U.S. patent number RE31,570 [Application Number 06/346,422] was granted by the patent office on 1984-05-01 for fluid flowmeter.
This patent grant is currently assigned to Tylan Corporation. Invention is credited to Charles F. Drexel.
United States Patent |
RE31,570 |
Drexel |
May 1, 1984 |
**Please see images for:
( Certificate of Correction ) ** |
Fluid flowmeter
Abstract
A flowmeter in which a laminar flow conduit is connected in
parallel to a flow restrictor comprising at least one disk having
an opening through opposite surfaces and at least one conduit from
the opening to the perimeter of the disk, each conduit having an
effective length to diameter ratio sufficient to assure laminar
fluid flow.
Inventors: |
Drexel; Charles F. (Los Angeles
County, CA) |
Assignee: |
Tylan Corporation (Carson,
CA)
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Family
ID: |
26994850 |
Appl.
No.: |
06/346,422 |
Filed: |
February 5, 1982 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
349169 |
Apr 9, 1973 |
03851526 |
Dec 3, 1974 |
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Current U.S.
Class: |
73/202.5;
138/42 |
Current CPC
Class: |
G01F
1/42 (20130101); G01F 1/40 (20130101) |
Current International
Class: |
G01F
1/42 (20060101); G01F 1/34 (20060101); G01F
1/40 (20060101); G01F 005/00 () |
Field of
Search: |
;73/202,203,204
;138/40,42,43,44 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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251194 |
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Apr 1926 |
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GB |
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520083 |
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Apr 1940 |
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GB |
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Primary Examiner: Goldstein; Herbert
Attorney, Agent or Firm: Nilsson, Robbins, Dalgarn,
Berliner, Carson & Wurst
Claims
I claim:
1. A flowmeter comprising:
a housing having a fluid inlet and a fluid outlet defining a first
fluid path therebetween .Iadd.and aligned along a first
direction.Iaddend.;
a flow restrictor in said first fluid path comprising at least one
disk having a front surface and a rear surface connected by a
perimeter surface, an opening through said front and rear surfaces
and at least one conduit through said perimeter surface to said
opening, said conduit being of a length to diameter ratio to
provide laminar flow;
means for supporting said restrictor in said first fluid path
whereby the flow therethrough is directed radially in either
direction.Iadd., normal to said first direction, .Iaddend.between
the perimeter and the opening of said at least one disk;
an elongate conduit defining a laminar flow second fluid path;
means for measuring the rate of flow of fluid through said elongate
conduit; and
means for connecting said second fluid path in parallel with said
first fluid path on opposite flow sides of said flow element.Iadd.;
said housing being constructed to as to redirect said radially
directed flow to flow parallel to said first
direction.Iaddend..
2. The flowmeter of claim 1 in which said conduit is defined as a
channel through the front surface of said disk.
3. The flowmeter of claim 1 in which said conduit comprises an
elongate passageway having an effective length substantially larger
than the effective hydraulic radius thereof.
4. The flowmeter of claim 1 in which the ratio of the length of
said passageway to the effective hydraulic radius thereof is at
least 1.5:1.
5. The flowmeter of claim 1 in which said opening is centrally
formed through said disk and said conduit radiates linearly
therefrom to said perimeter surface.
6. The flowmeter of claim 1 in which said disk is formed flat with
substantially even front and rear surfaces exclusive of said
conduit.
7. The flowmeter of claim 1 in which said flow element comprises a
plurality of juxtaposed disks, including said one disk, each disk
having a front surface and a rear surface connected by a perimeter
surface, each disk having an opening through said front and rear
surfaces and at least one conduit through said perimeter surface to
said opening, the opening of said plurality of disks being
aligned.
