Multi-siphon passive cooling system with liquid bridge

Abstract

A multi-siphon passive cooling system includes a heat exchanger thermally connected to a heat-generating component located within an enclosure; a distribution manifold located below the heat exchanger; a condensing unit located outside the enclosure and above the heat exchanger; and a first conduit thermally connected to the heat exchanger. The first conduit is fluidly connected to the distribution manifold and the condensing unit. The cooling system also includes a second conduit fluidly connected to the condensing unit and the distribution manifold; a liquid bridge fluidly connected to the first conduit and the second conduit or the distribution manifold; and a two-phase cooling medium circulated through a loop defined by the first conduit, the liquid bridge, the condensing unit, the second conduit, the heat exchanger, and the distribution manifold. The liquid bridge thus transfers the cooling medium in a liquid state from the first conduit to the second conduit or the distribution manifold.

Description

Technical Field

[0001] The present disclosure relates generally to wind turbines and, more particularly, to a multi-siphon passive cooling system for a wind turbine. Background Art

[0002] Wind power is considered one of the cleanest and most environmentally friendly energy sources currently available, and wind turbines are gaining increasing attention in this regard. A modern wind turbine typically consists of a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The rotor blades capture the kinetic energy of the wind using the known airfoil principle. The rotor blades transfer this kinetic energy in the form of rotational energy, which turns a shaft that connects the rotor blades to a gearbox (or, if a gearbox is not used, directly to a generator). The generator then converts the mechanical energy into electrical energy, which can be distributed to the utility grid.

[0003] Many known devices (e.g., generators, rectifiers, inverters, and transformers) are used to convert electrical power. Rectifiers are used to convert alternating current (AC) into direct current (DC), and inverters are used to convert DC current into AC current. Typically, rectifiers and inverters are integrated into the overall power conversion assembly (i.e., power converter) used in renewable electric power generation facilities (such as solar power generation fields and wind turbine fields). These devices typically generate a large amount of heat during power generation. At least some known power generation devices use liquid cooling systems to cool the main heat-generating components. These liquid cooling systems include active pumps that pump a working fluid to cool the power device, and these systems may also include fans and valves. In such systems, maintaining the flow rate of the working fluid in two or more branches of the liquid cooling system can be problematic because the resistance to the flow of the working fluid in some branches is greater than the resistance to the flow of the working fluid in other branches.

[0004] Liquid cooling systems that utilize pumps, fans, and / or valves are classified as active systems. The term "active" refers to the mechanical action performed by a pump to circulate the liquid cooling medium, or the forced airflow provided by a fan. All active systems require regular maintenance, which is crucial to system reliability. For example, if a pump fails, the entire cooling system will not be able to adequately cool the heat-generating components. This is particularly problematic for offshore wind turbines, where access and maintenance opportunities are limited. Summary of the Invention

[0005] Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

[0006] In one aspect, the present disclosure is directed to a passive cooling system. The passive cooling system includes: a heat exchanger thermally coupled to a heat-generating component located within an enclosure; a distribution manifold located below the heat exchanger; a condensing unit located outside the enclosure and above the heat exchanger; and a first conduit thermally connected to the heat exchanger. The first conduit is fluidly connected to the distribution manifold and the condensing unit. The cooling system further includes: a second conduit fluidly connected to the condensing unit and the distribution manifold; a liquid bridge fluidly connected to the first conduit and the second conduit or the distribution manifold; and a two-phase cooling medium circulated through a loop defined by the first conduit, the liquid bridge, the condensing unit, the second conduit, the heat exchanger, and the distribution manifold. Thus, the liquid bridge transfers the cooling medium in a liquid state from the first conduit to the second conduit or the distribution manifold.

[0007] In one embodiment, a cooling system may include: a plurality of heat exchangers thermally connected to a plurality of heat-generating components; and a plurality of first conduits connected in parallel between a distribution manifold and a condensing unit. In such an embodiment, each of the plurality of first conduits may be fluidly connected to one of the plurality of heat exchangers. In another embodiment, the cooling system may include two or more heat exchangers connected in series along one of the first conduits.

[0008] In further embodiments, the cooling system may further include a plurality of liquid bridges fluidly connected to the plurality of first and second conduits or the distribution manifold.

[0009] In additional embodiments, one of the plurality of liquid bridges may be fluidly connected to each of the plurality of first conduits and the second conduit or distribution manifold.

[0010] In certain embodiments, the liquid bridge may be a tubular member positioned at an oblique angle between the first conduit and the second conduit or distribution manifold. In alternative embodiments, the tubular member may include at least one trap.

