FIELD OF THE INVENTION:
[001] The present invention relates to an equal area based self-averaging square multi-port pitot airflow measuring device. Principally this invention is a cheaper, simpler, lighter and more reliable device than airfoil for secondary airflow measurement in power plants. This device overcomes the issues of enormous size of airfoil, which causes issues and high cost in transportation and erection, requirement of considerable space. In addition, this device improves the accuracy of measurement by creating higher recoverable pressure drop of the measuring fluid.

BACKGROUND OF THE INVENTION/PRIOR ART:
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[003] Air flow rate in power plants is determined by placing a primary element that restricts the flowing stream resulting in a pressure drop across the primary element. By measuring the pressure head or drop using differential pressure sensors or transmitters, one can determine the velocity using the Bernoulli’s equation. The volumetric or mass flow rates can be obtained from the velocity.
[004] Typically, in power plants airfoil is used as primary element for measurement of flow rates of secondary air. Alternatively, other flow measuring primary elements including venturi meter, pitot tubes are also being used in the recent past to measure secondary air flow. Any air flow measuring device should be accurate, reliable and exhibit repeatability. However, the airfoil has the following disadvantages:
1. It is bulky, occupies more space, therefore difficult for transporting and erecting.
2. Higher transportation and erection costs.
3. Unrecoverable pressure drop is as high as 20 mmwc.
4. Requirement of considerable straight lengths before and after for streamlining the flow.

[005] As an alternative, pitot tubes can be used for measuring airflow. A pitot tube is an instrument used to measure the rate of flow or quantity of a moving fluid in a conduit. It can measure linear, nonlinear, mass or volumetric flow rate of a fluid. While pitot tubes mitigate the disadvantages of airfoil, the design of pitot tube involves considerable challenges. This is because the induced recoverable pressure drop of the fluid whose flow is to be measured is normally low in such devices, thereby affecting the accuracy and sensitivity. Also, a single pitot tube cannot accurately measure flow in large ducts, where the flow across the cross section is not uniform. The proposed equal area based self-averaging square pitot airflow measuring device takes care of the above aspect with minimal unrecoverable pressure drop, higher induced recoverable flow pressure drop and better accuracy.

PRIOR ART SEARCH:
[006] US4154100 describes the novel method for stabilizing the pressure sensed by the downstream-facing port of a pitot tube type flow meter over a broad flow range, thereby providing a stable and repeatable flow coefficient. The invention comprises localizing the areas of boundary layer separation across deflecting surfaces located upstream of said port by sharply contouring the edges thereof and directing the flowing stream there across, and preventing reattachment of said boundary layer by positioning and contouring the surfaces contouring said port downstream of said sharply contoured edges so as to continuously lie within the wake of the fluid flowing around the latter over a broad range of flow rates. The invention also encompasses the improved averaging pitot-type flow meter characterized by flow deflecting means having sharply contoured edges on both sides thereof effective to fix the location at which boundary layer separation occurs over a broad range of laminar and turbulent flow conditions, an upstream-facing impact surface shaped to direct the flowing fluid across said sharply contoured edges, and a downstream-facing surface containing a port for sensing downstream pressure so contoured and positioned relative to said sharply contoured edges as to cooperate there with in preventing reattachment of the boundary layer under varying flow conditions.
[007] US4559836 describes an improved pitot tube type flow measuring instrument for use in pipes and other conduits characterized by a generally diamond-shaped sensor portion constituting a bluff body for splitting the flow that includes at least a large-radius leading edge in which three or more impact ports are located, a pair of planar portions diverging rearward from the leading edge to a transversely-spaced pair of much shorter radius side edges that cooperate therewith and the downstream-facing portion of the bluff body to define flow separation zones capable of stabilizing the flow coefficient over a broad range of flow conditions provided that the distance separating them is at least five times either of their radii. The invention further includes the unique method of mounting the probe in two-phase or multi-phase flowing systems where one of the fluids is a liquid and another a gas that calls for tilting the axis of the sensing portion thereof at an angle to the horizontal such that pools of the liquid are trapped in one end or the other depending upon whether the gaseous constituent is hot or cold.
[008] US6564651B1 discloses a high temperature gas flow sensing element module, using Pitot tube technology, for use within a fluid conduit consisting of a housing having an inlet, an outlet, and forming a hollow interior cross-sectional area. Individually, the gas flow sensing element modules fit easily through typical furnace access doors. Thus, in typical furnace retrofit applications, an array of equally sized gas flow sensing element modules are arranged adjacent one another in a manner such that the inside dimensions of the entire arrangement coincide with the internal dimensions of the plenum or duct opening into which it is inserted. Pressure averaging piping is used to provide average total and static pressure across the entire gas flow sensing element to differential pressure flow indicators and /or transmitting devices.
[009] US2014/0130608A1 discloses an apparatus and method for sensing position according to flow velocity. It includes at least two pitot tubes each defining a central axis is along mutually orthogonal axes. Each of at least two pressure sensors is positioned in fluid communication with a corresponding one of the at least two pitot tubes. A controller receives outputs from the at least two pressure sensors and analyses to determine at least one of an angular and translational velocity according to the outputs. A distance travelled is then determined according to the at least one of an angular and translational velocity.
[0010] US2014/0260671A1 discloses a pressure measurement system for measuring pressure in a conduit has a bluff body extending into the conduit. The bluff body has an upstream opening and a downstream opening. The upstream and downstream pitot tubes are slidably engaged within the bluff body. Both the upstream and downstream pitot tubes have their open end positioned in the upstream and downstream opening respectively. A differential pressure sensor is fluidly coupled to the upstream pitot tube and the downstream pitot tube to measure a pressure difference between the upstream pitot tube and the downstream pitot tube. The differential pressure is used to determine the flow rate.
[0011] These devices found in the above prior arts are not equal to the one proposed in the current invention and have certain drawbacks that restrict their use for continuous air flow measurements in ducts with high aspect ratio in a thermal power plant firing high ash containing coals. Hence, the present invention has been introduced.

OBJECTS OF THE INVENTION:
[0012] It is therefore an object of present invention to propose an equal area based self-averaging square pitot airflow measuring device as an alternate to airfoil and other pitot tubes for secondary airflow measurement in power plants firing high ash coals.
[0013] It is another object of the invention to obviate drawbacks of airfoil like bulky size and the demerit of other pitot tubes like very low recoverable flow pressure drop, reduced accuracy when used in ducts with high aspect ratio, which are addressed by the novel device of invention.

