RU2157970C2 - Pressure transducer for flowmeter - Google Patents

Abstract

FIELD: large-diameter tubes used for transportation of fluid medium carrying inclusions and abrasive impurities. SUBSTANCE: proposed pressure transducer is manufactured in the form of tubular body that has section-diffuser, section of maximum diameter and section-contraction arranged in sequence one after another in direction of flow. Holes for pressure tapping in proper cross-sections of tubular body are surrounded by averaging collectors located outside tubular body. Internal surface of section-diffuser has grooves distributed over perimeter which bottoms form specified angle together with line of gradient of internal surface. Sections of grooves are positioned one after another in longitudinal direction. Specified geometry of grooves enables profile of velocity of flow to be changed. EFFECT: reduced noise and vibration in extended pipe-lines, prevention of wear-out and cavitation. 7 cl, 7 dwg

Description

Technical field
The invention relates to measuring the flow rate of fluids in closed pipelines, in particular to pressure sensors for flow meters used in such cases.

State of the art
Typically, the pressure sensors used for the above purpose are flow diaphragms, measuring nozzles, and venturi tubes. The last of these devices are made in the form of a tubular body, the cross section of which gradually, in the direction of flow, decreases from the full size to about half the value, and then again increases to the original value. The pressure difference is measured between points located upstream of the flow and corresponding to the total cross section and points corresponding to the minimum cross section, while several holes are provided for pressure selection, distributed along the perimeter of the cross section plane and surrounded by an averaging collector forming an annular chamber.

 The pressure sensors of the type described above are not entirely satisfactory, for example, with respect to the losses observed during their operation, throughput, and due to oncoming vibration and noise.

 US Pat. No. 2,573,430 describes a flowmeter which, in order to reduce losses in the flow, is made without changing the cross section, while oblique openings are made in the wall of the pipeline; the axes of those located upstream are directed upstream, and the axes of those located downstream are directed downstream. The pressure difference between these holes depends primarily on friction and includes the components of the dynamic pressure. Although in one version of such a flow meter the flow cross-section is narrowed like a venturi, the pressure selection holes are located before and after the narrowest point, at the same distance from it and in places of the same cross section.

 The venturi tube according to German patent N 305339, designed to measure the speed of a free gas stream, has a section with an extension located behind the narrowest point, the cross-sectional area of which increases stepwise, which, according to the applicant, should provide insensitivity to the oblique blowing phenomenon.

 A device for measuring the pressure difference between two adjacent sections of the channel is known from German Patent No. 1022021; we are talking about the flow of gas transporting solid materials, when the pressure difference is measured in the first measuring section of a constant cross section, which is a function of the amount of solid material moved, and in the second measuring section, expanding like a diffuser, the pressure difference is measured, based on which the flow rate of the transported gas is calculated.

 A pressure sensor is also known for a flowmeter for measuring the flow rate of highly contaminated liquids containing solid particles. The known pressure sensor is made in the form of a tubular body with holes for sampling the pressure in the corresponding cross sections of the tubular body having successively arranged sections: cone-diffuser, section of maximum diameter and cone-confuser (Kremlevsky P.P. Flow meters and quantity counters. L., Engineering, 1989, p. 101). The pressure drop for calculating the flow rate of the fluid is determined on the site of the cone-confuser. In this case, an increase in the measured pressure drop and, therefore, an increase in the accuracy of determining the flow rate is achieved by increasing the maximum diameter and the associated lengths of the sections of the cone-diffuser and cone-confuser while maintaining the taper angle of the latter. This leads to an increase in the weight and dimensions of the pressure sensor, as well as to an increase in the energy loss of the fluid, which are significant disadvantages of the known pressure sensor.

Disclosure of Invention
An object of the present invention is to provide an improved pressure sensor for a flow meter.

 The solution to this problem is achieved due to the fact that the sensor in the form of a tubular body having a diffuser section, a section of the maximum cross section following it and a confuser section, according to the invention, in the region of the diffuser section, grooves are selected on its inner wall that have a certain geometric configuration and are able to change the profile of flow rates in the desired direction, and the maximum section has openings for the selection of maximum pressure.

