U.S. patent application number 12/547320 was filed with the patent office on 2011-03-03 for fluid flow conditioner.
This patent application is currently assigned to FLUID COMPONENTS INTERNATIONAL LLC. Invention is credited to Brian MCDOLE, Michael R. NOEL, Eric WIBLE.
Application Number | 20110048564 12/547320 |
Document ID | / |
Family ID | 43014449 |
Filed Date | 2011-03-03 |
United States Patent
Application |
20110048564 |
Kind Code |
A1 |
WIBLE; Eric ; et
al. |
March 3, 2011 |
FLUID FLOW CONDITIONER
Abstract
A device and method for conditioning media flowing within a
conduit enabling sensors placed within short straight run distances
to measure media flow with improved accuracy employing a thermal
flow instrument. A flow conditioner downstream of a media flow
measuring transducer has walls that diverge in the flow direction
to optimize readings of the media flow from the transducer.
Inventors: |
WIBLE; Eric; (Carlsbad,
CA) ; NOEL; Michael R.; (Encinitas, CA) ;
MCDOLE; Brian; (San Marcos, CA) |
Assignee: |
FLUID COMPONENTS INTERNATIONAL
LLC
San Marcos
CA
|
Family ID: |
43014449 |
Appl. No.: |
12/547320 |
Filed: |
August 25, 2009 |
Current U.S.
Class: |
138/37 ;
138/39 |
Current CPC
Class: |
G01F 1/6842
20130101 |
Class at
Publication: |
138/37 ;
138/39 |
International
Class: |
F15D 1/04 20060101
F15D001/04 |
Claims
1. A fluid flow conditioner device for use with a thermal flow
instrument having at least a pair of spaced parallel thermal flow
thermowells having sensing elements therein configured to be
arranged in the media flow in a conduit, the device comprising; a
wedge shaped element arranged a predetermined distance downstream
from said thermowells, said wedge shaped element having at least a
pair of walls that diverge in the flow direction; a shroud element
partially encompassing said wedge shaped element and said
thermowells, said shroud having an upstream opening therein, the
upstream opening being formed to permit the media to flow into said
shroud and to impinge upon said thermowells and said wedge shaped
element.
2. The device of claim 1, wherein said shroud element is formed
with opposing, space walls defining the upstream opening and
wherein said diverging walls of said shaped element have distal
ends that are spaced from said spaced walls of said shroud
downstream of said thermowells by a predetermined distance.
3. The device of claim 1, wherein said thermowells and said wedge
shaped element extend substantially coextensively into the interior
of said shroud.
4. The device of claim 1, wherein said pair of walls diverge from
an apex line defined by the diverging walls, the pair of diverging
walls that meet at the apex forming an angle in the range of
90.degree.-140.degree. downstream in the flow direction.
5. The device of claim 4, wherein the apex line is normal to the
flow direction and is substantially located between said
thermowells.
6. The device of claim 1, wherein at least one of said thermowells
includes a heated sensor and the other includes a reference sensor,
said heated sensor thermowell being spaced from a respective one of
said diverging walls by a predetermined distance.
7. A method for conditioning media flowing in a flow direction
within a conduit having at least a pair of spaced parallel thermal
flow thermowells having sensing elements therein and arranged in
the media flow in the conduit, the method comprising: diverging the
media as it flows past the thermowells by means of a wedge shaped
element having a pair of diverging walls positioned downstream in
the flow direction from the thermowells; and channeling the flowing
media around and past the wedge shaped element and the thermowells
by means of a shroud partially surrounding the wedge shaped element
and the thermowells, the shroud being formed with an opening
upstream from the thermowells in the flow direction.
8. The method of claim 7, wherein the shroud is formed with
opposing, spaced walls defining the upstream opening, and further
comprising positioning the pair of diverging walls of the wedge
shaped element such that the pair of diverging walls end adjacent
to and spaced from the spaced walls of the shroud by a
predetermined distance.
