JP7603557B2 - Method for estimating temperature of low-temperature liquefied gas mixture sample - Google Patents

Description

The present invention relates to a combustion/explosion test of a low-temperature liquefied gas mixture sample, and in particular to a method for estimating the temperature of a low-temperature liquefied gas mixture sample using an ignition method based on a melting cut.
Low-temperature liquefied gas mixture samples include mixtures of combustion-supporting low-temperature liquefied gas (e.g., liquid oxygen ( _LO2 )) and non-flammable low-temperature liquefied gas (e.g., liquid oxygen ( _LO2 )) with solid flammable substances (e.g., metal powder, resin powder, etc.), as well as mixtures of combustion-supporting low-temperature liquefied gas (e.g., liquid oxygen ( _LO2 )) with liquid flammable substances (e.g., liquid methane ( _LCH4 ), liquid propane ( _LC3H8 ) _, etc.).
Flammable substances also include oils and fats such as machine oil and grease.

In order to safely handle a mixture of combustion-supporting low-temperature liquefied gas and a flammable substance, it is necessary to measure the conditions that cause combustion or explosion, such as the explosive range, minimum ignition energy, and explosive power.
An example of a test device for performing such measurements is a combustion and explosion test device disclosed in Japanese Patent Laid-Open No. 2003-233996.

In addition, the ignition methods that can be used in the above combustion and explosion test equipment include (1) the discharge method, (2) the heating method, and (3) the melting method.
(1) The discharge method is a method of ignition by discharging electricity between a pair of electrodes placed at a distance from one another, and is described in Patent Documents 2 to 4 and Non-Patent Document 1 as Method B in the Notice on Explosives and High-Pressure Gas Control No. 37 (issued by the Safety Division of the Chemical Bureau, Ministry of International Trade and Industry, dated January 15, 1968).
The discharge method is widely used because the released energy can be easily quantified, it has good reproducibility, and the electrodes can be reused repeatedly.

(2) The heating method, as disclosed in Patent Documents 5 to 7, is a method in which an electric current is passed through a nichrome wire (hereinafter referred to as "Ni-Cr wire") to heat it, and the heat is used to heat the gas, which then ignites when the gas exceeds its spontaneous ignition temperature. The heating method requires low voltage and low current, and the amount of heat input can be easily estimated.

(3) The fusing method, as disclosed in Non-Patent Documents 1 and 2, involves passing a current (hereinafter referred to as "fusing current") through a platinum wire (hereinafter referred to as "Pt wire") or Ni-Cr wire to cause it to melt, and using the sparks released when the wire melts as the ignition source. The fusing method can use either AC or DC and requires only low voltage, so the cost of the power supply equipment and power supply is low, and it can produce a release energy of several joules to several tens of joules.

When preparing a low-temperature liquefied gas mixture sample, which is a mixture of combustion-supporting low-temperature liquefied gas and a flammable substance, and experimentally confirming whether or not it is explosive using the above-mentioned combustion and explosion test device, it is necessary to estimate the temperature and composition of the low-temperature liquefied gas mixture sample.
Therefore, it is essential to measure (estimate) the temperature accurately.

Also, if the flammable substance is something that dissolves very well in _LO2 , like liquid methane (hereafter referred to as _LCH4 ), it will be possible for it to dissolve over time, but because the densities of _LO2 and solid _CH4 are significantly different, whether it has dissolved and what the liquid composition is must be estimated from the temperature and pressure inside the liquefaction vessel.For this reason too, it is necessary to measure the temperature inside the liquefaction vessel.

If the temperature inside the liquefaction vessel cannot be measured accurately, the estimated composition will contain a large error.
Therefore, accurate measurement of the temperature inside the liquefaction vessel is important for accurately estimating the composition.

The most common methods for measuring the temperature of liquefied gas are to use (1) a thermocouple or (2) a platinum resistance thermometer.

