Thermal management in rotating machines

Abstract

A thermal management mechanism for heat evacuation is described. The thermal management mechanism includes a cooling jacket assembly 28 coupled to a heat source. The cooling jacket assembly 28 includes a cooling jacket core 30 which has multiple flow channels 32 and surrounds a sleeve 34. The cooling jacket assembly 28 evacuates heat from the heat source. A radiation shield 48 is connected to the heat source and evacuates radiative heat generated by the heat source. A method of evacuating heat from the heat source is also described.

Description

Thermal Management In Rotating Machines

[0001] Thermal Management In Rotating Machines

[0002] The invention relates generally to the field of thermal management and more specifically, to thermal management in rotating machines using high density fluids.

[0003] Currently available standard turbines usually employ steam as the working fluid for power generation. In certain industrial applications, air has also been employed for power generation. Employing high density fluids other than steam or air can improve the power generation efficiency. High density fluids can also ensure compact turbine designs with low footprint power plants as well as reduced emissions.

[0004] However, as turbines employing high density fluids are compact, they are typically designed to attain high operational speeds for better efficiencies. Due to the high speeds involved, several challenges are encountered while designing such turbines. For example, effectively managing the rotor dynamics, designing the appropriate bearings and employing the right sealing mechanism are a few of them. Amongst the various challenges faced in the design and operation of high density fluid turbines, sealing emerges as one of the most critical aspects. The efficiency and reliability of high density fluid turbines heavily depend on effective sealing mechanisms. The primary function of sealing is to minimize leakage of the high density working fluid from the high-pressure sections to the low-pressure sections within the turbine casing.

[0005] The high density fluid within the high-pressure sections of the turbine generally operates at temperatures exceeding 500℃ & pressures surpassing 210 bar. Sensitive components like bearings and generators are mounted in the low-pressure sections. An effective sealing mechanism should be able to withstand the high temperatures & pressures encountered in the high-pressure sections. If the sealing is ineffective, the high density fluid will not only lose pressure through leakages resulting in low efficiencies, but the leaked fluid can also damage the other components in the low-pressure sections within the turbine casing. Adequately sealing the interface between the high-pressure & low-pressure sections can prevent potential damage to the sensitive & critical components and ensure the integrity and reliability of the entire turbomachinery system.

[0006] Several types of seals such as Brush seals, Carbon seals, Mechanical seals, etc. are available for use. However, due to the extreme operating conditions characterized by high operational speeds, temperatures, and pressures, these traditional sealing methods exhibit high leakage rates or cannot withstand such demanding conditions. Among the available sealing options, certain sealing mechanism such as Dry Gas Seals are a viable solution because they can be engineered to operate at exceptionally high speeds up to 80,000 rpm, and can withstand exceedingly high-pressure applications, where pressures surpass 200 bar. This makes them particularly well-suited for sealing applications in high density fluid turbines, where conventional seals may not be suitable.

[0007] Sealing mechanism that are suitable for high density fluid turbines are typically equipped with components that mitigate leakage between the seals and the shaft of the turbine, as well as between the seals and the housing. However, those components within the seals impose a limitation on its operating temperature, reducing it to less than 160℃. As the seals are mounted in close proximity to heat sources within the turbomachinery, with temperatures exceeding 500℃, maintaining the temperature of the seals within the prescribed limits of around 160℃ becomes an exceptionally critical and challenging task. Without effective thermal management strategies to ensure that the operating conditions of the seals remain within acceptable temperature ranges, safeguarding the performance and longevity of the seal in the demanding environment of high density fluid turbomachinery cannot be ensured.

[0008] Therefore, there is a need for novel thermal management techniques that are suitable for use in high pressure and high temperature environments.

[0009] A thermal management mechanism for heat evacuation is described. The thermal management mechanism includes a cooling jacket assembly 28 coupled to a heat source. The cooling jacket assembly 28 includes a cooling jacket core 30 surrounding a sleeve 34 and disposed within end plates 40 & 42. The cooling jacket core 30 has multiple flow channels through which a cooling fluid is circulated at predetermined flow rates and pressures for evacuating heat from the heat source. The thermal management mechanism also includes a radiation shield 48 that is connected to the heat source for evacuating radiative heat generated by the heat source. A method of evacuating heat from the heat source is also described.