8. .[.The flowmeter of claim 7 in which .]. .Iadd.A flow meter
comprising:
a housing having a fluid inlet and a fluid outlet defining a first
fluid path therebetween;
a flow restrictor in said first fluid path comprising a plurality
of juxtaposed disks, including said one disk, each disk having a
front surface and a rear surface connected by a perimeter surface,
each disk having an opening through said front and rear surfaces
and at least one conduit through said perimeter surface to said
opening, said conduit being of a length to diameter ratio to
provide laminar flow, .Iaddend.the number of conduits carried by
one of said plurality of disks .[.is.]. .Iadd.being
.Iaddend.different from the number of conduits carried by another
of said plurality of disks.Iadd., the opening of said plurality of
disks being aligned;
means for supporting said retrictor in said first fluid path
whereby the flow therethrough is directed radially in either
direction between the perimeter and the opening of said at least
one disk;
an elongate conduit defining a laminar flow second fluid path;
means for measuring the rate of fluid through said elongate
conduit; and
means for connecting said second fluid path and parallel with said
first fluid path on opposite flow sides of said flow element.
.Iaddend.
9. A flowmeter comprising:
a housing having a fluid inlet and a fluid outlet defining a first
fluid path therebetween;
a flow restrictor in said first fluid path comprising at least one
disk having a front surface and a rear surface connected by a
perimeter surface, an opening through said front and rear surfaces
and at least one conduit through said perimeter surface to said
opening, said conduit being of a length to diameter ratio to
provide laminar flow;
an elongate conduit defining a laminar flow second fluid path;
means for measuring the rate of flow of fluid through said elongate
conduit; and
means for connecting said second fluid path in parallel with said
first fluid path on opposite flow sides of said flow element;
said housing comprising a wall defining said fluid inlet, said wall
being threaded, and including a retaining member in said inlet for
securing said flow restrictor in said first fluid path, said
retaining member being hollow and externally threaded to mate with
said housing wall thread, said retaining member being open at one
end and closed at its opposite end, said opposite end of said
retaining member abutting said flow restrictor at one of said front
and rear surfaces thereof, and means in said housing for retaining
the opposite surface of said flow restrictor against movement, said
retaining member being formed with at least one lateral opening
therethrough, the effective outer diameter of said flow restrictor
being smaller than the effective inner diameter of said inlet
whereby fluid introduced into said retaining member flows through
said lateral opening, through said conduit, into said disk opening
and out thereof to define said .[.second.]. .Iadd.first
.Iaddend.fluid path.
10. The flowmeter of claim 7 in which each said disk is formed with
a plurality of said conduits.
Description
FIELD OF THE INVENTION
The fields of art to which the invention pertains include the
fields of pressure differential measuring and testing devices,
flowmeters and conduit restrictors and flow elements.
BACKGROUND AND SUMMARY OF THE INVENTION
The prior art has developed a variety of linear flowmeters in which
a manometer or other device for measuring a pressure differential
is connected across opposite sides of a flow restrictor. The
restrictor comprises one or more passageways proportioned so that
under normal working conditions the resistance to flow through the
resistor as a whole is substantially proportional to the rate of
flow. There are certain levels of inaccuracies inherent in such
devices and methods have been developed to optimize the accuracy of
results obtained. See for example Goldsmith U.S. Pat. No. 3,071,001
and Weichbrod U.S. Pat. No. 3,071,160. See also application Ser.
No. 141,897, now U.S. Pat. No. 3,792,609 entitled Flow Splitter by
R. F. Blair, R. J. Hill and D. B. Le May of common assignment to
the present application.
In certain applications the flow rate of a fluid is measured not by
directly determining the pressure differential across a restrictor,
but by measuring the actual flow of a small portion of fluid. Such
applications require that the flow of the fluid be divided into two
or more paths with an exact ratio maintained between the individual
path flow rates. In a typical situation, such as in a mass
flowmeter, a very small percentage of the flow is diverted into a
measuring section. This percentage may be as small as 1 part in
40,000 and the flow measuring section is typically a very thin
tubular conduit which is much longer that its diameter so that
laminar flow prevails throughout the conduit. During laminar flow
of a fluid, the flow rate is directly proportional to pressure drop
and inversely proportional to viscosity. In contrast, during
turbulent flow, the flow rate is proportional to the square root of
pressure drop and largely independent of viscosity. Therefore, in
the design of a flowmeter in which the flow is split along parallel
paths, it is important to provide conditions that will assure
laminar flow in each path. Since the measuring section flow is
laminar, if the bypass flow were turbulent the flow ratio would be
a function of viscosity and would have an undesirable dependency
upon temperature and pressure. Such flow splitters are thus much
more prone to inaccuracies as a result of geometric configuration
than are pressure differential devices.