Patent No. 6178645 JP 2013-152196 A Japanese Patent Application Publication No. 11-201925 Patent No. 6596264 JP 2006-29629 A JP 2001-113156 A Patent No. 4764728 JP 2016-53487 A JP 2010-101859 A

FY2016 Ministry of Economy, Trade and Industry Commissioned High Pressure Gas Safety Measures Project (2) Examination of legal and technical issues related to the High Pressure Gas Safety Regulations and various products using high pressure gas Report (2017), High Pressure Gas Safety Institute, p. 11-p. 12, line 6 Research on the Explosive Hazards of Hydrogen, Ministry of Labor, Industrial Safety and Health Research Institute, Industrial Safety and Health Research Report RR-18-1 (1969)

The temperature of liquefied gas can be measured accurately by placing the sensor end in the liquid, but in the combustion and explosion test device, the signal wire passes through a vacuum insulation tank and a specimen container (hereafter referred to as the "liquefaction container") on the way to the specimen. For this reason, to measure temperature with high accuracy, it is necessary to use connectors made of the same material as the compensation conductors in these parts, but in addition to passing through a vacuum insulation tank, the pressure-resistant container must be able to withstand a pressure of 5 MPa.

For platinum resistance thermometers, three-wire or four-wire sensors are generally used to improve accuracy, but the specifications for the wiring connection from the sensor to the receiver must be exactly the same for three or four wires, and a dedicated receiver is required for both thermocouples and resistance thermometers.
Furthermore, since a current of about 1 mA is normally passed through a platinum resistance thermometer, the voltage at that time is measured, and the temperature is determined from the resistance value, the influence of self-heating of the platinum resistance thermometer cannot be avoided in the low temperature range, and the reliability of the indicated value decreases. Methods for canceling the influence of self-heating are disclosed in Patent Documents 8 and 9, which use fixed parameters or multiple power sources and sensors.
As described above, there are many factors that can cause errors in measuring the temperature of liquefied gas, including temperature drift, the sensor installation position, the connection method described above, and the like.

The ideal method for measuring the temperature of liquefied gas is to place a sensor in the liquid inside the liquefaction vessel, but this is cumbersome because the sensor and conductors are damaged every time the sample burns or explodes, making it necessary to replace or calibrate the sensor every time.
Furthermore, in order to install a sensor inside the liquefaction vessel, it is necessary to penetrate the sensor wire into the liquefaction vessel. As with the penetration parts of vacuum chambers and pressure-resistant vessels, there is the issue that sufficient gas leakage countermeasures and gas leakage inspection accompanying cooling (hereinafter referred to as cold leak check) are essential even at low temperatures.

Furthermore, when installing a temperature sensor, if the material is a substance that undergoes a combustion reaction with a liquefied gas such as LO ₂ , the combustion reaction will be indistinguishable from that of the test object. Therefore, the temperature sensor should be made of only non-combustible materials as much as possible.
Furthermore, in the presence of conductive materials, fusing electrodes containing conductive wires and other components come into electrical contact with the inner wall of the container, increasing the possibility of electrical leakage when current is applied. Therefore, it is necessary to configure the device with the minimum number of components necessary.
As described above, there are various problems associated with the method of installing a temperature sensor when measuring the temperature of a low-temperature liquefied gas mixed sample.

The present invention has been made to solve these problems, and aims to provide a method for estimating the temperature of a low-temperature liquefied gas mixed sample that can accurately estimate the temperature of the low-temperature liquefied gas mixed sample in a liquefaction vessel without using a temperature sensor.

The inventors have conducted extensive research to solve the above problems.
Since the configuration of the explosion test equipment differs depending on the ignition method described above, we first considered the optimal ignition method for conducting combustion and explosion tests on low-temperature liquefied gas mixture samples.
The above-mentioned discharge method requires a DC power source to determine the amount of released energy, and use in a low-temperature liquefied gas atmosphere requires a large voltage, which requires a large amount of cost for the equipment and wiring construction.
In addition, the energy density of the heating method varies depending on the surface area of the wire and the temperature difference, and is low. Also, the reproducibility is poor, making it unsuitable as an ignition method for ignition tests.

