Two-phase liquid-cooled power unit

Abstract

A two-phase liquid-cooled power plant includes multiple cooling circuits that recirculate each working fluid around a closed-loop fluid path and transition it between liquid and vapor states to cool multiple devices. A portion of each fluid path is integrated with or in thermal contact with the device. The working fluid evaporates in each portion of the fluid path, maintaining operating temperatures at or near each of the different phase transition temperatures. The cooling circuits can be used to maintain different operating temperatures for hollow primary and secondary winding coils in a power transformer, parallel-connected hollow winding excitation coils and a common magnetic core in an electrical reactor, power semiconductor devices mounted on heat sink(s) with embedded fluid paths, or power semiconductor devices through which each fluid path passes.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the benefit of priority to U.S. Patent Application No. 17 / 885,400, filed on August 10, 2022, which is hereby incorporated by reference in its entirety.

[0002] The present invention relates to cooling systems for electrical or mechanical systems such as single - phase or poly - phase power transformers, electrical reactors, power semiconductor devices, etc. More specifically, it relates to applications of two - phase liquid cooling that optimize the thermal design in which different devices operate at different temperatures and thermal loads using different processing fluids such as fluoroketones (FK), hydrofluoroethers (HFE), perfluorocarbons (PFC), hydrofluorocarbons (HFC), perfluorohexane (PFH), perfluoropolyethers (PFPE), chlorofluorocarbons (CFC), etc.

Background Art

[0003] Electrical systems such as single - phase or poly - phase transformers, electrical reactors, power semiconductors, or mechanical systems such as bearings generate heat. Heat can reduce system performance, damage important components, shorten their lifespan, and even cause fires.

[0004] Cooling systems are implemented to remove heat so that the operating temperature is below a specified temperature. The capacity of the cooling system is determined by the heat load and the specified operating temperature. In many cases, the cooling system is driven by the worst - case heat load or operating temperature within the system. Cooling systems require valuable space within the system, energy to remove heat, and increase the overall cost. In new systems, more heat is generated in a smaller volume, so a more efficient cooling system is needed.

[0005] Various cooling systems exist that are adapted to remove heat depending on the system's space, energy, and cost requirements. A heat sink is a passive heat exchanger that transfers heat generated by a device to a fluid medium (often air or coolant) and dissipates it from the device. These may take the form of “moving air” or “recirculating immersion systems.” A related approach can be called a “recirculating integrated system,” in which chilled water is directly recirculated through components such as the hollow primary or secondary windings of a power transformer to absorb and remove heat. In each of these configurations, heat is transferred from the device to the fluid, thereby raising the temperature of the fluid and causing the fluid to be removed from the device.

[0006] Another approach, known as "evaporative cooling" or "two-phase liquid cooling," utilizes the phase transition of a fluid from liquid to gas to absorb heat. The main advantage of this approach is that the phase change from liquid to gas at a fixed transition temperature has a much larger heat capacity or heat of vaporization than when the liquid is heated. When properly configured, these systems can provide cooling capabilities equal to or better than conventional systems while utilizing less space, less energy, and lower costs. A simple example is spraying a liquid onto a heat sink to vaporize it.

[0007] Evaporative cooling has been widely used to cool the primary and secondary windings of power transformers. Essentially, the power transformer is positioned vertically within a sealed chamber, with electrical leads connected through the case to the winding coils. A liquid, such as CFC or PFC, is pumped to the top of the power transformer and dispersed in a thin layer over the primary and secondary winding coils by a spray head system or similar mechanism. The primary and secondary winding coils are cooled by the evaporation of the liquid. The vapor is collected, condensed back into a liquid, and recirculated to the top of the power transformer. [Overview of the Initiative]

[0008] The following is an outline of the invention to provide a basic understanding of some aspects of the present invention. This outline is not intended to identify the main or important elements of the present invention or to define the scope of the present invention. Its sole purpose is to present some of the concepts of the present invention in a brief form as a prelude to a more detailed description and definition of the claims, which will be presented later.

[0009] The present invention provides a two-phase liquid cooling system in which multiple cooling circuits recirculate the processing fluid, transitioning between liquid and vapor states to cool multiple devices (and their heated surfaces), maintaining different operating temperatures at or near the liquid phase transition temperature. The processing fluid needs to be chemically inert, thermally stable, non-toxic, and exhibit high dielectric strength, and preferably commercially available. Suitable processing fluids are selected from fluorinated ketones (FK), hydrofluoroethers (HFE), perfluorocarbons (PFC), hydrofluorocarbons (HFC), perfluorohexane (PFH), perfluoropolyethers (PFPE), and chlorofluorocarbons (CFC), depending on the application.

[0010] In one embodiment, a two-phase liquid cooling system includes a pair of devices, each generating heat at its respective surface and operating at different operating temperatures. A pair of independent cooling circuits are configured to absorb the thermal load and cool each device. Each circuit comprises a closed-loop fluid path through which the work fluid is recirculated and transitions between liquid and vapor states. A portion of the fluid path is integrated with or in thermal contact with the surface of the device. The work fluid evaporates at the phase transition temperature within the portion of the fluid path, cooling the surface and maintaining the operating temperature of the surface at or near the first phase transition temperature. The work fluids in the cooling circuits exhibit different transition temperatures to accommodate the different thermal loads and operating temperatures of the different devices.

[0011] In one embodiment, each cooling circuit comprises a pump for recirculating the processing fluid within a closed-loop fluid path, a liquid pressure regulator for adjusting the pressure of the processing fluid, a vapor pressure regulator for adjusting the pressure of the vapor state of the processing fluid, and a condenser coupled to a cooling fluid reservoir for condensing the processing vapor into the processing fluid for recirculation. The cooling circuits are appropriately connected in series or parallel to a common cooling fluid (usually water) reservoir. Each cooling circuit may also include a vapor pressure sensor that senses the vapor pressure and feeds it back to the liquid pressure regulator to control the flow of the processing fluid.

[0012] In one embodiment, at least one of the cooling circuits includes an additional device located upstream of an existing device. The processing fluid flows through the fluid path to cool the additional device, keeping its operating temperature below the phase transition temperature of the processing fluid. In a particular embodiment, the device is a power semiconductor device coupled to a common heat sink. Part of the closed-loop fluid path is embedded in the common heat sink to cool the upstream device with the fluid and the downstream device, which operates at a higher temperature, with vapor.

[0013] In one embodiment, the work fluid is provided with a conductive solid granular medium (e.g., aluminum shot). The pump includes an electromagnetic pump (e.g., a dispersed AC induction coil) that generates a magnetic field moving within a closed-loop fluid path, and this magnetic field interacts with the conductive solid granular medium to generate a force that propels both the work fluid and the medium. The medium also plays a role in increasing the heat transfer capacity of the work fluid and more uniformly cooling the portion of the fluid path where vaporization occurs.

[0014] In one embodiment, the device and its surface are hollow winding coils wound around a common magnetic core, and when energized, current flows through the hollow winding coils, heating them up. The processing fluid(s) evaporates within the hollow winding coils.

