IE903435A1 - A method and a device for the mass flow measurement in a¹multiphase flow channel - Google Patents

Abstract

The invention relates to a method and an arrangement for mass-flow measurement in a duct (1), in which a multi-phase or multi-component flow prevails, the speed (V) and density ( delta ) being measured and the mass flow being calculated from these. According to the invention, the density is measured in two measuring planes (I, II) succeeding one another in the direction of flow, by means of photon-absorption measurement on the tomography principle, and the speed is derived from the local density measurement values by correlating the measurements in the two measuring planes.

Description

The invention relates to a method and a device for the mass flow measurement in a channel, in which there is a multiphase or multicomponent flow, whereby the speed and the density are measured and the mass flow is computed therefrom.

The mass flow measurement of currents consisting of fluids is necessary in many industrial processes. The mass flow in a cross-section S is defined by the following formula: m = g . v . S, in which is the density, v the flow speed and S the crosssectional area. The mass flow measurement thus requires the measurement of the density and the speed.

Difficulties arise when these measurement values vary locally or in time, as it is the case for multiphase or multicomponent flows .

In the book Measuring Technique in Gas-Liquid Two-Phase Flows by J.M. Delhaye and G. Cognet, published by Springer Verlag 1984, pages 435 to 454, a method for the mass flow measurement in two-phase flows is described, which relies on a magnet spin resonance method. This method is only suited for substances with polarizable molecules and moreover has not yet overcome the test stage. or example the . 17, by T.R. Coriolis force in a vibrating Further, it has already been proposed (see f book Mass flow measurements, 1984, FED vol Hedrick and R.M. Reimer, page 75) to use the for the measurement of the mass flow because - 2 tube system, the bending of the Coriolis force, is proportional such a method is not suited for tube, which is induced by the to the mass flow. However, two-phase flows.

Finally, reference is made to an essay in the journal Atomkernenergie/Kerntechnik, vol. 33, 1979, pages 139 to 143, in which it is proposed to measure the speed of the individual phases of the fluid by different markings of the fluid components with radio nuclides. However, in many cases, the use of radioactive substances needed therefor is not accepted.

It is thus device for with respe assembly , ing means . the aim of the invention the mass flow measuremen ct to the known methods a reliability in operation to propose a method and a t which are distinguished nd devices by a simple and the use of non-pollutThis aim is attained, as far as the method is concerned, in that the density in two measurement planes disposed one behind the other in flow direction is measured by means of a photon absorption measurement according to the tomographic principle and that the speed is deduced from the local density measurement values by correlation of the measurements in the two measurement planes.

As far as the device for implementing this method is concerned, reference is made to the corresponding claims.

The invention will now be explained more in detail with refer30 ence to the drawings .

Figur 1 shows schematically a device according to the invention cut along the axis of the flow channel.

The figures 2a and 2b show two cut views orthogonally to the - 3 representation according to figure 1 along the two measurement planes .

Figure 3 shows a variant to figure 1.

According to the method according to the invention, the mass flow is deduced from the measurement of the flow spee?d and density at different points in the flow cross-section according to the formula mentioned above. The density values are obtained by means of the gamma radiation or any other photon absorption measurement and evaluated for the different points according to the analysis method known from tomography. As to the local speed values, they are deduced by correlation measurements from the mentioned density measurements, which are carried out at two measurement planes disposed one behind the other in flow direction.

In figure 1 there is shown a rectilinear flow which the mass flow to be measured flows along successively through two measurement planes I disposed perpendicularly to the axis 3 of the distance between the two measurement planes is channel 1 , in an arr ow Zi and II wh ich are channel • The taken to be d.

Figure 2a shows a cross-section through the arrangement ac25 cording to figure 1 along the measurement plane I, and figure 2b along the measurement plane II.

In the measurement plane are disposed, whereas in system is disposed.

I, two identical measurement the measurement plane II one systems such a gamma 5’, 5 beams 8 , 9 Each system includes a source 4, 4' and 4 which emits radiation or other photon radiation. By collimators 5, respectively 6, 6', 6 in each measurement system three 7, 8, 9 respectively 7', 8', 9' or respectively or 7, - 4 are created which, beyond the channel 1, hit detectors 10, 11, respectively or 10', 11', 12' respectively or 10, 11, 12. The first measuring system constituted by the elements 4 to 6 and 10 to 12 is disposed in the first measuring plane I substantially perpendicularly to the second measuring system constituted by the elements 4' to 6' ands 10' to 12', and the beams 7, 8, 9 constitute with the beams 7', 8', 9' a matrix of nine crossing points in the channel in which the local density of the mass flow is measured according to the tomographic principle. To this end, a computer with corresponding software (not shown) is used which is fed with the digitalized detector signals .