9. The method of claim 7, wherein diverging the media is
accomplished by a pair of diverging walls which form a apex from
which the pair of walls diverge, wherein the apex is formed at
upstream ends of the pair of diverging walls in the flow direction
and the apex has an angle in a range of 90.degree.-140.degree.
facing downstream in the flow direction.
10. The method of claim 9, and further comprising providing the
thermowells spaced by a predetermined distance from the diverging
walls.
11. The method of claim 7, wherein the wedge shaped element has
generally a V-shape.
12. The method of claim 7 wherein the wedge shaped element has
generally a delta shape.
13. A fluid flow conditioner device for use with a thermal flow
instrument having at least a pair of spaced parallel thermal flow
thermowells having sensing elements therein configured to be
arranged in the media flow in a conduit, the device comprising: a
wedge shaped element arranged a predetermined distance downstream
from said thermowells, said wedge shaped element having at least a
pair of walls that diverge in the flow direction.
14. The device of claim 13, and further comprising a shroud element
partially encompassing said wedge shaped element and said
thermowells, said shroud element having passageways therethrough to
enable the media to flow through while encountering said wedge
shaped element and said thermowells.
15. The device of claim 13, wherein said pair of walls diverge from
an apex line defined by the diverging walls, the pair of diverging
walls that meet at the apex forming an angle in the range of
90.degree.-140.degree. downstream in the flow direction.
16. The device of claim 15, wherein the apex line is normal to the
flow direction and is substantially located between said
thermowells.
17. The device of claim 13, wherein at least one of said
thermowells includes a heated sensor and the other includes a
reference sensor, said heated sensor thermowell being spaced from a
respective one of said diverging walls by a predetermined
distance.
18. A fluid flow conditioner device for use with a thermal flow
instrument having at least one thermal flow thermowell having a
sensing element therein configured to be arranged in the media flow
in a conduit, the device comprising: a wall element arranged a
predetermined distance downstream from said thermowell, said wall
element being oriented diagonally with respect to the flow
direction; and a shroud element partially encompassing said wall
element and said thermowell, said shroud element having an upstream
opening therein, the upstream opening being formed to permit the
media to flow into said shroud and impinge upon said thermowell and
said wall element.
19. The device of claim 18, wherein said wall element is arranged
at an angle in the range of 45.degree.-70.degree. with respect to
the flow direction.
20. A fluid flow conditioner device for use with a thermal flow
instrument having at least a pair of spaced parallel thermal flow
thermowells having sensing elements therein configured to be
arranged in the media flow in a conduit, the device comprising: a
shroud element partially encompassing said thermowells, said shroud
element having an upstream opening therein configured to permit
media to flow into said shroud and impinging upon said
thermowells.
21. The device of claim 20, and further comprising at least one
wall member adjacent to and spaced from at least one said
thermowell at an angle of 45.degree.-70.degree. with respect to the
media flow direction.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to devices that condition
flowing media within a conduit, and more particularly, to such
devices that condition flowing media to enable more accurate
readings of thermal flow sensors used to measure the flowing
media.
BACKGROUND OF THE INVENTION
[0002] When using thermal flow meters, the accuracy of mass flow
rate measurements of media traveling within a conduit can be
adversely affected by random and unpredictable turbulence within
the flowing media, as well as by the fact that flow rates are not
uniform across the conduit cross section. Flow meters typically
employ high performance sensing elements that can be uniquely
designed for application requirements with precision signal
processing and calibration of sensing elements and transmitting
electronics. Random turbulence, or non-uniform flow, within the
flowing media introduces inconsistencies in the transducer
readings.
[0003] Thermal dispersion flow meters are well known and are
commonly used to measure the flow of media within a conduit.
Thermal technology utilizes the relationship between flow rate and
cooling effect for direct measurement of mass flow rate. The media
flowing in a conduit affects the temperature of sensing elements
and this effect is used to create an electrical signal that can be
processed to indicate the flow rate or mass flow rate of the media
within the conduit.
