JPH0242319A - Fluid measuring device - Google Patents

Abstract

PURPOSE:To measure the coefficient of viscosity at low cost by detecting pressure drop which occurs when fluid flows in a conduit by a differential pressure detecting means. CONSTITUTION:A signal from a detector (b) is amplified in a driving circuit (e), controlled to be a constant amplitude, and drives a driving coil (c), so that a closed loop is constituted. Therefore, a driving frequency becomes a natural frequency and density rho is calculated from the natural frequency by a arithmetic circuit (f). After the signals from the detectors (a) and (b) are shaped, the phases thereof are compared and Coriolis force is detected from a time difference corresponding to a phase difference so as to obtain mass flow (g). Therefore, the coefficient of viscosity mu can be computed by measuring the pressure drop in each flow. If the relation among the pressure drop, the mass flow (g) and the coefficient of viscosity mu is previously fixed, the coefficient of viscosity mucan be directly calculated from the pressure drop and the mass flow (g).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a fluid measuring device, more specifically, a Coriolis mass flowmeter and a method for measuring the pressure loss at the inflow and outflow ends of the Coriolis mass flowmeter to determine mass flow rate, density, The present invention relates to a fluid measuring device that calculates viscosity.

When the center of a conduit through which fluid flows supported between two points is vibrated, the direction between the supporting point and the vibrating part is equal to the vector product of the fluid flow direction and the vibration direction. It is known that a Coriolis force proportional to the mass flow rate is generated in the pipe, and since the directions of vibration are opposite between the supporting points of the conduit and the vibrating part, the Coriolis force is Coriolis mass flowmeters that detect as a phase difference with respect to a reference line have been attempted. When the conduit is straight, the phase difference to be detected is small, so the S/N ratio worsens and it is difficult to improve the accuracy of flow rate measurement.To solve this problem, the
No. 0-34683 discloses a Coriolis flowmeter in which the conduit is a curved conduit that is axially symmetrical about a second axis, and the first axis perpendicular to the second axis is used as a support point. This flowmeter is driven around the first axis at a natural frequency at the tip of the conduit, so that a torsional moment proportional to the Coriolis force acts around the second axis, and the torsional moment is transferred to both arms of the curved conduit. is detected as the time difference when passing through the reference plane of the curved conduit. This method has the characteristic of being able to measure with high sensitivity because the torsional rigidity around the second axis of the conduit is small, but it is also possible to measure the density of the fluid because it is excited around the first axis at a natural frequency. That is, the natural frequency is proportional to the square root of the ratio of the conduit's spring constant to the conduit mass, and the single tube mass is the sum of the unitary mass of the conduit and the mass of the fluid contained within the conduit. Since the mass of is calculated as the product of the pre-known internal volume of the conduit and the density, the natural frequency can be determined as a function of density. still,
A method of calculating the mass flow rate and fluid density by exciting a conduit at its natural frequency is disclosed in the above-mentioned Japanese Patent Publication No. 60-34683. The mass flow rate and density are determined by

In the vibrating Coriolis mass flowmeter described above, it was shown that the mass flow rate and density can be measured by exciting the vibration frequency at the natural frequency of the conduit containing the fluid.
When measuring fluids, it may be necessary to further measure the viscosity in order to know the properties of the fluid. In this case, it is necessary to install a separate viscometer, and the cost and location of the viscometer are It required a huge financial burden, such as securing the

The present invention has been made to solve the above-mentioned problems, and uses a Coriolis mass flowmeter to measure the pressure difference caused by viscosity in a conduit through which fluid flows, and calculates the mass flow rate and density. In addition, the viscosity is determined, and the object is to provide an inexpensive fluid measuring device with a simple configuration in which a pressure gauge is added to a Coriolis mass flow meter. That is, the fluid measurement device of the present invention includes a conduit of equal diameter supported and fixed between two points,
a driving means for driving the conduit at a natural frequency around a support point in the center of the conduit; a detection means for detecting a Coriolis force caused by a fluid flow between the moving means and the support point; differential pressure detection means for detecting a differential pressure of a fluid in a predetermined section; a mass flow rate of the fluid from the Coriolis force; a fluid density from the natural frequency; dimensional specifications of the conduit in the predetermined section; the mass flow rate; The fluid viscosity is calculated based on the density and the fluid pressure difference.

Figure 1 is a diagram showing the configuration and operation block diagram of the main body in the fluid measuring device of the present invention, and Figure (A) is a plan view;
(B) Figure is a sectional view taken along the arrow in Figure (A), (C)
The figure is an operation block diagram. In the figure, 1 is a board, and the board 1 is integrally provided with a support member 11 perpendicular to one end, and the support member 11 is fixedly fixed through a U-shaped conduit 2. are doing. The conduit 2 has openings which are an inlet 21 and an outlet 22.

It is fixed to the support member 11 near the opening on the first axis XX axis. Further, the conduit 2 has a second axis (y
-y), on which a driving means 3 for driving the conduit 2 is mounted.

