Two-phase liquid-cooled power device

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 August 10, 2022, which is incorporated herein by reference in its entirety.

[0002] The present invention relates to cooling systems for electrical or mechanical systems such as single-phase or multi-phase power transformers, electrical reactors, and power semiconductor devices, and more particularly to the application of two-phase liquid cooling to optimize the thermal design of different devices operating at different temperatures and heat loads using different process fluids such as fluoroketones (FKs), hydrofluoroethers (HFEs), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), perfluorohexanes (PFHs), perfluoropolyethers (PFPEs), and chlorofluorocarbons (CFCs). [Background technology]

[0003] Electrical systems such as single-phase or multi-phase transformers, electrical reactors, and power semiconductors, or mechanical systems such as bearings, generate heat, which can degrade system performance, damage or shorten the lifespan of critical components, or even cause fires.

[0004] Cooling systems are implemented to remove heat so that operating temperatures remain below a specified temperature. The capacity of a cooling system is determined by the heat load and the specified operating temperature. Often, cooling systems are 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 overall costs. Newer systems generate more heat in a smaller volume, requiring more efficient cooling systems.

[0005] A variety of cooling systems exist, adapted to remove heat depending on the space, energy, and cost requirements of the system. Heat sinks are passive heat exchangers that transfer heat generated by a device to a fluid medium (often air or a coolant liquid) where it is dissipated 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 recirculated directly through a component, 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 increasing the temperature of the fluid, which is then 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 receive 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 heating the liquid. When properly configured, these systems can provide equal or greater cooling capacity than traditional systems while utilizing less space, less energy, and at lower cost. A simple example is spraying a liquid onto a heat sink, causing the liquid to evaporate.

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

[0008] The following is a summary of the invention to provide a basic understanding of some aspects of the invention. This summary is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description and claim definitions that are presented later.

[0009] The present invention provides a two-phase liquid cooling system in which multiple cooling circuits recirculate a working fluid, transitioning it between liquid and vapor states to cool multiple devices (and their heated surfaces) and maintain different operating temperatures at or near the liquid's phase transition temperature. The working fluid should be chemically inert, thermally stable, non-toxic, exhibit high dielectric strength, and preferably commercially available. Depending on the application, suitable working fluids are selected from fluorinated ketones (FKs), hydrofluoroethers (HFEs), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), perfluorohexanes (PFHs), perfluoropolyethers (PFPEs), and chlorofluorocarbons (CFCs).

[0010] In one embodiment, a two-phase liquid cooling system includes a pair of devices that generate heat at their respective surfaces and operate at different operating temperatures. A pair of independent cooling circuits is configured to absorb the heat load and cool each device. Each circuit includes a closed-loop fluid path through which a working liquid is recirculated and transitions between a liquid state and a vapor state. A portion of the fluid path is integral with or in thermal contact with the surface of the device. The working liquid evaporates at a phase transition temperature within the portion of the fluid path to cool the surface and maintain the operating temperature of the surface at or near the first phase transition temperature. The working fluid within the cooling circuits exhibits different transition temperatures to accommodate the different heat loads and operating temperatures of the different devices.

[0011] In one embodiment, each cooling circuit includes, in a closed-loop fluid path, a pump for recirculating the processing liquid, a liquid pressure regulator for regulating the pressure of the processing liquid, a vapor pressure regulator for regulating the pressure of the processing liquid in its vapor state, and a condenser coupled to the cooling liquid reservoir for condensing the processing vapor into the processing liquid for recirculation. The cooling circuits are suitably connected in series or parallel to a common cooling liquid (usually water) reservoir. Each cooling circuit may also include a vapor pressure sensor for sensing vapor pressure and providing feedback to the liquid pressure regulator to control the flow of the processing liquid.

[0012] In some embodiments, at least one of the cooling circuits includes an additional device located upstream of an existing device. A processing liquid flows through the fluid path to cool the additional device and maintain its operating temperature below the phase transition temperature of the processing liquid. In certain embodiments, the devices are power semiconductor devices coupled to a common heat sink. A portion of the closed-loop fluid path is embedded in the common heat sink to liquid cool the upstream device and vapor cool the downstream device, which has a higher operating temperature.

[0013] In one embodiment, the processing fluid is provided with a conductive solid granular media (e.g., aluminum shot). The pump includes an electromagnetic pump (e.g., a distributed AC induction coil) that generates a moving magnetic field within a closed-loop fluid path, which interacts with the conductive solid granular media to create a force that propels both the processing fluid and the media. The media also serves to enhance the heat transfer capabilities of the processing fluid and provide more uniform cooling in the portion of the fluid path where vaporization occurs.