[0014] A still further object of the present invention is to propose an optimization to the location and number of total pressure and static pressure ports for the equal area based self-averaging multi square pitot airflow measuring device.

[0015] A still further object of the present invention is to propose an optimization of stagnation tube cut-off angle, square tube size, upstream and downstream lengths.

[0016] A still further object of the present invention is to improve the induced flow pressure drop of the measuring fluid to obtain greater accuracy in the flow measurement.

[0017] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY OF THE INVENTION:
[0018] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus/composition and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.
[0019] An equal area based self-averaging square multi-port pitot airflow measuring device is proposed as an alternative to airfoil and other existing pitot airflow measuring devices for the measurement of secondary air flow in thermal power plants firing high ash coal. This square pitot array is lighter in weight than the airfoil. The problem of choking of pressure tapping lines is also dispensed off. A prototype has also been developed and the CFD predictions are comparable with the actual measurements with the prototype. In order to cover the entire cross section of flow, adequate total and static pressure ports equally distributed across the flow cross section have been provided. The design of the equal area based self-averaging square multi-port pitot array is in such a way that equal area coverage is ensured even for ducts with high aspect ratio. The size of square tube and the stagnation tube cut-off angle for total pressure measurement is optimized using Computational Fluid Dynamics (CFD) simulations for obtaining minimum unrecoverable pressure loss and a higher differential pressure for flow measurement for the range of required flow conditions. The unrecoverable pressure drop of alternate square pitot device is around 10 times lower than the airfoil. The induced pressure drop is more than that of the existing pitot tubes to improve the accuracy of measurement.
[0020] The dimensions of the square pitot array depend on the size of the duct as per the following grouping:
a) Optimised square tube of size (S) that can be used according to both vertical (W) and horizontal (H) dimensions of the duct and to ensure blockage ratio between 15 to 30%;
b) Optimized square tube of size of for example 10 mm for static pressure sensing;
c) Optimum cut off angle of (a) ranging from 15 to 35° is used for stagnation pressure measuring ports;
d) Optimum connecting tube angle (ß) of the interconnecting manifold pipes ranging from 50 to 55°;
e) The square pitot assembly occupies less than 1/20th of the length of airfoil;
f) Due to low blockage ratio, the unrecoverable pressure drop is around 10 times lower than that of airfoil.

[0021] Said total pressure sensing ports array comprises a plurality of individual stagnation leg arranged across said interior cross sectional area such that they traverse equal area of the duct.

[0022] The multi-port square pitot device is applicable for flow measurement in non-circular and non-square ducts of any plant including a thermal power plant.
[0023] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
[0024] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.

[0025] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
[0026] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein:-
Figure 1 shows: a side orthographic view of an equal area based self-averaging square multi-port pitot, according to the present invention, for use with a rectangular duct.
Figure 2 shows: a front elevation view thereof;
Figure 3 shows: a side elevation view thereof;
Figure 4 shows: a top plan view thereof;
Figure 5 shows: a pneumatic flow schematic of an equal area based self-averaging square multi-port pitot airflow measuring device and its purging system for the present invention;
Figure 6 shows: multiple static pressure sensing ports (19) arranged in fluid communication with average static pressure tap (18) through static pressure tubes (20);
Figure 7 shows: an example of conduit according to the present invention.
Figure 8 shows: instrument piping.
Figure 9 shows: Test result of the present invention.
Figure 10 shows: Variation of calibration factor with flow.
[0027] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS:
[0028] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.
[0029] The present invention makes a disclosure regarding a technology pertaining to an equal area based self-averaging square multi-port pitot airflow measuring device.
[0030] As shown in Fig. 1, an equal area based self-averaging square multi-port pitot airflow measuring device, generally noted as, according to one embodiment of the present invention is disclosed for duct of a non-circular cross sectional inlet (2) and an outlet (3) in fluid communication mounted within a generally rigid flow passage (hot air duct) (1). In its preferred embodiment, the housing is made with the same vertical internal dimensions as the fluid conduit in which it is to be utilized, and as shown in this embodiment a rectangular housing is provided. An average total pressure tap (17) and an average static pressure tap (18) are provided protruding outward from the housing at the top, and will be described in greater detail below.
[0031] Stagnation legs (4, 5, 6, 7, 8 and 9): The term stagnation leg is used to refer to the square tubes which have openings on either end (11, 12, 13 and 14) directly facing the flow and used to measure the total pressure. These openings are referred to as total pressure sensing ports (11, 12, 13 and 14). The pressure measured by these ports is known as stagnation pressure or total pressure in accordance with the Bernoulli equation.
[0032] Static pressure sensing ports (19): The term static pressure sensing ports leg is used to refer to the tubes which have openings parallel to the flow and used to measure the pressure inside the conduit. The pressure measured by these ports is known as static pressure in accordance with the Bernoulli equation.
[0033] As shown more clearly in Fig. 2, Fig. 3 and also in Fig. 4, total pressure sensing ports (11, 12, 13 and 14) are affixed such that the inclined opening is facing the flow and traversing equal areas in the interior cross sectional area of hot air duct (1) for sensing the total pressure of fluid flowing into the hot air duct (1). Also, the static pressure sensing ports (19) are affixed such that the square opening is parallel to the flow and traversing the interior cross sectional area of the flow element along the horizontal dimension of the conduit for sensing the static pressure within the hot air duct (1). These ports will be more clearly described below. This arrangement allows for pitot tube flow principles to be utilized, sensing the averaged total pressure of the flowing gas with the total pressure sensing pitot tubes and the averaged static pressure within the conduit with the static pressure sensing pitot tube.
[0034] As shown best in Fig. 2, Fig. 3 and Fig. 4, the dimensions of the equal area based self-averaging square multi-port pitot airflow measuring device depends on the size of the duct and the total pressure ports (11, 12, 13 and 14) and the static pressure ports (19) are not placed randomly within the hot air duct (1). Rather, they are meticulously placed in a traversing manner. The total number and location of sensing ports (11, 12, 13 and 14) are positioned in accordance with the following guidelines:
1. If the duct horizontal dimension (H) is higher than the vertical dimension (W), multiple pitot array elements are to be used such that equal areas are traversed by the pitot array (Single element shown in the Fig. 1, 2, 3 and 4 and two elements shown in Fig. 7). The number of elements to be used is determined by aspect ratio of the conduit. If the horizontal (H) dimensions of the conduit is greater than two times the vertical (W) dimensions of the conduit, the horizontal (H) dimensions of the conduit is split into multiple number of pieces (n = H/W) and one element is provided for each such individual conduit. Each element shall cater to an individual conduit, whose horizontal conduit dimension (Hd = H/n) is less than vertical (W) dimensions of the conduit. The interconnect header (72) shall connect between each individual elements.
In Fig. 7, an example of conduit is shown whose horizontal dimension is twice that of the vertical dimension, hence two pitot array elements (74 and 75) are used. When two pitot array elements are used, interconnect header (71) is to be provided to connect the static pressure taps (18 in Fig. 1) from the elements to the average static pressure tap (73) and to connect the total pressure taps (17 in Fig. 1) from the elements to the average total pressure tap (72). Similarly, multiple pitot array elements can be used depending on the duct size and the average static pressure taps and average total pressure taps of each element can be connected through an interconnect header to get a single average static pressure tap and single average total pressure tap at the top of the conduit.
2. The conduit cross section is divided into for example 16 grids of equal areas. The location of static and total pressure ports are placed in traversing manner such that each total pressure port is placed at the geometric centre of the grid.
In Fig. 1, Fig. 2, Fig. 3 and Fig. 4, the parameters of duct like the vertical dimension (W) and duct horizontal dimension (H) are shown. The equal area based self-averaging square multi-port pitot average total pressure tap (17) and the average static pressure tap (18) are located at the mid-point on top of the hot air duct (1). The equal area based self-averaging square multi-port pitot is symmetrical to the axis of the pitot head. The length of the stagnation legs (4, 5, 6, 7, 8 and 9) are kept same and is geometrically determined as a function of vertical dimension W of the duct, square pipe size S and the angle of cutting (a) w.r.t to vertical.
3. Optimised square tube of size (S) can be used according to both vertical (W) and horizontal (H) dimensions of the duct. The blockage ratio for a particular duct is increased if the square tube size is increased. The blockage ratio is maintained within 15 – 30%. However, if bigger tubes are used, the conventional manufacturing processes like welding are simpler and the structural strength is also increased. Any size of square tube can be used for total pressure sensing ports, considering the commercial availability, ease of manufacturing and blockage ratio.
4. For static pressure ports (19), the square tube of size S used shall be as small as possible. However, to avoid ash clogging in thermal power plants, square tubes of for example 10 mm size are used for static pressure sensing.
5. The static pressure sensing port (19) has also a plurality of sensing ports located at a height of around 75% of the vertical dimension of the duct from top and oriented so as to face perpendicular to the gas flow through the fluid flow element module, placed at equal distances along the horizontal dimension (H) of the conduit.
6. Optimum cut off angle of (a) is used for stagnation pressure measuring ports. Based on CFD simulation and testing, this angle is optimized in the range of 15 -35°.

