Patent Grant
8215928
The field of the present invention generally pertains to the conception, design and manufacture of turbomachinery, such as blowers and compressors, and associated technologies integrating such devices, and more particularly to centrifugal-type motor driven blowers and compressors capable of operating at high temperatures for use in various applications from heat treat furnaces, fuel cell systems for transportation, and other commercial uses. The present invention also generally pertains to the cooling of such turbomachinery, and more particularly to cooling centrifugal-type motor driven machines capable of operating at high temperatures as described herein.
Historically, positive displacement machines and turbomachines, such as blowers and compressors, have been used to generate compressed or pressurized gas. Turbomachines are high technology machines that typically involve high engineering, production and assembly costs in order to achieve and maintain desired levels of performance and efficiency with reduced repair and safety concerns. Such high costs are typically due to complex design issues, lengthy assembly procedures, and detailed maintenance requirements, all greatly influenced by the operational requirements for the machinery. For example, fuel cell systems used in diverse stationary, mobile, military and commercial applications use blowers and compressors to pressurize high temperature process gas, but require the machinery to fit a tight footprint so as to not take up too much space, without compromising operation and efficiency of the overall system. Additionally, suitable blowers and compressors have long been desired to achieve high reliability and maintain high efficiency at high operating temperatures. Because of the high temperatures exerted on and by any systems using such machines, adequate insulation, cooling, design and safety precautions are required. However, these concerns must be addressed without affecting the desired size of the blowers and compressors.
There exist several patents on high temperature blowers for various applications that range from heat treat furnace blowers to blowers for simple cooking ovens. One such blower, as described in U.S. Pat. No. 2,694,157, uses a fan-bladed impeller, ball bearings, an electric motor, and secondary air to operate in a heat treat furnace environment with elevated temperatures. This prior art design, while good for a simple bulky application, lacks sufficient design features required to operate in an environment where the process gases are volatile or hazardous to the environment. These machines are also often very large in size due to low operational rotating speeds, and as so sized, are usually insufficient for installation many high temperature applications. Moreover, such blowers are often too big for many modern applications and the size cannot be reduced without compromising operation, efficiency, and safety, especially when used in high temperature applications. The blower also has low efficiency and uses ball bearings that require regular service intervals and can also cause contamination to the process through leaking seals. The use of such motor-driven machines—where process gas has been transported by various designs using oil lubricated ball bearings—are typically unreliable at high temperatures (about 1600° F.) due to oil coking and oil migration, insufficient cooling capacity, contamination, and safety hazards.
Another patent, U.S. Pat. No. 5,375,651, describes a high temperature draft blower for use in furnace applications at temperatures of about 400-450° F. The blower design uses a squirrel cage style impeller mated to a conventional motor using a heat shield to protect the motor from the elevated temperatures in the blower housing. The blower has an estimated overall efficiency of only about 20%, and uses an electric motor that is exposed to the environment. Such a design is undesirable due to high susceptibility to contamination, especially to the motor, which effects overall operation and efficiency of the blower.
U.S. Pat. No. 6,951,241 discusses a method of cooling a high temperature furnace blower motor to keep the internal bearings cool during operation to increase the life of the blower. The method uses holes provided in the motor housing and at the impeller back plate to cool the blower. Specifically, the holes allow external air to be drawn into the blower housing and over the motor and then into the impeller portion of the blower housing. Hot air goes out through an exhaust port incorporated into the blower housing design. Due to limited cooling capacity from such a design, the blower is highly inefficient. Noise levels are also very high, even where a secondary cooling fan—typically used in such a design—is eliminated. Moreover, the ball bearings used inside the blower do not reduce noise levels to satisfactory levels. Additionally, since the holes in the blower housing are critical to drawing in external air to cool the motor and the impeller in such a design, the blower cannot be hermetically sealed. As a consequence, the process gas can easily mix with ambient air, which can be hazardous, especially at the high temperatures to which such a blower may be subjected.
In view of the foregoing, there is a need for a blower design that can operate efficiency at high temperatures, in a small, compact size, without suffering from the drawbacks common to prior art blower designs that tend to affect performance, operation and efficiency, and moreover, tend to compromise product safety. Accordingly, it is a general object of the present invention to provide a high temperature blower that overcomes the problems and drawbacks associated with the use of blowers at high temperatures (e.g., about 1600° F.).
