CN1595072A - Vertex mass and flow measuring method - Google Patents

Abstract

This invention provides a vortex quality measurement method, which is the following: to open a press get hole in the upper part of the vortex generator 1/2D-D in the vortex flow meter and to open another hole in the down part of the vortex generator within1/2D; then to measure the pressure difference between the upper hole and the down hole by the pressure difference sensor; to divide the output pressure difference signals into two paths , wherein, one is to get the average value of the pressure difference as DeltaP and the other is to measure the wave frequency f of the pressure difference signals and after the division between these two value the result multiplies the relative meter parameter and directly get the quality flow. This invention is of simple structure and the output signals is only relative to the flow quality and the meter parameters is free of the impact of the temperature, pressure, component, viscidity and density and is applied to the quality flow measurement of the gas flow and liquid flow and steam.

Description

The vortex mass flow measuring method

Technical field

The present invention relates to a kind of vortex mass flow measuring method.

Background technology

In the prior art, in the industrial circles such as petrochemical complex, metallurgy, machinery, light textile, pharmacy, the flow metering of liquid, gas, steam generally can only obtain volumetric flow rate with conventional flowmeter survey, and mass rate often can only obtain in conjunction with temperature, pressure compensated mode by volumetric flow rate.But relation is complicated nonlinear relationship between the density of fluid and temperature, pressure, is difficult to represent with the simple mathematical relation, so this compensation method meeting produces bigger error.In addition, utilize the vortex street occurring principle in addition, adopt piezoelectric sensor and differential pressure pick-up to measure the pressure that fluid flows through behind the vortex shedder respectively and fall and the vortex street frequency, obtain mass rate.But this method needs multisensor, complex structure, and the piezoelectric sensor shock resistance is poor simultaneously, is difficult to overcome fully the influence of vibrations when industry spot is used.

Summary of the invention

The purpose of this invention is to provide a kind of vortex mass flow measuring method.

Upstream at the vortex shedder of vortex shedding flow meter The place opens a pressure port, in the downstream of vortex shedder In open another pressure port, measure the differential pressure of vortex shedder upstream and downstream with differential pressure pick-up, the differential pressure signal of output divides two-way, one the tunnel gets the mean value of differential pressure, obtain pressure and fall Δ P, the vibration frequency f of another drive test amount differential pressure signal is after both are divided by, be multiplied by relevant instrument coefficient again, can directly obtain mass rate.

The present invention is a kind of direct measurement to mass rate, simple in structure, no movement parts, output signal is only relevant with the fluid mass flow, and instrument coefficient is not subjected to the influence of temperature, pressure, composition, viscosity and the density of fluid, have characteristics such as accuracy of measurement height, applied range, long service life, can be used for the mass flow measurement of gas, liquid and steam.

Description of drawings

Fig. 1 is a vortex mass flow measuring principle synoptic diagram;

Fig. 2 is that fluid is flowed through behind the vortex shedder along the pressure-plotting of duct wall in the pipeline;

Fig. 3 is the fluid Pressure Fluctuation Signal figure behind the vortex shedder that flows through in the pipeline;

Fig. 4 is to be that vortex mass flow is measured correlate meter coefficient curve figure in the 50mm pipeline at diameter.

Embodiment

Upstream at the vortex shedder of vortex shedding flow meter

The place opens a pressure port, in the downstream of vortex shedder In open another pressure port, measure the differential pressure of vortex shedder upstream and downstream with differential pressure pick-up.The differential pressure signal of output divides two-way, and one the tunnel gets the mean value of differential pressure, obtains pressure and falls Δ P, and the vibration frequency f of another drive test amount differential pressure signal after both are divided by, is multiplied by relevant instrument coefficient again, can directly obtain mass rate.

The measuring principle of mass rate is as follows:

As shown in Figure 1, in fluid line, insert the vortex shedder of definite shape, after fluid flows through the generation body, the vortex that the body both sides can replace generation rule is taking place, claim again " vortex street ".Through deriving, satisfy following relation between vortex street frequency f and the rate of flow of fluid v:

$f=S_t\×\frac{v}{d}---\left(1\right)$

S in the formula _tBe Sr, d is the effective width that vortex shedder is met flow path direction.