The main parts of the driving means 3 include a driving coil 32 and a permanent magnet 33 that is inserted into the driving coil 32 and generates an electromagnetic force.The magnet 33 is fixed to a support plate 31, and the support plate 31 The drive coil 32 is fixed to the curved part of the mounting base 34.
and is arranged on the substrate 1. The detectors 41 and 42 are arranged at symmetrical positions in the conduit 2 with respect to the second axis and are electromagnetic detectors. The magnet 45 is magnetized in a direction perpendicular to the plane of the paper and is fixed to both arms of the conduit 2 by attachment bands 46.
The coil 44 is wound so as to intersect the magnetic flux of the magnet 45 and is fixedly mounted via the mounting base 43.

Further, a conduit 23 is disposed near the inflow and outflow ports 21 and 22 of the conduit 2 and communicates with the inflow and outflow ports 21 and 22, and is guided to the differential pressure detector 5, and the fluid flowing through the conduit 2 is Detect pressure loss.

The operation of the main body shown in FIGS. 1(A) and 1(B) is described above (
This will be explained using a block diagram of C). Note that the detectors (a) and (b) in FIG. 1C are the detectors 41.
42, and the drive coil (C) and differential pressure detector (d) correspond to the drive coil 32 and differential pressure detector 5, respectively. The signal from the detector (b) is amplified by the drive circuit (e), controlled to have a constant amplitude, and drives the drive coil (c) to form a closed loop. Therefore, the driving frequency is the natural frequency,
The density ρ is calculated from this natural frequency by the arithmetic circuit (f). Further, the signals from the detectors (a) and (b) are shaped and compared in phase, and the Coriolis force is detected from the time difference corresponding to the phase difference to determine the mass flow rate g. Further, in Newtonian fluid, the viscosity coefficient μ is determined as follows.

In a straight circular pipe, when the time-averaged velocity distribution on each cross section does not change, the ratio of pressure loss ΔP due to fluid friction will also be constant, where P□: pressure on the inlet side, ρ: fluid density, ■= flow rate,
P2: pressure on the outflow side, d: pipe diameter, Q = pipe length, λ:
is the pipe friction coefficient.

In other words, if the conduit shape is constant, the pressure loss will be the dynamic pressure ρv2/
2, and the proportionality constant is the tube friction coefficient λ. Here, the dynamic pressure ρv2/2 is the mass flow rate (g) and the density (
It is calculated because ρ) has been measured and is known, and the cross-sectional area of the conduit is also determined. However, the tube friction coefficient λ is a function of the Reynolds number (hereinafter referred to as Re). Here, ν is the kinematic viscosity coefficient −” (3) ν − ρ.

When the flow in a pipe is laminar, the pipe friction coefficient λ is simply inversely proportional to the viscosity coefficient μ, and the proportionality constant is also constant (1)
, (2), the viscosity coefficient μ is obtained as μ■ΔP (4), and the laminar flow limit is the flow velocity V with respect to the pressure loss ΔP.
is determined from the range in which is exactly squared. In addition, the pipe friction coefficient λ when the flow inside the pipe is turbulent depends on the roughness of the inner wall surface of the pipe, but since the roughness is determined for each flowmeter pipe, it is simply a function of Re. given as.

Therefore, by measuring the pressure loss ΔP at each flow rate, the viscosity coefficient μ can be calculated. Further, if the relationship between the pressure loss ΔP, the mass flow rate g, and the viscosity coefficient μ is determined in advance, the viscosity coefficient μ can be immediately calculated from the pressure loss ΔP and the mass flow rate g. If the conduit is a curved pipe, it will be affected by the secondary flow at the curved part, resulting in pressure loss, but in this case as well, if the shape and dimensions of the conduit are determined, it can be treated in the same way as for the straight pipe described above. The viscosity coefficient μ can be calculated by

According to the applicant's experiments, the pressure loss ΔP when the conduit is U-shaped as shown in FIG.

It is confirmed that ΔP = (Kg/cm") - (5) ρ, and if the density ρ and pressure loss ΔP are known, the pressure loss coefficient C can be found. Also, the pressure loss coefficient C and the mass flow rate g can be calculated. There is a relationship shown in Figure 2 between them, and this relationship was experimentally determined using the viscosity coefficient μ as a parameter in a given flowmeter.Therefore, the pressure loss coefficient C determined by equation (5), The viscosity coefficient μ can be calculated from the mass flow rate g.The above-mentioned relationship is stored in the arithmetic circuit f, and is calculated based on the memory.The corner point Ta of the viscosity coefficient μm (C1 to 14) in FIG. (j=5~12)
hail the transition region from laminar to turbulent flow. According to the method of calculating the viscosity coefficient μ from the experimentally determined equation (5) and Figure 2 for the U-shaped conduit found by Akito Motode, the viscosity coefficient μ is calculated as a function of the Re number in the laminar region and the turbulent region. The viscosity coefficient μ can be determined without calculating separately from the friction coefficient λ.

