High-speed gas foil bearing turboalternator and turbocompressor for reverse brayton cryocooler
Patent Information
- Authority / Receiving Office
- US · United States
- Patent Type
- Applications(United States)
- Current Assignee / Owner
- Filing Date
- 2025-02-11
- Publication Date
- 2026-08-13
Smart Images
Figure US20260235330A1-D00000_ABST
Abstract
Description
BACKGROUND
[0001] In space, long duration missions generally require a capability to store and maintain cryogenic propellant throughout the mission. Cryogenic propellants, such as liquid oxygen and liquid hydrogen, are difficult to maintain due to heating in space, which causes these propellants to boil off. A heat exchange system may be used to keep such propellants cool and in their liquid state. More ideally, a “zero-boiloff” approach, which would likely require extremely efficient heat exchangers, would allow for long-term, no-loss storage of cryogenic propellants, which is an important goal for lunar and Martian operations and space flight in general. For example, zero-boiloff storage would allow for efficient extraction operations of hydrogen and oxygen from lunar resources and also improve processes of transferring these propellants to fuel landers.
[0002] Refrigeration systems that operate below 120 K are commonly referred to as cryocoolers. There are several different types of cryocoolers that can be broadly categorized, such as recuperative (Joule-Thompson and Brayton) and regenerative (Gifford-McMahon, Stirling, pulse tube) cycles, for example. In reverse-Brayton cryocoolers, gas is compressed and expanded in turbomachinery. A Brayton cryocooler includes a compressor to pressurize a working gas, such as helium, which is cooled through a heat exchanger to reject heat to the environment. Next, the gas flows through a recuperator to precool the gas to a temperature close to the desired cooling temperature. The purpose of this precooling is to reduce the load on the refrigeration in a turbine of the cryocooler, thus increasing system efficiency. Next, the gas expands through the turbine, further dropping in temperature. The turbine exit is the coldest point in the cycle. The gas can subsequently flow through a load and absorb heat at the desired cryogenic temperature, where the gas, typically, warms up a few degrees. The low-pressure cold stream of gas then flows through the recuperator to precool the incoming high-pressure stream before returning to the compressor.
[0003] Given that achieving zero boil-off is a critical target for space exploration, cryocoolers represent one of the select refrigeration systems suitable for space voyages, including missions to the Moon and Mars. Nonetheless, there persists a growing demand for refrigeration systems that offer enhanced performance, reduced weight, and compact size.BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The disclosure will be understood more fully from the detailed description given below and from the accompanying figures of embodiments of the disclosure. The figures are used to provide knowledge and understanding of embodiments of the disclosure and do not limit the scope of the disclosure to these specific embodiments. Furthermore, the figures are not necessarily drawn to scale.
[0005] FIG. 1 is a schematic representation of a reverse-Brayton cycle cryocooler, according to some embodiments.
[0006] FIG. 2 is a schematic cross-section view of a cryogenic turboalternator with a turbine impeller and an overhung alternator magnet, both attached to a shaft that is supported by gas foil bearings, according to some embodiments.
[0007] FIG. 3 is a schematic cross-section view illustrating heat flow in a cryogenic turboalternator, according to some embodiments.
[0008] FIG. 4 is a schematic cross-section view of a cryogenic turboalternator configured so that working fluid entering the turboalternator is directed through the impeller without passing through gas foil bearings, according to some embodiments.
[0009] FIG. 5 is a schematic cross-section view of a cryogenic turboalternator configured so that working fluid entering the turboalternator is directed through the impeller and into gas foil bearings, according to some embodiments.
[0010] FIG. 6 is a schematic end-view cross-section of a gas foil bearing with a bump foil structure, according to some embodiments.
[0011] FIG. 7 is a schematic cross-section view illustrating heat flow in a gas foil bearing, according to some embodiments.
[0012] FIG. 8 is a flow diagram of operating a cryogenic turboalternator, according to some embodiments.