[0014] In one embodiment, the device and its surface are hollow wire coils wound around a common magnetic core, and when energized, current flows through the hollow wire coils, heating the coils and causing the processing fluid(s) to evaporate within the hollow wire coils.

[0015] In one embodiment, a power transformer includes single-phase or multi-phase primary (P) and secondary (S) hollow winding coils wound around a common magnetic core. One cooling circuit recirculates a first working liquid through the single-phase or multi-phase P hollow winding coils to cool the coils and maintain them at or near the transition temperature of the first working liquid. The other cooling circuit recirculates a second working liquid through the single-phase or multi-phase S hollow winding coils to cool the coils and maintain them at or near the transition temperature of the second working liquid, which is higher than the transition temperature of the first working liquid. In the case of multi-phase windings, each cooling circuit includes a liquid manifold for distributing the working liquid to the winding coils in parallel and a vapor manifold for collecting vapor from the multi-phase windings. In power transformers, secondary winding coils typically operate at higher current densities and therefore exhibit greater heat loads and higher operating temperatures than primary windings. The branch cooling system can be optimized to provide the required heat loads and different operating temperatures for both the P and S winding coils.

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

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

[0018] In another embodiment, a pair of power semiconductor devices are thermally coupled to a common heat sink but 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 device may be a semiconductor switching device such as an integrated gate commutated thyristor (IGCT) or MOSFET. Thyristors have multiple p / n junctions that are actively cooled. MOSFETs are field-effect devices (no p / n junctions), in which case the semiconductor substrate is actively cooled. Each power semiconductor is placed in a closed-loop fluid path in a separate cooling circuit. A working fluid is injected into the device, evaporates in direct contact with the p / n junction interface or semiconductor substrate at a transition temperature, exits the device as a vapor, and condenses back into a liquid for recirculation.

[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 the preferred embodiment, taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a layout diagram of an embodiment of a two-phase liquid cooling system in which separate cooling circuits recirculate different process liquids in closed-loop fluid paths to liquid cool a first device and cool a second device through phase transition to vapor, optimizing the overall thermal design of the system. [Figure 2] FIG. 1 illustrates a portion of a closed-loop fluid path in which a processing liquid flows in the liquid phase, absorbing heat and transferring it to the gas phase. [Figure 3] 1 is a diagram showing the relationship between the saturation temperature and specific energy of a fluorinated ketone in a saturated state and the vapor pressure. [Figure 4A] FIG. 1 is a diagram of a portion of a closed-loop fluid path through which a processing liquid containing a conductive solid granular medium flows, absorbs heat, and transitions to a gas phase in response to the interaction of the liquid-phase medium with a traveling wave generated by a distributed electromagnetic pump. [Figure 4B]FIG. 1 is a diagram of a portion of a closed-loop fluid path through which a processing liquid containing a conductive solid granular medium flows, absorbs heat, and transitions to a gas phase in response to the interaction of the liquid-phase medium with a traveling wave generated by a distributed electromagnetic pump. [Figure 5] FIG. 1 is a layout diagram of an embodiment of a two-phase liquid-cooled single-phase power transformer in which separate cooling circuits recirculate different process liquids through the single-phase hollow primary and secondary winding coils to maintain the operating temperatures of the coils at different levels. [Figure 6A] FIG. 1 is a side view of an embodiment of a two-phase liquid-cooled multi-phase power transformer in which separate cooling circuits recirculate different process liquids through the multi-phase hollow primary and secondary winding coils to maintain the operating temperatures of the multi-phase hollow primary and secondary winding coils at different levels. [Figure 6B] FIG. 1 is a top view of an embodiment of a two-phase liquid-cooled multi-phase power transformer in which separate cooling circuits recirculate different process liquids through the multi-phase hollow primary and secondary winding coils to maintain the operating temperatures of the multi-phase hollow primary and secondary winding coils at different levels. [Figure 7A] 1 is a table of design parameters for a two-phase liquid-cooled multi-phase power transformer. [Figure 7B] 1 is a table of parameters for various engineered fluorinated ketone fluids known as Novec™. [Figure 8A] FIG. 1 is a layout diagram of a two-phase liquid-cooled electric reactor in which independent cooling circuits recirculate different PFCs through multiple hollow-wound coils and heat sinks in thermal contact with a common magnetic core to maintain the operating temperatures of the coils and magnetic core at different levels. [Figure 8B] 1 is a table of design parameters for a two-phase liquid-cooled electric reactor in which independent cooling circuits recirculate different PFCs through multiple hollow-wound coils and heat sinks in thermal contact with a common magnetic core to maintain the operating temperatures of the coils and magnetic core at different levels. [Figure 9A] FIG. 1 is a side 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 a first device and evaporative cooling a second device. [Figure 9B] FIG. 1 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 a first device and evaporative cooling a second device. [Figure 10] FIG. 1 is a side view of a pair of power semiconductor devices on a common substrate in which different processing liquids are injected into the devices and vaporized to maintain the operating temperatures of the p / n junctions at different levels. DETAILED DESCRIPTION OF THE INVENTION