The proposed high temperature centrifugal blower of the present invention avoids the drawbacks common to prior art blower designs, such as those discussed above, by using a unique internal cooling circuit that is self-sustaining. There is need for a blower design for use at high temperatures that is hermetically sealed and thus does not allow any leaking of the process gas. The present invention also uses foil gas bearing technology that permits a sealed, contamination fee, high speed, efficient, self-cooling centrifugal blower system. Such foil gas bearing technology also has no sliding contact of surfaces, and hence, improves the efficiency and reduces noise levels in the unit.
In one aspect of the present invention, a high temperature, motor driven, foil gas bearing supported blower is provided. The blower comprises a blower hot side including a volute with a process gas inlet and a process gas outlet, a diffuser attached to the volute for directing the flow of the process gas through the volute, and an impeller mounted for rotation about a central longitudinal axis within the volute for processing the gas as it flows through the volute. The blower also comprises a blower cold side including a sealed motor housing defining an interior cavity, a rotating assembly disposed within the interior cavity of the motor housing, and a motor stator assembly mounted within the motor housing. The rotating assembly comprises a rotating shaft mounted for rotation about the central longitudinal axis and a motor rotor mounted on the rotating assembly for rotation therewith, wherein the impeller is mounted at an end of the rotating assembly for rotation therewith. The blower further comprises a thermal barrier positioned between the blower hot side and the blower cold side for reducing heat transfer from the blower hot side to the blower cold side.
The blower design of the present invention may utilize an innovative thermal choke plate assembly to define a thermal barrier separating the blower into a hot side and a cold side. Preferably, the thermal choke plate assembly provides a significant temperature gradient across the hot and cold sides of the blower.
In one aspect of a preferable thermal choke plate assembly, an outer choke plate is provided adjacent to the hot side of the blower and an inner choke plate is provided adjacent to the cold side of the blower. The outer and inner choke plates are connected to one another at a neck portion transition along the inner diameter of each respective choke plate. Additionally, spacers may be provided between the choke plates to add rigidity and stiffness, as well as to aid in the dissipation of heat between the choke plates.
In operation, the thermal choke plate assembly of the present invention blocks heat transfer from the hot side to the cold side of the blower, including by blocking heat conduction as heat dissipates through the choke plates. In particular, heat is dissipated from the thermal choke plate assembly as it passes from the outer choke plate to the inner choke plate to form a temperature gradient across the hot and cold sides of the blower. A radiation heat shield may also be mounted with the thermal choke plate assembly to block radiation from passing from the hot side of the blower to the cold side.
The blower design of the present invention may utilize an innovative fan ring design provided on the rotating assembly, preferably between the impeller and the motor rotor. The fan ring comprises a generally longitudinal hub portion having a first end and a second end and is mounted on the rotating assembly for rotation therewith. The fan ring also comprises a radial cooling fan at the second end and having a plurality of fan blades facing the blower cold side. The fan ring further comprises a bellows feature positioned intermediate the first and second ends and including a plurality of heat fins extending radially from the hub portion. Heat conducted from the impeller is dissipated by the fan ring.
The fan ring may also define a seal within the blower to block the leakage of process gas from the blower hot side to the blower cold side.
Moreover, a thermal choke plate assembly in accordance with an aspect of the present invention may work in conjunction with internal cooling components, such as an internally disposed fan ring, and a sealed motor housing to balance convection and radiation heat transfer across the blower.
In another aspect of the present invention, a rotating assembly is defined for use in a centrifugal blower. The rotating assembly comprises a rotating shaft mounted for rotation about an axis, an impeller mounted at a first end of the rotating shaft, at least two hydrodynamic foil bearing assemblies mounted in association with the blower for supporting the rotating shaft, a motor rotor forming an armature of the blower, said rotor being mounted for rotation with the rotating shaft, and a fan ring. A tie rod extending along the axis of rotation is provided for holding the impeller, the rotating shaft, the motor rotor, and the fan ring under preload.
The present invention may use foil gas conical bearings or foil gas journal bearings, or both.
