JP2005121430A - Liquid concentration detector, and fuel supply system for fuel cell equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a mixing condition of a liquid mixture with local nonuniformity estimated as a cause. <P>SOLUTION: This detector is provided with a liquid concentration sensor 31 for measuring a concentration of the liquid mixture mixed with liquids different in dielectric constants, by detecting a dielectric constant of the liquid mixture, and an ultrasonic transducer 32 provided in a flow passage 14 for the liquid mixture to irradiate the liquid mixture with an ultrasonic wave, and measures the concentration of the liquid mixture irradiated with the ultrasonic wave from the ultrasonic transducer 32. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid concentration detection device that detects a liquid concentration (mixing ratio) of a mixed liquid, such as a liquid fuel concentration of a fuel cell that operates using liquid fuel, and a fuel supply device for a fuel cell including the same. Is.

  In recent years, usage forms of small and portable information devices such as PDAs (electronic notebooks), computers, mobile phones and the like are collectively referred to as “mobile”, and devices of such usage forms are collectively referred to as “mobile”. The term “equipment” is widely used. In such a mobile device, its functions are increasing year by year, and the demand for a power source (battery) has become severe. However, the current mainstream batteries, such as lithium ion batteries, have not caught up with the evolution of mobile devices, and there is a need for the development of small and long-life power supplies.

Against this background, fuel cells are attracting attention as a promising power source that can support the enhancement of functions of mobile devices and can be operated for a long time, and research and development for its practical use has been earnestly advanced. Yes.
Currently, there are several types of fuel cells, and a direct methanol fuel cell (DMFC) that uses methanol as a direct fuel is promising as a fuel cell for mobile devices described above. . Such a direct methanol fuel cell system is disclosed, for example, in Japanese Patent Publication No. 2003-507859 and Japanese Patent Publication No. 2003-510777. In such a direct methanol fuel cell, the concentration of methanol diluted with water is important as a control parameter. Therefore, in the above publication, the dielectric constant of a mixed liquid in which water and methanol are mixed is used. A method for detecting the concentration is also disclosed.

Conventionally, in order to evenly blend a polymer substance that is not soluble in water with water or the like, the polymer is decomposed and dissolved by ultrasonic waves. (For example, refer to Patent Document 1 and Patent Document 2).
JP-A-11-71463 JP 2002-226598 A

As described above, in the direct methanol fuel cell, the methanol concentration diluted with water is important as its control parameter. Therefore, the methanol concentration is accurately detected by using the dielectric constant of the mixed liquid of water and methanol. It is required to do.
However, according to the experiments of the present inventors, when a pair of electrodes functioning as a capacitor is installed in a methanol aqueous solution and the methanol concentration is measured from the change in dielectric constant, as shown in FIG. Thus, unstable results were obtained in which the measured capacitance value fluctuated greatly.

That is, for the experimental results in FIG. 3, the horizontal axis indicates the time (seconds) from the start of measurement, and the vertical axis indicates the measured capacitance value (pF). In the case of (scale), it can be seen that there is considerable fluctuation in the range of approximately 53.4 pF to 53.7 pF from the start of measurement. Such fluctuations in measured values are presumed to be due to local non-uniformity (shading) in the aqueous methanol solution.
The above-mentioned fluctuations in the measured value are not preferable when the measured value of the methanol aqueous solution concentration is used directly as a control parameter for the methanol fuel cell, and an accurate concentration that does not fluctuate in order to appropriately control the fuel cell side. Measurement is desired. In particular, in the case of direct methanol fuel cells, in addition to being currently used at a methanol concentration of several percent, it is necessary to reduce the size of the cell itself, so a very small electrode is installed in the flow of aqueous methanol solution. Thus, the capacitance is detected. For this reason, if there is local shading in the aqueous methanol solution, it is easily affected, and as a result, fluctuations in detecting shading are detected, resulting in measurement errors. Therefore, in order to reduce such a measurement error of methanol concentration, it is desired to eliminate local nonuniformity.

Furthermore, in a direct methanol fuel cell, when a locally concentrated aqueous methanol solution is supplied, a phenomenon called crossover may occur, which is not preferable because it causes a reduction in battery life.
The present invention has been made in view of the above circumstances, and by improving the mixed state of the mixed liquid presumed to be caused by local non-uniformity, highly accurate concentration measurement that does not cause fluctuations in the measured value is achieved. It is an object of the present invention to provide a liquid concentration detection device that enables this and a fuel supply device for a fuel cell including the same.

