RU2157971C2 - Pressure transducer for flowmeter - Google Patents

Abstract

FIELD: measurement of flow rate of polluted fluid media in pipe-lines having large cross-sections. SUBSTANCE: pressure transducer has case with flange for connection to pipe-line and member creating pressure differential that comes in the form of at least one slot-shaped radius conduit with pipe unions for pressure tap. Cross-section of each conduit in longitudinal direction along flow is constant or varies with formation of diffuser and contraction. Member narrowing cross-section of conduit and overlapping width of conduit can be built in each radius conduit. EFFECT: decreased energy losses of flow, enhanced measurement accuracy in fluid media carrying large inclusions of solid particles. 8 cl, 49 dwg

Description

Technical field
The invention relates to measuring liquid flow in closed pipelines, in particular to pressure sensors for flow meters.

State of the art
Typically, pressure sensors are flow diaphragms, measuring nozzles, and venturi tubes, with which measurements are taken over the entire flow cross section and which are used to throttle to create a pressure drop. In pipelines of large cross-section, such sensors are of little use, in addition, they are heavy, bulky, and their manufacture requires a lot of labor and materials. Finally, the reliability and accuracy of measurements in these cases are unsatisfactory.

 From the description of the invention to the USSR author's certificate N 1076753, a narrowing device for measuring the flow rate of water in a channel is made, made with two curved surfaces facing each other with their convex parts forming a compressed section. The pressure drop is measured between the compressed and normal sections. This design is unsuitable for measuring the flow of fluids in closed channels and pipelines, which is its main disadvantage.

 From the description of US patent N 3449954 known flow meter for pipelines of large cross-section, along the perimeter of which are distributed several active pressure sensors; each of these sensors is a trapezoidal element protruding from the wall into the tube to a height insignificant compared to the radius of the tube; the trapezoidal element is provided with one hole for recording dynamic pressure in the incoming stream and an opening for recording pressure in the dead zone behind the element. Measurements are carried out only in certain areas near the wall; a complete profile of flow rates cannot be established.

 Known flow meters with hydraulic resistance, based on the dependence of the flow on the pressure drop created by the hydraulic resistance. As the latter, one or more capillary tubes (capillary flow meters), as well as slotted channels (slotted flow meters) are usually used (Kremlevsky P.P. Flow meters and quantity counters.- L .: Mashinostroenie, 1989, pp. 10-13, 114- 117).

 Known slit flow meter, the measuring section of which is made in the form of a gap with a height of hundredths to tenths of a millimeter between two parallel plate disks (Morsi SA The Pad and Quadresistor-Two methods of fluid flow measurement / Proc. Justr. Mech / End., 1976, vol . 190, p. 205). In this design, a linear relationship is achieved between the flow rate and the pressure drop in the laminar regime of only pure, pure liquids and gases, which is a drawback. Another disadvantage is the large pressure loss during the flow of the entire fluid flow through the slotted gap.

Disclosure of Invention
An object of the present invention is to provide a pressure sensor for a flow meter that is suitable for use on pipelines of large cross-section and at the same time is free from the above disadvantages.

 The solution to this problem is achieved due to the fact that in the pressure sensor, in accordance with the invention, at least one narrow radial strip is emitted from the whole stream, passing from the center to the outer perimeter and flowing along the built-in radius channel in which this strip creates a pressure differential between two points located in the direction of flow, one after one; in the case of a constant cross section of the radius channel, due to friction, and in the case of a longitudinal section changing in the longitudinal direction, due to acceleration and deceleration of the flow. The pressure drop is sensed on the respective fittings and its numerical value is determined using a suitable measuring device, such as a differential pressure gauge.

