SU877331A1 - Mass flow meter - Google Patents

Description

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The invention relates to a measurement technique and can be used to measure the instantaneous and / or total mass flow rate of gases or superheated vapors and automatically maintain a given value of flow.

A mass flow meter is known that contains a volume flow sensor and a density sensor made in the form of a capacitor formed by two semicircular fixed (sector) plates placed on the surface of a hollow dielectric drum rotating between fixed plates and periodically changing its capacitance.

The capacitance value of a capacitor is measured by a capacitive bridge, in the measuring diagonal of which a voltage occurs modulated with the drum rotation frequency, and the amplitudes (maximum and minimum) of this voltage are determined by the dielectric constant of the substance in the flow, i.e. its density P.

Closest to the present invention, there is a flow meter consisting of four identical capacitive transducers electrically connected in pairs for measurements of volumetric flow rate and gas density. The transducers are made in the form of multilayer flat capacitors, included in the working, and compensating shoulders of two automatic measuring quasi-balanced transformer bridges, measuring, respectively, the volume flow of the flowing flow;

15 and its density. The reversible electric motors of these transformer bridges are connected to resistive converters that are included in the projectile arms of an automatic

20 bridge resistor analog multiplier 2.

The known flow meter has an insufficient accuracy of measurement due to the influence of pressure losses at the inlet and outlet of the flat channels of the flow-through capacitor, as well as a rather complicated structure. The purpose of the invention is to improve the measurement accuracy while simplifying the design. The goal is achieved by the fact that in a mass flow meter containing volume flow and density sensors consisting of multi-plate capacitors are included in the shoulders of the measuring transformer of bridges, and an analog bridge multiplier, the capacitors of the volume flow sensor are arranged in series in the flow channel, and shortened plates are installed in series with guard electrodes, a density sensor capacitor is installed in the flow channel, and part of its plates are shortened Protective electrodes are installed at the inlet and outlet of the capacitor and the gap between the density capacitor plates is determined by the formula asobEo §0 is the dielectric permeability of the vacuum; the capacitance of the capacitor of the density sensor in vacuum J b and EO the gap between the plates, the width and length of the shortened plates of the densifier of the density sensor; and the gaps between the plates of the capacitors of the density and volume flow sensors are selected from the ratio H2 / n, Iar / ay, where H.,: gj., -. - The gap between the plastics of the capacitor of the volumetric flow sensor a J Qn and (1 is the gas flow through the capacitors of the density and volumetric flow sensors J is the capacitance of the capacitor of the volumetric flow sensor in a vacuum. In this case, a capacitor variable capacity. In Fig. 1 shows a flow meter sensor, a longitudinal section; Fig. 2 is a view A in Fig. 1; Fig. 3 is a section B-B in Fig. I in Fig. 4 is a section B-B in Fig. 1 ; in Fig. 5 a section of the GG in Fig. 2j in Fig. 6, the circuit of measuring transformer skeleton and bridge multiplier; Fig. 7 shows diagrams of single slotted flow channels measuring, volume flow density and density capacitors, as well as graphs of changes in flow pressure in them (ct and 5, respectively). The flow meter sensor (Fig. 1) consists of a set of flat tubes 1-P rectangular plates placed in rectangular cut-outs of flanges 12. The latter are welded to the cylindrical body 13. Plates 1-5 and 7-1.0 are covered on all sides with an electrical insulating layer of material with very low conductivity and wettability (for example, fluoroplastic. Plates 6 and 11 are made of stainless steel. Plates 2-5, as well as 9, 7, 10 are arranged successively one after the other. The plates and 8 have the same length equal to the length of these groups of plates 2-5 and 9, 7, 10. The groups of plates 9, 7, 10 and the plates and 8 are arranged so that the gaps between them and the plates 6 and II are several times smaller, than the gaps between the groups of plates 2-5 and plates I and 6. All groups of plates 2-5, as well as 9, 7, 10 together with plates I, 8, 6, II form flat long slots, in which the laminar flow regime is established medium supplied (and discharged to the sensor through flanges 14 and conical nozzles 15. Flanges 14 are given to conical nozzles 15 and to flanges 16, which are using bolts 17, nuts 18 through a fluoroplastic gasket 19 are tightly attached to flanges 12 of housing 13. The sensor is connected by flanges t4 to a pipeline (not shown, which carries the measured gas (superheated steam). The flow of the measured gas in the sensor flows into direction A. In the rectangular cut-outs of the flanges 12 (Fig. 2, carrier plates 20 are located, having from the inner side facing the flow, longitudinal grooves 21 and 22, into which the corresponding plates 1-5 and 7-10 are covered with fluoroplastic and thereby electrically isolated nye grounded by the carrier plates 20. The latter, moreover, vtolneny grooves 23 in; which are inserted metal plates 6, dividing the cross section of the flow part of the sensor into three flow channels. Plates 1–5 are placed in the central channel, and plates 7–10 are located in the peripheral channel. The faces of the plates 20 also have grooves 2A, in which metal plates 11 are placed, which are tightly attached (for example by soldering) to the plates 20.

