rate required to maintain safe submerged boiling under the designed heat load. The preset auxiliary start-up pressure threshold is determined based on the saturation pressure at the designed condensation temperature and the allowable operating pressure. The preset pressure over-limit threshold is higher than the preset auxiliary start-up pressure threshold but lower than the pressure relief valve setting pressure. The minimum safe submersion level is the lowest liquid level that ensures complete submersion and a safe liquid layer above the boiling enhancement structure.

[0062] During installation, the following steps are performed sequentially: fixing the sealed immersion chamber, installing the IGBT module, connecting the primary air-cooled condenser 104, laying the downcomer and liquid return pipeline, installing the gas-liquid separation buffer chamber and the serpentine tube bundle, and connecting all interfaces. During filling, a sealing check is performed first, followed by vacuuming and filling with a predetermined amount of liquid insulating coolant to the designed static liquid level.

[0063] When the system is running, the IGBT module generates heat, and the liquid insulating coolant boils to produce steam. After primary condensation by the first-stage air-cooled condenser 104, the condensate and uncondensed steam enter the gas-liquid separation buffer chamber through the downcomer. The uncondensed steam is condensed by seawater in the condensation section, and the condensate is subcooled in the subcooling section. The subcooled working fluid returns to the sealed immersion chamber through the liquid return pipeline, completing the passive circulation.

[0064] Example 2: This example illustrates the auxiliary circulation control process under extreme low wind speed and high temperature conditions. The hardware adopts the system of Example 1, and the monitoring and control unit continuously collects circulation flow rate, sealed immersion chamber pressure, liquid level status, and IGBT module temperature. Each parameter is obtained by a flow sensor installed in the liquid return pipeline, a pressure sensor at the top of the chamber or near the steam pipeline 106, a liquid level sensor on the side wall of the chamber, and an IGBT module temperature sensor, respectively.

[0065] Under normal conditions, the circulation flow rate is not lower than the preset flow rate threshold, the thermosiphon pressure head drives passive circulation, and the auxiliary circulation component stops. When the wind speed decreases or the temperature rises, causing the primary condensation capacity to decrease, the circulation flow rate falls below the preset flow rate threshold, and the pressure in the sealed immersion chamber exceeds the preset auxiliary start-up pressure threshold, it is determined that the thermosiphon pressure head is insufficient, and the monitoring and control unit starts the auxiliary circulation component to provide additional pressure head.

[0066] The auxiliary circulation component adopts an intermittent start-up mode. After startup, continuous monitoring is performed. When the circulation flow rate recovers to above the preset flow rate threshold and the pressure in the sealed immersion chamber drops below the preset auxiliary start-up pressure threshold, the auxiliary circulation component is stopped, and passive reflux is restored.

[0067] If the pressure continues to rise after the shielded magnetic drive circulating pump starts and reaches the preset pressure over-limit threshold, or if the IGBT module temperature approaches the temperature protection threshold, the monitoring and control unit outputs a load reduction command to reduce the converter output power or IGBT module switching losses. If the liquid level is below the minimum safe immersion level, the load is directly reduced and the abnormality is recorded. If the pressure continues to rise to the pressure relief valve's set pressure, the valve opens to release pressure.

[0068] The control logic is as follows: Collect parameters and compare the circulating flow rate with a preset flow rate threshold and the sealed immersion chamber pressure with a preset auxiliary start pressure threshold; start the auxiliary circulation component when both conditions are met; stop after the flow rate recovers and the pressure drops; reduce the load when the liquid level is abnormal, the pressure exceeds the limit, or the temperature is too high. The above control logic is hierarchical, with each step based on the judgment result of the previous step.

[0069] Example 3: The difference between this example and Example 1 is that the secondary seawater condenser 105 adopts a shell-and-tube heat exchanger, which is fixed on the basic structural components.

[0070] The tube side of the shell-and-tube heat exchanger is connected to the closed working fluid loop, while the shell side is connected to seawater. The tube inlet is connected to the gas-liquid separation buffer chamber, and the outlet is connected to the liquid return pipeline. The tube side is divided into a condensing section and a subcooling section, with the condensing section outlet connected to the subcooling section. Uncondensed steam enters the condensing section, and condensate enters the subcooling section, isolating the seawater in the shell side from the working fluid in the tube side for heat exchange.