[0015] In one embodiment, a power transformer comprises single-phase or multi-phase primary (P) hollow-winding coils and secondary (S) hollow-winding coils wound around a common magnetic core. One cooling circuit cools the coil by recirculating a first work fluid through the single-phase or multi-phase P hollow-winding coil, maintaining the coil at or near the transition temperature of the first work fluid. The other cooling circuit cools the coil by recirculating a second work fluid through the single-phase or multi-phase S hollow-winding coil, maintaining the coil at or near the transition temperature of the second work fluid, which is higher than the transition temperature of the first work fluid. In the case of multi-phase windings, each cooling circuit comprises a fluid manifold for distributing the work fluid in parallel to the winding coils and a steam manifold for collecting steam from the multi-phase coils. In a power transformer, the secondary winding coils typically operate at higher current densities and therefore exhibit a greater thermal load and higher operating temperature than the primary windings. The branched cooling system can be optimized to provide the necessary thermal load and different operating temperatures for both the P-winding and S-winding coils.

[0016] In another embodiment, the electric reactor comprises multiple hollow-winding excitation coils wound around a common magnetic core. One cooling circuit recirculates a first work fluid in parallel through the hollow-winding excitation coils, where the fluid vaporizes to cool the excitation coils and maintain the excitation coils at or near the transition temperature of the first work fluid. The first work fluid is recirculated in parallel through the multiple excitation coils via a liquid manifold and a vapor manifold. Part of the closed-loop fluid path of the other cooling circuit is embedded in a heat sink that is in thermal contact with the common magnetic core. A liquid / vapor manifold can be used to cool multiple heat sinks attached to the common magnetic core. A second work fluid vaporizes within the heat sinks to cool the common magnetic core and maintain its operating temperature at or near the transition temperature of the second work fluid.

[0017] In another embodiment, in at least one of the cooling circuits, a portion of the closed-loop path is embedded in a heatsink that is in thermal contact with the surface of the device.

[0018] In another embodiment, a pair of power semiconductor devices are thermally coupled to a common heatsink and electrically isolated. The two devices operate at different p / n junction or semiconductor substrate temperatures. For example, one device may be a silicon-controlled rectifier (SCR) or thyristor, and the other may be a semiconductor switching device such as an integrated gate rectifier thyristor (IGCT) or MOSFET. A thyristor has multiple p / n junctions that are actively cooled. A MOSFET is a field-effect device (without p / n junctions), in which case the semiconductor substrate is actively cooled. Each power semiconductor is placed in a closed-loop fluid path of a different cooling circuit, into which a processing fluid is injected, evaporates in direct contact with the p / n junction interface or semiconductor substrate at the transition temperature, is discharged from the device as vapor, condenses back into a liquid, and is recirculated.

[0019] These and other features and advantages of the present invention will be apparent to those skilled in the art from the following detailed description of preferred embodiments in conjunction with the accompanying drawings. [Brief explanation of the drawing]

[0020] [Figure 1] This is a layout diagram of an embodiment of a two-phase liquid cooling system in which independent cooling circuits recirculate different processing fluids in a closed-loop fluid path to liquid-cool a first device and cool a second device through a phase transition to vapor, thereby optimizing the overall thermal design of the system. [Figure 2] This figure shows a portion of a closed-loop fluid path in which the processing liquid flows in the liquid phase, absorbs heat, and transitions to the gas phase. [Figure 3] This is a diagram showing the relationship between the saturation temperature, specific energy, and vapor pressure of a fluorinated ketone in a saturated state. [Figure 4A] This is a diagram of a portion of a closed-loop fluid path in which a processed liquid containing a conductive solid granular medium flows, absorbs heat, and transitions to a gas phase in response to the interaction between traveling waves generated by a distributed electromagnetic pump and the liquid phase medium. [Figure 4B]It is a diagram of a part of a closed-loop fluid path in which a processing liquid containing a conductive solid granular medium flows, absorbs heat, and transfers to the gas phase according to the interaction between the traveling wave generated by the distributed electromagnetic pump and the liquid-phase medium. [Figure 5] It is a layout diagram of an embodiment of a two-phase liquid-cooled single-phase power transformer in which an independent cooling circuit recirculates different processing liquids through a single-phase hollow primary winding coil and a secondary winding coil, and maintains the operating temperatures of the coils at different levels. [Figure 6A] It is a side view of an embodiment of a two-phase liquid-cooled polyphase power transformer in which an independent cooling circuit recirculates different processing liquids through a polyphase hollow primary winding coil and a secondary winding coil, and maintains the operating temperatures of the polyphase hollow primary winding coil and the secondary winding coil at different levels. [Figure 6B] It is a top view of an embodiment of a two-phase liquid-cooled polyphase power transformer in which an independent cooling circuit recirculates different processing liquids through a polyphase hollow primary winding coil and a secondary winding coil, and maintains the operating temperatures of the polyphase hollow primary winding coil and the secondary winding coil at different levels. [Figure 7A] It is a table of design parameters of a two-phase liquid-cooled polyphase power transformer. [Figure 7B] It is a table of parameters of various processing fluorinated ketone fluids known as Novec (trademark). [Figure 8A] It is a layout diagram of a two-phase liquid-cooled electrical reactor in which an independent cooling circuit recirculates different PFCs through a plurality of hollow winding coils and a heat sink in thermal contact with a common magnetic core, and maintains the operating temperatures of the coil and the magnetic core at different levels. [Figure 8B] It is a table of design parameters of a two-phase liquid-cooled electrical reactor in which an independent cooling circuit recirculates different PFCs through a plurality of hollow winding coils and a heat sink in thermal contact with a common magnetic core, and maintains the operating temperatures of the coil and the magnetic core at different levels. [Figure 9A] It is a side view of a cooling circuit in which a part of a closed-loop fluid path is embedded in a heat sink that supports a pair of devices for liquid-cooling a first device and cooling a second device by vaporization. [Figure 9B] This is a cross-sectional view of a cooling circuit in which a portion of a closed-loop fluid path is embedded in a heat sink supporting a pair of devices for liquid cooling of a first device and vapor cooling of a second device. [Figure 10] This is a side view of a pair of power semiconductor devices on a common substrate, where different processing liquids are injected into the devices and vaporized to maintain different operating temperatures for each p / n junction. [Modes for carrying out the invention]

[0021] A two-phase liquid cooling system comprises two or more cooling circuits, which recirculate the processing fluid, transitioning between liquid and vapor states to cool multiple devices (and their heated surfaces), maintaining different operating temperatures at or near the liquid phase transition temperature. The processing fluid must be chemically inert, thermally stable, non-toxic, and exhibit high dielectric strength, preferably commercially available. Suitable processing fluids are selected from fluorinated ketones (FK), hydrofluoroethers (HFE), perfluorocarbons (PFC), hydrofluorocarbons (HFC), perfluorohexane (PFH), perfluoropolyethers (PFPE), and chlorofluorocarbons (CFC), depending on the application. For example, the cooling circuits can be used to maintain different operating temperatures for hollow primary and secondary winding coils of power transformers, parallel-connected hollow winding excitation coils and common magnetic cores of electric reactors, power semiconductor devices mounted on heat sinks with embedded fluid paths, or for each fluid path passing through a device or mechanical system such as a bearing. 3M (Trademark) manufactures a variety of processing fluids under the trademark name Novec (Trademark), which exhibit properties required for various applications and are examples of fluorinated ketones (FK) used in the embodiments described herein.