[0013] FIG. 9 is a flow diagram of operating a cryogenic turbocompressor from start-up to steady-state conditions, according to some embodiments.DETAILED DESCRIPTION
[0014] This disclosure describes a cryogenic turboalternator and turbocompressor that includes a magnet portion of an alternator that is positioned on a shaft in a way that improves, among other things, overall cooling efficiency of the turboalternator or turbocompressor. In particular, the magnet portion is on a shaft and is at or near an end of the shaft, which is supported by journal bearings. The magnet portion overhangs the journal bearings such that the magnet portion is not between the journal bearings. This relative positioning leads to the improved cooling efficiency by, for example, having the bearings, which generate heat during operation, at a decreased distance from the coldest portion of the turboalternator or turbocompressor, which can act as a heat sink. The resulting shortening of heat flow paths from bearings to heat sink may eliminate a need for circulating cooling fluid through the bearings, thereby improving thermal management so as to increase operating efficiency of the turboalternator or turbocompressor.
[0015] Although the following example embodiments and implementations are described as involving turboalternators, unless otherwise specified, turbocompressors may be substituted for turboalternators as described herein.
[0016] In some embodiments, the turboalternator may use gas foil bearings that provide relatively high load capacity and stability for operating at very high speeds and over a wide range of temperatures (e.g., 20 to 500 Kelvin). Gas foil bearings are configured to resist bearing failure of the turboalternator at cryogenic temperatures with high radial and axial loads. Moreover, the gas foil bearings may allow for an increase in the efficiency of the turboalternator, resulting in higher power regeneration and an overall increase in efficiency and lower power consumption of the cryocooler system in which the turboalternator is operating. In contrast, turboalternators utilizing other types of gas bearings, such as herringbone groove gas journal bearings, tilting pad gas journal bearings, and spiral groove gas thrust bearings, may have lower load capacities that result in reduced reliability of the turboalternator. Moreover, those bearing technologies may present a number of difficulties for manufacturing because they rely on tight tolerances and relatively complicated manufacturing processes. Manufacturing processes for turboalternators utilizing gas foil bearings may avoid such difficulties and complications.
[0017] In some embodiments, a cryogenic turboalternator comprises a shaft that includes a first end and a second end that is opposite the first end, an impeller (e.g., shrouded or unshrouded) at the first end of the shaft and configured to spin with the shaft, and a first journal bearing and a second journal bearing. The first journal bearing may be closer than the second journal bearing to the first end of the shaft. Also, the second journal bearing may be closer than the first journal bearing to the second end of the shaft. Though support is shared by both, the first journal bearing primarily supports the first end of the shaft and the second journal bearing primarily supports the second end of the shaft. The cryogenic turboalternator may also comprise a permanent magnet on the second end of the shaft. Like the impeller, the permanent magnet, which is part of an alternator that includes a stator, is configured to spin with the shaft. The permanent magnet overhangs on the shaft with respect to the first and the second journal bearings. In other words, the permanent magnet is not between the first and the second journal bearings and is instead in an overhung position with respect to the bearings. The cryogenic turboalternator may be configured to operate in a reverse-Brayton cycle cryocooler. In some implementations, the first and the second journal bearings may be gas foil bearings.
[0018] The cryogenic turboalternator may further comprise gas foil thrust bearings to axially support the shaft, a nozzle configured to provide a cryogenic working fluid to the impeller, and a cavity that is configured to receive the cryogenic working fluid from the impeller and allow the cryogenic working fluid to expand. This region is generally the coldest part of the turboalternator.
[0019] Bearing cavities, which comprise an annular region from a surface of the shaft to the first and the second journal bearings, respectively, may be configured to receive a portion of the cryogenic working fluid that is provided to the impeller. During operation, the bearing cavities may be pressurized by the cryogenic working fluid such that pressure of the cryogenic working fluid applied to the impeller is also applied to the bearing cavities. In some implementations, the flow path(s) to the bearing cavities may be deadheaded to prevent flowthrough of the cryogenic working fluid, as explained below.
[0020] In some cases, the impeller may be configured to receive a first portion of the cryogenic working fluid, which may be helium gas, for example, and the first and the second journal bearings (e.g., and thrust bearings) may be configured to receive a second portion of the cryogenic working fluid for cooling the first and the second journal bearings.
