RU2445602C2 - Inertia method of determining density and (or) mass flow of liquid (gas) - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method of determining density or mass flow of a liquid (gas) involves periodic longitudinal alternating-sign action on a liquid (gas) flowing through a straight section of a pipeline, which causes a change in the longitudinal velocity of the liquid (gas), onset of inertia forces, differential pressure, from which the density and/or mass flow of the liquid (gas) is determined. The method is characterised by that, in order to implement the method in practice and increase accuracy of determination, the pipeline has a constant cross-section, and the alternating-sign action on the liquid (gas) is excited in an extra pipeline using the same liquid (gas).

EFFECT: high accuracy of measuring density or mass flow of a liquid by reducing hydraulic pressure losses and increasing the range of flow rates.

2 dwg

Description

FIELD OF THE INVENTION

The invention relates to measuring technique, in particular to a method for determining the density and (or) mass flow rate of liquids (gases).

State of the art

Analogs of the invention:

1. Vibration Coriolis flowmeters (Kremlevsky P.P. Flowmeters and counters: Reference. - 4th ed., Revised and add. - L.: Mechanical Engineering, 1989, p.354).

Vibration Coriolis flowmeters - flowmeters in which an alternating Coriolis acceleration is communicated to a fluid (gas) stream. Devices based on this principle of action are widespread. This group of devices provides the main technical result - the ability to directly measure the mass flow of a substance. An additional technical result is the ability to measure the density of a substance. However, the analogues according to claim 1 have significant disadvantages:

- to reduce the measurement error, the measuring section of the flowing part is performed with a small flow area in order to ensure a high velocity of the medium. This leads to large hydraulic losses due to pumping of the medium;

- the measuring section of the flow part is subject to bending and torsional vibrations during operation. As a result, the design of the measuring device is significantly complicated, the requirements for its manufacture are tightened, and the cost increases;

- the vibrational principle of operation implies a small amplitude of the oscillations of the measuring tube, as a result of which the measuring device is prone to malfunction when measuring some flows of the medium being measured, for example, gas-liquid ones.

2. Differential-power flow meters (Kremlevsky P.P. Flowmeters and counters: Reference. - 4th ed., Revised and additional - L .: Mashinostroenie, 1989, p. 360).

Differential-power flowmeters are closest to the claimed invention according to the principle of action and also allow to achieve the main technical result - the measurement of the mass flow rate of the medium. At the same time, the analogs of claim 2 have a significant drawback - the dependence of the readings on the viscosity and the flow regime and, as a consequence, the increased measurement error.

3. A device for hydrodynamic density measurement (Patent RU 2273016 C2).

A device for hydrodynamic density measurement, the principle of which is based on the dependence of the differential pressure, depending on the flow rate, density and viscosity of the medium.

The disadvantages of the analogue:

- the effect of flow rate, density and viscosity of the medium on the pressure drop reduces the accuracy of the measurement;

- the measurement principle is based on the quadratic nature of the pressure drop increase with increasing speed, which can lead to a narrowing of the measurement range and to an increase in measurement error;

- high technical complexity and cost;

- low reliability of the hydrodynamic density measurement device.

4. The article "On the inertial method for simultaneously measuring the mass flow rate of a liquid and its density" (E.V. Mayorov, V. A. Onishchuk. Applied Physics "No. 6-2005, p. 18-23).

This development is adopted as a prototype, because by its principle of action is closest to the claimed invention. Common to the invention and the prototype is the nature of the effect exerted on the measured medium by the measuring device, namely, the effect of forcing the liquid to change its speed and its mass flow rate in accordance with a specific predetermined law. In the work of B.V. Mayorov and V.A. Onishchuk, the fundamental possibility of determining the mass flow rate and density of a liquid using a device representing a pipeline with oscillating walls is given. It is shown that for an ideal incompressible fluid, the pressure drop arising in the pipeline section with walls oscillating symmetrically with respect to the longitudinal axis of the pipeline is proportional to the mass flow rate and proportional to the density. A diagram is presented by which a real-life sample of a measuring device can be built. However, the device according to this description has a significant drawback: the complexity of the practical implementation. In practice, it is difficult to manufacture a pipeline with flexible (pliable) walls, which could make harmonic oscillations with a change in diameter, especially if, according to the requirements of the technology, it is necessary that the pipeline be made of metal. The described invention eliminates the above disadvantage.