In contrast to the above, the fusing method can use either AC or DC and requires low voltage, so the cost of power supply equipment and power supply is low, and the released energy is several to several tens of J. For these reasons, it is an appropriate method to use for determining whether a mixture is flammable or not.
From the above, the melting method is suitable as the ignition method for the combustion and explosion tests of low-temperature liquefied gas mixture samples, and the melting method was adopted as the ignition method.

Then, we discovered that by using the fusing method as the ignition method, the fusing wire can be used to measure temperature. The present invention was made based on this discovery, and specifically has the following configuration.

(1) A method for estimating the temperature of a low-temperature liquefied gas mixed sample according to the present invention is a method for estimating the temperature of the low-temperature liquefied gas mixed sample in a combustion/explosion test in which a fusing wire immersed in a low-temperature liquefied gas mixed sample is ignited by supplying a fusing current to the fusing wire, the fusing current being sufficient to fusing the fusing wire,
a calibration curve creation step of determining a resistance value for each of two or more pure substances, each having a known vapor pressure, when a current less than a fusing current is passed through the fusing wire for each type of substance, and creating a calibration curve showing the relationship between the resistance value and temperature based on the resistance value;
a test object resistance value calculation step of determining a resistance value when a current having the same value as that passed in the calibration curve creation step is passed through the low-temperature liquefied gas mixed sample, which is a test object;
and a temperature estimating step of estimating a temperature of the low-temperature liquefied gas mixed sample based on the resistance value calculated in the specimen resistance value calculating step and the calibration curve calculated in the calibration curve creating step,
The calculation of the resistance value in the calibration curve creation step and the test specimen resistance value calculation step is characterized in that the change in voltage when a current less than the fusing current is applied is recorded, the voltage value of the linear portion where the rate of increase of the voltage becomes constant is extrapolated to the time when the current is applied, the voltage at the time when the current is applied is estimated, and the resistance value is calculated based on the voltage and the current.

(2) The device described in (1) above is characterized in that it further includes a test specimen resistance correction step in which the relationship between the room temperature and the resistance value of the conductor portion, which is at room temperature, other than the fused electrode portion, which is the low-temperature portion, is measured in advance, and if there is a difference between the room temperature in the calibration curve creation step and the room temperature in the test specimen resistance calculation step, a correction is made to the resistance value in the test specimen resistance calculation step based on the relationship.

According to the present invention, it is possible to directly measure and estimate the temperature of a low-temperature liquefied gas mixed sample without providing equipment such as a sensor and receiver for temperature measurement.
Furthermore, no foreign matter is allowed to coexist within the liquefaction vessel, and the number of parts that need to be replaced each time a combustion or explosion occurs can be minimized.

1 is an explanatory diagram illustrating each step and its order of a method for estimating the temperature of a low-temperature liquefied gas mixed sample according to an embodiment of the present invention. FIG. FIG. 1 is a diagram showing the overall configuration of a combustion and explosion test apparatus used in a temperature estimation method for a low-temperature liquefied gas mixed sample according to an embodiment of the present invention, and is a partial vertical cross-sectional view of the combustion and explosion test apparatus. FIG. 3 is a diagram showing an installation state of a liquefaction vessel installed inside a pressure-resistant thermostatic vessel in the combustion and explosion test apparatus shown in FIG. 2 . FIG. 2 is a diagram showing positions at which temperature is measured when controlling the temperature of a low-temperature liquefied gas mixed sample. FIG. 1 is a diagram showing a configuration of a device used for ignition and temperature estimation in an embodiment of the present invention. 1 is a graph showing the value of the fusing current that melts a Pt wire or a Ni-Cr wire when the wire is immersed in _LN2 . 11 is a graph showing the change in voltage over time when a current less than the fusing current is applied to a fusing wire. 1 is a graph showing an example of a calibration curve showing the relationship between resistance value and liquefaction vessel temperature in the present embodiment. 1 is a graph showing the relationship between conductor resistance value and room temperature.

The temperature estimation method for a low-temperature liquefied gas mixed sample according to embodiment 1 of the present invention estimates the temperature of a low-temperature liquefied gas mixed sample using a fusing wire before ignition in a combustion/explosion test in which ignition is performed using a fusing method.
Prior to describing the temperature estimation method for a low-temperature liquefied gas mixed sample in this embodiment, an example of a test device used in the above-mentioned combustion and explosion test will first be described with reference to Figs. 2 to 6.