[0021] The cryogenic turboalternator may further comprise an alternator stator in a magnetic field of the magnet and a housing to contain the alternator stator, the shaft, and the first and the second journal bearings. The first and the second journal bearings may be configured to be primarily cooled via heat conduction through material of the housing and the shaft.
[0022] In other embodiments, a cryogenic turboalternator may comprise a shaft that includes an impeller on a first end of the shaft and an alternator magnet on a second end, opposite the first end, of the shaft. The turboalternator may also comprise a first journal bearing at a first location toward the first end of the shaft, a second journal bearing at a second location toward the second end of the shaft, and an alternator stator corresponding to the alternator magnet. The alternator stator and the alternator magnet may be further than the second journal bearing from the first journal bearing. The cryocooler turboalternator may be configured to operate in a reverse-Brayton cycle cryocooler. In some implementations, the first and the second journal bearings are gas foil bearings.
[0023] The cryogenic turboalternator may further comprise gas foil thrust bearings to axially support the shaft, a nozzle configured to provide a cryogenic working fluid to the impeller and a cavity that is configured to receive the cryogenic working fluid from the impeller and allow the cryogenic working fluid to expand.
[0024] In some cases, bearing cavities of the first and the second journal bearings are configured to be pressurized by the cryogenic working fluid such that pressure of the cryogenic working fluid applied to the impeller is also applied to the bearing cavities.
[0025] In some implementations, the cryogenic turboalternator may further comprise a housing to contain the alternator stator, the shaft, and the first and the second journal bearings. The first and the second journal bearings may be configured to be primarily cooled via heat conduction through solid material of the housing and the shaft.
[0026] FIG. 1 is a schematic representation of a reverse-Brayton cycle cryocooler 100, according to some embodiments. Cryocooler 100 is single-stage but claimed subject matter is not so limited. For example, some embodiments may involve two or more turboalternators that operate at two different temperatures. Cryocooler 100 is configured for a working fluid to cyclically flow therethrough. For example, relatively warm working fluid (e.g., helium gas) may enter (e.g., from the right in the figure) a compressor 102 to compress the working fluid. In some implementations, compressor 102 may be a turbo-compressor. The increase in pressure increases the temperature of the working fluid, which is subsequently cooled via a heat sink 104. The working gas leaving the heat sink flows into a recuperator 106, which further cools the working fluid. The working gas leaving the recuperator enters into a turbine or impeller 108 that is rotated by the working gas as it expands and gives up pressure. This expansion and concomitant lowering of pressure greatly cools the working fluid to cryogenic temperatures. Thus, the cold working fluid is in a thermal condition to provide refrigeration to a load 110 and is able to cool the load. This process, however, heats the working fluid by absorbing heat from the load via surfaces 112 at the load. The working gas leaving load 110 flows back into recuperator 106 where the working fluid exchanges heat with the working fluid that entered into the recuperator from compressor 102. This heat exchange heats the working fluid flowing toward compressor 102 while cooling the working fluid flowing toward impeller 108.
[0027] As described above, the working gas leaving the recuperator enters into impeller 108 and rotates the impeller. This rotation may be translated, via a shaft 114, to an alternator 116 to generate electricity, which may be contributed to the electrical power used to operate the cryocooler. Herein, an alternator such as 116, impeller 108, and shaft 114, among other things, form a turboalternator 118.
[0028] In some implementations, compressor 102 and alternator 116 (e.g., turboalternator) may use gas foil bearings, as described above.
[0029] In general terms, a recuperator, such as 106, is a type of heat exchanger having separate flow paths for the working fluid to be cooled and the working fluid to be heated, wherein heat is transferred through walls separating the two fluids. The fluids, which may be the same in both flow paths (e.g., in a closed loop system), may be gas, liquid, or a combination thereof. In some embodiments, such a heat exchange system may include a cylindrical shell that is configured to contain flowing pressurized cryogenic fluid (e.g., the working fluid), which may be helium gas, for example. Opposing flows of the fluid exchange heat with each other as they pass through the recuperator via a series of midplates and microtubes inside the shell.