Brief Description of the Drawings
The invention is explained in detail with reference to the drawings, in which:
FIG. 1 is a longitudinal section of a pressure sensor with three pressure points and three sections of grooves in the diffuser section;
FIG. 2 is a cross-sectional view taken along line 1-1 of FIG. 1;
FIG. 3 - details of the groove of the diffuser;
FIG. 4 - pressure sensor, side view;
FIG. 5 is a cross section along line 1-1 for an embodiment of a diffuser provided with consecutive grooves of three sections;
FIG. 6 - velocity distribution in the near-wall region of the flow in the initial section of the diffuser in the absence of grooves;
FIG. 7 - velocity distribution in the near-wall region of the flow in the initial section of the diffuser in the presence of grooves.

Embodiments of the invention
The pressure sensor through which the fluid flow flows from left to right is made in the form of a tubular body consisting of an inlet pipe (1) (for connection to a supply line), following a diffuser pipe (4), a section (5) of the maximum cross section, a confuser ( 8) and outlet pipe (9). One of the pressure sampling points (2) is formed on the inlet pipe (1) by openings (3), which are distributed along the perimeter of the cross section and communicate with the averaging collector (13) from the outside (12); a fitting (16) is attached to the manifold to select a pressure equal to the pressure (P ₁ ) in the section plane (2).

Similarly, in the section (5) of the maximum section having a length (l ₁ ) (Fig. 4), a section (6) is formed with holes (7) for pressure selection, which are surrounded on the outside by an averaging collector and due to which a maximum is created in the union (17) pressure (P ₂ ). On the outlet pipe (9), the openings (11) form a third section (10) for pressure selection (P ₃ ), which externally communicates with the averaging collector (15) with a fitting (18). On the inner surface (19) of the diffuser section (4), grooves (20) are made in the form of three sections arranged one after another with distribution of grooves around the perimeter; the bottom of the grooves (21) forms an angle (α ₁ ) with a slope line of the inner surface (19); the slope angle of the inner surface (α ₂ ) is equal to half the angle at the apex of the diffuser cone (α _o ), which can be from 10 ^o to 90 ^o , and the angle (α ₁ ) is greater than or equal to the slope of the inner surface; in other words, the bottom of the groove is parallel to the axis of the tubular body or oriented in the direction of flow in a diverging manner. The transition from the inner surface (19) to the beginning of the groove (20) is formed by the end surface of the groove (23), which is oriented along the normal to the axis of the tubular body.

 According to an exemplary embodiment, three sections of the grooves follow each other without gaps between them. However, a variant with only one section of grooves located along the perimeter, and a variant with several sections of grooves when a gap is maintained between adjacent sections, i.e. there remains a baseless surface in the form of a truncated cone.

 In the case of a variant with several consecutive sections, the grooves in the individual sections can be arranged one after another, as shown in (Fig. 2); they can also be offset from each other, as shown in (Fig. 5), and, according to (Fig. 5), the grooves of the first and third sections are located along the generatrix of the lateral surface of the cone, and the grooves of the second section occupy a place in the middle.

 The side surfaces (22) of the grooves in the examples presented are made parallel to each other; at the same time, they can diverge or converge in the direction of flow.

The dimensions of the grooves are as follows:
h / δ <1.0; b / h≤ 3; l ₂ / l ₃ ≤ 1.0; l ₄ / b≤2.0,
where h is the maximum depth of the grooves;
δ is the wall thickness of the diffuser section (4);
b is the width of the groove;
l ₂ is the length of the groove;
l ₃ - the length of the section of the diffuser;
l ₄ - the distance between adjacent grooves in one section when bypassing the outer perimeter.

The section (5) with the maximum cross section can be limited by the section plane with holes (7) for pressure selection, that is, practically have zero length, so that the diffuser section directly passes to the confuser section. In (figure 4) the length of the plot (5) is equal to (l ₁ ); the maximum length (l ₁ ) corresponds to the maximum diameter (d _max ) of the section of the maximum section;
l ₁ / d _max ≤ 1,0.

 The confuser (8) is made in the form of a conoidal nozzle.