[0004] Flow conditioning devices may be used to overcome random
turbulence properties that occur in applications where non-ideal
upstream flow conditions exist. These turbulence properties may be
caused by valves, bends, or elbows, for example, within the
conduit, as well as flow rates of the media, and viscosity
properties of different types of media. The elements employed by
thermal dispersion mass flow meters can suffer accuracy problems
due to non-ideal flow conditions in the vicinity of the sensing
elements. Such non-ideal flow conditions that exist upstream from
the sensing elements can create inaccuracies in the readings
obtained from the sensing elements.
[0005] Within the art of flow meters, numerous flow conditioning
devices have been taught. Examples of known flow conditioners are
those that use bars, perforated plates, tube bundles, or tab
structures to condition media to enhance sensor readings.
[0006] One turbulence inducing prior art device is disclosed in
U.S. Pat No. 5,780,737. This sensor employs a bar mounted closely
upstream from a transducer for the purpose of flow conditioning.
The bar generates a predictable vortex stream (turbulence) a short
distance upstream of a flow sensing element to counteract the
random or unpredictable turbulence that exists within the media
flowing through a conduit. The vortex stream generated by the flow
conditioning bar is consistent and predictable compared with the
non-conditioned turbulence within the flowing media upstream of the
bar. Thus, any existing random turbulence within the flowing media
is essentially overridden by the turbulence created by the vortex
generating bar.
[0007] A completely different type of flow conditioner is shown in
U.S. Pat. No. 4,929,088, which includes several radially, or
longitudinally, or both, spaced tabs to create a mixing effect as
well as conditioning the flow of the media in the conduit.
[0008] In order to measure media flowing within a conduit by means
of a thermal flow meter, minimum straight runs of the conduit are
typically needed for improved accuracy. In order to achieve optimum
performance in industrial flow metering systems, upstream and
downstream straight run requirements are typically quoted at about
20 conduit diameters upstream and about 10 diameters downstream.
These straight run lengths are typically necessary in order to
create a consistent flow profile and allow dissipation of the
turbulence in the media that may result from elements such as
bends, elbows, and valves in the conduits carrying the media.
Implementing straight runs of these lengths is not always easy and
sometimes impossible to satisfy in any particular installation.
Metering systems with insufficient straight run lengths can suffer
somewhat degraded meter accuracy if a consistent flow profile is
not able to be developed.
SUMMARY OF THE INVENTION
[0009] The embodiments disclosed herein address some shortcomings
in the prior art of measuring flowing media within a conduit. The
problems associated with the length of straight run requirements in
industrial flow metering for about 20 diameters upstream are
addressed by flow conditioners disclosed herein. Embodiments are
disclosed for flow conditioning that can be accomplished in
substantially shorter straight run lengths than required without
using flow conditioners. The embodiments disclosed herein provide
methods and systems for conditioning media that flows within a
conduit to reduce the impact that less than ideal media flow
profile has on transducers used to measure the flowing media,
thereby enhancing the accuracy of the transducers.
[0010] An embodiment of the invention provides a flow conditioner
that can be used with existing flow measurement systems.
[0011] Another embodiment provides a flow metering method that
conditions media flowing within a conduit to provide flow
velocities impinging the transducers which are consistent with the
nominal media velocity in the conduit.