[0071] Venturi guide tubes are installed at the seawater inlet and outlet of the shell side, with their axis intersecting or aligning with the dominant tidal current direction. The reciprocating water flow caused by waves and currents generates pulsating pressure differentials as it passes through the contraction, throat, and expansion sections, promoting seawater flow. Turbulence vortex generators are installed in the flow channels outside the inner tube bundle of the shell side, spaced apart along the direction of seawater flow, to enhance near-wall disturbance and heat transfer.

[0072] This embodiment retains the core structure and control logic of the closed working fluid loop. The insulating cooling fluid circulates within the loop, while seawater only enters the shell side, and the two do not come into contact. The supercooled liquid insulating coolant returns to the sealed immersion cavity via the liquid return pipeline, forming a density difference with the vapor-liquid two-phase mixture in the downcomer pipe, thus maintaining the thermosiphon circulation.

[0073] The two-phase immersion cooling system and control method for offshore wind turbines utilizing a natural wind-seawater staged cold source provided by this invention can be applied to the cooling of wind power converters in offshore wind turbine generator sets. The system utilizes external natural wind from the nacelle 102 for primary condensation, and seawater for secondary condensation and subcooling. A thermosiphon pressure head is formed by the height difference of the tower 101, and intermittent auxiliary circulation is provided under extreme operating conditions through auxiliary circulation components. The insulating cooling medium is always kept closed within the loop and does not come into contact with seawater, reducing the risk of corrosion and fouling.

[0074] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A two-phase immersion cooling system for offshore wind turbines utilizing a natural wind-seawater staged cold source, characterized in that, It includes a sealed immersion chamber, a primary air-cooled condenser, a secondary seawater condenser, steam piping, downcomer pipes, liquid return piping, and auxiliary circulation components; The sealed immersion cavity is installed inside the nacelle of the offshore wind turbine and houses the IGBT module of the wind power converter and the liquid insulating coolant. The steam pipeline connects the sealed immersion cavity to the primary air-cooled condenser, allowing the steam generated by the boiling of the liquid insulating coolant to enter the primary air-cooled condenser for natural air condensation. The downcomer connects the primary air-cooled condenser to the secondary seawater condenser, allowing the condensate and uncondensed vapor from the primary condenser to enter the secondary seawater condenser. The secondary seawater condenser uses seawater as a cold source and is isolated from the insulating cooling medium for heat exchange. It is used to perform secondary condensation of the uncondensed steam and to subcool the condensate. The insulating cooling medium is a general term for the liquid insulating cooling liquid and its steam. The liquid return pipeline connects the secondary seawater condenser to the sealed immersion chamber; The sealed immersion chamber, the primary air-cooled condenser, the secondary seawater condenser, the steam pipeline, the downcomer, and the liquid return pipeline together form a closed working fluid loop. The thermosiphon head, used to drive the passive circulation of the closed working fluid loop, is generated by the height difference of the offshore wind turbine tower and the density difference between the subcooled pure liquid column in the liquid return pipeline and the vapor-liquid two-phase mixture in the downcomer. The auxiliary circulation component is located in the liquid return pipeline and is used to supplement the circulation head when the circulation flow rate is lower than a preset flow rate threshold.

2. The two-phase immersion cooling system for offshore wind turbines utilizing a natural wind-seawater staged cold source as described in claim 1, characterized in that, The liquid insulating coolant is a hydrofluoroether-based insulating coolant. The atmospheric boiling point of the liquid insulating coolant is at least 40K lower than the maximum allowable junction temperature of the IGBT module, and the saturation pressure of the liquid insulating coolant at a condensation temperature of 28°C to 35°C does not exceed 0.3MPa gauge pressure.

3. The two-phase immersion cooling system for offshore wind turbines utilizing a natural wind-seawater staged cold source as described in claim 1, characterized in that, The substrate surface of the IGBT module is provided with a boiling enhancement structure, which includes a trench structure and a porous metal layer disposed on the surface of the trench structure. Under the design working pressure and static liquid level conditions of the liquid insulating coolant, the boiling enhancement structure ensures that the critical heat flux density corresponding to the IGBT module is not less than 1.8 times the peak heat flux density of the IGBT module.

4. The two-phase immersion cooling system for offshore wind turbines utilizing a natural wind-seawater staged cold source as described in claim 3, characterized in that, The sealed immersion chamber is equipped with a steam space and a mesh-type demister. The steam space is located above the free surface of the liquid insulating coolant, and the mesh-type demister is positioned between the free surface and the steam outlet of the sealed immersion chamber, ensuring that the amount of liquid droplets carried by the steam entering the steam pipeline is less than 1% by mass under rated operating conditions. The sealed immersion chamber is equipped with a liquid level sight glass, and the static liquid level of the liquid insulating coolant is configured to completely immerse the IGBT module and maintain a liquid layer of at least 50 mm above the boiling enhancement structure at the static liquid level.

