Background technology
Biphase gas and liquid flow extensively is present in commercial unit and the propulsion system, and void fraction is the important parameter in the diphasic flow research.Because it is a lot of to affect the factor of void fraction, situation is complicated, is difficult to calculate exact value by theoretical model, so still mainly rely at present the method for experiment to obtain void fraction.These methods commonly used comprise visual image method, sonde method, current method, quick-closing valve method etc., although wherein the quick-closing valve method can gather the average void fraction in a certain moment, but because the restriction of its method can not be carried out Real-time Collection to instantaneous average void fraction; Sonde method and visual image method all can only gather the Local Instantaneous void fraction, but can't obtain whole void fraction.The instantaneous void fraction of local average (hereinafter to be referred as burbling cavitation's share) is different from the instantaneous void fraction of ensemble average (hereinafter to be referred as whole void fraction), for example, in slug flow, when close and close with the shooting width of video camera when the length of gas bullet and liquid bullet, the value of burbling cavitation's share is near 0 or 1, and whole void fraction is near 0.5.Although under steady state condition, the time equal burbling cavitation's share and whole void fraction equate, under the pulsation operating mode, because burbling cavitation's share is along with flow constantly changes, so can not obtain by simple time averaging method.Although current method can be measured whole void fraction, be only applicable at present bubble flow.Therefore, need to set up a kind of method that can obtain average instantaneous void fraction under the pulsation operating mode.From published patent, existing method can not be obtained average instantaneous void fraction effectively and accurately, for example publication number is that CN1718999A, name are called in the patent document of " detection method of void fraction in a kind of biphase gas and liquid flow ", utilize sound spectrum resonance acoustic spectroscopy detection technique to detect the void fraction of oil field production profile logging, the method has easily and is disturbed, the shortcoming such as the measuring error of low discharge is large; Publication number is CN1967159A, name is called the patent document of " gas-liquid two-phase bubbly flow flow and gas volume fraction measuring method and device ", on the measuring tube tube wall in certain interval, the vortex shedding flow meter swirl generating body downstream that places gas-liquid two-phase bubbly flow, offer two tracting pressuring holes that are symmetrical in swirl generating body, measure differential pressure between these 2 with differential pressure pick-up, obtain respectively again frequency and the amplitude of this differential pressure signal through signal processing circuit, the last relevant correlation of substitution biphase gas and liquid flow calculates flow and the gas volume fraction of gas-liquid two-phase bubbly flow.Because of the use of the method based on vortex shedding flow meter, therefore be only applicable to the measurement of very fast flow velocity, the method is only applicable to the measurement of bubble flow in addition.
Summary of the invention
The object of the present invention is to provide a kind ofly can reach very high precision, the Local Instantaneous void fraction that utilizes convenient and swift, that applicability is strong obtains the method for whole instantaneous void fraction.
The object of the present invention is achieved like this:
Pressure, pressure reduction harvester are linked to each other with the tracting pressuring hole at duct survey section two ends, read pressure reduction, pressure and burbling cavitation's share raw data;
Burbling cavitation's share is composed as whole pipeline section is the initial value of measuring section void fraction, and calculated the true average velocity of gas phase;
The bubble that calculates in the whole pipeline section upstream portion by the true average velocity of gas phase that obtains will move to the needed time of burbling cavitation's share collection position, and perhaps the bubble in the downstream part has left the time that the void fraction collection position spends;
Utilize the described time to find corresponding void fraction data, these void fraction data calculation art mean values are obtained new whole void fraction, and judge: if the residual error of new and old void fraction is enough little, then new void fraction is the instantaneous void fraction of required integral body; If the residual error of new and old void fraction is undesirable, then with new void fraction assignment to the measuring section void fraction as new initial value, repeat said process and carry out iterative computation, until the residual error of the new and old void fraction of gained is enough little.
