CN101881640A - Vortex mass flow meter - Google Patents

Abstract

The invention discloses a vortex mass flow meter, comprising a measuring tube, a vortex generating body arranged in the measuring tube and a flow detection element. The measuring tube is composed of an inlet section, a contraction section, a throat part, an extension section and an outlet section which are connected in sequence, the inlet section and the outlet section are straight round tubes with the same diameters, the contraction section and the extension section are conical tubes with the same conical degrees, and the throat part is a straight round tube the inner diameter of which is smaller than that of the inlet section; and the vortex generating body and the flow detection element are both arranged on the throat part of the measuring tube. In the invention, the contraction section is used for adjusting flow field and improving flow speed, the extension section is used for restoring the tube diameter contracted by the contraction section, and the contraction section and the extension section can improve the pressure loss of the measuring loss. By installing the vortex generating body and the flow detection element on the throat part of the measuring tube, due to the acceleration action when flow passes through the contraction section, the lower limit flow value of a meter can be greatly reduced and the measuring range of the meter can be improved by measuring the flow at the throat part.

Description

Mass flowmeter for vortex street

Technical field

The present invention relates to the mass flowmeter for vortex street technical field, more particularly, particularly a kind of mass flowmeter for vortex street of wide-range.

Background technology

Vortex shedding flow meter is mainly used in the flow measurement of industrial pipeline medium fluid, as multiple media such as gas, liquid, steam.Be characterized in that the pressure loss is little, range ability is big, the precision height.No moving machinery part, so reliability height, maintenance is little.The instrument parameter can be steady in a long-term.Having the mock standard signal that digital pulse signal output is also arranged, easily and the supporting use of digital display circuit such as computing machine, is a kind of more advanced, desirable flowmeter.Vortex shedding flow meter then alternately produces the two row vortexs that well-regulated its frequency is proportional to flow velocity from vortex generation body both sides by triangular prism vortex generation body is set in fluid, obtain the volume flow value by the frequency of measuring whirlpool.

Present vortex shedding flow meter all adopts straight pipe to make the measuring tube of flowmeter when measuring mass rate, before and after vortex generation body, get differential pressure signal, owing to only depend on vortex generation body to produce differential pressure signal, cause its differential pressure value lower, then differential pressure value is lower when measuring low discharge, so the lower limit flow of flowmeter can not be too little, the range ability of flowmeter is wide inadequately.

Summary of the invention

In view of this, the invention provides a kind of mass flowmeter for vortex street, one of to solve the problems of the technologies described above.

For achieving the above object, the invention provides following technical scheme:

A kind of mass flowmeter for vortex street, comprise: measuring tube, be arranged on the eddy generator and the flow detecting element of described measuring tube inside, differential pressure pick-up and flow converter, be arranged on the described measuring tube and lay respectively on the described eddy generator, the upstream pressure tappings in downstream and downstream pressure tappings, the upstream pressure tappings links to each other with described differential pressure pick-up by the pressure pipe with the downstream pressure tappings, described measuring tube is by the entrance that links to each other successively, contraction section, throat, expansion segment and outlet section are formed, entrance is the identical straight pipe of diameter with outlet section, contraction section is the identical conical tube of tapering with expansion segment, and throat is the straight pipe of internal diameter less than the entrance internal diameter;

Described eddy generator and flow detecting element all are arranged on the throat of described measuring tube.

Preferably, in the above-mentioned mass flowmeter for vortex street, described upstream pressure tappings and downstream pressure tappings are separately positioned on the entrance and the outlet section of described measuring tube.

Preferably, in the above-mentioned mass flowmeter for vortex street, described upstream pressure tappings is arranged on 1/2nd places of the entrance axial length of described measuring tube;

Described downstream pressure tappings is arranged on 1/2nd places of the outlet section axial length of described measuring tube.

Preferably, in the above-mentioned mass flowmeter for vortex street, also comprise the rectifying frame that is installed on the described expansion segment.

Preferably, in the above-mentioned mass flowmeter for vortex street, described rectifying frame is the flow-guiding structure of cruciform or groined type.

Preferably, in the above-mentioned mass flowmeter for vortex street, the length of described rectifying frame on fluid flow direction to be measured is the diameter of bore of 0.5-0.8 entrance doubly.

Preferably, in the above-mentioned mass flowmeter for vortex street, the ratio of the internal diameter of described entrance and the internal diameter of described throat is greater than 1 and be not more than 2.6.

Preferably, in the above-mentioned mass flowmeter for vortex street, this mass flowmeter for vortex street is an integral structure.

