Note: Descriptions are shown in the official language in which they were submitted.
Dkt. No. 39D-331
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IMPROVED FLU I D MI X I NG DEVI CE
Background
The present invention relates to the field
fluid handling devices and more particularly to an
improved fluid mixing device. Still more particularly
the fluid mixing device may be adapted for use in mixing
liquids used in automated clinical chemistry
analyzers.
A common requirement in fluid handling systems
is the mixing of two fluid flows to form a third fluid
flow. For example, automated clinical chemistry
analyzers frequently require two fluid flows to be mixed
together to form a third fluid flow that is then
analyzed. A first fluid may be, for example, a patient
sample such as serum, plasma, urine or spinal fluid
(CSF). The second fluid may be a buffer which, when
combined with the first fluid, controls primarily the
pH, ionic strength and surfactant properties of the
resulting mixture.
One such system requiring the combination of
two fluid flows is the SYNCHRON CX~3 automated clinical
chemistry analyzer which is commercially available from
Beckman Instruments, Inc. (Brea, California 92621). In
this system, a probe carrying the patient sample is
aligned above a sample injection cell. The probe is
lowered into the cell with the tip of the probe coming
to rest within a mixing chamber. The sample is pumped
from the probe into the mixing chamber while a buffer
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solution is pumped through a separate conduit into the
mixing chamber. The resulting mixture flows from the
mixing chamber through an exit conduit to an electrolyte
measuring flow cell to measure sodium, potassium,
chloride and CO2. An essentially identical system is
disclosed in U.S. Patent Number 4,888,998, issued
December 26, 1989-
A cutaway side view of the mixing chamber in
such commercially available system is illustrated in
Figure S. As seen with reference to Figure 5, a mixing
chamber 100 includes a vertical conduit 108 which is
adapted to receive a probe 102 having a tip 104. A
lS conduit 106 is "T"-ed into the side of and is perpen-
dicular to the conduit 108. The conduit 106 is
connected to a source of buffer which is to mix with
sample ejected through the probe tip 104. An exit
conduit 110 forms a right angle with the conduit 108 to
draw the combined sample and buffer from the mixing
chamber 100.
Unfortunately, the "T" configuration of the
prior art system may impede mixing of the sample and
buffer for several reasons. As the sample flow from the
tip 104 meets the buffer flow from the conduit 106, the
flows may simply combine without mixing, resulting in
laminar, separate flows within the conduits 108 and
110. The degree of laminar, separate flow is influenced
3C by the vertical position of the tip 104 within the
conduit 108, thus making the system sensitive to routine
changes in probe tip position that occur, for example,
due to normal wear and tear and routine replacement of
the probe 102. Further, an air bubble may be trapped
directly below the tip 104 within the flow of sample
from the tip 104. Such an air bubble vibrates rapidly
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Dkt. No. 39D-331
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within the conduit 108, resulting in pulses or bursts of
sample within the flow of buffer. Also, air trapped
above the conduit 106, while not causing pulses or
bursts in the combined flow, does gradually break up,
flowing to the flow cell where such disbursed air can
collect, adversely affecting measurements.
One result of these limitations and drawbacks
may be inconsistent electrolyte measurements and
adversely affected average precision. Thus, there is a
need for improved fluid mixing to improve and stabilize
the performance of the measurement system.
The improved fluid mixing device of the
present invention overcomes the limitations noted in the
prior device. The improved fluid mixing device may be
formed directly in the sample injection cell and, more
particularly, may replace the mixing chamber found in
the prior art sample injection cell. In accordance with
the present invention, the improved fluid mixing device
includes a mixing chamber having a cylindrical side
wall, end walls and a major axis parallel to and coaxial
with the cylindrical side wall. A first fluid conduit
joins the mixing chamber at a first fluid port formed in
one of the end walls. A second fluid conduit joins the
mixing chamber at a second fluid port, the second port
being formed in the cylindrical side wall. The second
fluid conduit and second fluid port are offset with
respect to the major axis to direct a fluid flow from
the second conduit through the second port generally
along the side wall and around the major axis of the
mixing chamber, creating a swirling action within the
mixing chamber. A third fluid conduit joins the mixing
chamber at a third port in the other end and serves as
an exit conduit for the fluids mixed in the mixing
chamber.