BRIEF DESCRIPTION OF THE DRAWING
[0012] The purposes, advantages, and features of the invention will
be more fully understood from the following detailed description,
when read in conjunction with the accompanying drawing wherein:
[0013] FIG. 1 is an end view of a conventional flow meter mounted
to a fluid conduit segment;
[0014] FIG. 2 is a perspective illustration of an embodiment of a
flow conditioner according to the invention;
[0015] FIG. 3 is an enlarged illustration of an embodiment of the
shroud used in the FIG. 2 flow conditioner;
[0016] FIG. 4 show the end cap, the thermowells, and the wedge
shaped element of the flow conditioner of the present
invention;
[0017] FIG. 5 is an end view of the flow conditioner of FIG. 2;
[0018] FIG. 6 is a side view of the flow conditioner of FIG. 2;
[0019] FIG. 7 illustrates a media velocity diagram for a flow
metering system similar to the one in FIG. 1 with an embodiment of
a flow conditioner in accordance with the invention;
[0020] FIG. 8 illustrates a media velocity diagram for a flow
metering system similar to the one in FIG. 1, without a flow
conditioner of the present invention;
[0021] FIG. 9 is a plot of centerline versus straight run velocity
in conduit diameters for media flowing in a conduit without the
flow conditioner of the present invention; and
[0022] FIG. 10 is an end view, similar to FIG. 5, showing an
alternative embodiment according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] According to various embodiments for flow conditioning, the
media that flows within a conduit can be either a gaseous or a
liquid substance, so the term "fluid" may be used to include both.
Therefore, the embodiments described herein should not be seen as
limiting and the scope of the invention should be measured as
defined by the appended claims. These embodiments generally
describe gaseous media flowing within a conduit, but it should be
understood that liquid embodiments are also envisioned. Also, the
metering systems illustrated in these embodiments are generally
thermal flow meters to measure flow of media within a conduit using
transducer elements and it should be understood that other
measuring elements can also be used with the flow conditioners
described herein. Any type of thermal flow metering system may be
employed, including differential temperature, differential power,
and differential current, for example. It is also envisioned that
alterations may be made to the embodiments taught herein to
condition the flow of liquid media within a conduit.
[0024] A conventional mass flow meter is illustrated in FIG. 1.
Conduit 11 has T-connector 12 to which flow meter assembly 13 is
mounted. The flow meter has head 14 typically containing the
electronics of the instrument and having digital readout 15. Probe
16 extends from head 14 into conduit 11. At about the center of the
conduit is sensor 17 comprising transducers or sensing elements 21
and 22, which are protected in the media stream by protector 18.
The actual sensing elements reside within the cylindrical elements
shown, which are referred to as thermowells. The thermal flow meter
shown operates in a known manner.
[0025] FIGS. 2-6 illustrate an embodiment of flow conditioner and
sensor 25 formed in a cylindrically shaped device having a
longitudinal axis as indicated by centerline 30. Sensors 26 and 27
are the sensing elements of the thermal flow metering system,
similar to assembly 13 in FIG. 1, which measures flow of a media
flowing within a conduit such as conduit 11 in FIG. 1. An example
of such a metering system is model ST98, sold by Fluid Components
International LLC of San Marcos, Calif. The metering system shown
in FIG. 2 includes a flow conditioner comprised preferably of wedge
element 31 and shroud 32 that conditions the flow of the media in
the vicinity of flow sensing transducers 26 and 27 in order to
provide enhanced mass flow readings of the flowing media. The
transducers are typically thermowells containing thermal sensing
elements. Shroud 32 is mounted on cap 33 at the distal end of probe
16. The shroud surrounds wedge 31 and sensors 26 and 27. The distal
end of the metering system comprising sensors 26 and 27, wedge
element 31, and shroud 32, is inserted into a conduit (not shown in
this figure) in a manner that allows media to continue to flow
through the conduit. The sensor elements of the flow meter are at
the distal end of the cylindrical probe 16 which project through
the wall of the conduit in a conventional manner and are generally
positioned at approximately the center of the conduit, as shown in
FIG. 1.
