Patent Application
20120134832
This invention relates generally to pumps. More specifically, this invention relates to blood pumps, such as cardiac assist pumps that may be implanted in a patient.
Rotordynamic pumps, such as centrifugal, mixed-flow, and axial-flow pumps with mechanical bearings or magnetically suspended systems, have been widely used as ventricular assist devices to support patients with heart diseases. In magnetically levitated blood pumps, which generally include an impeller that is both magnetically suspended and rotated without mechanical means, an annular gap located between the rotor and stator suspension and drive components is conventionally designed to be relatively small. A narrow annular flow gap generally necessitates higher rotational speeds of the rotor in order to generate the desired pressure rise and flow rates needed to support patients. One adverse outcome of operating a rotor at high rotational speeds is a tendency for high turbulence flow characteristics within the blood (e.g., high shear stress) that increase the extent and rate of red blood cell damage. This is a challenge in developing a long-term implantable ventricular assist device. Additionally, it is desirable to provide such a pump that is able to generate a wide range of flow rate and sufficient pressure rise with high efficiency and smooth operation, and very low level of blood damage. While one can design a pump that operates adequately at nominal flow conditions using modern design methods and analysis tools such as computer-aided-design (CAD) and computational fluid dynamics (CFD), flow separations, vortices and unsteady stalls can still occur at off-design conditions in conventional designs.
Additionally, for centrifugal or mixed-flow blood pumps with shrouded impellers (i.e., a circumferentially revolved surface interconnecting the impeller blade tips), the fluid within the clearance space between a rotating front shroud and the stationary housing can demonstrate a complex three-dimensional structure, leading to retrograde leakage flow and strong disk friction loss. The combination of disk friction loss and the strong vortical flow not only lowers pump efficiency but also potentially induces hemolysis and thrombosis. A similar flow pattern can also occur at the back clearance space between a rotating back shroud and the stationary housing for centrifugal or mixed flow pumps with or without a front shroud. The level of shear stress within the clearance between the walls of a shroud and housing depends, at least in part, on the pump rotational speed.
For centrifugal or mixed-flow blood pumps with unshrouded or semi-open impellers, the lack of a front shroud introduces a problem due to the blade tip leakage flow from pressure-side to suction-side of the blades which occurs through the clearance between the rotating blade tip and the stationary housing. The leakage flow can also generate a jet leakage vortex that interacts with the primary flow, causing hydraulic loss and possibly inducing blood trauma. The shear stress exhibited in the gap or clearance between the blade tip gap and the stationary housing is very sensitive to the pump rotational speed as well as the magnitude of the gap itself.
At some off-design conditions, undesirable flow patterns such as flow separation, vortices, retrograde flow, and inlet pre-rotation can occur in all types of rotordynamic pumps. Impeller inlet and discharge recirculation can also occur at some off-design conditions. For example, impeller exit recirculation can occur on the shroud side as well as on the hub side. All these undesirable flow patterns not only cause hydraulic losses, but may also induce hemolysis and thrombosis. At some other off-design conditions, unsteady flow patterns such as surge can occur. A surge usually includes strong pressure and mass flow oscillations which vary over time. Such an unsteady flow pattern not only has a significant effect on the pump efficiency and potential blood damage, but also may have a strong impact on the stability of the pump operation.
In blood pumps having a mixed-flow impeller used in conjunction with a magnetically levitated and rotated design, the impeller can utilize centrifugal force in a greater extent to convert kinetic energy into potential energy (pressure rise). However, undesirable steady and unsteady flow patterns such as flow separation, vortices, inlet and outlet recirculation, and surge can also occur at impeller and stator blades region at off-design conditions. In particular at some off-design condition such as high flow rate operation, an unsteady surge can cause unstable operation of the pump.
Various embodiments of rotordynamic pumps for fluids are set forth herein in accordance with the present invention.
In accordance with one embodiment of the present invention, a pump for delivering continuous flow of fluids is provided. The pump includes a stator housing having an inlet and an outlet and a rotor hub disposed within the stator housing between the inlet and the outlet. The rotor hub includes a body having a leading portion position adjacent the inlet, a trailing portion positioned adjacent the outlet, and at least one impeller blade positioned at the leading portion. The pump further includes at least one principle stator vane extending radially inward from the stator housing and positioned between the inlet and outlet. At least one splitter vane is positioned adjacent the at least one principle stator vane, the at least one splitter vane exhibiting an axial length that is shorter than the at least one principle vane.
In accordance with one embodiment, the at least one principle stator vane includes a plurality of principle stator vanes, the at least one splitter vane includes a plurality of splitter vanes, and the plurality of principle vanes and the plurality of splitter vanes are arranged in a circumferentially alternating pattern.
