CN1023952C - Method for measuring flow and aridity of double-phase fluid containing steam (gas) and liquid - Google Patents

Abstract

The present invention provides a method for measuring the flow and the aridity of double-phase fluid containing steam (gas) and liquid according to the pulsation performance of double-phase fluid by a single throttling device and a pressure difference measuring instrument. The method can be used for measuring the double-phase fluid containing steam (gas) and liquid of high pressure, middle pressure and low pressure. A flow measuring error is smaller than 4%.

Description

Method for measuring flow and aridity of double-phase fluid containing steam (gas) and liquid

The present invention relates to a kind of flow and dryness factor measurement method of two phase fluid.

It is generally acknowledged flow and the mass dryness fraction of measuring two phase fluid, must adopt two covers or the above measurement instrument of two covers, i.e. multiple measurement instrument could realize.A kind of measurement instrument of two phase fluid is disclosed in CN85201644U, though it when measuring with an orifice plate as measuring sensor, but it still utilizes tested pipeline as another measuring sensor, and it still needs two cover differential pressure measurement instrument to realize the measurement of two phase fluid.The required instrument of multiple measurement is more, the cost height, expense is big, install complicated, utilize tested pipeline itself as measuring sensor, it is bigger that its shortcoming is that institute's pressure measurement difference is influenced by pipe roughness and caliber, and measuring accuracy is lower, and this method is not suitable for the measurement of high-pressure two-phase fluid, has therefore limited in industrial use.

The objective of the invention is to avoid above-mentioned weak point of the prior art, change multiple measurement instrument mode, and a kind of pulse characteristic measurement flow of two phase fluid and method of mass dryness fraction utilized is provided.Thereby make measurement instrument reduce half, and measuring accuracy is higher, can be used for the measurement of high, medium and low voltage vapour (gas)-liquid two phase fluid.

The present invention includes following several steps: 1. with a restriction device (profit in nozzle, orifice plate, the Venturi tube) as measuring sensor.2, utilize a pressure difference transmitter, the instantaneous differential pressure △ Pi that continuous coverage restriction device both sides are constantly changing in any a period of time; 3, constantly instantaneous differential pressure △ Pi signal is input in the microcomputer by pressure difference transmitter, and calculates the average pressure reduction △ P and the ripple amplitude △ B of two-phase fluid; 4,, utilize definite X of experimental technique and △ B/ △ P relation curve or its formula to try to achieve the mass dryness fraction x of two-phase fluid according to △ B/ △ P and hydrodynamic pressure P.5,, utilize Φ that experimental technique determines and △ B/ △ P relation curve or its formula to try to achieve Φ, and Φ and △ P substitution formula (1) are tried to achieve the total mass flow rate qm of two phase fluid according to △ B/ △ P and hydrodynamic pressure P.

${\mathrm{q\; m\; =\; 0.003998a\; d}}^2·\sqrt{\mathrm{△\; P}}·\sqrt{\mathrm{P\prime -\; \phi \; (\; P\prime \; -\; P\; ″)}}\mathrm{(\; 1\; )}$

In the formula:

The total mass flow rate of qm-two phase fluid (kg/h);

The a-coefficient of flow;

The opening diameter of restriction device (mm) under the d-duty;

The average pressure reduction of △ P-(Pa);

Density of liquid phase (kg/m in the two phase fluid under p '-duty ³);

P " vapour (gas) phase density (kg/m in the two phase fluid under the duty ³);

The average pressure reduction of △ P-(Pa);

Φ-average true volume void fraction, Φ and △ B/ △ P have certain functional relation under certain pressure, and its value can be determined by experimental technique.6, above-mentioned all processes is handled by microcomputer and automatic record.

Purpose of the present invention can also reach by following step:

Restriction device can be nozzle, orifice plate or Venturi tube, the restriction device of standard, off-gauge and other various opening shapes.

Microcomputer can be replaced by single board computer, one-chip computer and other processor.

Ripple amplitude △ B when flowing through restriction device in order to strengthen two phase fluid, at its upstream in the pipeline, install a vertical current to the arbitrary shape cross section column or the throttling element of shrinkage cavity is arranged.