In another aspect of the present invention, the blower housing is sealed and the motor of the present invention is preferably self-contained. An ingenious closed circuit, sealed and self-sustaining cooling cycle is formed within the blower housing to cool the motor and other internal components. The cooling circuit is aided by a fan ring mounted on the rotating assembly of the blower. A fan ring in accordance with an aspect of the present invention acts, in part, as a cooling fan to draw cooling air through the motor housing of the blower and to take heat from internal components therein. The fan ring also may act as a seal to prevent leakage of hot gas from the impeller into the motor housing. Further, the fan ring may act to dissipate such hot gas away from the rotating assembly and impeller. A secondary fan may be added to aid in circulating air within the blower housing. Additionally, hot process gas transported via the centrifugal blower is not allowed to escape through the blower housing to the atmosphere, improving the efficiency and safety of the system in which the blower is used.
The present invention is also directed to a method for cooling a centrifugal blower. The method includes the steps of providing a sealed blower housing having a front end and a rear end and defining an axial interior cavity, radially disposed cooling channels, a front end cavity and a rear end cavity, providing a plurality of cooling fins about the outer surface of the blower housing, said cooling fins being generally adjacent the radially disposed cooling channels inside the blower housing, and providing a rotating assembly within the axial interior cavity. The rotating assembly is mounted for rotation about an axis and comprises a rotating shaft, an impeller mounted at a first end of the rotating shaft and being disposed within a volute, and a fan ring adjacent to the impeller and having a radial cooling fan facing the rear end of the blower housing and including a plurality of fan blades. The method further includes drawing gas through the axial interior cavity of the blower housing along the rotating assembly by rotating the radial cooling fan, said gas taking up heat from components of the rotating assembly. The method further includes distributing the hot gas into the front end cavity and directing the hot gas to and through the radially disposed cooling channels. The hot gas is cooled as it passes through the radially disposed cooling channels by conducting heat from the hot gas from the cooling channels to the cooling fins where the heat may be released therefrom to the ambient air around the blower housing. The method further includes distributing the cooled gas to the rear end cavity where it may be drawn into and through the axial interior cavity by rotation of the radial cooling fan.
The method of the present invention may further include reducing heat transfer from the impeller. Such a reducing step can be achieved with a thermal choke plate assembly in accordance with the present invention, a fan ring in accordance with the present invention, or a combination of the two.
The present invention, in another aspect, is also directed to a method of cooling a blower comprising forming a thermal barrier in the blower to separate a blower hot side from a blower cold side and to reduce heat transfer therebetween. Such a thermal barrier may be formed by a thermal choke plate assembly in accordance with the present invention, a fan ring in accordance with the present invention, or a combination of the two.
The blower design of the present invention provides advantages in that it can achieve high reliability at high temperatures (preferably up to about 1600° F.), with high efficiency in a small size that is desirable for various applications.
Additionally, the design of the present invention provides advantageous operating levels with an overall operating efficiency above 50%.
The blower design of the present invention has the advantage of being compact without compromising operation capacity. Further, the blower design is easy to install in commercial and military systems, such as fuel systems for transportation, automotive exhaust after treatment systems, heat furnace blowers, and the like, to improve efficiency.
These and other features of the present invention are described with reference to the drawings of preferred embodiments of a foil gas bearing supported centrifugal-type blower. The illustrated embodiments of the blower of the present invention are intended to illustrate, but not limit the invention.