In one embodiment, the at least one impeller blade includes a plurality of impeller blades configured to provide both centrifugal flow and axial flow to fluid flowing therethrough. The impeller blades may include at least one principle blade and at least one splitter blade, the at least one splitter blade being axially shorter than the at least one principle blade. Additionally, the at least one principle blade may include a plurality of principle blades, the at least one splitter blade may include a plurality of splitter blades, and the plurality of principle blades and the plurality of splitter blades may be arranged in a circumferentially alternating pattern.
In one embodiment, a leading edge of each of the plurality of splitter vanes is positioned axially closer to the outlet than a leading edge of each of the plurality of principle vanes. Additionally, a leading edge of each of the plurality of splitter blades may be positioned axially closer to the outlet than a leading edge of each of the plurality of principle blades.
In one embodiment, the pump may include a shroud coupled with and at least partially enclosing the plurality of principle blades and the plurality of splitter blades.
In one embodiment, the trailing edge of each of the plurality of the principle blades axially coincides with a trailing edge of each of the plurality of splitter blades. Additionally, the trailing edge of each of the plurality of the principle vanes may axially coincide with a trailing edge of each of the plurality of splitter vanes.
In one embodiment, the rotor hub is configured to be magnetically suspended and rotated within the stator housing. Such an embodiment may be configured from materials that are blood and biologically compatible such that the pump may be configured as a blood pump and may be implanted within a patient.
In accordance with another embodiment of the present invention, another pump for delivering continuous flow of fluids is provided. The pump includes a stator housing having an inlet and an outlet and a rotor hub disposed within the stator housing between the inlet and the outlet. The rotor hub includes a body having a leading portion position adjacent the inlet, a trailing portion positioned adjacent the outlet, a plurality of principle impeller blades, and a plurality of splitter impeller blades, each of the plurality of splitter blades being axially shorter than each of the plurality principle blades. The plurality of splitter blades and the plurality of principle blades are arranged in an alternating circumferential pattern about the leading portion of the body. A plurality of principle stator vanes extend radially inward from the stator housing and are positioned between the inlet and outlet. A plurality of splitter stator vanes extend radially inward from the stator housing, wherein each of the plurality of splitter vanes exhibit an axial length that is shorter than each of the plurality of principle vanes.
In accordance with another embodiment of the present invention, a method of manufacturing a pump is provided. The method comprises providing a stator housing having an inlet and an outlet; providing a rotor hub having a mixed-flow impeller near a leading portion of the rotor hub; positioning the rotor hub within the stator housing to define an annular flow path through the stator housing; providing at least one principle stator vane extending from the stator housing; providing at least one splitter stator vane extending from the stator housing adjacent the at least one principle stator vane, the at least one splitter vane having an axial length that is shorter than the at least one principle vane.
In various exemplary embodiments, there may be provided a rotordynamic apparatus and method suitable long-term implantation into humans for artificial circulatory support. In one embodiment, there may be provided a rotordynamic blood pump and method including a flow path geometry characterized with high hydraulic efficiency, low power consumption, uniform flow fields, smooth operation, and low blood damage at both nominal flow and off-design conditions.
In another embodiment, there may be provided a rotordynamic blood pump suitable for easy arrangements of magnetic suspension and drive components along the annular portion of the flow path.
Exemplary embodiments may provide an apparatus and method for a fluid pump for pumping bloods and other fluids, which integrates a mixed-flow or high-specific speed centrifugal impeller having at least one impeller stage including both principle blades and shorter splitter blades spaced between the principle blades, and a stator having at least one stage of blades fitted with both principle and shorter splitter blades near the outflow end of the pump. The rotating impeller stage includes principle blades of a conventional length and in between the same number of shorter splitter blades arranged in an alternating circular pattern along the diverging inlet end of the rotor. The stator stage with one or more principle stator blades and the equivalent number of shorter splitter blades arranged alternatively in circumferential direction displaced on the rear converging surface of the stator housing.
