JP3122981B2 - Reversible flow measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible flow rate capable of measuring a flow rate with high accuracy even when the flow of a fluid flowing in a pipeline is reversed by using a throttle constituted by a symmetrical elliptic curve. It relates to a measuring device.

[0002]

2. Description of the Related Art As a reversible flow rate measuring apparatus of this type, a reversible flow rate measuring apparatus disclosed in Japanese Patent Application Laid-Open No. 51-2452 by the present applicant has been known. This flow rate measuring device has a symmetrical 1 /
It is formed by 4 elliptic curves and makes the range of the differential pressure gauge the same in both the forward and reverse directions. When the fluid specification is the same in both the forward and reverse directions, it can be applied to the flow measurement in both forward and reverse directions. I have.

At the time of measurement, similarly to a general concentric orifice plate, the pressure on the high pressure side and the pressure on the low pressure side are guided to a differential pressure gauge by a pressure guiding tube, the differential pressure is converted into an electric signal, and the flow rate is calculated from the output signal. It is configured as follows. That is, an orifice inlet that narrows the cross-sectional area of the pipe in the middle of the pipe,
If a restrictor having a symmetrical 1/4 elliptic curve on the outlet side is provided, when a fluid flows through the restrictor, a pressure difference occurs between the upstream side of the orifice and the throat portion (maximum flow velocity position) of the orifice. Since there is a certain relationship between the pressure difference and the flow rate, if the pressure difference is measured, the flow rate of the fluid flowing in the pipeline can be obtained by the following equation. W = CK · ΔP ^1/2 (1) where: W is the flow rate, C is the outflow coefficient, K is a constant (including the pipe diameter, fluid density, etc.), and ΔP is the differential pressure.

[0004] If the inlet and outlet sides of the orifice are constituted by symmetrical 1/4 elliptic curves as described above, the shape is optimal as a shape corresponding to a change in flow velocity. Therefore, when a restrictor is manufactured with this shape and a fluid is caused to flow to measure the pressure loss, the flow rate can be measured with a small pressure loss of 8% of the differential pressure.

[0005] For the same reason, a stable differential pressure with little fluctuation can be obtained by causing a fluid to flow at a constant speed. This is an excellent throttling mechanism capable of reducing a probability error that cannot be avoided as an error in measuring the differential pressure to zero.

The reason that the elliptic curve is optimal as the shape corresponding to the change in the flow velocity is because the shape of the water discharged by natural fall approximates this. That is, the shape of the natural fall of the fluid is a water column whose side surface is very similar to a part of the ellipse as shown in FIG. As a result, it is theoretically shown that even if a quarter-elliptical throttle is provided below the naturally falling fluid, no influence is exerted on the fluid.

[0007]

However, in the above-mentioned conventional reversible flow rate measuring device, when the flow direction of the fluid is switched, the two high pressure side pressure outlets are manually switched by an operator, and the flow of the fluid is changed. Since the pressure outlet on the upstream side in the direction is connected to the differential pressure gauge and the pressure outlet on the downstream side is closed, there is a problem that the operation is troublesome.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. It is an object of the present invention to provide two high pressure side pressure relief devices with a relatively simple structure when the flow direction of a fluid is switched. It is an object of the present invention to provide a reversible flow measuring device capable of automatically switching an outlet.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention relates to a diaphragm which is provided in the middle of a pipe and whose inlet and outlet sides have a symmetrical 1/4 elliptic curve, and a center of the diaphragm. A low pressure side pressure outlet provided in the
Two high pressure side pressure outlets provided at equal distances on both sides in the flow direction of the throttle, and a differential pressure gauge for detecting a differential pressure between the pressure at the high pressure side pressure outlet and the pressure at the low pressure side pressure outlet A switching valve for selectively connecting the two high pressure side pressure outlets to the differential pressure gauge; and switching means for operating in response to an output signal of the differential pressure gauge and switching the switching valve.