In the above-mentioned application Ser. No. 141,897 a number of
devices are disclosed incorporating a plurality of closely spaced
fluid passageways, e.g., defined by a plurality of screens, each
passageway defining a laminar flow path. Generally, improvements
over prior devices is thus obtained, but the pressure drop is
influenced by the compressive force used to assemble the device and
by variations in screen mesh. The effective diameters are quite
small, which can result in trapping of contaminants and resulting
plugging.
The present invention provides simple and economical methods for
assuring laminar flow in both the measuring section and bypass
section of a flow splitter so that a constant and predetermined
ratio is maintained across the entire range of flow rates to be
measured. The present construction overcomes the disadvantages
referred to above and additionally provides a wide range of flow,
as high as 1,000:1 or higher, obtained with facility and repeatable
accuracy. This has been accomplished by using as a flow restrictor
one or a juxtaposed plurality of disks, each having one or a
plurality of channels formed from its perimeter to an opening
through opposite sides of the disk. Fluid is directed to the
perimeter of the disk or disks and is conveyed by the conduits to
the opening. The conduits have sufficiently large length to
diameter ratios (or length to effective hydraulic radius, as
defined hereinafter) to assure laminar flow of the fluid. In an
exemplary embodiment, the flow restrictor comprises flat, smooth
sided juxtaposed disks, formed with central, aligned openings. The
central opening in each disk communicates via one or more conduits
radiating from the central opening to the perimeter of the
disk.
By juxtaposing a predetermined number of disks having a
predetermined number and shape of conduit, one can achieve any flow
ratio desired. There is only one flow path, radially inward (or
outward if flow is reversed); therefore, the passage size can be
precisely controlled. Furthermore, the conduits have sufficient
diamter so that plugging by contaminants can be avoided. The entire
construction can be made of metal and can be tightly assembled so
that seals are not required, enabling its use with otherwise
corrosive fluids.
The flow restrictor is combined with an elongate laminar flow
conduit, serving as a measuring section, to form a substantially
linear flowmeter. Such a meter includes a housing having a fluid
inlet and fluid outlet, the housing defining a fluid path between
the inlet and outlet. The flow restrictor is disposed in this fluid
path in parallel circuit with the measuring section conduit. Means
are provided for measuring the rate of flow of fluid through the
measuring section conduit, which means are known in the prior art
and constitute no part of the present invention. The result is a
compact structure of simple construction which demonstrates high
accuracy in measurements over a substantial range of flow
temperature and pressure conditions.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of the fluid flow paths in a
flow divider;
FIG 2 is a schematic illustration in cross-section of portions of a
flowmeter incorporating a flow restrictor of this invention;
FIG. 3 is an enlarged cross-sectional view of the flow restrictor
portion of the flowmeter of FIG. 2;
FIG. 4 is a front elevational view of an exemplary flow restrictor
disk used in the flow element of FIG. 3, taken on the line 4--4 of
FIG. 3.
FIG. 5 is a cross-sectional view of the flow restrictor disk of
FIG. 4, taken on line 5--5 of FIG. 4;
FIG. 6 is a cross-sectional view of the flow restrictor disk of
FIG. 4, taken on line 6--6 of FIG. 4;
FIGS. 7-14 are front views of alternative flow restrictor disks;
and
FIG. 15 is a perspective view of another alternative flow
restrictor disk.