FIG. 2 shows the overall structure of a combustion and explosion test device 1 for a low-temperature liquefied gas mixture sample that is ignited using a melting method.
The combustion and explosion test apparatus 1 has the same configuration as the "combustion and explosion test apparatus" described in Patent Document 1, so detailed description will be omitted and the main parts will be outlined below. Note that the names of the members used in the description are not necessarily the same as those of the "combustion and explosion test apparatus" in Patent Document 1.
In addition, the "combustion and explosion test device" of Patent Document 1 uses discharge ignition, and the components related to ignition are different, but this point will be explained in detail later.

As shown in Figures 2 and 3, the combustion and explosion test device 1 is equipped with a liquefaction container 5 for storing the low-temperature liquefied gas mixture sample 3, a pressure-resistant thermostatic container 7 for maintaining the low-temperature liquefied gas mixture sample 3 at a predetermined temperature, and a refrigerator 9 for generating cold heat to be transferred to the pressure-resistant thermostatic container 7.

The pressure-resistant thermostatic container 7 contains the liquefaction container 5 and has a container body 11 with pressure resistance in the event of an explosion, a first cold heat transfer mechanism 13 that transfers cold heat into the container body 11, a second cold heat transfer mechanism 15 that blocks heat from entering the container body 11, and a container holding mechanism 17 that holds the liquefaction container 5.

The first cold heat transfer mechanism 13 includes a cold base 19 that covers the bottom of the container body 11, and a cold rod 21 that is connected at one end to the cold base 19 and at the other end that passes through the container body 11 and is disposed outside the container body 11 (see FIG. 3). The cold rod 21 is connected to the refrigerator 9 via a cold heat transfer member 23.

The second cold heat transfer mechanism 15 includes a solid heat conductive member 25 that contacts the outer peripheral surface of the container body 11 and transfers cold heat to the outer peripheral surface, and the solid heat conductive member 25 is connected to the refrigerator 9.

The first cold heat transfer mechanism 13 and the second cold heat transfer mechanism 15 are also equipped with a temperature adjustment device (not shown) that adjusts the temperature of the cold rod 21 and the solid heat conduction member 25. The temperature of the cold rod 21 and the solid heat conduction member 25 is adjusted using a temperature sensor 31 (see FIG. 4) provided on the holding member 29 described below and heaters (not shown) equipped on the cold rod 21 and the solid heat conduction member 25, and the low-temperature liquefied gas mixture sample 3 in the liquefaction vessel 5 can be maintained at a predetermined temperature by controlling the heater so that the temperature of the temperature sensor 31 becomes a predetermined temperature.

As shown in Figures 3 and 4, the container holding mechanism 17 has a base plate 27 that contacts the cold base 19 of the first heat transfer mechanism 13, and a bridge-shaped holding member 29 that stands upright from the base plate 27, and the liquefaction container 5 is attached to the holding member 29. In addition, a temperature sensor 31 is provided near the portion of the holding member 29 where the liquefaction container 5 is fixed.

The combustion/explosion test apparatus 1 in this embodiment is equipped with a pressure-resistant constant temperature container 7 configured as described above, and thereby transfers the cold generated by the refrigerator 9 to the cold base 19 via the cold heat transfer member 23 and cold rod 21 of the first cold heat transfer mechanism 13, and further to the liquefaction container 5 via the base plate 27 and holding member 29, thereby cooling the liquefaction container 5.
The cold generated by the refrigerator 9 is transferred to the container body 11 via the solid heat conductive member 25 of the second cold heat transfer mechanism 15 to cool the container body 11 .
Furthermore, as described above, the first cold heat transfer mechanism 13 and the second cold heat transfer mechanism 15 adjust the temperatures of the cold heat transfer member 23 and the solid heat conduction member 25 based on the temperature of the holding member 29, and the temperature inside the liquefaction vessel 5 is maintained in equilibrium.

