Liquid level detecting apparatus

Abstract

To suppress erroneous detection of a liquid level in a liquid level detector.SOLUTION: The liquid surface level detection device includes a probe having a temperature sensor and a heater, and a cover that covers the probe, and the cover has an introduction port for introducing a liquid into the cover between a distal end portion of the cover and a temperature measurement point of the temperature sensor, so that even if the liquid scatters and comes into contact with the probe, erroneous detection of the liquid surface due to a decrease in the measured temperature of the temperature sensor can be suppressed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a liquid level detection device. [Background technology]

[0002] BACKGROUND ART There is known an apparatus for detecting a liquid level from a change in the temperature measured by a temperature sensor when the liquid level comes into contact with a probe equipped with a temperature sensor and a heater (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-113808 Summary of the Invention [Problem to be solved by the invention]

[0004] If the liquid splashes and comes into contact with the probe, the temperature measured by the temperature sensor may drop, resulting in a false detection of the liquid level. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] (1) According to one aspect of the present disclosure, there is provided a liquid level detection device including a probe having a temperature sensor and a heater, and a cover covering the probe. The cover has an inlet for introducing liquid into the cover between a tip of the cover and a temperature measurement point of the temperature sensor. According to this type of liquid level detection device, the cover that covers the probe can prevent splashed liquid from coming into contact with the probe, thereby preventing erroneous detection of the liquid level due to splashed liquid. (2) In the liquid level detection device of the above aspect, the width of the tip of the cover may be larger than the width of the portion of the cover having the inlet. According to the liquid level detection device of this configuration, it is possible to prevent the splashed liquid from entering the cover through the inlet. (3) In the liquid level detection device of the above aspect, the gap between the cover and the probe may be 1.5 millimeters or more. According to the liquid level detection device of this configuration, it is possible to prevent heat from being trapped between the cover and the probe. (4) In the liquid level detection device of the above aspect, the area of ​​the inlet may be equal to or greater than the area of ​​the inner diameter cross-sectional area of ​​the cover excluding the area occupied by the probe. According to the liquid level detection device of this configuration, it is possible to prevent heat from being trapped between the cover and the probe. (5) In the liquid level detection device of the above form, the cover may have an outlet for discharging gas from inside the cover between the base end of the cover and the temperature measurement point of the temperature sensor, and the area of ​​the outlet may be smaller than the area of ​​the inlet. According to the liquid level detection device of this aspect, it is possible to prevent the liquid level in the cover from being impeded from rising, and also to prevent the splashed liquid from entering the cover through the outlet. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a first explanatory diagram showing the configuration of a liquid level detection device according to a first embodiment. [Figure 2] FIG. 2 is a second explanatory diagram showing the configuration of the liquid level detection device of the first embodiment. [Figure 3] FIG. 2 is an explanatory diagram showing the configuration of a probe. [Figure 4] FIG. 10 is an explanatory diagram showing the relationship between the distance between the probe and the cover and the temperature of the inner wall of the cover. [Figure 5] FIG. 10 is an explanatory diagram showing the relationship between the area of ​​the inlet and the temperature of the inner wall of the cover. [Figure 6] FIG. 6 is an explanatory diagram showing the configuration of a liquid level detection device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] A. First embodiment: FIG. 1 is a first explanatory diagram showing the configuration of a liquid level detection device 10 in a first embodiment. FIG. 2 is a second explanatory diagram showing the configuration of the liquid level detection device 10. FIG. 3 is an explanatory diagram showing the configuration of a probe 20 of the liquid level detection device 10. As shown in FIG. 1, in this embodiment, the liquid level detection device 10 is attached to a tank TK that stores liquid hydrogen and detects the liquid level LS of the liquid hydrogen in the tank TK. The liquid level detection device 10 includes the probe 20, a cover 30, a joint unit 40 fixed to the tank TK, and a control unit 50. Note that in FIG. 1, a portion of the cover 30 is shown in cross section in order to show the probe 20.

[0009] As shown in FIG. 3, the probe 20 includes a sheath tube 21, a temperature sensor 22, and a heater 23. The sheath tube 21 is configured in a cylindrical shape with a bottom. The distal end of the sheath tube 21 has a dome-shaped bottom surface and serves as a free end. The proximal end of the sheath tube 21 is fixed to a joint 40. In this embodiment, the cross-sectional shape of the sheath tube 21 is cylindrical. The sheath tube 21 is formed of a metal material such as stainless steel.