Brief Description of the Drawings
The invention is explained in detail on the basis of the accompanying drawings, on which:
FIG. 1 - pressure sensor with one radius channel of constant cross section in longitudinal section;
FIG. 2 is a section along line 1-1 in FIG. 1;
FIG. 3 - pressure sensor with two radial channels passing into each other on the axis of the housing, located in the same planes and having a constant section; lengthwise cut;
FIG. 4 is a section along line 1-1 of FIG. 3;
FIG. 5 - pressure sensor with three or four radius channels of constant cross-section, docked on the axis of the housing and passing into each other, as well as uniformly distributed around the perimeter; longitudinal section according to lines 2-2 in FIG. 6 or 7;
FIG. 6 is a section along line 1-1 in FIG. 5 for the version with four radius channels;
FIG. 7 is a section along line 1-1 in FIG. 5 for the version with three radius channels;
FIG. 8 - pressure sensor with two radial channels, passing into each other on the axis of the housing, lying in the same plane and having consecutive diffuser and confuser sections; lengthwise cut;
FIG. 9 is a section along line 1-1 of FIG. eight;
FIG. 10 is a pressure sensor with one radial channel extending to the body axis, which has consecutive diffuser and confuser sections, in longitudinal section;
FIG. 11 is a section along line 1-1 of FIG. ten;
FIG. 12 is a pressure sensor with a radius channel in which the profiled strip of the outer wall forms successive narrowing in the form of a nozzle and a section in the form of a diffuser, in longitudinal section;
FIG. 13 is a section along line 1-1 of FIG. 12;
FIG. 14 is a pressure sensor with two radial channels passing into each other on the axis of the housing and located in the same plane, the profiled strips of the outer wall of which form consecutive narrowing in the shape of a nozzle and a section in the form of a diffuser, in longitudinal section;
FIG. 15 is a section along line 1-1 in FIG. fourteen;
FIG. 16 is a pressure sensor with two radius channels that pass into each other on the axis of the housing, are located in the same plane and the outer border of which forms successive sections in the form of a diffuser, confuser and diffuser in longitudinal section;
FIG. 17 is a section along line 1-1 of FIG. 16;
FIG. 18 is a section along line 2-2 of FIG. 16;
FIG. 19 is a pressure sensor with one radius channel, the outer boundary of which forms successive sections in the form of a diffuser, confuser and again a diffuser, in longitudinal section;
FIG. 20 is a section along line 1-1 of FIG. 19;
FIG. 21 is a section along line 2-2 of FIG. 19;
FIG. 22 is a pressure sensor with a radius channel, the outer border of which forms successive sections in the form of a similar diffuser, confuser and output diffuser, the inner surface creating a height restriction is located on the axis of the body and begins only in the section passing through the neck between the confuser sections and the subsequent diffuser, and, starting from here and up to the movement of the liquid, there is no internal height-limiting surface;
FIG. 23 is a section along line 1-1 of FIG. 22;
FIG. 24 is a section along line 2-2 of FIG. 22;
FIG. 25 is a pressure sensor with two radial channels passing into each other on the axis of the housing and located in the same plane, the outer border of which forms successive sections in the form of an inlet diffuser, a confuser and an output diffuser, moreover, symmetrical in the side walls cutouts.

FIG. 26 is a section along line 1-1 of FIG. 25;
FIG. 27 is a section along line 2-2 of FIG. 25;
FIG. 28 is a pressure sensor with one radius channel in which a built-in element is provided for limiting height, in longitudinal section;
FIG. 29 is a section along line 1-1 of FIG. 28;
FIG. 30 - pressure sensor with two radius channels adjacent to each other on the axis of the housing and located in the same plane, in the channels of which are built-in elements for limiting height, in longitudinal section;
FIG. 31 is a section along line 1-1 of FIG. thirty;
FIG. 32-43 - longitudinal or respectively transverse sections of pressure sensors with one radius channel, in which built-in elements of various configurations are created, creating a height limit;
FIG. 44 is a pressure sensor with two radial channels passing into each other on the axis of the housing and located in the same plane, which together have a massive round built-in element representing an internal height limit, a longitudinal section;
FIG. 45 is a section along line 1-1 in FIG.
FIG. 46, 47 - pressure sensor, as in FIG. 44, 45, where the built-in element is a ring;
FIG. 48, 49 - pressure sensor, in FIG. 44, 45, where the built-in element is a flow body.

