JP4963016B2 - Superconducting liquid level gauge - Google Patents

Description

  The present invention relates to a superconducting liquid level gauge.

In recent years, studies on the use of hydrogen as a fuel for moving bodies such as vehicles, ships, and aircraft or as a fuel for fuel cells have been underway. When hydrogen is used as a fuel, particularly when used as a fuel for a moving body, it is required to store a predetermined amount of hydrogen in a container.
Thus, when storing hydrogen in a container, the method of liquefying hydrogen and storing it in the state of a cryogenic fluid is known.

Various techniques for obtaining the remaining amount of liquid hydrogen, which is a cryogenic fluid stored in the container as described above, have also been proposed, and the remaining amount is obtained by measuring the liquid level of the cryogenic fluid. It is also known (e.g., see Patent Document 1.).
JP 2002-147694 A

  Non-Patent Document 1 described above discloses a technique for measuring the liquid level of a cryogenic fluid by providing two cylindrical electrodes and measuring the capacitance formed between the two electrodes. . This technology uses the difference in dielectric constant ε between liquid and gas, and measures the liquid level continuously by measuring the capacitance that changes according to the height of the liquid level. .

However, the above-described liquid level measurement has a problem that the measurement circuit of the measurement system becomes complicated because a high frequency power supply is required, and the measurement system becomes expensive and large.
In addition, if the dielectric constant of the cryogenic fluid in the liquid state or in the gaseous state is not uniform, the proportional relationship between the capacitance and the liquid level becomes inaccurate, and there is a problem that the accurate liquid level cannot be measured. It was.

  In addition, if the dielectric constant ratio, which is the ratio of the dielectric constant in the liquid state to the gaseous state of the cryogenic fluid, is small, there is a problem that the change in capacitance becomes small and the measurement of the liquid level becomes difficult. . For example, the dielectric constant ratio of oxygen and nitrogen is 1.48 to 1.43, whereas the dielectric constant ratio of hydrogen is 1.23, making it difficult to measure the liquid level compared to oxygen and nitrogen. There was a problem of becoming.

  The present invention has been made in order to solve the above-described problem, and is capable of accurately measuring the liquid level of a cryogenic fluid and simplifying and miniaturizing the structure thereof. The purpose is to provide an area meter.

In order to achieve the above object, the present invention provides the following means.
The superconducting liquid level meter according to the present invention includes a liquid level detector disposed in a protective tube having at least a part thereof disposed in a cryogenic fluid and having a through-hole on a side surface, and the liquid level detector. A power supply unit that supplies current, a resistance measurement unit that measures the electrical resistance of the liquid level detection unit , and a holding plate that is fixed to a protective tube and includes at least two through holes, The surface detection unit is made of magnesium diboride, the lower end of the liquid level detection unit is inserted and held in one through hole of the holding plate , and the cryogenic fluid flows out and flows into at least one other through hole. possible der Rukoto and said.

According to the present invention, since the liquid level detection unit is formed using magnesium diboride (hereinafter referred to as MgB ₂ ) that exhibits superconductivity at a temperature of about 39 K or less, for example, it is a cryogenic fluid. The liquid level of liquid hydrogen (about 20K) can be measured.
That is, the liquid level detection unit disposed in the liquid hydrogen is cooled to about 20K, and the resistance of the portion becomes substantially zero (superconducting state). On the other hand, the temperature of the liquid level detector disposed in the gas phase region above the liquid hydrogen liquid level (hereinafter referred to as the ledge portion) becomes higher than 39K, and the liquid level detector in the ledge portion has a predetermined resistance value. Shown (normal state). Therefore, by measuring the resistance value of the liquid level detection unit by the resistance measurement unit, the ratio between the superconducting region and the normal conducting region can be estimated, and the liquid level of liquid hydrogen can be estimated based on the result.