[0011] In one embodiment, the housing may comprise a nacelle of a wind turbine or solar power system. In such an embodiment, the condensing unit may be mounted atop the nacelle. In another embodiment, the heat-generating component(s) may comprise a generator rotor, a generator stator, a gearbox, a transformer, an inverter, a converter, or a combination thereof. In further embodiments, the cooling system may lack a pump or fan within the housing.

[0012] In another aspect, the present disclosure relates to a wind turbine. The wind turbine includes: a tower; a nacelle mounted atop the tower and defining an enclosed interior volume; a rotor mounted to the nacelle and having a rotatable hub and at least one rotor blade mounted to the hub; at least one heat-generating component positioned within the interior volume of the nacelle; and a passive cooling system for cooling the interior volume of the nacelle. The cooling system includes: a heat exchanger thermally coupled to the at least one heat-generating component; a distribution manifold located below the heat exchanger; a condensing unit located outside the nacelle and above the heat exchanger; a first conduit fluidly connected to the heat exchanger, the distribution manifold, and the condensing unit; a second conduit fluidly connected to the condensing unit and the distribution manifold; a liquid bridge fluidly connected to the first conduit and the second conduit or the distribution manifold; and a two-phase cooling medium circulated through a loop defined by the first conduit, the liquid bridge, the condensing unit, the second conduit, the heat exchanger, and the distribution manifold. Thus, the liquid bridge transfers the cooling medium in a liquid state from the first conduit to the second conduit or the distribution manifold. It should be further understood that the wind turbine may also include any of the additional features described herein.

[0013] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims.The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] A full and enabling disclosure of the invention, including the best mode thereof, to one of ordinary skill in the art is set forth in the specification with reference to the accompanying drawings, in which:

[0015] Figure 1 illustrates a perspective view of one embodiment of a wind turbine according to the present disclosure;

[0016] Figure 2 illustrates a schematic diagram of one embodiment of a cooling system according to the present disclosure;

[0017] Figure 3 illustrates a schematic diagram of another embodiment of a cooling system according to the present disclosure;

[0018] Figure 4 illustrates a schematic diagram of a first conduit and a heat exchanger thermally connected to a heat generating component according to the present disclosure;

[0019] Figure 5 illustrates a schematic diagram of yet another embodiment of a passive cooling system according to the present disclosure, particularly illustrating a liquid bridge fluidly connected to a first conduit and a distribution manifold;

[0020] Figure 6 illustrates a schematic diagram of one embodiment of a liquid bridge of a passive cooling system according to the present disclosure;

[0021] Figure 7 illustrates a schematic diagram of another embodiment of a passive cooling system according to the present disclosure;

[0022] Figure 8 A schematic diagram illustrating another embodiment of a liquid bridge of a passive cooling system according to the present disclosure; and

[0023] Figure 9 A schematic diagram of yet another embodiment of a passive cooling system according to the present disclosure is illustrated, particularly illustrating a plurality of liquid bridges fluidly connected to a plurality of first conduits and a distribution manifold. DETAILED DESCRIPTION

[0024] Reference will now be made in detail to embodiments of the present invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided to explain the present invention, not to limit the present invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the present invention. For example, features illustrated or described as part of one embodiment can be used together with another embodiment to produce yet another embodiment. Therefore, it is intended that the present invention encompass such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0025] Generally speaking, the present disclosure is directed to a multi-siphon cooling system having at least one liquid bridge for cooling heat-generating components. The cooling system described herein is particularly suitable for use in wind turbines. However, it should be understood that the cooling system may also be suitable for other applications, including but not limited to solar, hydro, energy storage, and the like, or combinations thereof.

[0026] Generally speaking, a thermosiphon generally refers to a passive, single-phase or two-phase cooling system in which heat is dissipated from a motor or electronic component through a phase change from liquid to vapor (e.g., boiling). The liquid-vapor mixture passively rises to a condenser due to buoyancy, where it returns to liquid form and flows downward again to the heat-generating component due to gravity. This cycle continues to passively remove heat from the component. In the present disclosure, this concept is extended to multiple heat-generating components, each with an associated heat exchanger, connected in a parallel / series configuration to form a passive, high-heat-transfer cooling system (referred to as a "multi-siphon"). In embodiments, the cooling system can be completely passive and thus may not require a pump or fan to circulate the cooling fluid through it, for example within the casing. Thus, by providing a wind turbine head with a multi-siphon system, pumps and / or blowers can be eliminated, and the size of the heat exchanger can be reduced, thereby reducing the overall volume and weight of the head. Furthermore, no additional power is required to circulate the cooling fluid. In this way, the cooling system described herein is reliable and requires little, if any, maintenance.