[0026] FIG. 3 is an enlarged perspective view of shroud 32. Shroud
32 and cap 33 of cylindrical probe 16 may be secured together by
any suitable means, such as as welding, or the use of an
appropriate adhesive, among others. Either end 35 or 36 of the
shroud may be secured to the cap since the shroud is shown here as
being symmetrical. However, there is no requirement that the shroud
be symmetrical. Cap 33 may be formed with a groove to receive an
appropriately shaped annular rim of the shroud, or either or both
the cap and the shroud may be shaped in any desired fashion to
facilitate them being secured together. Input opening 37 is defined
by peripheral rim 41, while peripheral rim 42 defines output
opening 38. From this view it can be seen that openings 37, 38 are
diametrically opposed and enable passage of flowing media
therethrough, even with wedge element 31 and sensors 26, 27
projecting therein. The media flows through openings 37, 38 in the
shroud in the direction of arrow A, as seen in FIGS. 2 and 3. Wedge
element 31 is mounted within shroud 32 such that it is downstream
of sensors 26, 27 in the direction of the flowing media.
Alternatives to the shape of the shroud will be discussed below
with respect to FIG. 5.
[0027] The sensor and flow conditioner 25 illustrated in FIG. 2
could be combined with an industry standard ST98 flow meter,
previously identified, with the added components of flow
conditioner elements 31 and 32. The ST98 instrument is an insertion
style, thermal dispersion mass flow meter that measures the
temperature difference between elements, here sensors 26, 27. In
the conventional manner for thermal flow instruments, one of the
elements is a reference sensor and the other is an active, or
heated, sensor. Flowing fluid dissipates heat from the active
sensor and the differential temperature, in relation to the current
or power applied to the active probe, for example, with the
conventional electronics of such a system, converts these data
points to a measure of mass flow of the fluid in the conduit.
[0028] Stated another way, shroud 32 and wedge element 31 are
components that can be configured with an industry standard
metering system, such as the ST98 thermal dispersion mass flow
meter. This metering system is identified for example only and the
flow conditioner of the invention can be employed with a variety of
thermal flow measurement systems.
[0029] Wedge element 31 as shown in FIGS. 2, 4, and 5, when viewed
in the direction of longitudinal axis 30, has a substantially
V-shape with walls 31a, 31b arranged to diverge from apex 45 in
direction A of the flowing media. The apex of V-shaped element 31
is shown essentially equidistant from sensors 26, 27 and extends at
least partially between the sensors (see FIG. 5). The specific
configuration and orientation of the embodiment shown in FIG. 2 is
illustrative of one embodiment and should not be viewed as limiting
the invention. For example, the size and/or shape of wedge element
31 can be altered, and this will be addressed below.
[0030] In differing embodiments, diverging walls 31a, 31b can be
arranged or positioned in various configurations. The diverging
walls can be formed to be various heights either relative to the
size and height of upstream opening 37, to shroud 32, or to the
projecting lengths of thermowells 26, 27. Height, as discussed
here, relates to a distance in the longitudinal direction from cap
33 of probe 16, and an embodiment is shown clearly in FIG. 6. It
may also be referred to as "length." Diverging walls 31a, 31b can
be formed to have a height nearly as high as opening 37 in the
direction of longitudinal axis 30. In the particular embodiment
shown, wedge 31 extends in length about 15% farther from cap 33
than do sensors 26, 27. Thus, the length of wedge 31 may be about
0.75 inch and the sensors could be about 0.66 inch in a typical
installation. However, the length could be shorter or longer than
the sensors and still function effectively, and the sensors and
wedge element can be longer or shorter, depending upon the size of
the conduit, or upon the type of media being measured.
[0031] The media flowing in the direction of arrow A is forced to
impact walls 31a, 31b and move around wedge element 31, as shown
graphically in FIG. 7.
[0032] One rationale for measuring the length of walls 31a, 31b in
the direction of longitudinal axis 30 to be in relation to the
height of sensors 26, 27, is that the sensing or heated areas
within the thermowells is normally somewhere near the linear center
of the probe in the direction of longitudinal axis 30. A good deal
of variance could then be allowed within embodiments using thermal
transducers in forming limits of the height of walls 31a, 31b in
the direction of longitudinal axis 30. These variances can be
employed for embodiments using different media and in different
circumstances to enhance the effectiveness of flow conditioner 25
in creating consistent flow velocities in the vicinity of sensors
26, 27.