Embodiments of the invention
The proposed pressure sensor consists of a housing (1), which, through at least one flange (2), when using a gasket (3), is connected to the flange (4) of the pipeline (5) supplying a fluid medium, the flow rate of which per unit time measured. The radius (g) of the channel in the housing serves as a characteristic linear dimension.

 A pressure-generating element (8) adjacent to the end surface of the inlet flange (2) is embedded in the housing (1) (for example, welded), which in the simplest case (Fig. 1,2) consists of a thin-walled, narrow body that is open at the back and front, forming a radius channel (9) with parallel side walls (10). Radius channel (9) of width (δ) and height (b), and in this example, the height (b = r) is equal to a constant value. This means that the contacting surfaces (12) that constrain the radius channel in height are flat and extend in the direction of the axis.

 The pressure-generating element (8) has sharp leading edges and cuts out from the total flow a part of the latter having a rectangular cross section and passing along the radius, while in this case this part of the flow does not change its cross section, that is, the flow is not accompanied by acceleration or deceleration.

 Outside from the element (8), near its leading and trailing edges, two pressure fittings (6 and 7) protrude, to which a suitable measuring device, in particular, a differential pressure gauge, is connected. The pressure difference arising during the passage of the fluid between the fittings (6 and 7) is determined in the above example, essentially only by friction between the side walls.

 To better average the irregularities in the flow, the pressure-generating element can form several radius channels. On (Fig. 3 and 4) presents an option according to which formed two located in the same plane of the radius channel, passing into each other on the axis of the housing; the flow passes in a plane of diameter perpendicular to the cross section of the body in the light.

On (Fig. 5, 6 and 7) two other variants of execution are shown, namely: on (Fig. 6) there is shown a variant of a pressure-generating element (8) with four radius channels (9), which are evenly distributed around the circle, forming each other another angle of 90 ^o and turning into each other on the axis of the housing (14).

On (Fig. 7) shows a variant with three radius channels (9), forming with each other an angle of 120 ^o . The channels can be located at any angle to each other, but it is preferable to distribute them evenly, that is, so that two adjacent (when moving around the periphery) channels form an angle between themselves (α 360 ^o / n), where n is the number of channels.

 The ratio between the width (δ) of the radius channel and the radius (r) is (δ / r = 0.05 - 0.0002). The inner surfaces of the side walls (10) are located at a distance (δ / 2) from the radial plane (11).

For the above options, according to (Fig. 1-7), the height (b) of any radius channel is constant and equal to the height (b ₁ ) at the entrance; in other words, a partial flow flows through the pressure-generating element without changing the speed. In other embodiments, the height of the radius channel (9), at a constant width (δ), is changed either externally using the corresponding profiled section (13) of the outer channel-limiting surface (12), as in (Fig. 8-27), or using parietal built-in elements, as in (Fig. 28-43), or using central built-in elements, as in (Fig. 44-49). Moreover, the relative position of divergent sections-diffusers, converging sections-nozzles and sections of inlet, outlet and mouths, with a constant cross section, can be different.

On (Fig. 8, 9 and 10, 11) two (or one, respectively) radial channels are shown with an input section having a constant section of height (b ₁ = r), the height of which (b) begins to increase, which leads to the formation of expansion a diffuser, and the increase in the height of the channel is created by a powder welded to the body (1), and the first fitting (7) for pressure selection is located in the place corresponding to the maximum cross section; Further, the height of the inlet section decreases with the transition to the confuser section and then to the exit section c (b = r), on which the second fitting (6) is located for pressure selection. Another alternation order of the confuser section and the diffuser section, which is created by profiling the outer boundary, is shown in (Figs. 12-15 and 38-43).

