JPS6014170Y2 - flow rate detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a detector for detecting the flow rate of a cryogenic evaporative liquid fluid.

When determining the flow rate of fluid flowing in a pipe, a detector as shown in FIG. 1 is usually constructed using an orifice and a differential pressure gauge.

That is, an orifice 2 is provided in the pipe 1, and the fluid pressure near the orifice 2 on the upstream and downstream sides is guided to the differential pressure gauge 5 through the impulse pipes 3 and 4, and the pressure is determined in advance from the output of the differential pressure gauge 5. The converter 7 outputs the flow rate based on related values such as the Reynolds number.

Note that 6 is a flow rate control valve that is interposed in the pipe 1 and adjusts the flow rate.

In the flow rate detector constructed in this way, liquid nitrogen or L
When measuring the flow rate of a liquid fluid such as NG which is at an extremely low temperature and has evaporative properties, the pipe 1 is sufficiently cold-insulated at the lower part of the impulse pipes 3 and 4.

However, the inside of the differential pressure gauge 5 and the intermediate portions and above of the pressure guiding tubes 3 and 4 are occupied by vaporized gas, and this is used as a gasification section.

(See Figure 2) Note that the dotted lines in Figure 2 are drawn assuming streamlines.

Now, if we change the opening degree of the flow control valve 6, the flow rate will change, and the pressure on the upstream and downstream sides of the orifice 2 will change.
The pressure fluctuation causes the liquid column at the bottom of the impulse pipes 3 and 4 to move up and down.

In addition, pressure is immediately transmitted to the differential pressure gauge 5 through an indirect process in which the liquid column compresses or expands the gas above it.

In such a detector, since the fluid to be measured is at an extremely low temperature and evaporates due to heat input, it is unavoidable and reasonable to transmit pressure through the gasification part. It is.

However, if the flow rate fluctuates rapidly, an unbalanced pressure response will occur due to the gasification portion.

For example, when the flow control valve 6 on the downstream side of the orifice 2 is suddenly contracted, the impulse pipe 3 on the upstream side of the orifice 2 is easily affected by the water hammer phenomenon, and the upstream flow as shown by the solid line in FIG. The side pressure Pυ is input to one side of the differential pressure gauge 5.

On the other hand, the pressure PL on the downstream side of the orifice 2 has no such influence, so it rises gently, and as a result, the differential pressure Pu
Pt is temporarily increased (flow rate increases), which is outputted by the converter 7 via the differential pressure gauge 5, resulting in an error.

The present invention eliminates these drawbacks, and includes a pipe having an orifice and a flow rate control valve for flowing evaporative liquid fluid, whose lower ends communicate with each other at positions across the orifice, and a gasification section is provided at the upper part. A flow rate detector for detecting the flow rate of an evaporative liquid fluid flowing in the piping, which comprises two pressure impulse pipes and a differential pressure gauge, each of which is connected to the upper end of the pressure impulse pipe, adjusts the flow rate of the pressure impulse pipe. characterized in that the volume of the gasification section on the side farther from the valve is at least twice the volume of the other gasification section,
The purpose is to treat flow rate measurement errors as a dynamic characteristic problem, improve only the dynamic characteristics without changing the static characteristics, and provide a flow rate detector free of measurement errors.

The present invention will be described below with reference to an embodiment of the device shown in FIG. 3. However, the structures and functions of the components having the same reference numerals as in FIG. 1 are the same, and therefore the description thereof will be omitted.

As shown in the figure, since a flow control valve 6 is interposed on the downstream side of the orifice 2, a spirally wound pressure guide pipe 8 is attached to the upstream side of the orifice 2, and its upper end communicates with the differential pressure gauge 5.

For example, if about half of the upper part of the impulse tube 4 is a gasification section, the length of the impulse tube 8 can be increased by making the impulse tube have a length 1.5 times the length of the impulse tube 4. The gasification section will have approximately twice the volume.

In addition, the volume of the gasification section may be increased by increasing the diameter of the pressure guiding pipe.

Now, taking as an example the case where the flow rate control valve 6 is suddenly contracted, since the piping 1 on the upstream side of the orifice 2 is relatively long, there is a pressure increase both above and downstream of the orifice 2.
The flow rate press-fitted into the upstream impulse pipe 8 does not pass through the resistance of the orifice 2, and the local pressure suddenly becomes larger than the set value due to the influence of pressure wave reflection. This is excessively larger than the press-in flow rate.

Therefore, as mentioned earlier, when the pressure impulse tube 3 like the conventional detector is used, the pressure P as shown by the solid line in FIG.
This is a temporary sharp increase in U.

This is because the ratio of the compression change to the volume of the gasification section at the initial stage of the impulse pipe 3 (before the rapid contraction of the flow rate control valve 6) becomes large.
This is because the rate of change in the detected pressure PU becomes large.

When converted to flow rate, such a reverse response amount is equal to 2 of the flow rate change value.
It reaches as much as 0%.

This is extremely disadvantageous for improving stability and coordination as a flow rate detector for automatically controlling the flow rate using the detected flow rate value as a feedback amount.

On the other hand, in the detector of this embodiment, the length of the impulse tube 8 is
The volume of the gasification section was made to be 1.5 times that of the pressure impulse pipe 4 or more due to the increase in the heat input area.

That is, the volume of the initial gasification section becomes large, and the differential pressure gauge 5 is measured from the upstream side of the orifice 2 through the gasification section of the impulse pipe 8.
The pressure transmission to the area becomes slower over time.

This improves the balance of pressure-sensitive responses by the impulse tubes 4 and 8, and the differential pressure of the pressure put PL on the upstream and downstream sides of the orifice 2 measured by the differential pressure gauge 5 has no reverse response, that is, the dotted line in FIG. You are guaranteed to get a highly accurate value as shown.

Note that when the flow rate control valve 6 is located upstream of the orifice 2, the volume of the gasification section of the impulse pipe downstream of the orifice 2 is
It goes without saying that it is better to make the upstream side more than twice as large.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a conventional detector, Fig. 2 is an explanatory diagram of its principle, and Fig. 3 is an explanatory diagram of a detector showing an embodiment of the present invention.
FIG. 4 is a graph of the measured pressure. 1... Piping, 2... Orifice, 4.
8... Impulse tube, 5... Differential pressure gauge, 6...
...Flow control valve.

Claims (1)

[Scope of utility model registration request] A piping that has an orifice and a flow rate control valve for flowing an evaporative liquid fluid has two impulse tubes whose lower ends communicate with each other at positions across the orifice and which have a gasification section at the top, and an upper end of the impulse tubes. and differential pressure gauges connected to each other, the flow rate detector detects the flow rate of the evaporative liquid fluid flowing in the piping. A flow rate detector characterized in that the volume is more than twice the volume of the conversion section.