The liquefaction vessel 5 seals the low-temperature liquefied gas mixture sample 3, which is the subject of the experiment, and is fixed to the holding member 29 as described above and placed in the center of the vessel body 11 of the pressure-resistant thermostatic vessel 7 (see FIG. 3).
As shown in FIG. 4, the liquefaction vessel 5 includes a cooling block 33 fixed to the holding member 29, and a cylindrical liquid reservoir portion 35 with a bottom.
The cooling block 33 has a gas inlet 37 for introducing gas. The gas introduced from the gas inlet 37 is cooled in the cooling block 33 to become liquid, and is stored in the liquid reservoir 35 .
When the flammable substance is liquid or solid at room temperature, the flammable substance may be introduced into the liquid reservoir 35 in advance.

An inlet joint 39 protrudes from above the cooling block 33, and a pair of conductors 41 pass through the inlet joint 39 and are inserted into the liquefaction vessel 5. A portion of the conductors 41 is covered with an insulating material 43 to prevent contact with the inner wall of the liquefaction vessel 5 or the like and causing a short circuit. It is preferable to use a material that is not combustible (such as an insulator if necessary) for the insulating material 43. Flammable materials are undesirable because they may cause combustion of things other than the specimen.

In the example shown in FIG. 4, a hermetic seal (an insulating joint consisting of a threaded joint, a pipe, and an insulator) is used as the lead-in joint 39 .
The lead-in joint 39 may be a hermetic seal or a sealing gland, and may be any type that can ensure insulation and airtightness at low temperatures.
In addition, the internal pressure of the liquefaction vessel 5 can be constantly monitored by a pressure detection device (not shown).

A fusing wire 45 is attached to the end of the pair of conducting wires 41 inserted in the liquefaction vessel 5, and the fusing wire 45 is disposed in the liquid reservoir 35. When adjusting the liquefaction of the low-temperature liquefied gas, the fusing wire 45 is adjusted so that it is immersed in the liquid. It is recommended to use a Pt wire for the fusing wire 45, but in systems that require a long time to prepare the liquid or in cases where the catalytic effect of the Pt surface is influential during preparation, Ni-Cr wire, tungsten wire, or other materials can be used. Silver brazing is preferable for connecting the fusing wire 45 and the conducting wires 41, and solder can also be used, although there is a risk of reaction when ignited.
It is necessary to install the conductor wire 41 and the fusing wire 45 so as not to come into contact with the inner wall of the liquefaction vessel 5 and cause a short circuit, but installing flammable insulating materials inside the liquefaction vessel 5 is not desirable because it may cause combustion of things other than the specimen. If necessary, it is recommended to use materials that are not likely to burn, such as insulators.

5, a constant voltage generator 47 is connected to the ends of the pair of conductors 41 on the outer side of the liquefaction vessel 5 to supply a current to the fusing wire 45. The constant voltage generator 47 can supply a current (fusing current) capable of fusing the fusing wire 45, and can also set and change the current value. The supply of current can be started and stopped by turning a switch 49 ON/OFF manually or by a signal from an external source.
In addition, the conductor 41 connecting the constant voltage generator 47 and the fusing wire 45 has a sufficient material and wire diameter to accommodate the current supplied from the constant voltage generator 47, and is connected to the constant voltage generator 47 and the fusing wire 45 so as to ensure stable use.
The fusing wire shown in the high pressure gas A method is a Pt wire φ0.3, so a constant voltage generator with a capacity of about 30A is sufficient for LO ₂ temperature (-183℃). Also, as long as the current value can be set, it does not matter whether it is DC or AC. The current and voltage shown in Figure 5 are connected to a data logger or recorder so that the changes can be recorded.
On the other hand, the conductor 41 from the constant voltage generator 47 to the fusing wire 45 must have a sufficient capacity and be connected in a manner that assumes a rush current of 30 A or more.

Next, a method for estimating the temperature of a low-temperature liquefied gas mixture sample, which is a specimen, in a combustion and explosion test performed using the combustion and explosion test apparatus 1 of this embodiment configured as described above will be described below with reference to Figures 1 to 9, showing specific examples.
As shown in FIG. 1 , the temperature estimation method for a low-temperature liquefied gas mixed sample according to this embodiment includes a calibration curve creation step, a specimen resistance value calculation step, a specimen resistance value correction step, and a temperature estimation step.
Each step will be described in detail below.

