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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
financial decisions, should not be based on machine-translation output.
The present invention relates to a method of detecting gas or vapor bubbles in a liquid, in
particular a high temperature, opaque liquid such as reactor coolant. In nuclear technology, the
presence of air bubbles in the coolant causes various obstacles, so its early detection is desired.
Na) In the case of an IJ-umf reactor, it is desirable to measure the sound pressure level in the
core, since the failure can often be detected in advance by changes in the frequency spectrum of
the noise in the sodium. In particular, the noise generated by the local boiling of sodium must be
reliably detected. Because in this case the reactor must be shut down immediately to prevent the
failure from increasing to melting of the fuel element. In the case of localized boiling, the bubbles
are sent by the stream into cold sodium, where they condense instantaneously. In this case, very
high peak pressures occur in a short time. Since this peak pressure is significantly more
pronounced than normal flow noise, the acoustic receiver should be designed for sensitivity and
frequency and its condensation noise. An object of the present invention is to detect gas or vapor
bubbles in a liquid by acoustic measurement. In this case it is assumed that the amount of air
bubbles affects the acoustic properties of the liquid, in particular in the ultrasonic range. In such
a system, an improved version of the ultrasonic transducer known, for example, from U.S. Pat.
No. 3,174,130 is used. In order to achieve this object, according to the present invention, the
amount of bubbles in the liquid is achieved by determining the inherent attenuation of the liquid
based on the attenuation of the ultrasonic signal. That is, it was found that the attenuation of the
ultrasonic signal was proportional to the amount of bubbles in the liquid. According to a
development of the invention, using two ultrasound transducers, the first transducer being an
ultrasound signal transmitter coupled to the monitored body and the second transducer being an
ultrasound signal Use as a receiver. In this case, the connection with the adult body is carried out
by connecting the transducer to the outside of the tube flowing through the liquid or by
disposing the transducer in the liquid. The amount of air bubbles in the liquid can be determined
from the amplitude, since the signals recorded at the receiver show different intensities in
response to the attenuation of the ultrasound signal in the liquid. According to a further
development of the invention, only one transducer is used and the winding is excited by the pulse
generator. In this case, the fade out time of the voltage generated in the transducer winding is a
measure of the degree of attenuation in the liquid and thus the amount of air bubbles. Such a
method is particularly economical, in which case the transducer is likewise placed outside the
liquid flow conduit or disposed within the liquid.
When placed in a liquid, it is advantageous as it can suppress sound waves in the solid of the
conduit structure. According to one embodiment of the invention, it is provided to pulsate the
transducer used as transmitter when using two ultrasound transducers. This avoids the
occurrence of unwanted resonances and improves the measurement accuracy. In principle, the
alternating voltage used to excite the transmitter can exhibit an arbitrary time course, for
example a sinusoidal waveform. However, when the frequency is constant, it is difficult to obtain
a constant output voltage. Because the transmission of vibrations from the transmitter to the
receiver is related to frequency and temperature. In order to avoid this problem, the excitation
frequency can be shifted so that an average value can be formed over a predetermined range of
mantissa fields so that errors can be compensated. However, it is also advantageous to excite the
acoustic transmitter with a short pulse whose duration is small compared to the transit time to
the acoustic receiver. In this way, the signal is not canceled by interference at the location of the
acoustic receiver. As an apparatus 100 for carrying out the method of the present invention, it is
preferable that an ultrasonic signal transmitter and a receiver are attached to a container
through which a liquid flows through a connecting rod. Bonding the converter to the liquid in
this way is particularly suitable for application to the reactor coolant circuit. Because the
circulation circuit is surrounded by a thermal insulator, the transducer is not directly exposed to
high temperatures due to the presence of the connecting rod. If both transducers are located at
opposite locations of the container, the vapor bubbles can be monitored over the entire cross
section of the container, which is very advantageous, for example, in monitoring the liquid
flowing in the conduit. The windings of the acoustic transmitter are advantageously connected
via relays, for example transformers, to periodically discharging capacitors. This produces a
suitable short excitation and pulse. According to yet another embodiment of the invention, the
ultrasound transmitter is formed as a magnetostrictive transducer. Magnetostrictive ultrasonic
transducers are characterized by their robust construction and good heat resistance and input
and output signals for the above-mentioned purposes compared to other ultrasonic generators. A
preferred embodiment of such a magnetostrictive ultrasonic transducer will now be described
with reference to the drawings. In this case, a transducer exhibiting axial opposite properties is
used in particular when detecting gas or vapor bubbles using two ultrasonic transducers,
whereas in some cases only one immersed in the liquid. A transducer with radial reflection
characteristics is used when measuring the fade-out time of the transducer.
