JP3164632U - Device for determining the flow rate of a bi-directional unsteady fluid flow - Google Patents

Abstract

Real-time flow measurement is made possible with high accuracy even when the flow fluctuates rapidly. In order to enable real-time flow measurement with high accuracy even when the flow fluctuates rapidly, a differential pressure between the total pressure and the static pressure is obtained and substituted into the Bernoulli equation. For this purpose, there is provided an apparatus having a measuring tube (1), a mechanism for detecting the differential pressure and density of the fluid, and an evaluation unit for calculating a flow rate based on the detected pressure difference and density of the fluid. The provided evaluation unit comprises a calculation unit for solving a normal nonlinear differential equation relating to the flow velocity in real time taking into account the pressure difference and the acceleration term relating to the flow velocity. The device has two sondes (2, 3) arranged substantially antiparallel to each other in both flow directions to detect the total pressure and arranged parallel to the fluid flow direction. One of the sondes (2) records the total pressure, and the other sonde (3) records the static pressure. [Selection] Figure 1

Description

  The present invention is a device for determining the flow rate of a bi-directional unsteady fluid flow, comprising a measuring tube, a mechanism for detecting the differential pressure and density of the fluid, and the detected pressure difference of the fluid. And an evaluation unit for calculating the flow rate based on the density, and the evaluation unit has a calculation unit for solving the normal nonlinear differential equation relating to the flow velocity in real time in consideration of the pressure difference and the acceleration term relating to the flow velocity. , Relating to the device.

  Patent Document 1 discloses a high-speed working pressure method that uses the restriction principle together with the unsteady Bernoulli method based on an existing constriction at a measurement location.

European Patent Publication No. 1716393

  Therefore, the subject of the present invention was an apparatus capable of determining a flow rate in real time with high accuracy against a rapidly changing flow.

  The apparatus for determining the flow rate of the unsteady fluid flow described at the beginning is, according to the invention, provided with two sondes arranged substantially antiparallel to each other and parallel to the fluid flow direction. One of the sondes records the total pressure, the other sonde records the static pressure, and a mechanism for detecting a differential pressure between these sondes is provided. With this type of device, an accurate determination of the flow rate in real time can be achieved even with an unsteady fluid flow. This is because the consideration of dynamic pressure (Staudruck) ensures the most direct and accurate conversion of flow direction and flow velocity into measurable pressure. This symmetrical arrangement allows the two sondes to swap their functions even when the flow direction changes.

  In order to remove the influence of gravity from the equation, particularly when measuring liquid flow, a further embodiment of the invention is characterized in that the measuring tube and the sonde are arranged substantially horizontally.

  In order to further improve the accuracy of the device of the present invention, the device of the present invention is provided with another mechanism at least temporarily for measuring the flow rate of the unsteady flow. The algorithm for calibrating the coefficients of is characterized in that it is implemented by comparing the mean value of the unsteady Bernoulli solution for unsteady flow with the solution for steady flow.

  There is a sedation section to make the unsteady flow a steady flow, as well as a further mechanism for measuring the flow of the steady flow, and within the evaluation unit an algorithm for calibrating the unsteady Bernoulli coefficients is An embodiment, characterized in that it is implemented by comparing the average value of the unsteady Bernoulli solution for steady flow with the solution for steady flow, is also used to further increase the accuracy of the flow measurement.

  The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 schematically shows a device with a symmetrical bi-directional Pitot tube for determining the flow rate of unsteady flow.

  In the measuring tube 1 for fluid flow, two pressure sondes 2, 3 spaced apart from each other and aligned in opposite directions are preferably arranged in a direction parallel to the flow direction. The sound 3 pointing in the direction transmits the static pressure, and the sound 2 in the direction opposite to the flow transmits the total pressure at the inlet of each pressure sensor. The output ends of the two pressure sensors are connected to the evaluation unit (4). In this evaluation unit, as a first step, a differential pressure between the values of the two sensors corresponding to the dynamic pressure is obtained.

  It is necessary to know the density of the flowing fluid both in determining the volume flow rate and in the mass flow rate. Here, it is customary to assume that the density between the measurement points is approximately constant. The fact that the density is invariant in time is not assumed when deriving the equations implemented in the apparatus, but of course, invariant in time is assumed for the approximation method as well. Thus, by measuring the average value over a defined time interval, i.e. by pseudo-stationary or by giving a fixed value to the density in particular (this can be meaningful especially for liquids) A value can be set.

  The formula implemented in the evaluation unit is obtained based on Euler's formula for a one-dimensional flow without vortices.

  This formula still includes terms related to external forces. For example, gravity is included as a gradient of gravity potential according to the following equation (2).

