`
`A DEVELOPMENT OF MICRO. SHEATH FLOW CHAMBER
`
`Ryo Miyake , Hiroshi Ohki +
`and Ryohei Yabe
`
`Isao Yamazaki
`
`Mechanical Engineering Research Lab.,
`Hitachi,Ltd.
`502 Kandatsu, Tsuchiura 300 JAPAN
`*Naka Works, Hitachi,Ltd.
`882 Ichige, Katsuta 312 JAPAN
`
`ABSTRACT
`is developed using
`sheath flow chamber
`A
`micro-machining.
`Sheath flow geometry is
`formed
`the two-dimensional passage configuration.
`A
`in
`viscous
`flow analysis using
`fFEM(Finite Element
`Method)
`helps
`to examine the inside
`flow of
`a
`smal]
`passage
`and
`design
`the
`passage
`configuration.
`B
`sheath flow chamber consists of
`The micro
`for sheath
`fluid,
`a constricted
`bent
`passages
`a capillary tube.
`The height of
`passage,
`and
`is
`300 ym.
`The
`viscous
`flow
`these passages
`analysis
`reveals that swirl
`flow is generated at
`the
`constricted passage,
`thus causing the
`sample
`flow to
`seatter. This result
`suggests
`that
`a
`sample flow guide plate is needed to eliminate the
`swirl
`flow and
`induce a flow to
`envelope
`the
`sample
`fluid.
`Experimental mesurement
`of
`the
`sample flow using a guide plate shows a the smooth
`constricted sheath
`flow is obtained and
`the
`velocity reaches
`3.0 m/s, nearly the same
`speed
`as the value obtained by the viscous analysis.
`
`1. INTRODUCTION
`Recent advancement of micro-machining aids in
`the development of portable particle analyzer as a
`fluid integrated micro system.
`A particle analyzer
`has
`a capability of
`measuring
`and
`displaying multiple
` spectro-
`photometoric properties of particles
`at
`rates
`speed particle
`flow. This
`instrument
`commonly
`exceeding 5,000 particles per second due to
`high-
`employs
`a
`fluid dynamic
`focusing flow chamber
`which allows
`one by one examination of the sample
`particles.
`The flow is called "sheath flow"
`as
`illustrated in Fig.1. Particles
`in
`suspension,
`entering the
`chamber via an
`axial
`nozzle,
`are
`enveloped in a coaxial buffer sheath. The
`coaxial
`stream is
`accelerated and constricted in
`the
`chamber
`and led to a capillary tube.
`Suspended
`particles
`flow along the center of the capillary
`tube one bye one.
`Crossland-Taylor made the first
`sheath flow
`chamber(1), considering fluid dynamic
`performance
`the
`chamber (2),(3),(4). There
`are
`several
`of
`types of flow chambers for different uses, most of
`which
`are made of glass.
`The
`flow
`chamber
`conventionally used for particle counting is shown
`in Fig.2.
`To obtain a
`high
`resolution,
`the
`objective has bigger numerical aperture(NA),
`that
`is,
`a short working distance.
`To
`avoid
`contact
`between the objective and Lhe cone,
`the
`capillary
`tube must
`be at least as long as
`the objective
`diameter.
`In
`this
`case, NA=0.4,
`the
`working
`dislance
`is 1.63mm and the objective diameter
`is
`30mm. Consequently,
`this chamber should be
`150mm
`long. This length is larger for the micro system,
`and
`it
`is difficult
`to
`apply
`a
` glass-made
`
`50mm——_
`
`nozzle
`
`t
`buffer
`sample
`Fig.2 Conventional Flow Chamber
`
`buffer
`(sheath fluid)
`
`sample
`nozzle
`
`
`I\eens
`
`articles
`
`capillary
`tube
`
`\ p
`
`scatterd
`light
`
`Fig.l Schematic Diagram
`of Flow cytometer
`(Emphasis on Flow Chamber)
`
` objective
`detector sample
`
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`-9/91/0000-0265$01.00
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`CHeesP(e
`
`00
`
`.
`
`© 1991 IEEE
`
`265
`
`

`

`a micro particle
`flow chamber to
`conventional
`analyzer made by micro-machining.
`In this study,
`as the first step of the development of the micro
`system,
`attention is paid to the
`development of
`the sheath flow chamber using micro-machining.