[0010] These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings.

[0011] is a diagrammatic representation of a high density fluid turbine in accordance with an embodiment of the invention.

[0012] is a schematic representation of a cooling jacket assembly employed in the high density fluid turbine in accordance with one aspect of the present technique.

[0013] is a schematic representation of a vent port employed in the high density fluid turbine in accordance with another aspect of the present technique.

[0014] is a schematic representation of a radiation shield employed in the high density fluid turbine in accordance with another aspect of the present technique.

[0015] is a schematic representation of radiation shield plates that form the radiation shield of, in accordance with aspects of the present technique.

[0016] is a schematic representation of an assembled radiation shield of, in accordance with aspects of the present technique.

[0017] The currently available turbines employing conventional working fluids, such as steam, have mostly reached peak levels of efficiency in term of generating power. One way of increasing the efficiency levels in turbines is by employing high to very high density fluids as the working fluid in the turbine. One such high density fluid is carbon dioxide at supercritical phase or supercritical carbon dioxide or sCO2. Similarly, other high density fluids known in the art, such as but not limited to hydrocarbons such as Propane, Ethane, Isobutane, Ammonia, R134a, etc., may also be used to improve the efficiency levels and the teachings below would be equally applicable with those fluids as well.

[0018] The high density fluid within the high-pressure sections of the turbine which mostly comprises rotary components such as the turbine rotor and blades, generally operates at temperatures exceeding 535℃ & pressures exceeding 210 bar. On the other hand, the low-pressure sections which house several sensitive stationary as well as rotating components, like bearings and generators, are at the temperature of around 150℃ & pressure of around 1 bar. Therefore, the temperature differential encountered at the interface is in the order of about 400℃ while the pressure differential is about 210 bar. The sensitive components in the low-pressure sections should not encounter the working fluid or the high temperatures & pressures. Therefore, the sealing mechanism has to prevent loss of working fluid pressure due to leakages apart from preventing the high temperature, high pressure working fluid in high-pressure sections from coming in contact with the sensitive components housed within the low-pressure sections. Thus, as noted before, when high density fluids are used, among other design & operational challenges, sealing the high temperature, high pressure working fluid is critical for efficient operation, but it is also technically challenging. Overcoming the challenges associated with sealing the high density working fluid and various other aspects of the high density fluid turbine will now be described in greater detail in the following embodiments.

[0019] is a diagrammatic representation of a high density fluid turbine 10, which can be considered to have two primary zones. The first primary zone is a high-pressure section 12 which includes a turbine or compressor impeller 14 coupled to a rotor shaft 16. A high density working fluid (or interchangeably a process gas or a process fluid) is fed into a volute 18 and the high density working fluid rotates the impeller 14. The rotating impeller 14 in turn rotates the rotor shaft 16 while the working fluid exits through a diffuser 20. The working fluid in this high-pressure section 12 is at a temperature of around 535℃ and pressure of around 210 bar.

[0020] The second primary zone is a low-pressure section 22 which houses several sensitive stationary & rotating components. For example, the low-pressure section 22 includes bearings 24 that support the rotating rotor shaft 16. Similarly, other components like thrust balancers, gearbox arrangement including gear wheels, generator rotor or motor rotor, etc. are also located within the low-pressure section 22. Power may be generated using a generator by the rotating rotor shaft 16. This low-pressure section 22 is generally at around 150℃ temperature & around 1 bar pressure.

[0021] A sealing component 26 is mounted behind the turbine or compressor impeller 14 at the overhang portion or the unsupported length of the rotor shaft 16 before the bearings 24. It may be noted that in one embodiment, the sealing component 26 includes Dry Gas Seals. Dry Gas Seals (DGS) are specialized sealing mechanisms in which a supply of clean and dry gas, usually the same as the working fluid or the process gas, is provided to the seal 26. This gas serves as a barrier between the rotating and stationary components. The pressure of the barrier gas is maintained at a higher level than the pressure of the process fluid so as to create a pressure differential that prevents leakage. In the case of DGS 26, it is typically equipped with seal faces coated with diamond, thus making the seal faces durable and resistant to wear. Polymer-based O-rings are also generally employed to further mitigate the leakage between the DGS and the shaft, and between the DGS and the housing. However, the use of polymer-based O-rings limits the operating temperature of the DGS to around 160℃. This is because the polymer-based O-rings can degrade significantly and become ineffective beyond 160℃. As the DGS is mounted in close proximity to the interface where the temperatures reach up to 535℃ in the turbomachinery, a set of thermal management techniques are employed so that the temperature can be brought down from around 535℃ to about 160℃. All the three modes of heat transfer, such as conduction, convection, and radiation are therefore employed to evacuate the heat and bring down the high temperatures to below 160℃, as will be explained in greater detail below.