Disclosure of invention

The existing analogues ([1] and [3]), designed to measure the density and mass flow rate of a liquid or gas medium, have a number of advantages, but in addition to them there are a number of disadvantages and limitations in application. Coriolis effect flow meters containing vibrating tubes (analogue [1]) perform the functions of measuring mass flow and density. The disadvantage of such devices is the occurrence of a large pressure drop caused by a significant narrowing of the cross section of the stream when it passes through vibrating pipes. A large pressure drop leads to an increase in the cost of operating the pipeline, since more energy is spent on pumping the medium, the load on the pumps and so on increases. The device for hydrodynamic measurement of the density of the medium (analogue [3]) also implies the presence of a pressure drop, depending on the flow rate, density and viscosity of the medium. In addition, the measurement principle described in the analogue of [3] contains the quadratic nature of the difference growth with increasing speed, which can lead to an increase in measurement error.

The described invention is a completely new way to determine the density and (or) mass flow rate of liquids (gases), and when implementing this method it is possible to obtain the following technical results:

- low pressure loss;

- simplicity and reliability in comparison with analogues;

- the ability to measure not only a single-phase homogeneous medium, but also mixtures of liquid or gas with a bulk product (pulp) or gas-liquid mixtures.

To disclose the essence of the invention in terms of measuring the density of liquids (gases), consider and comment on figure 1.

, с плотностью ρ. Данный участок трубопровода 3 назовем основным трубопроводом. Параллельно основному трубопроводу подключен еще один трубопровод 5, назовем его дополнительным трубопроводом, в котором плотно установлен поршень 4, приводимый в движение от внешнего источника энергии.Figure 1 shows a straight section of a pipeline of length L with a cross-sectional area S _osn through which a liquid (gas) flows, having a mass flow rate

, with density ρ. This section of pipeline 3 will be called the main pipeline. In parallel with the main pipeline, another pipeline 5 is connected, let's call it an additional pipeline, in which the piston 4 is tightly mounted, driven by an external energy source.

The piston performs a cyclic oscillation in an additional pipeline according to the law:

where x ₁ is the coordinate of the piston in the additional pipe, m;

And - the amplitude of the oscillations of the piston, m;

ω is the circular oscillation frequency of the piston, s ^-1 ;

t - current time, s.

At the points of connecting the additional pipeline to the main one, mass transfer chambers 1 and 2 are made, which ensure mixing of the liquid (gas) moving along the main pipeline 3 with the liquid (gas) leaving the additional pipeline 5, or performing the function of separating the liquid and taking part of it into additional pipeline.

Since the piston 4 in the auxiliary pipe 5 performs a reciprocating movement, each of the chambers alternately performs the functions of mixing and separation. So, in the first phase of the movement, part of the liquid is taken from the chamber 2 and fed into the chamber 1. In the second phase, when the piston 4 changes its direction of motion, part of the liquid will be taken from the chamber 1 and fed into the chamber 2. Since the flow direction is in the additional pipeline 5 and its speed, determined by the movement of the piston 4, change cyclically, then the longitudinal velocity of the liquid in the main pipe 3 in section L also changes in the same way. A change in speed means the presence of acceleration, which causes the appearance of inertia forces, acting them to liquid volume length L. Thus, the fluid pressure at the beginning and at the end portion of length L will vary. The pressure difference sensor 6 (Fig. 1) measures the value of the pressure difference arising on the length L of the main pipe 3.

The pressure difference is proportional to the density of the liquid (gas) and the acceleration of the piston:

where Δp is the measured pressure difference that occurs in the area L, Pa;

S _additional - the cross-sectional area of the additional pipeline, m ² ;

S _ost - the cross-sectional area of the main pipeline, m ² ;

ρ is the density of the measured medium (liquid or gas), kg / m ³ ;

- ускорение поршня, м/с²;

- piston acceleration, m / s ² ;

L is the length of the main pipeline, m

From the formula (2) we express the density of the measured medium:

where ρ is the density of the measured medium (liquid or gas), kg / m ³ ;

Δp is the pressure difference arising in the section L, Pa;

S _osn - the cross-sectional area of the main pipeline, m ² ;

S _additional - the cross-sectional area of the additional pipeline, m ² ;

L is the length of the main pipeline, m;

- ускорение поршня, м/с².

- piston acceleration, m / s ² .