FIG. 2 shows the relationship between the mass flow rate g and the pressure loss coefficient C for a plurality of fluids whose viscosity coefficient μ is known in advance. The viscosity coefficient μ is calculated based on the value, but if the relationship shown in Figure 2 is unknown, the pressure loss corresponding to the measured values of multiple mass flow rates for the relevant fluid is detected and the viscosity coefficient μ is calculated for each fluid. It is also possible to calibrate and store the viscosity coefficient and determine the viscosity coefficient from the measured values of pressure loss and mass flow rate based on the stored values.

Although the case in FIG. 2 is a relationship for Newtonian fluids, the latter case can also be applied to non-Newtonian fluids. The viscosity coefficients of all fluids are related to temperature, and the above relationship is shown as the viscosity coefficient corrected to the reference temperature. Therefore, as a matter of course, it is assumed that the relationship between viscosity change and temperature change is known in advance.

In Fig. 1, the differential pressure detector 5 is connected to the inlet 21° and the outlet 2
2, a pressure detector is attached to each pressure introduction pipe 23,
The output signal of this pressure detector may also be taken.

Figure 3 shows the case where it is installed on the outflow port 22 side.
(A) is a plan cross-sectional view, and (B) is a cross-sectional view taken along arrow 2-2 in (A). A mounting seat 24 is welded to the side surface of the outlet 22 of the conduit 2, and a pressure sensor 51 is screwed onto the mounting seat 24. Similarly, another pressure detector is installed on the inlet 21 side, and their output signals are calculated in the calculation circuit (f).

Although the above description is about a single conduit of equal diameter supported between two points, the present invention is also applicable to a case where conduits of the same shape and size are supported in parallel on the same support member. . In this case, since the same fluid is divided into the conduits supported in parallel, the vibrating body has a natural frequency substantially equal to that of the support member, so the support member is used as a vibration node and is shaped like a tuning fork. driven by The mass flow rate and density are sensed on the same principle as in the case of a single conduit, and the differential pressure sensing means sense the pressure loss of the laminar flow of fluid flowing through the parallel conduits.

1. As mentioned above, according to the fluid measuring device of the present invention, the physical quantities to be measured in the fluid, such as mass flow rate, density, and viscosity coefficient, are measured, and the viscosity coefficient simply represents the pressure loss flowing through the conduit. It can be measured at low cost by simply detecting it using a differential pressure detection means, without requiring an expensive viscometer or the like, and without requiring an installation location.

[Brief explanation of the drawing]

FIG. 1 is a plan view of the fluid measuring device of the present invention. (A) is a plan view, (B) is a sectional view taken along the line L-L in (A), and (C) is a block diagram explaining the present invention in detail.
FIG. 2 is a diagram showing the experimental results showing the relationship between the mass flow rate g and the pressure loss coefficient C using the fluid viscosity μ as a parameter, and FIG. 3 is an installation diagram of the pressure detector 51, and (A) is a side sectional view, and (B) is a sectional view taken along the Z-Z arrow in FIG. (A). DESCRIPTION OF SYMBOLS 1... Substrate, 2... Conduit, 3... Driving means, 41
．． 42...Detection means, 5...Differential pressure detector. Patent Applicant: OVAL Kiki Kogyo Co., Ltd. 1st grade Figure - IQg, o G (kg/rn in) Figure (B)

Claims (1)

[Claims] A conduit of equal diameter supported and fixed between one or two points, a driving means for driving the conduit at a natural frequency around the support point in the center of the conduit, and a drive means and a support point a detection means for detecting the Coriolis force caused by the fluid flow; a differential pressure detection means for detecting the differential pressure of the fluid in a predetermined section of the conduit;
The fluid density is determined from the natural frequency, the dimensional specifications of the conduit,
A fluid measuring device comprising calculation means for calculating fluid viscosity from the mass flow rate, fluid density, and fluid differential pressure. 2. The conduits are made of the same shape and size to distribute the fluid at equal flow rates, and the conduits are supported in parallel between two points, and the driving means is configured to rotate the conduits in a resonant frequency around each support point of each conduit. 2. The fluid measuring device according to claim 1, wherein the fluid measuring device is driven in phase. 3. Support the conduit in a U-shape axially symmetrically near the opening, measure the pressure loss inside the conduit using a differential pressure detection means that detects the pressure difference in the vicinity of the opening, and calculate the pressure loss and density in the measured value. Calculate the pressure loss coefficient by multiplying by
Claim 1, wherein the calculated value and the mass flow rate are compared with a stored value that stores the relationship between the mass flow rate and the pressure loss coefficient, which is detected in advance using the viscosity coefficient as a parameter, to determine the corresponding viscosity coefficient. Or the fluid measuring device according to item 2. 4. For a fluid that has a viscosity coefficient in a predetermined range and has a plurality of different viscosity coefficients, the viscosity coefficient is determined from the relationship between a plurality of different mass flow rates and the differential pressure of the fluid in a predetermined section of the conduit corresponding to the mass flow rate. 2. The fluid measuring device according to claim 1, wherein the fluid measuring device measures calibration, mass flow rate, density, and viscosity coefficient.