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In the embodiment of the invention disclosed
herein, the mixing chamber may form a first stage of a
mixing device or configuration. A second stage includes
positioning the third port off-center in the second end
and generally aligning the third fluid conduit with the
major axis. Yet a third stage of the mixing device or
configuration disclosed herein may include a fourth
conduit intersecting the third conduit. Center lines of
the third and fourth conduits are offset and do not
intersect.
In overall effect, the improved fluid mixing
device of the present invention thoroughly and
completely mixes the two streams of inlet fluids. When
used in the sample injection cell of the automated
clinical chemistry system described above, the improved
mixing results in more consistent performance and better
average precision in the measurement of electrolytes.
Description of the Drawings
Figure 1 is an overall exterior view of a
sample injection cell including an improved mixing
device or configuration in accordance with the present
i~nvention as well as a sample probe.
Figure 2 is an enlarged partial cross-section
view of the improved fluid mixing configuration of the
injection cell of Figure 1.
Figure 3 is a partial cross-section view taken
along line 3 - 3 of Figure 2 with the probe removed for
clarity.
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Figure 4 is a partial cross-section view taken
along line 4 - 4 of Figure 2.
Figure 5 is a partial cross-section view of a
mixing chamber of a prior-art sample injection cell.
Detailed Description
With reference to Figure 1, a sample injection
cell 10 may include an improved fluid mixing device or
configuration 12 in accordance with the present
invention. The sample injection cell 10 is generally a
vertical cylinder and may be formed from cast acrylic.
The cell 10 includes an upper portion 14 and a lower
portion 16. The upper portion 14 includes an open end
18 and tapered surfaces 20 leading to a vertical central
cylindrical bore 22. A horizontal conduit 24 leads to
and is in communication with the bore 22. The lower
portion 16 includes the mixing configuration 12 more
particularly described with reference to Figures 2 - 4
below. The upper and lower portions 14 and 16 are
joined by, for example, screws 26 (only one of which is
shown in Figure 1).
A sample probe assembly 28 includes a fluid
carrying conduit 30 which may be attached via a hose 32
to pumps, for example, for aspirating sample from sample
containers (not shown) and discharging the aspirated
sample into the cell 10. The probe assembly 28 includes
an arm 33 connected to a probe assembly positioning
device, all of which is well-known in the art. The
probe assembly 28 and cell 10, but for the mixing
configuration 12 of the present invention, may be as
used in the prior art commercially available SYNCHRON
CX 3 Clinical System described above and is otherwise
well-known in the art.
Dkt.~No. 39D-331
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Turning now to the improved fluid mixing
device or configuration 12 as seen in Figure 2, the
configuration 12 includes a mixing chamber 34 having a
cylindrical side wall 36 and upper and lower ends 38,
40, respectively. The cylindrical wall 36 of the mixing
chamber 34 includes a major central coaxial axis 37.
The axis 37 is inclined slightly with respect to
vertical and, in the embodiment disclosed herein, is
inclined approximately 8.5 degrees. The end 40 is
perpendicular to the axis 37 and the upper end 38 is
angled slightly from the axis 37 to be generally
horizontal ~as seen in Figure 2). Particularly, the
upper end 38 is angled about 81.5 degrees from the axis,
bringing the end 38 to its generally horizontal position
as just described.