[0022] is a schematic representation of a cooling jacket assembly 28 that is employed to reduce temperature via conduction in the high density fluid turbine 10. For bringing down the temperature via conduction, the cooling jacket assembly 28 is placed in the conduction path circumferentially around the DGS housing from a volute 18 to the DGS 26. The cooling jacket assembly 28 comprises a cooling jacket core 30 that may be constructed from highly conductive materials such as copper, aluminum, or other alloys known in the art. In one embodiment, the cooling jacket core 30 features numerous small holes or flow channels 32 to enhance the surface area and facilitate a high degree of heat exchange. However, the flow channels 32 in the cooling jacket core 30 may be designed in various shapes and configurations, including circular, rectangular, helical, serpentine, or any combination thereof. It may even assume irregular shapes. This cooling jacket core 30 allows circulation of a cooling fluid through the flow channels at predetermined flow rates and pressures. Suitable cooling fluids may include water, oil, CO2, or any other fluid known in the art that can dissipate heat quickly.

[0023] The cooling jacket assembly 28 further includes an intermediate sleeve 34 over which the cooling jacket core 30 is disposed to form a core assembly 36, as shown in. This enables the core assembly 36 to encircle the seal 26 so that the flow of the cooling fluid is confined within a cooling jacket housing 38. It may be noted that the sleeve 34 may be made of materials such as steel, copper, aluminum, alloys, or other known materials. To form the core assembly 36, the cooling jacket core 30 and the intermediate sleeve 34 may be joined together via welding, brazing, or other suitable methods. Two end plates 40 & 42 are located at both ends of the sleeve 34 to create an annular space, enabling inlet and outlet of the cooling fluid. Together, the core assembly 36, the cooling jacket housing 38 & the end plates 40 & 42 form the cooling jacket assembly 28 that is used for lowering the temperature via conduction.

[0024] The cooling jacket assembly 28 may be manufactured by various methods. For example, in the conventional manufacturing method, the cooling jacket core 30, the intermediate sleeve 34 and the two end plates 40 & 42 are manufactured separately and assembled together. The advantage of employing traditional methods to manufacture is that the cooling jacket core 30 may be made of high thermally-conducting materials such as copper or aluminum, while the sleeve 34 and the end plates 40 & 42 may be made of high strength materials such as steel or alloys which can withstand the high gas pressure & temperature. However the entire cooling jacket assembly 28 can be made as a single component or an integrated unit using non-traditional manufacturing methods, such as but not limited to casting, 3D printing, etc. It would be appreciated by one of ordinary skill in the art that the cooling jacket assembly 28 may be alternatively also formed as an integral part of the outer casing rather than welding or brazing with the casing of the high density fluid turbine 10. Regardless of the manufacturing method, the cooling jacket assembly 28 ensures structural integrity and thermal management.

[0025] Convective heat is generated when the high-temperature working fluid leaks behind the impeller 14. To evacuate heat due to convection as well as to address leakage of working fluid, a primary gas at a low temperature, for example below 100℃, is injected via the seal 26. Although any gas known in the art, for example, air, nitrogen, carbon dioxide, and the like may be used as the primary gas, in this embodiment, the primary gas used is the same as the process gas or the working fluid. The primary gas mixes with the high-temperature working fluid, thereby lowering the overall temperature of the fluid stream. The mixture of the primary gas and the process gas reaches a significantly lower temperature of less than around 160℃.illustrates a schematic representation of a vent port 44 that is used to evacuate convective heat. The mixed primary gas is piped through the vent port 44 provided on the volute 18 and then it is connected back to the compressor suction. A leakage gas vent path 46 is used to pipe the primary gas. This is illustrated in the detail view A. In a preferred embodiment, the width of the leakage gas vent 46 is about 0.1 mm for use with sCO2as the working fluid and CO2as the primary gas. Below this width, the working fluid may choke in the leakage gas vent 46 and evacuation of heat may not be feasible for this particular embodiment. However, the width of the leakage gas vent path 46 may depend of the working fluids and therefore may be different in different embodiments.