The present invention can also comprise:
1, the method for the true average velocity of described calculating gas phase is:
M wherein
gBe gas phase mass flow, A is that pipeline section is long-pending, and α is void fraction, ρ
gBe density of gas phase;
Wherein R is the gaseous state constant, and T is absolute temperature, P
InIt is the measuring section intermediate pressure; P
InDirectly measure acquisition by in the middle of measuring section, tracting pressuring hole being set; Perhaps P
InObtain in the following way: to same group of experiment condition, gather respectively measuring section pressure reduction and measuring section upstream pressure data with same differential pressure pickup, first pass gathers measuring section pressure reduction, is communicated with the pressure at measurement tracting pressuring hole place, upstream with atmosphere the differential pressure pickup low side is unloaded second time.Because the approximate linear distribution that is of the pressure between two tracting pressuring holes of measuring section, absolute pressure can be estimated as in the middle of the measuring section
P wherein
0Be atmospheric pressure, P
hBe the relative pressure in upstream tracting pressuring hole place, P
dBe the pressure reduction between two tracting pressuring holes, the advantage of estimating in this way pipeline pressure is need not be additionally again at measuring section punching and increase pressure collecting device, and shortcoming is that every group of operating mode need to gather respectively two secondary data.
2, describedly will move to the needed time of burbling cavitation's share collection position by the bubble in the true average velocity computation and measurement of the gas phase section upstream portion, perhaps the bubble in the downstream part has left the used time of void fraction collection position, utilize the time of trying to achieve to find in the corresponding void fraction data, the computing method of time are:
The upstream:
N is integer, and 1≤n≤(L-L
c)/2L
c
The downstream:
M is integer, and 1≤m≤(L-L
c)/2L
c,
Wherein n, m are numbering, are the segment numbers that the upstream portion of void fraction collecting device on the measuring section or downstream part are divided into some sections, L
cBe every section length, wherein Δ t is the time interval that void fraction gathers, and i is current time void fraction data number, the i that solves
xNamely be required certain section void fraction data number, if i
x+ 1 apart from n * L
cThe position is nearer, then selects i
x+ No. 1 void fraction is i
xOr i
x+ 1 representative share α of that section burbling cavitation constantly
nPerhaps α
m
3, each section void fraction data to finding, carry out integral mean or simplify after carry out arithmetic mean and obtain new whole instantaneous void fraction, its expression formula is:
Wherein int is the rounding operation symbol.
Involved pressure data among the present invention can also arrange that at the middle part of whole measuring section the pressure harvester obtains when arranging the pressure reduction harvester again.
Involved Local Instantaneous void fraction data among the present invention can also be to obtain by processing the data that other collecting devices such as probe gather.
The present invention is not only applicable to the acquisition of void fraction in the Steady Flow, also is applicable to the acquisition of void fraction in Periodic pulsing flow, UNSTEADY FLOW and the Multiphase Flow.
The invention has the beneficial effects as follows:
1, the present invention adopts the method for iterative computation, and is low to the raw data requirement, and under same raw data, the present invention can reach very high precision;
2, processing procedure of the present invention is simple, only needs raw data is read in computing machine, and computing machine can be processed automatically, and is convenient and swift;
3, the present invention can be applied to two-phase in the various situations and the calculating of polyphasic flow void fraction, applied range, and applicability is strong.
Embodiment
The invention will be further described below in conjunction with accompanying drawing institute example.
Biphase gas and liquid flow Local Instantaneous void fraction illustrates application process of the present invention as example in the pipeline to obtain by the visual image method:
1. obtaining of burbling cavitation's share: as shown in Figure 1, the length that the shooting function photographs is L
c, the distance between two tracting pressuring holes is L, then can be divided into (L-L to half of the whole measuring section of video camera updrift side
c)/2L
cSection, making the camera lens below is the 1st section, and being close to the mobile upstream portion of video camera is the 2nd section, and by that analogy, video camera upstream distal-most end is (L-L
c)/2L
cSection, then the bubble in the t moment i section is bound to appear at the video camera below through b after the time, if find this time b, just can find the constantly photo of correspondence of t+b, if supposing bubble volume in motion process is (hereinafter the further specifying) that does not change, the void fraction of then calculating by t+b moment photo is constantly corresponding void fraction of i section t.Same, the video camera downstream direction is also done identical processing.So, just can find the corresponding void fraction of each section, be constantly measuring section void fraction of t after being averaging.
In the pipeline pressure obtain calculating with the gas phase true velocity: for find t constantly each section will move to or leave time under the video camera, just need to know the true average velocity of t moment bubble motion, its expression formula is:
M in the formula
gBe gas phase mass flow, A is that pipeline section is long-pending, and α is void fraction, ρ
gBe density of gas phase.