[0010] A temperature sensor 22 and a heater 23 are disposed within the sheath tube 21. In this embodiment, the temperature sensor 22 is a thermocouple thermometer. Because it is used in a low-temperature environment, the thermocouple thermometer is preferably a K thermocouple thermometer or an E thermocouple thermometer. A temperature measurement point P of the temperature sensor 22 is disposed near the tip of the sheath tube 21. In this embodiment, the heater 23 is an electric heating wire that generates heat by resistance heating. The heater 23 is disposed near the temperature measurement point P of the temperature sensor 22 and heats the temperature measurement point P of the temperature sensor 22.

[0011] Filler 24 made of a powdered inorganic insulating material is filled inside sheath tube 21 between temperature sensor 22 and heater 23, between sheath tube 21 and temperature sensor 22, and between sheath tube 21 and heater 23. In this embodiment, filler 24 is made of magnesium oxide (MgO). Filler 24 ensures electrical insulation and thermal conductivity between temperature sensor 22 and heater 23, between sheath tube 21 and temperature sensor 22, and between sheath tube 21 and heater 23.

[0012] As shown in FIG. 2 , the cover 30 covers the probe 20 from its distal end to its proximal end, in other words, the sheath tube 21 from its distal end to its proximal end. The cover 30 is configured as a cylindrical tube with a bottom. The distal end of the cover 30 has a flat bottom surface and is a free end. The proximal end of the cover 30 is fixed to the joint portion 40. In this embodiment, the cross-sectional shape of the cover 30 is cylindrical. The diameter of the cover 30 is constant. Gaps are provided between the distal end of the cover 30 and the distal end of the probe 20, and between the side surfaces of the cover 30 and the probe 20. The gap between the distal end of the cover 30 and the distal end of the probe 20 is wider than the gap between the side surfaces of the cover 30 and the probe 20. A vibration-retaining member 45 made of polytetrafluoroethylene (PTFE) is arranged between the side surfaces of the cover 30 and the probe 20 to prevent misalignment between the central axes of the probe 20 and the cover 30. The cover 30 is formed of a metal material such as stainless steel. However, the material of the cover 30 may be any material that is not easily embrittled by liquid hydrogen, and may be a material other than a metal. Furthermore, when the liquid level detection device 10 detects the level LS of a liquid other than liquid hydrogen, the material of the cover 30 may be a material other than a material that is not easily embrittled by liquid hydrogen.

[0013] The side surface of the cover 30 has an inlet 31 for introducing liquid hydrogen into the cover 30 from outside the cover 30, and an outlet 32 ​​for discharging air or gaseous hydrogen from inside the cover 30 to outside the cover 30. The inlet 31 is provided in a portion of the side surface of the cover 30 between the temperature measurement point P of the temperature sensor 22 and the tip of the cover 30. More specifically, the inlet 31 is provided in a portion of the side surface of the cover 30 between the tip of the probe 20 and the tip of the cover 30. The distance between the inlet 31 and the tip of the probe 20 is greater than the distance between the inlet 31 and the tip of the cover 30. In this embodiment, the opening shape of the inlet 31 is circular. The outlet 32 ​​is provided in a portion of the side surface of the cover 30 between the temperature measurement point P of the temperature sensor 22 and the base end of the cover 30. More specifically, the outlet 32 ​​is provided in a portion of the side surface of the cover 30 near the base end of the cover 30. The distance between the outlet 32 ​​and the temperature measurement point P of the temperature sensor 22 is greater than the distance between the outlet 32 ​​and the base end of the cover 30. In this embodiment, the opening shape of the outlet 32 ​​is circular. When the liquid level LS in the tank TK rises, liquid hydrogen outside the cover 30 flows into the cover 30 through the inlet 31, and air and gaseous hydrogen inside the cover 30 are discharged to the outside of the cover 30 through the outlet 32.

[0014] 1, the control unit 50 is configured by a computer including a processor 51, a memory 52, an input / output interface 53, and an internal bus 54. The temperature sensor 22 and the heater 23 are connected to the input / output interface 53, for example, via a cable. The processor 51 controls the temperature sensor 22 and the heater 23 by executing a program PG pre-stored in the memory 52, and detects the liquid level LS of the liquid hydrogen. Note that at least a portion of the control unit 50 may be configured by a hardware circuit.