[0021] A two-phase liquid cooling system includes two or more cooling circuits that recirculate a working fluid between liquid and vapor states to cool multiple devices (and their heated surfaces) and maintain different operating temperatures at or near the liquid's phase transition temperature. The working fluid must be chemically inert, thermally stable, non-toxic, and exhibit high dielectric strength, preferably commercially available. Suitable working fluids are selected from fluorinated ketones (FKs), hydrofluoroethers (HFEs), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), perfluorohexanes (PFHs), perfluoropolyethers (PFPEs), and chlorofluorocarbons (CFCs), depending on the application. For example, cooling circuits can be used to maintain different operating temperatures for hollow primary and secondary windings of a power transformer, parallel-connected hollow winding excitation coils and a common magnetic core of an electrical reactor, power semiconductor devices mounted on heat sink(s) with embedded fluid paths, or power semiconductor devices where each fluid path passes through a device or mechanical system such as a bearing. 3M™ Company manufactures a line of process fluids under the trade name Novec™ that exhibit the properties required for a variety of applications and are examples of fluorinated ketones (FKs) 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 through 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, and heat of vaporization of 119 kJ / kg, which can be used for the first cooling circuit. The representative first device 110 is a back-iron heat sink in an electrical reactor, which consumes relatively little power due to eddy current losses in the iron. The representative second device 112 is a hollow electrical winding coil within the same electrical reactor, which consumes more power due to Joule losses in the conductor. In this example, a first portion of the closed-loop fluid path 105 is embedded in the heat sink (Device 1 110), and a second portion of the closed-loop fluid path 105 is integrally formed with the hollow electrical winding coil (Device 2 112). The working liquid 111 passes through the heat sink in a liquid state, absorbing heat Q2 and cooling the heat sink. The liquid temperature increases from T1 to T2, but remains liquid. The processing liquid 111 enters the hollow electrical winding coil in a liquid state and absorbs sufficient heat Q2 to vaporize at least a portion of the liquid inside the winding coil at a 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 liquid flow 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 and 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, excluding a small amount dissipated by the pump and piping arrangement. A feature of the present invention is that each of the four devices can be cooled at an optimal design temperature close to the specific transition temperature specific to the design current density or heat dissipation of each component device, rather than operating at a common, non-optimal liquid-to-vapor transition temperature. Two representative fluids used, Novec™ 7200 and Novec™ 7500, have significantly different vaporization heat energy levels and transition temperatures, and can be applied to a common final fluid heat exchanger loop in which the loops for 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. The excellent electrical dielectric properties of two-phase fluids provide electrical isolation for all four devices.

[0025] A key feature of two-phase liquid cooling systems is that the closed-loop fluid path makes the system orientation-independent. The system can be turned upside down, on its side, or rocked back and forth without affecting cooling performance. This is critical for applications that may be mounted on moving land vehicles, ships, or aircraft. Many conventional cooling systems, especially those utilizing vapor cooling, require a stable, upright position.

[0026] The closed-loop fluid path also improves coverage of hot device surfaces that require cooling. Spraying a liquid onto a hot surface or device inevitably results in uneven coverage and leaks, but passing the liquid through the surface or device ensures even coverage across the entire surface, resulting in more uniform cooling of the surface.

[0027] FIG. 2 shows an electrical hollow conductor 200 with an inlet manifold 201 and an outlet manifold 206, through which electrical current is injected or excited and through which a working fluid 202 is transported. The working fluid enters the inlet 201 and flows through the hollow conductor, which is also an electrical metallic conductor, such as forming the windings of an electrical reactor or transformer. Over a distance along the conductor, the accumulated heat exceeds the heat of vaporization (e.g., 119 kJ / kg for 3M™ Novec™ 7200), and the working fluid 202 transforms into a vapor 204 within the conductor at the vapor transition point and exits as a vapor through the outlet 206. The exact location of the vapor transition point has been found to vary depending on the actual electrical load and the resulting power dissipation losses within the conductor. From a design perspective, it is desirable for the vapor transition point, with maximum power dissipation, to be within the last half of the hollow conductor's path. A single conductor can be repeated multiple times in a primary or secondary winding configuration, allowing for multiple winding turns, as is the common practice when coils are electrically connected in series and electrically in parallel.