[0027] Aspects discussed herein disclose a cooling and heat dissipation system having a thermosiphon comprising one or more cooling loops, each of which includes at least one heat exchanger thermally coupled to a heat-generating component. Such a cooling system can be used, for example, to thermally manage power converters, inverters, transformers, gearboxes, or generators in wind turbines, solar power systems, and the like. Additionally, the cooling and heat dissipation system can be used to thermally manage hermetically sealed motors (e.g., pitch or yaw drives). The cooling system includes a first conduit, a condensing unit, a second conduit, a distribution manifold, and at least one liquid bridge, all connected in a loop. The liquid bridge refers to the fluid connection between the rising liquid-vapor column (riser) and the descending liquid condensate column (downer) from the evaporator. Thus, the liquid bridge serves to separate liquid from the rising liquid-vapor mixture and return the liquid to the inlet side. The liquid bridge also reduces pressure drop in the system by providing parallel paths for the liquid. The liquid bridge can be a single, conventional tube inclined at an angle connecting the riser and downcomer, or multiple bridges, with at least one bridge for each heat source (e.g., evaporator). The bridge may also be reinforced with one or more traps (such as a P-trap) to improve liquid-vapor separation. In addition, the liquid bridge of the present disclosure may also reduce the total refrigerant mass flow rate through the evaporator and thus reduce the evaporator heat load, thereby reducing its size and / or cost.

[0028] The condenser is disposed above the first and second conduits and the heat exchanger associated with the heat generating component. It should be noted herein that the term "above..." as used herein means that the condenser is physically located at a higher position relative to the first conduit and the heat generating component. Thus, the condensing unit is configured to receive a two-phase fluid from the first conduit and dissipate the extracted heat to the ambient atmosphere to produce a single-phase fluid. It should be noted herein that the term "single-phase fluid" refers to a liquid medium. Similarly, the term "two-phase fluid" may refer to a mixture of a liquid and a gaseous medium, or a gaseous medium.

[0029] Referring now to the accompanying drawings, Figure 1 A side view of a wind turbine 10 is shown. As shown, wind turbine 10 generally includes a tower 12 extending from a support surface 14 (e.g., the ground, a concrete pad, an offshore platform, or any other suitable support surface). Furthermore, wind turbine 10 may also include a nacelle 16 mounted on tower 12 and a rotor 18 coupled to nacelle 16. Rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to and extending outward from hub 20. For example, rotor 18 may include three rotor blades 22 (as shown). However, rotor 18 may include more or fewer than three rotor blades 22. Each rotor blade 22 is spaced about hub 20 to facilitate rotating rotor 18, enabling kinetic energy from wind energy to be converted into usable mechanical energy, and subsequently, electrical energy. For example, hub 20 may be rotatably coupled to a generator (not shown) positioned within nacelle 16 to permit electrical energy to be generated.

[0030] Now refer to Figure 2 , illustrates a schematic diagram of one embodiment of a passive cooling system 200 according to the present disclosure. Various components within a wind turbine's nacelle (or housing) 16 require cooling. For example, such heat-generating components may include a transformer 201, a converter 202, a gearbox 203, or a generator 204 (including both a generator rotor and / or a generator stator). Figure 2 The specific components shown in the figure are only an example, and the nacelle may omit certain heat generating components or add other components. For example, since the rotor is directly connected to the generator, a direct drive wind turbine does not have a gearbox, so the gearbox will be omitted in this embodiment. Figure 2 As shown in FIG, all heat generating components 201 - 204 are located or housed within the housing 16 .

[0031] Each heat-generating component 201-204 is thermally connected to a first conduit 210', 210", 210'", and the first conduit is fluidically connected to a distribution manifold 220 and a condensing unit 230 located outside the housing 16 and above the heat-generating components 201-204. A second conduit 240 is fluidically connected to the condensing unit 230 and the distribution manifold 220. One or more of the conduits 210, 240 contains a two-phase cooling medium. When the two-phase cooling medium is heated by absorbing thermal energy from the heat-generating components 201-204, the two-phase cooling medium becomes gaseous and rises, and when the cooling medium is cooled in the condensing unit 230, the cooling medium returns to a liquid state.