[0015] The method for detecting the liquid level LS using the liquid level detection device 10 will now be described. When the heater 23 heats the temperature sensor 22 while the tip of the probe 20 is located in liquid, almost all of the heat from the heater 23 is dissipated into the liquid, and the measured temperature of the temperature sensor 22 does not change. On the other hand, when the heater 23 heats the temperature sensor 22 while the tip of the probe 20 is located in gas, the heat from the heater 23 is not easily dissipated into the gas, and the measured temperature of the temperature sensor 22 increases. Then, if the heater 23 starts heating the temperature sensor 22 while the tip of the probe 20 is located in gas, and the tip of the probe 20 comes into contact with the liquid while the heater 23 is heating the temperature sensor 22, the measured temperature of the temperature sensor 22 drops. Therefore, the control unit 50 can determine whether the tip of the probe 20 is located in liquid or gas from the change in the measured temperature of the temperature sensor 22 when the heater 23 is heating the temperature sensor 22. In this embodiment, the control unit 50 starts heating the temperature sensor 22 with the heater 23 before the liquid level LS has reached the tip of the probe 20, and when the temperature measured by the temperature sensor 22 drops by a predetermined amount or more, detects that the liquid level LS has reached the tip of the probe 20. In this embodiment, since the tip of the probe 20 is located near the ceiling surface of the tank TK, the control unit 50 can detect that the tank TK is full by detecting the liquid level LS.

[0016] The control unit 50 controls the supply of power to the heater 23 so that the heater 23 heats the temperature sensor 22 with a power of 5 to 10 [W]. By setting the power to 5 [W] or more, the liquid level LS can be detected appropriately, and by setting the power to 10 [W] or less, the generation of a large amount of boil-off gas of liquid hydrogen can be suppressed. For example, when set to 10 [W], the amount of power per hour of the heater 23 is 10 [W] × 3600 [s] = 3.6 × 10 4 [J], and the latent heat of vaporization of liquid hydrogen is 446 [J / g], so the amount of vaporized liquid hydrogen is 3.6 × 10 4 [J] / 446[J / g]=81[g]. If the volume of the tank TK is 20[kg], the evaporation rate (BOR) is 81×10-3 [kg] / 20 [kg] × 100 = 0.4 [%]. In order to reduce the evaporation rate, it is preferable to perform full tank detection periodically or at specified timings for short periods of time rather than constantly. For example, it is preferable to perform full tank detection only while the tank TK is being filled with liquid hydrogen. In this case, it is preferable that the control unit 50 starts supplying power to the heater 23 before the tank TK becomes full, and immediately stops supplying power to the heater 23 upon detecting that the tank TK is full. Note that, when measuring continuous changes in the position of the liquid level LS in the tank TK, a level meter can be installed in the tank TK in addition to the liquid level detection device 10 used as a level switch.

[0017] FIG. 4 is an explanatory diagram showing the relationship between the distance between the probe 20 and the cover 30 and the temperature of the inner wall of the cover near the inlet 31. In FIG. 4, the temperature of the inner wall of the cover calculated by CAE analysis is represented by a circle. The temperature of the inner wall of the cover refers to the temperature of the inner wall of the cover 30. The distance between the probe 20 and the cover 30 refers to the distance between the outer wall of the side of the sheath tube 21 and the inner wall of the side of the cover 30. The analysis conditions for the CAE analysis are as follows: The temperature of the inner wall of the cover is the temperature at a position 50 mm above the tip of the sheath tube 21. The heater 23 is positioned 100 mm above the tip of the sheath tube 21. The flow of gaseous hydrogen is laminar, and the density is 1.3378 kg / m 3 ], viscosity is 1.5e -5The inner wall temperature of the cover was calculated using different inner diameters of the cover 30, with the following conditions: the pressure was 1 [Pa·s], the specific heat was 12,000 [J / (kg·K)], the thermal conductivity was 0.02 [W / (m·K)], the diameter of the inlet 31 was 4.0 [mm] (inlet velocity was 1 [m / s]), the diameter of the outlet 32 ​​was 2.0 [mm] (pressure was 0 [Pa]), the temperature of the gaseous hydrogen was -253 [°C], the outer diameter of the sheath tube 21 was 3.2 [mm], and the temperature of the sheath tube 21 was -153 [°C]. The inner wall temperature of the cover was calculated using different inner diameters of the cover 30. The wider the gap between the sheath tube 21 and the cover 30, the lower the inner wall temperature of the cover. In other words, the wider the gap between the sheath tube 21 and the cover 30, the less likely heat is to be trapped inside the cover 30. 4, in order to prevent heat from building up inside the cover 30, the gap between the sheath tube 21 and the cover 30 is preferably 1.5 mm or more, more preferably 1.7 mm or more, and even more preferably 2.0 mm or more. In this embodiment, the gap between the sheath tube 21 and the cover 30 is secured to be 1.5 mm or more.