On (Fig. 16-27) other configurations of channels are shown, when the first section - the input diffuser with (b> b ₁ ) goes into the confuser section, and the last into the neck with (b <b ₁ = r), starting with which the height the channel returns to the destination (b ₁ = r) of the radius of the pipeline, and a portion is formed of the outlet diffuser. The fittings (7 ₁ , 7 ₂ ) for pressure selection are located at points corresponding to the maximum and minimum sections.

 On (Fig. 28-43) presents options when a change in the height of the radius channel or, respectively, of both radius channels located in a common plane, is achieved thanks to the built-in elements. In (Fig. 28-31), the integrated element (17) in each radius channel is a triangular throttling element narrowing the cross section with a sharp tearing edge (18), which is located directly in front of the nozzle (7) for pressure selection, placed downstream . Built-in elements (19) with a linearly rising edge for incoming flow, which goes into the constant height section of the tear-off edge, or element (20) with a once curved edge for incoming flow (Fig. 34), or element (21) with double curved edge for the oncoming flow (Fig. 36), which provides a smooth entry of the flow.

 On (Fig. 38-43) options are presented when the built-in element does not end with a sharp edge of flow separation, but the channel, starting from the narrowest point formed by it in the neck, where the second pressure fitting (7) is located, again expands in a similar way to inlet heights (b = r).

 By means of the central built-in elements shown in FIGS. 44-49, obviously, a confuser-diffuser configuration is created from two radius channels located in the same plane, the first pressure connection (6) being located upstream of the built-in element in the section plane (25), and the second nozzles (7) for pressure selection are located in the narrowest place of the channel in the section plane (26). Element (22) is a massive round plate, element (23) is a ring, and element (24) is a teardrop-shaped body around which forms two channels, similar to what is observed in Venturi tubes.

Принцип работы описанного выше датчика давления следующий: поток текучей среды, поступающей из трубопровода (5), протекает через корпус (1), причем большая часть потока обтекает создающий давление элемент (8), не встречая значительного сопротивления.The length of the built-in elements (17-24) is between (l _max ) and (l _min ) at
l _max = l _1max + l ₂ + l _3max
and
l _min = l _1min + l ₂ + l _3min ,
where l ₂ is the length of the built-in element in the longitudinal direction;
l _min and l _max - the minimum and, accordingly, the maximum length of the sections of stabilization of flows located in front of and behind the built-in element, for which the following formulas are valid:

The principle of operation of the pressure sensor described above is as follows: the fluid flow coming from the pipeline (5) flows through the housing (1), and most of the flow flows around the pressure-generating element (8) without encountering significant resistance.

 A substantially smaller part of the flow enters and flows through one or more radius channels.

где P₆ и P₇ - давление в штуцерах (6 и 7), a γ -удельный вес текучей среды.In the radius channels of constant cross-section (Fig. 1-7), the fluid flows at a constant speed and undergoes a pressure loss due to friction between the side walls so that a negative pressure gradient exists in the measurement section, i.e. there is a pressure drop that amounts to :

where P ₆ and P ₇ are the pressure in the fittings (6 and 7), and γ is the specific gravity of the fluid.

которая в данном случае (b > г) обусловлена также и взаимодействием статического давления с динамическим.In radius channels having a diffuser-confuser configuration (b> r, Fig. 8-11) in the diffuser section up to the nozzle (7), the flow slows down and thereby the pressure increases to a maximum value (P ₇ ) in the maximum channel section, in the following the confuser section, the flow accelerates again, which leads to a pressure drop in the nozzle (6) to the value (P ₆ ). This positive pressure gradient leads to a pressure difference:

which in this case (b> r) is also due to the interaction of static and dynamic pressure.