Plates 1-5, 7-10, 6 and 11 and 20 are fixed in the flanges 12 from the longitudinal displacement of the fluoroplastic by gaskets 19 (FIG. 1) and the flanges 16 also having rectangular notches, but their internal dimensions are smaller than the sizes of the rectangular notches. flanges 12 for the thickness of the plates 11 and 20. The length of the plates 2 and 9 is determined by the limiting value of the Reynolds criterion so that the laminar flow regime stabilizes on it with the formation of a parabolic shape velocity in the narrow interjacent plates. These plates are grounded. Similarly, plates 5 and 10 are of such length that a non-linear pressure drop takes place on it due to output losses. These plates are also grounded.

Plates 3 and 4 have the same length and are arranged one after the other. Plates I and 8 have a length equal to the total length of the plates 2-5, plate 7 is the length equal to twice the length of the plate 3 (or 4). In the gaps between plates 1 and 3 and 1 and 4, as well as 7 and 8, linear pressure drops of the measured medium occur due to viscous friction.

Plates I and 3 and 1 and 4 form two, successively placed in the stream, capacitors for measuring the volume flow. Plates 1 for them are common. Plates 3 and A (as well as 2 and 5) are placed in the central part of the cross-section of the flow-through part of the sensor alternately with plates 1 (Figures 1, 3 and 4). All plates 2 and 5, located in the grooves 21 (figure 2) in front of and behind the plates 3 and 4,

electrically connected to each other and to the housing 13 (i.e., grounded). Similarly, all plates 1, 3 and 4 are electrically respectively interconnected, forming three multi-plate electrodes of two measuring capacitors.

Plates 7 and 8 form one multi-plate capacitor placed in two peripheral parts.

(Figures 1, 3 and 4) of the cross section of the flow path of the sensor. This condenser is designed to measure the density of a flowing stream. Everything

the plates 9 and 1 O, located in the slots 22 (FIG. 2) in front of and behind the plates, are electrically interconnected and to the housing 13 (i.e., grounded). Similarly, all plates 7 and 8 are electrically respectively interconnected.

For such an electrical connection of the plates 1-10 in the carrier plates 20 (Fig. 2) transverse

grooves 25 (Fig.4 and 5). The ends of the plates extending from the grooves 21 and 22 into the grooves 25 are freed from the fluoroplastic coating, and electrical conductors 26-28 (respectively, plates 1, 3 and 4) and 29 and 30 (respectively

plates 7 and 8) (figure 4). These electrical conductors are connected to five electrical connectors (figure 5), consisting of threaded nuts 31, fluoroplastic seals 32, coaxial rods 33 and push-in threaded bushings 34. Threaded nuts 31 are welded to the housing 13. Through holes in it to the rods 33 are attached electrical conductors 26-30 (figure 5). Outside of the electrical inlets, there are five coaxial RF cables (not shown) for secondary devices.

The sensor body 13 with the flanges 12 and 16 and the cone nozzle 15 (Fig. 1) is thermally insulated and has the temperature of the pipeline and the medium to be measured. For accurate measurements, the sensor is temperature controlled.