[0030] FIG. 2 is a schematic cross-section view of a cryogenic turboalternator 200 with a turbine or impeller 202 and an overhung alternator magnet 204, both attached to a shaft 206 that is supported by journal bearings 208. For example, turboalternator 200 may be the same as or similar to turboalternator 118, which is implemented in reverse-Brayton cycle cryocooler 100. Dimensions of the various parts of turboalternator 200 are not necessarily illustrated to scale. There may be a substantial symmetry between an upper portion of the turboalternator above an axis 209 and a lower portion of the turboalternator below axis 209. Thus, the figure illustrates only the upper portion for clarity. A housing 210 comprising a thermally conductive material 211 may enclose and support various elements of the cryocooler. Journal bearings 208 may be configured to be primarily cooled via heat conduction through material 211 of the housing and the shaft.
[0031] In some embodiments, shaft 206 includes a first end 212 and a second end 213 that is opposite the first end. Turbine (or impeller in embodiments of a turbocompressor) 202 is at the first end of the shaft and configured to spin with the shaft. Journal bearings 208 may include a first journal bearing 208A and a second journal bearing 208B. The first journal bearing may be closer than the second journal bearing to first end 212 of the shaft. Also, the second journal bearing may be closer than the first journal bearing to second end 213 of the shaft. First journal bearing 208A may substantially support first end 212 of shaft 206 and second journal bearing 208B may substantially support second end 213 of the shaft, though both bearings support the shaft to some degree. Overhung alternator magnet 204 may be a permanent magnet(s) on the second end of the shaft. Like the impeller, the permanent magnet, which is part of an alternator 214 that includes a stator 216, is configured to spin with the shaft. The permanent magnet overhangs on the shaft with respect to the first and the second journal bearings. As mentioned above, the cryogenic turboalternator may be configured to operate in a reverse-Brayton cycle cryocooler, such as 100. In some implementations, the first and the second journal bearings may be gas foil bearings.
[0032] Cryogenic turboalternator 200 may further comprise gas foil thrust bearings 218 to axially support shaft 206 via a radially protruding portion 220 of the shaft. An input 222 on an input side of turbine (or impeller) 202 may be configured to provide a cryogenic working fluid to the impeller. A cavity (not illustrated) on an output side of the impeller may be configured to receive the cryogenic working fluid from the impeller and allow the cryogenic working fluid to expand (e.g., a pressure drop).
[0033] Bearing cavities 224, which include an annular region from a surface 226 of shaft 206 to the first and the second journal bearings, respectively, may be configured to receive a portion of the cryogenic working fluid that is provided to the impeller during operation of the turboalternator. Other bearing cavities may be thrust bearing cavities, which include the gaps between surfaces of gas foil thrust bearings 218 and the surface of shaft 206. In some implementations, bearing cavities 224 may be deadheaded to prevent flowthrough of the cryogenic working fluid. For example, the bearing cavities and any connecting volumes that can fill with working fluid may not be connected to any exit such that the only way for working fluid to exit these volumes is via a path 228 taken originally by the working fluid to enter these volumes. Path 228 may originate at or near turbine (or impeller) 202. Accordingly, the bearing cavities may be configured to be pressurized by the cryogenic working fluid that is present at input 222 such that the pressure of the cryogenic working fluid applied to turbine 202 is also applied to the bearing cavities. The complete amount of pressurization may not occur, however, until after the bearing cavities are filled by an inrushing flow of working fluid subsequent to an initial startup of the cryocooler.
[0034] FIG. 3 is a schematic cross-section view illustrating heat flow in cryogenic turboalternator 200, according to some embodiments. Such heat flow may occur while the turboalternator operates in a cryocooler such as 100. Example heat flow is indicated by arrows 302. Generally, heat flows from various sources of heat in the cryogenic turboalternator to areas that are maintained at a relatively cold state by flow of the cryogenic working fluid. These cold areas are at or near turbine (or impeller) 202, input 222, and the general area around the input side of turbine (or impeller) 202 and the cavity (not illustrated) on the output side of the impeller, which receives the cryogenic working fluid from the impeller during operation. These general cold areas are indicated by arrows 304.