From technique scheme as can be seen, mass flowmeter for vortex street provided by the invention is formed by measuring tube being designed quinquepartite, be that entrance is the identical straight pipe of diameter with outlet section, contraction section is the identical conical tube of tapering with expansion segment, and throat is the straight pipe of internal diameter less than the entrance internal diameter.The effect of contraction section is to adjust the flow field and improve flow velocity, and the effect of expansion segment is that the contracted caliber of convergent section is returned to original caliber.Contraction section and expansion segment can both improve the pressure loss of measuring tube.By eddy generator and flow detecting element all being arranged on the throat of measuring tube,, improve the range ability of flowmeter because fluid through the accelerating effect of contraction section, so measure flow in throat, can effectively reduce the lower limit flow value of flowmeter.

Description of drawings

In order to be illustrated more clearly in the embodiment of the invention or technical scheme of the prior art, to do to introduce simply to the accompanying drawing of required use in embodiment or the description of the Prior Art below, apparently, accompanying drawing in describing below only is some embodiments of the present invention, for those of ordinary skills, under the prerequisite of not paying creative work, can also obtain other accompanying drawing according to these accompanying drawings.

The structural representation of the measuring tube that Fig. 1 provides for the embodiment of the invention;

The structural representation of the mass flowmeter for vortex street that Fig. 2 provides for the embodiment of the invention;

The electrical principle block diagram of the flowmeter that Fig. 3 provides for the embodiment of the invention;

The structural representation of the rectifying frame that Fig. 4 provides for the embodiment of the invention;

Fig. 5 is the side view of Fig. 4.

Embodiment

The invention discloses a kind of mass flowmeter for vortex street,, improve the range ability of flowmeter to reduce the lower limit flow value of flowmeter.

Below in conjunction with the accompanying drawing in the embodiment of the invention, the technical scheme in the embodiment of the invention is clearly and completely described, obviously, described embodiment only is the present invention's part embodiment, rather than whole embodiment.Based on the embodiment among the present invention, those of ordinary skills belong to the scope of protection of the invention not making the every other embodiment that is obtained under the creative work prerequisite.

See also Fig. 1, the structural representation of the mass flowmeter for vortex street that the structural representation of the measuring tube that Fig. 2, Fig. 1 provide for the embodiment of the invention, Fig. 2 provide for the embodiment of the invention.

Wherein, 1 is entrance, and 2 is contraction section, 3 is throat, and 4 is expansion segment, and 5 is outlet section, 6 is eddy generator, and 7 is flow detecting element, and 8 is rectifying frame, 9 is ring flange, and 10 is the upstream pressure tappings, and 11 is the downstream pressure tappings, 12 is upstream pressure pipe, 13 is downstream pressure pipe, and 14 is differential pressure pick-up, and 15 is flow converter.

Mass flowmeter for vortex street provided by the invention, comprise: measuring tube, the eddy generator 6 that is arranged on described measuring tube inside and flow detecting element 7, differential pressure pick-up 14 and flow converter 15, be arranged on the described measuring tube and lay respectively at the upstream pressure tappings 10 and the downstream pressure tappings 11 of described eddy generator 6 upstream and downstream, upstream pressure tappings 10 links to each other with described differential pressure pick-up 14 with downstream pressure pipe 12 by upstream pressure pipe 12 respectively with downstream pressure tappings 11.Wherein, measuring tube is made up of the entrance 1, contraction section 2, throat 3, expansion segment 4 and the outlet section 5 that link to each other successively, and entrance 1 is the identical straight pipes of diameter with outlet section 5, and their the internal diameter all inside nominal diameter D with flowmeter is identical.Contraction section 2 is the identical conical tube of tapering with expansion segment 4.Throat 3 is that one section internal diameter is D ₁Straight pipe, be connected with the outlet of contraction section 2 and the inlet of expansion segment 4 respectively, constitute the symmetric figure structure, eddy generator 6 and flow detecting element 7 all are arranged on the throat 3 of measuring tube.Contraction section 2 is that diameter is narrowed down to D from D ₁Conical tube, expansion segment 4 is from D diameter ₁Expand the conical tube of D to.

The effect of contraction section 2 is to adjust the flow field and improve flow velocity.The effect of expansion segment 4 is the contracted caliber D of convergent section ₁Return to original caliber D.Contraction section 2 and expansion segment 4 can both improve the pressure loss of measuring tube.The present invention is by all being arranged on eddy generator 6 and flow detecting element 7 throat 3 of measuring tube, because fluid makes the flow velocity at the rate of flow of fluid unit rate of flow meter mouth place of the throat that flows through improve (D/D through the accelerating effect of contraction section ₁) ²Doubly.So measure flow in throat, can effectively reduce the lower limit flow value of flowmeter, improve the range ability of flowmeter.