To measure the difference in capacitances of flow capacitors of volumetric flow, composed of plates I and 3 and I and 4 (Figures 1, 4 and 5), an automatic quasi-equilibrium transformer bridge (volumetric flow meter) is used. The bridge 35 (Fig. 6) contains a sinusoidal voltage generator 36, a voltage transformer 37 having two multifilar windings 38, a selective amplifier with phase discriminator 39 having a bipolar output, a DC amplifier 40 that controls a reversible electric motor 41 The arms of the bridge 35 include flow capacitors 42 and 43, made up of plates 1 and 3 and I and 4, respectively. The increased (at flow rate) capacity of the measuring capacitor 42 is compensated for by a linear variable connected with capacitor 44 the scarlet motor 41, which is also connected to the arrow 45, indicating the volume flow rate on the scale, and an accurate resistive converter 46. A transformer bridge 47 is used to measure the capacitance of the flow density capacitor made up of plates 7 and 8 (Figures 1, 3 and 4) (Figs similar to bridge 35. This bridge contains a voltage generator 48, a voltage transformer 49 with windings 50, a selective amplifier 51, a DC amplifier 52, an electric motor 53. A flow capacitor (B4 made up of plates 7 and 8 and high intramural stable and tunable capacitor 55. The compensation Uwe lichenie flow capacity capacitor 54, conductive dependent on the density of the measured gas is effected linear nym variable capacitance capacitor 56 associated with the shaft elektrodvi. 53. An arrow 57 is also attached to it, indicating on the scale the density of the measured flux, and a precise resistive transducer 58. Resistive transducers 46 and 58 are included in the opposite shoulders of a resistive bridge 59, which also contains a constant resistor 60 and a rheochord 61 controlled by a shaft an electric motor 62 connected to the output of the amplifier 63. The shaft of the electric motor 62 is also associated with an arrow 64 indicating the mass flow on the scale. The plates 11 have holes 65 (Fig. 1) for filling the space between the housing 13 and the plates L 1 and 20 with the medium to be measured. The flow meter works as follows. With a constant sensor temperature (and plates 1-11) (Fig. 1) and in the absence of flow and pressure, i.e. in vacuum, the dielectric constant of the medium in the sensor is one and the capacitances of the capacitors 42 and 43 (Fig. 6), made up of plates 1 and 3 and 1 and 4 (Fig. 1), are the same. Transformer bridge 35 (Fig. 6), being in equilibrium, shows zero volume flow rate. The capacitance of the capacitor 54, which is of plate 7 and 8, is equal to the capacitance of the tuned capacitor 55. Transformer bridge 47 at equilibrium, shows a zero density value. The resistive bridge 59 is thus balanced at a zero flow reading. When the pipeline and the sensor are filled with measured gas with pressure and constant temperature corresponding to the required mode, but in the absence of a gas flow (at zero flow), the dielectric constant of the gas between all the plates of the sensor is the same and is greater than one. The capacitance of the capacitors 42 and 43 (Fig. 6) is also the same, and the bridge 35 gives zero readings of the volumetric flow. The capacitance of the capacitor 54 becomes larger than the capacitance of the capacitor 55 and the transformer bridge 47 is automatically balanced by increasing the capacitance of the linear capacitor 56. The arrow 57 of the bridge 47, on the other hand, deviates on a scale proportional to the density of the gas being measured and changes the value of the resistive converter 58. As a result, the resistive - The bridge 58 is balanced with a non-zero indication of the arrow 64 on the scale. In order to prepare the flow meter for measurement, a tuned capacitor 55 (FIG. 6) of the transformer bridge 47 is balanced on the zero pointer of arrow 57 on the scale of this bridge. As a result, the resistive bridge 59 gives zero readings. If there is a flow of gases in the pipeline, they enter the sensor articulated by the flanges 14 (FIG. 1) with the return flanges of the pipeline. The flow of gases through the cone nozzle 15 enters narrow long slots between plates 1 and 2-5, 6 and 2-5, as well as between plates 9, 7, 10 and 8; b and 9, 7, 10; And 9, 7, 10. In these narrow cases, a laminar flow regime is established with viscous friction. The maximum flow rate of gases (or superheated steam) must meet the limit value of the Reynolds criterion (i.e., 2300) for the laminar mode between the plates of the measuring capacitors of the volumetric flow, i.e. 1 and 2-5. In the initial area between plates 1 and 2, 2 and 6, 8 and 9, 6 and 9, 9 and 11, a nonlinear change in pressure occurs due to the available losses at the inlet (Fig. 7). Then, the motion mode begins to stabilize and a parabolic distribution of the flow velocity begins to be established over the thickness of the gap. Laminar flow enters the areas of the cracks (figure 1) between the plates 1-3, 1-4, 6-3, 6-4 and, respectively, 7-8, 6-7, 7-11. There is a linear change in the pressure of the current medium, described by the Poiseyl law, and part of the non-linear pressure loss spent on the formation of a parabolic velocity profile. The total pressure drop occurring in the gaps on the length of the plate 3 and 4 is proportional to the volume flow rate of the flowing flow taking into account corrections for pressure losses . This same volumetric flow rate is proportional to the correspondingly smaller pressure drops occurring on the shorter length of each plate 3 and 4. Due to the presence of pressure drops on these plates 3 and 4, in the slits between plates 1 and 3 and 1 and 4, unequal average pressures laziness. Moreover, the average pressure on plate 3 is greater than the average pressure on plate 4. These average pressures correspond to unequal average densities and dielectric permeabilities in capacitors composed of plates 1 and 3 and 1 and 4. The average dielectric constant in the capacitor of plates 1 and 3 is larger than the capacitor of plates 1 and 4. The capacity of capacitor 42 (Fig. 6) of plates 1 and 3, which is located first in the direction of movement of the laminar flow, increases compared with the capacity of capacitor 43 of plates 1 and 4. ) placed in the second stream. Due to the resulting difference in the capacitances of these capacitors 42 and 43 of the capacitors 42 and 43, the balance of the transformer bridge 35 with the transformer voltage 37 is disturbed, the shoulders of which include these capacitors. The capacitance difference between the capacitors 42 and 43 is compensated for by an increase in the capacitance of the balancing capacitor 44 controlled by the electric motor 41. After the bridge 35 is automatically balanced, arrow 45 indicates the measurement result of the volume flow on the scale. In the peaks between plates 8 and 9, 7 and 10, as well as 6N9, 7 and 10, 11 and 9, 7 and 10 of the density meter condenser, a pressure differential is set equal to the difference on plates 1 and 2-5. This differential drops the gas flow through the slots of this capacitor in proportion to the third degree of the ratio of the gaps between the plates of the density meter condenser and the volume flow condenser. If the gap between the plates of the density meter condenser is reduced by an order of magnitude compared to the gap between the plates of the volume flow rate sensor, then the gas flow through the slots of the density meter capacitor becomes three orders less, i.e. is negligible and is accounted for by the amendment in the calculated ratio of the flow meter. Due to the low flow rate in the condenser of the densitometer for the section of the hydrodynamic flow stabilization with nonlinear pressure losses, it is also small and focused on the length of the plates 9. In practice, the pressure distribution along the length of the plate 8 is linear (Fig.7). Moreover, the pressure in the middle section of the plate 7 is greater than at the junction of the plates 3 and 4 of the volume flow capacitor. Due to the pressure difference on the plate 7, the average pressure of the current medium over the length of the plates 7 and 8 becomes greater than the initial pressure, which corresponds to the initial (zero) setting of the balance of the transformer bridge (Fig.6). As the pressure increases on plastias 7 and 8, the average density and dielectric constant of the gas between the plates 7 and 8 increase, and the capacitance of the capacitor 54 increases. The transformer bridge is automatically balanced by increasing the capacitance of the linear and equilibration capacitor 56 by the required amount.

