Abstrict This disclosure relates to a flow meter having an improved flow
restrictor for creating laminar flow in the flow meter. The improved
flow restrictor is an adjustable bypass or flow restrictor which
comprises a stack of alternate slotted discs and non-slotted, smaller
diameter, washers with a diameter of 80% of the slotted discs, to
form a plurality of micro-channels 0.09 mm square and 3 mm long
which is a length to area ratio sufficient to assure laminar fluid
flow through the flow meter.
Claims What is claimed is:
1. In a flow meter, a flow restrictor assembly comprising, in combination,
inlet means for introducing a fluid located within said flow meter
with an input portion of said flow restrictor; flow restrictor means
coupled to said inlet means for creating laminar fluid flow, said
flow restrictor means comprising a first plurality of washers each
having a center aperture, and a second plurality of discs each having
a center aperture and a plurality of radially extending slots passing
through the front and rear surfaces of each disc and in communication
with said center aperture, each one of said second plurality of
discs being located between a pair of said first plurality of washers,
the center apertures of said first plurality of washers being lined
up with the center apertures of said second plurality of discs;
and outlet means for permitting the laminar fluid to flow out an
output portion of said flow restrictor, said outlet means comprising
all the center apertures of said first plurality of washers and
said second plurality of discs and said plurality of radially extending
slots in communication with said center apertures of said second
plurality of discs.
2. The apparatus of claim 1 wherein said first plurality of washers
being smaller in diameter than said second plurality of discs.
3. The apparatus of claim 2 wherein said first plurality of washers
having a diameter approximately 80% the diameter of said second
plurality of discs.
4. The apparatus of claim 1 wherein each one of said plurality
of radially extending slots of each of said second plurality of
discs extending from said center aperture of each of said second
plurality of discs to a point spaced from the outer peripheral surface
of each of said second plurality of discs.
5. The apparatus of claim 4 wherein said first plurality of washers
being smaller in diameter than said second plurality of discs.
6. The apparatus of claim 5 wherein a portion of each one of said
plurality of radially extending slots of each of said second plurality
of discs being above the peripheral surface of each of said pair
of said first plurality of washers.
7. The apparatus of claim 6 wherein a capillary channel is defined
by each one of said plurality of radially extending slots in each
of said second plurality of discs and by one of said pair of washers
being in contact with the front surface and the other of said pair
of washers being in contact with the rear surface of each disc located
between its pair of washers, the input portion of said capillary
channel being said portion of each one of said plurality of radially
extending slots of each disc located above the peripheral surfaces
of said pair of washers in contact with each disc, the output portion
of said capillary channel being said center aperture of said disc.
8. A method for creating laminar fluid flow in a flow meter comprising
the steps of:
providing a first plurality of washers each having a center aperture;
providing a second plurality of discs each having a center aperture
and a plurality of slots extending radially from said center aperture
of said disc and passing through the front and rear surfaces of
said disc; and
forming flow restrictor to create laminar fluid flow in a flow
meter by alternately stacking washers and discs together with each
disc being between two washers thereby providing, in combination,
a plurality of channels in each of said discs for carrying fluid
through each of said discs for creating laminar fluid flow.
9. A method in accordance with claim 8 wherein each of said discs
having a larger diameter than each of said washers.
10. A method in accordance with claim 9 wherein each of said channels
extending beyond the peripheral outer surface of each washer to
provide a fluid inlet and the center aperture of each of said discs
being part of a fluid outlet for said flow restrictor.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to flow meters and methods of
flow meter operation and more particularly, to flow meters and methods
of flow meter operation having flow restrictors for insuring laminar
flow in the flow meter.
2. Description of the Prior Art
The prior art contains a number of examples of flow meters using
manometers for measurement of pressure differentials created by
various types of flow restrictors such as orifices, needle valves,
porous plugs or a multi-path assembly of capillary tubes with a
high length to diameter ratio. There are also examples of flow meters
where instead of measuring a pressure differential, a small percentage
of fluid flow is diverted to a capillary where the rate of flow
is evaluated by various external means. Flow meters based on in-stream
rotary vanes and rotameters do not usually use flow restrictors
or by-pass arrangements except for setting the range of flow.
For obtaining maximum accuracy in flow measurement, it is very
desirable to insure that laminar flow is achieved through the flow
meter at least between the input and output portions of a measurement
loop used to measure the flow rate of the fluid flow through the
flow meter. Thus, for example, it is extremely critical in order
to accurately control deposition rates of the fluid at an upstream
control location that the flow meter read-out or indication be linear
or truly representative of the rate of fluid flow.
One of the major obstacles in achieving the ultimate objective
of accurately controlling deposition rates which can, for example,
be extremely critical in the fabrication of complex Integrated Circuits
or Chips forming parts of a semiconductor wafer, is to obtain and
maintain laminar flow (over a large range of pressure differentials)
through the flow meter measuring the rate of flow of a fluid through
a deposition apparatus.