[0022] Referring to FIG. 1, an embodiment of a two-phase liquid cooling system 100 includes a first cooling circuit 101 and a second cooling circuit 103. The closed-loop fluid paths 105 and 107 of these circuits include a condenser 104 and 118, a pump 102, and a coolant reservoir 132 for recirculating a coolant liquid 117 such as water, and are suitably connected to a common output cooling path 109. The closed-loop fluid path 105 includes a condenser 104, a liquid pump 106 at an input temperature T1, a liquid pressure regulator 108, a first heat generating device 110 with an output temperature T2 as a liquid, a second heat generating device 112 with an output temperature T3 as a vapor, a vapor pressure sensor 114 suitably configured to measure the vapor pressure and provide a control signal to the liquid pressure regulator 108 to control the flow rate, a vapor pressure regulator 116 for maintaining an appropriate vapor pressure for a specific vapor transition temperature, and a return path to the condenser 104 for recirculating the process liquid 111 and transferring it between the liquid phase and the vapor phase to cool the device. It is understood that temperature T1 is lower than temperature T2, and temperature T2 is lower than temperature T3. The heat Q1 and Q2 generated by devices 110 and 112 are transferred to the coolant reservoir 132 or a similar cooling source via the condenser 104 at an inlet temperature T7 and an outlet temperature T8 (T7 < T1). A suitable two-phase liquid is Novec (trademark) 7200 from 3M (trademark). This has a transition temperature of 76 oC has a heat of vaporization of 119 kJ / kg and can be used in the first cooling circuit. A typical first device 110 is a back iron heat sink for an electric reactor, which has relatively low power consumption due to eddy current losses in the iron, and a typical second device 112 is a hollow electric winding coil in the same electric reactor, which has high power consumption due to Joule losses in the conductor. In this example, the first portion of the closed-loop fluid path 105 is embedded in the heat sink (device 1 110), and the second portion of the closed-loop fluid path 105 is integrally formed with the hollow electric winding coil (device 2 112). The processed liquid 111 passes through the heat sink in a liquid state, absorbing heat Q2 and cooling the heat sink. The temperature of the liquid rises from T1 to T2, but it remains in a liquid state. The processing liquid 111 enters the hollow electric winding coil in liquid form and absorbs enough heat Q2 inside the winding coil to vaporize at least a portion of the liquid at the vapor transition temperature T3, thereby maintaining the operating temperature of the winding coil at or near the vapor transition temperature T3.

[0023] Similarly, the closed-loop fluid path 107 is configured to include a condenser 118, a liquid pump 120 with an input temperature T4, a liquid pressure regulator 122, a third heat generating device 124 having an output temperature T5 as a liquid / vapor mixture, a fourth heat generating device 126 having an output temperature T6 as vapor, a vapor pressure sensor 128, a vapor pressure regulator 130 configured to measure the vapor pressure and provide a control signal to the liquid pressure regulator 122 to control the flow rate, and a return path to the condenser 118 for recirculating the process liquid 113 and transferring the process liquid 113 between the liquid phase and the vapor phase to cool the device. It is understood that the temperature T4 is lower than the temperature T5, and the temperature T5 is lower than the temperature T6. The heat Q3 and Q4 generated by the devices 124 and 126 are transferred to a coolant reservoir 132 or a similar cooling source through the condenser 118 at the inlet temperature T8 and the outlet temperature T9 (T7 < T8 < T9). A suitable two-phase fluid is Novec (trademark) 7600 from 3M (trademark). This has a transition temperature of 128 °C and a heat of vaporization of 89 kJ / kg and can be used in the second cooling circuit. A representative third device 124 is a hollow primary winding coil in an electrical transformer that operates at a dissipation power sufficient to vaporize the fluid in contact with the inner wall of the hollow conductor, and a representative fourth device 126 is a hollow electrical winding coil in the same electrical transformer having a greater power dissipation loss capable of vaporizing the entire flow of liquid within the hollow conductor. In this example, the first portion of the closed-loop fluid path 107 is integrally formed with the hollow primary winding coil (device 1 124), and the second portion of the closed-loop fluid path 107 is integrally formed with the hollow electrical winding coil (device 2 126). The process liquid 113 passes through the hollow primary winding coil in the liquid state, absorbs the heat Q2, and cools the heat sink. The temperature of the liquid rises from T4 to a temperature T5 sufficient to form a liquid / vapor mixed flow. The process liquid 113 enters the hollow electrical winding coil, absorbs a heat Q2 sufficient to further vaporize the mixed flow at the vapor transition temperature T6 inside the winding coil, thereby maintaining the operating temperature of the winding coil at or near the vapor transition temperature T6.

[0024] It is understood that the cooling liquid reservoir 132 absorbs the total heat Q1+Q2+Q3+Q4 from all four devices, except for a small amount of heat dissipated by the pump and tubing arrangement. A feature of the present invention is that each of the four devices can be cooled at an optimal design temperature close to a specific transition temperature inherent to the design current density or heat dissipation of each component device, rather than operating at a common, less optimal transition temperature from liquid to vapor. Two representative fluids used, Novec® 7200 and Novec® 7500, which have significantly different vaporization heat energy levels and transition temperatures, can be applied to a common final fluid heat exchanger loop, in which the loops of path 1 and path 2 are arranged in series. Alternatively, the fluid paths can be connected in parallel to a common liquid reservoir, or each can be connected to its own dedicated liquid reservoir. Because two-phase fluids have excellent electroelectric properties, electrical isolation is achieved for all four devices.

[0025] A key feature of two-phase liquid cooling systems is that, due to their closed-loop fluid pathways, the system is direction-independent. The system can be inverted, rotated, or rocked back and forth without affecting its cooling performance. This is crucial for applications where the system may be installed in moving land vehicles, ships, or aircraft. Many conventional cooling systems, especially those utilizing vapor cooling, require a stable, upright orientation.

[0026] Closed-loop fluid pathways also improve coverage of high-temperature device surfaces that require cooling. Spraying liquid onto hot surfaces or devices inevitably results in uneven application and missed spots, but passing liquid through the surface or device ensures uniform coating across the entire surface, leading to more uniform cooling.

[0027] Figure 2 shows an electrically hollow conductor 200 with an inlet manifold 201 and an outlet manifold 206, through which current is injected or excited, and a working fluid 202 is also transported. The working fluid enters the inlet 201 and flows through the hollow conductor, which is also an electrically metallic conductor, such as forming the windings of an electric reactor or transformer. Along the distance along the conductor, the accumulated heat exceeds the heat of vaporization (e.g., 119 kJ / kg when using 3M® Novec® 7200), and the working fluid 202 transitions to vapor 204 within the conductor at the vapor transition point, which is then discharged as vapor from the outlet 206. The exact location of the vapor transition point is known to vary depending on the actual electrical load and the resulting power dissipation losses within the conductor. From a design perspective, it is desirable that the vapor transition point at maximum power dissipation be within the last half of the path of the hollow conductor. By repeating a single conductor multiple times in a primary or secondary winding structure, multiple winding turns can be enabled, similar to the common method in which coils are electrically connected in series and electrically connected in parallel.

[0028] Furthermore, a temperature-dependent vapor pressure 220 is generated within the hollow conductor, as shown in Figure 3. For a specific fluid, Novec® No. 649, the saturation temperature 222 is 49°C to 96°C, and the vapor pressure range is 1 to 4 bar. Figure 3 also shows that the heat of vaporization 224 decreases slightly as the vapor pressure increases, but this is within an acceptable range.