[0033] As shown in FIGS. 5 and 7, wedge element 31 is mounted
downstream of sensors 26, 27 such that the flowing media will pass
through opening 37 and encounter the sensors before impacting upon
walls 31a, 31b of wedge element 31. The presence of the diverging
walls just downstream from the sensors dramatically increases the
velocity of the media observed in the vicinity of and surrounding
the sensors, compared to similar arrangements for such probes
without wedge element 31. This phenomenon will be further discussed
below with respect to FIG. 7.
[0034] FIG. 8 illustrates velocity patterns that have been observed
for a prior art flow metering system, such as that shown in FIG. 1,
having thermal sensors 21, 22 but without flow conditioner 25. The
nominal flow at the center of the conduit, in this example, is
about 25 feet per second. The legend for the velocity pattern is
shown in the chart to the left of the velocity diagram, and the
following describes the flow velocity with respect to the legend.
LR is areas having a flow rate of about 34.5 feet per second; 0 is
areas having a flow rate of about 30.7 feet per second; Y is areas
with a flow rate of about 25-30 feet per second, that is,
approximately nominal flow velocity; LG is areas with a flow rate
of about 23 feet per second, near nominal flow velocity; G is areas
with a flow rate of about 19 feet per second; LB is about 10 feet
per second; and B is areas with a flow rate of about 4 to about 8
feet per second. As clearly evident from FIG. 8, the flow rates are
much higher at a distance from sensors 21, 22, and there is
substantially no, or insignificant, 25 fps flow in contact with the
sensor elements. In fact the flow rates in contact with sensors 21,
22 are not at all consistent with the nominal flow of 25 fps, and
the average velocity of the media in contact with the sensors is
well below the nominal flow rate. Immediately upstream of sensors
21, 22, the velocities are shown as about 19 fps and immediately
downstream of these sensors the velocities of the media are all the
way down to 8 to 10 fps. The low rate between the sensors is
actually higher than the nominal flow rate, but that flow area is
not in contact with the sensors The flow velocities in close
vicinity of sensors 21, 22 are not truly representative of the
nominal flow rate of the media in the conduit, which is the flow
with respect to which the flow meter is intended to measure.
Therefore, the mass flow rate detected by sensors 21, 22 may not
fairly represent what is actually happening within the conduit.
[0035] FIG. 7 illustrates velocity patterns that have been observed
for a flow metering system, such as that shown in FIG. 2 having
thermal sensors 26, 27, except that in FIG. 7 flow conditioner 25
is included with flow meter assembly 13.
[0036] In this case the nominal flow rate is about 40 feet per
second. The legend for the velocity pattern will now be described,
with reference to the chart to the left of the velocity diagram. R
is areas having a flow rate of about 40 feet per second or higher;
LR is areas having a flow rate of about 33 feet per second; 0 is
areas having a flow rate of about 28 feet per second; Y is areas
with a flow rate of about 24 feet per second; LG is areas with a
flow rate of about 20 feet per second; G is areas with a flow rate
of about 16 feet per second; LB is areas with a flow rate of about
8-12 feet per second; and B is areas with a flow rate of between 0
and about 4 feet per second. It can be clearly seen from FIG. 7
that the flow rates in the vicinity of sensors 26, 27 are much more
consistent with the nominal flow rate upstream of flow metering
system 13 than was observed for the flow in the metering system of
FIG. 8. The flow rates in contact with sensors 26, 27 range from
higher than 40 fps down to about 26 fps. Since both probes are
significantly partially surrounded by media flow at or above about
40 fps, the readings of the flow meter will be much more accurate
than is the meter of FIG. 8. These flow rates in the close vicinity
of sensors 26, 27 are very much consistent with the nominal flow
rate in the conduit.