[0018] FIG. 5 is an explanatory diagram showing the relationship between the total area of ​​the inlet 31 and the cover inner wall temperature at the periphery of the outlet 32. In FIG. 5, the cover inner wall temperatures calculated by the CAE analysis are represented by circles. The analysis conditions for the CAE analysis are as follows. The inner diameter of the cover 30 is 8.0 [mm], the distance between the sheath tube 21 and the cover 30 is 2.4 [mm], and the cover inner wall temperature is calculated by changing the total area of ​​the inlet 31. The other analysis conditions are the same as those for the CAE analysis related to FIG. 4. As shown in FIG. 5, in order to prevent heat from being trapped inside the cover 30, the total area of ​​the inlet 31 should be set to (4.0 [mm] × 4.0 [mm] × π) - (1.6 [mm] × 1.6 [mm] × π) = 42 [mm]. 2 In this embodiment, since there is one inlet 31, the total area of ​​the inlets 31 is the same as the area of ​​one inlet 31. The area of ​​the inlet 31 is equal to or greater than the area of ​​the inner diameter cross-sectional area of ​​the cover 30 excluding the portion occupied by the probe 20.

[0019] According to the liquid level detection device 10 of the present embodiment described above, the cover 30 covering the probe 20 is provided, thereby preventing liquid hydrogen scattered within the tank TK from contacting the tip of the probe 20. Here, it is preferable to shorten the time required to fill the tank TK with liquid hydrogen. However, increasing the amount of liquid hydrogen filled into the tank TK per unit time creates a gas-liquid two-phase flow state within the tank TK, making liquid hydrogen more likely to splash within the tank TK. If scattered liquid hydrogen comes into contact with the tip of the probe 20, the measured temperature of the temperature sensor 22 may drop, potentially resulting in erroneous detection of the liquid level LS. In this embodiment, the probe 20 is covered by the cover 30, making it difficult for scattered liquid hydrogen to come into contact with the tip of the probe 20. Furthermore, an inlet 31 for introducing liquid hydrogen into the cover 30 is provided on the side of the cover 30 between the tip of the cover 30 and the tip of the probe 20. Therefore, as the liquid level LS in the tank TK rises, liquid hydrogen comes into contact with the tip of the probe 20. Therefore, in this embodiment, the liquid level LS of the liquid hydrogen can be detected correctly, and erroneous detection of the liquid level LS due to scattered liquid hydrogen can be prevented.

[0020] Furthermore, in this embodiment, the gap between the cover 30 and the probe 20 is 1.5 millimeters or more, which prevents heat from building up inside the cover 30. If liquid hydrogen splashes and comes into contact with the outer wall of the cover 30 while heat is trapped inside the cover 30, the temperature measured by the temperature sensor 22 may drop, potentially resulting in an erroneous detection of the liquid level LS. In this embodiment, because heat is prevented from building up inside the cover 30, it is possible to prevent erroneous detection of the liquid level LS caused by splashed liquid hydrogen coming into contact with the outer wall of the cover 30.

[0021] Furthermore, in this embodiment, the area of ​​the inlet 31 is equal to or greater than the area of ​​the inner diameter cross-sectional area of ​​the cover 30 excluding the portion occupied by the probe 20, which prevents heat from building up inside the cover 30. This prevents erroneous detection of the liquid level LS caused by splashed liquid hydrogen coming into contact with the outer wall of the cover 30.

[0022] Furthermore, in this embodiment, an outlet 32 ​​for discharging air and gaseous hydrogen to the outside of the cover 30 is provided in a portion of the side surface of the cover 30 between the base end of the cover 30 and the temperature measurement point P of the temperature sensor 22. This inhibits the liquid level LS from rising inside the cover 30, thereby preventing a difference in the height of the liquid level LS between inside and outside the cover 30. This makes it possible to detect the liquid level LS at the correct timing. Furthermore, in this embodiment, the area of ​​the outlet 32 ​​is smaller than the area of ​​the inlet 31. This prevents scattered liquid hydrogen from entering the cover 30 through the outlet 32.