[0035] As shown in Fig. 2 and Fig. 3, optimised number of total pressure sensing ports (11, 12, 13 and 14) of stagnation leg (4, 5, 6, 7, 8 and 9) are arranged in fluid communication and anchored to an interconnected manifold (10). Fig.1 and Fig. 2 show the location of interface ports (52) in stagnation legs for interconnected manifolds. In Fig. 5, the first view is normal to the flow and right hand side view for Fig. 1 and Fig. 2 and other 3 figures are 90° clockwise rotational views thereof. 4 types of different location of interface ports (52) are in stagnation legs as shown in Fig. 1. These are top interface port in left top row corner stagnation leg (4), top interface ports in middle bottom row corner stagnation leg (5), top interface port in right top row corner stagnation leg (6), bottom interface port in left bottom row corner stagnation leg (7), bottom interface port in middle bottom row corner stagnation leg (8), bottom interface port in right bottom row corner stagnation leg (9). The location of interface ports in the stagnation legs (4, 5, 6, 7, 8, 9) has been optimized based on CFD analysis. In addition, the left top (4) and bottom (7) row corner stagnation legs are having interface ports on right hand side of the stagnation legs and the top (5) and bottom (8) row middle stagnation legs are having two side of interface ports (10) on stagnation legs. The right top (6) and right bottom (8) row corner stagnation legs are having interface ports on left hand side of the stagnation legs. The left top (4) and right bottom (8) stagnation legs are inversions and similarly the right top (6) and left bottom (7) are inversions.
[0036] As shown in Fig. 5, each stagnation leg (4, 5, 6, 7, 8, 9) is affixed to the interconnected manifold (50) by a conventional manner like welding. Each total pressure has multiple sensing ports oriented so as to face directly toward the inlet, thereby providing unrestricted fluid communication between the impacting fluid flowing into the hot air duct (1), through the total pressure ports (11, 12, 13 and 14), and to the interconnected manifold (50). The interconnected manifold (50) thereby consolidates this combined pressure and sends it to the average total pressure tap (17) as shown in Fig. 1. As shown in Fig. 6, three numbers of static pressure sensing ports (19) are also arranged in fluid communication with average static pressure tap (18) through static pressure tubes (20). The static pressure sensing port (19) has also a plurality of sensing ports located at a height of 75% of the vertical dimension of the duct from top and oriented so as to face perpendicular to the gas flow through the fluid flow element module, placed at equal distances along the horizontal dimension (H) of the conduit. In contrast to this, classic Pitot tubes (Prior art) consist of a concentric double tube, wherein the inside tube having a port facing into the flowing stream for sensing total pressure and the outside tube having radially aligned holes for sensing static pressure.
[0037] The distance between every stagnation leg centre can be called as the pitch and the pitch is geometrically calculated using the horizontal dimension (H) of the duct. The location of interconnected manifold is optimized based on CFD studies. The distance between the intersect of interconnected manifold and the stagnation legs is geometrically determined using the pitch and connecting tube angle (ß), shown in Fig. 2. Based on studies, the connecting tube angle (ß) is optimized to be in the range of 50 – 55°. The distance between duct top plate, in which the average total pressure tap is located and the location of total pressure ports rows is geometrically determined using vertical dimension (W) of the duct.
[0038] As shown in Fig. 2, Fig. 3 and Fig. 4, the multitude of stagnation legs (4, 5, 6, 7, 8 and 9) are connected to the head Pitot through the interconnected manifolds (10) and cross pipes of interconnected manifold (25) and three averaging total pressure pipes (two at the sides - 15 and one central pipe – 16). The three remaining static pressure measuring tubes are made in such a way that the openings to measure static pressure (19) are at the same level. These connections allow for the use of a differential pressure instrument for determining average flow rate and/or transmitting a flow rate signal.
[0039] The material chosen for square pitot assembly includes erosion resistant and does not oxidize up to a temperature of at least 400°C. Generally, carbon steel is used for fabrication of the square pitot assembly. The material of the housing is same as that of the duct [1].
[0040] The materials given above are as example without restricting scope of the invention to the same. Thus, other materials readily apparent to a person skilled in the arts are understood to be within purview of the invention.
[0041] All the tubes are square in shape and of same size. Further, the tubes are connected/interconnected to each other and in flow communication.
[0042] Generally, ash-clogging problem may occur during operation in the pressure tapping lines of flow measuring device used in coal fired steam generator. Due to bigger openings, the ash clogging may not occur in this square pitot device. However, considering trouble free operation, ash purging system is proposed to clean the device.
[0043] The square pitot assembly occupies only 1/20th of the length of the present airfoil for 210 MW capacity boiler. Hence, this device is more suitable for plants with layout constraints. Due to low blockage ratio, the unrecoverable pressure drop is around 10 times lower than that for airfoil. Also, the induced pressure drop is higher thereby improving the measurement accuracy. Also, there is around a 25% increase in flow dp when compared with other pitot array designs.
[0044] This equal area based self-averaging square multi-port pitot can be suitably extended for any duct shape, in particular, for ducts with high aspect ratio. Such ducts, whose horizontal dimension is much larger than vertical dimension, are prevalent in power plants due to layout constraints. In such cases, other pitot array based measurements do not provide equal area coverage and hence the flow measured is not accurate.