DETAILED DESCRIPTION
As required, details of illustrative embodiments of the invention
are disclosed. However, it is to be understood that these
embodiments merely exemplify the invention which may take forms
different from the specific illustrative embodiments disclosed.
Therefore, specific structural and functional details are not
necessarily to be interpreted as limiting, but as a basis for the
claims.
The invention will first be described with respect to a particular
type of restrictor or flow element disk as illustrated in FIGS.
2-6. Subsequently, alternative disk configurations will be
described as illustrative in FIGS. 7-15. The invention will be
described with respect to fluid flowing from left to right in FIGS.
1-3, but the devices described herein are as effective with a
reverse fluid flow.
Referring to FIG. 1, fluid paths A and B constitute the flow
through a flowmeter from the inlet at P.sub.1 to the outlet
P.sub.2. The line labeled PATH A represents fluid flow through the
measuring section of the flowmeter and the line designated PATH B
represents fluid flow through the bypass section of the flowmeter.
The pressure drop is the same across each path. It is desired to
have the flow rate in PATH A divided by the flow rate in PATH B be
a constant at all times. In the particular embodiments illustrated
herein, PATH A is a tube of sufficient elongation to assure laminar
flow. PATH B must also assure laminar flow, otherwise the flow
ratio would have an undesirable dependency upon temperature and
pressure.
Flow through channel may be characterized by the nondimensional
parameter known as the Reynold's number where
where .phi. is the density of the fluid, v.sub.m is the mean
velocity in the conduit, u is the fluid viscosity and m is the
hydraulic radius defined as the conduit are a divided by the
conduit perimeter. The effective diameter of the conduit can be
considered to be 4m. The Reynold's number expresses the ratio of
the inertia forces to the viscous forces in the fluid. For low
values of R, the flow is laminar, while for high values of R,
inertia forces predominate and the flow tends to be turbulent. The
Reynold's number transition generally occurs in the range of about
1,600 to about 2,800 Reynold's number. For any particular
structure, the transition Reynold's number can be determined by
noting the mean velocity at which fluid of known density and
viscosity flows in a turbulent manner and applying the information
to the formula set forth above. The following embodiments
illustrate a number of specific structures to accomplish laminar
flow in the bypass section, PATH B, in combination with laminar
flow in the measuring section, PATH A. Each of these embodiments
provide a flow restrictor in the fluid path through the bypass
section, PATH B, defined radially inward (or outward) flow through
conduits having length to effective diameter ratios sufficiently
large to assure laminar fluid flow. In each of the embodiments, the
fluid being measured is gaseous, but the structure and concepts are
applicable to liquids as well.
Referring now to FIGS. 2 and 3, a flowmeter 10 is illustrated
incorporating a flow splitter in accordance with this invention.
The flowmeter includes a housing 12 bored and counterbored to
define a passageway 14 formed with inlet and outlet ports 16 and
18, respectively, for the fluid whose flow is to be measured. A
reduced diameter portion 20 defines an annular shoulder 22 for
receiving a flow restrictor 24 and an upstream flow directing
hollow cylindrical nut 25. The flow restrictor 24 includes one or a
plurality of channeled disks 27 which will be described hereinafter
in more detail. A passageway region 26 is threaded and received the
flow restrictor 24 and the matingly threaded cyindrical nut 25. The
cylindrical nut 25 is formed with notches 30 across its far end so
as to be readily threaded into the passageway 14 against flow
restrictor 24 to secure the flow restrictor 24 in abutment with the
shoulder 22. An expanded diameter passageway region 32 defines a
shoulder 34 spaced from the end of the cylindrical nut 25 for
receiving a filter screen 36. The passageway region 32 is threaded
and receives a matingly threaded cylindrical securing member 38 for
abutment against the filter screen 36, securing the screen 36 in
place.