`
`2.MICRO SHEATH FLOW CHAMBER
`
`is made
`A micro sheath flow chamber, which
`To
`form
`using photo-etching,
`is shown in Fig.3.
`the sheath flow geometry,
`two glass plates (A) and
`(E),
`and three thin metal plates (SUS 316, 100 ym
`thick) (B),(C) and (D) are used.
`The sample
`flow
`passage
`is
`carved only in plate
`(C),
`so
`the
`sample
`flow is expected to be enveloped
`by
`the
`sheath fluid.
`The five plates are bonded together
`and equipped with a sample fluid tube,
`two
`sheath
`fluid tubes and an outlet tube, as shown in Fig.4.
`Here, fluid dynamic focusing flow of sample
`fluid
`from the nozzle is illustrated.
`is
`chamber
`Because
`the
`top surface of the
`with
`absolutely flat,
`there is no
`interference
`length
`objective.
`Therefore,
`the capillary tube
`can
`be
`shortened as necessary,
`as
`examined
`in
`chapter 3.
`The micro sheath flow chamber is
`15mm
`long,
`1/10 the length of a conventional
`chamber.
`In addition, photo-etching remarkably improves the
`flow passage accuracy of the flat
`flow chamber.
`Therefore
`mass production of
`chambers
`with
`easier
`‘homogeneous
`fluid dynamic performance
`is
`than that of conventional chambers.
`On
`the other hand, closer
`investigation of
`fluid
`dynamic
`focusing
`performance
`is
`the
`necessary because the flow passage is now almost
`two-dimensional.
`
`3.DESIGN OF PASSAGE CONFIGURATION
`
`3.1 Examination using viscous flow analysis
`
`As shown in Figure 4, each plate has the same
`Therefore,
`the
`sample
`
` passage configuration.
`
`sheath
`
`
`
`sanple fluid
`sheath
`fluid=========~—
`Nozzle Area in detail
`
`
`
`between
`and
`both sheath fluids
`fluid is
`put
`the
`sheath
`constricted only in one direction as
`fluid flows.
`the
`sample
`To check whether or not
`fluid is focused 3-dimensionally,
`investigation
`of
`the inside flow is necessary.
`A viscous
`flow
`analysis using a Finite Element Method(5)
`is
`employed
`to examine
`the
`inside
`flow.
`Flow
`analysis
`is effective for the chamber because
`it
`is
`too
`small
`to
`investigate using only
`an
`experimental approach.
`I[t has been confirmed that
`FEM simulates the actual
`flow well,especially
`in.
`the small passage with laminar flow(6).
`the
`The 3-dimensional mesh configuration for
`FEM is
`shown in Fig.5. The passage
`is divided
`into 4870
`elements. This model has
`three
`inlet
`ports and an outlet port.
`Two of the inlet ports
`are for sheath fluid, and the other is for
`sample
`fluid.
`As
`a
`expedient,
`the
`co-ordinates
`are
`adopted as shown in the same figure. The velocity
`at
`the
`sample fluid port is given for
`a
`sample
`flow rate of lwl/s, and the velocity at the sheath
`fluid port is given for a flow rate of
`120 wl/s.
`The
`conventional chamber
`is usually adopts
`these
`same flow rates.
`
`sheath fluid
`
`1004M
`
`_ boundary
` sample fluid
`boundary
`
`
`sample fluid
`boundary
`
`in detail
`y
`
`
`
`
`
`
`boundary outlet
`
`
`300 um
`
`Fig.3 Fabrication
`of Flow Chamber
`
`Fig.5
`
`3-Dimensional Mesh Configuration
`
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`
`

`

`layer
`boundary
`skewed
`the
`7 describes
`Figure
`the
`caused by the above mentioned phenomenon and
`generation of
`the secondary flow in
`the
`cross-
`section of the passage.
`The center stream flows
`outward toward both the upper and lower parts near
`the outer side-wall and returns to the inner side-
`
`wall. This causes two paths of circulation§that
`are symmetrical
`from the center and become 4 swirl
`flows at the constricted passage.
`small
`the
`It may
`be
`noted that in
`passage
`the stream is remarkably subject
`to
`viscosity,
`thus, causing secondary flow.
`flow
`According to this calculation,
`the swirl
`axial
`velocity
`is 5%~10% of the velocity in
`the
`swirl
`flow.