The flow rate calculation formula also can be transformed to when practical application

${\mathrm{q\; m\; =\; 0.003998\; a\; d}}^2·\sqrt{\mathrm{△\; p}{}_{\mathrm{\rho \prime }}}·\sqrt{\mathrm{1\; ·}\frac{\mathrm{\rho \prime /\; p\prime ·1}}{\mathrm{p\prime /\; p\prime +\; c}}}\mathrm{(\; 2\; )}$

In the formula:

The total mass flow rate of qm-two phase fluid (kg/h);

C-is under certain pressure, and C and △ B/ △ P have certain funtcional relationship, and its value can be determined by experimental technique.

The drawing of accompanying drawing is described as follows:

Fig. 1 be the aperture of orifice plate than β=0.6 o'clock, X and the △ B/ △ P relation curve determined with experimental technique.

Fig. 2 be the aperture of orifice plate than β=0.6 o'clock, Φ and the △ B/ △ P relation curve determined with experimental technique.

Fig. 3 measures process flow diagram for the invention process.(1) flow of inlet water measuring diaphragm among the figure; (2) water inlet sample cock; (3) steam generator; (4) outlet sample cock; (5) steam-water separator; (6) pressure tap; (7) column; (8) restriction device; (9) high-pressure stop valve; (10) microcomputer.

In conjunction with the embodiments the present invention is further described.

Embodiment:

Use the flow and the steam quality of method MEASUREMENT OF STEAM-WATER two phase fluid of the present invention.

Fig. 3 measures process flow diagram for the invention process, restriction device is installed in the exit of steam generator, carbonated drink two-phase flow equals flow of inlet water, internal diameter of the pipeline D=67mm, restriction device is the sharp-edged aperture, orifice plate inner diameter d=40.2mm, the hole of orifice plate and the ratio beta of round tube inside diameter=0.6, the corner connection pressure, the column of a diameter of phi 14mm of tipping is to strengthen its ripple amplitude in the pipeline at 14D place, orifice plate upstream, select sensitivity and all higher 1151 pressure difference transmitters and 1151 pressure units of measuring accuracy to carry out the measurement of pressure reduction and pressure, before measuring pressure difference transmitter is transferred to minimum damping time.

Instantaneous differential pressure △ Pi and hydrodynamic pressure P are become the current signal of 4～20mA respectively by 1151 pressure difference transmitters and pressure unit, again through current/voltage conversion I/V, analog-digital conversion a/d, be input in the microcomputer, microcomputer is measured instantaneous differential pressure △ Pi once every 20～35 μ s, following data processing is done in continuous sampling 200 times, can obtain average pressure reduction △ P and ripple amplitude △ B.

$\mathrm{△\; P\; =}\frac{\underset{\mathrm{i\; =\; 1}}{\overset{\mathrm{200}}{\mathrm{\Σ}}}{\mathrm{△\; P}}_i}{\mathrm{200}}\mathrm{△\; B\; =}\sqrt{\frac{\underset{\mathrm{i\; =\; 1}}{\overset{\mathrm{200}}{\mathrm{\Σ}}}{\mathrm{(\; △\; P}}_i{\mathrm{-\; △\; P\; )}}^2}{\mathrm{200}}}$

△ B/ △ P and measured pressure P according to having tried to achieve check in Φ by Fig. 2, and with Φ and △ Pa substitution formula (1), can calculate the mass rate qm of carbonated drink two phase fluid.

△ B/ △ P and measured pressure P according to having tried to achieve directly check in steam quality x by Fig. 1.

After microcomputer is finished dealing with to data, can show and note flow qm, mass dryness fraction x and pressure P automatically.

Calculated example 1: known: average pressure reduction △ P=32055Pa

Ripple amplitude △ B=439Pa

Hydrodynamic pressure P=14.76MPa

Ask: the mass rate qm of carbonated drink two phase fluid and steam quality x.