[0029] Referring to Figures 4A and 4B, an embodiment of the two-phase liquid cooling system 400 includes a work liquid 402 to which a conductive solid granular medium 414 is added. This medium is introduced into a hollow electrical conductor 403 at an inlet 410, vaporized within the hollow electrical conductor, discharged at an outlet 420, condensed, and recirculated. The medium 414 may be used to enhance the overall cooling capacity, improve the uniformity of cooling on the hollow electrical conductor 403, and propel the work liquid 402 around the fluid path. The medium 414 is suitable for both electrical and thermal conductivity. Suitable materials are aluminum or magnesium alloys, which are lightweight and highly thermally conductive materials and can preferably be formed into small spherical balls or "shots." The medium 414 is designed to accept the heat content from the hollow electrical conductor but not melt. The work liquid flow is to which the medium 414 is added before entering the system 400, and this medium continues to flow throughout the system and is discharged at an outlet 420. The medium 414 absorbs (and removes) heat in the first half of the hollow electrical conductor before vaporizing, thereby improving the distribution of heat absorption and cooling the conductor more uniformly. The size of the conductive medium is small enough, for example, 0.065 inches in diameter, so that it passes through the liquid pump, vapor pressure sensor, hydraulic pressure sensor, and condenser, as shown in Figure 1, and is continuously recirculated. The excess heat content of the conductive medium 414 is efficiently transferred via the condenser to the external cooling liquid reservoir in Figure 1.

[0030] An electromagnetic pump 412 can be used to propel the medium 414 and the processing liquid 402 through the hollow electrical conductor 403. The electromagnetic pump 412, such as a coaxial electromagnetic pump, induces magnetic waves that travel through the gap 422 between the walls of the hollow electrical conductor, generating eddy currents 425 in the medium 414. The medium 414 is propelled by the cross product of the strength of the eddy currents 425 induced from the AC magnetic field B 427 of the electromagnetic pump and the strength of the B magnetic field, as shown in Figure 4B. In a preferred embodiment, the B magnetic field in the hollow conductor may be 1.5 to 1.7 Tesla in strength. The conductive medium 414 absorbs heat from the electrical conductor, and this heat is first transferred to the fluid 402 in the first part of the coolant path. The electromagnetic pump does not need to be continuous, and as shown in Figure 4A, the pump is divided to allow for bending and curvature of the electrical hollow conductor along the actual winding.

[0031] If the capacity of the electromagnetic pump 412 is sufficient and a sufficient amount of conductive medium 414 is used as the primary transport means, the conventional type of mechanical liquid pump 106 or 120 shown in Figure 1 can be replaced solely by the electromagnetic pump 412. The vapor transition point in the hollow conductor preferably occurs within the last half of the entire flow path.

[0032] Referring to Figure 5, an embodiment of the two-phase liquid-cooled single-phase transformer 500 includes independent first cooling circuits 502 and second cooling circuits 504, which are interconnected via condensers 532 and 534, respectively, to provide combined heat to a cooling liquid reservoir 546, independently cooling the primary hollow winding coil 512 and secondary hollow winding coil 514, respectively, wound around a common magnetic core 506, maintaining their desired operating temperatures and forming a closed magnetic circuit structure 516 with a magnetic AC flux path 517. The primary hollow winding coil 512 is powered from an AC single-phase power supply 510. The secondary hollow winding coil 514 drives an electrical load 550 connected to its electrical terminals.

[0033] Pump 548 supplies coolant to condenser 532, which is shared with cooling circuit 502, at inlet temperature T7 and outlet temperature T8, and then transfers the coolant to condenser 534, which is shared with cooling circuit 504, at outlet temperature T9. Coolant reservoir 546 absorbs most of the heat generated by the primary and secondary hollow-wound coils. The combination of the temperature difference T9-T7 and the flow rate, along with the small amount of heat dissipated in the tubing connecting the various components, determines the cooling capacity in watts. In a preferred embodiment, the coolant is an ethylene glycol aqueous mixture with an outlet temperature T7 in the range of 10-15°C, and pump 548 is a vane-type liquid pump with a constant-pressure internal regulator.

[0034] The first cooling circuit 502 includes a closed-loop fluid path 508 that recirculates the processing liquid 511, which transitions between liquid and gas phases, to cool the primary hollow winding coil 512. The processing liquid 511 enters the primary hollow winding coil 512 as a liquid at temperature T2, removes the Joule loss heat generated by the excitation of the winding coil 512, causes a phase change to vapor within the hollow conductor, and is discharged from the outlet at a temperature T3 close to the boiling point (transition temperature) of the processing liquid. The vapor circulates through the closed-loop fluid path 508 via a vapor pressure sensor 526, a vapor pressure regulator 530, and a condenser 532, thereby lowering the temperature of the processing liquid to T1 and returning the vapor to a liquid state. A pump 520 ensures a constant flow of processing liquid to the liquid pressure regulator 522 at an output temperature T2. The vapor pressure sensor 526 outputs a control signal 528 that functions as a feedback control signal to the liquid pressure regulator 522, limiting the liquid pressure to a value within the safe operating point of a hollow conductor that may be constructed with thin walls where the burst strength is limited. A suitable processing liquid is 3M® Novec® 649, with a transition temperature of 49°C and a heat of vaporization of 89 kJ / kg.

[0035] The second cooling circuit 504 includes a closed-loop fluid path 509 that recirculates the processing liquid 513, which transitions between liquid and gas phases, to cool the secondary hollow winding coil 514. The processing liquid 513 enters the secondary hollow winding coil 514 as a liquid at temperature T5, removes the Joule loss heat generated by the excitation of the winding coil 514, causes a phase change to vapor within the hollow conductor, and is discharged from the outlet at a temperature T6 close to the boiling point (transition temperature) of the processing liquid. The vapor circulates through the closed-loop fluid path 509 via a vapor pressure sensor 540, a vapor pressure regulator 544, and a condenser 534, thereby lowering the coolant temperature to T4 and returning the vapor to a liquid state. A pump 536 ensures a constant flow of the processing liquid 513 to a liquid pressure regulator 538 at an output temperature T5. The vapor pressure sensor 540 outputs a control signal 542 that functions as a feedback control signal to the liquid pressure regulator 538, limiting the liquid pressure to a value within a safe operating point of a hollow conductor that may be constructed with thin walls. A suitable fluid for the secondary coolant path is 3M's Novec® 7500, with a transition temperature of 128°C and a heat of vaporization of 89 kJ / kg.

[0036] It is clear that the heat dissipated by the secondary winding 514 results in a higher temperature rise and higher boiling point than the heat dissipated by the primary winding 512. Furthermore, in a preferred embodiment, a thermal barrier 518 is present between the primary and secondary windings. The thermal barrier may be a fiberglass epoxy material or mica. A key feature of the present invention is that the temperature difference between the boiling points of the two working liquids is significant at 128°C-49°C, i.e., 79°C. For a particular selected coolant, the primary winding 512 is a high-voltage winding with additional dielectric insulation, and has a voltage of 9.0 A / mm². 2 A current density lower than the possible current density of the secondary winding 514 (e.g., 5.0 A / mm²) 2) has. Therefore, the resistance loss or Joule loss of the primary winding 512 is reduced, and a processing fluid with a low boiling point can be used in the primary winding 512. The system 500 is equipped with four electrical inline insulators 524, which serve to electrically insulate the excitation current or load current from flowing into the liquid pressure regulators 522, 538 and the steam sensors 526, 540, or from them into the metal conductors constituting the coolant tubes.

[0037] Referring to Figures 6A and 6B, an embodiment of the two-phase liquid-cooled three-phase power transformer 700 comprises three primary hollow winding coils 702, 704, and 706 and three secondary hollow winding coils 708, 710, and 712, wound coaxially in pairs around three legs 714, 716, and 718 of a magnetic core 719. The primary and secondary hollow winding coils are connected to an AC power source and an AC load via primary winding connectors 724 and 726, respectively. The ampere-turns of the primary and secondary coils are approximately the same, but because the volume allocated to the secondary coils is smaller, the secondary coils operate at a higher average temperature than the primary coils. As a result, the primary hollow winding coils can circulate a work fluid with a lower boiling point than another work fluid circulating within the secondary hollow winding coils.