[0037] In order to obtain the advantageous flow around the sensors
that is depicted in FIG. 7, some exemplary dimensions are here set
forth. The angle of apex 45 between the sides of wedge 31 can range
from about 90.degree.-140.degree., and preferably about
120.degree.. The distance between walls 31a, 31b and respective
sensors 26, 27 (gaps 51, 52 in FIG. 5) is about 0.015-0.045 inch,
preferably about 0.030 inch. From FIG. 5 it can be seen that apex
45 is shown at about the centerline between sensors 26, 27. For a
120.degree. apex, this is preferred, but not exactly mandatory. For
other apex angles, the position of the apex with respect to the
centerline between the sensors will vary, it being preferable to
maintain the distance from walls 31a, 31b to the sensors generally
in the 0.030 in range.
[0038] While the foregoing discussion relates to the symmetric
arrangement of walls 31a, 31b, apex 45, and thermowells 26, 27,
those relationships are not required for embodiments of the
invention to function in a useful manner. The relationships between
one of the wedge walls and its adjacent thermowell is primarily
relevant only for the active sensor. The wedge wall adjacent to the
reference sensor is not nearly as important. Thus, the apex could
be moved up or down (with respect to the FIG. 5 orientation), as
long as the venturi-like effect is maintained with respect to the
sensor that is the active or heated one. Further, if the apex angle
is increased to greater than about 120.degree., the apex might
reside left of a tangent line from thermowell 26 to thermowell 27.
Conversely, with a sharper angle, less than about 120.degree., the
apex could project beyond the right tangent line from the
thermowells.
[0039] As can be seen from FIG. 7, a venturi-like effect is created
as the media flows around sensors 26, 27 and is confined by wedge
walls 31a, 31b. This has the effect of at least partially
surrounding the sensor element with the media being measured
flowing at or near the nominal flow rate, or at least averaging the
nominal flow rate. By actual measurements, the flow velocity
through gaps 51, 52 is greater than the nominal flow rate, thus
resulting in the average being near the nominal flow rate.
[0040] FIG. 9 shows how unpredictably varied the centerline
velocity of flow is from about 5 to about 18 diameters after a
disturbance source, such as a bend, elbow, or valve, for example.
It is very easy to understand that a thermal flow transducer that
is inserted into the conduit at any point less than about 20
diameters downstream from the cause of unstable flow can provide
inaccurate readings. Certainly there is much greater heat
dissipation in the active sensor element at three to five
diameters, where the flow rate is about 54, fps while the nominal
flow rate is 50 fps and settles in to that velocity at about 20
diameters.
[0041] Referring again to FIGS. 2 and 7, in conjunction with the
conventional sensor in FIG. 8 the improvements observed using a
conventional flow meter with a flow conditioner comprising wedge
element 31 and shroud 32 is a result of increased velocity of the
flowing media in the vicinity of sensors 26, 27 after passing
through opening 37 in shroud 32. The diverging walls 31a, 31b of
the wedge element forces flowing media to move around the wedge
element and to enhance the media velocity through gaps 51 and 52.
Flowing media is forced to move either above the wedge element, or
through crevices 53, 54 between the distal ends of walls 31a, 31b
and the sides of shroud 32, after impacting walls 31a, 31b,
resulting in the average velocity of the flowing media in the
vicinity of the sensors being maintained at about the nominal
velocity. Because flow conditioner 25 makes the media flow around
the thermowells predictable and consistent, inconsistencies in the
velocity of the flowing media around sensors 26, 27 is reduced,
thereby enhancing the accuracy of the readings derived from the
sensors.