The density p ' of water=608.3kg/m in the two phase fluid under the duty ³

Vapour density p "=93.8kg/m in the two phase fluid under the duty ³

Aperture diameter d=40.2mm

Coefficient of flow a=0.6618

According to △ B/ △ P=0.0137, p=14.76MPa checks in Φ=0.87 by Fig. 2

(1) the mass rate qm of calculating carbonated drink two phase fluid

${\mathrm{q\; m\; =\; 0.003998\; a\; d}}^2·\sqrt{\mathrm{△\; p}}·\sqrt{\mathrm{p\prime \; -\; \phi \; (\; p\prime -\; p\; ″\; )}}$

＝9702kg/h

Actual measurement steam generator flow of inlet water is 9750kg/h, relative error 0.5%.

(2) ask steam quality x

According to △ B/ △ P=0.0137, P=14.76MPa, directly checking in mass dryness fraction x=0.72 by Fig. 1 is 0.73 with the definite steam quality of assay method, and error is 1%.

Calculated example 2: known: average pressure reduction △

P=29324Pa ripple amplitude △

B＝1447Pa

Hydrodynamic pressure P=8.04MPa

Ask: the mass rate qm of carbonated drink two phase fluid and steam quality x.

The density p ' of water=722kg/m in the two phase fluid under the duty ³

Density the p "=42.8kg/m of steam in the two phase fluid under the duty ³

Aperture diameter d=40.2mm

Coefficient of flow a=0.6618

According to △ B/ △ P=0.0493, P=8.04MPa checks in Φ=0.85 by Fig. 2

(1) the mass rate qm of calculating carbonated drink two phase fluid

${\mathrm{q\; m\; =\; 0.003998\; <figure-callout\; id="2"\; label="ad"\; filenames="881052175\_DRIMG3.png"\; state="\{\{state\}\}">a\; d</figure-callout>}}^2·\sqrt{\mathrm{△\; p}}·\sqrt{\mathrm{p\prime \; -\; \phi \; (\; p\prime -\; p\; ″\; )}}$

＝8806kg/h

Actual measurement steam generator flow of inlet water is 8660kg/h, relative error 1.7%.

(2) ask steam quality x

According to △ B/ △ P=0.0493, P=8.04MPa, directly check in x=0.39 by Fig. 1, steam quality 0.34 its error of determining with assay method is 5%.

Method of the present invention only needs a differential pressure measurement instrument, is to use minimum a kind of, simple in structure of measurement instrument in the various two-phase flowmeters, low price, precision is higher, can measure in big pressure limit, but also can measure the flow and the pressure of monophasic fluid.

Claims (1)

1, a kind of method of utilizing each phase flow rate in mobile pulse characteristic MEASUREMENT OF STEAM (gas) liquid two-phase that is produced of phase fluid is characterized in that this method may further comprise the steps:

A. utilize the instantaneous differential pressure △ P of pressure difference transmitter, be input in the microcomputer,, obtain average pressure reduction △ P and ripple amplitude △ B and △ B/ △ P through data processing with the restriction device both sides.

B. according to the Φ=F under the different pressures P value of having demarcated out ₁(△ B/ △ P) and X=F ₂(△ B/ △ P) relation curve or its formula are tried to achieve Φ and fluid mass dryness fraction X,

C. resulting △ P and Φ substitution following formula are tried to achieve two-phase flow total mass flow rate q _m

$q_m\mathrm{=\; a\; ·\; \epsilon \; ·\; A\; ·}\sqrt{\mathrm{2\; △\; P}}·\sqrt{\mathrm{P\prime -\; \phi \; (\; P\prime \; -\; P\; ″)}}$

In the formula: q _m-two-phase fluid total mass flow rate (kg/s)

Coefficient of flow under the a-duty;

Expansion coefficient when ε-fluid flows through restriction device;

A-throttling element perforated area (m ²);

The average differential pressure of △ P-(Pa);

Density of liquid phase (kg/m in the two-phase fluid under P '-duty ³);

P " vapour (gas) phase density (kg/m in the two-phase fluid under the duty ³);

Φ-average true volume steam quality.

D. known X and q _mCan try to achieve each phase flow rate in vapour (gas) the liquid two-phase.

q″ _m=q _m·X

q′ _m=q _m(1-X)

In the formula:

Q " _m-vapour (gas) phase mass rate;

Q ' _m=liquid phase mass rate.

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