Simultaneously, fluid can produce pressure in the upstream and downstream that body takes place and fall after flowing through body taking place, Δ p,

$\stackrel{\‾}{\mathrm{\Δp}}=\frac{1}{2}{C}_P{\mathrm{\ρv}}^2---\left(2\right)$

C in the formula _PBe pressure coefficient, ρ is a fluid density.

(1) formula obtains after divided by (2):

$\frac{\stackrel{\‾}{\mathrm{\Δp}}}{f}=\frac{C_{P}d}{2\mathrm{St}}\left(\mathrm{\ρv}\right)---\left(3\right)$

Because St and C _PBe constant in certain reynolds number range, d is the width of vortex shedder, also is constant, so Δ p/f is proportional to ρ v.

Mass rate Q _mFundamental equation be:

Q _m＝Aρv (4)

A is the sectional area of fluid line in the formula.Compare (3) formula and (4) formula, can get:

$Q_m=K_m\frac{\stackrel{\‾}{\mathrm{\ΔP}}}{f}---\left(5\right)$

In the formula, K _mBe the mass flow coefficient of instrument, promptly instrument coefficient is constant, can measure by experiment.

As long as measure the differential pressure signal of vortex shedder upstream and downstream, therefrom obtain vortex street frequency values f and the fluid pressure that body takes place of flowing through and fall Δ p, just can obtain mass rate.

Utilize above-mentioned principle to measure mass rate, in the specific implementation, also will consider the pressure position of differential pressure signal, with the measuring accuracy of the flow of ensuring the quality of products.Different pressure positions can obtain different measurement results.

Calculating through numerical simulation, is under 50mm and the different in flow rate condition at pipe diameter, and along the pressure distribution of duct wall as shown in Figure 2, vortex shedder is positioned at the x=0.1mm place.As seen from the figure, in the upstream of vortex shedder

The place, it is constant that force value keeps substantially, in this position pressure, can obtain flow through original pressure signal before the vortex shedder of fluid.After fluid flow through the generation body, pressure descended fast, after body takes place

The place, pressure falls and reaches maximum, and pressure in this position can guarantee that enough pressure falls.Under identical flow conditions, the Pressure Fluctuation Signal result of calculation of diverse location as shown in Figure 3.Body takes place after In, pressure has the undulatory property of rule, and frequency stabilization has been crossed

After, it is unstable that the undulatory property of pressure can become.Therefore, from measuring the angle of vortex street frequency, body also should be after taking place in the position of downstream pressure point In.

To different pipe diameters, the different fluid medium also calculates.Comprehensive various result of calculation is thought the upstream of pressure position at vortex shedder

The place reaches the downstream at vortex shedder

In, can guarantee that enough pressure falls, the undulatory property of vortex and measure linear degree preferably.

By above-mentioned measuring method, be in the pipeline of 50mm at diameter, with water medium, carry out actual measurement, the result is as shown in Figure 4.As seen from the figure, mass rate and Δ p/f have the better linearity relation, and the slope of straight line is instrument coefficient.Therefore, by the method, can record mass rate easily.

Claims (3)

1, a kind of vortex mass flow measuring method is characterized in that: in the upstream of the vortex shedder of vortex shedding flow meter The place opens a pressure port, in the downstream of vortex shedder

In open another pressure port, measure the differential pressure of vortex shedder upstream and downstream with differential pressure pick-up, the differential pressure signal of output divides two-way, one the tunnel gets the mean value of differential pressure, obtain pressure and fall Δ P, the vibration frequency f of another drive test amount differential pressure signal is after both are divided by, be multiplied by relevant instrument coefficient again, can directly obtain mass rate.

2, a kind of vortex mass flow measuring method according to claim 1 is characterized in that: said upstream and downstream pressure position: the upstream pressure port with the distance that the body fluoran stream surface takes place is

The downstream pressure port should be less than or equal to the distance that the body fluoran stream surface takes place

3, a kind of vortex mass flow measuring method according to claim 1, it is characterized in that: said differential pressure pick-up is single differential pressure pick-up, can realize the measurement of mass rate, differential pressure pick-up requires to have the dynamic response characteristic that can record the vortex street frequency.

Images