A slightly enlarged b~re 42 immediately above
the end 38 receives and supports a rigid washer 44. A
second slightly enlarged bore 46 immediately above the
bore 42 receives and holds a quad ring 48. The quad
ring 48 is retained within the bore 46 by clamping
pressure applied via the upper portion 14. The quad
rind 48 provides a seal between the upper portion 14 and
lower portion 16 and, as is described below, provides a
seal between the removable probe conduit 30 and the
mixing configuration 12.
The probe conduit 30 may be considered a first
fluid conduit when the probe is positioned as shown in
Figure 2 with the probe seated against the quad ring
- 48. The probe conduit 30 or first fluid conduit enters
the mixing chamber 34 through the upper end 38 and is
angled, in the embodiment disclosed herein,
approximately 8.5 degrees with respect to the major axis
37.
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A second fluid conduit 50 (Figures 2 and 3) is
in communication with the mixing chamber 34. The second
fluid conduit 50 narrows to include a reduced portion 56
proximate the mixing chamber 34 and enters the mixing
chamber 34 via a port 58. The conduit 50 including the
reduced portion 56 is offset with respect to the axis 37
and enters the mixing chamber 34 off-center as
illustrated in Figure 3 such that fluid flow through the
port 58 is directly substantially around the axis 37 and
along the cylindrical wall 36.
. A third fluid conduit 52 exits mixing chamber
34 through the lower end 40 via a port 60. A center
- 15 line of the conduit 52 is generally parallel to the axis
37 of the mixing chamber 34.
A fourth fluid conduit 62 is in communication
with the lower end of the fluid conduit 52. The center
line of the conduit 62, as seen in Figure 4, is offset
with respect to the center line of the conduit 52 and is
slightly displaced such that the center line of the
conduit 62 falls substantially at the periphery or is
tangential with respect to the wall of the conduit 52.
The conduits 52 and 62 are joined at an intersection
ïdentified generally at 64.
A drain conduit 66 (Figures 2 and 3) is also
in communication with the mixing chamber 34 at a port
68. The drain conduit 66 is offset with respect to the
axis 37 and is generally horizontal as seen in Figure
2. The port 68 is located near the upper end 38 to help
reduce the amount of air that may otherwise become
trapped at the top of the mixing chamber 34.
Dkt. No. 39D-331
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In operation (Figures 1 - 4), the probe
assembly 28 is inserted into the cell 10 with probe tip
coming to rest within the mixing chamber 34. A
tapered surface 72 formed on the outside of the conduit
30 and proximate the tip 70 is urged against the quad
ring 48, sealing the tip 70 within the mixing chamber
34. Fluid sample, which may be in the form of liquid
patient serum, is held within the probe conduit 30. The
conduit 50 is connected to a source of fluid, such as
liquid buffer as described above.
With the probe tip 70 positioned within the
mixing chamber 34, pumping means (not shown) are
operated to eject the serum sample from the probe
conduit 30 into the mixing chamber. Simultaneously,
pumping means pumps diluent or buffer via the fluid
conduit 50 through the port 58 into the mixing chamber
34. Advantageously, the stre~m formed by the buffer
entering the mixing chamber 34 creates a rapid fluid
vortexing action about the axis 37 within the chamber
34. Interference by the probe conduit 30 in the flow
from the conduit 50 and port 58 prevent a coherent
vortex or cyclone from forming within the mixing chamber
34, introducing turbulence into the vortex to help
prevent the sample from becoming trapped within the
center of the vortex. Gas bubbles which generally
collect between the port 58 and the rigid washer 44 are
immediately sweep away by this rapid vortexing fluid
action within the mixing chamber 34.
As seen in Figure 2, the probe conduit 30,
which may also be considered as a first fluid conduit,
is generally vertical and is thus angled slightly (in
the embodiment disclosed, about 8.5 degrees) with
respect to the axis 37. The angle difference directs
the fluid flow from the conduit 30 toward the lower
Dkt. No. 39D-331
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bottom corner of the mixing chamber 34 and into the
rapidly circulating or spinning wall or side of the
fluid vortex created within the mixing chamber 34. The
fluid flow from the conduit 30 is not injected into the
center of the vortex created within the mixing chamber
34 where it might otherwise become entrapped, decreasing
the mixing action. The result is a thorough and rapid
mixing of the two fluids within the mixing chamber 34.