Upstream pressure tappings 10 and downstream pressure tappings 11 are separately positioned on the entrance 1 and the outlet section 5 of described measuring tube.Preferably, upstream pressure tappings 10 is arranged on 1/2nd places of entrance 1 axial length of described measuring tube; Downstream pressure tappings 11 is arranged on 1/2nd places of outlet section 5 axial lengths of described measuring tube.By differential pressure pick-up 14 differential pressure signal is converted to electric signal, be sent to another input end of flow converter 15, carry out signal Processing and computing.

Measuring process of the present invention: fluid enters contraction section 2 with flow velocity U from entrance 1, because the speed-raising effect of contraction section 2, when fluid was flowed through contraction section 2, flow velocity was brought up to U from U ₁, and U ₁(D/D for U ₁) ²Doubly.Fluid is with higher flow velocity U ₁Enter throat 3 from contraction section 2.Be provided with vortex generation body 6 and flow detecting element 7 in throat 3.Along with flowing of fluid, vortex generation body 6 produces Karman vortex streets, and vortex signal is detected by flow detecting element 7, and is transported to flow converter 15 and handles.When fluid is flowed through measuring tube,, cause the pressure loss of fluid owing to the throttling action of contraction section 2, throat 3, expansion segment 4.

Locate at the entrance 1 of measuring tube and the centre position of outlet section 5, be provided with upstream pressure tappings 10 and downstream pressure tappings 11,, take out the flow through front end of measuring tube and the pressure differential of rear end by upstream pressure pipe 12 and downstream pressure pipe 13, be pressure loss Δ P, deliver to differential pressure pick-up 14.Through differential pressure pick-up 14, measure differential pressure signal, deliver to another input end of flow converter 15 and handle.

Two paths of signals obtains mass rate through the conversion process and the computing of converter 15.The electrical principle block diagram of flowmeter as shown in Figure 3.

The present invention is in the differential pressure measurement link, in order to obtain stable differential pressure, in downstream pressure tappings 11 the place aheads, rectifying frame 8 has been installed at the rear portion of expansion segment 4, the fluid that contains vortex that flows out from throat is carried out rectification, adjust the flow field, eliminate the disturbance of vortex, reduce the pressure surge at downstream pressure tappings 11 places, improve the degree of stability of differential pressure.This rectifying frame 8 is the flow-guiding structure of cruciform or groined type.As Fig. 4, shown in Figure 5, according to the latus rectum difference of flowmeter, rectifying frame can be selected 0.5 millimeter corrosion resistant plate manufacturing to 1.5 millimeters thick for use.Rectifying frame 8 is treating that the length on the flow direction of fluid measured is (0.5-0.8) D (D is the inside nominal diameter of flowmeter, i.e. the internal diameter of entrance 1).

The present invention is by changing shrinkage ratio D/D ₁Or the method for the coning angle of contraction section 2 changes, regulates the range ability of flowmeter.Shrinkage ratio can be according to the inside nominal diameter D of flowmeter, and the minimum stream value of detected fluid is selected to determine.Usually the span of shrinkage ratio is: 1＜D/D ₁≤ 2.6.

The present invention adopts integral structure, with the measuring tube of flowmeter, and vortex generation body 6, flow detecting element 7, differential pressure pick-up 14, flow converter 15 is designed to one, has characteristics such as integrated intelligent.

The present invention has used the discharge characteristic and the drag characteristic of vortex shedding flow meter, by measuring the pressure loss of vortex signal frequency and flowmeter, realizes the measurement of mass rate.It is wide that this flowmeter has range ability, no movable member, reliability height, easy for installation, characteristic such as the Applicable media type is many.It can measure the mass rate of fluid, also the volumetric flow rate of measurable flow body.Flowmeter can be widely used in the flow measurement of gas in the industries such as metallurgy, electric power, chemical industry, oil, rock gas, light industry, liquid, steam etc.

The discharge characteristic of flowmeter

The axial section of the measuring tube of flowmeter as shown in Figure 1.The flow measurement buret is by entrance 1, contraction section 2, and throat 3, expansion segment 4, outlet section 5 is formed.Entrance 1 and outlet section 5 are that diameter is the straight pipe of D; Throat is that diameter is D ₁Straight pipe; Contraction section is that diameter is narrowed down to D from D ₁Conical tube; Expansion segment is from D diameter ₁Expand the conical tube of D to.