5. The two-phase immersion cooling system for offshore wind turbines utilizing a natural wind-seawater staged cold source as described in claim 1, characterized in that, The primary air-cooled condenser is installed on the windward side of the nacelle cover of the offshore wind turbine. The primary air-cooled condenser includes an inlet header, an outlet header, and multiple rows of parallel finned tube bundles. The air inlet surface of the fins of the multiple rows of parallel finned tube bundles is passively oriented towards the incoming flow direction as the offshore wind turbine yaws. The outlet header is connected to the downcomer pipe.

6. The two-phase immersion cooling system for offshore wind turbines utilizing a natural wind-seawater staged cold source as described in claim 1, characterized in that, The downcomer pipe is laid downwards along the inner wall of the offshore wind turbine tower. The downcomer pipe is inclined downwards along the flow direction of the condensate and uncondensed steam after the first-stage condensation, with an angle of not less than 5° to the horizontal plane, ensuring smooth downward flow of the condensate and uncondensed steam under gravity and preventing liquid accumulation. A gas-liquid separation buffer chamber is provided between the downcomer pipe and the second-stage seawater condenser. The gas-liquid separation buffer chamber has an inlet, a steam outlet, and a condensate outlet. The inlet is connected to the downcomer pipe. The second-stage seawater condenser is divided into a condensation section and a subcooling section along the working fluid flow direction. The condensation section is located upstream and is used to condense uncondensed steam. The subcooling section is located downstream and is used to subcool the condensate. The outlet of the condensation section is connected to the subcooling section, allowing the liquid formed by the condensation of uncondensed steam in the condensation section to enter the subcooling section. The condensate outlet is connected to the condensation section, and the condensate outlet is connected to the subcooling section.

7. The two-phase immersion cooling system for offshore wind turbines utilizing a natural wind-seawater staged cold source as described in claim 6, characterized in that, When the offshore wind turbine adopts a monopile foundation, the secondary seawater condenser includes a serpentine tube bundle submerged in seawater. The serpentine tube bundle is fixed to the outer wall of the underwater section of the monopile foundation by a segmented, assembled arc-shaped jacket. A heat-conducting filling layer is provided between the segmented, assembled arc-shaped jacket and the outer wall of the underwater section of the monopile foundation. The inside of the serpentine tube bundle is connected to the closed working fluid loop, and the outside of the serpentine tube bundle is in contact with seawater.

8. The two-phase immersion cooling system for offshore wind turbines utilizing a natural wind-seawater staged cold source as described in claim 6, characterized in that, When the offshore wind turbine adopts a jacket foundation or a floating foundation, the secondary seawater condenser includes a shell-and-tube heat exchanger. The tube side of the shell-and-tube heat exchanger is connected to the closed working fluid loop, and the shell side of the shell-and-tube heat exchanger is connected to seawater. Venturi guide pipes are provided at the seawater inlet and outlet of the shell side, and a turbulence vortex generator is provided inside the shell side.

9. The two-phase immersion cooling system for offshore wind turbines utilizing a natural wind-seawater staged cold source as described in claim 1, characterized in that, The thermosiphon pressure head satisfies the following relationship: in, The effective vertical height difference between the outlet of the secondary seawater condenser and the free liquid surface within the sealed submerged cavity. The average density of the subcooled pure liquid column in the liquid reflux pipeline. The average density of the vapor-liquid two-phase mixture in the downcomer pipe. It is the acceleration due to gravity. The total pressure drop of the closed working fluid loop under the design heat load is denoted as .

10. The two-phase immersion cooling system for offshore wind turbines utilizing a natural wind-seawater staged cold source according to claim 1, characterized in that, The auxiliary circulation assembly includes a shielded magnetic drive circulation pump, a one-way bypass valve, and isolation valves disposed at both ends of the shielded magnetic drive circulation pump. The one-way bypass valve is connected in parallel with the shielded magnetic drive circulation pump. The one-way bypass valve only allows the liquid insulating coolant to flow from the secondary seawater condenser to the sealed immersion chamber; when the shielded magnetic drive circulation pump stops working, the liquid insulating coolant flows back through the one-way bypass valve; when the shielded magnetic drive circulation pump starts, it provides additional pressure head to the liquid return pipeline.

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