WORKING OF THE INVENTION
[0045] Once the equal area based self-averaging square multi-port pitot airflow measuring device is installed, instrument piping in Fig. 8 is installed in order to connect the average total pressure tap (17) of the device to the H port of the DP transmitter (T) through impulse pipeline (36) and ball valve (32). Similarly, the average static pressure tap (18) is connected through impulse pipeline (35) and ball valve (31) to the L port of differential pressure transmitter for indicating the flow differential pressure (DP) as shown in Fig. 8. The impulse pipelines (33 and 34) are connected to the purging air line for removal of any ash clogging. This flow DP and the ambient temperature are transmitted to the control system and the flow rate is determined using the DP and flow constant for the device.

TEST RESULT
[0046] The equal area based self-averaging square multi-port pitot was designed for a 600 X 600 mm square duct and was calibrated at Fluid Control Research Institute (FCRI), Palakkad. It was tested with air medium and the test result is shown in Fig. 9. Also, the variation of calibration factor with flow is shown in Fig. 10. It is observed that the flow constant of the device remains constant for this device over the range of flow for which it was tested.
[0047] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0048] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.
[0049] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogues to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.
[0050] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.
[0051] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0052] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0053] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
FIELD OF THE INVENTION:
[001] The present invention relates to an equal area based self-averaging square multi-port pitot airflow measuring device. Principally this invention is a cheaper, simpler, lighter and more reliable device than airfoil for secondary airflow measurement in power plants. This device overcomes the issues of enormous size of airfoil, which causes issues and high cost in transportation and erection, requirement of considerable space. In addition, this device improves the accuracy of measurement by creating higher recoverable pressure drop of the measuring fluid.

BACKGROUND OF THE INVENTION/PRIOR ART:
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[003] Air flow rate in power plants is determined by placing a primary element that restricts the flowing stream resulting in a pressure drop across the primary element. By measuring the pressure head or drop using differential pressure sensors or transmitters, one can determine the velocity using the Bernoulli’s equation. The volumetric or mass flow rates can be obtained from the velocity.
[004] Typically, in power plants airfoil is used as primary element for measurement of flow rates of secondary air. Alternatively, other flow measuring primary elements including venturi meter, pitot tubes are also being used in the recent past to measure secondary air flow. Any air flow measuring device should be accurate, reliable and exhibit repeatability. However, the airfoil has the following disadvantages:
1. It is bulky, occupies more space, therefore difficult for transporting and erecting.
2. Higher transportation and erection costs.
3. Unrecoverable pressure drop is as high as 20 mmwc.
4. Requirement of considerable straight lengths before and after for streamlining the flow.

[005] As an alternative, pitot tubes can be used for measuring airflow. A pitot tube is an instrument used to measure the rate of flow or quantity of a moving fluid in a conduit. It can measure linear, nonlinear, mass or volumetric flow rate of a fluid. While pitot tubes mitigate the disadvantages of airfoil, the design of pitot tube involves considerable challenges. This is because the induced recoverable pressure drop of the fluid whose flow is to be measured is normally low in such devices, thereby affecting the accuracy and sensitivity. Also, a single pitot tube cannot accurately measure flow in large ducts, where the flow across the cross section is not uniform. The proposed equal area based self-averaging square pitot airflow measuring device takes care of the above aspect with minimal unrecoverable pressure drop, higher induced recoverable flow pressure drop and better accuracy.