`If the sample fluid flows into this
`flow, it expands to both the upper and lower walls
`of
`the passage,
`and
`scatters
`to
`the whole.
`capillary region.
`To make
`the
`sample
`fluid
`constrict 3-dimensionally, further improvement of
`the passage configuration is necessary.
`
`bent
`
`constricted
`passage
`
`
`capillary
`tube
`
`
`swirl
`flow
`
`Fig.6 Velocity Vector in Cross-section
`at Constricted Passage
`total flow rate
`Qt=121yl/s
`sample flow rate
`Qs=
`Iluyl/s
`
`‘in
`shown
`result of this calculation is
`A
`the
`in
`This
`shows the velocity vector
`Fig.6.
`the
`cross-section at
`the constricted passage(
`It
`position of
`Omm
`in
`the X-coordinates
`).
`reveals four swirl
`flows around its axis,
`which,
`judging from their symmetrical pattern, may
`be
`caused by the upper two passages for sheath fluid.
`In fact, further examination of this upper
`stream
`indicates the generation of strong secondary flow.
`The upper passage for sheath fluid is
`the
`bent
`passage with an axis radius of about 2mm
`and
`a
`height
`is
`0.3mm.
`In
`this
`small passage,
`the
`boundary Jayer of the stream is filled because the
`viscosity by the wall exerts to the center of
`the
`stream.
`The
`velocity
`distribution
`becomes
`the
`parabolic,
`that
`is,
`the velocity of
`center
`becomes much larger than that close to the wall,
`as shown in Fig.7. At
`the bent passage,
`there
`is
`centrifugal
`force
`upon
`the
`stream,
`and
`it
`increases
`as the velocity increases.
`Sinee
`the
`pressure
`is almost
`the same in
`the «-direction,
`the
`center stream under large
`centrifugal
`force
`beats the pressure gradient and flow outward.
`On
`the other hand,
`the stream clase to the wall
`is
`beaten by the pressure gradient and flows
`inward.
`
`bent
`the
`
`3.2 Modification of sample nozzle
`
`the
`at
`flow
`swirl
`the
`To
`eliminate
`it is necessary to weaken the
`constricted passage,
`secondary
`flow at the upper bent passage.
`One
`effective method would be to install a flow guide,
`for letting the center stream of the bent passage
`flow inward,
`in the constricted passage.
`The flow
`guide is shown in Fig.8. This flow guide prevents
`the
`sample
`fluid
`from
`scattering
`at
`the
`constricted passage. We call it a
`"sample
`flow
`guide plate".
`This plate is
`also useful
`for
`making the sample fluid constrict from all
`sides.
`This effect is discussed later.
`the
`Further calculation for the passage with
`in
`sample
`flow guide plate has been carried out
`order
`to check its
`effectiveness.
`The
`result
`shows
`that
`the velocity vector
`in
`the
`cross-
`section of the constricted passage is less than |%
`of
`the velocity in
`the
`axial
`flow.
`This
`indicates
`that
`the
`swirl
`flow
`is
`almost
`eliminated.
`Next, another effect of the sample flow guide
`is disscussed.
`The viscous
`flow analysis
`plate
`also shows that this guide plate induces the
`flow
`which
`envelopes the sample fluid from all
`sides.
`
`fisaee
`
`Fig.8 Sheath Flow Chamber
`with Sample Flow Guide Plate
`
`Width of sample channel
`Thickness of plate
`
`300 aM
`100 um
`
`growth of laminar
`
`direction
`of
`pressure
`gradient
`
`boundary layer
`
`centrifugal
`force
`
`skewed
`boundary
`layer
`
`
`
`
`secondary
`flow
`
`~ four
`}
`swirl
`Flows
`
`Fig.7 Secondary Flow at Bent Passage
`
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`

`
`
`Fig.9
`
`Velocity Distribution of Z-direction
`ttt
`Cross-section at 66 um
`from Upper Wall
`
`3.3 Length of capillary tube
`
`the
`flow analysis also gives
`viscous
`The
`appropriate length for the capillary tube.
`most
`The capillary tube accelerates the
`sample
`flow.
`After the fluid enters the the capillary tube,
`the
`velocity distribution becomes parabolic due to the
`shear
`stress caused by the wall.