High efficiency, low blood damage, and smooth operation at design and off-design conditions are the critical requirements for a long term implantable blood pump. High efficiency is accomplished with the inclusion of splitter blades for both impeller and stator. The leading edges of both the impeller and stator shorter splitter blades are staggered with respect to principle blades, and initiate subsequently to the leading edge of the principle blades and overlap a portion of the principle blades wherein both principle and splitter blades preferably terminate at the same position in meridional section. Such an arrangement lessens the flow blockage at the impeller inlet side, thus improving the uniformity of flow field at the impeller inlet region by preventing undesirable flow patterns such as the pre-rotation, retrograde flow, and inlet circulation from occurrence at the design and off-design conditions. Because splitter blades take some percentage of pressure loading from the principle blades, it makes the pressure distribution more uniform along the entire blade region and especially on the outlet side of the impeller blades and stator blades at all operating conditions. Therefore, the flow at the outlets of the impeller and stator blades becomes difficult to separate. Outflow circulation and vortices are further prevented from occurrence. All these improvements in flow field and pressure distribution result in an increased pump efficiency. The higher efficiency provides the benefit of low temperature rise of the motor and longer battery life. As contact with bodily tissues is inherent, the reduction in operating temperatures minimizes related trauma to surrounding body tissues.
Red blood cell damage in blood pumps is mainly related to the shear stress and exposure time of the red blood cells passing through the flow paths. A uniform flow field without separation and vortices due to the consideration of splitter blades leads to a low shear stress and short exposure time. Among other things, embodiments of the present invention device address such issues. Embodiments of the present invention further provide smooth operation at design and off-design conditions because the configuration of the splitter blades fitted into the impeller and stator can, to a great extent, prevent from occurrence of undesirable steady and unsteady flow patterns such as the separation, inlet pre-rotation, retrograde flow, inlet and outlet circulation, and surge as well.
The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:
Embodiments are described more fully below in sufficient detail to enable those skilled in the art to practice the system and method. However, embodiments may be implemented in many different forms and the present invention should not be construed as being limited to the embodiments set forth herein. The following detailed description is, therefore, not to be taken to be limiting in any sense. For purpose of illustration, discussions of the invention will be made in reference to its utility as a cardiac assist blood pump. However, it is to be understood that the technology may have a variety of wide applications to many types of turbomachinery including, for example, commercial and industrial pumps, compressors, and turbines.
Referring to
The pump 100 includes a stator housing 102 having an inlet 104 and an outlet 106. A rotor hub 108 having a generally cylindrical configuration is disposed within the stator housing 102 forming a clearance gap or an annulus 110 between rotor hub 108 and stator housing 102. The rotor hub 108 includes a leading portion 112 (i.e., leading with respect to intended fluid flow through the pump 100) that exhibits a generally conical geometry and that is positioned near the inlet 104. Additionally, the rotor hub 108 includes a trailing portion 114 (i.e., trailing with respect to intended fluid flow through the pump 100) that exhibits a generally conical geometry and that is positioned near the outlet 106.
The pump 100 includes a mixed-flow (or high-specific speed centrifugal) type impeller with principle impeller blades 116 of a first length and shorter splitter blades 118. The principle and splitter blades 116 and 118 may be positioned, for example, on the leading portion 112 of the rotor hub 108. The leading edge of the splitter blades 118 is staggered behind (or placed axially downstream of) the leading edge of principle blades 116 but axially upstream relative to the trailing edge of the principle blades 118 so that the splitter blades 118 overlap at least a portion of principle blades 116 in meridional section or along the axial flow path. In the embodiment shown in
Downstream of impeller blades 116 and 118, stator vanes are positioned near the outlet 106 adjacent the trailing portion 114 of the rotor hub 108. The stator vanes include principle vanes 120 and shorter splitter vanes 122 which extend radially inward from the stator housing 102. The stator vanes 120 and 122 help to recover kinetic energy of the fluid (e.g., blood) and lead the fluid to flow axially through the outlet 106. The leading edge of the splitter vanes 122 is staggered behind, or positioned axially downstream from, the leading edge of principle vanes 120. The trailing edge of both principle stator vanes 120 and splitter stator vanes 122 terminate at approximately the same meridional or axial position. There are blade tip clearances or gaps between the lengthwise lower surface of the stator vanes 120 and 122 and the rotating rotor hub 108. The extent of both blade tip clearances and the vane tip clearances can have significant effects on the pump's performance including, for example, pump head and efficiency. Additionally, these clearances can have a significant impact on the amount of damage that may occur to the blood cells. In one particular embodiment, both the impeller blade tip clearances and the stator vane tip clearances are may be approximately 0.1 mm to approximately 0.2 mm. However, the clearances may be set at other distances depending on a variety of factors as will be appreciated by those of ordinary skill in the art.
In one particular embodiment, the ratio of the averaged streamline-wise meridional length of the splitter stator vanes 122 to that of principle stator vanes 120, as well as the impeller splitter blades 118 to the impeller principle blades 116, is approximately 0.6 to approximately 0.75. In other words, the axial length of a splitter stator vane 120 is approximately 0.6 to approximately 0.75 as long as the axial length of a principle stator vane 120 (and likewise for the splitter impeller blades 118 relative to the principle impeller blades 116).