[0032] The first loop consists of a first conduit 210', a transformer 201, a condensing unit 230, a second conduit 240, and a distribution manifold 220. The second loop consists of a first conduit 210", a converter 202, a condensing unit 230, a second conduit 240, and a distribution manifold 220. The third loop consists of a first conduit 210'", a gearbox 203, a generator 204, a condensing unit 230, a second conduit 240, and a distribution manifold 220. Multiple first conduits 210', 210", and 210'" form parallel flow paths between the distribution manifold and the condensing unit. Each path may have a heat-generating component connected in series with the first conduit 210'", the gearbox 203, and the generator 204, as shown. The cooling medium is in its liquid state in the distribution manifold 220, which is the lowest element in the system because gravity is used to collect and return the liquid cooling medium to the distribution manifold 220. Liquid cooling medium also exists in the lower portion of first conduits 210', 210", and 210'". During operation of wind turbine 10, heat is generated by heat-generating components 201-204, which is transferred to the cooling medium. The cooling medium undergoes a phase transition to a gaseous state, and a thermosiphon naturally forms as the gas rises along first conduits 210', 210", and 210'" toward condensing unit 230.

[0033] As mentioned, the condensing unit 230 is located outside the housing 16 (or nacelle) and is exposed to natural convection cooling caused by wind. In some embodiments, the condensing unit 230 may also include a fan outside the nacelle 16 to enhance heat transfer between the two-phase fluid or gas and the ambient air. Such a system may be useful in situations where wind speed is insufficient to remove all heat from heat-generating components within the nacelle. The gaseous cooling medium in the condensing unit 230 cools down and changes phase back to its liquid state, which is denser than the gaseous state. This liquid cooling medium flows through the second conduit 240 toward the distribution manifold 220. The natural force of convection is the driving force for the circulation of the cooling medium. The hot vapor rises to the condensing unit 230, and the cooler liquid flows to the distribution manifold 220 via the second conduit 240. Therefore, the cooling system 200 does not require the use of pumps or fans to circulate the cooling medium throughout the system 200 (i.e., within the nacelle 16). The hotter components also self-regulate the flow rate of the cooling medium through the first conduits 210 ′, 210 ″, 210 ′″.

[0034] Still refer to Figure 2 , the cooling system 200 may further include a vapor spreader 250, which is inserted between the first conduits 210', 210", 210'' and the condensing unit 230 and is fluidly connected to the first conduits 210', 210", 210'' and the condensing unit 230. In certain embodiments, the vapor spreader 250 may be a diffuser that enables the gaseous cooling medium to expand and effectively fill the condensing unit 230. Furthermore, in embodiments, the vapor spreader 250 may also reduce the pressure of the vapor and reduce its condensation temperature. Moreover, the vapor spreader 250 may be disposed within the housing 16, partially within and outside the housing 16, or entirely outside the housing. In another embodiment, the vapor spreader 250 may be attached to the housing / nacelle 16 (e.g., Figure 2 ), or the condensing unit 230 may be attached to the housing / nacelle 16.

[0035] The two-phase cooling medium described herein may have a boiling point of about 60°C or less at a typical operating pressure of about 6 bar or less (as a non-limiting example). In addition, the temperature range of the boiling point may be selected to sufficiently cool the electronic components (e.g., transformers, converters, etc.) and prevent them from overheating. Coolants with higher boiling points (e.g., water with a boiling point of 100°C) become too hot before they phase change to gas and cause the electronic components to experience overheating conditions. Thus, examples of satisfactory cooling media may include dodecafluoro-2-methylpentan-3-one (e.g., 3M TM Novec TM 649, a trademark of 3M), Novec TM7000, R245fa, R1233zd(e), or fluids with the chemical composition CF3CF2C(O)CF(CF3)2. Other less environmentally friendly alternatives could be 1,1,1,2-tetrafluoroethane, R-134a, 2,3,3,3-tetrafluoropropylene, or HFO-1234yf; however, these may not be available in liquid form for the required period of time or within the required temperature range.

[0036] Now refer to Figure 3 , illustrates a schematic diagram of another embodiment of a cooling system 300 according to the present disclosure. As shown, the condensing unit 230 is attached to the housing or nacelle 16, and the vapor spreader (e.g. Figure 2 In addition, as shown, the first conduits 210', 210", 210'" are directly fluidically connected to the condensing unit 230. This embodiment (and Figure 2 An advantage of the embodiment shown in FIGURE 2 is that the nacelle 16 can be sealed. External vents to allow air into the nacelle 16 are not required, which can be advantageous in sandy, dusty, or saltwater environments. Furthermore, a sealed nacelle reduces or eliminates the ingress of contaminants into the nacelle's interior, which is beneficial for the various components housed therein (i.e., the generator rotor, generator stator, transformer, converter, etc.). Another advantage of the cooling systems 200, 300 described herein may be that the condensing unit 230 only needs to be elevated above the upper portion of the first ducts 210', 210", 210'" to achieve natural convection. This allows the condensing unit 230 to be attached directly to the top of the nacelle 16. In other words, a large or significant height difference between the condensing unit 230 and the heat-generating components 201-204 is not required for the system to function properly. Due to the significant wind loads experienced at such a high altitude above the nacelle 16, permanently elevating the condensing unit 230 (e.g., on top of a pole) can be highly problematic. Thus, the condensing unit 230 is more stable, safe, and reliable when attached to the nacelle, either directly or via the vapor spreader 250. Furthermore, orienting the condensing unit 230 perpendicular to the wind flow eliminates the need for an electric fan. When the wind blows at a reduced rate, the associated heat load to be dissipated will also be reduced.