The present invention employs the following means in order to solve the above problems.
The liquid concentration detection device of the present invention is provided in a liquid concentration sensor for measuring the liquid concentration of a mixed liquid obtained by mixing liquids having different dielectric constants by detecting the dielectric constant of the mixed liquid, and in the flow path of the mixed liquid. And at least one ultrasonic wave generating means for irradiating the mixed liquid with ultrasonic waves, and measuring the liquid concentration of the mixed liquid irradiated with ultrasonic waves from the ultrasonic wave generating means. .

  According to such a liquid concentration detection device, the liquid concentration of the mixed liquid irradiated with ultrasonic waves from at least one ultrasonic wave generating means is measured. Measurements can be performed.

  A fuel supply device for a fuel cell according to the present invention is a fuel supply device for a fuel cell that supplies a mixed liquid obtained by mixing fuel and an electrolyte to the fuel cell, and a fuel storage container for storing liquid fuel. An electrolyte storage container for storing a liquid electrolyte, a mixing container for mixing the fuel and the electrolyte supplied from the fuel container and the electrolyte container, and a mixed liquid from the mixing container to the fuel cell to form a closed circuit A liquid feeding means for circulating the flow path, a liquid concentration sensor for measuring the liquid concentration of the mixed liquid obtained by mixing liquids having different dielectric constants by detecting the dielectric constant of the mixed liquid, and the flow path for the mixed liquid And a liquid concentration detection device for measuring the liquid concentration of the mixed liquid irradiated with ultrasonic waves from the ultrasonic wave generating means. It is characterized in that configured by Bei.

  According to such a fuel supply device for a fuel cell, there is provided a liquid concentration detection device for measuring the liquid concentration of the mixed liquid in which the local concentration unevenness is eliminated by irradiating ultrasonic waves from the ultrasonic wave generation means. Therefore, a highly accurate and stable measured value of the liquid concentration can be obtained as a control parameter for controlling the fuel cell.

In the fuel supply apparatus for a fuel cell according to the present invention, the liquid concentration sensor is disposed in a flow path connecting the mixing container and the fuel cell, and the ultrasonic wave generating means is the mixing container and the liquid concentration sensor. It is preferable that it is arrange | positioned in the flow path which connects between.
In this case, it is preferable that the ultrasonic wave generating means is particularly disposed in the vicinity of the outlet of the mixing tank.

  In the fuel cell fuel supply apparatus of the present invention, it is preferable that the ultrasonic wave generating means is disposed in the liquid feeding means.

  Furthermore, in the fuel supply device for a fuel cell according to the present invention, the ultrasonic wave generator may be disposed on the outer wall side of the flow channel, the mixing tank, and / or the outer wall side of the liquid feeding means.

  According to the liquid concentration detection apparatus of the present invention, since the liquid concentration of the mixed liquid irradiated with ultrasonic waves is measured, the concentration measurement can be performed in a state in which the local concentration non-uniformity is eliminated, and there is variation. Stable and highly accurate measurement values can be obtained.

  In addition, according to the fuel supply device of the fuel cell according to the present invention, since the liquid concentration detection device for measuring the liquid concentration of the mixed liquid irradiated with ultrasonic waves is provided, the local concentration unevenness is eliminated. The concentration of the mixed liquid can be measured. For this reason, the fuel supply device of the fuel cell has a remarkable effect that the measurement value of the liquid concentration with high accuracy and stability can be obtained as a control parameter without variation, and the output control of the fuel cell can be easily and accurately performed. It is done. Since a methanol aqueous solution having a uniform concentration can be circulated as a fuel in a direct methanol fuel cell, the crossover phenomenon is prevented and the battery life is improved.