When fluid was flowed through measuring tube throat 3, the vortex generation body 6 that is installed in throat 3 produced Karman vortex street, and the flow detecting element 7 that the vortex signal is installed in throat detects.Vortex frequency f is:

$f=\mathrm{<figure-callout\; id="1"\; label="Sr\; U"\; filenames="HSA00000166483900011.png,HSA00000166483900012.png"\; state="\{\{state\}\}">Sr</figure-callout>}\frac{U_{}}{}\frac{{}_1}{\mathrm{md}}---\left(1\right)$

According to the fluid continuity principle, the flow velocity U of measuring tube entrance 1 and the flow velocity U of throat 3 ₁The pass be:

${\mathrm{<figure-callout\; id="1"\; label="U"\; filenames="HSA00000166483900011.png,HSA00000166483900012.png"\; state="\{\{state\}\}">U</figure-callout>}}_1={\left(\frac{D}{D_1}\right)}^{2}U---\left(2\right)$

So: $f=\mathrm{Sr}\frac{U}{\mathrm{md}}{\left(\frac{D}{D_1}\right)}^2---\left(3\right)$

More than in two formulas:

The f-vortex frequency, Hz;

The Sr-Strouhal number;

D-vortex generation bulk properties width, m;

The circulation area of body both sides and the ratio of throat's area of a circle take place in m-;

U ₁-throat mean flow rate, m/s;

The mean flow rate of U-flowmeter entrance and outlet section, m/s;

D ₁-throat diameter, m;

D-entrance and outlet section diameter (flowmeter inside nominal diameter), m.

The drag characteristic of flowmeter

When fluid was flowed through measuring tube, because the throttling action of contraction section 2, expansion segment 4 and the vortex generation body 6 of measuring tube, the pressure loss that causes fluid was Δ P, and Δ P is made up of three parts:

ΔP＝ΔP ₁+ΔP ₂+ΔP ₃ (4)

In the formula: Δ P ₁The pressure loss of-contraction section 2, Pa;

Δ P ₂The pressure loss of-throat 3, Pa;

Δ P ₃The pressure loss of-expansion segment 4, Pa.

Each section pressure loss is respectively:

${\mathrm{\&Delta;P}}_1=\frac{1}{2}{\mathrm{<figure-callout\; id="1"\; label="C\; D"\; filenames="HSA00000166483900011.png,HSA00000166483900012.png"\; state="\{\{state\}\}">C</figure-callout>}}_D{\mathrm{\&rho;<figure-callout\; id="1"\; label="U"\; filenames="HSA00000166483900011.png,HSA00000166483900012.png"\; state="\{\{state\}\}">U</figure-callout>}}_1^2=\frac{1}{2}{\mathrm{<figure-callout\; id="1"\; label="C\; D"\; filenames="HSA00000166483900011.png,HSA00000166483900012.png"\; state="\{\{state\}\}">C</figure-callout>}}_D\mathrm{\&rho;}{\left(\frac{D}{D_1}\right)}^4{U}^2---(5-1)$

${\mathrm{\&Delta;P}}_2=\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="C\; D"\; filenames="HSA00000166483900012.png"\; state="\{\{state\}\}">C</figure-callout>}}_D{\mathrm{\&rho;<figure-callout\; id="1"\; label="U"\; filenames="HSA00000166483900011.png,HSA00000166483900012.png"\; state="\{\{state\}\}">U</figure-callout>}}_1^2=\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="C\; D"\; filenames="HSA00000166483900012.png"\; state="\{\{state\}\}">C</figure-callout>}}_D\mathrm{\&rho;}{\left(\frac{D}{D_1}\right)}^4{U}^2---(5-2)$

${\mathrm{\&Delta;P}}_3=\frac{1}{2}{\mathrm{<figure-callout\; id="3"\; label="C\; D"\; filenames="HSA00000166483900012.png"\; state="\{\{state\}\}">C</figure-callout>}}_D{\mathrm{\&rho;U}}^2---(5-3)$

In the formula: C _D1-contraction section resistance coefficient;

C _D2-throat resistance coefficient;

C _D3-expansion segment resistance coefficient.