[0037] Now refer to Figure 4, illustrates a schematic diagram of a first conduit 210''' and a heat exchanger 460 thermally connected to a heat generating component 203 in accordance with the present disclosure. As shown, the heat exchanger 460 can be an annular or spiral first conduit 210''' that is thermally connected to the component 203, or the heat exchanger can include a separate cooling loop that circulates a heat transfer medium. For example, the heat exchanger 460 can include a heat transfer loop 461 that passes in or around the component 203. The loop 461 can be configured in a counter-flow arrangement relative to the first conduit 210''' (as shown), or in a cross-flow arrangement in which the heat transfer medium in the loop 461 travels approximately orthogonal to the flow in the first conduit 210'''. The loop 461 and the conduit 210''' can also be configured in a parallel flow arrangement in which the two flows travel in the same direction. The heat transfer medium in loop 461 can be air or a fluid, which can exchange heat with the flow through first conduits 210', 210", 210'" using a parallel plate heat exchanger, in which the fluids in fluid loop 203 and first conduits 210', 210", 210'" flow through alternating paths in parallel or opposite directions. Other types of heat exchangers may also include, but are not limited to, cross-flow heat exchangers. Heat transfer from component 203 to heat exchanger 460 may also occur through radiation or conduction effects. For example, a highly thermally conductive material (e.g., copper or aluminum) may be attached to component 203, and first conduits 210', 210", 210'" may be embedded within or attached to the highly thermally conductive material. The highly thermally conductive material connected to component 203 may also have internal flow conduits or channels that are fluidically connected to first conduit 210 at the inlet and outlet. The internal flow conduits or channels may have extended surfaces for increasing surface area that enhances heat transfer from the heat generating components to the fluid.An additional heat exchanger 460 (and corresponding first conduit) may be thermally attached to each heat generating component that is desired to be cooled.

[0038] Now refer to Figure 5 , illustrates a schematic diagram of yet another embodiment of a passive cooling system 400 according to the present disclosure. As shown, the passive cooling system 400 includes one or more heat exchangers 402 associated with one or more heat-generating components located within a housing 404 (such as, for example, the nacelle 16 of the wind turbine 10). For example, as described herein, in embodiments, the heat-generating component(s) may include the generator 204 (e.g., a generator rotor or a generator stator), the gearbox 203, the transformer 201, the converter 202, or any combination thereof of the wind turbine 10.

[0039] Furthermore, as shown, cooling system 400 includes a distribution manifold 406 located below heat exchangers 402 and a condensing unit 408 located outside housing 404 and above heat exchangers 402. Furthermore, as shown, cooling system 400 includes a first conduit 410 fluidly connected to each of heat exchangers 402. Furthermore, as shown, first conduit 410 is fluidly connected to distribution manifold 406 and condensing unit 408. For example, as shown, cooling system 400 may include a plurality of first conduits 410 connected in parallel between distribution manifold 406 and condensing unit 408. In such an embodiment, as shown, each of the plurality of first conduits 410 may be fluidly connected to one of the plurality of heat exchangers 402. In another embodiment, cooling system 400 may include two or more heat exchangers 402 connected in series along one of the first conduits 410.

[0040] Still refer to Figure 5 , cooling system 400 also includes a second conduit 412 fluidly connected to condensing unit 408 and distribution manifold 406. Furthermore, as shown, cooling system 400 includes at least one liquid bridge 414 fluidly connected to each of first conduits 410 and second conduit 412 or distribution manifold 406. More specifically, as shown, cooling system 400 may include a plurality of liquid bridges 414 fluidly connected to the plurality of first conduits 410 and second conduits 412 or distribution manifold 406. In a particular embodiment, as shown, one of the plurality of liquid bridges 414 may be fluidly connected to each of the plurality of first conduits 410 and second conduits 412 or distribution manifold 406. Thus, a two-phase cooling medium (e.g., vapor to liquid) may circulate through a loop defined by heat exchanger 402, first conduits 410, liquid bridges 414, condensing unit 408, second conduits 412, and distribution manifold 406. Thus, the liquid bridge 414 transfers the cooling medium in a liquid state from the first conduit 410 to the second conduit 412 or the distribution manifold 406 .