[0042] It has been found that sides 55, 56 of the shroud, coupled
with crevices 53, 54 (FIG. 5) combine to increase flow around
sensors 26, 27. Although they can vary, it has been found that by
making crevices 53, 54 to be about 0.0120 inch, the meter has
consistent and accurate output. Sides 55, 56 are shown to have an
included arc of about 55.degree., and they could range between
about 25.degree. and about 75.degree..
[0043] In FIG. 5 the shroud is shown with input opening 37 and
output opening 38 while the spacing between sides 55, 56 and the
distal ends of the walls 31a, 31b is, in some embodiments,
beneficial to the accuracy of the meter with which the low
conditioner functions, the shape and size of output opening 38 is
not in itself significant. Once the media has encountered
thermowells 26, 27 and walls 31a, 31b, and crevices 53, 54, it is
not relevant how the media egresses from the flow conditioner.
[0044] As an alternative embodiment, wedge element in combination
with the sensors (FIG. 4) provides improved mass flow readings,
even without the shroud. This structure is a simplified and
effective flow conditioner. The combination with shroud 32 (FIGS. 2
and 5) provides even greater degrees of accuracy for the meter.
From the physical standpoint, shroud 32 protects the rather
delicate sensor elements from being damaged by impurities and
debris that may be flowing with the media in the conduit.
Additionally, the shroud has a synergistic effect on the accuracy
of the mass flow readings for the meter equipped with wedge 31,
because it affects the flow of media through the shroud, It has
also been found that the shroud alone, without the wedge, improves
the meter accuracy. This is yet another alternative embodiment. The
flow conditioner, whether it employs the wedge only with the
thermowells, the shroud only with the thermowells, or combines the
wedge and the shroud with the thermowells, tends to moderate
upstream disturbances.
[0045] In some instances thermals flow metering systems employ a
single sensor, which operates on a time share basis. That is,
instead of having one heated, or active sensors, and one
non-heated, or reference, sensor, the single sensor switches
between being the heated sensor and being the reference sensor. In
such an embodiment only a single diagonal wall would replace the
wedge element and would be arranged in close proximity to the
thermowell containing the sensor. That proximity is discussed in
greater detail below. Such an embodiment is shown in FIG. 10. In
this embodiment, the sensors in thermowells 26, 27 are combined
into a single, time-shared sensor element. Only a single vane 31
having a wall 31b adjacent to the thermowell is required. When the
sensor is the active, or heated, sensor, the media flow through gap
58 increases the velocity around at least a portion of the
thermowell. As stated previously, the flow around the thermowell
when it is functioning as the reference sensor is not of particular
significance because it represents the ambient temperature of the
media and is not a measure of thermal dissipation. Other than
operating in a time shared manner, the FIG. 10 embodiment functions
in substantially the same way as the other embodiments presented
herein. The angle of wall 31b with respect to the media flow
direction A is about 45.degree.-70.degree..
[0046] The sensors are mounted to and extend through cap 33 in a
conventional manner. Wedge 31 may be mounted to cap 33 by any
suitable means, such as welding, brazing, or through the use of a
suitable adhesive. Similarly, shroud 32 is also secured to cap 33.
It is also possible to mold or machine the cap and shroud together
or even the cap, shroud and wedge together.
[0047] It is contemplated that the media with which the structure
of the embodiments of the invention that are shown and suggested
here can be any type of fluid, whether a liquid or a gas. Further,
while wedge 31 is shown having an open V-shape, it could be a
filled in wedge, giving it a delta shape, or it could be arcuate,
either convex or concave. In other words, the downstream shape of
wedge 31 is generally not significant. It is the shape and position
of walls 31a, 31b, interacting primarily with thermowells 26, 27,
and shroud 32, that provides the most advantageous function of the
embodiments of the invention. While the wall or walls of wedge 31
are shown to be continuous, they could function as necessary for
the embodiments contemplated even if they were formed as a screen,
or with a plurality or a multiplicity of holes, or with slots. The
media would flow over such non-continuous surfaces sufficiently to
be efficacious.
* * * * *