 The described pressure sensor works according to the following principle. The fluid enters from the inlet pipe through an inlet pipe (1) of equal diameter to a portion of the diffuser (4). In the grooves (20), longitudinal vortex flows arise with a rarefaction inside, while in the rest of the flow a positive pressure gradient is created in the diffuser. The effect consists in accelerating the flow in the boundary layer in section (2) and in reducing the flow resistance along the inner surface (19).

On (Fig. 6) shows the distribution of velocities in the near-wall flow at the beginning of the diffuser section (which corresponds to the section plane 2) at an inclination angle α _{2 of the} inner surface (19) for the variant without grooves, and the average velocity vector (V ₁ ) is lying outside border layer. Fig. 7 shows the flow characteristics with grooves (20), which, forming the end surfaces (23) and the bottom (21), lead to a mutual angular orientation; in this case (α ₁ = α ₂ ), that is, the bottom (21) of each groove is parallel to the axis. The angle of inclination (α ₂ ) of the inner surface (19) is less than the separation angle (α _sep (α _sep > α ₂ )); nevertheless, at the edge of the end surface (23), there is a local detachment and the formation of longitudinal vortices between the side surfaces (22) of the grooves, which results in a drop in pressure inside the longitudinal vortices and a decrease in flow resistance along the inner surface of the diffuser (19). A velocity profile is formed at which in the boundary layer there is an increase in velocity by (Δ V) to the value (V ₂ ). These processes are repeated in all sections of the grooves following each other in the direction of flow.

As a result, the grooves have such an effect that even in section (2) the fluid velocity is greater and the pressure is less than in the supply pipe, and the minimum pressure (P ₁ ) is created in the nozzle (16) through the holes (3) for pressure selection.

In the plane (6) with the maximum cross section, the fluid reaches its lowest speed, and therefore, in the nozzle (17) through the holes (7) the maximum pressure is created (P ₂ ).

In confuser (8), the flow accelerates again and enters the outlet section (10) with a higher speed and lower pressure than in the pipeline, so that as a result, the minimum pressure is created in the holes (11) for pressure selection and, accordingly, the fitting (18) ( P ₃ ).

Q = Q₂ = Q₁₀
где D - диаметр трубопровода, в котором измеряют расход Q;
P₁, P₂, P₃ - давление в местах отбора давления (2, 6 или 10);
β - постоянный множитель:

α₃, α₄ - поправочные коэффициенты:

где kc₁, kc₂, kc₃ - поправочные члены, учитывающие неравномерность распределения скоростей в соответствующих сечениях (2, 6 и 10);
ε_D коэффициент уширения потока в диффузоре между плоскостями сечения (2 и 6):)
ε_D W₂/W₆ (W₂₍₆₎ - площади поперечного сечения в плоскостях (2 или 6);
ε_C - коэффициент сужения потока в плоскости сечения (10):
ε_C= W_c/W₁₀,
где W_с и W₁₀ - площадь суженного потока в сечении (10) и площадь сечения (10) выходного патрубка;
m=W₁₀/W₆;
ζ_1-2 коэффициент, учитывающий потери вследствие трения между плоскостями сечений (2 и 6);
ζ_2-3 коэффициент, учитывающий потери вследствие трения между плоскостями сечений (6 и 10).Instruments for measuring the pressure drop, for example differential pressure gauges, are connected to the fittings (16, 17, 18), due to the readings of which it becomes possible to determine the flow rate (volume / time) in the cross-section planes (2 and 10) according to the following formulas:

Q = Q ₂ = Q ₁₀
where D is the diameter of the pipeline in which the flow rate Q is measured;
P ₁ , P ₂ , P ₃ - pressure in places of pressure selection (2, 6 or 10);
β is a constant factor:

α ₃ , α ₄ - correction factors:

where kc ₁ , kc ₂ , kc ₃ are correction terms that take into account the uneven distribution of velocities in the corresponding sections (2, 6, and 10);
ε _{D is the} coefficient of broadening of the flow in the diffuser between the section planes (2 and 6) :)
ε _D W ₂ / W ₆ (W _{2 (6)} - the cross-sectional area in the planes (2 or 6);
ε _C is the coefficient of narrowing of the flow in the section plane (10):
ε _C = W _c / W ₁₀ ,
where W _with and W ₁₀ - the area of the narrowed flow in section (10) and the cross-sectional area (10) of the outlet pipe;
m is W ₁₀ / W ₆ ;
ζ _1-2 coefficient taking into account losses due to friction between the planes of sections (2 and 6);
ζ _2-3 coefficient taking into account losses due to friction between the planes of sections (6 and 10).