[0023] B. Second embodiment: 6 is an explanatory diagram showing the configuration of a liquid level detection device 10b according to a second embodiment. The second embodiment differs from the first embodiment in that the cover 30 has a flange 35. The other configurations are the same as those of the first embodiment unless otherwise specified.

[0024] The flange 35 is a portion that protrudes radially outward from the outer wall of the cover 30. In this embodiment, the flange 35 is provided at the tip of the cover 30. The inlet 31 is located on a portion of the side surface of the cover 30 between the flange 35 and the tip of the probe 20. The flange 35 is configured in the shape of an annular plate. The width of the flange 35, in other words, the diameter of the flange 35, is larger than the diameter of the portion of the cover 30 other than the flange 35. Therefore, the width of the tip of the cover 30 is larger than the width of the portion of the cover 30 where the inlet 31 is provided. The flange 35 may have multiple through holes, as in punched metal. The flange 35 may be configured in a mesh shape rather than a plate shape. Multiple flanges 35 may be provided.

[0025] According to the liquid level detection device 10b of this embodiment described above, the flange 35 is provided on the cover 30, thereby preventing scattered liquid hydrogen from entering the cover 30 through the inlet 31. Therefore, it is possible to effectively prevent erroneous detection of the liquid level LS caused by scattered liquid hydrogen.

[0026] C. Other Embodiments: (C1) In each of the above-described embodiments, the probe 20 includes a thermocouple thermometer as the temperature sensor 22 and a heating wire as the heater 23. However, the probe 20 may include a resistance temperature detector instead of the thermocouple thermometer and the heating wire. A resistance temperature detector has the property that its electrical resistance changes depending on the temperature. Since the temperature of the resistance temperature detector can be measured using the electrical resistance when current is passed through it, the resistance temperature detector functions as the temperature sensor 22 that measures the temperature of the temperature measurement point P. Furthermore, the resistance temperature detector generates heat when current is passed through it, and therefore functions as the heater 23 that raises the temperature of the temperature measurement point P.

[0027] (C2) In each of the above-described embodiments, the distance between the cover 30 and the probe 20 is 1.5 millimeters or more. In contrast, the distance between the cover 30 and the probe 20 may be smaller than 1.5 millimeters.

[0028] (C3) In each of the above-described embodiments, the area of ​​the inlet 31 is equal to or greater than the area of ​​the inner diameter cross-sectional area of ​​the cover 30 excluding the portion occupied by the probe 20. In contrast, the area of ​​the inlet 31 may be smaller than the area of ​​the inner diameter cross-sectional area of ​​the cover 30 excluding the portion occupied by the probe 20.

[0029] (C4) In each of the above-described embodiments, the area of ​​the outlet 32 ​​is smaller than the area of ​​the inlet 31. However, the area of ​​the outlet 32 ​​may be equal to or larger than the area of ​​the inlet 31.

[0030] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0031] 10, 10b...liquid level detection device, 20...probe, 21...sheath tube, 22...temperature sensor, 23...heater, 24...filler, 30...cover, 31...inlet, 32...outlet, 35...flange, 40...joint, 45...sway prevention material, 50...control unit, 51...processor, 52...memory, 53...input / output interface, 54...internal bus, LS...liquid level, P...temperature measurement point, PG...program, TK...tank

Claims

1. A liquid level detection device, a probe having a temperature sensor and a heater; a cover for covering the probe; Equipped with The liquid level detection device, wherein the cover has an inlet for introducing liquid into the cover between the tip of the cover and the temperature measurement point of the temperature sensor.

2. 2. The liquid level detection device according to claim 1, A liquid level detection device, wherein the width of the tip of the cover is greater than the width of the portion of the cover having the inlet.

3. 2. The liquid level detection device according to claim 1, A liquid level detection device, wherein the gap between the cover and the probe is 1.5 millimeters or more.

4. 2. The liquid level detection device according to claim 1, A liquid level detection device, wherein the area of ​​the inlet is equal to or greater than the area of ​​the inner diameter cross-sectional area of ​​the cover excluding the area occupied by the probe.

5. 2. The liquid level detection device according to claim 1, the cover has an exhaust port for exhausting gas from inside the cover between a base end of the cover and the temperature measurement point of the temperature sensor, A liquid level detection device, wherein the area of ​​the outlet is smaller than the area of ​​the inlet.

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