SU870943A1 - Device for measuring small volume consumption of gases and vapors - Google Patents

Description

(54) DEVICE FOR MEASURING SMALL VOLUME COSTS OF GASES AND VAPORS

I

The invention relates to the field of measurement technology and can be used to measure small volumetric flow rates of gases and vapors.

Flow resistance transducers with hydraulic resistance are known, the pressure loss of which depends on the flow rate l j.

The closest is a device for measuring small volumetric flow rates of gases and vapors, containing multi-plate flat capacitors installed in two measuring sections and included in the bridge measuring circuit 2.

The known device has a low measurement accuracy due to the presence of pressure losses at the inlet and outlet of the flat channels of the flow sensor, as well as a rather complicated structure.

 The purpose of the invention is to improve the measurement accuracy.

This is achieved by the fact that in a device for measuring small volumetric flow rates, comprising multi-plate flat capacitors installed in two measuring sections and included in a bridge measuring circuit, multi-plate capacitors are installed in two consecutive measuring sections, one plate of capacitors (through one pass t through both measuring sections, while the others are separately separated for each measuring section, sequentially with separate plates at the entrance th measuring section and the outlet of the second set guarding electrodes, and the magnitude of the flow channels clearance gap between the capacitor plates oppedel by the formula

cue „

In where C is the vacuum capacitance of identical capacitors; NDS value of the average gap (thickness, channel); the length of the shortened plate b is the width of the channel between the plates of the capacitors; C.Q is the dielectric constant of vacuum. FIG. 1 is a side view of the flow meter sensor; figure 2 is the same, top view on fig.Z - section of the flow channel of the sensor along the line A-A in figure 1; figure 4 - section bb in figure 2; on fig.Z - section along bb In figure 4; figure 6 - diagram of the measuring transformer bridge; Fig. 7 is a diagram of a single slit-flow channel and a graph of the change in pressure of the medium along its length. The flowmeter sensor of FIG. 1 consists of flat plates 1-6, placed in rectangular cut-outs of flanges 7, welded to a cylindrical body 8. Plates 1-5 are coated on all sides with an electrically insulating layer with very low conductivity and wettability, for example, fluoroplastic. Plates 6 are made of stainless steel. All plates 1-6 are placed in such a way that they form long flat slits, in which the laminar flow regime is established, we control the medium supplied (and retracted) to the driver through the pipeline through the flanges 9 and conical nozzles 10 that mate with it. These nozzles are welded The flanges 9 and the flanges 1 1, with which the nozzles 10 are tightly attached to the flanges 7 of the casing 8 with the help of fluoroplastic gaskets 12, bolts 3 and nuts 14 8, are rectangular cutouts of the flanges 7 (figure 2) and have supporting plates 15 that have internal, facing to the flow, side longitudinal grooves 16, in Plates 1-5 are densely inserted, covered with fluoroplastic and thereby electrically insulated from the grounded carrier plates 15. Grooves 17 are mounted on the narrow faces of Gshastin 15, in which metal plates 6 are laid tightly attached to the plates 15. Plates 1- 5, 6, and 15 are held in the flanges 7 from the longitudinal displacement of the fluoro-formation gaskets 12 and the flanges 11 (Fig. 1), which have a square rectangular cuts, but smaller in size than the rectangular cuts in the fins of the 34 Plates 2 (Fig. 1 ) have a length sufficient to stabilize the laminar regime ma flow, and grounded. Similarly, plates 5 have a length sufficient to prevent loss of pressure at the outlet, and are also grounded. Plates 3 and 4 have the same length. They have a linear drop in pressure of the controlled medium due to viscous friction. Plates 1,3 and 1,4 form two successively placed in the capacitor stream. Plates 1 for them are common. Plates 3 and 4, and also 2 and 5 are placed alternately with plates 1 in the transverse section of the sensor (Figs 1, 3 and 4). All plates 2 and 5 are electrically interconnected and the housing 8. Similarly, all plates 1,3 and 4 are electrically -connected respectively. Dp of such a connection in the carrier plates 15 are transverse grooves 18 (Figures 4 and 5). The ends of the plates extending from the grooves 16 into the grooves 18 are freed from the fluoroplastic film and electroconductors 19, 20 and 21, respectively, are connected to them to parallel plates 1, 3 and 4. These conductors are connected to three electric wires (Fig. 5) from threaded nuts 22, fluoroplastic seals 23, coaxial rods 24 and pressure nuts 25. Threaded nuts 22 are welded to the housing 8 and through the holes, 19,20 and 21 electroconductors attached to the rods 24 are three coaxial radiofrequency outside the electrical leads cable to the secondary surf yelling. The sensor is covered with thermal insulation and has a pipeline temperature. It is thermostatically controlled for accurate measurements. The secondary device is an automatic quasi-balanced transformer bridge with analog or digital output (and, if necessary, with a regulating device) designed to accurately measure the capacitance difference of capacitors made up of plates 1-3 and 1-4. The bridge (Fig. 6) consists of a shoulder voltage transformer 26, on the primary winding 27 of which a supply voltage is applied. With the secondary, in-phase, windings 28, the same voltages are supplied over coaxial cab, ate through the corresponding