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

[0029] Referring to FIGS. 4A and 4B, a system embodiment of a two-phase liquid cooling system 400 includes a working liquid 402, to which a conductive solid granular medium 414 is added, introduced into a hollow electrical conductor 403 at an inlet 410, vaporized within the hollow electrical conductor, and discharged at an outlet 420, where it is condensed and recirculated. The medium 414 may be used to increase overall cooling capacity, improve cooling uniformity on the hollow electrical conductor 403, and propel the working 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, highly thermally conductive materials that 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 working liquid flow is doped with the medium 414 before entering the system 400, and the medium continues to flow throughout the system and exit through an outlet 420. The medium 414 accepts (and removes) heat from the first half of the hollow electrical conductor before vaporizing, thereby improving the distribution of heat acceptance and more uniformly cooling the conductor. The size of the conductive medium is small enough, e.g., 0.065 inches in diameter, to pass through the liquid pump, vapor pressure sensor, liquid pressure sensor, and condenser, as shown in FIG. 1, and be continuously recirculated. The excess heat content of the conductive medium 414 is efficiently transferred via the condenser to the external cooling liquid reservoir, also shown in FIG. 1.

[0030] An electromagnetic pump 412 can be used to propel the medium 414 and working liquid 402 through the hollow electrical conductor 403. The electromagnetic pump 412, such as a coaxial electromagnetic pump, induces magnetic waves traveling 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 eddy currents 425 induced by 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 within the hollow conductor may have a strength of 1.5 to 1.7 Tesla. The conductive medium 414 absorbs heat from the electrical conductor, and this heat is first transferred to the fluid 402 in the first portion of the coolant path. The electromagnetic pump need not be continuous; as shown in Figure 4A, the pump can be segmented to allow for bending and curvature of the electrical hollow conductor along its 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 mechanical liquid pump 106 or 120 shown in Figure 1 can be replaced by only the electromagnetic pump 412. The vapor transition point within the hollow conductor preferably occurs within the last half of the entire flow path.

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

[0033] Pump 548 supplies cooling liquid to condenser 532, shared with cooling circuit 502, at an inlet temperature T7 and an outlet temperature T8, and then transfers the cooling liquid to condenser 534, shared with cooling circuit 504, at an outlet temperature T9. Cooling liquid reservoir 546 absorbs most of the heat generated by the primary and secondary hollow winding coils. The temperature difference T9-T7 combined with the flow rate determines the cooling capacity in watts, along with the small amount of heat dissipated in the tubing connecting the various components. In a preferred embodiment, the cooling liquid is an ethylene glycol-water 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 a working liquid 511, which transitions between liquid and vapor phases, to cool a primary hollow winding coil 512. The working liquid 511 enters the primary hollow winding coil 512 as a liquid at a temperature T2, removes Joule heat loss generated by the excitation of the winding coil 512, causes a phase change to vapor within the hollow conductor, and exits through an outlet at a temperature T3 near the boiling point (transition temperature) of the working liquid. The vapor circulates in 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 working liquid to T1 and converting the vapor back to a liquid. A pump 520 ensures a constant flow of working liquid to a liquid pressure regulator 522 at an output temperature T2. Vapor pressure sensor 526 outputs a control signal that serves as a feedback control signal 528 to liquid pressure regulator 522 to limit the liquid pressure to a value within the safe operating point for hollow conductors that may be constructed with thin walls with limited burst strength. A suitable working liquid is Novec™ 649 from 3M™, which has 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 a working liquid 513, which transitions between liquid and vapor phases, to cool a secondary hollow winding coil 514. The working liquid 513 enters the secondary hollow winding coil 514 as a liquid at a temperature T5, removes Joule heat loss generated by the excitation of the winding coil 514, and causes a phase change to vapor within the hollow conductor. The working liquid is then discharged from the outlet at a temperature T6 near the boiling point (transition temperature) of the working liquid. The vapor circulates in the closed-loop fluid path 509 via a vapor pressure sensor 540, a vapor pressure regulator 544, and a condenser 534, which reduces the coolant temperature to T4 and converts the vapor back to a liquid. A pump 536 ensures a constant flow of the working liquid 513 to a liquid pressure regulator 538 at an output temperature T5. Vapor pressure sensor 540 outputs a control signal 542 that serves as a feedback control signal to liquid pressure regulator 538 to limit the liquid pressure to a value within the safe operating point of hollow conductors that may be constructed with thin walls. A suitable fluid for the secondary coolant path is Novec™ 7500 from 3M™, which has 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 a higher boiling point than the heat dissipated by the primary winding 512. Additionally, in a preferred embodiment, a thermal barrier 518 exists between the primary and secondary windings. The thermal barrier may be a fiberglass epoxy material or mica. An important feature of the present invention is that the temperature difference between the boiling points of the two processing liquids is significant at 128°C - 49°C, or 79°C. For the particular coolant selected, the primary winding 512 is a high voltage winding with additional dielectric insulation and is rated at 9.0 A / mm 2 A current density lower than the current density of the secondary winding 514 (e.g., 5.0 A / mm 2), thus reducing resistive or joule losses in the primary winding 512 and allowing the use of a lower boiling point process fluid in the primary winding 512. The system 500 includes four electrical in-line insulators 524 that provide electrical insulation to prevent excitation or load currents from flowing to or from the liquid pressure regulators 522, 538 and vapor sensors 526, 540 into the metallic conductors that make up the coolant tubing.