Upstream and downstream taps, in the form of bore holes 40 and 42,
respectively, in the housing, are provided for disposing respective
attachment ends 44 and 46 of a measuring section tube 48 on
opposite sides of the combination of flow directing nut 25 and flow
restrictor 24. The attachment ends 44 and 46 are tubular members
through which the ends of the measuring section tube 48 are tightly
secured, so that fluid flowing into the attachment ends 44 and 46
is conducted entirely through the measuring section tube 48. The
measuring section tube is very thin and elongate; in this exemplary
embodiment the tube 48 has an inside diameter of 0.010 inch and a
length of 3.1 inches. Thermal elements 50 and 52 on the outside of
the tube detect the mass flow rates of fluid passing through the
tube 48. The method by which this is accomplished is known to the
art and per se does not constitute a part of this invention.
The flow restrictor 24 consists of a plurality of juxtaposed
channeled disks 27 stacked together to create a desired pressure
drop and flow rate. This particular illustration incorporates seven
disks each with flat parallel surfaces and 0.005 inch in width.
There can be as few as 1 disk 27 or as many as 20 or more,
depending upon the desired pressure drop and capacity of the
housing 12.
Referring to FIGS. 4, 5 and 6, in this particular embodiment each
of the disks 27 is formed flat, as a washer, with a central opening
54 through the opposite parallel surfaces. In the illustration,
four conduits or channels 56 are formed through the front surface
58 of the disk radiating from the central opening 54 outwardly to
the perimeter 60 of the disk. The channels 56 serve to conduct
fluid from the periphery of the disk 27 to the opening 54.
Each disk should be flat and its surfaces smooth and free from
burrs or unevenness that would interfere with fluid flow in the
channels 56 or cause the disks 27 to be separated. Sufficient
smoothness can be achieved with chemical etching. In this
particular embodiment the diameter of the disk 27 is 0.480 inch,
the diameter of the central opening is 0.270 inch and the length of
the channel is 0.105 inch. The channel 56 is rectangular in
cross-section and has height and width dimensions of 0.0025 inch
and 0.0085 inch, respectively. Thus, the cross-sectional area of
each channel 56 is 0.000021. The effective hydraulic radius of the
channel can be calculated as the radius of a circle having an
equivalent cross-sectional area; in this case the effective
hydraulic radius is 0.0026 inch. Accordingly, each channel has a
length to effective hydraulic radius of about 40:1. Generally, the
ratio of length to effective hydraulic radius should be at least
4:1 and can be as high as 200:1 or higher. The mesh filter 36
located upstream of the flow element 24 passes 5 micron particles.
In view of the much larger channel diameter, the flow element 24 is
protected from clogging from contaminants in the fluid stream.
Referring back to FIG. 3, the cylindrical nut 25 operates in
conjunction with the flow restrictor 27 to direct fluid through the
conduits 56 radially inwardly to the central opening 54. For this
purpose, the nut 25 is hollow and open at its upstream end 62 and
closed at its downstream end by an end wall 64. The annular side
wall 66 of the nut defines a plurality of openings 68 adjacent the
end wall 64. In this embodiment four such openings are formed, each
0.093 inch in diameter. Additionally, for purposes of aligning the
disks 27, three elongate cylindrical pins 70, each threaded at its
end are disposed in threaded openings therefor in the downstream
surface of the end wall 64. The pins jut from the end wall 64 a
distance sufficient to carry the disks 27 for alignment
thereof.
In assembly, the desired number of disks 27 are merely stacked on
the pins 70 to define the flow element 24. The nut 66 is then
threaded into the passageway region 26 so that the flow element 24
abuts the shoulder 34 and the nut end wall 64 abuts the flow
element 24 and presses the component disks 27 together. No seals
are required since the components can be tightly assembled. In
place of the pins 70, one can provide nibs on the perimeter of the
disks 27. Alternatively, one can use a jig protruding through the
outlet port 18 to align the disks prior to tightening. The
remainder of the flowmeter is assembled as known to the art and
flowmeter electronics are assembled in the housing as known to the
prior art, and which are not per se a part of the invention
herein.