PRIOR ART SEARCH:
[006] US4154100 describes the novel method for stabilizing the pressure sensed by the downstream-facing port of a pitot tube type flow meter over a broad flow range, thereby providing a stable and repeatable flow coefficient. The invention comprises localizing the areas of boundary layer separation across deflecting surfaces located upstream of said port by sharply contouring the edges thereof and directing the flowing stream there across, and preventing reattachment of said boundary layer by positioning and contouring the surfaces contouring said port downstream of said sharply contoured edges so as to continuously lie within the wake of the fluid flowing around the latter over a broad range of flow rates. The invention also encompasses the improved averaging pitot-type flow meter characterized by flow deflecting means having sharply contoured edges on both sides thereof effective to fix the location at which boundary layer separation occurs over a broad range of laminar and turbulent flow conditions, an upstream-facing impact surface shaped to direct the flowing fluid across said sharply contoured edges, and a downstream-facing surface containing a port for sensing downstream pressure so contoured and positioned relative to said sharply contoured edges as to cooperate there with in preventing reattachment of the boundary layer under varying flow conditions.
[007] US4559836 describes an improved pitot tube type flow measuring instrument for use in pipes and other conduits characterized by a generally diamond-shaped sensor portion constituting a bluff body for splitting the flow that includes at least a large-radius leading edge in which three or more impact ports are located, a pair of planar portions diverging rearward from the leading edge to a transversely-spaced pair of much shorter radius side edges that cooperate therewith and the downstream-facing portion of the bluff body to define flow separation zones capable of stabilizing the flow coefficient over a broad range of flow conditions provided that the distance separating them is at least five times either of their radii. The invention further includes the unique method of mounting the probe in two-phase or multi-phase flowing systems where one of the fluids is a liquid and another a gas that calls for tilting the axis of the sensing portion thereof at an angle to the horizontal such that pools of the liquid are trapped in one end or the other depending upon whether the gaseous constituent is hot or cold.
[008] US6564651B1 discloses a high temperature gas flow sensing element module, using Pitot tube technology, for use within a fluid conduit consisting of a housing having an inlet, an outlet, and forming a hollow interior cross-sectional area. Individually, the gas flow sensing element modules fit easily through typical furnace access doors. Thus, in typical furnace retrofit applications, an array of equally sized gas flow sensing element modules are arranged adjacent one another in a manner such that the inside dimensions of the entire arrangement coincide with the internal dimensions of the plenum or duct opening into which it is inserted. Pressure averaging piping is used to provide average total and static pressure across the entire gas flow sensing element to differential pressure flow indicators and /or transmitting devices.
[009] US2014/0130608A1 discloses an apparatus and method for sensing position according to flow velocity. It includes at least two pitot tubes each defining a central axis is along mutually orthogonal axes. Each of at least two pressure sensors is positioned in fluid communication with a corresponding one of the at least two pitot tubes. A controller receives outputs from the at least two pressure sensors and analyses to determine at least one of an angular and translational velocity according to the outputs. A distance travelled is then determined according to the at least one of an angular and translational velocity.
[0010] US2014/0260671A1 discloses a pressure measurement system for measuring pressure in a conduit has a bluff body extending into the conduit. The bluff body has an upstream opening and a downstream opening. The upstream and downstream pitot tubes are slidably engaged within the bluff body. Both the upstream and downstream pitot tubes have their open end positioned in the upstream and downstream opening respectively. A differential pressure sensor is fluidly coupled to the upstream pitot tube and the downstream pitot tube to measure a pressure difference between the upstream pitot tube and the downstream pitot tube. The differential pressure is used to determine the flow rate.
[0011] These devices found in the above prior arts are not equal to the one proposed in the current invention and have certain drawbacks that restrict their use for continuous air flow measurements in ducts with high aspect ratio in a thermal power plant firing high ash containing coals. Hence, the present invention has been introduced.

OBJECTS OF THE INVENTION:
[0012] It is therefore an object of present invention to propose an equal area based self-averaging square pitot airflow measuring device as an alternate to airfoil and other pitot tubes for secondary airflow measurement in power plants firing high ash coals.
[0013] It is another object of the invention to obviate drawbacks of airfoil like bulky size and the demerit of other pitot tubes like very low recoverable flow pressure drop, reduced accuracy when used in ducts with high aspect ratio, which are addressed by the novel device of invention.

[0014] A still further object of the present invention is to propose an optimization to the location and number of total pressure and static pressure ports for the equal area based self-averaging multi square pitot airflow measuring device.

[0015] A still further object of the present invention is to propose an optimization of stagnation tube cut-off angle, square tube size, upstream and downstream lengths.

[0016] A still further object of the present invention is to improve the induced flow pressure drop of the measuring fluid to obtain greater accuracy in the flow measurement.

[0017] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY OF THE INVENTION:
[0018] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus/composition and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.
[0019] An equal area based self-averaging square multi-port pitot airflow measuring device is proposed as an alternative to airfoil and other existing pitot airflow measuring devices for the measurement of secondary air flow in thermal power plants firing high ash coal. This square pitot array is lighter in weight than the airfoil. The problem of choking of pressure tapping lines is also dispensed off. A prototype has also been developed and the CFD predictions are comparable with the actual measurements with the prototype. In order to cover the entire cross section of flow, adequate total and static pressure ports equally distributed across the flow cross section have been provided. The design of the equal area based self-averaging square multi-port pitot array is in such a way that equal area coverage is ensured even for ducts with high aspect ratio. The size of square tube and the stagnation tube cut-off angle for total pressure measurement is optimized using Computational Fluid Dynamics (CFD) simulations for obtaining minimum unrecoverable pressure loss and a higher differential pressure for flow measurement for the range of required flow conditions. The unrecoverable pressure drop of alternate square pitot device is around 10 times lower than the airfoil. The induced pressure drop is more than that of the existing pitot tubes to improve the accuracy of measurement.
[0020] The dimensions of the square pitot array depend on the size of the duct as per the following grouping:
a) Optimised square tube of size (S) that can be used according to both vertical (W) and horizontal (H) dimensions of the duct and to ensure blockage ratio between 15 to 30%;
b) Optimized square tube of size of for example 10 mm for static pressure sensing;
c) Optimum cut off angle of (a) ranging from 15 to 35° is used for stagnation pressure measuring ports;
d) Optimum connecting tube angle (ß) of the interconnecting manifold pipes ranging from 50 to 55°;
e) The square pitot assembly occupies less than 1/20th of the length of airfoil;
f) Due to low blockage ratio, the unrecoverable pressure drop is around 10 times lower than that of airfoil.

[0021] Said total pressure sensing ports array comprises a plurality of individual stagnation leg arranged across said interior cross sectional area such that they traverse equal area of the duct.

[0022] The multi-port square pitot device is applicable for flow measurement in non-circular and non-square ducts of any plant including a thermal power plant.
[0023] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
[0024] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.