[0026] Turning now to, to shield the seal 26 from the radiative heat from the volute 18, an actively cooled radiation shield 48 is utilized. The radiation shield 48 is coupled to the outer casing of the seal 26, with a very narrow clearance 46 maintained between the volute 18 and the radiation shield 48 as illustrated in. It is through this gap 46 that the mixed gas flows and connects to the vent port 44. As previously described with reference to, any reduction in this clearance may result in gas choking, potentially diminishing the flow rate of the mixed gas passing through the leakage gas vent path 46 and consequently leading to a gradual increase in the temperature of the mixed gas. Therefore, to prevent the gap from narrowing by thermal expansion, a material with low coefficient of thermal expansion or one that exhibits minimal thermal expansion at high temperatures is chosen for constructing the radiation shield 48. This ensures that the integrity of the gap 46 between the radiation shield 48 and the volute 18 is maintained over prolonged operation. This meticulous approach guarantees effective thermal management and optimal performance of the seal 26 within the high density fluid turbomachinery.

[0027] The surface of the radiation shield 48 is designed to have high thermal emittance so that heat radiation from the volute 18 can be prevented. Furthermore, the internals of the radiation shield 48 are actively cooled with a cooling fluid or a coolant such as, but not limited to water, thermic oil, refrigerant fluid, or the process gas itself, such as for example CO2. Additionally, a fluid flow path 50 is incorporated within the internal structure of the radiation shield 48 wherein a meshed rib structure 52 is provided to increase the surface area for heat transfer. This is illustrated in greater detail in detail view B &, which is a schematic diagram of radiation shield plates 54 & 56 that form the radiation shield 48 of. As illustrated, the radiation shield 48 includes two plates, 1stplate 54 & a 2ndplate 56. The 1stplate 54 includes a coolant inlet 58 and a coolant outlet 60, shown in detail view C &. It also includes mounting holes 62 that allow the radiation shield 48 to be coupled to the DGS 26. The 2ndplate 56 has flow distribution passages 64 that allow the coolant to flow and be distributed throughout the radiation shield 48. Both the 1stplate 54 & 2ndplate 56 include the meshed ribs 52 that channelize the coolant within the radiation shield 48. A coolant outlet passage 66 is provided in the 2ndplate 56 and allows the exit of the coolant through the coolant outlet 60 in the 1stplate 54.

[0028] As noted above, in the present embodiment the radiation shield 48 is made with two plates. The two radiation shield plates 54 & 56 are assembled together, creating an inlet and outlet path for the coolant as described above. The radiation shield plates 54 & 56 are welded together at the edges to form the radiation shield assembly 48. This is illustrated in, which illustrates the assembled radiation shield 48. As shown, the two radiation shield plates 54 & 56 are welded together at the edges 68. It may be noted that the meshed ribs 52 present in the two radiation shield plates 54 & 56 may be designed to be complementary to each other such that the ribs in the two plates interlock or are meshed together. This increases the surface area and therefore facilitates a higher heat evacuation rate. Furthermore, as the radiation shield 48 is actively cooled, it helps to maintain lower temperatures, thereby increasing the effectiveness of the radiation shield. In the current embodiment, a 2-plate construction is adopted for ease of manufacturing the meshed ribs 52 via conventional methods. However, as would be appreciated by one of ordinary skill in the art, it is not necessary that radiation shield plates 54 & 56 be made separate. Instead in alternative embodiments, the two radiation shield plates 54 & 56 can be built as a single unit with internal cooling path via other machining techniques such as 3D printing, casting, etc. that is known in the art.

[0029] Similarly, although the present technique has been described with reference to application in seals, the techniques above may equally be applied to other applications where the temperature differential is high and significant reduction in temperature is desired. Appropriate design modifications that would be apparent to one of ordinary skill in the art may be made to achieve a similar configuration for heat dissipation.

