JPS6161008A - Differential pressure generator - Google Patents

Abstract

PURPOSE:To measure exactly a flow rate by eliminating an adhesion of a scale as an insulator from the surface of a reducing mechanism to be inserted into a passage, so that a correct differential pressure to the flow rate is generated. CONSTITUTION:As for a differential pressure generator, generally, an orifice plate 1, a flow nozzle 2, etc. are given, but with respect to each of them, an adhesion of a scale is observed in case of a feed water flow meter, etc. of a boiler. This cause is due to an electrical interaction of the potential of the surface of a metal of the differential pressure generator contacting to a fluid, and an ionized scale component in the fluid. In order to eliminate this action, the differential pressure generator itself is constituted of insulating ceramics, or there is a method for adopting a system for covering the surface with an insulator by using a metallic material such as stainless steel, etc. as a base material, but it is practical that a metallic base material manufactured with a high accuracy is covered with ceramics of about several micra - scores of micra thick by means of vapor-deposition or ion plating, etc. In this way, a thermal expansion is determined by a quality of the metallic base material, and the measurement can be executed with a high accuracy.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a differential pressure generator for flow measurement, and is particularly applicable to feed water, spray water, and recirculation around boilers or nuclear reactors that require flow measurement of high-temperature, high-pressure water. This invention relates to a differential pressure generator suitable for measuring water.

[Background of the invention]

Conventionally, a differential pressure generator with a throttle mechanism has been used to measure the flow rate of water supply systems, etc. For example, since this differential pressure generator was made of 5O8304, scale adhesion to the differential pressure generator due to electrical phenomena caused by ionization of iron oxide was unavoidable, and flow rate measurement due to changes in opening area and opening shape was inevitable. There was a problem that an error occurred.

However, although scale adhesion is known, there are no papers that mention that the cause is ionized iron.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a measuring instrument that accurately measures a flow rate by realizing a differential pressure generator that generates a correct differential pressure with respect to the flow rate while eliminating scale adhesion.

[Summary of the invention]

It has been found that scale adhesion is caused by ions in the fluid being attracted by the metal surface potential of the differential pressure generator. Focusing on this, in the present invention, adhesion can be prevented by making the differential pressure generator itself an insulator. The present invention can be realized, for example, by coating or vapor depositing an insulating ceramic on a metal surface.

[Embodiments of the invention]

An embodiment of the invention is shown in FIG. Examples of differential pressure generators include general traps, orifice plate 1 in the same figure (a), flow nozzle 2 in the same figure (Fig. Adhesion of scale is observed. It has been newly found that this scale adhesion is due to the electrical interaction between the potential of the metal surface of the differential pressure generator that comes into contact with the fluid and the ionized scale components in the fluid. In order to eliminate this electrical interaction, in the present invention, the surfaces of the orifice plate and flow nozzle are made of an insulating material. For example, the shaded area in Figure 1 is an insulator.As a means of constructing the surface with this insulator, the differential pressure generator itself may be constructed of insulating ceramic, or a metal material such as stainless steel may be used as the base material. Another method is to cover the surface with an insulating material. The possibility of realization is that it is currently difficult to accurately manufacture ceramics with a diameter of 600 f1 or more, and measurement errors may occur due to the difference in temperature expansion coefficient with the piping side. It is more practical to cover the manufactured metal base material with a ceramic thickness of several microns to several tens of microns by means such as vapor deposition or ion blating. As a result, thermal expansion is determined by the properties of the metal base material, allowing highly accurate measurement.

Taking the orifice plate 1 of FIG. 1(a) as an example, FIG. 2 shows the installation state of the pipe 3 (FIG. 1(a)) and an example of scale adhesion (FIG. 1(b))'. As shown in the figure, the orifice plate 1 is a donut-shaped plate with holes and is fixed to the pipe 3 by a flange or the like. The fluid flowing at a flow rate corresponding to the inner diameter of the pipe is constricted by the orifice plate 1, and the differential pressure generated thereby is detected by the differential pressure detector 6, and the flow rate is detected by signal processing. At this time, as is well known, if the opening area ratio of the orifice plate 1 changes, the differential pressure generated will differ even with the same flow rate, resulting in an error in flow rate measurement.

In the conventional example, the scale 4 is often attached as shown in the figure, which results in the apparent opening area of the orifice plate 1 becoming smaller, the differential pressure generated at the same flow rate increases, and the measured flow rate decreases. This will include a large error.

The mechanism of scale adhesion will be explained with reference to FIG. Generally, the metal surface of a differential pressure generator or the like has a positive charge, and in still water, negatively charged ions adhere to this surface to maintain balance. When the flow rate of the fluid increases, these negative ions are forcibly removed, and the positive charge on the metal surface spreads over a long distance.
The mechanism is explained by the fact that negatively charged scale components adhere to metal surfaces. Therefore, if the influence of the charge on the surface of this metal (corresponding to the base material of the differential pressure generator) is removed, scale adhesion will be reduced.

〔Effect of the invention〕

According to the present invention, scale adhesion to the differential pressure generator for flow rate measurement is removed, and the accuracy of flow rate measurement can be maintained at a high level.

This makes it possible to accurately manage boiler performance and improve efficiency.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of coating the surface of a differential pressure generator with an insulating material according to the present invention, FIG. 2 is an explanatory diagram of scale adhesion, and FIG. 3 is an explanatory diagram of the scale adhesion mechanism. 1... Orifice plate, 2... Flow nozzle,
3... Piping, 4... Adhering scale, 5... Insulating material coated on the surface, 6... Differential pressure detector. Figure 1 Figure 1 (C) 10CC'@plane ShiC' Figure 52 Figure 3 Distance

Claims (1)

[Claims] 1. In a differential pressure generator that measures the flow rate by inserting a throttle mechanism into the flow path and detecting the differential pressure between the upstream and downstream sides thereof, at least the surface of the throttle mechanism is made of an insulator. pressure generator.