[0025] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
[0026] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein:-
Figure 1 shows: a side orthographic view of an equal area based self-averaging square multi-port pitot, according to the present invention, for use with a rectangular duct.
Figure 2 shows: a front elevation view thereof;
Figure 3 shows: a side elevation view thereof;
Figure 4 shows: a top plan view thereof;
Figure 5 shows: a pneumatic flow schematic of an equal area based self-averaging square multi-port pitot airflow measuring device and its purging system for the present invention;
Figure 6 shows: multiple static pressure sensing ports (19) arranged in fluid communication with average static pressure tap (18) through static pressure tubes (20);
Figure 7 shows: an example of conduit according to the present invention.
Figure 8 shows: instrument piping.
Figure 9 shows: Test result of the present invention.
Figure 10 shows: Variation of calibration factor with flow.
[0027] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS:
[0028] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.
[0029] The present invention makes a disclosure regarding a technology pertaining to an equal area based self-averaging square multi-port pitot airflow measuring device.
[0030] As shown in Fig. 1, an equal area based self-averaging square multi-port pitot airflow measuring device, generally noted as, according to one embodiment of the present invention is disclosed for duct of a non-circular cross sectional inlet (2) and an outlet (3) in fluid communication mounted within a generally rigid flow passage (hot air duct) (1). In its preferred embodiment, the housing is made with the same vertical internal dimensions as the fluid conduit in which it is to be utilized, and as shown in this embodiment a rectangular housing is provided. An average total pressure tap (17) and an average static pressure tap (18) are provided protruding outward from the housing at the top, and will be described in greater detail below.
[0031] Stagnation legs (4, 5, 6, 7, 8 and 9): The term stagnation leg is used to refer to the square tubes which have openings on either end (11, 12, 13 and 14) directly facing the flow and used to measure the total pressure. These openings are referred to as total pressure sensing ports (11, 12, 13 and 14). The pressure measured by these ports is known as stagnation pressure or total pressure in accordance with the Bernoulli equation.
[0032] Static pressure sensing ports (19): The term static pressure sensing ports leg is used to refer to the tubes which have openings parallel to the flow and used to measure the pressure inside the conduit. The pressure measured by these ports is known as static pressure in accordance with the Bernoulli equation.
[0033] As shown more clearly in Fig. 2, Fig. 3 and also in Fig. 4, total pressure sensing ports (11, 12, 13 and 14) are affixed such that the inclined opening is facing the flow and traversing equal areas in the interior cross sectional area of hot air duct (1) for sensing the total pressure of fluid flowing into the hot air duct (1). Also, the static pressure sensing ports (19) are affixed such that the square opening is parallel to the flow and traversing the interior cross sectional area of the flow element along the horizontal dimension of the conduit for sensing the static pressure within the hot air duct (1). These ports will be more clearly described below. This arrangement allows for pitot tube flow principles to be utilized, sensing the averaged total pressure of the flowing gas with the total pressure sensing pitot tubes and the averaged static pressure within the conduit with the static pressure sensing pitot tube.
[0034] As shown best in Fig. 2, Fig. 3 and Fig. 4, the dimensions of the equal area based self-averaging square multi-port pitot airflow measuring device depends on the size of the duct and the total pressure ports (11, 12, 13 and 14) and the static pressure ports (19) are not placed randomly within the hot air duct (1). Rather, they are meticulously placed in a traversing manner. The total number and location of sensing ports (11, 12, 13 and 14) are positioned in accordance with the following guidelines:
1. If the duct horizontal dimension (H) is higher than the vertical dimension (W), multiple pitot array elements are to be used such that equal areas are traversed by the pitot array (Single element shown in the Fig. 1, 2, 3 and 4 and two elements shown in Fig. 7). The number of elements to be used is determined by aspect ratio of the conduit. If the horizontal (H) dimensions of the conduit is greater than two times the vertical (W) dimensions of the conduit, the horizontal (H) dimensions of the conduit is split into multiple number of pieces (n = H/W) and one element is provided for each such individual conduit. Each element shall cater to an individual conduit, whose horizontal conduit dimension (Hd = H/n) is less than vertical (W) dimensions of the conduit. The interconnect header (72) shall connect between each individual elements.
In Fig. 7, an example of conduit is shown whose horizontal dimension is twice that of the vertical dimension, hence two pitot array elements (74 and 75) are used. When two pitot array elements are used, interconnect header (71) is to be provided to connect the static pressure taps (18 in Fig. 1) from the elements to the average static pressure tap (73) and to connect the total pressure taps (17 in Fig. 1) from the elements to the average total pressure tap (72). Similarly, multiple pitot array elements can be used depending on the duct size and the average static pressure taps and average total pressure taps of each element can be connected through an interconnect header to get a single average static pressure tap and single average total pressure tap at the top of the conduit.
2. The conduit cross section is divided into for example 16 grids of equal areas. The location of static and total pressure ports are placed in traversing manner such that each total pressure port is placed at the geometric centre of the grid.
In Fig. 1, Fig. 2, Fig. 3 and Fig. 4, the parameters of duct like the vertical dimension (W) and duct horizontal dimension (H) are shown. The equal area based self-averaging square multi-port pitot average total pressure tap (17) and the average static pressure tap (18) are located at the mid-point on top of the hot air duct (1). The equal area based self-averaging square multi-port pitot is symmetrical to the axis of the pitot head. The length of the stagnation legs (4, 5, 6, 7, 8 and 9) are kept same and is geometrically determined as a function of vertical dimension W of the duct, square pipe size S and the angle of cutting (a) w.r.t to vertical.
3. Optimised square tube of size (S) can be used according to both vertical (W) and horizontal (H) dimensions of the duct. The blockage ratio for a particular duct is increased if the square tube size is increased. The blockage ratio is maintained within 15 – 30%. However, if bigger tubes are used, the conventional manufacturing processes like welding are simpler and the structural strength is also increased. Any size of square tube can be used for total pressure sensing ports, considering the commercial availability, ease of manufacturing and blockage ratio.
4. For static pressure ports (19), the square tube of size S used shall be as small as possible. However, to avoid ash clogging in thermal power plants, square tubes of for example 10 mm size are used for static pressure sensing.
5. The static pressure sensing port (19) has also a plurality of sensing ports located at a height of around 75% of the vertical dimension of the duct from top and oriented so as to face perpendicular to the gas flow through the fluid flow element module, placed at equal distances along the horizontal dimension (H) of the conduit.
6. Optimum cut off angle of (a) is used for stagnation pressure measuring ports. Based on CFD simulation and testing, this angle is optimized in the range of 15 -35°.

