RU178057U1 - FLOWMETER - Google Patents

Abstract

The utility model relates to measuring technique, designed to determine the flow rate of a medium with stable and unstabilized flows in round pipelines. The flowmeter includes a tube, which contains three pairs of holes located on the frontal and aft parts of the tube so that the axial line passing through the centers of the holes of each pair is normal to the central axis of the tube, and each pair of holes is connected respectively to a full and static pressure meter . The technical result is an increase in the accuracy of determining the flow rate of the coolant. 2 ill.

Description

The utility model relates to the field of measurement technology, is intended to determine the flow rate of a medium with stabilized and unstabilized flows in round pipelines.

A flow meter is known that includes a pipe section in which a speed sensor is installed at a certain distance from the pipe wall. For example, in the center of the pipe (the point where U = U _max , the center of the pipe). To determine the flow rate of coolant measured coolant velocity at the sensor installation U _MOD define coolant flow rate Q = k _v U _MOD F _TP where k _v - a predetermined flow rate coefficient, k _v = U _cp / U _MOD (flow rate of liquid and gas techniques. speed measurements at one point of the pipe cross-section GOST 8.361-79. [1]).

The main disadvantage of this flow meter is that to determine the flow rate it is necessary to know the value of k _v . The flow coefficient k _v largely depends on the roughness coefficient ξ. Depending on ξ, the discrepancy in the values of k _v can reach 6-7% (P.V. Lobachev, F.A. Shevelev Measurement of the flow of liquids and gases in water supply and sewage systems. Ed. 2nd, revised and supplemented. Moscow . Stroyizdat 1985, [2]).

The closest flowmeter in terms of technical nature and the achieved result, including a tube with a number of openings on the frontal part, connected to a full pressure meter and openings on the back, connected to a static pressure meter, located normally to the pipe axis (P.P. Kremlevsky Flowmeters and counters of the amount of substance: Reference: Book 1.-5th ed. revised and supplemented - St. Petersburg: Polytechnic, 2002. - 409 pp., ill. Page 160, [3]).

In FIG. 1 shows an example of a known flow meter, 1 — flange, 2 — tube, 3 — plug, 4 — tube for taking static pressure, 5 — openings for taking full pressure. There are various options for the selection of static and total pressure, [3], p. 159.

на лобовой и кормовой сторонах трубки, где

суммарное давление, создаваемое отверстиями на лобовой стороне трубки, Р_ст давление, измеренное на кормовой стороне трубки. Расход теплоносителя вычисляется как

, где α_р - коэффициент расхода, ρ - плотность теплоносителя, F_тp - площадь трубы.The flow rate of the coolant using a known flow meter is as follows. Pressure difference measured

on the front and aft sides of the tube, where

the total pressure created by the holes on the frontal side of the tube, P _{article the} pressure measured on the aft side of the tube. The coolant flow rate is calculated as

where α _p - flow coefficient, ρ - heat carrier density, F _tp - pipe area.

, создаваемое отверстиями на лобовой стороне трубки, зависит от многих факторов: размер отверстий, расстояний между отверстиями, число отверстий. Давление Р_ст, измеряемое на кормовой части трубки, также зависит от ряда факторов: установки датчика для измерения статического давления, размера отверстий и т.д. Таким образом, основной недостаток расходомера состоит в том, что коэффициент расхода расходомера зависит от многих факторов - размеров отверстий, расстояний между отверстиями, числа отверстий. В связи с этим расходомер для обеспечения точности требует калибровки в условиях, близких к тем, в которых расходомер будет использован.Total pressure

created by the holes on the front of the tube depends on many factors: the size of the holes, the distance between the holes, the number of holes. The pressure P _st measured at the stern of the tube also depends on a number of factors: the installation of the sensor for measuring static pressure, the size of the holes, etc. Thus, the main disadvantage of the flow meter is that the flow coefficient of the flow meter depends on many factors - the size of the holes, the distance between the holes, the number of holes. In this regard, to ensure accuracy, the flow meter requires calibration under conditions close to those in which the flow meter will be used.