[0037] 6A and 6B, an embodiment of a two-phase liquid-cooled three-phase power transformer 700 includes three primary hollow winding coils 702, 704, 706 and three secondary hollow winding coils 708, 710, 712 wound in coaxial pairs around three legs 714, 716, 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 a primary winding connection 724 and a secondary winding connection 726, respectively. Although the primary and secondary coils have approximately the same ampere-turns, the secondary coils operate at a higher average temperature than the primary coils due to the smaller volume allocated to the secondary coils. As a result, the primary hollow winding coils can circulate a process liquid with a lower boiling point than another process liquid circulating in the secondary hollow winding coils.

[0038] The manifold is implemented to separate the different working liquids 720 and 722 into three parallel streams that are fed in parallel to the primary (secondary) hollow winding coils and collect the hot vapor from the primary (secondary) hollow winding coils. The manifold is in the closed-loop fluid path of the cooling circuit of a single-phase power transformer, as shown in Figure 5. The manifold can be expanded to accommodate any multi-phase implementation of N primary hollow winding coils and M secondary hollow winding coils.

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

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

[0041] Electrical insulators 750 separate the primary and secondary circuits from each other and prevent current circulation within the manifold. These electrical insulators may consist of hollow tubes of fiberglass epoxy material aligned with electrical hollow conductors that carry 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 feed the inlet manifolds 732 and 742.

[0042] Figure 7A is a table 790 of 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 secondary winding has a higher current density than the primary winding. The table shows the practical application of two different process fluids with significantly different boiling points, 76°C and 128°C, to suit the hollow conductor primary and secondary windings, respectively. Figure 7B is a table 792 for 3M™ Novec™ process fluids, showing various boiling / transition temperatures and associated key design parameters.

[0043] 8A and 8B, an embodiment of a two-phase liquid-cooled single-phase electric reactor 800 is shown, in which a pair of hollow electrical winding coils 812 and 814 are evenly distributed on opposite sides of a common magnetic core 810. Coils 812 and 814 are electrically connected in parallel via electrical cables 836 and 840. An AC power source 890 is connected via hollow electrical winding coil 814. The heat sink is divided into a pair of thermally conductive blocks 820A and 820B in thermal contact with opposite sides of 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 processing liquid 824 as a liquid at temperature T2 to an inlet manifold 830, which separates the flow of processing liquid 824 into hollow electrical winding coils 812 and hollow electrical winding coils 814 through liquid inlet line 832. Processing liquid 824 is vaporized within each hollow winding coil and exits the other end of coils 812 and 814. Coils 812 and 814 are coupled directly and via vapor return line 834 to outlet manifold 840, which collects and condenses 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 working liquid 862 as a liquid at temperature T5 to an inlet manifold 870, which separates the flow of working liquid 862 into hollow tubes or channels 816 and 818 embedded in thermally conductive blocks 820A and 820B of the heat sink. Working liquid 862 vaporizes within each hollow tube or channel and exits at the other end, which is coupled to an outlet manifold 880, which collects and condenses vapor at a common vapor outlet 882 at temperature T6.

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

[0047] Referring to Figures 9A and 9B, a two-phase liquid cooling system 900 includes first and second devices (mechanical or electrical) 910 and 920 attached to a solid substrate or thermal base 940 using optional thermal pads 930 to provide low thermal resistance between the mating surfaces. Only one working liquid 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 for multiple or parallel cooling circuit paths. The solid substrate 940 is embedded with an array of hollow tubes or channels 904, which form part of a closed-loop fluid path to circulate the working liquid 902 and transfer heat from both devices 910 and 920. A phase change occurs within the tubes embedded in the substrate 940. The system 900 allows the two devices 910 and 920 to dissipate equal or significantly different heat. For example, processing liquid 902 enters the substrate as liquid 950 at temperature T1, receives heat Q1 from device 1, raising the temperature of the liquid to T2, and receives additional heat Q2 from device 2, causing a phase transition to vapor 960 at temperature T3. This is a simple, compact, and efficient heat sink design for cooling devices that may operate at different temperatures, or devices that may 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 to do so.