[0035] As shown in Fig. 2 and Fig. 3, optimised number of total pressure sensing ports (11, 12, 13 and 14) of stagnation leg (4, 5, 6, 7, 8 and 9) are arranged in fluid communication and anchored to an interconnected manifold (10). Fig.1 and Fig. 2 show the location of interface ports (52) in stagnation legs for interconnected manifolds. In Fig. 5, the first view is normal to the flow and right hand side view for Fig. 1 and Fig. 2 and other 3 figures are 90° clockwise rotational views thereof. 4 types of different location of interface ports (52) are in stagnation legs as shown in Fig. 1. These are top interface port in left top row corner stagnation leg (4), top interface ports in middle bottom row corner stagnation leg (5), top interface port in right top row corner stagnation leg (6), bottom interface port in left bottom row corner stagnation leg (7), bottom interface port in middle bottom row corner stagnation leg (8), bottom interface port in right bottom row corner stagnation leg (9). The location of interface ports in the stagnation legs (4, 5, 6, 7, 8, 9) has been optimized based on CFD analysis. In addition, the left top (4) and bottom (7) row corner stagnation legs are having interface ports on right hand side of the stagnation legs and the top (5) and bottom (8) row middle stagnation legs are having two side of interface ports (10) on stagnation legs. The right top (6) and right bottom (8) row corner stagnation legs are having interface ports on left hand side of the stagnation legs. The left top (4) and right bottom (8) stagnation legs are inversions and similarly the right top (6) and left bottom (7) are inversions.
[0036] As shown in Fig. 5, each stagnation leg (4, 5, 6, 7, 8, 9) is affixed to the interconnected manifold (50) by a conventional manner like welding. Each total pressure has multiple sensing ports oriented so as to face directly toward the inlet, thereby providing unrestricted fluid communication between the impacting fluid flowing into the hot air duct (1), through the total pressure ports (11, 12, 13 and 14), and to the interconnected manifold (50). The interconnected manifold (50) thereby consolidates this combined pressure and sends it to the average total pressure tap (17) as shown in Fig. 1. As shown in Fig. 6, three numbers of static pressure sensing ports (19) are also arranged in fluid communication with average static pressure tap (18) through static pressure tubes (20). The static pressure sensing port (19) has also a plurality of sensing ports located at a height of 75% of the vertical dimension of the duct from top and oriented so as to face perpendicular to the gas flow through the fluid flow element module, placed at equal distances along the horizontal dimension (H) of the conduit. In contrast to this, classic Pitot tubes (Prior art) consist of a concentric double tube, wherein the inside tube having a port facing into the flowing stream for sensing total pressure and the outside tube having radially aligned holes for sensing static pressure.
[0037] The distance between every stagnation leg centre can be called as the pitch and the pitch is geometrically calculated using the horizontal dimension (H) of the duct. The location of interconnected manifold is optimized based on CFD studies. The distance between the intersect of interconnected manifold and the stagnation legs is geometrically determined using the pitch and connecting tube angle (ß), shown in Fig. 2. Based on studies, the connecting tube angle (ß) is optimized to be in the range of 50 – 55°. The distance between duct top plate, in which the average total pressure tap is located and the location of total pressure ports rows is geometrically determined using vertical dimension (W) of the duct.
[0038] As shown in Fig. 2, Fig. 3 and Fig. 4, the multitude of stagnation legs (4, 5, 6, 7, 8 and 9) are connected to the head Pitot through the interconnected manifolds (10) and cross pipes of interconnected manifold (25) and three averaging total pressure pipes (two at the sides - 15 and one central pipe – 16). The three remaining static pressure measuring tubes are made in such a way that the openings to measure static pressure (19) are at the same level. These connections allow for the use of a differential pressure instrument for determining average flow rate and/or transmitting a flow rate signal.
[0039] The material chosen for square pitot assembly includes erosion resistant and does not oxidize up to a temperature of at least 400°C. Generally, carbon steel is used for fabrication of the square pitot assembly. The material of the housing is same as that of the duct [1].
[0040] The materials given above are as example without restricting scope of the invention to the same. Thus, other materials readily apparent to a person skilled in the arts are understood to be within purview of the invention.
[0041] All the tubes are square in shape and of same size. Further, the tubes are connected/interconnected to each other and in flow communication.
[0042] Generally, ash-clogging problem may occur during operation in the pressure tapping lines of flow measuring device used in coal fired steam generator. Due to bigger openings, the ash clogging may not occur in this square pitot device. However, considering trouble free operation, ash purging system is proposed to clean the device.
[0043] The square pitot assembly occupies only 1/20th of the length of the present airfoil for 210 MW capacity boiler. Hence, this device is more suitable for plants with layout constraints. Due to low blockage ratio, the unrecoverable pressure drop is around 10 times lower than that for airfoil. Also, the induced pressure drop is higher thereby improving the measurement accuracy. Also, there is around a 25% increase in flow dp when compared with other pitot array designs.
[0044] This equal area based self-averaging square multi-port pitot can be suitably extended for any duct shape, in particular, for ducts with high aspect ratio. Such ducts, whose horizontal dimension is much larger than vertical dimension, are prevalent in power plants due to layout constraints. In such cases, other pitot array based measurements do not provide equal area coverage and hence the flow measured is not accurate.

WORKING OF THE INVENTION
[0045] Once the equal area based self-averaging square multi-port pitot airflow measuring device is installed, instrument piping in Fig. 8 is installed in order to connect the average total pressure tap (17) of the device to the H port of the DP transmitter (T) through impulse pipeline (36) and ball valve (32). Similarly, the average static pressure tap (18) is connected through impulse pipeline (35) and ball valve (31) to the L port of differential pressure transmitter for indicating the flow differential pressure (DP) as shown in Fig. 8. The impulse pipelines (33 and 34) are connected to the purging air line for removal of any ash clogging. This flow DP and the ambient temperature are transmitted to the control system and the flow rate is determined using the DP and flow constant for the device.