[0038] The manifold is implemented to separate the different processing fluids 720 and 722 into three parallel flows, which are supplied in parallel to the primary (secondary) hollow winding coils to collect hot vapor from the primary (secondary) hollow winding coils. The manifold is located within the closed-loop fluid path of the cooling circuit of the single-phase power transformer, as shown in Figure 5. The manifold can be expanded to accommodate any multiphase implementation of N primary hollow winding coils and M secondary hollow winding coils.

[0039] For use with primary hollow-winding coils, a common primary inlet 730 supplies the processing liquid 720 as a liquid at temperature T2 to a primary inlet manifold 732, which then separates the flow of the processing liquid 720 into three primary inlets 734a, 734b, and 734c, each connected to one end of three primary hollow-winding coils 702, 704, and 706, respectively. The processing liquid 720 is vaporized within each primary hollow-winding coil and discharged from the other end of the coil, which is connected to three primary outlets 736a, 736b, and 736c, which are then collected by a primary outlet manifold 738 and discharged as a vapor stream at temperature T3 from a common primary outlet 739.

[0040] For use in secondary hollow-winding coils, a common primary inlet 740 supplies the processing liquid 722 as a liquid at temperature T5 to the primary inlet manifold 742, which then separates the flow of the processing liquid 722 to three primary inlets 744a, 744b, and 744c, which are connected to one end of three secondary hollow-winding coils 708, 710, and 712, respectively. The processing liquid 722 is vaporized within each secondary hollow-winding coil and discharged from the other end of the coil, which is connected to three primary outlets 746a, 746b, and 746c, which are then collected by the primary outlet manifold 748 and discharged as a vapor stream at temperature T6 from a common primary outlet 749.

[0041] The electrical insulators 750 separate the primary and secondary circuits from each other, preventing the circulation of current within the manifold. These electrical insulators may consist of hollow tubes made of fiberglass epoxy material aligned in a straight line with the hollow electrical conductors carrying the liquid or vapor. The system includes vapor pressure regulators 784, 786 and two vapor pressure sensors 780, 782 that provide feedback signals to liquid pressure regulators 788, 790 that supply to the inlet manifolds 732, 742.

[0042] Figure 7A is Table 790 of the design parameters for a 3000 kVA three-phase two-phase liquid-cooled power transformer with a 4160-volt primary winding and a lower-voltage secondary winding. In this transformer, the current density of the secondary winding is higher than that of the primary winding. The table shows examples of the actual application of two different work fluids with significantly different boiling points of 76°C and 128°C to suit the primary and secondary windings, respectively, which have hollow conductors. Figure 7B is Table 792 of 3M® Novec® work fluids, showing various boiling / transition temperatures and the associated key design parameters.

[0043] Referring here to Figures 8A and 8B, an embodiment of a two-phase liquid-cooled single-phase electric reactor 800 is shown, in which a pair of hollow electric winding coils 812 and 814 are evenly distributed on opposite sides of a common magnetic core 810. The coils 812 and 814 are electrically connected in parallel via electrical cables 836 and 840. An AC power supply 890 is connected via the hollow electric winding coil 814. The heat sink is divided into a pair of thermal conduction blocks 820A and 820B that are in thermal contact with the opposite side of the magnetic core 810. Table 801 shows the design parameters for a 100 kVAR single-phase electric reactor.

[0044] In the closed-loop fluid path of the first cooling circuit, a common liquid inlet 822 supplies the processing liquid 824 as a liquid at temperature T2 to the inlet manifold 830, which separates the flow of the processing liquid 824 into two: one to the hollow electric winding coil 812 and the other to the hollow electric winding coil 814 via the liquid inlet line 832. The processing liquid 824 is vaporized within each hollow winding coil and discharged from the other ends of coils 812 and 814. Coils 812 and 814 are directly coupled to the outlet manifold 840 and also via the vapor return line 834, which collects and condenses the vapor at a common vapor outlet 842 at temperature T3.

[0045] In the closed-loop fluid path of the second cooling circuit, a common liquid inlet 860 supplies the processing liquid 862 as a liquid at temperature T5 to the inlet manifold 870, which separates the flow of the processing liquid 862 into hollow tubes or channels 816 and 818 embedded in the heat conduction blocks 820A and 820B of the heat sink. The processing liquid 862 is vaporized in each hollow tube or channel and discharged from the other end. The other end is connected to an outlet manifold 880, which collects and condenses the vapor at a common vapor outlet 882 at temperature T6.

[0046] In a preferred embodiment, the boiling point of the second processing fluid 862 flowing through the heat sink is lower than that of the first processing fluid 824 in the hollow electrical winding coils 812, 814, because the dissipation losses of the core are typically much lower than the power losses of the electrical windings.

[0047] Referring to Figures 9A and 9B, the two-phase liquid cooling system 900 comprises first and second devices (mechanical or electrical) 910 and 920, which are mounted to a solid substrate or thermal base 940 using optional thermal pads 930 to reduce thermal resistance between the junction surfaces. Only one processing fluid 902 is used, and only one cooling circuit is shown. However, the inlet manifold 970 and outlet manifold 980 can be machined to allow connection points to multiple paths or parallel paths of the cooling circuit. The solid substrate 940 has an array of hollow tubes or channels 904 embedded in it, which form part of a closed-loop fluid path to circulate the processing fluid 902 and transfer heat from both devices 910 and 920. A phase transition occurs within the tubes embedded in the substrate 940. The system 900 allows the two devices 910 and 920 to dissipate heat equally or at a significantly different rate. For example, the processing liquid 902 enters the substrate as liquid 950 at temperature T1, receives heat Q1 from device 1, raises the liquid temperature to T2, receives additional heat Q2 from device 2, and undergoes a phase transition to vapor 960 at temperature T3. This is a simple, compact, and efficient heat sink design for cooling devices that can operate at different temperatures, or devices that can operate at similar temperatures but have significantly different heat dissipation requirements. For example, device 1 may operate at a lower temperature than device 2, or device 1 may operate at a similar temperature but require much less heat dissipation.

[0048] Referring to Figure 10, an embodiment of the two-phase liquid cooling system 1000 recirculates different processing fluids through power semiconductor devices 1002 and 1004 to provide internal cooling according to the heat dissipation requirements and operating temperature of each device by vaporization of the liquids. For example, thyristors and insulated-gate bipolar transistors (IGBTs) may have different heat dissipation Q1 or Q2 due to their significantly different conduction current densities, different substrate material resistances, or different substrate material diameters / volumes. Therefore, processing fluids with different transition temperatures and different heat capacities are required.

[0049] In this particular embodiment, thyristors 1002 and 1004 comprise device-centered semiconductor wafers 1010, 1012, each having electrically and thermally conductive cathode material 1020, 1022 and anode material 1030, 1032. Thyristors 1002 and 1004 have cathode leads 1070, 1072, triggered PNPN junction semiconductors 1074, 1076, and gate leads 1060, 1062 for controlling the thyristors. Each device is encapsulated within ceramic shells 1056, 1058 that form a void space around the semiconductor wafer. Most of the heat generated in Q1 and Q2 is conducted through thyristor substrates 1013, 1014 to the anodes 1030, 1032, which are electrically connected to a common mounting base 1080 with limited thermal capacity as a heat sink. Some of the heat is conducted to the ceramic shell through cathodes 1020, 1022 and the void space, and dissipated through the surrounding air. These heat sink mechanisms may be insufficient to dissipate heat and maintain the desired operating temperature, or they may need to be designed for "worst-case" devices with maximum heat dissipation requirements.

