CN104897737A - Gas holdup measuring method for eight-electrode rotary electric field-type conductivity sensor - Google Patents

Abstract

The invention relates to a gas holdup measuring method for an eight-electrode rotary electric field-type conductivity sensor. The adopted sensor comprises four pairs of electrodes which are uniformly distributed on the same cross section on the inner wall of a pipe wall; electrodes in each pair are opposite to each other. The method comprises the following steps: exerting sinusoidal signals, of which the initial phases are different, on the four pairs of electrodes respectively for excitation, wherein the phase difference between every two adjacent electrodes is 45 degrees, so that a rotary measurement electric field can be generated on the cross section; collecting the output signal of the sensor when a gas-phase fluid and a liquid-phase fluid pass through the sensor; calculating the normalized conductivity of the rotary electric field-type conductivity sensor; calculating the gas holdup according to the normalized conductivity of the rotary electric field-type conductivity sensor. The method has the advantages that the measurement is relatively accurate; the structure is simple.

Description

Eight electrode rotary Electric field conductivity sensor gas holdup measuring methods

Art

The invention belongs to fluid measurement technical field, relate to a kind of conductivity sensor.

Background technology

Two-phase flow phenomenon is extensively present in the traditional industries such as petroleum engineering, chemical engineering, metallurgical engineering, nuclear engineering, Aeronautical And Astronautical Engineering and infant industry field.Biphase gas and liquid flow refers to the mixed flow system of gas phase and liquid phase Incompatible Substance.Owing to there is the difference in the physical property such as density, viscosity between composition each in biphase gas and liquid flow, under the impact of the factors such as flow, pressure, gravity and pipeline shape, cause biphase gas and liquid flow flow parameter measurement very difficult.Cross section gas holdup is an important flow parameter in biphase gas and liquid flow commercial Application system, its accurate measurement for production run metering, control and operational reliability all significant.

Two-phase flow gas holdup measuring technique mainly comprises ultrasonic method, optical method, rays method, capacitance method, conductance method etc.Because conductivity sensor has the plurality of advantages such as clear principle, structure is simple, response is stable, be widely used in polyphasic flow parameter measurement, early stage in sensor research and development, many employings plate electrode measures thickness of liquid film, in order to avoid the disturbance of sensor convection, the ring electrode sensor embedding upward vertical tube road inwall arises at the historic moment, such as annular electro derivative sensor, to wall type ring-type conductivity sensor.And adopt one direction excitation to receive to wall type ring-type conductivity sensor, there is limitation in Electric Field Distribution directivity, be subject to flow pattern impact.In order to address this problem, the people such as M.Merilo are at " Void fraction measurementwith arotating electric field conductance gauge " (Journal ofHeatTransfer, 1997, Vol 99, P330) rotating electric field formula conductometry is proposed, producing wheel measuring electric field by being applied to respectively by three-phase alternating current on three pairs of electrodes arranging around tube wall to synthesize, eliminating the measuring error that flow media skewness causes to a certain extent.However, first whether first three wheel measuring electric field produced electrode synthesis is that optimum measurement mode fails to provide demonstration from theoretical analysis and experimental verification angle.

Summary of the invention

For the problems referred to above, the object of this invention is to provide a kind of measurement comparatively accurately and the two-phase flow gas holdup measuring method of simple possible, technical scheme of the present invention is as follows:

A kind of eight electrode rotary Electric field conductivity sensor gas holdup measuring methods, the sensor adopted comprises the four pairs of electrodes be evenly distributed on the same cross section of inner-walls of duct, and often pair of electrode position is positioned opposite; If four pairs of electrodes are followed successively by A, B, C and D, A and B is adjacent, and B and C is adjacent, and C and D is adjacent, and D and A is adjacent.Following method is adopted to carry out gas holdup measurement:

(1) encourage the sinusoidal signal that four pairs of electrodes apply initial phase different respectively, the phase differential between adjacent electrode is 45 °, thus can synthesize the measurement electric field producing and rotate on cross section;

