Low flow high pressure flowmeter

Abstract

The application relates to a low-flow high-pressure flowmeter belonging to the pipeline engineering field. The low-flow high-pressure flowmeter comprises a straight section, a converging section, a throat section and a diverging section which are sequentially connected, wherein the converging section comprises a variable-taper conical wall, the taper gradually increases from 17-19 degrees at the inlet to 21-23 degrees at the outlet; the effective diameter of the throat section is 0.35-0.45 times the nominal diameter of the pipeline, and the axial length is 2.5-3 times the effective diameter; and the taper of the conical wall of the diverging section is 6-8 degrees. The flowmeter can effectively improve the differential pressure under the small-flow working condition, maintain the linear relationship between the flow and the square root of the differential pressure under the high-pressure working condition, and improve the measurement precision under the small-flow high-pressure working condition.

Description

Technical Field

[0001] This invention belongs to the field of pipeline engineering, and specifically relates to a low-flow-rate, high-pressure flow meter. Background Technology

[0002] Standard Venturi flow meters are widely used in petroleum, chemical, and thermal engineering fields to measure fluid flow rates in industrial settings. However, standard Venturi flow meters employ a fixed constriction taper, fixed throat diameter, and linear flaring section design. Under extreme conditions of low flow rate and high back pressure, the fluid velocity increase through the throat is small, the differential pressure signal before and after throttling is weak, and the measurement linearity is severely distorted, making it difficult to meet the performance requirements of special applications such as nuclear heating reactors. Therefore, providing flow meters with higher detection accuracy under low flow rate and high back pressure conditions has significant practical value. Summary of the Invention

[0003] The purpose of this invention is to provide a low-flow-rate high-pressure flow meter to improve the detection accuracy of the flow meter in scenarios with low flow rate and high back pressure.

[0004] According to an embodiment of the present invention, a low-flow-rate high-pressure flow meter is provided, comprising a straight section, a constricted section, a throat section, and a flared section connected in sequence. The constricted section has a tapered wall with a gradually increasing taper, the taper gradually increasing from the inlet to the outlet. The inlet taper of the constricted section is 17°-19°, and the outlet taper is 21°-23°. The effective diameter of the throat section is 0.35-0.45 times the nominal diameter of the pipe being measured, and the axial length of the throat section is 2.5-3 times the effective diameter. The taper of the flared section is 6°-8°.

[0005] The flowmeter's constriction section adopts a gradually increasing large constriction ratio constriction structure, which steepens the cone slope, allowing the measured medium to be effectively concentrated and rapidly increasing the medium's velocity under low flow conditions. By using a throat section with a smaller diameter and longer axial length, the throttling and acceleration effect is further improved, resulting in a larger differential pressure. Compared to the flared section of a traditional Venturi tube, the flared section uses a cone surface structure with a smaller taper, which enables a smooth and slow release of the medium flow, avoiding pressure backflow and offset under high back pressure conditions, reducing differential pressure attenuation loss, and ensuring stable differential pressure retention.

[0006] Furthermore, in some embodiments, the high-pressure side pressure tap is located on the straight section, and the flow field of the section where the high-pressure side pressure tap is located is a flat DC field; the low-pressure side pressure tap is located at the axial center of the throat section.

[0007] Furthermore, in some embodiments, the pressure tapping section of the high-pressure side pressure tapping point is set to an ellipse, the pressure tapping cavity is configured as a flared structure, and the equivalent diameter of the pressure tapping opening is 8mm-12mm.

[0008] Furthermore, in some embodiments, the pressure tapping chamber of the low-pressure side pressure tapping point is configured with a constricted structure, with an inlet diameter of 4mm-6mm and an outlet diameter of 10mm-14mm.

[0009] Furthermore, in some embodiments, the pressure tapping openings of the high-pressure side pressure tapping point and the low-pressure side pressure tapping point adopt a rounded corner structure.