Further, since it is not necessary to supply a high-frequency current to the liquid level detection unit, there is no need to provide a high-frequency power source, and the measurement circuit can be simplified and miniaturized.
Since the change in the liquid level is measured based on the change in the resistance value due to the temperature change in the liquid level detection unit, the change in the liquid level can be accurately measured without being affected by the nonuniformity of the dielectric constant in the cryogenic fluid. Furthermore, since it is not affected by the dielectric constant ratio between the dielectric constant of the cryogenic fluid in the gas state and the dielectric constant in the liquid state, the change in the liquid level can be measured accurately.

In the above invention, it is desirable that a heat generating part for generating heat is provided in the liquid level detecting part so as to be thermally connected.
According to the present invention, since the heat generating part is thermally connected to the liquid level detecting part, the liquid level detecting part can be heated and the liquid level of the cryogenic fluid can be measured more accurately.
That is, by heating the liquid level detection unit, the liquid level detection unit arranged in the ledge portion is cooled by heat conduction, and the temperature of the liquid level detection unit in the ledge portion can be prevented from being cooled to 39K or less. Therefore, the position of the liquid level estimated by the liquid level gauge of the present invention can be prevented from being higher than the actual position of the liquid level.

In the above invention, the heat generating portion is provided so as to be thermally connected to one end portion of the liquid level detecting portion, and the other end portion of the liquid level detecting portion is disposed in the cryogenic fluid. It is desirable that
According to the present invention, since the heat generating part is thermally connected to the one end part, the liquid level detecting part can be heated from one end part, and the liquid level of the cryogenic fluid can be more accurately determined. Can be measured.

That is, since the other end portion is disposed in the cryogenic fluid, the one end portion is disposed in the ledge portion, and the heating portion concentrates the portion disposed in the ledge portion of the liquid level detection portion. Can be heated. Therefore, it can prevent that the temperature of the liquid level detection part in an ledge part is cooled to 39K or less, and can improve the measurement precision of a liquid level.
Moreover, since the heat generating portion is arranged in the ledge portion, it is possible to prevent the cryogenic fluid from being heated by the heat generating portion, and it is possible to prevent the storage stability of the cryogenic fluid from being lowered.

In the said invention, it is desirable that the said heat generating part is provided so that it may connect thermally with the whole said liquid level detection part.
According to the present invention, since the heat generating part is thermally connected to the entire liquid level detection part, the entire liquid level detection part can be heated, and the liquid level of the cryogenic fluid can be measured more accurately. be able to.
That is, as compared with the case where the liquid level detection unit arranged in the ledge part is heated by heat conduction, the liquid level detection part in the ledge part is cooled to 39K or less by directly heating the liquid level detection part. And the measurement accuracy of the liquid level can be improved.

According to the superconducting liquid level meter of the present invention, since the liquid level detection unit is formed using magnesium diboride (hereinafter referred to as MgB ₂ ), the resistance of the liquid level detection unit is measured by the resistance measurement unit. By measuring the value, the ratio between the superconducting region and the normal conducting region can be estimated, and the liquid level of liquid hydrogen, which is a cryogenic fluid, can be accurately measured, and its structure can be simplified. It is possible to reduce the size and size.

[First Embodiment]
Hereinafter, a first embodiment of the superconducting liquid level gauge according to the present invention will be described with reference to FIGS. 1 to 3.
FIG. 1 is a schematic diagram illustrating the configuration of the superconducting liquid level gauge in the present embodiment.
As shown in FIG. 1, the superconducting liquid level meter 1 includes a measuring unit 5 disposed in a container 3 in which liquid hydrogen (cryogenic fluid) LH is stored, and a power source (power source) that supplies current to the measuring unit 5 Part) 7 and a resistance measuring part 9 for measuring the electrical resistance in the measuring part 5.
The measuring unit 5 is arranged such that the longitudinal axis thereof and the liquid level change direction of the liquid hydrogen LH are substantially parallel. The power source 7 and the resistance measuring unit 9 are arranged outside the container 3 so that heat generated from these devices does not enter the liquid hydrogen LH in the container 3.