The electroacoustic transducer in FIG. 1 comprises a magnetostrictive element with a core 3 of
ferromagnetic material. Since the core 3 is provided with a slit, the two 5s are connected in
series. The reference numeral 6 denotes a lead wire of the coils 4 and 5 accommodated in the
pipe upward. The magnetostrictive element is housed in a cladding tube l with a thick bottom 2
and its core 3 is brazed to the bottom 2 of the cladding tube l. This converter can also be inserted
into a conduit not shown here. In order to prevent corrosion in the conduit, the lower end 7 and
the upper guide ring 8 of the cladding bottom 2 are hardened with stellite or the like. When the
transducer is used in boiling liquid, the bottom is conically shaped to prevent air bubbles from
sticking to the bottom. The electroacoustic transducer in FIG. 2 is clad in the same manner. For
example, four longitudinal holes 23 are provided in the core 22 and four coil wound portions 27
are formed therebetween. Two carp A / 24.25 are wound on the coil winding part 27 and these
coils 24.25 are connected in series with one another as in the embodiment of FIG. It is formed of
a conductive wire. The number of holes and the number of coils associated therewith depend on
the size of the core 22; in the case of a core of 16 cranes with a diameter of four, four holes and
two coils are sufficient. In this case, the number of turns of the side coil is about 10, but is shown
by two in the drawing for the sake of simplicity. The transducer is small, and in the case of a
device actually made, the diameter of the transducer is 16-18. The transducer can be immersed
directly in the liquid to detect noise in the liquid. Since the leads are provided in the upper
cladding, their pressing and connections are unnecessary. In the embodiment of FIG. 1, when
used as an acoustic receiver, the sound pressure is mainly transmitted axially from the bottom 2,
ie to the core 3, whereas in the case of the embodiment of FIG. It is transmitted radially from
around 1, ie to the core 22. The coil wraps 9 to 27 elastically deform in the case of a core,
whereby the flux changes caused by the magnetostrictive principle induce a voltage in the coils
4, 5 to 24.25. It works even at very low frequencies due to the above-mentioned acoustic
receiver's direct contact. Furthermore, since the resonance frequency can be determined very
high by means of a corresponding design of the structural part, for example, in the case of liquid
iron), in the case of I, a sound pressure e measurement in the range of i, 100 kH2 or less IN / m ''
can do.
The transducer can be used both as an acoustic transmitter and as an acoustic receiver without
changing the structure. In the case of an acoustic receiver, the coils 4.5 to 24.25 can be biased to
increase the sensitivity. These coils are polarized such that when the cores 3, 22 are
mechanically stressed, the voltage developed in the coils is added. FIG. 3 shows a device for
detecting bubbles of vapor or gas in a liquid according to the invention, in which a transducer of
the type shown in FIG. 1 is provided. 12 ° 13 is a converter, and one of the converters 12 is an
acoustic transmitter, and an AC voltage is supplied from an oscillator 16. The other transducer
13 is an acoustic receiver whose output voltage is amplified by an amplifier 17 and displayed by
a display 18. Both transducers 12.13 are provided via connecting rods to, ii in a conduit 8
through which a liquid 19 for monitoring bubbles or bubbles of vapor flows. The connecting rods
11 J, 11 are welded to the conduit 8. The transducer can be welded to the connecting rod or can
be pressed and supported by a clamping device not shown here. The liquid 19 is, for example,
liquid sodium. The length of the connecting rod is such that the transducer can be provided
outside the thermal insulator 20 of the conduit 8. The transducer is provided with a support flt
14.15. The device described above acts such that the acoustic transmitter 12 applies vibrations
to the receiver 13 via the connecting rod 10, the conduit 8 and the liquid 19 in the conduit 8 and
the connecting rod 11. Since the liquid 19 absorbs acoustic energy in accordance with the gas
content of the liquid '19, the gas content in the liquid 19 can be determined from the amplitude
of the output signal of the amplifier 17. A schematic diagram of a pulse generator used as the
oscillator 16 is shown in FIG. The terminals R and Mp are supplied with a power supply voltage
of, for example, 220 volts. The capacitor C1 is charged through the reactor Dr1 and the rectifier
N1 at a positive half wave. When the charging voltage of the capacitor C1 reaches the Zener
voltage of the Zener diode N2, a current flows through the Zener diode N2, and the thyristor TI is
fired. That is, the capacitor C1 is discharged through the primary winding of the transformer M1.