ｖ．．．流速
ｐ．．．圧力
ρ．．．密度
ｓ．．．流れ方向での空間座標
ｚ．．．外力、例えば重力に平行な空間座標
ｔ．．．時間
Ｆ_ｓ．．．流れ方向における外力の成分
ｇ．．．重力場の強さ

v. . . Flow rate p. . . Pressure ρ. . . Density s. . . Spatial coordinates in the flow direction z. . . Spatial coordinates t. Parallel to external forces, eg gravity. . . Time F _s . . . External force component in the flow direction g. . . Gravity field strength

  However, assuming that the density is locally constant, the following equation is obtained:

  By integrating the position of one pressure sonde 2 or 3 with respect to the other pressure sonde 3 or 2, the following equation is obtained.

  When using a substantially horizontal tube 1 or sondes 2, 3 arranged at substantially the same height, the effect of gravity can be eliminated from the equation. This is particularly advantageous in the case of liquids, while in the case of gases the influence of gravity can be ignored anyway.

For the velocity of the fluid flow at the inlet of the pressure sonde 2 for the total pressure, a value of zero is assumed, and based on the assumption that the density is locally constant, between the positions of the two pressure sondes 2, 3 The term dv / dt is also considered constant. When the sign for the pressure difference p ₁ -p ₂ between the two pressure sondes 2 and 3 is Δp and the distance between the two openings is Δs, Equation (5) is obtained for the instantaneous value of the flow velocity v. .

  In the steady case where the acceleration term dv / dt = 0, the well-known formula (6) is established.

  Next, the process moves to an unsteady mass flow rate, and the unsteady volume flow rate is processed in the same manner.

  If q = A · ρ · v with respect to the mass flow rate, and A is the cross-sectional area of the pipe, the following equation is obtained from equation (5).

  In an actual application example, the following equation is obtained from Equation (7) in consideration of bidirectional flow.

ただし、Ｃ_１およびＣ_２は実験によって最適化可能な係数である。

However, C ₁ and C ₂ are coefficients that can be optimized by experiment.

  The integration of this differential equation to determine the instantaneous mass flow q (t) and the average mass flow is performed by a method known per se (numerical, analog computer).

To optimize and calibration coefficients C ₂ related constant part of equation (8), the flow is considered point is stationary. An alternative measurement method that is also suitable for unsteady flows, such as flow measurement based on the propagation time of the ultrasonic signal, determines the flow value so that the value from the solution of the differential equation corresponds to the value measured directly using the reference system. Fit coefficients to.

To ensure that the second coefficient C ₁ may optimize or calibration, it can be provided, for example an alternative high dynamic measurement method. In this measuring method, after calibrating and optimize other factors, the value adaptation of the coefficients C ₁ and from the solution of the differential equation, is again consistent with the direct measured value.

In another embodiment, the unsteady flow can be sedated to a steady flow. In this case, unsteady Bernoulli coefficients can be calibrated by comparing the average value of the unsteady Bernoulli solution for unsteady flow with the reference system measurements for steady flow. Again the flow of the decision, in order to calibrate the coefficients C ₁ for the term of the differential equation for the non-constant portions may be carried out by a measurement method alternative to the flow that is at that time constant.

Claims (4)

An apparatus for determining the flow rate of a bi-directional unsteady fluid flow, comprising a measuring tube (1), a mechanism for detecting the differential pressure and density of the fluid, a detected pressure difference of the fluid and An evaluation unit for calculating a flow rate based on the density, and the evaluation unit has a calculation unit for solving a normal nonlinear differential equation relating to a flow velocity in real time in consideration of a pressure difference and an acceleration term relating to the flow velocity. In the device,
Two sondes (2, 3) are provided which are arranged substantially antiparallel to each other and parallel to the direction of fluid flow, one of which (2) provides the total pressure and the other An apparatus comprising a mechanism (4) for recording a static pressure by the sonde (3) and detecting a differential pressure between the sondes (2, 3).   2. Device according to claim 1, characterized in that the measuring tube (1) and the sonde (2, 3) are arranged substantially horizontally.   Another mechanism is provided at least temporarily for measuring the flow rate of the unsteady flow, and an algorithm for calibrating the coefficient of the unsteady Bernoulli equation in the evaluation unit is an unsteady Bernoulli equation for the unsteady flow. 3. An apparatus according to claim 1 or 2, characterized in that it is implemented by comparing the mean value of the solution with the solution for a steady flow.   A sedation section for making the unsteady flow a steady flow, as well as a further mechanism for measuring the flow of the steady flow, are provided, and within the evaluation unit, an algorithm for calibrating the coefficients of the unsteady Bernoulli equation 4. The device according to claim 1, wherein the device is implemented by comparing the mean value of the unsteady Bernoulli solution for unsteady flow with the solution for steady flow.

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