`The capillary
`tube
`has such an inlet region, which varies with
`the velocity distribution. Generally,
`this
`is
`known as the “inlet length"(7). At
`the lower part
`of
`this
`region,
`the pressure loss
`increases
`in
`vain
`with
`the
`length of
`the
` capillary(7).
`Therefore,
`it may
`be thought
`that
`this
`inlet
`length is the minimum acceleration length.
`center
`Figure 11
`shows
`the growth of
`the
`velocity in the capillary tube obtained from the
`analysis.
`It is normalized by the mean velocity
`(=1.6m/s).
`In a square tube,
`the center velocity
`is close to 2.1 times the mean velocity along
`the
`inlet
`length. This figure shows that
`the center
`velocity is almost 2.1 times the mean velocity for
`a distance of only 2mm. This result suggests that
`a distance of 2mm is enough for the acceleration.
`Therefore,
`the length of the capillary is fixed at
`4mm, with 2 of the 4 provided for detection.
`
`
`
`0.8
`
`Lek
`
`1.6
`
`the
`distribution in
`The z-direction velocity
`cross section at 66m from the upper wall is shown
`in Fig.9. This indicates that the sheath stream
`from the bend passage goes over the front of
`the
`guide plate (
`the region with a positive velocity
`)
`and down between the plates(the region with a
`negative
`velocity).
`Similarly,
`there
`is
`a
`symmetrical
`sheath stream below the plates which
`goes
`under
`the plates
`and
`up
`between
`then.
`Therefore,
`the sample fluid is enveloped by
`both
`sheath streams.
`The locus of the
`sample
`fluid
`using computational simulation is shown in Fig.10.
`This
`shows
`that the sample fluid is
`constricted
`into a 20um diameter at the capillary tube.
`This
`value
`is almost equal
`to the width of the
`sample
`flow,
`given
`by the flow visualization that
`is
`mentioned in the next chapter.
`
`sample flow guide plate
`
`eapillary tube
`width: 300ugm
`
`Fig.10
`
`Computational Simulation
`of Sample Fluid
`
`Only half the region is simulated
`because the flow from each side
`is
`symmetrical.
`
`distance from inlet(x=0) (mm)
`
`Fig.11 Growth of Center Velocity
`in Capillary Tube(calculated)
`
`mean velocity :
`total flow rate
`
`ve=1.6m/s
`Qt=133u1/s
`
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`

`
`
`
`
`4. INVESTIGATION USING FLOW VISUALIZATION
`
`4.1 Check of sheath flow
`
`formed
`check whether the sheath flow is
`To
`and how narrowly the sample flow is constricted in
`the micro
`sheath
`flow
`chamber,
`a
`flow
`visualization
`technique,
`which
`employs
`a
`microscope,
`is used.
`The experimental setup for flow visualization
`consists of a flow system, a lighting system and a
`microscope-TV camera system.
`by
`The
`sample
`and sheath fluid is driven
`The
`pressurized air
`and regulated by valves.
`flow
`sheath flow rate is measured by a float-type
`meter, and a laminar flow meter is used to measure
`the
`sample flow rate. The flow rate ranges
`from
`30-300 wl/s for the sheath flow rate and 0.1-3.0
`ul/s for the sample flow rate.
`The
`laminar
`flow
`meter was manufactured
`specifically for
`this
`experiment as there was no equipment available
`to
`measure
`such
`a
`small
`flow rate.
`It has
`a
`capillary tube(140ym in diameter,
`100mm long) with
`pressure transducers at each ends, and shows
`good
`linearity.
`A light source with optical fibers is used to
`the
`sample
`flow.
`<A
`colour
`TV
`camera-—
`light
`microscope system makes it possible to observe the
`sample
`flow.
`To observe the sample flow,
`sample
`water is dyed by the uranine( Cagll)gQgNag), which
`is diluted with water 1,000 times by weight.
`The
`sheath
`fluid is filtered water.
`Uranine
`émits
`green fluorescence under lighting.
`
`flow direction
`eoae
`
`
`
`
`
`is
`sample flow observed near the nozzle
`The
`in Fig.12. Figure 12(a) shows the flow of
`shown
`chamber without the sample flow guide plate.
`the
`The photograph confirms that the sample
`flow is
`scattered at the capillary tube as was
`indicated
`by
`the flow analysis.
`On the other hand,
`figure
`12(b)
`shows that smooth fluid dynamic focusing of
`the
`sample flow are obtained in the chamber with
`the
`guide plate.
