Rotary kinetic fluid motors or pumps – Bearing – seal – or liner between runner portion and static part – Dynamically created seal
Reexamination Certificate
2000-06-23
2003-07-22
Kwon, John (Department: 3747)
Rotary kinetic fluid motors or pumps
Bearing, seal, or liner between runner portion and static part
Dynamically created seal
C415S170100
Reexamination Certificate
active
06595743
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to rotary pumps, preferably rotary axial pumps with hydrodynamic bearing, for impelling a liquid through at least one stage with minimum friction and minimum or no shear forces transmitted to the fluid, and more preferably the invention relates to a hydraulic bearing and a continuous axial-flow rotary pump for use in pumping fluids having particles or components the integrity of which must be protected, such as for blood circulation assistance, either in intravascular or extravascular circuits, with no, or at least extremely minimized, damage in the red cells and platelets, and no, or extremely minimized, thrombus formation.
While particular reference will be made in the present specification to a blood pump, it should be understood that the present pump is for use in any other field wherein any fluid must be transferred or conveyed from one place to another one, either in a closed circulation system or in any open circuit or path, the fluid being preferably a fluid where care of its integrity must be taken.
2. Description of the Prior Art
It is well known to provide an axial-flow rotary pump comprising a generically cylindrical casing and/or stator with a rotor, or a plurality of rotors mounted inside the stator to drive a fluid through the pump. The driving of the liquid to transfer the same from an inlet of the pump to a pump outlet is based in the provision of energy to the liquid to increase the fluid pressure thereof. This energy, however, provides several undesired side effects. The elimination of these effects without impairing the pumping efficiency of the pump has been the aim of many developments in the field of pumps, particularly when handling of sensitive fluids, such as explosives, blood, etc., is involved.
Contours, sizes, assemblies and relative positions of the different parts, as well as the stationary and movable surfaces of a pump are aspects and parameters that must be defined when designing the pump. The final objective of the design is to get a maximum efficiency of the pump with a minimum or no side effects resulting from the energy transferred to the fluid during the impelling thereof. Particularly in the case of a blood pump design, the aim is to reach to a pump having a maximum efficiency without side effects causing blood damage and/or blood clotting during operation. Another important objective is to have a pump having a minimum size.
The side effects resulting from the energy transferred during rotation of the pump comprise the generation of secondary or side flows, vortex, cavitation and separation of the flow from the surfaces of the stationary and movable parts of the pump.
The continuous fluid flow behavior through a rotary pump provided with blades is mathematically defined by the Euler equation. According to Euler, pressure energy imparted by the rotor is proportional to the increment of the tangential component of velocity. Analysis of the Euler equation is made through the so called velocity triangles shown in
FIG. 1
for a conventional scheme. Vectors represent averaged velocities on a flow surface and the letter references used in
FIG. 1
are:
&ohgr;
angular speed
R
radius
u = &ohgr; · R
rotation velocity
C
absolute velocity
W
relative velocity
C
u
tangential component
of absolute velocity
index
1
is used for the pump inlet
index
2
is used for the pump outlet
The Euler equation applied to a conventional rotary pump is:
(
R
·
C
u
)
2
-
(
R
·
C
u
)
1
=
g
·
H
η
·
ω
where,
H Head
G Acceleration due to gravity
&eegr; Efficiency
if C
u1
=0, we have
C
u2
=
g
·
H
R
2
·
η
·
ω
This is the reason why traditional pump designs include stator blades at the pump outlet, thus trying to reduce as much as possible the tangential component of the velocity and transform the kinetic energy into pressure energy.
Although many efforts have been made to eliminate or at least reduce the above mentioned side effects, by reducing or eliminating the above tangential component, for example, no solutions have been found hereinbefore. When a small Reynold's number is involved, that is when one handles small pumps and/or viscous liquids, stator blades at the pump outlet can not effectively reduce the tangential component of the velocity and transform kinetic energy into pressure energy, no matter the shape or number of blades provided. Therefore, flow separation and side flows are formed at the stator blades which cause hemolysis and blood clotting.
It is also well known to provide an axial-flow rotary pump comprising a generically cylindrical casing or stator with a rotor, or a plurality of rotors mounted inside the stator to drive a fluid, such as a liquid, through the pump. The driving of the liquid to transfer the same from an inlet of the pump to a pump outlet is based in the provision of kinetic energy to the liquid to increase the pressure thereof. This kinetic energy, however, while providing the impelling of the fluid it also provides several undesired side effects. The elimination of these effects without impairing the pumping efficiency of the pump has been the aim of the many developments in the field of pumps, particularly when the handling of sensitive fluids, such as explosives, blood, etc., is involved.
Regarding blood pumps, it is known that the rotary pumps for pumping blood, particularly those to be implanted in the human body, for circulatory assistance, causes severe damages in the blood, i.e. hemolysis. The higher or lesser extent at which the blood is damaged will depend on many factors, one the main factors being the high shear forces or stresses affecting the red cells and platelets, such stresses appearing in zones between pump components with relative movements and close to each other or, worst, in contact with each other.
According to Publication No. 85-2185; 1985; from the National Institute of Health (NIH), entitled “Guidelines for Blood-Material Interactions”, it is generally accepted that the quantity of red cells and platelets damaged by shear stresses depends on the intensity or magnitude of the stresses and the period of time the red cell and/or platelet is exposed to the stresses for a determined quantity of hematocrit. The hematocrit is the volume percentage of red cells in the blood.
FIG. 3
shows experimental results of blood damage, illustrated in curves corresponding to the tolerance of blood to shear forces, with the shear stresses shown in the Y-axis and the exposure time shown in the X-axis. The region above the curves corresponds to a significant particle destruction. It is shown that the shear stress that can be tolerated by the red cells is below 10 dynes/cm2. There are some regions in the rotary blood pumps, such as in the hydrodynamic bearing housings and in the gap or clearance between the peripheral edge of the pump blades and the inner surface of the stationary casing, housing or stator, wherein the shear forces and stresses generated by the relative movement between the rotor and the casing surfaces exceed the above mentioned tolerated stress value.
The hydrodynamic bearings have shown a good behavior to support mechanical components in relative movement because of the fluid pressure increase in the bearing cavity. This effect requires an important circulating flow to guarantee a continuous operation of the pump and high shear stresses are involved due to the relative speed of the pump components. In gap between the periphery of the blades and the inner surface of the casing a high pressure drop is generated because the high pressure side of the blade and the low pressure side of the blade are joined at this periphery. In addition, like in the hydrodynamic bearings, the shear stresses are high due to the flow speed gradients in the area.
Blood is a tissue composed of plasma and several types of suspended particles having different densities. The plasma is the liquid portion of the blood and is constituted by about 90
Kazatchkov Lev
Varela Lucas
Fulbright & Jaworski L.L.P.
IMPSA International Inc.
Kwon John
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