FIG. 2 is a longitudinal sectional view illustrating the configuration of the measurement unit in FIG.
As shown in FIG. 2, the measurement unit 5 includes a substantially cylindrical protective tube 11, a liquid level detection unit 13 made of MgB ₂ wire disposed in the protection tube 11, and platinum that heats the liquid level detection unit 13. The heat generating part 15 which consists of a resistance wire is comprised roughly.

A through-hole 17 is formed in the side surface of the protective tube 11 so that the liquid hydrogen LH can flow between the inside and the outside of the protective tube 11, and the liquid level inside the protective tube 11 and the liquid level outside are almost the same. Configured to match.
Holding plates 19 </ b> A and 19 </ b> B for holding the liquid level detection unit 13 are disposed at both ends of the protective tube 11. The holding plate 19A, 19B is inserted with the liquid level detection unit 13 and the like, and a hole to be held is formed. The holding plate 19 </ b> A is disposed in the vicinity of the upper end (upper end in FIG. 2) of the protective tube 11 and is directly fixed to the protective tube 11. On the other hand, the holding plate 19B is disposed in the vicinity of the lower end (the lower end in FIG. 2) of the protective tube 11, and is fixed to a distal end metal fitting to be described later via a bushing.

At the lower end of the protective tube 11, there are provided an upper pusher 21 that holds the holding plate 19 </ b> B, a lower pusher 23, and a tip fitting 25 that holds both the pushings 21 and 23.
The tip metal fitting 25 is formed in a substantially cylindrical shape, and an internal thread portion is formed on the inner peripheral surface thereof so as to be screwed with the pushings 21 and 23. On the outer peripheral surfaces of both pushings 21 and 23, male screw portions that are screwed into the female screw portion of the above-described tip metal fitting 25 are formed. The upper bushing 21 is screwed from above to below, and the lower bushing 23 is screwed from below to above.

The liquid level detection unit 13 is made of MgB ₂ (magnesium diboride), and is a superconducting wire 27 having a diameter of about 1 mm and one lead electrically connected to the lower end of the superconducting wire 27. The wire 29 and the other lead wire 31 electrically connected to the upper end portion are schematically configured.
One lead wire 29 is a lead wire formed of copper and having an insulating film formed around the lead wire 29. The lead wire 29 is folded from the lower end of the protective tube 11 and led out from the upper end of the protective tube 11 through the protective tube 11. It is. The other lead wire 31 is a lead wire also serving as a resistance heating wire formed from manganin, and is led out from the upper end of the protective tube 11 to the outside.

The heat generating portion 15 is generally configured by a resistance heating wire 33 formed of platinum and an insulator 35 around which the resistance heating wire 33 is wound.
The insulator 35 is an insulator formed in a substantially cylindrical shape from alumina, and a superconducting wire 27 is disposed therein. Further, the insulator 35 is disposed at the upper end of the superconducting wire 27 and above the holding plate 19A. The resistance heating wire 33 is wound around the insulator 35, and its end is connected to a power source (not shown), and generates heat when power is supplied.

Next, the effect | action in the superconducting liquid level meter 1 which consists of said structure is demonstrated.
A current flows from the power supply 7 to the superconducting wire 27 of the superconducting liquid level gauge 1 through one lead wire 29 and the other lead wire 31. Then, the position of the liquid surface of the liquid hydrogen LH stored in the container 3 is estimated by measuring the electric resistance value of the superconducting wire 27 in the resistance measuring unit 9.

Specifically, the lower end side of superconducting wire 27 in measurement unit 5 is immersed in liquid hydrogen LH, and the portion of superconducting wire 27 immersed in liquid hydrogen LH is at the temperature of liquid hydrogen LH (about 20 K). To be cooled. Since the superconducting transition temperature of MgB ₂ forming the superconducting wire 27 is about 39K, the superconducting wire 27 cooled to about 20K becomes a superconducting state, and the electric resistance becomes substantially zero.