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In this case, the arrow 57 indicates on the scale the value of the density of the gas being measured at an average pressure in the condenser 54 and the resistance value of the resistive converter 58 changes accordingly.

When the resistances of the resistive converters 46 and 58 increase, the resistive bridge 59 automatically balances at the changed resistance of the rheochord 61. This bridge indicates the mass flow equal to the product of the volume flow and density by an arrow 64 on the scale. The gas flow through the capacitor of the densitometer 54 (Fig. 6) of the plates 7 and 8 is taken into account by introducing an amendment to the calculation formula.

At the end portion of the slots, between the plates 1–5, 8–10, and also 5 and 6, 6–10, 10, and 11, there is a nonlinear change in the pressure of the flowing medium due to the output losses. The gas flow (steam) after these flat slots is directed into the cone nozzle 15 and then into the pipeline connected with the sensor by the flange 14. The space between the sensor body 13 and the plates I1 and 20 is filled with the measured medium through the holes 65 (Fig. 1) and is at the pressure of the measured medium.

When moving between plates of a compressible fluid (gas or superheated steam) due to isothermal throttling, an increase in volumetric flow occurs, which is taken into account by introducing an appropriate correction in the calculation formula for volumetric flow.

The scale of the transformer bridge 35 (Fig. 6) is graduated in accordance with the dependence of the volume flow rate on the change in the dielectric constant of the measured gas, which is described by the following relationship

RI taH °

PD

7T, Ml P) to

PO CUH € II

R, T and | - gas constant,

temperature and viscosity of the measured gas, respectively;

b - EO - width and length of plates 3 and 4;

77331 .12

H is the average gap between plates 1 and 3 (4);

RL Hg - specific polarization 5. and the dielectric constant of gas at an average pressure in the channels at the junction of the plates 3 and 4;

10 K is the correction factor for the expansion of the measured gas; n number in parallel

enabled channels. volume flow capacitor

CL is the correction factor for the gas flow rate through the density meter capacitor.

