RU2518253C1 - Method of fluid flow rate measurement - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: method involves measurement of rotation speed of a sensor and further processing of results. The speed measurements are carried out for at least two sensors rotating at different levels, the sensors are chosen so that to have different size and/or weight.

EFFECT: improving accuracy of fluid flow measurement with different properties, including those altering in the course of operation, in wide range.

3 cl, 1 dwg

Description

The present invention relates to measuring technique and can be used to measure the flow of liquids, including for evaluating the performance of submersible oil pumps during operation.

A well-known method of measuring the flow rate of a homogeneous liquid using a ball tachometric flow meter (see, for example, RF patent No. 2278969 C1, IPC E21B 47/10, G01F 1/06, publ. 06/27/2006), in which form an annular channel for rotation of the sensitive element at the level of which a sensor is installed and the rotation frequency is fixed, followed by processing the results, while a ball made of a material with a density close to the density of the liquid is used as a sensitive element. For subsequent processing of the results, the flow meter is pre-calibrated in the laboratory for liquid, the flow rate of which will be measured.

The method of determining the flow rate by the speed of rotation of the ball in any tachometric flow meter is quite simple. The frequency depends on two groups of parameters: the first group includes parameters that determine the geometry of the flowmeter — these are the dimensions of the flow channels, the radius of the ball and its mass (or the density of the material of the ball), the size of the channel in which the ball rotates, the radius of the ball’s orbit; the second group includes parameters that directly characterize the liquid: its volumetric flow rate, viscosity and density. By fixing the parameters of the first group with a specific flowmeter version, we can obtain the dependence of the ball rotation frequency on the volumetric flow rate of the liquid with the given properties (viscosity and density). Usually, in this case, the range of measured flow rates is limited by the linear portion of the flow versus frequency dependence, i.e. there is a simple functional relationship between the volumetric flow rate Q and the speed of rotation of the ball f: Q = a ₁ f + A ₂ . Coefficients a ₁ and a _{2 are} determined in bench conditions at the stage of calibration of the flow meter. The measured frequency of rotation of the ball and the known a ₁ and a ₂ and calculate the volumetric flow rate of the liquid. The known method is characterized by the maximum ease of removal and processing of the information electric signal, proportional to the flow rate.

However, a significant drawback of the method is the low reliability of the results when measuring fluid flow with unknown or changing properties that cannot be taken into account when calibrating the flow meter. Therefore, its use as a universal sensor, in particular when measuring the flow rate of produced well fluid, is impossible.

The proposed method allows with high accuracy in a wide range to measure the flow rate of liquids with different properties, including those that vary in a known interval during operation.

The specified technical result is achieved by the fact that in the method of measuring fluid flow, including measuring the speed of rotation of the sensing element and subsequent processing of the results, according to the invention, the rotation speed of at least two sensing elements rotating at different levels is measured, and the sensing elements are used with different sizes and / or mass.

In this case, the mass ratio of sensitive elements rotating at different levels can be in the range of 1-4, and the ratio of their characteristic sizes in the range of 1-1.5.

This ratio of the mass and size of the sensitive elements makes it possible to provide a significant difference in the frequencies of their rotation and to reduce the influence of the error in determining the frequencies themselves on the accuracy of flow measurement.

In the case when the density of the liquid is known and remains unchanged or changes slightly during the measurement process, and the flow meter is calibrated in the laboratory on liquids with different viscosities, the method can be implemented using a tachometric flow meter in which two sensing elements are used. If, during the measurement process, both viscosity and fluid density change, the rotation speed should be measured using three sensing elements rotating at different levels.

The functional dependence of the rotation frequencies of each of the three sensitive elements f ₁ , f ₂ and f ₃ on the parameters of the problem has the following general form:

f1 = F (Q, ν, ρ, gs, m ₁ , r ₁ )

f2 = F (Q, ν, ρ, gs, m ₂ , r ₂ ))

f3 = F (Q, ν, ρ, gs, m ₃ , r ₃ ))

where Q is the volumetric flow rate of the liquid, ν is the viscosity of the liquid, ρ is the density of the liquid, the geometric parameters of the flowmeter are indicated as gs, m ₁ , m ₂ , m ₃ are the masses of the sensitive elements, r ₁ , r ₂ , r ₃ are the characteristic dimensions of the sensitive elements (for balls, for example, these are the radii). In the obtained system of three equations, three quantities are unknown: Q, gs, ν, ρ; therefore, this system of equations is solvable when measuring in three orbits of rotation of the sensitive elements.

