JP2010243245A - Ultrasonic flow meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To treat the inner surface of a tubular body made of fluororesin for measurement and to give hydrophilicity. <P>SOLUTION: The tubular body 2 for measurement is placed from the inlet 3 to the outlet 4 for a fluid under measurement F. Ultrasonic transducer 7, 8 are attached to cranked corner parts 5, 6 of the tubular body 2 so that they face each other. The tubular body 2 is made of fluororesin, and the wettability of its inner surface is modified with a treatment liquid to prevent air bubbles contained in a liquid flowing through the tubular body 2 from adhering to the inner surface. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultrasonic flowmeter using a measurement tube that is difficult to cause bubbles to adhere to the measurement tube.

  From the viewpoint of chemical stability, fluororesin piping is used in a measurement tube in an ultrasonic flowmeter used in a conventional semiconductor manufacturing apparatus or the like as it is molded and processed.

JP-A-9-314041 Japanese Unexamined Patent Publication No. Sho 63-120745

  A fluororesin is a material that is particularly excellent in chemical stability among many polymer materials, and an application product of a fluororesin is used as an advantage. However, if a measurement fluid containing bubbles is passed through a fluororesin measurement tube provided in an ultrasonic flowmeter used in a semiconductor manufacturing apparatus or the like, the bubbles easily adhere to the inner surface of the tube. Thus, the progress of the ultrasonic beam is hindered and accurate flow measurement is disabled. As described above, the bubbles are attached to the inner surface of the tubular body because the fluororesin has water repellency and the liquid hardly gets wet with the surface of the fluororesin.

  Patent Document 1 discloses a method for significantly improving the hydrophilicity of a material surface by coating with a photocatalyst in order to improve the water repellency of the surface of a fluororesin.

  Patent Document 2 discloses a pretreatment method for extracting fluorine from the surface of the fluororesin in order to improve the adhesion between the fluororesin and other materials.

  The object of the present invention is to eliminate the above-mentioned problems, improve the wettability of the inner surface of the measurement tube made of fluororesin to the liquid to prevent the adhesion of bubbles, and the measurement liquid contains bubbles. Another object of the present invention is to provide an ultrasonic flowmeter that does not degrade the measurement accuracy.

  The ultrasonic flowmeter according to the present invention for achieving the above object is an ultrasonic flowmeter using a measurement pipe made of fluororesin, by allowing a treatment liquid to act on the inner surface of the measurement pipe, It is characterized in that the wettability of the liquid flowing to the inner surface is improved, and the bubbles contained in the measuring liquid are prevented from adhering to the inner surface of the measuring tube.

  According to the ultrasonic flowmeter of the present invention, bubbles in the measurement liquid are prevented from adhering to the inner surface of the measurement pipe made of fluororesin, and the occurrence of malfunction in flow measurement is suppressed.

It is a block diagram of the liquid flow part of an ultrasonic flowmeter.

The present invention will be described in detail based on the embodiments shown in the drawings.
FIG. 1 shows a configuration diagram of a liquid passing portion 1 of an ultrasonic flowmeter, and a measuring tube 2 is arranged from an inlet portion 3 of a measuring fluid F toward an outlet portion 4. Ultrasonic transmitters / receivers 7 and 8 are attached to the corners 5 and 6 of the measurement tube 2 bent in a crank shape so as to face each other. The measuring tube 2 is made of a fluororesin, and its inner surface is processed by a processing method described later.

  Ultrasonic beams are alternately emitted from the ultrasonic transmitters / receivers 7, 8, and are repeatedly transmitted to the ultrasonic transmitter / receivers 8, 7 on the other side via the measurement fluid F in the measurement tube 2. In this process, the arrival time of the ultrasonic beam traveling in the same direction as the flow direction of the measurement fluid F to the other side is reduced, and the arrival time of the ultrasonic beam traveling in the opposite direction is increased. Based on these arrival time differences, the velocity of the measurement fluid F is obtained, and the flow rate can be obtained from the product of the fluid velocity and the cross-sectional area of the measurement tube 2. However, if bubbles adhere to the inner surface of the measurement tube 2, the progress of the ultrasonic beam may be blocked, and the flow rate measurement may be impossible.

  In order to improve the wettability of the inner surface of the measurement tube 2 made of fluororesin to the liquid, for example, as described in Patent Document 2, a pretreatment method for extracting fluorine from the surface of the fluororesin is employed. This method is used for the purpose of lowering the surface tension of the fluororesin surface to improve wettability, and remarkably relieves the water repellency of the fluororesin. The treatment liquid used in the pretreatment step contains metallic sodium, which acts on the fluororesin to extract surface fluorine and simultaneously produces sodium fluoride.