[0041] More specifically, Figure 6, a detailed schematic diagram of a portion of a multi-siphon cooling system 400 is illustrated, specifically depicting an embodiment of a liquid bridge 414. In the illustrated embodiment, by way of example, the liquid bridge 414 provides a fluid connection between an ascending column of liquid-vapor from one of the heat exchangers 402 (i.e., the first conduit(s) 410) and a descending column of liquid condensate (i.e., the second conduit 412 or distribution manifold 406). More specifically, as shown, the first conduit(s) 410 may include a flow splitter 416 for capturing liquid. For example, in certain embodiments, the flow splitter 416 may be a cyclonic flow splitter or a chevron demister. Similarly, the second conduit 412 or distribution manifold 406 may include a mixer 418 for receiving the captured liquid and mixing it with the descending liquid condensate. Thus, the liquid bridge(s) 414 described herein serve to separate liquid from the rising liquid-vapor mixture and return the liquid to the inlet side of the cooling system 400. The liquid bridge(s) 414 described herein also reduce pressure drop in the system 400 by providing parallel paths for the liquid.

[0042] Now refer to Figure 7 , illustrates a schematic diagram of another embodiment of a cooling system 400. As shown, the heat generator component of cooling system 400 can be the stator 205 of generator 204. More specifically, as shown, stator 205 includes a thermosyphon jacket 206 wrapped around its outer diameter. Furthermore, as shown, jacket 206 can also include one or more channels 211 extending along its periphery from the bottom to the top of stator 205. More specifically, as shown, these channels are parallel and can be connected at the top and bottom by inlet and outlet manifolds 207 and 209. Thus, in this embodiment, heat from stator 205 causes the liquid in jacket 206 to convert into vapor. Furthermore, as shown, the vapor passively rises to the top of stator 205 and collects at manifold 207. Due to buoyancy and thermal contact with cooler air at condensing unit 408, the collected vapor passively rises further. The vapor condenses back into liquid form, which is then returned to inlet manifold 209 to continue the cycle. Although Figure 7 Not shown, but cooling system 400 may also include a liquid bridge as described herein to separate liquid from vapor at outlet manifold 207 and thereby return the liquid to inlet manifold 209 by passing through a condenser. This supply reduces system pressure drop to improve thermosyphon mass flow rate and thus improve the thermal performance of the system.

[0043] Now refer to Figure 8 and Figure 9, illustrates various embodiments of the liquid bridge 414 of the passive cooling system 400 described herein. In particular, Figure 8 As shown in , the liquid bridge(s) 414 described herein may be a tubular member 420 that is inclined at a certain angle (e.g., ranging from 0 degrees to 90 degrees) between the first conduit 410 and the second conduit 412 or the distribution manifold 406. In another embodiment, as Figure 9 As shown in , the liquid bridge(s) 414 described herein may also include one or more traps 422 (such as P-traps or running traps) to improve liquid-vapor separation. Thus, in such embodiments, such trap(s) 422 are configured to prevent the flow of vapor through the liquid bridge.

[0044] Approximate language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that may permissibly vary without causing a change in the basic function to which it relates. Thus, a value modified by a term or terms such as "approximately," "approximately," and "substantially" should not be limited to the precise value specified. At least in some instances, approximate language may correspond to the precision of the instrument used to measure the value. Here and throughout the specification and claims, range limitations may be combined and / or interchanged, and unless the context or language indicates otherwise, such ranges are identified and include all subranges contained therein. Such terms as applied to a particular value of a range apply to both values and, unless otherwise dependent on the precision of the instrument measuring the value, may indicate + / - 10% of the value(s).

[0045] Various aspects and embodiments of the invention are defined by the following numbered clauses.

[0046] Clause 1: A passive cooling system, comprising:

[0047] a heat exchanger thermally connected to a heat generating component within the housing;

[0048] a distribution manifold located below the heat exchanger;

[0049] a condensing unit located outside the housing and above the heat exchanger;

[0050] a first conduit fluidly connected to the heat exchanger, the distribution manifold, and the condensing unit;

[0051] a second conduit fluidly connected to the condensing unit and the distribution manifold;

[0052] a liquid bridge fluidly connected to the first conduit and the second conduit or the distribution manifold; and

[0053] a two-phase cooling medium that circulates through a loop defined by the first conduit, the liquid bridge, the condensing unit, the second conduit, the heat exchanger, and the distribution manifold,

[0054] The liquid bridge transfers the cooling medium in a liquid state from the first conduit to the second conduit or the distribution manifold.