It is proposed that the flow meter includes a tube with a series of holes on the frontal part connected to a full pressure meter and holes on the back connected to a static pressure meter, placed normally to the axis of the pipe, characterized in that the tube contains three pairs of holes located on the frontal and aft parts of the tube so that the axial line passing through the centers of the holes of each pair is normal to the central axis of the tube, with each pair of holes connected respectively to the floor meter th and static pressure.

The technical result, which the proposed utility model aims to achieve, is to increase the accuracy of determining the flow rate of the coolant, which is ensured by the fact that the tube contains three pairs of holes located on the frontal and rear parts of the tube so that the axial line passing through the centers of the holes of each pair normally located on the central axis of the tube, each pair of holes being connected respectively to a full and static pressure meter.

The achievement of the technical result, which consists in increasing the accuracy of determining the flow rate of the coolant, is ensured by the fact that the tube contains three pairs of holes located on the frontal and rear parts of the tube so that the axial line passing through the centers of the holes of each pair is located normally to the central axis of the tube, moreover, each pair of holes is connected respectively to a meter of total and static pressure. This arrangement of the holes allows one to obtain, based on the known velocity coefficients (determined previously during the calibration of the flowmeter), the flow velocities at points with known coordinates. Further, based on the use of a single universal velocity profile [5] and certain (measured) velocities, the flow rate of the coolant is determined with an accuracy of no worse than 1.5%, [5].

In FIG. 2 is a schematic illustration of a flow meter. The flow meter includes the following basic elements. The body of the flow meter 1, made in the form of a cylindrical tube with three pairs of holes 2-2, 3-3, 4-4, placed on the front and aft parts of the tube so that the axial line passing through the centers of the holes of each pair is located normally to the central axis of the tube , 5 - capillary tubes for connecting pair openings 2-2, 3-3, 4-4 to measuring instruments of full and static pressure. The casing is installed normally to the axis of the pipeline, in which the flow rate of the coolant is determined. The coordinates of the holes relative to the pipe in which the flowmeter is installed are as follows: x ₁ = r ₀ , x ₂ = 0.5⋅r ₀ , x ₃ = 1.5⋅r ₀ . The holes with the help of capillaries 5 are connected in pairs to measuring instruments of full and static pressure.

The flow meter works as follows:

,

,

, где - P_0i - полное давление в соответствующем отверстии на лобовой части трубки, Р_стi - давление в соответствующем отверстии на кормовой части трубки. Разности давлений между лобовыми и кормовыми точками поверхности трубки используются для определения локальных скоростей потока, набегающего на трубку (см. далее).1. Measured differential (difference) pressure generated during the flow around the flowmeter in the frontal and rear parts of the tube, for paired holes

,

,

where - P _0i is the total pressure in the corresponding hole on the front of the tube, P _sti is the pressure in the corresponding hole on the aft of the tube. The pressure differences between the frontal and aft points of the tube surface are used to determine the local velocities of the flow incident on the tube (see below).

2. Using an absolute pressure sensor, the pressure is measured in the cross section of the pipeline in which the flow meter R ^meas .

3. Using a temperature sensor, the temperature is measured in the cross section of the pipeline in which the flow meter T ^meas .

4. Using the values of temperature T ^ISM and pressure P ^ISM , using the special program unit installed in the signal processing unit, the thermophysical properties of the medium flowing in the pipeline are calculated, namely, the density and kinematic viscosity.

,

,

, где ρ - плотность среды,

- коэффициенты скорости, предварительно определенные в калибровочных экспериментах, либо расчетным путем.5. Based on the measured pressure drops and the calculated density of the medium, local flow rates in the pipeline are calculated at known distances from the base of the sensor (from one of the pipe walls)

,

,

where ρ is the density of the medium,

- speed coefficients previously determined in calibration experiments, or by calculation.

6. Based on the calculated local flow rates, the flow rate of the coolant is calculated. For this, the type of velocity profile in the pipe (stabilized or unstabilized flow) is preliminarily determined [4, 5] as follows.

6.1. Based on a single universal logarithmic profile

U = A _k ln (x) + B _{k the} coefficients A _k and B _k are calculated

where i, j, k = 1, 2, 3.