A turbomachine in accordance with the present invention is generally illustrated in
As shown in
As shown in
Further, the outer and inner choke plates 18 and 20 may be separated by spacers that add stiffness to the assembly 16. For example, as shown in
The hot side 12 of the blower 10 generally comprises a volute 26, a diffuser 30, and a centrally disposed centrifugal impeller 32 mounted for rotation within the blower 10 about a central longitudinal axis A. All components on the hot side 12 must be able to withstand extreme temperatures. The volute 26 includes an inlet 27 for the process gas to be processed, and a peripherally disposed outlet 28 for discharging processed gas. The volute inlet 27 is generally aligned with the central longitudinal axis A of the blower 10. The diffuser 30 is attached to the volute 26 by using machine screws. The diffuser 30 can also be electron beam welded to the volute 26. The diffuser 30 includes a plurality of low solidity vanes (not shown) radially disposed on and about a diffuser plate (seen in cross-section in
The impeller 32 is part of a rotating assembly mounted for rotation within the blower housing. The rotating assembly, generally designated herein by reference numeral 34, is illustrated in
Though the rotating assembly 34 is illustrated in
When the rotating assembly 34 is mounted in position within a fully assembled blower 10, the impeller 32 is positioned on the hot side 12 of the blower 10. As seen more particularly in
The impeller 32 is preferably designed for optimum flow coefficient and for various speeds and flows. As shown more particularly in
In operation, the blower 10 draws gas axially through the volute inlet 27 and pressurizes the gas while passing it through the impeller blades 33. The impeller 32 raises the pressure of the process gas by centrifugal action. The processed gas is passed through the diffuser 30 to increase the pressure furthermore. The processed gas exits the blower 10 after finally passing through the volute channel 29. In many applications with which the present invention is intended to be used, including fuel cell systems for transportation, automotive exhaust after treatment systems, heat furnace blowers, and various additional commercial and military uses, the process gas is typically drawn in at extremely high temperatures—e.g., about 1600° F. In order to avoid the drawbacks and complications of prior art blower designs, the blower 10 must adequately accommodate the high temperatures through the hot side 12 while restraining heat transfer to the cold side 14.
Materials chosen for the volute 26, diffuser 30 and the impeller 32 are high temperature capable and have similar coefficients of thermal expansion so as to maintain the same axial and radial clearances between the shroud contour of the volute 26 and impeller blades 33 while running at extreme speeds and temperature.
The hot side 12 of the blower 10 further includes a radiation heat shield 50 positioned against the exterior surface of the volute 26. The radiation heat shield 50 has a polished surface, preferably manufactured from a highly polished metallic material, facing the hot side 12 with low emissivity and high reflectivity, that, in operation, blocks heat from the hot side 12 and more preferably reflects back heat radiated by the volute 26, the diffuser 30 and the impeller 32. Preferably, the radiation heat shield 50 is slip fitted onto a step provided in the outer choke plate 18, which is likewise fitted against the volute 26. The radiation heat shield 50 may be spot welded to the outer choke plate 18 where desired.
As noted above, and shown more particularly in
Heat may be transferred to the outer choke plate 18 via all three modes of heat transfer. However, the dominant mode of heat transfer to the outer choke plate 18 is conduction, as illustrated by the arrows in
The neck portion 24 of the thermal choke plate assembly 16 can also assist in dissipating heat generated by the impeller 32. For example, the neck portion 24 is preferably disposed adjacent to the rotating assembly 34. Heat from the rotating assembly 34 may be conducted to the thermal plate assembly 16 via the neck portion 24. The heat passes to the inner choke plate 20 from which it may be dissipated to the ambient air.
The radiation heat shield 50 reflects significant amount of heat from the hot side 12 back to the volute 26, where the surface is rough and has higher absorption properties, thus keeping the face of the outer choke plate 18 cooler. This cooler face conditions the outer choke plate 18 to take up heat conducted from the volute 26 and move it radially inwardly towards the neck portion 24 where the outer and inner choke plates 18 and 20 meet. Heat conducted to the inner choke plate 20 travels radially outwardly away from the neck portion 24, where it is cooled due to the design of the inner choke plate 20 coupled with natural convection and radiation heat transfer to the atmosphere.
Natural convection may be enhanced by designing thin sections into the choke plates 18 and 20. Due to such thin sections on the plates, along with providing a wider surface area for increased natural convection, heat transfer to the atmosphere is significantly enhanced and a thermal barrier is created between the hot side 12 and the cold side 14 of the blower 10 that provides a significant temperature gradient across the thermal barrier. Another way to minimize the heat flow between the hot side 12 and the cold side 14 is to use ceramic spacers instead of metal between the plates 18 and 20.
The blower 10 of the present invention also incorporates a very unique cooling fan design described herein as the fan ring 36, shown in
As shown in
The fan ring 36 is provided within the blower 10 to form an internal thermal barrier. In a preferred embodiment of the present invention, the fan ring 36 works in conjunction with the thermal choke plate assembly 16 to define an extensive thermal barrier to block all modes of heat transfer between the hot side 12 and the cold side 14 of the blower 10. Though shown as a component that forms part of the rotating shaft of the rotating assembly 34, the fan ring 36 may also be designed as a separate piece that is mounted on a rotating shaft and fitted into position.