<Calibration curve creation process>
The calibration curve creation process is a process in which two or more pure substances with known vapor pressures are used to determine the resistance value for each type of substance when a current less than the fusing current is passed through the fusing wire 45, and a calibration curve showing the relationship between resistance value and temperature is created based on the resistance values.

When carrying out this process, first, the value of the fusing current that melts the fusing wire 45 at the operating temperature is measured in advance. As an example, Fig. 6 shows a graph showing the fusing current of a Pt wire and a Ni-Cr wire when used while immersed in liquid nitrogen (hereinafter referred to as " _LN2 "). As shown in Fig. 6, for example, when a Pt wire with a wire diameter of φ0.3 is immersed in _LN2 , the Pt wire melts when a current of about 30 A or more is supplied to the Pt wire.
The fusing current is determined by the electrical resistance and melting temperature specific to the fusing wire type, wire diameter, the temperature difference between the melting temperature and the liquefied gas, and the heat transfer coefficient, so if these conditions are the same, there is no significant difference between _LN2 and, for example, _LO2 .
In this example, the fusing current is 30A, so the current less than the fusing current is set to, for example, 20A.

The constant voltage generator 47 can be a PSW-360L30 manufactured by Texio Technology Co., Ltd. It is set so that when the resistance of the path including the fusing wire 45 is low, a preset current flows, and when the resistance is sufficiently high, a current value that automatically results in a preset potential difference flows.

The resistance value is calculated by recording the change in voltage when a current less than the fusing current is applied, extrapolating the voltage value of the straight line portion where the voltage increase rate becomes constant to the time when the current is applied, estimating the voltage at the time when the current is applied, and calculating the resistance value based on this voltage and the current.
In this way, by using a method of extrapolating the voltage trend, it is possible to correct the output response delay of the constant voltage power supply.

Specifically, the liquefaction vessel 5 is cooled, and pure oxygen gas, which is a combustion supporting gas, and pure methane gas, which is a combustible gas, are introduced and liquefied, and after confirming that sufficient equilibrium has been reached, 20 A is applied to the fusing wire 45. An example of the voltage change upon application is shown in Figure 7. The light gray line in Figure 7 is the extrapolation auxiliary line. The voltage extrapolated values in LO ₂ and LCH ₄ at atmospheric pressure were 4.0128 V and 4.1054 V, respectively.
Voltage V = current A · resistance Ω, and using this, the resistance values for LO ₂ are 0.20064 Ω and for LCH ₄ are 0.20527 Ω.
Since the temperatures of _LO2 and _LCH4 at atmospheric pressure are 90K and 111.6K, respectively, it is possible to obtain FIG. 8 showing a calibration curve showing the relationship between resistance value and temperature.

<Test object resistance value calculation step>
The specimen resistance value calculation step is a step of determining a resistance value when a current having the same current value as that in the calibration curve creation step is passed through the low-temperature liquefied gas mixed sample 3, which is the specimen.
Specifically, a mixed gas of oxygen _O2 and methane _CH4 is introduced into the liquefaction vessel 5 and cooled to liquefy, and 20 A is applied to the fusing wire 45 in the same manner as in the calibration curve creation process, and the voltage at the time of application is calculated. The voltage at the time of application is calculated in the same manner as in the calibration curve creation process, by extrapolating the voltage value of the linear portion where the voltage increase rate becomes constant at the time of application of the current, and estimating the voltage at the time of application of the current. The voltage at the time of application in this example was 4.0214 V.
Since the input current is 20 A and the input voltage is 4.0214 V, the resistance value is calculated as 0.20107 Ω.

<Test Object Resistance Value Correction Process>
The specimen resistance value correction process is a process in which the relationship between the room temperature and the resistance value of the conductor part, which is at room temperature, other than the fused electrode part, which is a low-temperature part, is measured in advance, and if there is a difference between the room temperature in the calibration curve creation process and the room temperature in the specimen resistance value calculation process, a correction is made to the resistance value in the specimen resistance value calculation process based on this relationship.