 The proposed pressure sensor for flowmeters due to the formation of longitudinal vortices in the grooves can reduce losses during the passage of the fluid and increase the flow rate coefficients, as well as the pressure difference, in particular in long or branched piping systems consisting of pipes of large diameter and used to transport liquids or gases. The vibro-acoustic properties of such systems are significantly improved, namely, noise and vibration are significantly reduced. It is possible to completely avoid the wear of the measuring section due to its abrasion by abrasive impurities in the stream. The sensor can be reliably operated even when the fluid contains inclusions whose size is in order of magnitude comparable to the diameter of the pipe. Finally, there are no restrictions regarding the maximum fluid velocity, since there is no risk of cavitation in the measuring section.

Industrial applicability
The proposed pressure sensor for a flow meter can find application in pressure-sensitive gas-hydraulic systems for various purposes with a nominal diameter of pipelines from 10 to 2500 mm for measuring the flow rate of single and multiphase fluids containing inclusions of various physical, mechanical or chemical composition. Particularly promising is the use of the sensor in medium and large diameter pipelines (250-2500 mm), as well as in pipelines with increased hydroabrasive or cavitation corrosion-erosion wear. Among the possible areas of use of the sensor are the following:
- water supply and sanitation of populated areas and industrial enterprises;
- gas and oil industry;
- heat and gas supply and ventilation of populated areas and industrial enterprises;
- chemical and petrochemical industry;
- development of mineral deposits hydraulically;
- hydrotransport of tailings of concentration plants;
- systems for the transportation and distribution of liquid and gaseous fuels in the energy sector;
- Hydrotransport systems of mortars and mixtures;
- irrigation systems in agriculture (irrigation and drainage);
- technological gas-hydraulic systems of the food industry, for example, in winemaking when pumping delicious wines, in the dairy industry, when pumping juices, etc.

Claims (8)

1. The pressure sensor for the flow meter, made in the form of gradually changing its cross section of the tubular body with holes for pressure selection at successive points that are distributed along the perimeter of the section planes, and on the outside of the tubular body, which has successive another diffuser section (4), a maximum section (5) and a confuser section (8) are surrounded by an averaging collector (13, 14, 15), characterized in that in the region of the diffuser section on its inner surface (19), grooves distributed around the perimeter (20) have been made, the bottom of which forms an angle α ₁ greater than or equal to the angle of inclination α _{2 of the} inner surface with the slope of the inner surface (19), where α ₂ ≥ 1 / 2α _o , where α _o is the diffuser opening angle while the transition from the inner surface (19) to the beginning of the groove is formed by the end surface (23) of the groove oriented normal to the axis of the tubular body, and the section (5) of the maximum section has openings (7) for selecting the maximum pressure (P ₂ ). 2. The pressure sensor according to claim 1, characterized in that the angle of the diffuser solution is from 10 to 90 ^o .  3. The pressure sensor according to claim 1, characterized in that the grooves (20) are made in sections arranged one after the other.  4. The pressure sensor according to claim 3, characterized in that the sections of the grooves (20) are located with the formation of a gap between them.  5. The pressure sensor according to claim 3 or 4, characterized in that the grooves of the consecutive sections are mixed relative to each other.  6. A pressure sensor according to any one of claims 1 to 5, characterized in that the side walls (22) of the grooves (20) are parallel to one another. 7. The pressure sensor according to claim 6, characterized in that the grooves has the following dimensions:

where h is the maximum depth of the grooves;
δ is the wall thickness of the diffuser;
b is the width of the grooves;
l ₂ - the length of the grooves in one section;
l ₃ - the length of the section of the diffuser;
l ₄ - the distance between adjacent grooves along the outer perimeter. 8. The pressure sensor according to any one of claims 1 to 7, characterized in that the length l ₁ of the maximum cross section takes on values between zero and a value equal to the diameter d _max of the maximum cross section.

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