.
The fluids continue their vortexing action,
and are forced through the port 60 into the fluid
conduit 52. At the interface formed by the port 60
between the mixing chamber 34 and the conduit 52,
further turbulence is created. The port 60 in effect
slices off the advancing rapidly vortexing fluid within
the mixing chamber 34. This slicing, rotation-inducing
action creates further mixing and in turn creates a
vortexing or rotational fluid action or movement within
the conduit 52. At the intersection 64, the rotating
column of fluid moving through the fluid conduit 52 is
again subject to not only a change in direction but a
further change in rotation, the advancing fluid creating
yet another rotational or vortexing action within the
conduit 62.
~ Stated somewhat differently, the mixing
configuration 12 may be considered as including three
distinct mixing stages. The first stage comprises the
mixing chamber 34 in which the rapid vortexing and
injection action between first and second fluid flows is
created. The second stage includes the port 60 which
"slices" this rapidly rotating fluid mass as the mass
advances from the mixing chamber 34 into the fluid
conduit 52. The intersection 64 and the conduit 62 form
yet a third mixing stage, with the change in direction
of the fluid mass as well as the creation of yet another
Dkt. No.-39D-331
2035067
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vortexing or rotational effect within the conduit 62 yet
further enhancing the mixing action of the configuration
12.
Once sample injection and mixing is completed
as just described the probe 30 may be raised slightly,
wash fluid introduced via the conduit 24 with the drain
conduit 66 operating to aspirate or drain the wash fluid
from the sample cell 10.
The present invention provides significant
improvements over the prior-art system described in the
Background. The placement of the port 58 near the upper
end 38 and flow of fluid from port 58 parallel to the
upper end 38 substantially reduces the -volume of air
that could be trapped with the mixing chamber 34. The
rapid vortexing action created within the chamber 34
rapidly and completely sweeps aqy trapped air from the
chamber 34. This action passes entrapped air through
the electrolyte measuring flow cell before measurements
are made and eliminates air that might otherwise become
trapped in the flow from the conduit 30, leading to
bursts or pulses of sample entrained within the buffer
flow. Further, the rapid vortexing action within the
chamber 34, as well as the mixing occurring at the port
6~-and intersection 64 eliminates laminar flow otherwise
present in the prior-art system. The mixing distance of
the prior-art system in Figure 5, that is, the linear
length of the fluid travel within the conduits 108, 110
through which mixing may occur before the fluid leaves
the cell is effectively many times multiplied by the
vortexing, sectioning and rotational actions created by
the mixing configuration 12.
Thus, the mixing device or configuration 12 of
the present invention overcomes the limitations of the
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prior art, providing rapid, sure, effective mixing
without substantial increased costs or external parts.
It is to be recognized that modifications to
the present invention are possible to accommodate
varying liquid viscosities and flow rates. For example,
the flow rate of fluid from the port 58 may be effected
by the diameter of the reduced portion 56 and the speed
at which fluid rotates within the mixing chamber can be
altered by the amount by which the port 58 is offset
from the axis 37. Further, the conduit 30 and end 70
may be replaced by a conduit entering the mixing chamber
34 through a port formed in the end 38. In such an
instance, such a port and conduit should direct the
fluid flow into the fluid wall or side of the spinning
fluid vortex to accomplish rapid, thorough mixing. Such
modifications and others may be developed through
routine experimentation where high "shutter" speed video
recording may be used to assist in the evaluation of
such modifications.
It will be further recognized by those ski]led
in the art that the present invention is not to be
limited to the particular embodiment disclosed herein
but is to be afforded the full scope of the claims
appended hereto.