The relationship between the room temperature and the resistance of the conductor part at room temperature is found by shorting the end of the conductor part in the room temperature range shown in Figure 5, and measuring the resistance by performing the same operation as in the above-mentioned calibration curve creation process without changing the length of the conductor (hereinafter referred to as "length") or the material of the connection part, but changing only the room temperature. The relationship between the room temperature and the resistance obtained in this way is shown in Figure 9.
If the room temperature differs between when the calibration curve is created and when the test object resistance value of the low-temperature liquefied gas mixed sample 3 is calculated, correction is performed with reference to Fig. 9. Under the conditions of Fig. 9, it is sufficient to increase or decrease the slope of the straight line by 0.75 x ^10-3 Ω/K per difference in room temperature.

<Temperature Estimation Process>
The temperature estimation step is a step of estimating the temperature of the low-temperature liquefied gas mixed sample 3 based on the resistance value obtained in the specimen resistance value calculation step and the calibration curve obtained in the calibration curve creation step.
Specifically, in this example, the room temperature was the same in the calibration curve creation process and the test specimen resistance value calculation process, and the test specimen resistance value was 0.20107 Ω, so 92.0 K was obtained as the temperature of the low-temperature liquefied gas mixed sample 3 from FIG.
Furthermore, if the temperature of the low-temperature liquefied gas mixture sample 3 is known, the concentration of each low-temperature liquefied gas can be estimated from the gas-liquid equilibrium curve.
In this example, the methane concentration in the low-temperature liquefied gas mixture sample 3 at atmospheric pressure (0.1 MPa Abs) and 92.0 K could be estimated to be 20 vol% (gas phase concentration is approximately 6%) from the O ₂ --CH ₄ gas-liquid equilibrium curve.

As described above, according to this embodiment, it is possible to directly measure and estimate the temperature of the sample liquid without using any equipment such as a sensor and a receiver for temperature measurement.
Further, there are other advantages such as no foreign matter being allowed to coexist within the liquefaction vessel 5 and the need for replacement parts for each combustion or explosion being minimized.

In addition to the above-mentioned effects, the present embodiment can also provide the effect of providing superior resolution to that of a typical resistance temperature detector.
This point will be explained in detail below.
The JIS C 1604 standard specifies the resistance value of a resistance thermometer (Pt100Ω) as shown in the table below in a simplified form.

From the table above, if we consider the relationship between temperature and resistance to be linear, the slope between -100°C and -200°C is (60.2-18.5)/100=0.417(Ω/K). The current supplied to a typical platinum resistance thermometer is 1mA, so the resolution is 1× ^10-3 A×0.1417Ω/K=0.417× ^10-3 (V/K) because I・R=V.
8 is 0.2143×10 ^-3 (Ω/K), but because the supply current is 20 A, it becomes 0.2143×10 ^-3 Ω/K×20A=4.28×10 ^-3 V/K, which is expected to provide approximately 10 times the resolution.This has the advantage that it can be used with general-purpose voltage measuring equipment.

Although the specimen resistance correction process was explained above, this is performed when the room temperature is different between the calibration curve creation process and the specimen resistance calculation process. If there is no difference in room temperature between the two processes as in this example, there is no need to perform this process.

However, since the test specimen resistance value correction step is extremely important in the present invention in which the fusible wire is at an extremely low temperature, this point will be explained below.
The equation of the straight line showing the relationship between the resistance value and temperature of the fusion wire shown in FIG.
R(Ω) = 0.2143 × ^10-3 × T(K) + 0.18136 ... (1).
The equation of the straight line showing the relationship between the resistance value and temperature in the conductor 41 shown in FIG.
R(Ω)=0.75× ^10-3 ×T(K)-0.03975・・・(2).