(2) when gas-liquid two-phase fluid flows through sensor, pick-up transducers outputs signal;

(3) the normalized conductance rate G of fluid-mixing is defined _efor the conductivityσ of mixed phase _mwith full electrical conductivity of water σ _wratio, the normalized conductance of eight electrode rotary Electric field conductivity sensors is defined as the mean value calculation normalized conductance value of four pairs of electrode normalized conductances, calculates rotating electric field conductivity sensor normalized conductance

(4) rotating electric field conductivity sensor normalized conductance is utilized calculate gas holdup.

Preferably, conductivity sensor gas holdup measuring method, is characterized in that, Electrode opening angle θ is 22.5 °.Electrode axis is 0.004m to height H, and electrode radial thickness T is 0.001m.

The eight electrode rotary Electric field conductivity sensor gas holdup measuring methods that the present invention proposes, rotating electric field is produced to synthesize respectively to the sinusoidal excitation signal four pairs of electrodes applying phase 45 degree, and pair cross-section measurement electric field has carried out sensitivity theory analytical calculation, determine eight electrode optimum geometry parameters, to reach best cross section gas holdup measurement effect.Have the following advantages:

(1) the rotating electric field formula conductivity sensor that the present invention relates to has that version is simple, fast response time, and stability is high, is convenient to advantages such as installing and measuring.

(2) gas holdup mensuration of the present invention, centering low flow velocity biphase gas and liquid flow gas holdup is measured and all can be used, and calculates simple, and accuracy is higher.

(3) gas holdup mensuration of the present invention is applicable to the gas holdup measurement that vertical gas liquid two-phase bubble flow, slug flow and mixed shape flow down.

Accompanying drawing explanation

Fig. 1 is rotating electric field formula conductivity sensor geometric parameter schematic diagram: (a) stereographic map; (b) sectional view; (c) front elevation

Fig. 2 is rotating electric field formula conductivity sensor energisation mode schematic diagram.

Fig. 3 is rotating electric field formula conductivity sensor finite element fission structural drawing.

Fig. 4 is that biphase gas and liquid flow three kinds of flow patterns four couples of electrode signal figure, (a) (b) (c) are respectively bubble flow, slug flow, mixed shape stream.

Fig. 5 tests plate between the aqueous phase flow demarcated of air and liquid twophase flow experiment measurement data normalized conductance value and analogue means and gas phase flow rate.

Fig. 6 biphase gas and liquid flow gas holdup measurement effect figure.

Embodiment

Below in conjunction with drawings and Examples, the present invention is described in detail.

Feature of the present invention is the structural dimension optimization by sensor, pipeline section produces and measures sensitivity field comparatively uniformly, and the structure of biphase gas and liquid flow rotating electric field formula conductivity sensor of the present invention and dimensionally-optimised and measuring method comprise the following steps:

The ring-like conductivity sensor structure of (1) eight electrode pair wall as shown in Figure 1, is made up of four pairs of stainless steel electrodes.As shown in Figure 2, encourage the sinusoidal signal that four pairs of electrodes apply initial phase different respectively, A is 0 °, and B is 45 °, and C is 90 °, and D is 135 °, can synthesize the measurement electric field producing and rotate like this on cross section.

(2) the present invention adopts Finite Element Method to be optimized sensor construction size, utilizes simulation software ANSYS to set up rotating electric field formula conductivity sensor model, as shown in Figure 3.During modeling, setting upward vertical tube road internal diameter D=0.02m, upward vertical tube road length L=0.2m, electrode radial thickness T, electrode axis to height H, Electrode opening angle θ, aqueous phase resistivity δ _w=1000 Ω m, electrode resistance rate δ _s=1.7241e-8 Ω m.Adopt free partition patterns to carry out stress and strain model, during imposed load, adopt sinusoidal excitation.Emulation mode is: when ANSYS modeling, measures bead cross section being put into a diameter 0.5mm in a model, and simulated bubble moves.When bead is in diverse location, the voltage of exciting electrode also follows change, therefore by the sensitivity of the voltage reflection conductivity sensor of exciting electrode change.Bead often converts a coordinate, can calculate the Sensitirity va1ue at this coordinate.By the coordinate of bead traversal all positions, cross section, upward vertical tube road, obtain this sensitivity profile to electrode.