The fan ring 36 of the present invention further includes a bellows-resembling feature 60 comprising a plurality of heat fins 61 extending radially outwardly from an intermediate section of the hub portion 56. A radial cooling fan 62 extends radially outwardly from the opposite end 58 of the hub portion 56 and includes a plurality of aerodynamic blades 63 facing the cold side 14 of the blower 10 and profiled to accommodate various speeds and provide various cooling flows.
During operation, heat is conducted through the impeller 32 to the fan ring 36. The bellows feature 60 of the fan ring 36 presents thermal resistance to this heat flow. That is, heat flows from one thin heat fin 61 to the next and so forth. Heat is dissipated from the ends of the fins 61 by via convection and radiation heat transfer. The heat dissipation through the fins 61 is enhanced by the whirl caused by rotation of the rotating assembly 34, thereby causing forced convection on the fins' surfaces. Consequently, the first heat fin—i.e., closest to the impeller 32—tends to be the hottest and the last fin—i.e., closest to the cold side 14 of the blower 10—tends to be the least hot.
The bellow-resembling feature 60 on the fan ring 36 also acts as a knife edge seal that blocks the leakage of hot gas past the impeller 32 by using the tips of the heat fins 61 as a labyrinth seal. The profile of the heat fins 61 may also be tapered. The tip clearance between the heat fins 61 and the neck portion 24 of the thermal choke plate assembly 16 and the inside diameter of the thermal choke plates 18 and 20 is kept to a desirable tolerance to avoid excess flow leakage and rubbing between the fan ring 36 and the thermal choke plate assembly 16, while accommodating thermal growth of both the rotating and stationary parts of the blower 10. The design of the rotating assembly 34 is intended to have a minimal contact area between rotating and stationary parts, which design helps reduce heat transfer within the blower 10 further.
When acting as a cooling fan, the fan ring 36 draws air through the cold side 14 of the blower 10 by taking away heat from various cold side components, such as bearings and the motor. The fan ring 36 also acts to push air through cooling channels formed within the machine housing 52. The internal cooling process is discussed in more detail below. The fan blades 63 stay relatively cooler that the rest of the fan ring 36. Thus, the unique design of the fan ring 36 acts as a thermal barrier, minimizes heat transfer and avoids demagnetization of the motor magnet due to excessive heat when a permanent magnet motor is used.
Accordingly, all the three modes of heat transfer are innovatively blocked by aspects of the present invention. More particularly, convection is balanced by the fan ring 36, as well as cooling fins provided on the machine housing 52, as described in more detail below. Similarly, conduction is blocked by the thermal choke plate assembly 16 and the fan ring 36. Lastly, radiation is blocked by the use of polished surfaces, such as the radiation heat shield 50 to reflect heat away from the cold side 14. Hence the cold side 14 of the blower 10 is kept cool from the hot side 12 of the blower 10.
The cold side 14 of the blower 10, generally shown in
The motor of the present invention may be a switched reluctance, induction or brushless DC permanent magnet motor. In general, the motor comprises the motor rotor 40 mounted to or forming part of the rotating assembly 34, and the motor stator assembly 66 disposed around the motor rotor 40 and press fitted into the machine housing 52. In this regard, the machine housing 52, may also be referred to as a “motor housing” or more generally a “blower housing” when used with a particular type of machine, such as, for example, blower 10.
In a preferred motor design, the motor rotor 40 includes a permanent magnet and the motor stator assembly 66 includes coils encircling the motor rotor 40 to operatively interact with the permanent magnet. Preferably, the motor is controlled by a sensorless controller (not shown), which can either be mounted on the machine housing 52 or located along side of it. Thus, the blower 10 gets its input power through the controller, which energizes the motor stator assembly 66, which in turn interacts with the motor rotor 40 to rotate the rotating assembly 34, with impeller 32, at desired high speeds.