It is noted that both the radial clearance and the axial length of the annulus 110 or annular gap can have a significant effect on pump performance and possible blood damage. For a magnetically suspended and rotated blood pump, the sizing of the annulus 110 also has an effect on the radial and yaw stiffness of the suspension system. From a point view of hydrodynamics, the radial gap of the annulus 110 should be made as large as reasonable possible, while for the consideration of magnetic suspension system, the radial gap of the annulus 110 should be small enough, and the axial length of the annulus 110 should long enough, to maintain a stable rotation of the rotor hub 106 within the stator housing 102.
It is noted that the components of the pump 100 are shown in relatively simplistic forms for sake of clarity in the associated description. For example, the magnetic and electronic components that might be utilized in association with a magnetic levitated pump are not specifically shown. However, one of ordinary skill in the art will recognize that such components will be inherently placed in or adjacent to the stator housing 102 and within the rotor hub 108 to provide such a magnetically levitated pump. One example of a completely magnetically suspended system associated with a pump is described in U.S. Patent Application Publication No. 20110237863 entitled MAGNETICALLY LEVITATED BLOOD PUMP WITH OPTIMIZATION METHOD ENABLING MINIATURIZATION, the disclosure of which is incorporated by reference herein in its entirety.
In one particular embodiment, such as seen in
In one embodiment, the trailing edge of the splitter blades 118 (i.e., the edge closer to the outlet 106) may axially coincide with the trailing edge of the principle blades 116. Similarly, the trailing edge of the splitter vanes 122 may axially coincide with the trailing edge of the principle vanes 120. Also, the trailing edge angles of the splitter blades 118 may exhibit substantially the same angle as the trailing edge of the principle blades 116. Likewise, the trailing edge angles of the splitter vanes 122 may exhibit substantially the same angle as the trailing edge of the principle vanes 120. However, the positions and trailing edge angles of the splitter blades may be optimized by CFD.
As noted above, the leading edge position of the splitter blades 118 (or splitter vanes 122) may generally axially staggered downstream of the leading edges of the principle blades 116 (or principle vanes 120). The circumferential positions and the leading edge angles of the splitter blades 118 (or splitter vanes 122) may be determined by inverse design methods and CFD optimization so that the pressure loading in both the splitter blades 118 (or splitter vanes 122) and the principle blades 116 (or principle vanes 120) is uniform. The principle stator vanes 120 may be designed so that the leading edge angles generally match the flow out of impeller blades 116 and 118. The trailing edge angles of both the principle vanes 120 and splitter vanes 122 may be approximately 90° so that the blood can be led to the outlet 106 uniformly and smoothly without much turbulence. The geometry of the converging trailing portion 114 of the rotor hub, along with the stator vanes 120 and 122 may be designed and optimized by CFD to further recover potential energy (pressure) from the kinetic energy of the fluid flow.
With more particular reference to
With more particular reference to
Referring briefly to
The difference from the embodiment described with respect to
The pumps and components formed herein may be formed using a variety of manufacturing techniques as will be appreciated by those of ordinary skill in the art. Some examples of techniques that may be used in manufacturing pumps and components of the present invention are set forth in U.S. patent application Ser. No. 12/XXX,XXX (attorney docket number 52722.0108), entitled BLOOD PUMP WITH SEPARATE MIXED-FLOW AND AXIAL-FLOW IMPELLER STAGES COMPONENTS THEREFOR AND RELATED METHODS, filed on even date herewith, the disclosure of which is incorporated by reference herein in its entirety. Additionally, the incorporated application includes non-limiting examples of pump dimensions that are applicable to the present invention for certain embodiments.
While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims. It is specifically noted that any features or aspects of a given embodiment described above may be combined with any other features or aspects of other described embodiments, without limitation. It is also noted that features set forth in association with the embodiments expressly described herein may be combined with features set forth in the various documents previously incorporated by reference without limitation.
This application claims priority to U.S. Provisional Patent Application No. 61/394,220, filed Oct. 18, 2010, and entitled BLOOD PUMP WITH SPLITTER IMPELLER BLADES AND SPLITTER STATOR BLADES. This application also claims priority to U.S. Provisional Patent Application No. 61/394,213 filed Oct. 18, 2010, entitled BLOOD PUMP WITH SEPARATE MIXED-FLOW AND AXIAL FLOW IMPELLER STAGES. The disclosures of the above referenced priority applications are incorporated by reference herein in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 61394220 | Oct 2010 | US | |
| 61394213 | Oct 2010 | US |