electrical leads to parallel-connected plates 3 and 4. Plates 1, which are common to capacitors with plastics 3 and 4, are connected in block diagonal to block 29 through a corresponding elativrovod and cable, consisting of a phase-sensitive selective amplifier, control circuit of a balancing capacitor 30 and measurement result indication schemes. In the plates 6, the holes 31 are filled to fill the space between the housing 8 and the plates 6 and 15 in a controlled environment.

The device works as follows.

At a constant temperature, the sensor and the absence of a flow of capacitors made up of plates 1-3 and 1-4 are the same. A secondary device with an equilibrium transformer bridge indicates zero readings.

The medium flow of the wire through the tapered nozzle enters the long gaps between the plates 1-4.5 and also between the tstasins 6 and 2, 3, 4, 5. In these narrow slits, a laminar flow regime is established with viscous friction. The maximum flow rate of the monitored flow must meet the Reynolds limit criterion for laminar flow for these purposes. .

In the initial region between plates 1 and 2, as well as 6 and 2, a nonlinear change in pressure occurs due to the pressure losses at the inlet (Fig. 7). Here, the mode moves or stabilizes and a parabolic distribution of the velocity of the controlled flow is established over the thickness of the gap. The length of the plates 2 is selected by the limiting value of the Reynolds criteria for the corresponding upper limit of the measurement device and the dynamic viscosity of the controlled flow. The stabilized laminar flow enters the gaps between the plates 1-3 and 1-4 and 6-3, 6-4, respectively. Here there is a linear change in the pressure of the current environment, described by the Poiseuille law. The total pressure drop occurring on the length of the plates 3 and 4 is proportional to the volume flow rate of the flowing stream. The same volumetric flow rate is proportional to the pressure differential arising

on the length of each plate 3 and 4, if their lengths are the same. Due to the presence of pressure differences on plates 3 and 4, unequal average pressures are established in the gaps between plates 1.3 and 1.4. Moreover, the average pressure on the plate 3 is greater than the average pressure on the plate 4. These average pressures and nets are the same as the average density and di-. electrical permeability in capacitors composed of plates of 1.3 and 1.4. The average dielectric constant in a capacitor of plates is 1.3 more than in a capacitor of a plate of 1.4. Accordingly, the capacitance of the capacitor (of the plates 1.3) located first in the direction of flow of the laminar flow increases, as compared with

0 capacitor (of plates 1.4), placed second in the stream.

Due to the resulting difference in the capacitances of these capacitors, the balance of the transformer bridge (Fig. 6) on the voltage transformer 26 is disturbed, on whose shoulders these capacitors are included. The difference between the capacitors of the plates 1.3 and 1.4 is compensated by increasing the capacitance of the balancing capacitor 30, controlled by unit 29, which, after completion of the balancing of the bridge, indicates the measurement result.

five

 At the end portion of the slots between plates 1.5 and 6.5, there is a nonlinear change in pressure of the flowing medium due to output losses. Ambient controlled environment flow

0 flat slots are guided into the cone nozzle 10 and then into the pipeline articulated with the sensor by a flange 9. The space between the sensor body 8 and the plates 6 and 15 is filled

5 controlled medium through the holes 31 in the plates 6.

When moving between plates G; bi 2-5 of compressible medium, due to the resulting "pressure difference, there is throttling and a corresponding increase in volumetric flow rate, which is taken into account by introducing an amendment to the design flow formula.

Claims (2)

1. Kremlevsky P.P. Flow meters and quantity counters. L., Mechanical Engineering, 1975. Chapter 5. 2. USSR author's certificate on application / No. 2713961 / 18-10, cl. in 01 F 1/64, 01/17/79 (prototype). FIG. 2 AT AT Fy FIG. ff N