For example, when the temperature T is 92K, the resistance value of Pt is given by the regression line of equation (1):
R = 0.2143 × 10 ^-3 × 92K + 0.18136 = 0.2011 Ω.
In addition, when the room temperature is 10°C, the regression line of equation (2) gives:
R = 0.75 × 10 ^-3 × 283K-0.03975 = 0.1725Ω.
Here, when the room temperature is 11° C., based on the straight line in FIG. 9, the impedance increases by 0.00075 Ω from 0.1725 Ω to 0.17325 Ω.
However, if the resistance value is not corrected, that is, if the difference in room temperature is not taken into account, 0.00075 Ω will be mistaken for a fused wire (Pt). In that case, from formula (1),
0.2011+0.00075=0.2143× ^10-3 ×T(K)+0.18136. From this, T=95.6K.
This temperature difference is 3.6 K compared to 92.0 K. In other words, by performing the test specimen resistance value correction process, such errors do not occur, and the test specimen resistance value correction process, which corrects the resistance value based on the room temperature difference, is of great significance.

In the present invention, it is necessary to collect the fusing wire resistance value (FIG. 8) in advance to prepare the calibration curve. However, since it is essential to perform a cold leak check in advance on the liquefaction vessel 5 used in the combustion and explosion test of the low-temperature liquefied gas mixed sample 3, the calibration curve preparation work can be performed before or after the cold leak check work, so this work does not become a heavy burden.
Here, a brief explanation of cold checks will be given.
When the device is assembled at room temperature (such as by installing the liquefaction vessel 5), and then cooled, distortion occurs at the joints of the piping and vessel due to thermal contraction, which may result in minute gas leaks from the joints. Since the presence or absence of such leaks cannot be confirmed without actually cooling, a cooling and leak check is performed in advance, which is called a cold leak check.

REFERENCE SIGNS LIST 1 Combustion and explosion test device 3 Low-temperature liquefied gas mixture sample 5 Airtight container 7 Pressure-resistant thermostatic container 9 Refrigerator 11 Container body 13 First cold heat transfer mechanism 15 Second cold heat transfer mechanism 17 Container holding mechanism 19 Cold base 21 Cold rod 23 Cold heat transfer member 25 Solid heat conductive member 27 Base plate 29 Holding member 31 Temperature sensor 33 Cooling block 35 Liquid reservoir 37 Gas inlet 39 Introduction joint 41 Conducting wire 43 Insulating material 45 Fusing wire 47 Constant voltage generator 49 Switch

Claims (2)

A method for estimating the temperature of a low-temperature liquefied gas mixed sample in a combustion and explosion test in which a fusing wire immersed in a low-temperature liquefied gas mixed sample is ignited by supplying a fusing current to the fusing wire, the fusing current being sufficient to fusing the fusing wire, the method comprising:
a calibration curve creation step of determining a resistance value for each of two or more pure substances, each having a known vapor pressure, when a current less than a fusing current is passed through the fusing wire for each type of substance, and creating a calibration curve showing the relationship between the resistance value and temperature based on the resistance value;
a test object resistance value calculation step of determining a resistance value when a current having the same value as that passed in the calibration curve creation step is passed through the low-temperature liquefied gas mixed sample, which is a test object;
and a temperature estimating step of estimating a temperature of the low-temperature liquefied gas mixed sample based on the resistance value calculated in the specimen resistance value calculating step and the calibration curve calculated in the calibration curve creating step,
The method for estimating the temperature of a low-temperature liquefied gas mixed sample is characterized in that the calculation of the resistance value in the calibration curve creation process and the test specimen resistance value calculation process involves recording the change in voltage when a current less than the fusing current is applied, extrapolating the voltage value of the straight line portion where the voltage increase rate becomes constant at the time of current application, estimating the voltage at the time of current application, and calculating the resistance value based on the voltage and the current. The method for estimating the temperature of a low-temperature liquefied gas mixture sample according to claim 1, further comprising a test specimen resistance correction step of measuring in advance the relationship between the room temperature and the resistance value of the conductor portion, which is at room temperature, other than the fused electrode portion, which is the low-temperature portion, and correcting the resistance value in the test specimen resistance calculation step based on the relationship if there is a difference between the room temperature in the calibration curve creation step and the room temperature in the test specimen resistance calculation step.

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