  In order to treat the inner surface of the measuring tube 2, the surface treatment liquid is an organic solvent that does not react with metallic sodium, dimethylhydrofuran (THF), 1.3-dimethyl-2-imidazolicin (DMI), dimethyl A liquid dispersed in acetamide (DMA) or the like is used. Of these dispersions, sodium metal and naphthalene are gradually added to a solution of one kind or a mixture of several kinds, or a mixed solution in which THF coexists, and the mixture is allowed to stand for 24 hours, and then sufficiently stirred to prepare. .

  In order to treat the inner surface of the measurement tube 2 with the treatment liquid thus prepared, the treatment liquid sucked with a syringe-like injector or the like may be injected into the measurement tube 2. Furthermore, in order to remove the produced sodium fluoride, it is preferable to sufficiently wash with pure water.

  As the surface treatment method, if the surface of the fluororesin can be improved, for example, an ammonia method using a treatment liquid prepared by adding 1% metallic sodium to liquid ammonia, water, caustic soda and alcohol 3: 1. A caustic soda method using a processing solution prepared by mixing at a ratio of 1: 1, or a naphthalene method using a processing solution prepared by adding 128 g of naphthalene and 23 g of sodium metal to 1 liter of THF is also applicable.

  Also, anthracene can be used in place of the naphthalene described above. Furthermore, as the alkali metal to be used, metallic lithium, metallic potassium, etc. can be used in addition to metallic sodium.

  Table 1 shows a case where a measuring tube 2 made of a fluororesin tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA) is used for an ultrasonic flowmeter, and the inner surface is surface-treated by the above method. The measurement state is compared with the case of processing.

  The measurement fluid F performs an experiment on pure water mixed with bubbles and a CMP slurry, and indicates the number of times measurement failure occurred during measurement for 15 hours for each error duration. The error continuation time is a time width in which the measurement value cannot be obtained because the progress of the ultrasonic beam is prevented by the bubble attachment even when the measurement fluid F flows in the measurement tube 2.

Table 1
Measurement liquid Pure water Error duration Immediately after treatment No treatment 1 second 2 times 73 times 2 to 5 seconds 2 35
6-10 seconds 0 9
11-20 seconds 0 26
21 seconds or more 0 131

Measurement liquid CMP slurry error duration 2 months after treatment No treatment 1 second 16 times 51 times 2 to 5 seconds 11 65
6-10 seconds 0 2
11-20 seconds 0 1
21 seconds or more 0 2

  When pure water is allowed to flow without treating the inner surface of the measurement tube 2, the number of occurrences of malfunctions due to the attachment of bubbles for one second lasts 73 times for 21 hours or more within the measurement time of 15 hours. The number of occurrences reached 131 times.

  However, if pure water is flowed immediately after the inner surface of the measuring tube 2 is treated, the number of occurrences that last for 1 second is 2 times, the number of occurrences that last for 2 to 5 seconds is 2 times, and no more. It turns out that it decreases drastically.

  In addition, when the CMP slurry was passed through the unprocessed measurement tube 2, the number of occurrences of the error duration that lasted 1 second reached 51 times, and the number of occurrences that lasted 2 to 5 seconds reached 65 times. On the other hand, in the measurement tube 2 after passing through the liquid for 2 months after the treatment, the number of occurrences lasting for 1 second is 16 times, and the number of occurrences lasting 2 to 5 seconds is 11 times. It can be seen that it persists afterwards.

  By processing the inner surface of the measurement tube 2, the mixed bubbles are easily discharged, so that there is no fluid pressure fluctuation due to the attached bubbles, and stable flow rate control is possible.

  In addition, when bubbles are less likely to adhere to the inner surface of the measurement tube 2, the work time for removing bubbles that is spent at the start of liquid flow is shortened, and the measurement efficiency is further improved.

  In addition to the above-mentioned PFA, New PFA, polytetrafluoroethylene, polytrifluorinated ethylene, tetrafluoroethylene / hexafluoropropylene copolymer can be used as the fluororesin.

DESCRIPTION OF SYMBOLS 1 Flowing part of ultrasonic flowmeter 2 Tube for measurement 3 Inlet part 4 Outlet part 5, 6 Corner part 7, 8 Ultrasonic transmitter

Claims (3)

  In an ultrasonic flowmeter using a measurement pipe made of fluororesin, a treatment liquid is allowed to act on the inner surface of the measurement pipe, thereby increasing the wettability of the liquid flowing against the inner surface. An ultrasonic flowmeter characterized by preventing bubbles contained therein from adhering to the inner surface of the measuring tube.   2. The ultrasonic flowmeter according to claim 1, wherein a solution prepared by adding metallic sodium and naphthalene to a single or complex solution having a high boiling point and does not react with metallic sodium is used as the treatment liquid.   The ultrasonic flowmeter according to claim 1, wherein a solution obtained by mixing tetrahydrofuran (THF) with a single or complex solution having a high boiling point and not reacting with sodium metal is used as the treatment liquid.

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