On the other hand, predetermined electric power is supplied to the resistance heating wire 33 of the heat generating part 15, and a predetermined amount of heat is generated in the resistance heating wire 33. The heat generated in the resistance heating wire 33 is transferred to the superconducting wire 27 through the insulator 35, and heats the superconducting wire 27 from the upper end side.
In the other lead wire 31 that also serves as a resistance heating wire, a predetermined amount of heat is generated by passing a current. The heat generated in the other lead wire 31 is directly transmitted to the superconducting wire 27 and heats the superconducting wire 27 from the upper end side.

  The portion disposed in the ledge portion of the superconducting wire 27 is heated by the resistance heating wire 33 and the other lead wire 31 as described above, and is maintained at a temperature higher than the superconducting transition temperature (about 39 K). Therefore, the part arrange | positioned at the ledge part of the superconducting wire 27 is maintained in a normal conduction state, and shows a predetermined electrical resistance value.

  The predetermined amount of heat is preferably the minimum amount of heat at which the boundary between the superconducting region 27 and the normal state region coincides with the liquid level of the liquid hydrogen LH. By setting the minimum amount of heat, it is possible to prevent the heat input to the liquid hydrogen LH from increasing and to prevent the storage stability of the liquid hydrogen LH from decreasing.

Next, the measurement result in the superconducting liquid level meter 1 having the above configuration will be described.
FIG. 3 is a diagram showing a liquid level measurement result of the liquid hydrogen LH by the superconducting liquid level gauge 1 of FIG.
In FIG. 3, the horizontal axis indicates the liquid level position (liquid level) of the liquid hydrogen LH in the container 3 as a percentage, and the state without the liquid hydrogen LH is 0%. The vertical axis represents the electrical resistance value of the superconducting wire 27 measured by the resistance measuring unit 9.
Also, the solid line A in FIG. 3 is a prediction line based on the calculation showing the relationship between the liquid hydrogen LH and the resistance, and ◯ is an actual measurement value by the superconducting liquid level gauge 1 according to the present embodiment, These are actual measured values by the superconducting liquid level gauge 1 when power is not supplied to the heat generating portion 15.

Solid line A, the temperature of liquid hydrogen LH is a uniform 20K, temperature resistance value of the superconducting wire 27 in the 20K based on the assumption that it is 0.0075Ω / cm, from the heat calculation and MgB ₂ physical properties Estimated.
Further, ○ is the superconducting wire 27 supplies a current _{I 0} of 450 mA, which is a measure of the case of supplying the currents _{I 1} of 62mA to the heat generating portion 15. The measured value at this time is a value when the output voltage is in a steady state.

3, supplies the constant current I ₀ to the superconducting wire 27, in the case of supplying a constant current I ₁ to the heat generating portion 15 (○ in the figure), the measured liquid level substantially linear relationship between the resistance It is shown that it is on the solid line A, and it is shown that the liquid level can be estimated by measuring the resistance.
Further, when power is not supplied to the heat generating portion 15 (Δ in the figure), the resistance value measured at a predetermined liquid level is smaller than the solid line A, and the liquid level cannot be estimated accurately. It is shown.

According to the above structure, forming the superconducting wire 27 using the MgB _2, which exhibits superconductivity at about 39K below the temperature, it can be measured liquid level of the liquid hydrogen LH (approximately 20K).
That is, the superconducting wire rod 27 immersed in the liquid hydrogen LH is cooled to about 20K, and the resistance at that portion becomes substantially zero (superconducting state). On the other hand, the temperature of the superconducting wire 27 arranged in the ledge portion becomes higher than 39K, and the portion shows a predetermined resistance value (normal conduction state). Therefore, by measuring the electrical resistance value of the superconducting wire 27 by the resistance measuring unit 9, the ratio between the superconducting region and the normal conducting region can be estimated, and the liquid level of the liquid hydrogen LH can be estimated.