Thus, by measuring the pressure difference Δp, we can determine the density of the liquid (gases). The proportionality coefficient between density and pressure drop is a combination of the geometric dimensions of the device and the acceleration of the piston, i.e. values determined during calibration and almost unchanged during operation.

The mass flow rate of the measured medium moving along the main pipe 3 does not affect the measured density value.

To disclose the essence of the invention in terms of measuring the mass flow rate of a liquid (gas), consider and comment on figure 2.

, с плотностью ρ. Данный участок трубопровода 3 назовем основным трубопроводом. Параллельно основному трубопроводу 3 подключен еще один трубопровод 5, назовем его дополнительным трубопроводом, в котором плотно установлен поршень 4, приводимый в движение от внешнего источника энергии.Figure 2 shows a pipeline 3 with a cross-sectional area S _osn through which flows a liquid (gas) having a mass flow rate

, with density ρ. This section of pipeline 3 will be called the main pipeline. In parallel with the main pipeline 3, another pipeline 5 is connected, let's call it an additional pipeline in which the piston 4 is tightly mounted, driven by an external energy source.

The piston 4 performs a cyclic oscillation in an additional pipeline according to the law:

where x ₁ is the coordinate of the piston in the additional pipe, m;

And - the amplitude of the oscillations of the piston, m;

ω is the circular oscillation frequency of the piston, s ^-1 ;

t - current time, s.

At the points of connection of the additional pipeline 5 to the main pipeline 3, mass transfer chambers 1 and 2 are made (Fig. 2). The mass transfer chamber is a section of the main pipeline 3 with a perforated (permeable) wall. The length of the mass transfer chamber 1 is L ₁ , the mass transfer chamber 2 is L ₂ . The pressure difference sensors 6 and 7 (figure 2) measures the value of the pressure difference that occurs on the length of the mass transfer chamber L ₁ and L ₂ . Thus, during the measurement process in the mass transfer chambers, the liquid (gas) moving along the main pipe 3 will mix with the liquid (gas) leaving the additional pipe 5, or the liquid (gas) will be separated and its part will be taken into the additional pipe 5 .

The value of the pressure difference arising in each mass transfer chamber during the measurement process will be equal to:

where Δp ₁ is the pressure difference arising in the area L ₁ , Pa;

ρ is the density of the measured medium (liquid or gas), kg / m ³ ;

- ускорение поршня, м/с²;

- piston acceleration, m / s ² ;

S _additional - the cross-sectional area of the additional pipeline, m ² ;

L ₁ - the length of the mass transfer chamber 1, m;

S _osn - the cross-sectional area of the main pipeline, m ² ;

- массовый расход измеряемой среды (жидкость или газ), кг/с;

- mass flow rate of the measured medium (liquid or gas), kg / s;

- скорость поршня, м/с;

- piston speed, m / s;

Δp ₂ is the pressure difference arising in the area L ₂ , Pa;

L ₂ - the length of the mass transfer chamber 2, m;

From formulas (5) and (6) it can be seen that by measuring the pressure difference Δp ₁ or Δp ₂ , we can determine the density and mass flow rate of the liquid (gas). The mass flow rate and the density of the liquid (gas) can be obtained from formulas (5) and (6) using mathematical calculations.

и плотности ρ жидкости (газа).Thus, to determine the density and mass flow rate of a liquid (gas) or only the mass flow rate or only the density of a liquid (gas), it is possible to measure both pressure drops Δp ₁ or Δp ₂ or any one of them, and then using mathematical calculations, calculate mass flow rate

and density ρ of the liquid (gas).

The implementation of the invention

In the presentation of the Disclosure of the invention describes in detail a method for determining the density and mass flow rate of a liquid (gas), as well as the principle of operation and design.

Claims (1)

The inertial method for determining the density or mass flow rate of a liquid (gas) or simultaneously determining the density and mass flow rate of a liquid (gas) consists in giving the liquid (gas) moving along a straight section of the pipeline a cyclic longitudinal alternating action causing a change in the longitudinal velocity of the liquid (gas), the appearance of inertia forces, the pressure difference, which determines the density or mass flow rate of a liquid (gas) or the density and mass flow rate of a liquid (gas), characterized in that, with For practical implementation and to increase the accuracy of determination, the pipeline has a constant cross section, and the alternating effect on the liquid (gas) is excited in the additional pipeline by the same liquid (gas).

Images