[0055] Clause 2. The passive cooling system of clause 1, further comprising: a plurality of heat exchangers thermally connected to a plurality of heat-generating components; and a plurality of first conduits connected in parallel between the distribution manifold and the condensing unit, wherein each of the plurality of first conduits is fluidly connected to one of the plurality of heat exchangers.

[0056] Clause 3. The passive cooling system of Clause 2, further comprising: two or more heat exchangers connected in series along one of the first conduits.

[0057] Clause 4. The passive cooling system of Clause 2, further comprising: a plurality of liquid bridges fluidly connected to the plurality of first conduits and the second conduits or the distribution manifold.

[0058] Clause 5. The passive cooling system of Clause 4, wherein one of the plurality of liquid bridges is fluidly connected to each of the plurality of first conduits and the second conduit or the distribution manifold.

[0059] Clause 6. The passive cooling system of any preceding clause, wherein the liquid bridge comprises a tubular member positioned at an oblique angle between the first and second conduits or the distribution manifold.

[0060] Clause 7. The passive cooling system of Clause 6, wherein the tubular member further comprises at least one trap.

[0061] Clause 8. The passive cooling system of any preceding clause, wherein the enclosure comprises a nacelle of a wind turbine or solar power system.

[0062] Clause 9. The passive cooling system of clause 8, wherein the condensing unit is fixed to a roof of the nacelle.

[0063] Clause 10. The passive cooling system of any preceding clause, wherein the one or more heat generating components include at least one of: a generator rotor, a generator stator, a gearbox, a transformer, an inverter, or a converter.

[0064] Clause 11. The passive cooling system of any preceding clause, wherein the cooling system lacks a pump or fan within the housing.

[0065] Clause 12. A wind turbine comprising

[0066] tower;

[0067] a nacelle mounted atop the tower, the nacelle defining an enclosed interior volume;

[0068] a rotor mounted to the nacelle, the rotor comprising a rotatable hub and at least one rotor blade mounted to the hub;

[0069] at least one heat-generating component positioned within the interior volume of the nacelle; and

[0070] a passive cooling system for cooling the interior volume of the nacelle, the passive cooling system comprising:

[0071] a heat exchanger thermally connected to the at least one heat-generating component;

[0072] a distribution manifold located below the heat-generating component;

[0073] a condensing unit located outside the cabin and above the heat-generating component;

[0074] a first conduit thermally connected to the heat generating component, the first conduit fluidly connected to the distribution manifold and the condensing unit;

[0075] a second conduit fluidly connected to the condensing unit and the distribution manifold;

[0076] a liquid bridge fluidly connected to the first conduit and the second conduit or the distribution manifold; and

[0077] a two-phase cooling medium that circulates through a loop defined by the first conduit, the liquid bridge, the condensing unit, the second conduit, the heat exchanger, and the distribution manifold,

[0078] The liquid bridge transfers the cooling medium in a liquid state from the first conduit to the second conduit or the distribution manifold.

[0079] Clause 13. The wind turbine of clause 12, further comprising: a plurality of heat exchangers thermally connected to a plurality of heat-generating components; and a plurality of first conduits connected in parallel between the distribution manifold and the condensing unit, wherein each of the plurality of first conduits is fluidly connected to one of the plurality of heat exchangers.

[0080] Clause 14. The wind turbine of clause 13, further comprising: two or more heat exchangers connected in series along one of the first ducts.

[0081] Clause 15. The wind turbine of clause 13, further comprising: a plurality of liquid bridges fluidly connected to the plurality of first ducts and the second ducts or the distribution manifold.

[0082] Clause 16. The wind turbine of clause 15, wherein one of the plurality of liquid bridges is fluidly connected to each of the plurality of first conduits and the second conduit or the distribution manifold.

[0083] Clause 17. The wind turbine of clauses 12 to 16, wherein the liquid bridge comprises a tubular member positioned at an oblique angle between the first and second ducts or the distribution manifold.

[0084] Clause 18. The wind turbine of Clause 18, wherein the tubular member further comprises at least one trap.

[0085] Clause 19. The wind turbine according to clauses 12 to 18, wherein the condensing unit is fixed on top of the nacelle.

[0086] Clause 20. The wind turbine of clauses 12 to 19, wherein the one or more heat generating components comprise one of: a generator rotor, a generator stator, a gearbox, a transformer, or a converter of the wind turbine.

[0087] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims and may include other examples that occur to those skilled in the art. If such other examples include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims, they are intended to be within the scope of the claims.