From formula, can find out gas phase true velocity and two unknown quantity α and ρ
gRelevant, density of gas phase wherein
R is the gaseous state constant, and T is absolute temperature, P
InBe absolute pressure in the middle of the measuring section in the pipeline, P
InCan directly measure acquisition by in the middle of measuring section, tracting pressuring hole being set; P
InAlso can directly obtain in the following way: to same group of experiment condition, gather respectively measuring section pressure reduction and measuring section upstream pressure data with same differential pressure pickup, first pass gathers measuring section pressure reduction, be communicated with the pressure at measurement tracting pressuring hole place, upstream with atmosphere the differential pressure pickup low side is unloaded second time.Because the approximate linear distribution that is of the pressure between two tracting pressuring holes of measuring section, absolute pressure can be estimated as in the middle of the measuring section
P wherein
0Be atmospheric pressure, P
hBe the relative pressure in upstream tracting pressuring hole place, P
dBe the pressure reduction between two tracting pressuring holes, the advantage of estimating in this way pipeline pressure is need not be additionally again at measuring section punching and increase pressure collecting device, and shortcoming is that every group of operating mode need to gather respectively two secondary data.
Owing to distribute along duct orientation pressure approximately linear, so pipeline middle part pressure is average pressure in the pipeline, density is average density, so bubble motion is the average external volume of bubble in whole measuring section motion process to the volume at measuring section middle part, therefore suppose bubble in the measuring section pipeline in the motion process constancy of volume be rational.
3. the iterative computation of whole void fraction: the another one unknown quantity is constantly measuring section void fraction α of t in the gas phase true velocity calculating formula, and α is amount to be asked, and therefore need utilize the method for iteration to find the solution.As shown in Figure 2, at first read in pressure reduction, pressure and burbling cavitation's share data of utilizing the image processing to obtain, and the void fraction variable assignments in the algorithm is as initial value, calculate the true average velocity of gas phase according to these data, recycling gas phase true average velocity calculates each section will move to or leave time under the video camera, find corresponding burbling cavitation share, again these void fractions are averaged and obtain new measuring section void fraction, and judge: if the residual error of new and old void fraction is enough little, then new void fraction is required result; If the residual error of new and old void fraction is undesirable, then with new void fraction assignment to the void fraction variable as new initial value, and calculate, until the residual error of the new and old void fraction of gained is less than setting value next time.
Be subjected to the impact of bubble velocity and video camera capture rate, take the video camera upstream as example, the 2nd section is integer to n(n, and 1≤n≤(L-L
c)/2L
c) section may pass through video camera soon, and video camera capture less than, in addition, during computing time, can be with distance divided by speed under the permanent operating mode, but under the pulsation operating mode, change all the time owing to speed, should the row integral equation, its discrete form is:
(n is integer, and 1≤n≤(L-L
c)/2L
c)
Wherein Δ t is the time interval (video camera is taken photograph and is spaced apart 0.04 second in the application example of the present invention) of continuous two photos, and i is current time photo numbering.The i that solves
xNamely be required photo numbering, if i
x+ 1 apart from n * L
cThe position is nearer, then selects i
x+ 1 pictures, calculate void fraction be n section current time void fraction α
nBe averaging and can obtain new measuring section void fraction:
So iterate, when the void fraction results change was measuring section void fraction net result in enough hour.Figure 3 shows that the whole instantaneous average void fraction of gained after burbling cavitation's share and the program iterative computation 3 times, 10 times, 20 times, can find out the iterative computation through program, the degree of accuracy of acquired results improves constantly, and more can reflect the truth of whole measuring section void fraction.
Above-mentioned description to embodiment is that the researchist for the ease of this technical field can understand and apply the invention.Be familiar with the researcher in this field and obviously can easily make various modifications to these embodiment, and the conventional method of this explanation is applied among other embodiment, for example the present invention, slightly makes to change the method and is equally applicable to come computation and measurement section void fraction by burbling cavitation's share that sonde method obtains as embodiment with the visual image method.Therefore the invention is not restricted to the embodiment here, by prompting of the present invention, all should be within protection scope of the present invention to improvement and modification that the present invention makes.