The secondary winding of the transformer M1 is connected to the coil W1 of the transmitter 12.
The coil W1 and the coil W2 described later correspond to the pair of coils 4, 5 to 24. 25 in FIG.
1 and FIG. 2, respectively.
Transformer M1 is used to potentially isolate the excitation winding from the power supply. The
reactor Drl has the purpose of limiting the power supply current after firing of the thyristor T1.
The zener diode N2 ensures that the gas voltage is independent of fluctuations in the supply
voltage. The pulse voltage applied to the coil W1 of the transmitter 12 acts to expand the cores 3
and 22 of the transmitter 12 due to magnetostriction. The cores 3, 22 are supported by the
support device 14 and provide the connecting rod 10 and the conduit 8 with gas. The gas (which
has been attenuated by the liquid 19) is transmitted 1 to the core 3, 22 of the acoustic receiver
13, which is mechanically stressed on it, so that this coil W2 (FIG. 5) Voltage is induced in the A
commercially available amplifier with small noise input is connected to the coil W2 of the
receiver 13. In this case, the sensitivity can be increased by using an amplifier whose input
resistance is matched to the small coil resistance of the acoustic receiver. An embodiment of such
an amplifier is shown in FIG. The coil W2 of the acoustic receiver 13 is supplied via the resistor
R1 with a bias current which provides the necessary biasing of the core. The alternating voltage
generated in the coil winding by the receiver 8 is amplified by the two emitter-grounded
transistors Tel and Te3. The operating points of these transistors are adjusted by negative
feedback resistors R2 and R3. Capacitors 02, 0B and 04 act as high pass filters. The apparatus
for measuring the fade-out time in FIG. 6 comprises the coil W2 of the converter, the amplifier
17 described above and a diode N3 for rectifying the voltage smoothed by the capacitor C5.
Furthermore, this voltage is limited by the protective resistor R4 to the height of the threshold
voltage of the further diode N4. Therefore, at the output of this circuit, a constant voltage is
generated until the voltage induced in the coil W2 reaches a minimum value. The vapor or gas
bubbles in the liquid to be monitored reduce the time during which this constant voltage occurs.
Brief description of the drawings
FIG. 1 is a longitudinal sectional view of a magnetostrictive acoustic receiver or transmitter used
in the present invention, FIG. 2 is a longitudinal sectional view of a magnetostrictive acoustic
receiver or a transmitter according to another embodiment, and FIG. FIG. 4 is a block diagram of
the apparatus for detecting bubbles of gas or vapor in liquid according to the invention, FIG. 4 is
a connection diagram of a circuit for pulse generation of an acoustic transmitter based on FIG. 1
or FIG. Alternatively, FIG. 6 is a schematic diagram of a circuit for amplification and evaluation of
an output signal of an acoustic receiver based on FIG.
1.21 · · · cladding tube, 8.22 · · · ferromagnetic core, 4.5, 24. 25 · · · coil · 8 · · conduit, 9 · · · · 27
coil winding portion, DESCRIPTION OF SYMBOLS 10 ... 11 ... Connection bar, 12.18 ... Converter,
14.15 ... Support apparatus, 16 ... Oscillator, 17 ... Amplifier, 18 ... Display, 19 * Monitored liquid.
Fig、 2
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