The method is implemented as follows.

Before use, the flow meter is calibrated in laboratory conditions in order to obtain the dependence of fluid flow on the speed of each sensing element at different viscosities and densities of the test fluid.

Next, choose a mathematical procedure that allows for two frequencies to uniquely determine both the flow rate and viscosity of the liquid, or three frequencies - flow rate, viscosity and density of the liquid. This procedure can be implemented in various ways, for example, by constructing direct functional dependencies Q = Q (f ₁ , f ₂ , f ₃ ), ν = ν (f ₁ , f ₂ , f ₃ ), ρ = ρ (f ₁ , f ₂ , f ₃ ) according to the measured data or using the technology of a trained neural network with input parameters f ₁ , f ₂ , f ₃ and output parameters Q, ν, ρ without constructing explicit dependencies; any other numerical algorithms for converting the rotational speeds of sensitive elements into fluid flow are also possible.

As an example, we show the implementation of a method for measuring the flow rate of a liquid whose density does not change during measurements, i.e. in the case when it is enough to use two sensing elements.

At the calibration stage, we construct a set of dependences of the fluid flow on the rotation frequency of each sensitive element Q (f ₁ ), Q (f ₂ ) at various viscosities from the proposed range. As sensitive elements used ferroresin balls with a radius of r ₁ = 3.25 mm with a mass of m ₁ = 0.63 g and a radius of r ₂ = 2.5 mm with a mass of m ₂ = 0.23 g. Figure 1 shows a part of linear dependences Q = a ₁ f + a ₂ obtained with the following viscosity values: 1-7 cSt; 2-48 cSt, 3-126 cSt, 4-303 cSt, which determine the coefficients a ₁ and a ₂ for each experimentally found linear function.

It should be noted that a change in the size and / or mass of the sensitive element leads to a change in the slope of the linear function Q (f), i.e. to a change in the coefficient a ₁ .

The values of the coefficients are entered into the controller of the device that processes the signal from the flow meter, thus forming the initial space of possible solutions.

для каждой измеренной вязкости (см. левую часть фиг.1). Из полученного набора частот выбирают частоту $$f_{1\min }^{*}$$

, наиболее близкую по величине к реально измеренной f₁ и по ней определяют ближайший расход Q'?? а также ближайшую вязкость, для которой получена зависимость Q(f₁). С учетом линейной связи между расходом и частотой, реальный расход жидкости Q вычисляют из уравненияAfter measuring the rotational speeds f ₁ and f _{2 of} two sensitive elements for one of the measured rotational speeds, for example, the second sensitive element f _{2, a} set of flow rates is determined from the previously obtained dependences Q (f ₂ ), each of which corresponds to its viscosity (see the right part figure 1). For this set of costs using inverse linear relationships for the first sensitive element f ₁ (Q) find the corresponding possible set of rotational speeds of the first sensitive element $$f_{\mathrm{one}}^{*}$$

for each measured viscosity (see the left part of figure 1). From the obtained set of frequencies, select the frequency $$f_{\mathrm{one}\min }^{*}$$

closest in magnitude to the actually measured f ₁ and from it determine the nearest flow rate Q '?? as well as the nearest viscosity, for which the dependence Q (f ₁ ) is obtained. Given the linear relationship between flow rate and frequency, the actual flow rate Q is calculated from the equation

. $$Q=Q\text{'}\text{'}+\frac{f_{\mathrm{one}}-f_{\mathrm{one}\min }^{*}}{f_{\mathrm{one}\min }^{*}}\cdot Q\text{'}\text{'}$$

.

Thus, the application of the inventive method allows, when determining the volumetric flow rate of the liquid from the rotational speeds of sensitive elements of different size and / or mass, to automatically take into account the viscosity and density of the measured liquid.

Claims (3)

1. The method of measuring fluid flow, including measuring the speed of rotation of the sensitive element and subsequent processing of the results, characterized in that the measurement of rotation speed is carried out for at least two sensitive elements rotating at different levels, and the sensitive elements are selected with different sizes and / or mass. 2. The method of measuring fluid flow according to claim 1, characterized in that sensitive elements are used with a mass ratio in the range from 1 to 4. 3. The method of measuring fluid flow according to claim 1, characterized in that use sensitive elements with a size ratio in the range of 1-1.5.