The scale of the transformer bridge 47 (Fig. 6) is graduated in accordance with the dependence on the dielectric constant value of the measured 25 gas, described by the following relation,

li-1.

kz, (1}

fr

. ..,

where K, gj - specific polarization

and the dielectric constant of gas at medium pressure on plates 7 and 8,

Ka is the correction factor, which increases the pressure in the capacitor of the plates 7 and 8. The scale of the analog multiplier 55 is graduated in terms of mass flow rate ratio, kg / s:

 nA (i - i;

yn

y p

.k, -h-kz

4t

Tg

o -, .- h)

(3)

The proposed design of the mass flow sensor allows determining the size of the gaps between the plates I and 3, 4, as well as 7 and 8 (Fig. 1).

capacitors, respectively, 42 and

43 volume flow and 54 density

(Fig.6) electrical measurements;

which significantly improves accuracy

Claims (2)

graduation scale flow meter. For this, the sensor is vacuumized before being installed in the pipeline and the vacuum capacitances of capacitors 42 and 43 and 54 (Fig. 6), made up of plates 1-3, 1-4, 7, are grounded. Ground plates 2, 5, 9 and 10 and 20 are security electrodes. In this case, the scale of the flow meter is graded according to the following ratio, m / s: Q §1 NF (b4ji l hf-Kz Viol T f where about 8.85419-10 Pf / mm is the dielectric constant of vacuum; C. n and vacuum tanks of flow capacitors 41 (42) and 54, respectively; LSui S L - changes in the capacitance of volume flow capacitors 42 and 43 and density capacitors 54 and 55, respectively, when measuring flow. For technical measurements, correction factors for the expansion of the measured medium, for the gas flow through the condenser density meter and to increase the pressure in it l w with ratios of m: v, n .. 15) ySr 1 P 2) y ;. 4H.o, oe "f ,,". E p second virial coefficient of measured gas equation) pressure loss ratio at the inlet of slot channels, the number of parallel connected channels of the density meter capacitor; the gap between the plates of the densitometer capacitor. The proposed device allows accurate measurements of the mass flow rate of gases and superheated vapors both at high overpressures and in vacuum (1-750 mbar), (the marginal relative error can be tO, 5% or less), 114 accurate measurements like malyss and high costs. The flow rate is determined by the number of parallel-connected slot channels of the volume flow sensor and the gap between them; a linear scale of the flow meter and flow measurement within the whole scale are provided, and it is also possible to accurately measure the pulsating flow rates due to small pressure losses at the sensor, very short time to establish the capacitance of flow capacitors and balancing bridge meters. When measuring periodically pulsating flow rates with a period longer than the time taken to establish the meter readings, the measurement error can reach ± 1.5% or less, i.e. The proposed device provides the ability to accurately measure the flow rate of gases and superheated vapors in a wide range of changes from parameters, which directly determines the mode of operation of the process equipment in the organic CI industry, chemical and petrochemical, energy, aviation, etc., as well as in research works. A mass flow meter comprising volume flow and density sensors consisting of multi-plate flat capacitors included in measuring transformer bridge bridges and an analog bridge multiplier, the volume flow sensor capacitors arranged in series in the flow channel, and its shortened plates are installed in series with guard electrodes, characterized in that, in order to improve measurement accuracy while simplifying the design, the density sensor capacitor Credited in the flow channel and part of its plates vtolnena shortened and consistently with their input and output capacitor mounted guarding electrodes, the size of the gap between the capacitor plates density is determined by the formula 1 oSo 16 - permittivity of vacuum; C 2 - the capacitance of the capacitor of the density sensor in vacuum, b and EO gap between the plates, the width and length of the shortened plates of the capacitor density sensors; and the gaps between the plates of the capacitors of the density and volume flow sensors are selected from the ratio Hi / H 7Qif / avi where X is the gap between the plates B 1 pngTRNGYgpp; volume flow sensor condenser; 1 Qy is the gas flow rate through the capacitors of the density sensors and the volume flow rate I C /) g is the capacity capacitor of the volume flow sensor in a vacuum. At the same time, a variable capacitor is installed in the shoulder of the transformer bridge, which measures the density. Sources of information taken into account in the examination 1. The copyright certificate. USSR №504088, cl. G 01 F 1/00, 1974. 2. USSR author's certificate for application number 2747406 / 18-10, cl. G 01 F 1/64, 02.04.79. It 20 n B-s L 7 3 6 7 8 (Pa. 8-5 fefr ii gb g Q Gi I.C. t wml9 (rig. S ffli / lff x x x