Flowmeter loss of total pressure Δ P is:

$\mathrm{\&Delta;P}=\frac{1}{2}[C_{D1}{\left(\frac{D}{D_1}\right)}^4+C_{D2}{\left(\frac{D}{D_1}\right)}^4+C_{D3}]{\mathrm{\&rho;<figure-callout\; id="2"\; label="U"\; filenames="HSA00000166483900012.png"\; state="\{\{state\}\}">U</figure-callout>}}^2=\frac{1}{2}{C}_D{\mathrm{\&rho;U}}^2---\left(6\right)$

From (6) formula as can be known, the total drag coefficients C of flowmeter _DFor:

$C_D=C_{D1}{\left(\frac{D}{D_1}\right)}^4+C_{D2}{\left(\frac{D}{D_1}\right)}^4+{\mathrm{<figure-callout\; id="3"\; label="C\; D"\; filenames="HSA00000166483900012.png"\; state="\{\{state\}\}">C</figure-callout>}}_D.---\left(7\right)$

Mass rate

, can obtain after arrangement divided by (3) formula with (6) formula:

$\mathrm{\&rho;U}=\frac{2\mathrm{Sr}}{C_D\mathrm{md}}{\left(\frac{D}{D_1}\right)}^2\frac{\mathrm{\&Delta;P}}{f}---\left(8\right)$

Mass rate q _mFor:

$q_m=\frac{\mathrm{\&pi;}}{4}{\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="HSA00000166483900012.png"\; state="\{\{state\}\}">D</figure-callout>}}^2\mathrm{\&rho;U}=\frac{\mathrm{\&pi;}{\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="HSA00000166483900012.png"\; state="\{\{state\}\}">D</figure-callout>}}^2\mathrm{Sr}}{{2C}_D\mathrm{md}}{\left(\frac{D}{D_1}\right)}^2\frac{\mathrm{\&Delta;P}}{f}=K_m\frac{\mathrm{\&Delta;P}}{f}---\left(9\right)$

Make (9) formula K _mBe mass flow coefficient, then:

$K_m=\frac{{\mathrm{\&pi;<figure-callout\; id="2"\; label="D"\; filenames="HSA00000166483900012.png"\; state="\{\{state\}\}">D</figure-callout>}}^2\mathrm{Sr}}{{2C}_D\mathrm{md}}{\left(\frac{D}{D_1}\right)}^2---\left(10\right)$

In (9) and (10) formula:

q _m-mass rate, kg/s;

K _m-mass flow coefficient.

Mass rate q as can be seen from (9) formula _mP is directly proportional with pressure loss Δ, and f is inversely proportional to vortex frequency.Because other amount in the formula all is known quantitative really,, just can realize the measurement of mass rate as long as therefore measure pressure loss Δ P and vortex frequency f.

To the above-mentioned explanation of the disclosed embodiments, make this area professional and technical personnel can realize or use the present invention.Multiple modification to these embodiment will be conspicuous concerning those skilled in the art, and defined herein General Principle can realize under the situation that does not break away from the spirit or scope of the present invention in other embodiments.Therefore, the present invention will can not be restricted to these embodiment shown in this article, but will meet and principle disclosed herein and features of novelty the wideest corresponding to scope.

Claims (8)

1. mass flowmeter for vortex street, comprise: measuring tube, be arranged on the eddy generator and the flow detecting element of described measuring tube inside, differential pressure pick-up and flow converter, be arranged on the described measuring tube and lay respectively on the described eddy generator, the upstream pressure tappings in downstream and downstream pressure tappings, the upstream pressure tappings links to each other with described differential pressure pick-up by the pressure pipe with the downstream pressure tappings, it is characterized in that, described measuring tube is by the entrance that links to each other successively, contraction section, throat, expansion segment and outlet section are formed, entrance is the identical straight pipe of diameter with outlet section, contraction section is the identical conical tube of tapering with expansion segment, and throat is the straight pipe of internal diameter less than the entrance internal diameter;

Described eddy generator and flow detecting element all are arranged on the throat of described measuring tube.

2. mass flowmeter for vortex street according to claim 1 is characterized in that, described upstream pressure tappings and downstream pressure tappings are separately positioned on the entrance and the outlet section of described measuring tube.

3. mass flowmeter for vortex street according to claim 2 is characterized in that, described upstream pressure tappings is arranged on 1/2nd places of the entrance axial length of described measuring tube;

Described downstream pressure tappings is arranged on 1/2nd places of the outlet section axial length of described measuring tube.

4. mass flowmeter for vortex street according to claim 1 is characterized in that, also comprises the rectifying frame that is installed on the described expansion segment.

5. mass flowmeter for vortex street according to claim 4 is characterized in that, described rectifying frame is the flow-guiding structure of cruciform or groined type.

6. according to claim 4 or 5 described mass flowmeter for vortex street, it is characterized in that the length of described rectifying frame on fluid flow direction is the diameter of bore of 0.5-0.8 entrance doubly.

7. mass flowmeter for vortex street according to claim 1 is characterized in that, the ratio of the internal diameter of described entrance and the internal diameter of described throat is greater than 1 and be not more than 2.6.

8. mass flowmeter for vortex street according to claim 1 is characterized in that, this mass flowmeter for vortex street is an integral structure.

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