и

для каждой пары значений A_k и B_k. Сравнивают полученные значения

и

с наперед заданным значением ε. В качестве е принимают малую величину 0,01÷0,001.6.2. Values are calculated

and

for each pair of values of A _k and B _k . Compare the values obtained

and

with a predetermined value of ε. As e take a small value of 0.01 ÷ 0.001.

,

означает, что поток в сечении установки расходомера стабилизированный. В этом случае расход теплоносителя определяют по зависимостям для стабилизированного течения. В противном случае по зависимостям для нестабилизированного течения.6.3. Condition

,

means that the flow in the cross section of the flowmeter installation is stabilized. In this case, the coolant flow rate is determined by the dependences for a stabilized flow. Otherwise, according to the dependences for an unstabilized flow.

6.4. The flow rate of the coolant in the case of a stabilized flow is determined by the dependence [5]:

where r = r ₀ -x is the distance from the center of the pipe;

r ₀ is the radius of the pipe;

x is the distance from the pipe wall;

- среднее значение коэффициентов A_k;

- the average value of the coefficients A _k ;

- среднее значение коэффициентов B_k;

- the average value of the coefficients B _k ;

n is 3;

κ is the Karman constant;

ν is the kinematic viscosity of the medium;

δ _in - the thickness of the viscous sublayer.

In the case of an unstabilized profile, the coolant flow rate is determined on the basis of the particular form of the velocity profile W (r, ϕ):

where W (r, ϕ) is a particular type of velocity profile defined on the basis of the velocities determined by the flowmeter and the general form of the velocity profile.

The general view of the velocity profile is determined on the basis of theoretical concepts and / or preliminary model experiments.

An example of a specific implementation.

Verification of the proposed flowmeter was carried out as follows. The flow meter (tube diameter) was installed in the pipe with an internal diameter of 90 mm normal to the axis of the pipeline. Water was pumped through the pipe, the water flow rate and differential (differences) pressures formed during the flow around the flowmeter in the frontal and rear parts of the tube were measured. Based on the measured pressure drops, the velocities were determined

,

,

.Previously, experimental determination of the velocity coefficients for holes on the frontal and stern parts of the tube was carried out

,

,

.

Using the measured pressure drops and the calculated density of the medium, local flow rates in the pipeline were calculated at known distances from one of the pipe walls. Next, the flow rate of water through the pipe was determined according to the dependence for a stabilized flow (2).

The measurements were performed on a pipe section with a stabilized velocity profile at the stand of JSC ENITS. The experiments were performed in the following range of operating parameters: pressure 0.1-0.3 MPa, temperature 33-47 ° C, number Re = 30250-245000. The maximum error in determining the flow rate using the proposed flow meter was 1-1.5%.

List of sources used

1. The flow rate of liquid and gas. The methodology for measuring speed at one point in the pipe section. GOST 8.361-79.

2. P.V. Lobachev, F.A. Shevelev Measurement of the flow of liquid and gases in water supply and sanitation. Ed. 2nd, revised and supplemented. Moscow. Stroyizdat 1985, [2]).

3. P.P. Kremlin Flowmeters and counters of the amount of substance: Reference: Book. 1.-5th ed. reslave. and add. - SPb .: Polytechnic, 2002. - 409 p.: Ill. Page 160).

4. RF patent for the invention 2597673 C1, IPC ³ G01F 1/34 (2006.01). The method of determining the flow rate of the coolant speed sensors / E.A. Boltenko, M.V. Davydov, B.M. Korolkov // Application No. 2015119713/28, dated May 25, 2015, published September 20, 2016, Bull. Number 26

5. RF patent for the invention 2601382 C1, IPC3 G01F 1/100 (2006.01). The method of determining the flow rate of the medium in round pipelines with a stable flow / E.A. Boltenko, M.V. Davydov // Application No. 2015151303/28, dated November 30, 2015, published November 10, 2016, Bull. Number 31

Claims (1)

A flow meter comprising a tube with a series of openings on the front end connected to a full pressure meter and openings on the back connected to a static pressure meter located normally to the axis of the pipe, characterized in that the tube contains three pairs of openings located on the front and rear parts of the tube so that the axial line passing through the centers of the holes of each pair is normal to the central axis of the tube, with each pair of holes connected respectively to a full and static meter someone pressures.

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