The present invention adopts checkout area homogeneity error parameter (SVP) and sensor relative sensitivity (S _avg) as optimization aim.Sensor relative sensitivity (S _avg) implication refer to and be defined as the mean value of all positions, cross section relative sensitivity:

$S_{\mathrm{avg}}=\frac{1}{M}\underset{j=1}{\overset{M}{\mathrm{\Σ}}}{S}_j$

The homogeneity error parameter (SVP) that cross section is measured in definition is:

$\mathrm{SVP}=\frac{S_{\mathrm{dev}}}{S_{\mathrm{avg}}}\×100\%$

In formula, S _devfor measuring the standard deviation of the relative sensitivity of diverse location on cross section, it is defined as:

$S_{\mathrm{dev}}={\left(\frac{1}{M}\underset{j=1}{\overset{M}{\mathrm{\Σ}}}{(S_j-S_{\mathrm{avg}})}^2\right)}^{1/2}$

Obviously, S _avgvalue is larger, and represent that transducer sensitivity is higher, SVP value is less, and namely homogeneity error is less.

Single factor test shift process is adopted to be optimized design.Only change one of them factor, all the other are fixed, and experiment of then progressively arranging in pairs or groups is compared, and the arranging scheme obtained, is called single factor alternate method, are also isolated factor method.

First, fixed electorde subtended angle θ and electrode radial thickness T, changes electrode axis to height H, homogeneity error parameter (SVP) and sensor relative sensitivity (S _avg) as shown in the table.Can find out, when electrode axis is 0.004m to height H, the distribution character of sensitivity field is best.Therefore, electrode axis is fixed as 0.004m to height H.

Then, fixed electorde axial height H and electrode radial thickness T, changes Electrode opening angle θ, homogeneity error parameter (SVP) and sensor relative sensitivity (S _avg) as shown in the table.Can find out that the distribution character of sensitivity field is best when Electrode opening angle θ is 22.5 °.Therefore, Electrode opening angle θ is fixed as 22.5 °.

Finally, fixed electorde subtended angle θ and electrode axis, to height H, change electrode radial thickness T, homogeneity error parameter (SVP) and sensor relative sensitivity (S _avg) as shown in the table.Can find out that the distribution character of sensitivity field is best when electrode radial thickness T is 0.001m.Therefore, electrode radial thickness T is fixed as 0.001m.

By being optimized the sensor size, can obtain sensor optimized parameter is: Electrode opening angle θ is fixed as 22.5 °, and electrode axis is fixed as 0.004m to height H, and electrode radial thickness T is fixed as 0.001m.Now, S _avgbe 75.9804%, SVP be 0.2172.

Also the emulation of sensitivity field has been carried out to six electrode rotary Electric field conductivity sensors (structure that M.Merilo proposes) simultaneously, its optimized parameter is that Electrode opening angle θ is fixed as 30 °, electrode axis is fixed as 0.003m to height H, and electrode radial thickness T is fixed as 0.001m.Its S _avgbe 66.1191%, SVP be 0.2768.Can find out, eight electrode rotary Electric field conductivity sensors are all better than six electrode structures from sensitivity intensity or homogeneity aspect, therefore, and final selection eight electrode structures.

(3) be arranged on the vertical rising oil gas liquid phase stream pipeline that caliber is 20mm by eight electrode rotary Electric field conductivity sensors of design, when gas-liquid two-phase fluid flows through sensor, pick-up transducers outputs signal.Biphase gas and liquid flow gas holdup experiments of measuring verification method, its process is: experiment selects fluid media (medium) to be water and air from the beginning, select industrial peristaltic pump and air pump to carry out the conveying of aqueous phase and gas phase respectively, fixing gas phase velocity of flow adjust aqueous phase flow rate is to obtain different operating mode proportionings.The flow of setting aqueous phase and gas phase also passes in upward vertical tube road simultaneously, after the flow state of two-phase flow is stable, gathers conductivity sensor signal.