[0050] Therefore, the thyristors are inserted into closed-loop fluid paths of various cooling circuits that circulate various processing fluids 1090, 1092 through the gaps between thyristors 1002 and 1004, and the processing fluids evaporate through direct contact with the PNPN junction semiconductors 1074, 1076, extracting heat from the device. The processing fluid 1090 is introduced as a liquid at port 1040 of thyristor 1002, flows around the semiconductor wafer 1010, specifically the PNPN junction semiconductor 1074, where it vaporizes at transition temperature T1 and is discharged as vapor at port 1050. Similarly, the processing fluid 1092 is introduced as a liquid at port 1042 of thyristor 1004, flows around the semiconductor wafer 1012, specifically the PNPN junction semiconductor 1076, where it vaporizes at transition temperature T2 and is discharged as vapor at port 1052.

[0051] The vapor outlet ports 1050 and 1052 are individually connected to two or more different condensers, allowing for repeated transfer of vapor to a liquid state using multiple condensers. The two work liquids are held in separate cooling circuits throughout. The condensers may have heat exchange with an external airflow or a closed-loop reservoir pump system, as shown in Figure 1. The two work liquids may have significantly different boiling points T1 and T2 due to the vastly different heat dissipation within each device. In an alternative embodiment, the common mounting block 1080 does not have to be made of a thermally conductive material, in which case the two cooling circuits extract most of the heat Q1 and Q2 from the device and then transfer this heat to the two condensers in the arrangement of Figure 1. System 1000 may be extended to a larger semiconductor device array that enables internal vapor cooling inside a number of semiconductor devices. This concept is valid for field-effect devices and other types of power semiconductors such as MOSFETs that dissipate heat on p-type or n-type silicon or silicon carbide substrates.

[0052] While several exemplary embodiments of the present invention have been illustrated and described, those skilled in the art will likely envision numerous variations and alternative embodiments. Such variations and alternative embodiments are intended and can be implemented without departing from the scope of the invention, as defined in the appended claims.

Claims

1. A two-phase liquid cooling system, First and second devices, each generating heat on a first surface and a second surface, wherein the first and second devices are designed to operate at different first and second operating temperatures, A first cooling circuit comprising a first closed-loop fluid path, wherein a first processing fluid selected from fluorinated ketones (FK), hydrofluoroethers (HFE), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), perfluorohexanes (PFHs), perfluoropolyethers (PFPEs), and chlorofluorocarbons (CFCs) is recirculated in the first closed-loop fluid path, the first portion of the fluid path is integrated with or thermally in contact with the first surface, the first processing fluid evaporates within the first portion of the fluid path at a first phase transition temperature to cool the first surface, and the operating temperature of the first surface is maintained at or near the first phase transition temperature, the first cooling circuit, A second cooling circuit comprising a second closed-loop fluid path, wherein a second processing fluid selected from FK, HFE, PFC, HFC, PFH, PFPE, and CFC is recirculated in the second closed-loop fluid path, the second portion of the fluid path is integrated with the second surface or is in thermal contact with the second surface, the second processing fluid evaporates within the second portion of the fluid path at a second phase transition temperature to cool the second surface, and the operating temperature of the second surface is maintained at or near the second phase transition temperature, the second cooling circuit comprises The first and second processing liquids exhibit different first and second phase transition temperatures and different heats of vaporization. The first surface and the first portion of the closed-loop fluid path are integrated into a hollow winding coil wound around a magnetic core, and the hollow winding coil is energized to pass an electric current through it, and the first processing fluid evaporates within the hollow winding coil to cool it. The aforementioned two-phase liquid cooling system.

2. A two-phase liquid cooling system, First and second devices, each generating heat on a first surface and a second surface, wherein the first and second devices are designed to operate at different first and second operating temperatures, A first cooling circuit comprising a first closed-loop fluid path, wherein a first processing fluid selected from fluorinated ketones (FK), hydrofluoroethers (HFE), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), perfluorohexanes (PFHs), perfluoropolyethers (PFPEs), and chlorofluorocarbons (CFCs) is recirculated in the first closed-loop fluid path, the first portion of the fluid path is integrated with or thermally in contact with the first surface, the first processing fluid evaporates within the first portion of the fluid path at a first phase transition temperature to cool the first surface, and the operating temperature of the first surface is maintained at or near the first phase transition temperature, the first cooling circuit, A second cooling circuit comprising a second closed-loop fluid path, wherein a second processing fluid selected from FK, HFE, PFC, HFC, PFH, PFPE, and CFC is recirculated in the second closed-loop fluid path, the second portion of the fluid path is integrated with the second surface or is in thermal contact with the second surface, the second processing fluid evaporates within the second portion of the fluid path at a second phase transition temperature to cool the second surface, and the operating temperature of the second surface is maintained at or near the second phase transition temperature, the second cooling circuit comprises The first and second processing liquids exhibit different first and second phase transition temperatures and different heats of vaporization. The first and second devices each comprise single-phase or multi-phase hollow primary and secondary winding coils wound around a common magnetic core to form a power transformer, and the first and second processing fluids evaporate within the single-phase or multi-phase hollow primary and secondary winding coils, respectively, to cool each coil. The aforementioned two-phase liquid cooling system.

3. A two-phase liquid cooling system, First and second devices, each generating heat on a first surface and a second surface, wherein the first and second devices are designed to operate at different first and second operating temperatures, A first cooling circuit comprising a first closed-loop fluid path, wherein a first processing fluid selected from fluorinated ketones (FK), hydrofluoroethers (HFE), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), perfluorohexanes (PFHs), perfluoropolyethers (PFPEs), and chlorofluorocarbons (CFCs) is recirculated in the first closed-loop fluid path, the first portion of the fluid path is integrated with or thermally in contact with the first surface, the first processing fluid evaporates within the first portion of the fluid path at a first phase transition temperature to cool the first surface, and the operating temperature of the first surface is maintained at or near the first phase transition temperature, the first cooling circuit, A second cooling circuit comprising a second closed-loop fluid path, wherein a second processing fluid selected from FK, HFE, PFC, HFC, PFH, PFPE, and CFC is recirculated in the second closed-loop fluid path, the second portion of the fluid path is integrated with the second surface or is in thermal contact with the second surface, the second processing fluid evaporates within the second portion of the fluid path at a second phase transition temperature to cool the second surface, and the operating temperature of the second surface is maintained at or near the second phase transition temperature, the second cooling circuit comprises The first and second processing liquids exhibit different first and second phase transition temperatures and different heats of vaporization. The second device is a magnetic core, the first and third devices are hollow winding coils wound around the magnetic core to form an electric reactor, the first processing fluid flows in parallel through the hollow winding coil and vaporizes within the hollow winding coil, the second portion of the second closed-loop fluid path is embedded in a heat sink that is in thermal contact with the magnetic core, and the second processing fluid vaporizes within the heat sink to cool the magnetic core. The aforementioned two-phase liquid cooling system.

4. The system according to claim 3, wherein the first cooling circuit comprises an inlet manifold that distributes the first processing liquid so that it flows in parallel through the hollow winding coil and vaporizes, and an outlet manifold that collects and condenses the vapor from the hollow winding coil and returns it to a liquid state for recirculation, and the second cooling circuit comprises an inlet manifold that distributes the second processing liquid so that it flows through a plurality of heat sinks that are in thermal contact with the magnetic core and vaporizes, and an outlet manifold that collects and condenses the vapor from the plurality of heat sinks and returns it to a liquid state for recirculation.