Claims

1. A passive cooling system, comprising: a heat exchanger thermally connected to a heat generating component within the housing; a distribution manifold located below the heat exchanger; a condensing unit located outside the housing and above the heat exchanger; a first conduit fluidly connected to the heat exchanger, the distribution manifold, and the condensing unit; a second conduit fluidly connected to the condensing unit and the distribution manifold; a liquid bridge fluidly connected to the first conduit and the second conduit or the distribution manifold; as well as a two-phase cooling medium that circulates through a loop defined by the first conduit, the liquid bridge, the condensing unit, the second conduit, the heat exchanger, and the distribution manifold, The liquid bridge transfers the cooling medium in a liquid state from the first conduit to the second conduit or the distribution manifold.

2. The passive cooling system according to claim 1, further comprising: A plurality of heat exchangers thermally connected to a plurality of heat-generating components, and a plurality of first conduits connected in parallel between the distribution manifold and the condensing unit, wherein each of the plurality of first conduits is fluidly connected to a corresponding one of the plurality of heat exchangers.

3. The passive cooling system according to claim 2, further comprising: Two or more heat exchangers are connected in series along one of the first conduits.

4. The passive cooling system according to claim 2, further comprising: A plurality of liquid bridges are fluidly connected to the plurality of first conduits and the second conduits or the distribution manifold.

5. The passive cooling system according to claim 4, wherein: One of the plurality of liquid bridges is fluidly connected to each of the plurality of first conduits and the second conduit or the distribution manifold.

6. The passive cooling system according to claim 1, wherein: The liquid bridge includes a tubular member positioned at an oblique angle between the first conduit and the second conduit or the distribution manifold.

7. The passive cooling system according to claim 6, wherein: The tubular member further includes at least one trap.

8. The passive cooling system according to claim 1, wherein: The housing comprises a nacelle of a wind turbine or solar power system.

9. The passive cooling system according to claim 8, wherein: The condensing unit is fixed on the top of the nacelle.

10. The passive cooling system according to claim 1, wherein: The one or more heat generating components include at least one of the following: a generator rotor, a generator stator, a gearbox, a transformer, an inverter or a converter.

11. The passive cooling system according to claim 1, wherein: The cooling system lacks a pump or fan within the housing.

12. A wind turbine comprising tower; a nacelle mounted atop the tower, the nacelle defining an enclosed interior volume; a rotor mounted to the nacelle, the rotor comprising a rotatable hub and at least one rotor blade mounted to the hub; at least one heat-generating component positioned within the interior volume of the nacelle; as well as a passive cooling system for cooling the interior volume of the nacelle, the passive cooling system comprising: a heat exchanger thermally connected to the at least one heat-generating component; a distribution manifold located below the heat-generating component; a condensing unit located outside the cabin and above the heat-generating component; a first conduit thermally connected to the heat generating component, the first conduit fluidly connected to the distribution manifold and the condensing unit; a second conduit fluidly connected to the condensing unit and the distribution manifold; a liquid bridge fluidly connected to the first conduit and the second conduit or the distribution manifold; and a two-phase cooling medium that circulates through a loop defined by the first conduit, the liquid bridge, the condensing unit, the second conduit, the heat exchanger, and the distribution manifold, The liquid bridge transfers the cooling medium in a liquid state from the first conduit to the second conduit or the distribution manifold.

13. The wind turbine of claim 12, further comprising: A plurality of heat exchangers thermally connected to a plurality of heat-generating components, and a plurality of first conduits connected in parallel between the distribution manifold and the condensing unit, wherein each of the plurality of first conduits is fluidly connected to a corresponding one of the plurality of heat exchangers.

14. The wind turbine of claim 13, further comprising: Two or more heat exchangers are connected in series along one of the first conduits.

15. The wind turbine of claim 13, further comprising: A plurality of liquid bridges are fluidly connected to the plurality of first conduits and the second conduits or the distribution manifold.

16. The wind turbine of claim 15, wherein: One of the plurality of liquid bridges is fluidly connected to each of the plurality of first conduits and the second conduit or the distribution manifold.

17. The wind turbine of claim 12, wherein: The liquid bridge includes a tubular member positioned at an oblique angle between the first conduit and the second conduit or the distribution manifold.

18. The wind turbine of claim 17, wherein: The tubular member further includes at least one trap.

19. The wind turbine of claim 12, wherein: The condensing unit is fixed on the top of the nacelle.

20. The wind turbine of claim 12, wherein: The one or more heat generating components include one of the following: a generator rotor, a generator stator, a gearbox, a transformer or a converter of the wind turbine.

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