[0035] The various sources of heat in cryogenic turboalternator 200 are, among other things, bearing cavities 224, which experience frictional shear forces in the lubricating fluid (e.g., the working fluid) therein while shaft 206 spins. The friction leads to heat generation in the bearing cavities of the first and the second journal bearings, as well as those of thrust bearings 218.
[0036] During operation of the turboalternator, alternator 214, which includes magnet 204 and stator 216, generates electricity via the magnetic interaction between the stator and the spinning magnet(s) on shaft 206. This magnetic interaction and the resulting generated electricity create heat. Even so, the bearings may generate a greater amount of heat compared to alternator 214. Thus, it may likely be beneficial to locate both of the bearings closer than the alternator to the general cold areas (e.g., 304), which can act as a heat sink. Because alternator 214 may likely generate a smaller amount of heat as compared to journal bearings 208, the alternator may be located further than the journal bearings from the cold regions. In other words, first journal bearing 208A and second journal bearing 208B are closer than the alternator to the impeller. Herein, the impeller may be described as being located on a first end 306 of the shaft while alternator 214 (e.g., overhung alternator magnet 204) is located on a second end 308, opposite the first end, of the shaft. Relatively speaking, first journal bearing 208A substantially supports first end 306 of shaft 206 and second journal bearing 208B substantially supports second end 308, which includes overhung alternator 214.
[0037] As mentioned above, gas foil thrust bearings 218 may also generate an amount of heat. This generated heat may be substantially higher than that generated in the bearing cavities of the first and the second journal bearings. Accordingly, cryogenic turboalternator 200 may be configured so that the thrust bearings are closer to cold areas 304.
[0038] As arrows 302 indicate, heat from these various heat sources flows to cold areas 304 via the thermally conductive material 211 of housing 210. Heat conduction is facilitated, in part, by thermal contact between the housing and the journal and thrust bearings, as indicated by dashed regions 310.
[0039] FIG. 4 is a schematic cross-section view of cryogenic turboalternator 200 which, as described above, may be configured so that a working fluid 402 entering the turboalternator during its steady-state operation is directed through turbine 202 without passing through (bearing cavities of) gas foil bearings 208 and 218. For example, flow paths to bearing cavities 224 may be deadheaded to prevent flowthrough of the cryogenic working fluid so that all of working fluid 402 flows to the impeller. In other words, the bearing cavities and any connecting volumes that can fill with working fluid 402 may not be connected to any exit such that the only way for the working fluid to exit these volumes is via path 228 taken originally by the working fluid to enter these volumes.
[0040] Input 222 on the input side of turbine 202 may provide the cryogenic working fluid 402 to the impeller. Substantially all of this working fluid traverses the impeller to a cavity (not illustrated) on the output side of the impeller. As explained above, this cavity may be configured to receive the cryogenic working fluid from the impeller and allow the cryogenic working fluid to expand.
[0041] The situation for steady-state operation of the turboalternator is somewhat different from its initial start-up, when a relatively small portion of the working fluid 402 flows into the bearing cavities. As explained above, at start-up, bearing cavities 224 receive a portion of the cryogenic working fluid that is provided to the impeller during operation of the turboalternator. Accordingly, the bearing cavities may be pressurized by the cryogenic working fluid that is present at input 222 such that the pressure of the cryogenic working fluid applied to turbine 202 is also applied to the bearing cavities. This pressurization may not occur, however, until after the bearing cavities are filled by an inrushing flow of working fluid subsequent to an initial startup of the cryocooler.