[0010] Furthermore, in some embodiments, the constricted section and the throat section are connected by a transition arc, the radius of which is 0.8 to 1.2 times the inner diameter of the throat section.

[0011] Furthermore, in some embodiments, the inner wall of the low-flow-rate high-pressure flow meter is subjected to a smooth polishing process.

[0012] Furthermore, in some embodiments, the low-flow-rate high-pressure flow meter further includes a first pressure transmitter, a second pressure transmitter, and an output device. The output device is signal-connected to the first pressure transmitter and the second pressure transmitter, respectively. The first pressure transmitter measures the pressure at the high-pressure side pressure tap, and the second pressure transmitter measures the pressure at the low-pressure side pressure tap. The output device calculates and outputs the flow rate value based on the pressure difference measured by the first pressure transmitter and the second pressure transmitter.

[0013] Furthermore, in some embodiments, a curved equalizing ring is also provided on the outer periphery of the straight segment and the throat segment.

[0014] Furthermore, in some embodiments, the measurement error of the low-flow high-pressure flow meter under rated operating conditions does not exceed 1%, the data fluctuation range does not exceed ±0.8%, and the effective differential pressure retention rate is not less than 92%. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a low-flow-rate high-pressure flow meter in one embodiment; Figure 2 This is a photograph of the pressure tapping opening at the high-voltage side pressure tapping point in one embodiment.

[0016] Meaning of the reference numerals in the attached figures: 1-Straight section; 2-Narrowing section; 3-Throat section; 4-Expanding section; 5-Pressure tapping point on the high-pressure side; 6-Pressure tapping point on the low-pressure side; 7-First pressure transmitter; 8-Output device; 9-Second pressure transmitter; 10-Bent pipe type equalizing ring; 11-Pressure tapping opening; 12-Rounded corner.

[0017] The purpose of the above-described drawings is to provide a detailed description of the present invention so that those skilled in the art can understand the technical concept of the invention, and is not intended to limit the invention. For the sake of brevity, the above-described drawings only schematically depict the structures related to the technical features of the present invention, and do not depict the complete structure and all details strictly according to actual scale. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0019] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment herein. The phrase appearing in various places in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive, independent, or alternative embodiments. Those skilled in the art will understand that the embodiments herein can be combined with other embodiments without causing structural conflicts.

[0020] In this description, unless otherwise explicitly specified and limited, the technical terms "installation," "connection," "joining," etc., should be interpreted broadly, for example, referring to movable connections, fixed connections, or integration. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application based on the specific circumstances.

[0021] In this description, terms such as "upper," "lower," "left," "right," "lateral," "longitudinal," "height," "length," and "width," which indicate orientation or positional relationships, are intended to accurately describe the embodiments and simplify the description, rather than limiting the parts or structures involved to have a specific orientation, or to be installed or operated in a specific orientation, and should not be construed as limiting the embodiments in this document.

[0022] In this description, terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating relative importance or limiting the number, specific order, or primary / secondary relationship of the described technical features. In this description, "multiple" means at least two.

[0023] Venturi flow meters are widely used in fields such as petroleum, chemical, pharmaceutical, and nuclear engineering where fluid flow rate monitoring is required. Existing Venturi flow meters employ a fixed constriction taper, fixed throat diameter, and conventional linear flaring section design. Their structural parameters follow standardized values ​​from general national standards, typically only suitable for ordinary operating conditions. Under special extreme conditions, they still suffer from functional and reliability deficiencies. On one hand, under low flow rate conditions, the velocity increase when the medium flows through the fixed throat is small, resulting in low differential pressure signals before and after throttling and a poor signal-to-noise ratio. This makes it difficult for the differential pressure transmitter to accurately measure the differential pressure signal in the lower detection range, leading to severe distortion of measurement linearity and measurement errors exceeding ±5% under low load conditions. On the other hand, under high back pressure conditions, in conventional Venturi flow meters, the effective differential pressure formed by throttling is easily offset and suppressed by the high back pressure, causing the differential pressure difference between the high and low pressure taps to remain consistently low. The linear relationship between flow rate and differential pressure deviates from the calibration curve, resulting in large drift and fluctuations in measurement data and a decrease in measurement accuracy.