In the present invention, the differential pressure gauge measures the pressure P on the high pressure side.
The differential pressure (P1-P2) between 1 and the pressure P2 on the low pressure side is detected, and the flow rate is calculated. When the high-pressure side pressure P1 is lower than the low-pressure side pressure P2 depending on the flow direction of the fluid, the output signal of the differential pressure gauge becomes smaller than the zero point, whereby the switching means operates to switch the switching valve. When the switching valve is switched, the high pressure side pressure outlet on the upstream side opens with respect to the flow of the fluid, and the high pressure side pressure outlet on the downstream side closes.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. FIG. 1 is a schematic configuration diagram showing one embodiment of a reversible flow measurement device according to the present invention, and FIG. 2 is a cross-sectional view of an elliptical flow meter. In these figures, the reversible flow measuring device 1 includes an elliptical throttle flow meter 3 provided in the middle of a pipe 2. The elliptical restrictor flow meter 3 includes a measuring pipe 4 composed of a straight pipe having an inner diameter D, and a restrictor 5 provided in the center of the measuring pipe 4. The measuring pipe 4 has one low-pressure side and two high-pressure sides. , A total of three pressure outlets 6, 7, 8 are provided.
The throttle 5 is formed in a cylindrical body having an outer diameter equal to the inner diameter of the measuring tube 4, and has a フ ィ elliptical orifice 10 whose inlet and outlet are bilaterally symmetric. Such orifice 1
0 is the initial velocity of the fluid, v0, the gravitational acceleration at the drop opening, the drop distance is S, and the maximum drop distance is Sma, as shown in the above-mentioned Japanese Patent Application Laid-Open No. 51-2452.
x, when the radius of the water column at the drop distance S is r, the central opening (throat portion) 10a is determined by the radius r of the water column that falls naturally from the circular opening at a constant flow rate k. Note that the radius r is obtained by the following equation.

[0012]

(Equation 1)

The pressure outlet 7 on the low pressure side is located at the center of the throttle 5,
In other words, it communicates with the insertion hole 9 formed in the radial direction in the maximum thickness portion. The two high pressure outlets 6, 8
The throttles 5 are provided on both sides in the flow direction at equal distances (L3). The throttle diameter ratio d / D of the orifice 10 is 0.1 to 0.8, the dimension L1 on the inflow side is D / 2,
The outflow side dimension L2 is D / 2, and the distance L3 from the throttle 5 to the high pressure side pressure outlets 6, 8 is 25 mm to D.

As described above, the inlet and outlet openings of the orifice 10 are formed in a symmetrical quarter elliptical shape, and the two high-pressure outlets 6, 8 are equidistant on both sides in the fluid flow direction of the throttle 5. L3, and the low pressure side pressure outlet 7 is communicated with the insertion hole 9 provided in the center of the throttle 5, when the fluid flows from the arrow A direction and the arrow B direction. The measurement conditions can be exactly the same.

In the case of such a structure, the outflow coefficient C determined by the shape of the diaphragm 5 can be made very close to the ideal value 1. It is clear that this is an ideal state as compared with C = 0.61 in the case of a general concentric orifice plate. Therefore, the differential pressure ΔP at the low-pressure and high-pressure side pressure outlets represented by the general formula ΔP = V · r / C ² · k (3) is equal to the differential pressure ΔP under the same conditions as compared with the concentric orifice plate. Pressure ΔP
, The measurement range of the high-speed fluid is widened. In the above equation (3), V is the flow velocity, r is the specific weight of the fluid, C is the outflow coefficient, and k is a constant.

Further, a decrease in the differential pressure means that the pressure loss PL is reduced. Therefore, according to the general formula PL = ΔP (1-β ² ) (4), the throttle ratio is the same. The pressure loss in the case is also smaller than that of the concentric orifice plate. Therefore, it is advantageous to use the apparatus for utilizing the energy of fluid after measurement. Where β
Is the ratio of the reduced diameter to the inner diameter of the pipe.

Further, in general, when the straight pipe portion of the pipe upstream of the throttle is short and the flow becomes irregular, it is necessary to lengthen the straight pipe portion to rectify the stream lines. When the present elliptical flowmeter 3 having a large diameter is used, it is possible to save the length of the straight pipe by reducing the throttle ratio accordingly.

As described above, the reason why the outflow coefficient C is increased and the pressure loss is reduced is that the inlet and outlet sides of the throttle 5 form a part of an ellipse, so that the flow velocity distribution is substantially reduced as shown in FIG. This is because the flow becomes straight and the flow separation phenomenon does not occur. Further, the divergence angle on the outlet side of the throttle 5 according to the present invention becomes zero at the throat portion 10a where the flow velocity is the maximum, and gradually increases in proportion to the decrease in the flow velocity. Therefore, in many cases, it is possible to make approximately L = D.