[0048] 10, an embodiment of a two-phase liquid cooling system 1000 recirculates different process fluids through power semiconductor devices 1002 and 1004 to provide internal cooling through liquid evaporation depending on the heat dissipation requirements and operating temperature of each device. For example, thyristors and insulated gate bipolar transistors (IGBTs) may have different heat dissipation Q1 or Q2 due to significantly different conduction current densities, different resistivities of substrate materials, or different diameters / volumes of substrate materials. Therefore, process 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 and 1012 having cathode material 1020 and 1022, respectively, and anode material 1030 and 1032, both of which are electrically and thermally conductive. Thyristors 1002 and 1004 have cathode leads 1070 and 1072, triggered PNPN junction semiconductors 1074 and 1076, and gate leads 1060 and 1062 for controlling the thyristor. Each device is encapsulated in a ceramic shell 1056 and 1058, which forms an air gap around the semiconductor wafer. Most of the heat generated in Q1 and Q2 is conducted through the thyristor substrates 1013 and 1014 and then to the anodes 1030 and 1032, which are electrically connected to a common mounting base 1080 with limited thermal capacity as a heat sink. Some heat is conducted through the cathodes 1020, 1022 and void spaces into the ceramic shell and removed through the surrounding air. These heat sink mechanisms may be insufficient to remove the heat and maintain the desired operating temperature, or may need to be designed for a "worst case" device with maximum heat dissipation requirements.

[0050] Thus, the thyristors are inserted into closed-loop fluid paths of various cooling circuits that circulate various working liquids 1090, 1092 through the gaps of the thyristors 1002 and 1004, where the working liquids extract heat from the devices by vaporizing due to direct contact with the PNPN junction semiconductors 1074, 1076. Working liquid 1090 is introduced as a liquid at port 1040 of the thyristor 1002, flows around the semiconductor wafer 1010, specifically the PNPN junction semiconductor 1074, where it vaporizes at a transition temperature T1, and exits as a vapor at port 1050. Similarly, working liquid 1092 is introduced as a liquid at port 1042 of the thyristor 1004, flows around the semiconductor wafer 1012, specifically the PNPN junction semiconductor 1076, where it vaporizes at a transition temperature T2, and exits as a vapor at port 1052.

[0051] The vapor outlet ports 1050, 1052 are individually connected to two or more different condensers, allowing for repeated transition of the vapor to a liquid state using multiple condensers. The two process liquids are maintained 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 FIG. 1. The two process liquids may have significantly different boiling points T1 and T2 due to significantly different heat dissipation within each device. In an alternative embodiment, the common mounting block 1080 may not be a thermally conductive material, in which case the two cooling circuits extract most of the device's heat, Q1 and Q2, and then transfer this heat to the two condensers in the arrangement of FIG. 1. The system 1000 may be extended to larger semiconductor device arrays, enabling internal vapor cooling within multiple semiconductor devices. This concept also works for other types of power semiconductors, such as MOSFETs, which are field-effect devices and dissipate heat with p-type or n-type silicon or silicon carbide substrates.

[0052] While several illustrative embodiments of the invention have been shown and described, numerous variations and alternative embodiments will occur to those skilled in the art. Such variations and alternative embodiments are contemplated and can be made without departing from the scope of the invention, as defined in the appended claims.

Claims

1. 1. A two-phase liquid cooling system comprising: first and second devices that generate heat at a first surface and a second surface, respectively, the first and second devices being designed to operate at different first and second operating temperatures; a first cooling circuit comprising a first closed-loop fluid path through which a first processing liquid selected from fluorinated ketones (FKs), hydrofluoroethers (HFEs), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), perfluorohexanes (PFHs), perfluoropolyethers (PFPEs), and chlorofluorocarbons (CFCs) is recirculated, a first portion of the fluid path being integral with or in thermal contact with the first surface, the first processing liquid evaporating within the first portion of the fluid path at a first phase transition temperature to cool the first surface and maintain the operating temperature of the first surface at or near the first phase transition temperature; a second cooling circuit comprising a second closed-loop fluid path in which a second processing liquid selected from FK, HFE, PFC, HFC, PFH, PFPE, and CFC is recirculated, a second portion of the fluid path being integral with or in thermal contact with the second surface, the second processing liquid evaporating within the second portion of the fluid path at a second phase transition temperature to cool the second surface and maintain the operating temperature of the second surface at or near the second phase transition temperature; the first and second processing liquids exhibit different first and second phase transition temperatures and different heats of vaporization; The two-phase liquid cooling system.