In operation, fluid is fed into the inlet 16 whereupon it is
filtered by the filter screen 36 and travels into the hollow nut
25, through the holes 68 to the perimeters of the stacked disks 27,
radially through the conduits 56, to and through the alinged disk
openings 54 and emerging from the outlet 18. A portion of the fluid
stream is diverted through the measuring section tube 48, flowing
therethrough to meet the emerging fluid at the outlet 18. As a
result of the present configuration, flow through both the
measuring section tube 48 and flow element 24 are laminar, yielding
accurate measurements over a substantial range of flow, temperature
and pressure conditions.
The foregoing assembly provides only one flow path for PATH B
referred to in FIG. 1, radially inwardly, or outward for reverse
operation. Importantly, each disk 27 has sufficient thickness to
retain dimensional integrity when squeezed by the nut 25. Because
of the flatness of the disks 27, the flow meter is not
significantly affected by variations in compressive force caused by
tightening of the nut 27. Installation of the flow directing
components is simple and requires no calibration adjustments for
predetermined combinations of disks. Importantly, the present
construction permits channels of substantial length allowing
substantial cross-section for high length:hydraulic radius ratios.
Accordingly, relatively large size particles can pass through the
system without plugging the flow restrictor. Furthermore, the
entire assembly can be formed of metal, without requiring seals,
allowing use of the flow restrictor with otherwise corrosive
fluids.
The particular structure of the disks 27 can be varied in number
and in configuration to accomodate various flow ranges. Disks
having 1-60 or more channels can be used, as well as disks having
non-linear channel shapes such as will be described below, in any
combination of from 1-40 disks or more to achieve any particular
flow range. The desired arrangement can be obtained with simple
experimentation or by calculations using the Reynold's number
equation given above. Thus, it has been found that a flow range of
5 to 5,000 standard cubic centimeters per minute could be achieved
by stacking 1-20 disks comprising one to three differently
configurated disks having one, 10 and 50 channels. The diameter of
the disk opening 54 and the diameter of the disk itself can be
varied to suit particular needs.
Referring to FIGS. 7-15, a variety of disk configurations are
shown. In FIG. 7, a disk 77 is shown having a central opening 74
and a single channel 76 linearly formed in one surface from the
opening 74 to the perimeter of the disk 77. In FIG. 8, a disk 87 is
shown having a central opening 84 and 10 channels 86 radiating from
the opening 84 to the disk perimeter. In FIG. 9, a disk 97 is shown
having a central opening 94 and 50 radiating channels 96.
In FIG. 10, a disk 107 is shown having a central opening 104 and
four curved channels 106 extending from the opening 104 to the disk
perimeter in pinwheel fashion.
In FIG. 11, a disk 117 is shown having a central opening 114 and a
single spirally formed channel 116 connecting the opening 114 to
the disk perimeter.
In FIG. 12, a disk 127 is shown having a central opening 124 and a
series of maze-like concentric channels 126 therearound connected
by short channels 125 to provide communication between the opening
124 and disk perimeter.
In FIG. 13, a disk 137 is shown having a central opening 134 and a
plurality of circular channels 136 annularly disposed about the
opening 134, connected to the opening 134 and disk perimeter by
short channels 135.
In FIG. 14 a disk 147 is shown having a central opening 144 and a
plurality of diamond-shaped channels 146 annularly disposed about
the opening 144, connected to the opening 144 and disk perimeter by
short channels 145.
In FIG. 15, a disk 157 is shown having a central opening 154 and a
plurality of channels 156 in the form of elongate conduits drilled
through the body of the disk 157 from the perimeter 159 to the
opening 154.
Each of the disks illustrated in FIGS. 7-15 can be substituted for
one or more disks in the embodiment illustrated in FIG. 3. Other
variations are also permissable; for example the opening in each
disk can be off-center and means; such as a jig or appropriately
spaced alignment pins on the nut 25 can be provided for
alignment.
* * * * *