[0042] FIG. 5 is a schematic cross-section view of a cryogenic turboalternator 500 configured so that a working fluid 502 entering the turboalternator is directed through an impeller 504 and into journal bearings 506 and thrust bearings 508, according to some embodiments. This is in contrast to turboalternator 200 that is configured so that working fluid 402 entering the turboalternator during its steady-state operation is directed through turbine 202 without passing through (bearing cavities of) the journal and thrust bearings. In turboalternator 500, bearing cavities 510 need not be deadheaded and flowthrough of the cryogenic working fluid can occur so that not all of working fluid 502 flows to the impeller. For example, impeller 504 may be configured to receive (and output) a first portion 512 of cryogenic working fluid 502, which may be helium gas, for example, and journal bearings 506 and thrust bearings 508 may be configured to receive a second portion 514 of the cryogenic working fluid for cooling these bearings. The second portion, which may be about 5% of the incoming flow (e.g., 502), for example, may then flow out of turboalternator 500 via a path(s) 516.
[0043] Turboalternator 500 includes an alternator that comprises a stator 518 and a magnet 520, which is located between journal bearings 506. This is in contrast to turboalternator 200 that has its alternator (e.g., stator 216 and magnet 204) in an overhung position relative to the journal bearings.
[0044] There may be a substantial symmetry between an upper portion of the turboalternator above an axis 522 and a lower portion of the turboalternator below axis 522. Thus, the figure illustrates only the upper portion for clarity. A housing 524 comprising a thermally conductive material 526 may enclose and support various elements of the cryocooler. Journal bearings 506 and thrust bearings 508 may be configured to be cooled by heat conduction through material 526 of the housing, and shaft 528, and by flow of second portion 514 of the cryogenic working fluid. Journal bearings 506 and thrust bearings 508 may be gas foil bearings.
[0045] FIG. 6 is a schematic end-view cross-section of a gas foil bearing 600 with a bump foil structure, according to some embodiments. Journal and thrust bearings of turboalternators 200 and 500, for example, may be gas foil bearings that are similar to or the same as 600. Gas foil bearing 600 includes a foil bearing housing 602, a bump foil 604, and a top foil 606. A central region 608 may be occupied by a shaft such as 206, for example. Bearing cavities, such as 224, may comprise a gap between the shaft and top foil 606. In some implementations, this gap may be less than one thousandth of an inch, though claimed subject matter is not limited in this respect. These bearing cavities, including spaces surrounding bump foil 604, may fill with working fluid, which lubricates the bearings. For turboalternator 500, the working fluid may also function as a cooling fluid for the bearings, which generate friction-based heat during their operation. For turboalternator 200, the working fluid need not function as a flowing heat-carrying cooling fluid for the bearings because their generated heat may be thermally conducted away via the material (e.g., 211) of turboalternator housing 610 (e.g., 210), as explained below.
[0046] FIG. 7 is a schematic cross-section view illustrating heat flow in a gas foil bearing 700, which may be the same as or similar to 600, according to some embodiments. Gas foil bearing 700 includes a foil bearing housing 702, a bump foil 704, and a top foil 706. A central region may be occupied by a shaft 708, for example. A bearing cavity 710 comprises a gap between the shaft and top foil 706 and may fill with working fluid 712, which lubricates the bearings. During operation, the working fluid experiences frictional shear forces which lead to heating working fluid 712. An arrow 714 indicates heat flow from the working fluid into shaft 708. This heat flow is among other paths of flow that allow for cooling the working fluid. For example, arrows 716 indicate other paths of heat flow via top foil 706, bump foil 704, foil bearing housing 702, and a turboalternator housing 718, which may be the same as or similar to 510. Such thermally conductive paths allow heat to escape the working fluid in the bearing cavity and may eliminate a need for a cooling fluid to circulate through the bearing cavities, as in the case for turboalternator 500, for example. All things being equal except for the lack or presence of working fluid flowing through the bearings, turboalternator 200 may have a greater efficiency as compared to turboalternator 500. Also, in some implementations, bearings in turboalternator 200 may operate at temperatures that are generally warmer than those of bearings in turboalternator 500. The warmer temperatures may allow the bearings in turboalternator 200 to perform better than the bearings in turboalternator 500.
[0047] FIG. 8 is a flow diagram 800 of operating cryogenic turboalternator 200 from start-up to steady-state conditions, according to some embodiments. As described above, cryogenic turboalternator 200 may be configured so that working fluid 402 entering the turboalternator during its steady-state operation is directed through turbine 202 without passing through (bearing cavities of) gas foil bearings 208 and 218.