In the past, various techniques were developed to obtain laminar
flow in a flow meter. For example, U.S. Pat. No. 3851526 discloses
various flow restrictor configurations or embodiments for attempting
to obtain laminar flow in a flow meter. In this specific prior art
patent example, ducts or grooves were formed either ordinarily on
or radially through discs in a pattern emanating from a center hole
in each disc. Various disc embodiments were disclosed each having
specific flow path lengths and configurations. A major problem associated
with the various disclosed discs of this prior art patent is the
complexity of fabrication.
A need existed to provide a simpler and less complex (and therefore
less costly) flow restrictor configuration that would achieve the
goal of obtaining laminar flow through a flow meter. A further need
existed for a simpler and less complex flow restrictor for a flow
meter which will provide laminar flow characteristics over a reasonable
range of fluid flow and fluid temperature and which can be adjusted
in small repeatable increments of flow restriction.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide
an improved flow meter and method of flow meter operation.
It is a further object of this invention to provide an improved
flow meter having an improved flow restrictor.
It is a further object of this invention to provide an improved
flow meter and method of flow meter operation having an improved
adjustable flow restrictor.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of both the measurement flow path
and the restrictor flow path within the flow meter of this invention.
FIG. 2 is an elevational, partially cut away, sectional view of
the flow meter of this invention showing both the measurement channel
or path and details of the flow restrictor arrangement along the
main fluid flow path.
FIG. 3 is an enlarged cross sectional view of the flow restrictor
assembly of FIG. 2 using multiple discs.
FIG. 4 is an enlarged elevational view of a single flow restrictor
disc having a center hole or opening and showing a plurality of
uniform width radial slots or slits going through the disc from
the front to back surfaces thereof.
FIG. 5 is an enlarged view of a flat washer member (having a center
hole or opening) which is used together with the slotted or slitted
disc of FIG. 4 in the flow restrictor of FIGS. 2 and 3.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with one embodiment of this invention, there is provided
in a flow meter, a flow restrictor assembly comprising, in combination,
inlet means for introducing a fluid located within said flow meter
with an input portion of said flow restrictor; flow restrictor means
coupled to said inlet means for creating laminar fluid flow, said
flow restrictor means comprising a first plurality of washers each
having a center aperture, and a second plurality of discs each having
a center aperture and a plurality of radially extending slots passing
through the front and rear surfaces of each disc and in communication
with said center aperture, each one of said second plurality of
discs being located between a pair of said first plurality of washers,
the center apertures of said first plurality of washers being lined
up with the center apertures of said second plurality of discs;
and outlet means for permitting the laminar fluid to flow out an
output portion of said flow restrictor, said outlet means comprising
all the center apertures of said first plurality of washers and
said second plurality of discs and said plurality of radially extending
slots in communication with said center apertures of said second
plurality of discs.
In accordance with another embodiment of this invention, there
is provided a method for creating laminar fluid flow in a flow meter
comprising the steps of: providing a first plurality of washers
each having a center aperture; providing a second plurality of discs
each having a center aperture and a plurality of slots extending
radially from said center aperture of said disc; and forming a flow
restrictor to create laminar fluid flow in a flow meter by alternately
stacking washers and discs together with each disc being between
two washers thereby providing, in combination a plurality of channels
in each of said discs for carrying fluid through each of said discs
for creating laminar fluid flow.
The foregoing and other objects, features and advantages of this
invention will be apparent from the following more particular description
of the preferred embodiments of the invention as illustrated in
the accompanying drawings.
Reference to FIG. 1 shows two distinct flow paths through the disclosed
flow meter device of FIG. 2. Flow input 10 branches into paths 10A
and 10B. The flow path 10B is a fluid flow measurement path. The
path 10A is a schematic representation of the flow restrictor assembly
of FIG. 2 where flow is from a plurality of apertures (formed by
the outer portions of the slots in the disc of FIG. 4) located in
a circle approximately one millimeter in from the outer perimeter
of the FIG. 4 disc or discs which are perferably about 11.8 mms
in diameter thence in a radial direction downward or inward along
all the radial slots or slits to a hole in the center of the disc
(which hole is 4 mms in diameter) and through hole 34 (see FIGS.
2 and 3) to a point 10C (see FIG. 1) where recombination with the
flow path 10B occurs. Shown on the path 10B of FIG. 1 are sensor
elements 12 and 12A which measure fluid flow in a measurement loop
in a manner well known in the art and not a part of this disclosure.
FIG. 2 shows an external view of flow meter 24 partly cut away
to show the interior portion of the flow meter 24 including a base
member 22. Illustrated schematically in FIG. 2 is the flow meter
measurement path or capillary 10B with the (preferably resistor)
sensing elements 12 and 12A and the main flow path in and out of
the flow meter 24. Shown at 24A is a socket for connecting the sensing
elements 12/12A to external circuits (not shown).
Input/output tubing 10D is fastened to the flow meter 24 by hexagon
nuts 12B and conventional compression fittings screwed into internal
threads 20 which are a part of the inlet and outlet before and after
the restrictor assembly. The flow resistor assembly comprises an
externally threaded hollow retaining fixture 14 which has a screw
driver slot 14A to facilitate its installation within the flow meter.