2. 2. The system of claim 1, wherein the first surface and the first portion of the closed-loop fluid path are integrated into a hollow wound coil wound around a magnetic core, and the hollow wound coil is energized to pass an electric current therethrough, and the first working liquid evaporates within the hollow wound coil to cool the hollow wound coil.

3. 2. The system of claim 1, wherein 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 working liquids evaporate within the single-phase or multi-phase hollow primary and secondary winding coils, respectively, to cool the respective coils.

4. 2. The system of claim 1, wherein the second device is a magnetic core, the first device and the third device are hollow wound coils wound around the magnetic core to form an electrical reactor, the first working fluid flows in parallel through the hollow wound coils and vaporizes within the hollow wound coils, the second portion of the second closed-loop fluid path is embedded in a heat sink in thermal contact with the magnetic core, and the second working liquid vaporizes within the heat sink to cool the magnetic core.

5. 5. The system of claim 4, wherein the first cooling circuit comprises an inlet manifold that distributes the first working fluid to flow through the hollow winding coils in parallel and vaporize, and an outlet manifold that collects vapor from the hollow winding coils, condenses it, and returns it to a liquid state for recirculation, and the second cooling circuit comprises an inlet manifold that distributes the second working fluid to flow through a plurality of heat sinks in thermal contact with the magnetic core and vaporize, and an outlet manifold that collects vapor from the plurality of heat sinks, condenses it, and returns it to a liquid state for recirculation.

6. 2. The system of claim 1, wherein the first device includes a power semiconductor device disposed in the first closed-loop fluid path, and the first processing liquid enters the power semiconductor device through an inlet, evaporates due to direct contact with a p / n junction or a substrate of the power semiconductor device forming the first surface, and exits through an outlet as a vapor.

7. The system of claim 1 , wherein the first portion of the closed-loop fluid path is embedded in a heat sink in thermal contact with the first surface.

8. 10. The system of claim 1, further comprising a third device disposed upstream of the first device in the first closed-loop fluid path, the first cooling circuit including a third portion of the first closed-loop fluid path that is integral with or in thermal contact with a third surface of the third device, and the first processing liquid cools the third surface to maintain the operating temperature at the third surface below the first phase transition temperature.

9. 9. The system of claim 8, wherein the first and third devices include power semiconductor devices coupled to a common heat sink, and wherein 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.

10. 2. The system of claim 1, wherein 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 regulating the pressure of the first processing liquid, a vapor pressure regulator for regulating the pressure of the first processing liquid in a 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.

11. 11. The system of claim 10, 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 regulating the pressure of the second processing liquid, a vapor pressure regulator for regulating the pressure of the second processing liquid in a vapor state, and a second condenser coupled in series between the first condenser and the cooling liquid reservoir for condensing the second processing vapor into the second processing liquid for recirculation.

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

13. 11. The system of claim 10, wherein the first processing fluid comprises an electrically conductive solid granular medium, the pump comprises an electromagnetic pump, the electromagnetic pump generates a moving magnetic field in the first closed-loop fluid path, the moving magnetic field interacting with the electrically conductive solid granular medium to generate an electric force that propels the processing fluid and the electrically conductive solid granular medium, and the electrically conductive solid granular medium increases heat transfer from the first surface prior to vaporization of the first processing liquid to more uniformly cool the first surface.

14. 10. The system of claim 1, wherein the first processing fluid includes a conductive solid granular medium, further comprising an electromagnetic pump generating a magnetic field that moves within the first closed-loop fluid path, the magnetic field interacting 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 increasing heat transfer from the first surface prior to vaporization of the first processing liquid to more uniformly cool the first surface.

15. 1. A two-phase liquid cooling system comprising: a power transformer comprising single-phase or multi-phase hollow primary and secondary winding coils wound around a common magnetic core, the coils being energized to cause current to flow through the coils and generate heat; a first cooling circuit comprising a first closed-loop fluid path in which a first processing liquid selected from fluorinated ketones (FKs), hydrofluoroethers (HFEs), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), perfluorohexanes (PFHs), perfluoropolyethers (PFPEs), and chlorofluorocarbons (CFCs) is recirculated through the single-phase or multi-phase hollow primary winding coil and vaporizes within the coil at a first phase transition temperature T1 to cool the coil and maintain an 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 in which a second working liquid selected from FK, HFE, PFC, HFC, PFH, PFPE, and CFC is recirculated through the single-phase or multi-phase hollow secondary winding coil and vaporizes within the coil at a second phase transition temperature T2 to cool the coil and maintain the operating temperature of the coil at or near the second phase transition temperature T2>T1; The two-phase liquid cooling system.