[0024] To overcome the aforementioned problems of the prior art, embodiments of the present invention provide a low-flow-rate, high-pressure flow meter. For example... Figure 1 As shown, the flow meter includes a straight section 1, a constricted section 2, a throat section 3, and a flared section 4. Compared to a conventional Venturi flow meter, this flow meter has undergone structural adjustments. First, the fixed taper of the constricted section's conical surface in a conventional Venturi flow meter is replaced with a gradually increasing taper. The taper gradually increases from the inlet to the outlet of the constricted section 2, with an inlet taper of 17°-19° (18° in a preferred embodiment) and an outlet taper of 21°-23° (22° in a preferred embodiment). In contrast, the taper of a conventional Venturi constricted section is typically fixed at 10°-15°. By steepening the conical wall of the constricted section, the accumulation of the medium during flow can be effectively accelerated, especially under low flow conditions, effectively increasing the flow velocity of the medium and thus increasing the basic differential pressure generation. Furthermore, the throat diameter of a conventional venturi tube is 0.5-0.6 times the nominal diameter of the pipe being measured, and its axial length is 1-1.5 times the throat diameter. This results in small velocity changes and insufficient differential pressure generation at low flow rates. In contrast, the effective diameter of throat section 3 is 0.35-0.45 times the nominal diameter of the pipe being measured, and its axial length is 2.5-3 times its own effective diameter. This elongated throat section effectively enhances the throttling and acceleration effect, generating a larger effective differential pressure value and improving signal strength even under low flow and high back pressure conditions. Simultaneously, the cone wall taper of the flared section 4 is 6°-8°, significantly smaller than the 7°-10° of a conventional venturi tube. This structure allows for a smooth and gradual release of the medium velocity, preventing pressure backflow in the flared section 4 from offsetting the throttling differential pressure under high back pressure conditions, thereby reducing differential pressure attenuation loss. In a preferred embodiment, curved equalizing rings are respectively provided circumferentially on the straight segment 1 and the throat segment 3.

[0025] The flow meter sets the high-pressure side pressure tap 5 in the straight section 1 near the inlet section of the constriction section 2, within the flat DC field of the undisturbed steady flow region, to accurately collect the original static steady pressure of the pipeline and avoid interference from the throttling flow field on the pressure. The low-pressure side pressure tap 6 is set at the axial center of the throat section 3 to maximize the collection of the lowest static pressure value of the throat and reduce the interference between the throttling flow field and the flow field of the flared section 4.

[0026] In a preferred embodiment, the flow meter uses a first pressure transmitter 7 connected to the high-pressure side pressure tap 5 and a second pressure transmitter 9 connected to the low-pressure side pressure tap 6 instead of the differential pressure transmitter in a conventional Venturi flow meter. The output device 8, which is connected to the signals of the first pressure transmitter 7 and the second pressure transmitter 9, reads the pressure at the high-pressure side pressure tap 5 and the low-pressure side pressure tap 6 respectively. Based on the difference between the measured pressure values, the flow rate value is further calculated and output. This effectively avoids the problem that the differential pressure is too low under low flow and high back pressure conditions, making it difficult for the differential pressure transmitter to read effective data.