Referring again to FIG. 1, the high-pressure and low-pressure side pressure outlets 6, 7, and 8 are connected to a differential pressure gauge 12 via a pressure guiding tube 11, respectively. Also, the high pressure side pressure outlet 6,
Solenoid valves 13A and 13B are provided between the pressure gauge 8 and the differential pressure gauge 12, respectively. By controlling the opening and closing of these solenoid valves 13A and 13B by the changeover switch 15, the two high pressure side pressure outlets 6 and 8 are fluidized. Is selectively connected to the differential pressure gauge 12 in accordance with the flow direction. That is, when the flow direction of the fluid is the A direction, the electromagnetic valve 13
A is opened to connect the high pressure side pressure outlet 6 to the differential pressure gauge 12, while the solenoid valve 13B is closed to disconnect the high pressure side pressure outlet 8 and the differential pressure gauge 12 and change the fluid flow direction to the B direction. Then, the solenoid valve 13B is opened to connect the high pressure side pressure outlet 8 to the differential pressure gauge 12, while the solenoid valve 13A is closed to disconnect the high pressure side pressure outlet 6 from the differential pressure gauge 12. The changeover switch (switching means) 15 for controlling the opening and closing of the solenoid valves 13A and 13B is a two-pen type with an alarm output for recording an output signal from the solenoid valve driving power supply 16 and the differential pressure gauge 12 on a recording sheet. It is connected to a recorder 14. Recorder 14
Is configured to transmit an alarm signal when the output signal from the differential pressure gauge 12 becomes smaller than the zero point, and to switch the changeover switch 15.

The differential pressure gauge 12 includes a well-known semiconductor pressure sensor (not shown) for converting the amount of diaphragm distortion caused by a change in pressure into an electric signal. Therefore, when the pressure P1 at the high pressure side pressure outlet 6 or 8 and the pressure P2 at the low pressure side pressure outlet 7 are guided to the semiconductor pressure sensor via the pressure guiding tube 11, and the differential pressure ΔP (= P1 -P2) is detected. The flow rate W of the fluid flowing through the pipe 2 is set as described above (1).
It can be calculated by an equation.

However, the above equation (1) gives the outflow coefficient C
Is satisfied when the discharge coefficient C changes depending on the number of Reynolds nozzles. Even when the flow rate W is obtained, the change in the discharge coefficient C appears as an error. Therefore, the flow rate is actually measured as follows.

The number of Reynolds nozzles is expressed by the following equation as a function of the flow rate. RD = K2.W (5) where RD is the number of Reynolds nozzles, and K2 is a constant (including tube diameter, density, etc.).

FIG. 4 is a diagram showing the relationship between the outflow coefficient C and the number of Reynolds nozzles RD. The relationship between the differential pressure ΔP and the flow rate W in the above equation (1) is obtained by first calculating the Reynolds number RD from the equation (5) based on the flow rate of 100%, and then calculating the outflow coefficient C from FIG.
Is calculated and substituted into equation (1) to calculate the differential pressure at a flow rate of 100%. If the differential pressure gauge 12 is adjusted to this differential pressure, a flow rate of 0 to 100% can be measured.

Next, the operation of the reversible flow rate measuring device 1 having the above-described structure will be described. First, the case where the fluid is flowing in the forward direction (the direction of arrow A) will be described. At this time, it is assumed that the upstream high pressure side pressure outlet 6 is connected to the differential pressure gauge 12 and the downstream high pressure side pressure outlet 8 is closed. In this state, when the fluid passes through the elliptical restrictor flow meter 3 through the pipe 2, the pressure P1 at the high pressure side pressure outlet 6 and the pressure P2 at the low pressure side pressure outlet 7 (P1>
P2) is led to the differential pressure gauge 12 via the pressure guiding tube 11, and the differential pressure .DELTA.P (P1 -P2) is detected by the differential pressure gauge 12 to calculate the flow rate, which is output to the recorder 14 as a current signal.
In the recorder 14, the forward flow pen is driven by the current signal to record the flow rate on the recording paper.