16. 16. The system of claim 15, wherein the first and second cooling circuits each comprise a pump for recirculating the processing liquid, a liquid pressure regulator for regulating the pressure of the processing liquid, a vapor pressure regulator for regulating the pressure of the processing liquid in a vapor state, and a condenser coupled to a common cooling liquid reservoir for condensing the processing vapor into the processing liquid for recirculation.

17. 16. The system of claim 15, wherein each working fluid includes an electrically conductive solid granular medium, and wherein the first and second cooling circuits each include an electromagnetic pump that generates a magnetic field that moves within the closed-loop fluid path, the magnetic field interacting with the electrically conductive solid granular medium to generate an electric force that propels the working liquid and the electrically conductive solid granular medium, the electrically conductive solid granular medium increasing heat transfer from the hollow primary or secondary wound coil to more uniformly cool the coil before the working liquid vaporizes.

18. the hollow primary and secondary winding coils are multi-phase coils having N and M winding coils, respectively; the first cooling circuit further comprising a 1:N inlet manifold for flowing the first working liquid in parallel through the N hollow primary winding coils to vaporize, and an N:1 outlet manifold for collecting vapor from the winding coils and condensing it back to a liquid state for recirculation; the second cooling circuit further comprising a 1:M inlet manifold for flowing the second working liquid through the M hollow secondary winding coils in parallel for vaporization, and an M:1 outlet manifold for collecting vapor from the winding coils and condensing it back into a liquid state for recirculation; The system of claim 15.

19. 1. A two-phase liquid cooling system comprising: a first and second power semiconductor device, each having one or more heat-generating p / n junctions or semiconductor substrates within a sealed case, the first and second power semiconductor devices configured to operate at different operating temperatures; a first cooling circuit comprising a first closed-loop fluid path in which a first working liquid selected from fluorinated ketones (FK), hydrofluoroethers (HFE), perfluorocarbons (PFC), hydrofluorocarbons (HFC), perfluorohexane (PFH), perfluoropolyethers (PFPE), and chlorofluorocarbons (CFC) enters the sealed case of the first power semiconductor device, evaporates at a first phase transition temperature T1 upon direct contact with the one or more p / n junctions or semiconductor substrate to cool the one or more p / n junctions or semiconductor substrate and maintain the operating temperature of the one or more p / n junctions or semiconductor substrate at or near T1, exits the case as a vapor, and is condensed back into liquid and recirculated; a second cooling circuit comprising a second closed-loop fluid path in which a second working 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 upon direct contact with the one or more p / n junctions or semiconductor substrate to cool the one or more p / n junctions or semiconductor substrate and maintain the operating temperature of the p / n junctions at or near T2, exits the case as a vapor, and is condensed back into liquid and recirculated; The two-phase liquid cooling system.

20. 20. The system of claim 19, 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 fluid, a vapor pressure sensor for sensing vapor pressure and feeding it back to the liquid pressure regulator to control liquid flow rate, a vapor pressure regulator for adjusting the vapor pressure of the processing liquid in a vapor state, and a condenser coupled to a common cooling liquid reservoir for condensing the processing vapor into the processing liquid for recirculation.

21. 20. The system of claim 19, wherein each processing fluid includes an electrically conductive solid granular medium, and wherein the first and second cooling circuits each include an electromagnetic pump that generates a magnetic field that travels within the closed-loop fluid path, the magnetic field interacting with the electrically conductive solid granular medium to generate an electric force that propels the processing liquid and the electrically conductive solid granular medium.

22. 1. A two-phase liquid cooling system comprising: first and second power semiconductor devices thermally coupled to a common heat sink and electrically isolated, the first power semiconductor operating 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 a fluorinated ketone (FK), a hydrofluoroether (HFE), a perfluorocarbon (PFC), a hydrofluorocarbon (HFC), a perfluorohexane (PFH), a perfluoropolyether (PFPE), and a chlorofluorocarbon (CFC), the fluid path having first and second portions embedded within the common heat sink below the first and second semiconductor devices, respectively; the working liquid flows through a first portion of the fluid path to cool the first power semiconductor p / n junction or semiconductor substrate, and evaporates and flows through a second portion of the fluid path to cool the second power semiconductor p / n junction or semiconductor substrate; The two-phase liquid cooling system.

23. 23. The system of claim 22, 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 to control liquid flow rate; a vapor pressure regulator for adjusting the vapor pressure of the processing liquid in a vapor state; and a condenser coupled to a cooling liquid reservoir for condensing the processing vapor into the PFC liquid for recirculation.

24. 23. The system of claim 22, wherein the processing fluid includes a conductive solid granular medium, and further comprising an electromagnetic pump, the electromagnetic pump generating a magnetic field that travels within the closed-loop fluid path, the magnetic field interacting 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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