[0027] Under certain operating conditions, the medium being tested may contain contaminants such as dust, particles, or viscous media, which can easily lead to flow meter blockage. In a preferred embodiment, to reduce the risk of blockage, the pressure tapping cross-section of the high-pressure side tapping point 5 is set to an elliptical shape, such as... Figure 2 As shown, the pressure tapping chamber adopts an flared structure, with the cross-sectional area increasing closer to the pipeline centerline. The equivalent diameter of the pressure tapping opening 11 is 8mm-12mm, and it is equipped with a rounded corner 12 to prevent impurities from accumulating on the wall. The pressure tapping chamber at the low-pressure side 6 adopts a constricted structure, with the cross-sectional area decreasing closer to the pipeline centerline. Its inlet diameter is 4mm-6mm, and its outlet diameter is 10mm-14mm, forming a self-cleaning flow guiding structure that allows impurities in the medium to be automatically flushed out with the fluid, preventing blockage of the pressure tapping holes. Furthermore, the inner wall of the flowmeter adopts a smooth polished structure. The constricted section 2 and the throat section 3 are connected by a transition arc structure, with the radius of the transition arc being 0.8-1.2 times the inner diameter of the throat section 3, to effectively eliminate dead zones and prevent impurity contamination and deposition.

[0028] According to the fluid mechanics formula for measuring throttling flow rate, Q=K A (Where Q is the volumetric flow rate of the medium, K is the flow coefficient, A is the throttling flow area of ​​the throat, ΔP is the differential pressure before and after throttling, and ρ is the density of the medium). The flow rate Q is proportional to the square root of the differential pressure ΔP. However, in conventional Venturi tubes, the throat flow area A is too large, the constriction taper is small, and under conditions where the flow rate Q is small, the velocity change is small, and the ΔP value is very low, making it difficult for the differential pressure transmitter to accurately acquire the signal. Under high back pressure conditions, the static pressure base of the pipeline foundation is large, and the effective throttling differential pressure ΔP is significantly offset, causing the actual result to deviate from the effective range of the above linear measurement formula. The flowmeter provided in this application, by designing the conical wall of the constriction section 2 as a gradually tapered structure with a larger taper, reduces the diameter of the throat section 3 and increases its axial length, effectively increasing the flow velocity v of the medium flowing through the throat section 3 under the same small flow rate Q. According to Bernoulli's equation... = (Where, P1 is the static pressure at the unthrottled section upstream of the pipe, P2 is the static pressure at the minimum cross-section of throat section 3, V1 is the average fluid velocity at the unthrottled section upstream of the pipe, and V2 is the average fluid velocity at the minimum cross-section of throat section 3.) As the velocity V2 increases, the static pressure P2 within throat section 3 decreases significantly, while P1 on the high-pressure side remains unchanged, resulting in a corresponding significant increase in the effective differential pressure ΔP. Under high back pressure conditions, the baseline ΔP generated by the basic throttling increases substantially, and the linear relationship between flow rate and differential pressure under low flow rate and high back pressure conditions can continue to remain stable, thus avoiding problems such as insufficient measurement accuracy and data drift.

[0029] Under low-flow, low-load conditions (below 10% of rated flow), the measurement error of a conventional Venturi flowmeter is ±(5.2-8.5)%, while that of a Bartholomew averaging pitot tube exceeds ±9%. The low-flow, high-pressure flowmeter provided in this embodiment of the invention has a measurement error of no more than ±1%, and the data linearity deviation normalization optimization ratio exceeds 87%. Under high-pressure conditions, the data drift fluctuation of a conventional Venturi flowmeter exceeds ±6%, while the data fluctuation amplitude of the low-flow, high-pressure flowmeter provided in this embodiment of the invention does not exceed ±0.8%, with a measurement stability normalization improvement of 85% and no data drift or distortion. Under the same low-flow conditions, the low-flow, high-pressure flowmeter provided in this embodiment of the invention generates an effective differential pressure value that is 2.8 to 3.5 times that of a conventional Venturi flowmeter, improving the differential pressure signal-to-noise ratio by more than 3 times. Under high back pressure conditions, the effective differential pressure retention rate exceeds 92%, far higher than the 55%-65% level of a conventional Venturi flowmeter, significantly enhancing the differential pressure's resistance to back pressure interference. Meanwhile, the low-flow high-pressure flow meter provided in this embodiment of the invention has an effective measurement range ratio of up to 1:50, which far exceeds that of conventional Venturi tube flow meters and Barrel flow meters (effective measurement range ratio of about 1:10-1:20). It can fully cover various operating conditions of deep peak shaving and low flow start-up and shutdown of the unit as well as full load, high flow, and high back pressure continuous operation, and the versatility of the diameter is significantly improved.