TEST RESULT
[0046] The equal area based self-averaging square multi-port pitot was designed for a 600 X 600 mm square duct and was calibrated at Fluid Control Research Institute (FCRI), Palakkad. It was tested with air medium and the test result is shown in Fig. 9. Also, the variation of calibration factor with flow is shown in Fig. 10. It is observed that the flow constant of the device remains constant for this device over the range of flow for which it was tested.
[0047] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0048] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.
[0049] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogues to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.
[0050] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.
[0051] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0052] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0053] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims:WE CLAIM :

1. An equal area based self-averaging square multi-port pitot airflow measuring device comprises a housing having inlet (2) and an outlet (3) in fluid communication mounted within a non-circular and non-square duct [1], wherein the housing accommodates pitot comprising an array of total pressure sensing ports [11-14] traversing the interior cross sectional area of said conduit for sensing the total pressure of fluid flowing into multiple flow sensing stagnation legs [4-9]; an equal area based self-averaging square multi-port pitot average total pressure tap (17) and an average static pressure tap (18) are located on top of the hot air duct (1) so as to measure pressure.

2. The equal area based self-averaging square multi-port pitot airflow measuring device as claimed in claim 1, wherein the housing is made with the same vertical internal dimensions as the fluid conduit in which it is to be placed, in which static pressure sensing ports leg [19] forming tubes have openings parallel to the flow and used to measure the static pressure inside the conduit [1], in which the material of the housing is same as that of the duct [1].

3. The equal area based self-averaging square multi-port pitot airflow measuring device as claimed in claim 1 or 2, wherein total pressure sensing ports (11, 12, 13 and 14) are provided that the inclined opening is facing the flow and traversing equal areas in the interior cross sectional area of hot air duct (1) for sensing the total pressure of fluid flowing into the hot air duct (1), in which the static pressure sensing ports (19) are affixed that the square opening is parallel to the flow and traversing the interior cross sectional area of the flow element along the horizontal dimension of the conduit for sensing the static pressure within the hot air duct (1).

4. The equal area based self-averaging square multi-port pitot airflow measuring device as claimed in claims 1-3, wherein the total number and location of sensing ports (11, 12, 13 and 14) are positioned in accordance with the following guidelines:
- If the duct horizontal dimension (H) is higher than the vertical dimension (W), multiple pitot array elements are to provided that equal areas are traversed by the pitot array, in which the number of elements is determined by aspect ratio of the conduit, wherein if the horizontal (H) dimensions of the conduit is greater than two times the vertical (W) dimensions of the conduit, the horizontal (H) dimensions of the conduit is split into multiple number of pieces (n = H/W) and one element is provided for each such individual conduit, in which each element caters to an individual conduit, whose horizontal conduit dimension (Hd = H/n) is less than vertical (W) dimensions of the conduit, and the interconnect header (72) is connected between each individual elements.

5. The equal area based self-averaging square multi-port pitot airflow measuring device as claimed in claims 1-4, wherein the length of the stagnation legs (4, 5, 6, 7, 8 and 9) is kept same and is determined as a function of vertical dimension W of the duct, square pipe size S and the angle of cutting (a) with respect to vertical, in which optimised square tube of size (S) is used according to both vertical (W) and horizontal (H) dimensions of the duct, and the blockage ratio is maintained within 15 – 30%.

6. The equal area based self-averaging square multi-port pitot airflow measuring device as claimed in claims 1-5, wherein for static pressure ports (19), the square tube of size S used is as small as possible for example 10 mm diameter tube for static pressure sensing, in which the static pressure sensing port (19) has a plurality of sensing ports located at a height and oriented so as to face perpendicular to the gas flow through the fluid flow element module placed at equal distances along the horizontal dimension (H) of the conduit, wherein cut off angle of (a) in the range of 15 -35° is used for stagnation pressure measuring ports.

7. The equal area based self-averaging square multi-port pitot airflow measuring device as claimed in claims 1-6, wherein total pressure sensing ports (11, 12, 13 and 14) of stagnation leg (4, 5, 6, 7, 8 and 9) are arranged in fluid communication and anchored to an interconnected manifold (10), in which multiple types of different location of interface ports (52) are in stagnation legs for interconnected manifolds including top interface port in left top row corner stagnation leg (4), top interface ports in middle bottom row corner stagnation leg (5), top interface port in right top row corner stagnation leg (6), bottom interface port in left bottom row corner stagnation leg (7), bottom interface port in middle bottom row corner stagnation leg (8), bottom interface port in right bottom row corner stagnation leg (9), wherein the left top (4) and bottom (7) row corner stagnation legs are having interface ports on right hand side of the stagnation legs and the top (5) and bottom (8) row middle stagnation legs are having two side of interface ports (10) on stagnation legs, in which the right top (6) and right bottom (8) row corner stagnation legs are having interface ports on left hand side of the stagnation legs, wherein the left top (4) and right bottom (8) stagnation legs are inversions and the right top (6) and left bottom (7) are inversions.

8. The equal area based self-averaging square multi-port pitot airflow measuring device as claimed in claims 1-7, wherein each stagnation leg (4, 5, 6, 7, 8, 9) is affixed to the interconnected manifold (50), in which each total pressure has multiple sensing ports oriented so as to face directly toward the inlet, thereby providing unrestricted fluid communication between the impacting fluid flowing into the hot air duct (1) through the total pressure ports (11, 12, 13 and 14), and to the interconnected manifold (50), wherein the interconnected manifold (50) consolidates the combined pressure and sends it to the average total pressure tap (17), in which multiple static pressure sensing ports (19) are arranged in fluid communication with average static pressure tap (18) through static pressure tubes (20).

9. The equal area based self-averaging square multi-port pitot airflow measuring device as claimed in claims 1-8, wherein the distance between the intersect of interconnected manifold and the stagnation legs is determined using the pitch and connecting tube angle (ß), which is in the range of 50 – 55°.

10. The equal area based self-averaging square multi-port pitot airflow measuring device as claimed in claims 1-9, wherein multitude of stagnation legs (4, 5, 6, 7, 8 and 9) are connected to the head Pitot through the interconnected manifolds (10), cross pipes of interconnected manifold (25) and three averaging total pressure pipes (two at the sides [15] and one central pipe [16]), in which the three remaining static pressure measuring tubes are provided that the openings to measure static pressure (19) are at the same level; and the equal area based self-averaging square multi-port pitot can be suitably extended for any duct shape, in particular, for ducts with high aspect ratio.
, Description:AN EQUAL AREA BASED SELF-AVERAGING SQUARE MULTI-PORT PITOT AIRFLOW MEASURING DEVICE