The third measuring system constituted by the elements 4 to 6 and 10 to 12 which is disposed in the measuring plane II, is assembled and disposed in the same way as one of the measuring systems in the first measuring plane, namely the system with the elements 4' to 6' and 10' to 12'. Because of this, the signals of these two systems show partially identical informations, since characteristical stochastic density patterns in the fluid successively pass through both measuring planes .

Likewise, between the signals of the detectors 10, 11, 12 and those of the detectors 10, 11 and 12 there are partially correlated signals. In this case, the identity of the information is however limited to the crossing points, which are defined between these two beam systems when projecting the two measuring planes onto each other.

By detail ed correlation analysis of the measurement signals from the two measurement planes I and II the speed of the flow can be determined at the same points distributed over the channel cross-section in the form of a matrix. By this evalua35 tion of the measurement signals of the two planes the time - 5 delay of characteristical common patterns in the signals of the two measurement planes can be determined and thus the speed of the flow at said crossing points in consideration of the distance d between the two measurement planes can be def i5 ned.

The mass flow according to the formula cited above is then computed not from the mean density and speed values over the entire cross-section, but as the sum of the local mass flow values at said crossing points, which, as mentioned above, is proportional to the density and to the speed at the respective matrix point. This evaluation system leads to substantially more precise results, than if firstly the mean density and the mean speed were evaluated.

Figure 3 shows a variant to figure 1, in which the two measurement planes I and II are inclined towards each other like a saddle roof, a common photon source 4”' being disposed at the ridge line. The collimators 5' and 5 are here combined in one common colimator 5' which thus includes respectively three passage channels for the radiation in each of the planes I and II. The distance between the two measurement planes is no more constant in this case, like in the case of figure 1, but since the measurements of the density and the speed are local measu25 rements at predefined points of the measurement planes, for which respectively the value d is known from the geometrical disposition, also in this case the local mass flow values and therefrom the entire mass flow can be precisely computed.

Besides, the figures 2a and 2b can be interpreted in the same way as images cut through the measurement planes I and II according to figure 3.

The invention is not limited in detail to the embodiments shown and explained. Thus, more than three beams can emerge - 6 from each source, so that the matrix of the measurement points in the channel cross-section has more than three lines and columns. As a photon source, apart from a gamma source also an X-ray source or a similar radiation source can be used. The two measurement systems in the measurement plane I need not be perpendicular to each other; it is sufficient if the beams are disposed in such a way that they define a matrix of crossing points well distributed over the cross-section of the channel.

Further, a second measurement system can be disposed in the measurement plane IT, so that even in this plane there are two systems like in plane I, see figure 2a. In this case, however, the two beam systems in each system must geometrically coincide with respect to a projection of the two measuring planes onto each other. Although this embodiment with a total of four beam systems is more complicated than that of figure 2b, it has the advantage of a higher reliability due to the additional signal informations.

Claims (6)

1. A method for the mass flow measurement in a channel, in which there is a multiphase or multicomponent flow, whereas the speed and the density are measured and the mass flow is computed therefrom, wherein the density is measured in two measurement planes disposed one behind the other in flow direction by means of a photon absorption measurement according to the tomographic principle and the speed is deduced from the local density measurement values by correlation of the measurements in the two measurement planes.

2. A device for implementing the method according to claim 1, wherein in a first measurement plane of the channel, two 15 measuring systems consisting of respectively one photon source, a collimator and a detector assembly are disposed in such a way that respectively at least three beams in this first measurement plane run through the channel, which hit the detectors beyond the channel, the beams of one measuring 20 system intersecting those of the other measuring system at points distributed in this common plane in the form of a matrix, in the second measuring plane of the channel, at least one further measuring system is disposed which consists of a photon source, a further collimator and further detectors in 25 the same geometrical disposition as one of the measuring systems in the first measurement plane, and a processing apparatus is provided which evaluates measurement signals of the detectors tomographically and in a correlating way. for implementing the method according to claim 1, a first measurement plane of the channel, two systems consisting each of a photon source, a and a detector assembly, are disposed in such a way tively at least three beams radiate in this first plane of the channel, which plane is inclined to

3. A device wherein in measurement collimator that respec measurement the axis of the channel, said beams hitting beyond the channel the detectors of the corresponding detector assembly, these beams of the one measurement system intersecting those of the other measurement system at points which are dis tributed in this common measurement plane in the form of a matrix, the second measurement plane is inclined with respect to the channel axis in such a way that a common photon source disposed at the intersection line of both planes feeds this measurement system in the second measurement plane as well, as one of the two measurement systems of the first measurement plane, and a processing apparatus is provided, which evaluates the measurement signals of the detectors tomographically and correlatingly.

4. A device according to one of claims 2 to 3, wherein the processing apparatus is a programm controlled digital computer .

5. A device according to one of claims 2 to 4, wherein the collimators are built up in such a way that at least three beams emerge from each photon source in a measurement plane.

6. A device according to any preceding claim substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.