The blower 10 is hermetically sealed. It uses a high temperature compressible gasket 53 between the volute 26 and the outer thermal choke plate 18. It also uses a slightly thinner compressible gasket 54 sandwiched between the inner thermal choke plate 20 and the machine housing 52. An end cover 72 is attached to the rear of the machine housing 52 to enclose the internal components on the cold side 14 of the blower 10. On o-ring seal is used between the end cover 72 and the machine housing 52. Hence no process gas can escape through the machine housing 52, which improves the efficiency and safety of the system in which the blower 10 is used.
The gas is drawn to the fan ring 36 by the cooling fan 62, which pushes and distributes the gas into a front end cavity 76 formed between the machine housing 52 and the thermal choke plate assembly 16 (Stage B). The gas also passes through a series of holes 78 provided in the front journal bearing sleeve 64a to move hot gas into the front end cavity 76. The fan ring 36 directs this hot gas radially toward a series of radially disposed cooling channels 80 provided in the machine housing 52 (Stage C). The hot gas is cooled as it passes through the cooling channels 80. Specifically, the hot gas in the cooling channels 80 contacts the walls of the machine housing 52. The heat is conducted through the walls from the inside of the machine housing 52 to a plurality of cooling fins 82 disposed about the outer surface of the machine housing 52. Heat is then released from the exposed fin surfaces to the ambient air around the machine housing 52 via natural convection and radiation.
The plurality of cooling fins 82 is provided over the outer surface of the machine housing 52. Preferably, the cooling fins 82 are integrally formed into the machine housing 52. Alternatively, a separate fin housing, including a plurality of fins, may be fitted inside the machine housing 52 to form an annular space therebetween that acts as a cooling jacket for cooling gas to pass through. As noted, the cooling fins 82 dissipate heat to the atmosphere via natural convection and radiation heat transfer.
After passing through the cooling channels 80 (Stage C) and attaining the lowest temperature of the cooling cycle, the gas is distributed to a rear end cavity 84 defined by the end cover 72 (Stage D). From the rear end cavity 84, the gas is drawn through the axial interior cavity of the machine housing 52 across the components of the rotating assembly 34. Thus, continued operation of the cooling fan 62 of the fan ring 36, redistributes the gas from the rear end cavity 84 across and along the rotating assembly 34 (Stage A), thus repeating the cooling cycle. Accordingly, the blower 10 of the present invention utilizes a unique self-sustaining cooling system aided by the hermetically sealed design of the blower 10.
Additional cooling capability can be provided in the blower 10 by adding a secondary cooling fan, preferably provided on the rear end of the rotating assembly 34, much in the general manner illustrated in the alternate embodiments shown in
High temperature capability is one of the core technical challenges of any blower design for use in high temperature applications. Materials chosen for construction of the blower 10 are widely recognized materials for high temperature applications. These materials permit even thermal growth in the system due to heat. This avoids warpage due to stressed joints and connections. The materials used are also preferably corrosion resistant at elevated temperatures. This allows any process gas to be used with the blower 10 of the present invention.
The blower 10 of the present invention addresses many of the concerns and drawbacks associated with prior art blowers in high temperature operations by using the technology of foil gas bearings that allow a sealed, contamination free, high speed, efficient, self cooling centrifugal blower system. As noted, the cold side 14 of the blower 10 illustrated in
To achieve high efficiency and high temperature applicability the blower 10 must be a high speed machine and should have high temperature capability, which may be achieved by supporting the rotating assembly 34 on foil gas conical bearings 86 as shown in
Hence conical bearings have fewer parts compared to standard bearings and consequently less associated losses. Conical bearings are also cheaper and have better load carrying capacities. Moreover, conical bearings have three times as much load carrying capacity as of a standard bearing. Correspondingly, power loss is about one-third the loss of a standard bearing.
As shown in
The various embodiments of a blower assembly described and illustrated herein can be used in various commercial and military applications, including fuel cell anode blowers, fuel cell systems for transportation, automotive exhaust after treatment systems, heat furnace blowers, and the like.
The foregoing description of embodiments of the invention has been presented for the purpose of illustration and description, it is not intended to be exhaustive or to limit the invention to the form disclosed. Obvious modifications and variations are possible in light of the above disclosure. The embodiments described were chosen to best illustrate the principles of the invention and practical applications thereof to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
This application claims the benefit of U.S. Provisional Application No. 60/976,971, filed Oct. 2, 2007, which is incorporated herein by reference.
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