Для конфигурации диффузор-конфузор-диффузор (фиг. 16-27) в плоскости штуцера (7₁) скорость достигает минимального значения и создается максимальное давление (P_7-1), в то время как из-за ускорения до плоскости штуцера (7₂) там развивается максимальная скорость и создается минимальное давление (P_7-2). Разность давлений рассчитывается по формуле:

В случае размещения в радиусном канале встроенных элементов (фиг. 29-49) между сечением (26), где поток сужен и где расположен штуцер (7) и сечением (25), где через штуцер (6) регистрируется более высокое давление невозмущенного потока, создается разность давлений, рассчитываемая по уравнению:

На основе величин падения давления, возникающего на создающем давление элементе, расход через последний определяют из соотношения:

где - α₁ коэффициент протекания для отдельного радиусного канала;
f - площадь узкого сечения;
g - ускорение силы тяжести.The above is also true for the confuser-diffuser configuration at (b <r) (Fig. 12-15), when the maximum pressure is selected in the nozzle (6) located upstream from the sections of the change in cross section, while in the case of narrowing cross-section with a fitting (7), an increased speed leads to a pressure drop to a value (P ₇ ), which allows us to determine the pressure difference by the formula:

For the diffuser-confuser-diffuser configuration (Fig. 16-27) in the nozzle plane (7 ₁ ), the speed reaches the minimum value and the maximum pressure is created (P _7-1 ), while due to acceleration to the nozzle plane (7 ₂₎ ) there maximum speed develops and minimum pressure is created (P _7-2 ). The pressure difference is calculated by the formula:

In the case of placement of built-in elements in the radius channel (Figs. 29-49) between the cross-section (26), where the flow is narrowed and where the nozzle (7) is located and the cross-section (25), where a higher pressure of the unperturbed flow is detected through the nozzle (6), creates a pressure difference calculated by the equation:

Based on the values of the pressure drop occurring on the pressure-generating element, the flow through the latter is determined from the relation:

where - α ₁ leakage coefficient for a single radius channel;
f is the narrow sectional area;
g is the acceleration of gravity.

где α₂ - поправочный коэффициент, учитывающий возможные различия в скоростях в трубопроводе (5) и в датчике давления;
F - площадь поперечного сечения трубопровода (5) в свету;
F₁ - площадь поперечного сечения на входе отдельного радиусного канала (9), а именно:
F₁= b₁×δ = r×δ.
Если создающий давление элемент состоит из нескольких радиусных каналов (n ≥ 2), для каждого из которых измерено падение давления (ΔP₁, ΔP₂, ΔP_n), то по завершении частичных расчетов определяют среднее падение давления (ΔP_сред), или среднюю разность давлений по уравнению:

Располагая этой величиной, суммарный расход текучей среды через датчик давления рассчитывают для случая (n ≤ 2) по уравнению:

где α₃- коэффициент, учитывающий взаимодействие потоков текучей среды в области перехода нескольких радиусных каналов друг в друга на оси (14) корпуса, причем:
в случае n = 1 α₃ = 1,
в случае n ≥ 2 α₃ ≠ 1.Having this ratio, the total flow rate (Q) through the pipeline is found by the equation:

where α ₂ is a correction factor that takes into account possible differences in speeds in the pipeline (5) and in the pressure sensor;
F is the cross-sectional area of the pipeline (5) in the light;
F ₁ - the cross-sectional area at the entrance of a separate radius channel (9), namely:
F ₁ = b ₁ × δ = r × δ.
If the pressure-generating element consists of several radius channels (n ≥ 2), for each of which a pressure drop (ΔP ₁ , ΔP ₂ , ΔP _n ) is measured, then after partial calculations are completed, the average pressure drop (ΔP _medium ), or the average difference pressure by the equation:

Having this value, the total fluid flow through the pressure sensor is calculated for the case (n ≤ 2) according to the equation:

where α ₃ - coefficient taking into account the interaction of fluid flows in the transition region of several radial channels into each other on the axis (14) of the housing, and:
in the case n = 1 α ₃ = 1,
in the case n ≥ 2 α ₃ ≠ 1.