Approximately one half of the downstream length of the hollow retaining
fixture 14 (see FIG. 3 for greater clarity) is not threaded and
has a smaller external diameter equal to approximately 80% of the
threaded diameter portion of the fixture 14 thus leaving a circular
chamber 16A. Four holes 16 allow a fluid entering the input portion
of the hollow fixture 14 to move outwardly and reach the cavity
or chamber 16A and then flow through the capillary channels formed
by alternately stacked discs 28 and washers 32 (see FIGS. 4 and
5 for a clearer view of a disc 28 and a washer 32) to outlet center
hole 34 and thence along the outlet center hole 34 and the output
portion of the restrictor or retaining fixture 14.
FIG. 3 is an enlarged sectional view showing, in greater detail,
the restrictor assembly shown in FIG. 2. The internally threaded
inlet and outlet portions of the restrictor assembly are shown more
clearly in FIG. 3. Passage or conduit 18 connects to the flow meter
capillary 10B (see FIG. 2). The retaining fixture 14 is shown installed
with its intermediate blind or imperforate wall portion 34A holding
a stack of the center apertured washers 32 alternating with the
slotted or slitted, capillary center apertured discs 28 within the
cavity which is formed by the space located between the inside of
the wall portion 16A and the outside of cap member 36A which is
located at the output end portion of the retaining fixture 14 in
front of the stack of alternate washers 32 and disc 28. This cavity
is machined within the base member 22 to allow the discs 28 a clearance
of 0.1 mms from the edge of the discs 28 to the wall of cavity 16A
to allow fluid flow around the periphery of the discs 28. Holes
16 which are radial allow the fluid in the flow meter to flow through
the hollow center of the retaining fixture 14 to reach the circular
chamber 16A and then flow into the cavity space located between
the inside of the wall portion 34A and the outside of the cap member
36A and then radially inward through the slits in each of the discs
28 and out through the center output hole 34 which has the same
diameter as the center holes in the washers 32 and the discs 28
and is formed by all the center holes 34 of each of the center holes
of the washers 32 and the discs 28. Each disc 28 and 32 is accurately
centered in the cavity space 16A by a triangular extension 34B attached
to the end of retaining fixture 14. These center apertured washers
32 and 28 are centered by the triangular extension 34B on retaining
fixture 14 which is accurately dimensioned to fit the center holes
of washers 28 and 32 with a clearance of not more than 0.05 mms.
Fluid flow is from cavity 16A through the capillary slits 30 in
washers 28 to the center hole 34 and outward through the gaps around
triangular extension 34B. The stack of the washers 32 and the discs
28 is immobilized or fixed in place by tensioning the retaining
fixture 14 against the stack with a screwdriver inserted in the
slot 14A.
FIG. 4 shows a greatly enlarged view of one of the capillary or
slotted discs 28 used in the flow restrictor protion of the flow
meter. In a practical example of a preferred embodiment of one of
the discs 28 in use, the disc diameter is 11.8 mms, the disc thickness
is 0.09 mms. Forty slits 30 (although forty-eight slits are shown
in FIG. 4) in the disc 28 are preferably chemically milled from
points 1.0 mms from the edge of the disc 28 directly to the center
hole 34. This forms a circle of spaced apart slits equivalent to
a circle 10.8 mms in diameter. Width of each of the forty slits
30 is preferably 0.09 mms which is equal to the disc thickness.
The center hole diameter 34 is preferably 4.0 mms.
FIG. 5 shows an enlarged view of one of the washers 32 which when
centered on each of the (or opposite) sides of each of the discs
28 permits each slit 30 to be a capillary channel 0.09 mms square.
Preferably the diameter of each of the spacing washers 32 is 10
mms, diameter of the center hole 32 is the same as for the discs
28 which is 4.0 mms and the washer thickness is 0.09 mms. Thus,
the length of each capillary channel formed with the covered disc
28 is approximately 3.0 mms.
OPERATION OF THE FLOW RESTRICTOR
From the specification, it can be shown the preferred minimum number
of capillary channels formed by one of the restrictor discs 28 is
forty and the number of channels increases in increments of 40 as
each of the discs 28 is added to the alternating washers 32. More
than twenty discs can be accommodated in the cavity space formed
by the inside portion of the member 34A and the outside portion
of the cap 36A. Dimensions of the flow restrictor components depicted
in this specification are based on an actual fluid flow meter and
are furnished only as one example thereof. Variations of the dimensions
of the flow restrictor components can be made, as desired. Furthermore,
the diameter of the retaining fixture 14 threaded section 20 and
the cavity space which includes chamber 16A can be altered, as desired,
to accommodate different flow rates. The disc and washer diameters
can also be changed, as desired. Also, the number of the slits 30
in each of the discs 28 (see FIG. 4) can also be changed, the only
constraint being that the channel length to diameter ratio be kept
high enough to maintain laminar flow at flow rates of interest through
the flow restrictor assembly.
While the invention has been described with respect to a preferred
physical embodiment constructed in accordance therewith, it will
be apparent to those skilled in the art that various modifications
and improvements may be made without departing from the scope and
spirit of the invention. |