Hereinafter, an embodiment of a liquid concentration detection device according to the present invention and a fuel supply device for a fuel cell including the same will be described with reference to the drawings.
FIG. 1 is a configuration diagram showing a fuel supply device of a direct methanol fuel cell as a first embodiment of the present invention. The fuel supply device 10 is a fuel supply device for a fuel cell that supplies a mixed liquid (aqueous methanol solution) obtained by mixing methanol as fuel and electrolyte water to a fuel cell (DMFC) 20. The fuel supply device 10 includes a methanol tank 11 as a fuel storage container that stores methanol as a liquid fuel, a water tank 12 as an electrolyte storage container that stores water as a liquid electrolyte, and a methanol tank 11. And a mixing tank 13 which is a mixing container for mixing methanol and water supplied from the water tank 12, and a mixed liquid of methanol / water is supplied from the mixing tank 13 to the fuel cell 20 to circulate in the closed circuit channel 14. And a liquid concentration detector 30 for measuring the methanol concentration in the mixed liquid.

Each of the methanol tank 11 and the water tank 12 includes a flow rate control means (not shown). As a specific example of the flow rate control means, there is a flow rate control valve or the like that performs opening / closing control or opening degree adjustment in response to a control signal from a control unit (not shown) provided in the fuel cell.
The pump 15 is also operated by receiving control signals such as operation / stop and operation speed from the control unit, as in the above-described flow rate control means.

  The liquid concentration detection device 30 is provided at an appropriate position between the liquid concentration sensor 31 that measures the liquid concentration of the mixed liquid by detecting the dielectric constant of the mixed liquid and the flow path 14 of the mixed liquid described above. The ultrasonic transducer 32 is an ultrasonic generator that irradiates the flowing mixed liquid with ultrasonic waves. Note that one ultrasonic transducer 32 may be provided at least in one place, but a plurality of ultrasonic transducers 32 may be provided as necessary.

  The liquid concentration sensor 31 has a pair of electrodes functioning as a capacitor installed in a mixed liquid, and detects a dielectric constant that changes according to the concentration of the mixed liquid existing between the electrodes by a circuit board (not shown) to perform mixing. It measures the methanol concentration of the liquid. That is, a liquid mixture obtained by mixing liquids having different dielectric constants, such as methanol and water, measures the liquid concentration using the fact that the dielectric constant changes according to the mixing ratio. . The methanol concentration measured by the liquid concentration detection device 30 is input to a control unit (not shown) of the fuel cell 20 and used as a control parameter for output control.

  The ultrasonic transducer 32 irradiates the mixed liquid whose liquid concentration is measured with ultrasonic waves, and is installed, for example, between the mixing tank 13 and the fuel cell 20, more specifically on the upstream side of the fuel cell 20. The liquid concentration sensor 30 is preferably disposed in the flow path 14 between the liquid concentration sensor 31 and the liquid concentration sensor 31. As described above, when the ultrasonic vibrator 32 is disposed on the outlet side of the mixing tank 13 and on the upstream side of the liquid concentration sensor 31 and irradiated with ultrasonic waves, primary stirring is performed in the mixing tank 13, and the concentration is further increased. Secondary mixing can be performed by applying reliable and efficient ultrasonic irradiation to the mixed liquid to be measured. The ultrasonic transducer 32 is installed in the vicinity of the outlet of the mixing tank 13 at a position as far as possible from the liquid concentration sensor 31 so that the liquid concentration sensor 31 is not affected by the ultrasonic waves. It is desirable to apply ultrasonic irradiation to the aqueous methanol solution that has been mixed and flowed into the flow path 14.

The illustrated ultrasonic transducer 32 is installed on the outer wall that is outside the flow path 14, and irradiates the mixed liquid that flows inside the pipe line of the flow path 14 with ultrasonic waves that pass through the thickness of the pipe line. ing. As the ultrasonic transducer 32, a piezoelectric element such as piezoelectric ceramics can be used.
As described above, when the ultrasonic transducer 32 is installed on the outer wall side of the flow path 14, it is necessary to increase the output of the ultrasonic wave as compared with the case where it is installed in the flow path 14, but it is not in direct contact with the mixed liquid. For example, it is not necessary to take measures to ensure corrosion resistance, waterproofness, and the like.

  In the fuel supply device 10 having the above-described configuration, methanol and water supplied from the methanol tank 11 and the water tank 12 are mixed in the mixing tank 13 by the flow rate control means, and an aqueous methanol solution having a desired liquid concentration is obtained. This aqueous methanol solution passes through the ultrasonic vibrator 32, the liquid concentration detection device 30, and the fuel cell 20 in this order by the operation of the pump 15 and circulates in the flow path 14. For this reason, the mixed liquid whose concentration is measured by the liquid concentration detection device 30 is the one that has been irradiated with ultrasonic waves from the ultrasonic transducer 32.