где F₁ - сумма площадей поперечных сечений радиусных каналов на входе (F₁= n×b₁= n×r×δ);
F₂ - площадь поперечного сечения зоны перехода нескольких радиусных каналов на оси (14) датчика давления.Given the above formula, the flow rate Q of fluid in the pipeline (5) for the case (n ≤ 2) is calculated by the equation:

where F ₁ is the sum of the cross-sectional areas of the radius channels at the input (F ₁ = n × b ₁ = n × r × δ);
F ₂ is the cross-sectional area of the transition zone of several radius channels on the axis (14) of the pressure sensor.

 The proposed pressure sensor for the flow meter can significantly reduce the cost of materials and manufacturing and significantly increase the throughput of the pipeline while reducing energy loss and improving the accuracy of measurements and the reliability of the measuring system, and the same is true for fluids containing large inclusions of solid particles whose dimensions exceed the width of the radius channels.

Industrial applicability
The proposed pressure sensor can be used in various gas-hydraulic systems with channels of any cross section with a nominal diameter of 10 to 2500 mm for measuring the flow rate of single and multiphase fluids with solid inclusions, the minimum size of which is larger than the characteristic size of the radius channel.

Among the applications you can specify:
- water supply, heat and gas supply and ventilation of populated areas and industrial enterprises;
- gas and oil industry;
- chemical and petrochemical industry;
- systems for the transportation and distribution of liquid and gaseous fuels in the energy sector;
- irrigation systems in agriculture;
- technological gas-hydraulic systems in the food industry.

Claims (9)

 1. A pressure sensor for a flowmeter designed to measure the flow of fluids in closed pipelines, consisting of a housing (1) with a flange (2) for connection to the flange (4) of the pipeline (5) and containing a pressure-generating element (8) with fittings ( 6, 7) for pressure selection, characterized in that said element (8) is fixed in the housing (1) and represents at least one slot-like radius channel, the width (δ) of which is small compared to its height, the side parallel walls ( 10) which are located symmetrically on both sides of radial plane (11) at a distance from it, which is half (δ / 2) of the width of the channel, and which has at least one contact surface (12), creating a channel height restriction.  2. The pressure sensor according to claim 1, characterized in that the surface creating a height restriction is flat, and the cross-sectional area of the radius channel is constant.  3. The pressure sensor according to claim 1, characterized in that the height-limiting surface is curved, while the cross-sectional area of the radius channel changes in the longitudinal direction along the flow with the formation of the section - diffuser and section - confuser.  4. The pressure sensor according to any one of claims 1 to 3, characterized in that it contains several radius channels evenly distributed over the volume, passing into each other on the axis (14) of the housing.  5. The pressure sensor according to any one of claims 1 to 4, characterized in that the ratio between the width (δ) of each radius channel and the radius of the pipeline (5) is 0.05 - 0.0002. 6. The pressure sensor according to any one of claims 1 to 5, characterized in that the height (b ₁ ) of the radius channels at the inlet is equal to the radius (r) of the pipe (5).  7. A pressure sensor according to any one of claims 1 to 5, characterized in that the element (8) has sharp leading edges.  8. The pressure sensor according to any one of claims 1 to 7, characterized in that in each radius channel there is an integrated element overlapping the width (δ) of the channel, narrowing the cross section. 9. The pressure sensor according to claim 8, characterized in that the length (l) of the elements causing a narrowing of the flow is between the values of l _max and l _min at
l _max = l _1max + l ₂ + l _3max
and
l _min = l _1min + l ₂ + l _3min ,
where l ₂ is the length of the built-in element in the longitudinal direction;
l _1max , l _3max , l _1min , l _3min is the maximum and minimum length of the flow stabilization sections located respectively in front of (l ₁ ) and behind (l ₃ ) the built-in element, and
l _1min = l _3min = (1-100) δ
and
l _1max = l _3max = (100-1000) δ.

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