[0030] The techniques described above provides several significant advantages in managing the temperature of seals that are in close proximity to heat sources, such as the rotary components of turbomachinery. For example, the unique combination and construction of the cooling jacket assembly 28 and the radiation shield 48 ensures that although the seal 26 is mounted close to the high-temperature heat source, viz. the high-pressure section 12, the temperature of the seal can be maintained well within the prescribed limit that can be handled by the seal. By employing all three modes of heat transfer, such as conduction, convection, and radiation, the present techniques ensure a holistic approach to temperature regulation by enhancing the efficiency of heat dissipation. Moreover, flexibility in the design of the cooling jacket assembly 28 allows for various configurations, optimizing heat exchange efficiency to suit specific system requirements and operating conditions. Similarly, the actively cooled radiation shield 48 prevents the seal 26 from being affected by radiative heat from the volute 18, maintaining a consistent temperature within the prescribed limit and preventing potential performance degradation or failure. Furthermore, the incorporation of a fluid flow path 50 within the internal structure of the radiation shield 48 along with a meshed rib structure 52 maximizes the surface area for heat transfer, thereby optimizing the cooling efficiency of the radiation shield. Additionally, placing the seal 26 in close proximity to the impeller 14 minimizes the shaft overhang that may be available after the bearing 24, thereby mitigating potential rotor-dynamic complications as well.

[0031] While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

A thermal management mechanism for heat evacuation, comprising:a cooling jacket assembly 28 coupled to a heat source comprising a cooling jacket core 30 having a plurality of flow channels 32 surrounding a sleeve 34 and configured to evacuate heat from the heat source; anda radiation shield 48 coupled to the heat source and configured to evacuate radiative heat generated by the heat source.The thermal management mechanism of claim 1, wherein the heat source comprises a high-pressure section 12.The thermal management mechanism of claim 1, wherein the cooling jacket core 30 is made using high thermally-conducting materials.The thermal management mechanism of claim 1, wherein the cooling jacket core 30 comprises a plurality of flow channels 32 configured to facilitate heat exchange using cooling fluids.The thermal management mechanism of claim 4, wherein the plurality of flow channels 32 are designed in circular shape, rectangular shape, helical shape, serpentine shape, or any combination thereof.The thermal management mechanism of claim 1, wherein the sleeve 34 is manufactured using high strength materials.The thermal management mechanism of claim 1, wherein the cooling jacket core 30 and the sleeve 34 are coupled via welding, brazing, or any combination thereof.The thermal management mechanism of claim 1, wherein the cooling jacket assembly 28 comprises end plates 40 & 42 that are manufactured using high strength materials.The thermal management mechanism of claim 8, wherein the cooling jacket core 30, the sleeve 34 and the end plates 40 & 42 are manufactured as an integrated unit.The thermal management mechanism of claim 1, wherein the radiation shield 48 comprises a material with low coefficient of thermal expansion.The thermal management mechanism of claim 1, wherein a surface of the radiation shield 48 is designed with high thermal emittance.The thermal management mechanism of claim 1, wherein the radiation shield 48 comprises a fluid flow path 50 with a meshed rib structure 52 configured to increase the surface area for heat transfer.The thermal management mechanism of claim 1, wherein the radiation shield 48 is actively cooled via a cooling fluid.A method of evacuating heat from a heat source, comprising:circulating a cooling fluid through a plurality of flow channels in a cooling jacket core 30 of a cooling jacket assembly 28 for lowering heat via conduction;passing a primary gas at a low temperature via a vent port 44 on a volute 18;evacuating convective heat via the primary gas through a leakage gas vent path 50; andevacuating radiative heat generated by the heat source via a radiation shield 48 coupled to the heat source.The method of claim 14, wherein circulating the cooling fluid comprises circulating the cooling fluid at predetermined flow rates and pressures.The method of claim 14, wherein evacuating radiative heat comprises actively cooling the radiation shield 48.The method of claim 16, wherein actively cooling the radiation shield 48 comprises passing a coolant via a fluid flow path 50 in the radiation shield 48.The method of claim 14, wherein evacuating radiative heat comprises radiating heat by using radiation shield 48 having high thermal emittance.

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