5. A two-phase liquid cooling system, First and second devices, each generating heat on a first surface and a second surface, wherein the first and second devices are designed to operate at different first and second operating temperatures, A first cooling circuit comprising a first closed-loop fluid path, wherein a first processing fluid selected from fluorinated ketones (FK), hydrofluoroethers (HFE), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), perfluorohexanes (PFHs), perfluoropolyethers (PFPEs), and chlorofluorocarbons (CFCs) is recirculated in the first closed-loop fluid path, the first portion of the fluid path is integrated with or thermally in contact with the first surface, the first processing fluid evaporates within the first portion of the fluid path at a first phase transition temperature to cool the first surface, and the operating temperature of the first surface is maintained at or near the first phase transition temperature, the first cooling circuit, A second cooling circuit comprising a second closed-loop fluid path, wherein a second processing fluid selected from FK, HFE, PFC, HFC, PFH, PFPE, and CFC is recirculated in the second closed-loop fluid path, the second portion of the fluid path is integrated with the second surface or is in thermal contact with the second surface, the second processing fluid evaporates within the second portion of the fluid path at a second phase transition temperature to cool the second surface, and the operating temperature of the second surface is maintained at or near the second phase transition temperature, the second cooling circuit comprises The first and second processing liquids exhibit different first and second phase transition temperatures and different heats of vaporization. The first device includes a power semiconductor device arranged in the first closed-loop fluid path, the first processing liquid enters the power semiconductor device from the inlet, evaporates upon direct contact with the p / n junction or substrate of the power semiconductor device forming the first surface, and is discharged as vapor from the outlet. The aforementioned two-phase liquid cooling system.

6. A two-phase liquid cooling system, First and second devices, each generating heat on a first surface and a second surface, wherein the first and second devices are designed to operate at different first and second operating temperatures, A first cooling circuit comprising a first closed-loop fluid path, wherein a first processing fluid selected from fluorinated ketones (FK), hydrofluoroethers (HFE), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), perfluorohexanes (PFHs), perfluoropolyethers (PFPEs), and chlorofluorocarbons (CFCs) is recirculated in the first closed-loop fluid path, the first portion of the fluid path is integrated with or thermally in contact with the first surface, the first processing fluid evaporates within the first portion of the fluid path at a first phase transition temperature to cool the first surface, and the operating temperature of the first surface is maintained at or near the first phase transition temperature, the first cooling circuit, A second cooling circuit comprising a second closed-loop fluid path, wherein a second processing fluid selected from FK, HFE, PFC, HFC, PFH, PFPE, and CFC is recirculated in the second closed-loop fluid path, the second portion of the fluid path is integrated with the second surface or is in thermal contact with the second surface, the second processing fluid evaporates within the second portion of the fluid path at a second phase transition temperature to cool the second surface, and the operating temperature of the second surface is maintained at or near the second phase transition temperature, the second cooling circuit comprises The first and second processing liquids exhibit different first and second phase transition temperatures and different heats of vaporization. The first closed-loop fluid path further comprises a third device located upstream of the first device, wherein the first cooling circuit includes a third portion of the first closed-loop fluid path which is integrated with or in thermal contact with a third surface of the third device, and the first processing fluid cools the third surface and maintains the operating temperature at the third surface below the first phase transition temperature. The aforementioned two-phase liquid cooling system.

7. The system according to claim 6, wherein the first and third devices include power semiconductor devices coupled to a common heat sink, and the third and first portions of the closed-loop fluid path are embedded in the common heat sink to liquid-cool the third power semiconductor device and vapor-cool the first power semiconductor device.

8. A two-phase liquid cooling system, First and second devices, each generating heat on a first surface and a second surface, wherein the first and second devices are designed to operate at different first and second operating temperatures, A first cooling circuit comprising a first closed-loop fluid path, wherein a first processing fluid selected from fluorinated ketones (FK), hydrofluoroethers (HFE), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), perfluorohexanes (PFHs), perfluoropolyethers (PFPEs), and chlorofluorocarbons (CFCs) is recirculated in the first closed-loop fluid path, the first portion of the fluid path is integrated with or thermally in contact with the first surface, the first processing fluid evaporates within the first portion of the fluid path at a first phase transition temperature to cool the first surface, and the operating temperature of the first surface is maintained at or near the first phase transition temperature, the first cooling circuit, A second cooling circuit comprising a second closed-loop fluid path, wherein a second processing fluid selected from FK, HFE, PFC, HFC, PFH, PFPE, and CFC is recirculated in the second closed-loop fluid path, the second portion of the fluid path is integrated with the second surface or is in thermal contact with the second surface, the second processing fluid evaporates within the second portion of the fluid path at a second phase transition temperature to cool the second surface, and the operating temperature of the second surface is maintained at or near the second phase transition temperature, the second cooling circuit comprises The first and second processing liquids exhibit different first and second phase transition temperatures and different heats of vaporization. The first cooling circuit comprises a pump for recirculating the first processing liquid in the first closed-loop fluid path, a liquid pressure regulator for adjusting the pressure of the first processing liquid, a vapor pressure regulator for adjusting the pressure of the first processing liquid in vapor state, and a first condenser coupled to a cooling liquid reservoir for condensing the first processing vapor into the first processing liquid for recirculation. The first processing fluid comprises a conductive solid granular medium, the pump comprises an electromagnetic pump, the electromagnetic pump generates a magnetic field moving within the first closed-loop fluid path, the moving magnetic field interacts with the conductive solid granular medium to generate an electric force that propels the processing fluid and the conductive solid granular medium, the conductive solid granular medium increases heat transfer from the first surface before the first processing fluid vaporizes, thereby cooling the first surface more uniformly. The aforementioned two-phase liquid cooling system.

9. The system according to claim 8, wherein the second cooling circuit comprises a pump for recirculating the second processing liquid in the second closed-loop fluid path, a liquid pressure regulator for adjusting the pressure of the second processing liquid, a vapor pressure regulator for adjusting the pressure of the second processing liquid in vapor state, and a second condenser connected in series between the first condenser and the cooling liquid reservoir for condensing the second processing vapor into the second processing liquid for recirculation.

10. The system according to claim 8, wherein the first cooling circuit further comprises a vapor pressure sensor that senses vapor pressure and provides feedback to the liquid pressure regulator in order to control the flow rate of the processing liquid.

11. A two-phase liquid cooling system, First and second devices, each generating heat on a first surface and a second surface, wherein the first and second devices are designed to operate at different first and second operating temperatures, A first cooling circuit comprising a first closed-loop fluid path, wherein a first processing fluid selected from fluorinated ketones (FK), hydrofluoroethers (HFE), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), perfluorohexanes (PFHs), perfluoropolyethers (PFPEs), and chlorofluorocarbons (CFCs) is recirculated in the first closed-loop fluid path, the first portion of the fluid path is integrated with or thermally in contact with the first surface, the first processing fluid evaporates within the first portion of the fluid path at a first phase transition temperature to cool the first surface, and the operating temperature of the first surface is maintained at or near the first phase transition temperature, the first cooling circuit, A second cooling circuit comprising a second closed-loop fluid path, wherein a second processing fluid selected from FK, HFE, PFC, HFC, PFH, PFPE, and CFC is recirculated in the second closed-loop fluid path, the second portion of the fluid path is integrated with the second surface or is in thermal contact with the second surface, the second processing fluid evaporates within the second portion of the fluid path at a second phase transition temperature to cool the second surface, and the operating temperature of the second surface is maintained at or near the second phase transition temperature, the second cooling circuit comprises The first and second processing liquids exhibit different first and second phase transition temperatures and different heats of vaporization. The first processing liquid comprises a conductive solid granular medium, and further comprises an electromagnetic pump that generates a magnetic field moving within the first closed-loop fluid path, wherein the magnetic field interacts with the conductive solid granular medium to generate an electrical force that propels the processing liquid and the conductive solid granular medium, and the conductive solid granular medium increases heat transfer from the first surface before the first processing liquid vaporizes, thereby cooling the first surface more uniformly. The aforementioned two-phase liquid cooling system.