[0048] At 802, the turboalternator is started. Subsequently, at 804, a relatively small portion of the working fluid 402 flows into the bearing cavities while a larger portion flows into turbine 202. In other words, at start-up, bearing cavities 224 receive a portion of the cryogenic working fluid that is provided to the impeller during operation of the turboalternator. Accordingly, the bearing cavities may be pressurized by the cryogenic working fluid that is present at input 222 such that the pressure of the cryogenic working fluid applied to turbine 202 is also applied to the bearing cavities. The full amount of pressurization may not occur, however, until after the bearing cavities are filled by the inrushing flow of working fluid, at 806. At this point, the working fluid continues to flow to turbine 202 but stops flowing into the bearing cavities after bearing the cavities are filled. In some implementations, a percentage of the flow first cools thrust bearing (a main loss driver) and radial bearings and returns to the inlet. There may be liquid (non-working fluid) cooling channels in the bearing housing, which helps to keep bearings and the motor cool.
[0049] Following 806, at 808, subsequent to the initial startup of the cryocooler, input 222 on the input side of turbine 202 may provide all of the cryogenic working fluid 402 to the impeller. Substantially all of this working fluid traverses the impeller to a cavity (not illustrated) on the output side of the impeller. As explained above, this cavity may be configured to receive the cryogenic working fluid from the impeller and allow the cryogenic working fluid to expand.
[0050] FIG. 9 is a flow diagram 900 of operating a cryogenic turbocompressor from start-up to steady-state conditions, according to some embodiments. As described above, the cryogenic turbocompressor may be configured so that working fluid 402 entering the turbocompressor during its steady-state operation is directed through impeller 202 without passing through (bearing cavities of) gas foil bearings 208 and 218.
[0051] At 902, the turbocompressor is started. Subsequently, at 904, a relatively small portion of the working fluid 402 flows into the bearing cavities while a larger portion flows into impeller 202. In other words, at start-up, bearing cavities 224 receive a portion of the cryogenic working fluid that is provided to the impeller during operation of the turbocompressor. Accordingly, the bearing cavities may be pressurized by the cryogenic working fluid that is present at input 222 such that the pressure of the cryogenic working fluid applied to impeller 202 is also applied to the bearing cavities. The full amount of pressurization may not occur, however, until after the bearing cavities are filled by the inrushing flow of working fluid, at 906. Though the working fluid may continue to flow to the impeller, there may be a bypass flow into thrust bearing cavities and a subsequent flow through radial bearing cavities, cooling them before returning to an inlet that may be flow-limited by a flow restrictive device, for example.
[0052] Following 906, at 908, subsequent to the initial startup of the cryocooler, input 222 on the input side of impeller 202 may provide all of the cryogenic working fluid 402 to the impeller. Substantially all of this working fluid traverses the impeller to a cavity (not illustrated) on the output side of the impeller. As explained above, this cavity may be configured to receive the cryogenic working fluid from the impeller and allow the cryogenic working fluid to expand
[0053] The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the disclosure. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the systems and methods described herein. The foregoing descriptions of specific embodiments or examples are presented by way of examples for purposes of illustration and description. They are not intended to be exhaustive of or to limit this disclosure to the precise forms described. Many modifications and variations are possible in view of the above teachings. The embodiments or examples are shown and described in order to best explain the principles of this disclosure and practical applications, to thereby enable others skilled in the art to best utilize this disclosure and various embodiments or examples with various modifications as are suited to the particular use contemplated. It is intended that the scope of this disclosure be defined by the following claims and their equivalents.
Claims
1. A Brayton cryogenic turboalternator or turbocompressor comprising:a shaft including a first end and a second end that is opposite the first end;an impeller at the first end of the shaft and configured to spin with the shaft;a first journal bearing and a second journal bearing, whereinthe first journal bearing is closer than the second journal bearing to the first end of the shaft,the second journal bearing is closer than the first journal bearing to the second end of the shaft, andthe first journal bearing substantially supports the first end of the shaft and the second journal bearing substantially supports the second end of the shaft; anda permanent magnet on the second end of the shaft and configured to spin with the shaft, wherein the permanent magnet overhangs on the shaft with respect to the first and the second journal bearings.