Assuming that the solenoid valve 13A is closed and the solenoid valve 13B is opened when the fluid flows in the direction of arrow A, contrary to the above, the downstream high pressure side pressure outlet 8 is connected to the differential pressure gauge 12 And the upstream high pressure side pressure outlet 6 is closed, so that the pressure P1 becomes smaller than the pressure P2. Therefore, since the output of the differential pressure gauge 12 becomes smaller than the zero point, the recorder 14 sends an alarm signal, switches the changeover switch 15, opens the solenoid valve 13A, closes the solenoid valve 13B, and sets the upstream high pressure side pressure. The outlet 6 is opened, and the downstream high-pressure outlet 8 is closed. As a result, the pressure P1 at the high pressure side pressure outlet 6 is guided to the differential pressure gauge 12 in the same manner as described above, and normal flow measurement can be performed. Therefore,
When the fluid flows, there is no problem even if the downstream high pressure side pressure outlet 8 is open and the upstream high pressure side pressure outlet 6 is closed.

Next, when the flow of the fluid is switched in the opposite direction (the direction of arrow B), the upstream high pressure side pressure outlet 6 is switched.
Is smaller than the pressure P2 and the output of the differential pressure gauge 12 becomes smaller than the zero point, the recorder 14 sends an alarm signal and switches the changeover switch 15. When the changeover switch 15 is switched, the solenoid valve 13A is closed while the solenoid valve 13B is opened. Therefore, the differential pressure gauge 12 has the pressure P1 of the upstream high pressure side pressure outlet 8 and the pressure P1 of the low pressure side pressure outlet 7.
(P1> P2), the differential pressure is detected by the differential pressure gauge 12, the flow rate is calculated, and the current signal is recorded by the recorder 1
4 As a result, the reverse flow pen of the recorder 14 operates to record the flow rate on the recording paper.

In the reversible flow measuring device having such a structure, when the flow direction of the fluid is switched, the two high pressure side pressure outlets can be automatically switched. No need to switch valves,
Easy to handle. In this respect, since the conventional reversible flow measuring device of this type is a manual type, in an application in which the flow direction is reversed, the measurer cannot instantaneously switch the pressure outlet, and the angle of the angle is not so large. Although performance cannot be exhibited, this is not the case in the present invention.

In the above embodiment, two solenoid valves 13A and 13B are used as switching valves.
Three three-way valves may be used, and the selector switch 15 may be directly switched by a signal from the recorder 14.

[0029]

As described above, in the flow rate measuring apparatus according to the present invention, a restrictor provided in the middle of a pipe and having an orifice inlet and outlet sides formed of a symmetrical 1/4 elliptic curve, A low pressure side pressure outlet provided at the center, two high pressure side pressure outlets provided at equal distances on both sides in the flow direction of the throttle, a pressure at these high pressure side pressure outlets and the low pressure side pressure A differential pressure gauge for detecting a differential pressure from the pressure at the outlet, a switching valve for selectively connecting the two high pressure side pressure outlets to the differential pressure gauge, and a switching valve operated by an output signal of the differential pressure gauge to switch the switching valve. Since the switching means is provided, the two high pressure side pressure outlets can be automatically switched when the flow direction of the fluid is switched.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of a reversible flow rate measuring device according to the present invention.

FIG. 2 is a sectional view of an elliptical throttle flowmeter.

FIG. 3 is a diagram showing a flow velocity distribution in a throttle.

FIG. 4 is a diagram showing the relationship between the outflow coefficient and the number of Reynolds nozzles.

FIG. 5 is a diagram showing that a streamline of a jet approximates an ellipse.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reversible flow rate measuring device, 2 ... Piping, 3 ... Elliptical flow meter, 4 ... Measuring pipe, 5 ... Restrictor, 6 ... High pressure side pressure outlet, 7
... low pressure side pressure outlet, 8 ... high pressure side pressure outlet, 11 ... pressure guide tube, 10 ... orifice, 12 ... differential pressure gauge, 13A, 13
B: Solenoid valve, 14: 2-pen recorder, 15: switch, 16: power supply.

Continuation of the front page (56) References JP-A-58-60218 (JP, A) JP-A-51-2452 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01F 1 / 42 G01F 1/44

Claims (1)

(57) [Claims] 1. A restrictor provided in the middle of a pipe and comprising a symmetrical 1/4 elliptic curve with orifice inlet and outlet shapes, a low pressure side pressure outlet provided at the center of the restrictor, and a flow of the restrictor. Two high pressure side pressure outlets respectively provided at equal distances on both sides in the direction, and a differential pressure gauge for detecting a differential pressure between the pressure at the high pressure side pressure outlet and the pressure at the low pressure side pressure outlet, A reversible flow rate measuring device, comprising: a switching valve for selectively connecting two high pressure side pressure outlets to the differential pressure gauge; and switching means for operating the output valve of the differential pressure gauge to switch the switching valve. .