Moreover, since it is not necessary to supply a high frequency current to the measurement part 5, it is not necessary to provide a high frequency power source, and the measurement circuit in the superconducting liquid level gauge 1 can be simplified and downsized.
Since the change in the liquid level is measured based on the change in the electrical resistance value due to the temperature change in the superconducting wire 27, the change in the liquid level can be accurately measured without being affected by the nonuniformity of the dielectric constant in the liquid hydrogen LH. . Further, since it is not affected by the dielectric constant ratio between the dielectric constant of gaseous hydrogen and the dielectric constant of liquid hydrogen, the change in the liquid level can be measured accurately.

Since the heat generating part 15 is thermally connected to the upper end of the superconducting wire 27, it can be heated from the upper end side of the superconducting wire 27, and the liquid level of the liquid hydrogen LH can be measured more accurately.
That is, by heating the superconducting wire 27, the superconducting wire 27 disposed in the ledge portion is cooled by heat conduction, and the temperature of the superconducting wire 27 disposed in the ledge portion is about 39K, which is the superconducting transition temperature. It can prevent being cooled below. Therefore, the position of the liquid level estimated by the superconducting liquid level gauge 1 can be prevented from being higher than the actual position of the liquid level.

As described above, a wire formed on a substantially straight line may be used as a superconducting wire, or a wire formed in a spiral shape may be used as a superconducting wire, and there is no particular limitation.
Further, as described above, the superconducting wire 27 may be disposed so that the longitudinal axis direction thereof and the liquid level change direction of the liquid hydrogen LH are substantially parallel to each other. The superconducting wire 27 may be arranged so that the longitudinal axis direction is oblique, and is not particularly limited.

  As described above, the total length of the superconducting wire 27 can be increased by forming the superconducting wire 27 in a spiral shape or by arranging it at an angle with respect to the liquid surface of the liquid hydrogen LH. By increasing the total length of the superconducting wire 27, the amount of heat generated from the super traditional wire 27 itself can be increased, and the liquid level position of the liquid hydrogen LH can be estimated more accurately.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS.
The basic configuration of the superconducting liquid level gauge of this embodiment is the same as that of the first embodiment, but the configuration of the heat generating portion is different from that of the first embodiment. Therefore, in the present embodiment, only the vicinity of the heat generating portion will be described with reference to FIGS. 4 and 5, and description of other components and the like will be omitted.
FIG. 4 is a schematic diagram illustrating the configuration of the superconducting liquid level meter according to the present embodiment.
In addition, the same code | symbol is attached | subjected to the component same as 1st Embodiment, and the description is abbreviate | omitted.
As shown in FIG. 4, the superconducting liquid level meter 101 includes a measuring unit 105 disposed in the container 3 in which the liquid hydrogen LH is stored, a power source 7 that supplies current to the measuring unit 5, and a measuring unit 105. A resistance measuring unit 9 that measures electrical resistance is schematically configured.

FIG. 5 is a longitudinal sectional view illustrating the configuration of the measurement unit in FIG.
As shown in FIG. 5, the measurement unit 105 includes a substantially cylindrical protection tube 11, a liquid level detection unit 13 made of MgB ₂ wire disposed in the protection tube 11, and platinum that heats the liquid level detection unit 13. The heat generating unit 115 is composed of a resistance wire.
The heat generating portion 115 is generally configured by a resistance heating wire 133 formed of platinum and an insulator 135 around which the resistance heating wire 133 is wound.
The insulator 135 is an insulator formed in a substantially cylindrical shape from alumina, and the superconducting wire 27 is disposed therein. The insulator 135 is disposed so as to cover substantially the entire superconducting wire 27. The resistance heating wire 133 is wound around the insulator 135 and the end thereof is connected to a power source (not shown), and generates heat when electric power is supplied.

Next, the operation of the superconducting liquid level gauge 101 having the above configuration will be described.
Since the method for estimating the liquid surface position of the liquid hydrogen LH using the superconducting wire 27 is the same as that in the first embodiment, the description thereof is omitted.