`In the capillary tube,
`the
`sample flow is constricted to about 20ym in width.
`This is almost
`the same as the value given by
`the
`simulation in Chapter 3.
`
`4.2 Speed of sample flow
`
`source with optical
`the light
`Instead of
`fibers,
`a couple of double pulse lamps ( under
`1 »sec pulse width, 60H2) are equipped to measure
`the
`speed of the sample flow. Pulse light
`from
`each
`lamp radiales at intervals of 20sec to
`the
`sample flow containing particles(3ym in diameter).
`A
`TV
`camera catches the two images of
`the
`same
`particle
`in the same video frame. The two
`images
`at the capillary(x=3mm) are shown in Fig.13.
`The
`length between these two images is
`the distance
`that the particle flows during a 20ysec
`interval.
`Therefore,
`the speed is obtained by dividing the
`length by the distance travelled in one
`interval.
`That is,
`the velocity is 3.0m/s when x=3mm.
`This
`value
`is
`close to the result of
`the
`calculated
`sample velocity.
`Ee:
`is
`experimentally confirmed
`capillary length of
`4mm
`is
`enough
`adequate acceleration.
`
`a
`that
`to obtain
`
`
`
`sample fluid scattered
`
`
`
`
`
`
`
`
`
`(b)With Sample Flow Guide Plate
`
`Fig.12
`
`Sample Flow near Nozzle
`total flow rate
`Qt=121 ul/s
`sample flow rate : Qs=
`1 il/s
`dye : uranine
`
`Fig.13
`
`Video Image of Particles
`in Capillary Tube
`
`Sequential double pulse lights
`shows the distance that
`the
`particle flows during one interval.
`The distance is 60ym in this case.
`Interval of pulse lights : 20ysec
`Center velocity :
`3.0m/s
`Diameter of particles :
`3 em
`
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`

`5.CONCLUDING REMARKS
`
`a particle
`for
`flow chamber
`sheath
`A micro
`analyzer was developed using micro-machining.
`Sheath
`flow geometry
`is
`formed
`in
`the
`two-
`dimensional
`passage configuration. Viscous
`flow
`analysis using FEM effectively investigates
`the
`flow of
`the
`small
`region,
`and
`reveals
`the
`influences of viscosity, such as the
`growth of
`secondary
`flow at the small bent
`passage.
`The
`speed of the sample is experimetally confirmed
`to
`be 3m/s in the micro sheath flow chamber.
`
`REFFERENCES
`
`a
`
`(1) Crossland-Tayler,P.J.; A Device for Counting
`Small Particles
`suspended in a Fluid
`through
`Tube: Nature Vol.171, No.4340, pp 37-38, 1953.
`(2) Eisert,W.G., Ostertag,R.
`and Niemann,E.-G.;
`Simple
`Flow Microphotometer
`for
`Rapid
`Cell
`Population Analysis: Rev. Sci.
`Inst., Vol
`46,
`No.8, pp.1021-1024 ,1975.
`(3) Kachel,V., Kordwig,E. and Glossner,E&.; Uniform
`Lateral Orientation, Caused by Flow Forces,
`of
`Flat Particles
`in Flow-Through Systems:
`J.
`of
`Histochemistry and Cytochemistry: Vol.25, No.7,
`pp.774-780 ,1977.
`(4) Eisert,W.G., Dennenloehr,M.; Nozzle Design for
`the
`Generation’
`of
`Plane
`Liquid
`Surfaces:
`Cytometry, Vol.1, No.4, pp.249-253, 1981.
`and
`(5)
`Ikegawa,M.,
`Shikano,Y.,
`Katoh,C.
`Symposium
`Nakano,S.:
`Proceedings of the Ist Int.
`on
`Supercomputer
`for Mechanical
`Engineering.
`JASME, pp.58-65, March, 1988.
`(6) Ohki,W., Miyake,R., Yamazaki,I., and Kaneko,T.
`; Proceedings of the 2nd Int.
`Symposium on Fluid
`Control
`Measurement
`Mechanics
`and
`Flow
`Visualization,
`pp.245-249, 5-9
`September
`1988,
`Sheffield England.
`(7) Hermann,Schlighting ; Boundary-Layer Theory;
`MeGRAW-HiLL,Ine.,NewYork US, 1979.
`
`270
`
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