  The aqueous methanol solution that has been irradiated with ultrasonic waves in this way has the liquid concentration detector 30 measure the liquid concentration (methanol concentration) from the change in dielectric constant, and this liquid concentration controls the output of the fuel cell 20. Used as. The liquid concentration measurement here is obtained by detecting the capacitance between the detection electrodes in the liquid concentration sensor 31, calculating the dielectric constant from the capacitance, and then calculating the liquid concentration from the dielectric constant.

  In the graph of the experimental results shown in FIG. 3, the horizontal axis represents the time (seconds) from the start of measurement, and the vertical axis represents the measured capacitance value (pF), and the change in the measured value according to the elapsed time. It is shown. According to this experimental result, in the case of the lower ultrasonic wave (left scale), after the measurement value decreases approximately linearly from about 37.9 pF immediately after the start of measurement to about 37.75 pF ± A stable value is obtained that is within the range of 0.05 pF and is free from severe fluctuations (no variation). From these experimental results, it can be interpreted that the aqueous methanol solution that has been irradiated with ultrasonic waves has been solved with local unevenness of density and has an aqueous solution with a uniform concentration.

As sample water for this experiment, an aqueous methanol solution mixed with 100 ml of water at a ratio of 3 ml of methanol is used. This sample water was put into a beaker, and the mixed liquid was irradiated with ultrasonic waves by immersing the whole beaker in a 50 W ultrasonic cleaner for 30 seconds. In addition, the capacitance is measured by arranging a pair of flat plate electrodes in the sample water after the irradiation of ultrasonic waves, and measuring the measurement values obtained by measuring at 10 second intervals while applying a predetermined AC voltage. Plotted in FIG.
Moreover, also about the experimental result without an ultrasonic wave, the electrostatic capacitance was measured on the completely same conditions except ultrasonic irradiation.

By the way, in the experimental results repeatedly performed under the same conditions except for the ultrasonic irradiation, the measured value of the capacitance is about 37.75 pF when there is an ultrasonic wave and about 38.05 pF when there is no ultrasonic wave. There is always a similar difference. This difference is presumed to be due to the fact that the uniformity is increased by the mixing and stirring effect of ultrasonic waves, and the influence of methanol having a low dielectric constant is more prominent.
In addition, in the case of the presence of ultrasonic waves, there is a substantially linear change for the first approximately 50 seconds. Such a change occurs when the liquid concentration sensor is put into a solution and the electrode concentration of the liquid concentration sensor is the highest. This is presumed to be due to the fact that time for realignment of polar molecules to the surface is necessary. It is also speculated that different changes other than a substantially linear change are exhibited depending on the electrode surface material and the capacitance detection circuit method.

Subsequently, a second embodiment of the present invention will be described with reference to FIG.
The direct methanol fuel cell fuel supply apparatus 10A shown in FIG. 2 is different in the installation position and the number of ultrasonic transducers 32, and the other configuration is the same as that of the first embodiment. Accordingly, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.
In the case of FIG. 2, the ultrasonic transducer 32 is installed inside the mixing tank 13 and in the flow path 14 connecting the mixing tank 13 and the liquid concentration sensor 31. That is, the first ultrasonic irradiation is performed in the mixing tank 13 in which methanol and water are mixed, and the second ultrasonic irradiation is performed in the vicinity of the upstream side of the liquid concentration detection sensor 31 that actually performs concentration measurement. Is going.

  With such an arrangement of the ultrasonic vibrator 32, it is possible to perform stirring by ultrasonic irradiation twice in the mixing tank 13 and the upstream side of the liquid concentration sensor 31. It is possible to more reliably form a methanol aqueous solution in a mixed state. Further, since the ultrasonic transducer 32 is disposed inside the mixing tank 32 and the flow path 14, the same effect can be obtained with a small output as compared with the case where it is installed outside.

The ultrasonic transducer 32 in the present invention is not limited to the first and second embodiments described above, and can be changed as appropriate.
That is, the aqueous methanol solution circulates in the closed circuit channel 14 and is supplemented with a necessary amount of methanol or water as appropriate to maintain a desired concentration. As long as it is inside, it may be installed anywhere except in the vicinity of the upstream side and downstream side of the liquid concentration sensor 31. Accordingly, the ultrasonic transducer 32 can be installed not only at the flow path 14 connecting the mixing tank 13 and the fuel cell 20 described above, but also at an appropriate place of the pump 15 or other part of the flow path 14. Good. Note that the mixing tank 13 is also a part of the flow path through which the aqueous methanol solution circulates, so that the ultrasonic vibrator 32 can be installed alone or in combination with other parts.