Predetermined power is supplied to the resistance heating wire 133 of the heat generating part 115, and a predetermined amount of heat is generated in the resistance heating wire 133. The heat generated in the resistance heating wire 133 is transmitted to the superconducting wire 27 through the insulator 135 and heats the entire superconducting wire 27.
In the other lead wire 31 that also serves as a resistance heating wire, a predetermined amount of heat is generated by passing a current. The heat generated in the other lead wire 31 is directly transmitted to the superconducting wire 27 and heats the superconducting wire 27 from the upper end side.

The portion immersed in the liquid hydrogen LH of the superconducting wire 27 is cooled from the superconducting transition temperature by the liquid hydrogen LH and is in a superconducting state.
On the other hand, the portion disposed in the ledge portion of the superconducting wire 27 is heated by the resistance heating wire 133 and the other lead wire 31 as described above, and is maintained at a temperature higher than the superconducting transition temperature (about 39 K). Therefore, the part arrange | positioned at the ledge part of the superconducting wire 27 is maintained in a normal conduction state, and shows a predetermined electrical resistance value.

  The predetermined amount of heat is preferably the minimum amount of heat at which the boundary between the superconducting region 27 and the normal state region coincides with the liquid level of the liquid hydrogen LH. By setting the minimum amount of heat, it is possible to prevent the heat input to the liquid hydrogen LH from increasing and to prevent the storage stability of the liquid hydrogen LH from decreasing.

According to the above configuration, since the heat generating portion 115 is thermally connected to the entire superconducting wire 27, the entire superconducting wire 27 can be heated, and the liquid level of the liquid hydrogen LH can be more accurately determined. Can be measured.
That is, compared with the case where the superconducting wire 27 arranged in the ledge portion is heated by heat conduction, the temperature of the superconducting wire 27 arranged in the ledge portion is 39 K or less by directly heating the superconducting wire 27. It is possible to prevent the liquid from being cooled and to improve the measurement accuracy of the liquid level.

The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in the above-described embodiment, the description has been made by applying to the liquid temperature using liquid hydrogen as the cryogenic fluid whose liquid level position is to be measured. However, the present invention is not limited to the liquid level measuring method. In addition, the present invention can be applied to those that measure the liquid level position of various other cryogenic fluids.

It is the schematic explaining the structure of the superconducting liquid level meter which concerns on 1st Embodiment in this invention. It is a longitudinal cross-sectional view explaining the structure of the measurement part of FIG. It is a figure which shows the liquid level measurement result of the liquid hydrogen by the superconducting liquid level meter of FIG. It is the schematic explaining the structure of the superconducting liquid level meter which concerns on 2nd Embodiment in this invention. It is a longitudinal cross-sectional view explaining the structure of the measurement part of FIG.

Explanation of symbols

1,101 Superconducting liquid level gauge 7 Power supply (power supply unit)
9 Resistance measurement unit 13 Liquid level detection unit 15,115 Heat generation unit LH Liquid hydrogen (Cryogenic fluid)

Claims (4)

A liquid level detection unit disposed in a protective tube having at least a part thereof disposed in the cryogenic fluid and having a through hole on a side surface;
A power supply unit for supplying current to the liquid level detection unit;
A resistance measurement unit for measuring the electrical resistance of the liquid level detection unit;
A holding plate fixed to the protective tube and provided with at least two through holes ,
The liquid level detection unit is formed from magnesium diboride,
A lower end of the liquid level detection unit, the held are inserted into the first through-hole of the holding plate, superconducting liquid other at least one through hole to the cryogenic fluid and said outflow inlet capable der Rukoto Area meter.   2. The superconducting liquid level gauge according to claim 1, wherein a heat generating section for generating heat is provided on the liquid level detecting section so as to be thermally connected. The heat generating part is provided so as to be thermally connected to one end of the liquid level detecting part,
The superconducting liquid level gauge according to claim 2, wherein the other end of the liquid level detector is disposed in the cryogenic fluid.   3. The superconducting liquid level gauge according to claim 2, wherein the heat generating part is provided so as to be thermally connected to the entire liquid level detecting part.

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