[0030] Furthermore, when operating continuously in media containing dirt and impurities, conventional Venturi flow meters and Barrel flow meters have an average clogging failure cycle of 15-30 days, requiring shutdown for cleaning; while the flow meter with anti-clogging design provided in this embodiment of the invention extends the failure cycle to more than 360 days under the same operating conditions, reduces the maintenance frequency by more than 90%, and the long-term measurement accuracy decay does not exceed 0.3%, basically achieving maintenance-free continuous operation.

[0031] The purpose of the above embodiments is to provide a further detailed description of the present invention in conjunction with the accompanying drawings, so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, optimization or equivalent substitution of the technical features involved, as well as combination of implementation methods in different embodiments without causing structural and principle conflicts, all fall within the protection scope of the present invention.

Claims

1. A low-flow-rate, high-pressure flow meter, comprising a straight section, a constricted section, a throat section, and a flared section connected in sequence, characterized in that, The conical wall of the constricted section adopts a gradual taper, with the taper gradually increasing from the inlet to the outlet of the constricted section. The taper at the inlet of the constricted section is 17°-19°, and the taper at the outlet of the constricted section is 21°-23°. The effective diameter of the throat section is 0.35 to 0.45 times the nominal diameter of the pipe being measured, and the axial length of the throat section is 2.5 to 3 times the effective diameter of the throat section. The taper of the conical wall of the flared section is 6°-8°.

2. The low-flow-rate high-pressure flow meter according to claim 1, characterized in that, The high-pressure side pressure tap is located on the straight section, and the flow field at the section where the high-pressure side pressure tap is located is a flat DC field; the low-pressure side pressure tap is located at the axial center of the throat section.

3. The low-flow-rate high-pressure flow meter according to claim 2, characterized in that, The pressure tapping section of the high-pressure side pressure tapping point is set to an ellipse, and the pressure tapping cavity is configured as a flared structure with an equivalent diameter of 8mm-12mm.

4. The low-flow-rate high-pressure flow meter according to claim 2, characterized in that, The pressure tapping chamber of the low-pressure side pressure tapping point is configured with a constricted structure, with an inlet diameter of 4mm-6mm and an outlet diameter of 10mm-14mm.

5. The low-flow-rate high-pressure flow meter according to claim 3 or 4, characterized in that, The pressure tapping openings of the high-pressure side pressure tapping point and the low-pressure side pressure tapping point adopt a rounded corner structure.

6. The low-flow-rate high-pressure flow meter according to claim 1, characterized in that, The constricted section and the throat section are connected by a transition arc, the radius of which is 0.8 to 1.2 times the inner diameter of the throat section.

7. The low-flow-rate high-pressure flow meter according to claim 1, characterized in that, The inner wall of the low-flow-rate high-pressure flow meter is smooth and polished.

8. The low-flow-rate high-pressure flow meter according to claim 2, characterized in that, It also includes a first pressure transmitter, a second pressure transmitter, and an output device. The output device is signal-connected to the first pressure transmitter and the second pressure transmitter, respectively. The first pressure transmitter measures the pressure at the high-pressure side pressure tap, and the second pressure transmitter measures the pressure at the low-pressure side pressure tap. The output device calculates and outputs the flow rate value based on the pressure difference measured by the first pressure transmitter and the second pressure transmitter.

9. The low-flow-rate high-pressure flow meter according to claim 1, characterized in that, The straight section and the outer periphery of the throat section are also provided with a bent tube type equalizing ring.

10. The low-flow-rate high-pressure flow meter according to claim 1, 2, or 8, characterized in that, The low-flow-rate high-pressure flow meter has a measurement error of no more than 1% under rated operating conditions, a data fluctuation range of no more than ±0.8%, and an effective differential pressure retention rate of no less than 92%.

Images