2. The cryogenic turboalternator or turbocompressor of claim 1, wherein the cryogenic turboalternator or turbocompressor is configured to operate in a reverse-Brayton cycle cryocooler.
3. The cryogenic turboalternator or turbocompressor of claim 1, wherein the first and the second journal bearings are gas foil bearings.
4. The cryogenic turboalternator or turbocompressor of claim 1, further comprising gas foil thrust bearings to axially support the shaft.
5. The cryogenic turboalternator or turbocompressor of claim 1, further comprising a nozzle configured to provide a cryogenic working fluid to the impeller.
6. The cryogenic turboalternator or turbocompressor of claim 5, further comprising a cavity that is configured to receive the cryogenic working fluid from the impeller and allow the cryogenic working fluid to expand.
7. The cryogenic turboalternator or turbocompressor of claim 5, wherein a bearing cavity comprising an annular region from a surface of the shaft to the first and the second journal bearings is configured to receive a portion of the cryogenic working fluid that is provided to the impeller.
8. The cryogenic turboalternator or turbocompressor of claim 7, wherein the bearing cavity is configured to be pressurized by the cryogenic working fluid such that pressure of the cryogenic working fluid applied to the impeller is also applied to the bearing cavity.
9. The cryogenic turboalternator or turbocompressor of claim 7, wherein the bearing cavity is deadheaded to prevent flowthrough of the cryogenic working fluid.
10. The cryogenic turboalternator or turbocompressor of claim 1, wherein the impeller is configured to receive a first portion of a cryogenic working fluid and the first and the second journal bearings are configured to receive a second portion of the cryogenic working fluid for cooling the first and the second journal bearings.
11. The cryogenic turboalternator or turbocompressor of claim 10, wherein the cryogenic working fluid is helium gas.
12. The cryogenic turboalternator or turbocompressor of claim 1, further comprising:an alternator stator in a magnetic field of the magnet; anda housing to contain the alternator stator, the shaft, and the first and the second journal bearings, wherein the first and the second journal bearings are configured to be primarily cooled via heat conduction through solid material of the housing and the shaft.
13. A cryogenic turboalternator or turbocompressor comprising:a shaft including an impeller on a first end of the shaft and an alternator magnet on a second end, opposite the first end, of the shaft;a first journal bearing at a first location toward the first end of the shaft;a second journal bearing at a second location toward the second end of the shaft; andan alternator stator corresponding to the alternator magnet, wherein the alternator stator and the alternator magnet are further than the second journal bearing from the first journal bearing.
14. The cryogenic turboalternator or turbocompressor of claim 13, wherein the cryocooler turboalternator or turbocompressor is configured to operate in a reverse Brayton cycle cryocooler.
15. The cryogenic turboalternator or turbocompressor of claim 13, wherein the first and the second journal bearings are gas foil bearings.
16. The cryogenic turboalternator or turbocompressor of claim 13, further comprising gas foil thrust bearings to axially support the shaft.
17. The cryogenic turboalternator or turbocompressor of claim 13, further comprising a nozzle configured to provide a cryogenic working fluid to the impeller.
18. The cryogenic turboalternator or turbocompressor of claim 17, further comprising a cavity that is configured to receive the cryogenic working fluid from the impeller and allow the cryogenic working fluid to expand.
19. The cryogenic turboalternator or turbocompressor of claim 17, wherein bearing cavities of the first and the second journal bearings are configured to be pressurized by the cryogenic working fluid such that pressure of the cryogenic working fluid applied to the impeller is also applied to the bearing cavities.
20. The cryogenic turboalternator or turbocompressor of claim 13, further comprising:a housing to contain the alternator stator, the shaft, and the first and the second journal bearings, wherein the first and the second journal bearings are configured to be primarily cooled via heat conduction through solid material of the housing and the shaft.