Obtain the method measuring normalized conductance value as follows:

The normalized conductance rate G of definition fluid-mixing _efor the conductivityσ of mixed phase _mwith full electrical conductivity of water σ _wratio, expression formula is:

$G_e=\frac{{\text{\σ}}_m}{{\mathrm{\σ}}_w}=\frac{V_m}{V_w}$

Wherein, σ _mand σ _wconductivity during conductivity and the pure water of fluid-mixing respectively, V _mthe measuring voltage of sensor often pair electrode, V _wthe measuring voltage of sensor when being pure water.Rotating electric field conductivity sensor normalized conductance is defined as the mean value of four pairs of electrode normalized conductances, is defined as:

$G_e^{*}=\frac{1}{4}(G_e^A+G_e^B+G_e^C+G_e^D)$

Wherein, the normalized conductance value of A phase, B phase, C phase, D phase electrode respectively.

(4) experimental verification and result: Fig. 4 gives the measuring-signal of three kinds of flow patterns (bubble flow, slug flow, load in mixture stream) lower sensor, can see from signal, there is a little difference in synchronization four pairs of electrode signals, this is caused by flow media non-uniform Distribution.Be averaged the measuring-signal of four pairs of electrodes and ask for normalized conductance value, this addresses this problem to a certain extent preferably, also can reflect the flow characteristics of biphase gas and liquid flow better simultaneously.The normalized conductance value of biphase gas and liquid flow measurement result with experimental correlogram version between aqueous phase flow and gas phase flow rate as shown in Figure 5.Can find out, normalized conductance value has satisfied susceptibility and resolution characteristic to gas phase content.

Gas holdup y under utilizing quick-closing valve to record each operating mode in experiment _g, utilize least square method to obtain biphase gas and liquid flow gas holdup and measure statistical model:

$y_g^{\mathrm{Pre}}=-0.982G_e^{*2}+0.091G_e^{*}+0.799$

Gas holdup measurement effect as shown in Figure 6, through adding up rotating electric field conductivity sensor biphase gas and liquid flow gas holdup measurement result mean absolute error is 0.023.

Claims (3)

1. eight electrode rotary Electric field conductivity sensor gas holdup measuring methods, the sensor adopted comprises the four pairs of electrodes be evenly distributed on the same cross section of inner-walls of duct, and often pair of electrode position is positioned opposite; If four pairs of electrodes are followed successively by A, B, C and D, A and B is adjacent, and B and C is adjacent, and C and D is adjacent, and D and A is adjacent.Following method is adopted to carry out gas holdup measurement:

(1) encourage the sinusoidal signal that four pairs of electrodes apply initial phase different respectively, the phase differential between adjacent electrode is 45 °, thus can synthesize the measurement electric field producing and rotate on cross section;

(2) when gas-liquid two-phase fluid flows through sensor, pick-up transducers outputs signal;

(3) the normalized conductance rate Ge defining fluid-mixing is the conductivity of mixed phase and the ratio of full electrical conductivity of water, the normalized conductance of eight electrode rotary Electric field conductivity sensors is defined as the mean value calculation normalized conductance value of four pairs of electrode normalized conductances, calculates rotating electric field conductivity sensor normalized conductance;

(4) rotating electric field conductivity sensor normalized conductance is utilized to calculate gas holdup.

2. conductivity sensor gas holdup measuring method according to claim 1, is characterized in that, Electrode opening angle θ is 22.5 °.

3. conductivity sensor gas holdup measuring method according to claim 1, is characterized in that, electrode axis is 0.004m to height H, and electrode radial thickness T is 0.001m.