Further, the installation position of the ultrasonic transducer 32 may be either outside or inside the mixing tank 13 or the flow path 14.
In addition, this invention is not limited to embodiment mentioned above, In the range which does not deviate from the summary of this invention, it can change suitably.

The liquid concentration detection device of the present invention is particularly suitable as a means for detecting the concentration of methanol in an aqueous methanol solution in a direct methanol fuel cell. In addition to this, for example, alcohols whose dielectric constant changes depending on the mixing ratio are used. It can also be widely used as a concentration detection means for detecting the concentration of an aqueous solution, that is, the mixing ratio of a plurality of liquids having different dielectric constants.
The liquid concentration detection device of the present invention can also be used as a concentration detection means for detecting the concentration of an aqueous solution obtained by dissolving a solid or powder such as vitamin in water.

1 is a system diagram showing a first embodiment of a fuel supply device for a fuel cell according to the present invention. It is a systematic diagram showing a second embodiment of a fuel supply device of a fuel cell according to the present invention. It is a graph of the experimental result which shows the effect of this invention, and the relationship between the elapsed time (second) and the measured value of an electrostatic capacitance (pF) is shown about the case where an ultrasonic wave is irradiated to methanol aqueous solution, and the case where it does not irradiate. Yes.

Explanation of symbols

10, 10A Fuel supply device 11 Methanol tank (fuel storage container)
12 Water tank (electrolyte storage container)
13 Mixing tank (mixing container)
14 flow path 15 pump (liquid feeding means)
20 Fuel cell (DMFC)
30 Liquid Concentration Detection Device 31 Liquid Concentration Sensor 32 Ultrasonic Vibrator (Ultrasonic Generator)

Claims (6)

  A liquid concentration sensor for measuring a liquid concentration of a mixed liquid obtained by mixing liquids having different dielectric constants by detecting a dielectric constant of the mixed liquid; and an ultrasonic wave is provided to the mixed liquid provided in the flow path of the mixed liquid. A liquid concentration detection apparatus comprising: at least one ultrasonic wave generation unit that irradiates, and measuring a liquid concentration of a mixed liquid irradiated with ultrasonic waves from the ultrasonic wave generation unit. A fuel supply device for a fuel cell for supplying a fuel cell with a mixed liquid obtained by mixing a fuel and an electrolyte,
A fuel storage container for storing liquid fuel;
An electrolyte storage container for storing a liquid electrolyte;
A mixing container for mixing the fuel and electrolyte supplied from the fuel container and the electrolyte container;
A liquid feeding means for supplying the mixed liquid from the mixing container to the fuel cell to circulate through the flow path of the closed circuit, and a liquid concentration of the mixed liquid formed by mixing liquids having different dielectric constants to detect the dielectric constant of the mixed liquid A liquid concentration sensor for measuring by this, and at least one ultrasonic wave generation unit that is provided in the flow path of the mixed liquid and irradiates the mixed liquid with ultrasonic waves, and the ultrasonic wave is irradiated from the ultrasonic wave generation unit A liquid concentration detection device for measuring the liquid concentration of the mixed liquid;
A fuel supply device for a fuel cell, comprising:   The liquid concentration sensor is disposed in a flow path connecting the mixing container and the fuel cell, and the ultrasonic wave generating means is disposed in a flow path connecting the mixing container and the liquid concentration sensor. The fuel supply device for a fuel cell according to claim 2, wherein the fuel supply device is a fuel cell.   4. The fuel supply apparatus for a fuel cell according to claim 3, wherein the ultrasonic wave generating means is disposed in the vicinity of the outlet of the mixing tank.   3. The fuel supply device for a fuel cell according to claim 2, wherein the ultrasonic wave generating means is disposed in the liquid feeding means. The fuel of the fuel cell according to any one of claims 2 to 5, wherein the ultrasonic wave generator is disposed on an outer wall side of the flow path, the mixing tank, and / or the liquid feeding means. Feeding device.

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