12. The system according to any one of claims 1 to 11, wherein the first portion of the closed-loop fluid path is embedded in a heat sink that is in thermal contact with the first surface.

13. A two-phase liquid cooling system, A power transformer comprising single-phase or multi-phase hollow primary and secondary winding coils wound around a common magnetic core, wherein the coils are energized to conduct current and generate heat, and the power transformer comprises A first cooling circuit comprising a first closed-loop fluid path, wherein a first processing liquid selected from fluorinated ketones (FK), hydrofluoroethers (HFE), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), perfluorohexanes (PFHs), perfluoropolyethers (PFPEs), and chlorofluorocarbons (CFCs) is recirculated through a single-phase or multi-phase hollow primary winding coil, evaporates within the coil at a first phase transition temperature T1 to cool the coil, and maintains the operating temperature of the coil at or near the first phase transition temperature T1, A second cooling circuit comprising a second closed-loop fluid path, wherein a second processing fluid selected from FK, HFE, PFC, HFC, PFH, PFPE, and CFC is recirculated through the single-phase or multi-phase hollow secondary winding coil, evaporates within the coil at a second phase transition temperature T2, cools the coil, and maintains the operating temperature of the coil at or near the second phase transition temperature T2. The two-phase liquid cooling system comprising the above.

14. The system according to claim 13, wherein the first and second cooling circuits each comprise a pump for recirculating the processing liquid, a liquid pressure regulator for adjusting the pressure of the processing liquid, a vapor pressure regulator for adjusting the pressure of the processing liquid in vapor state, and a condenser connected to a common cooling liquid reservoir for condensing the processing vapor into the processing liquid for recirculation.

15. The system according to claim 13, wherein each processing fluid contains a conductive solid granular medium, and the first and second cooling circuits each include an electromagnetic pump that generates a magnetic field moving within the closed-loop fluid path, the magnetic field interacts with the conductive solid granular medium to generate an electric force that propels the processing fluid and the conductive solid granular medium, and the conductive solid granular medium increases heat transfer from the hollow primary or secondary winding coil before the processing fluid vaporizes, thereby cooling the coil more uniformly.

16. The hollow primary and secondary winding coils are multiphase coils having N and M winding coils, respectively. The first cooling circuit further comprises a 1:N inlet manifold that flows the first processing liquid in parallel within the N hollow primary winding coils to vaporize it, and an N:1 outlet manifold that collects the vapor from the winding coils and condenses it back into a liquid state for recirculation. The second cooling circuit further comprises a 1:M inlet manifold that flows the second processing liquid in parallel to the M hollow secondary winding coils to vaporize it, and an M:1 outlet manifold that collects the vapor from the winding coils and condenses it back into a liquid state for recirculation. The system according to claim 13.

17. A two-phase liquid cooling system, First and second power semiconductor devices, each having one or more p / n junctions or semiconductor substrates that generate heat within a sealed case, wherein the first and second power semiconductor devices are configured to operate at different operating temperatures. A first cooling circuit comprising a first closed-loop fluid path, wherein in the first closed-loop fluid path, a first processing liquid selected from fluorinated ketones (FK), hydrofluoroethers (HFE), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), perfluorohexanes (PFHs), perfluoropolyethers (PFPEs), and chlorofluorocarbons (CFCs) enters the sealed case of the first power semiconductor device, evaporates at a first phase transition temperature T1 through direct contact with one or more p / n junctions or semiconductor substrates, cools the one or more p / n junctions or semiconductor substrates, maintains the operating temperature of the one or more p / n junctions or semiconductor substrates at or near T1, exits the case as vapor, condenses back into a liquid, and is recirculated, A second cooling circuit comprising a second closed-loop fluid path, wherein in the second closed-loop fluid path, a second processing liquid selected from FK, HFE, PFC, HFC, PFH, PFPE, and CFC enters the sealed case of the second power semiconductor device, evaporates at a second phase transition temperature T2 > T1 through direct contact with one or more p / n junctions or semiconductor substrates, cools the one or more p / n junctions or semiconductor substrates, maintains the operating temperature of the p / n junctions at or near T2, exits the case as vapor, condenses back into liquid, and is recirculated, and the second cooling circuit and Equipped with, Each processing fluid contains a conductive solid granular medium, and the first and second cooling circuits each include an electromagnetic pump, the electromagnetic pump generates a magnetic field that moves within the closed-loop fluid path, and the magnetic field interacts with the conductive solid granular medium to generate an electric force that propels the processing fluid and the conductive solid granular medium. The aforementioned two-phase liquid cooling system.

18. The system according to claim 17, wherein the first and second cooling circuits each comprise a pump for recirculating the processing liquid, a liquid pressure regulator for adjusting the pressure of the processing liquid, a vapor pressure sensor for sensing vapor pressure and feeding it back to the liquid pressure regulator in order to control the liquid flow rate, a vapor pressure regulator for adjusting the vapor pressure of the processing liquid in vapor state, and a condenser connected to a common cooling liquid reservoir for condensing the processing vapor into the processing liquid for recirculation.

19. A two-phase liquid cooling system, A first and second power semiconductor device thermally coupled to a common heat sink and electrically isolated, wherein the first power semiconductor device operates at a lower p / n junction or semiconductor substrate temperature than the second power semiconductor device, A closed-loop fluid path for recirculating a processing liquid selected from fluorinated ketones (FK), hydrofluoroethers (HFE), perfluorocarbons (PFC), hydrofluorocarbons (HFC), perfluorohexane (PFH), perfluoropolyethers (PFPE), and chlorofluorocarbons (CFC), wherein the fluid path comprises a first and a second portion of which are embedded in the common heat sink beneath the first and second power semiconductor devices, respectively. The processing fluid cools the p / n junction or semiconductor substrate of the first power semiconductor device by passing through the first portion of the fluid path, evaporates in the second portion of the fluid path, and flows to cool the p / n junction or semiconductor substrate of the second power semiconductor device. The aforementioned two-phase liquid cooling system.

20. The system according to claim 19, comprising: a pump for recirculating the processing liquid; a liquid pressure regulator for adjusting the pressure of the processing liquid; a vapor pressure sensor for sensing vapor pressure and providing feedback to the liquid pressure regulator in order to control the liquid flow rate; a vapor pressure regulator for adjusting the vapor pressure of the processing liquid in vapor state; and a condenser connected to a cooling liquid reservoir for condensing the processing vapor into the PFC liquid for recirculation.

21. The system according to claim 19, wherein the processing liquid comprises a conductive solid granular medium, and further comprises an electromagnetic pump, the electromagnetic pump generates a magnetic field that moves within the closed-loop fluid path, and the magnetic field interacts with the conductive solid granular medium to generate an electric force that propels the processing liquid and the conductive solid granular medium.

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