Power generation element and power generation device

Abstract

The present invention achieves effective power generation using liquid flow.　This power generation element has a carbon material installed on the surface of a flow path through which a liquid flows. The carbon material is installed across a region where the liquid has an irregular flow and a region including a developed flow.

Description

Power generating element, power generating device

[0001] The present invention relates to a power generating element and the like.

[0002] With the increase in global energy demand, there is a demand for the development of alternative means of energy harvesting. In recent years, power generation systems using liquid flow have attracted attention. For example, Patent Literature 1 discloses a technology in which a fluid such as seawater is flowed over the surface of graphene, and the graphene generates power from the fluid flow.

[0003] US Patent Application Publication No. 2021 / 0021213

[0004] The technology disclosed in Patent Document 1 is insufficient to realize effective power generation by liquid flow, for example, from the viewpoint of obtaining a large electromotive force.

[0005] The present invention has been made in view of the above-mentioned problems, and one of its objects is to realize effective power generation using the flow of liquid.

[0006] According to one aspect of the present invention, there is provided a power generation element in which a carbon material is placed on the surface of a flow path through which a liquid flows, and the carbon material is placed across a region in which the liquid flowing through the flow path includes an irregular flow and a region in which the liquid includes a developed flow.

[0007] According to the present invention, it is possible to realize effective power generation by using a liquid flow.

[0008] 1A and 1B are schematic plan views of a microflow chip; 1C and 1D are schematic views of a microflow chip; 1D and 1E are schematic views of a microflow chip; 1E and 1F ...

[0009] An example of an embodiment of the present invention will now be described with reference to the drawings. The components described in this embodiment are merely examples and are not intended to limit the scope of the present invention.

[0010] <Principle> First, the principle of this embodiment will be described. In the following, graphene is exemplified as the carbon material, and water (pure water) is exemplified as the liquid.

[0011] Through experiments, the inventors of the present application have obtained the following three main findings: (1) Continuous generation of electromotive force using microchannels (2) The magnitude of the electromotive force is proportional to the Reynolds number (3) State transition of the water flow is necessary to obtain a large electromotive force Each of these findings will be explained below.

[0012] (1) Continuous generation of electromotive force using a microchannel Figure 1 is an example of a graph showing continuous generation of electromotive force using a microchannel, where the horizontal axis represents time t (s) and the vertical axis represents electromotive force per unit flow channel area (μV / mm 2Graphene, a type of carbon material and nanocarbon, was placed on a substrate to form a microchannel, and an experiment was conducted in which water was continuously introduced (a water flow was applied) into this microchannel.

[0013] In this embodiment, the microchannel may refer to a microscale channel, for example, a channel with a height (depth) of 1 mm or less.

[0014] This graph shows the change in electromotive force when the introduction of water into the microchannel is started at time "t = 0" and stopped at time "t = 60." Looking at this graph, it can be seen that continuous power generation (continuous generation of electromotive force) by graphene is achieved in the above section.

[0015] (2) The magnitude of the electromotive force is proportional to the Reynolds number. The inventors of the present invention conducted an experiment to examine the relationship between the Reynolds number and the electromotive force.

[0016] FIG. 2 is an example of a graph showing the relationship between the Reynolds number and the electromotive force, where the horizontal axis represents the Reynolds number and the vertical axis represents the electromotive force per unit flow path area (μV / mm 2 ) is shown. The Reynolds number is defined as a dimensionless number that represents the ratio of the inertial force to the viscous force of a fluid. This graph shows the results of plotting the electromotive force against the Reynolds number by changing the channel size (channel width "w" and height "h"). In this case, a microchannel with a channel height of 1 mm or less is used.

[0017] The results show that: - The larger the Reynolds number, the larger the electromotive force, regardless of the flow channel size; - The electromotive force increases almost linearly with the Reynolds number, regardless of the flow channel size; - For the same Reynolds number, the magnitude of the electromotive force differs depending on the flow channel size. In this example, the electromotive force is largest when w = 1.0 [mm] and h = 0.5 [mm].

[0018] The inventors of the present invention quantified the amount of electricity generated at the interface between graphene and flowing water and found that the electromotive force per unit flow area increases almost linearly with the flow velocity. In contrast, the results in Figure 2 show that the electromotive force per unit flow area does not depend only on the flow velocity, but also on the flow path size (the degree of increase in electromotive force depends on the flow path size).

[0019] (3) State transition of water flow is necessary to obtain a large electromotive force. The inventors of the present application conducted a simulation to confirm how the state of water flow in a flow channel affects the electromotive force.

[0020] Figure 3 shows an example of the configuration of a channel used in the simulation. The simulation was performed using a channel with the shape shown in the figure. In this figure, the x-axis represents the length of the channel, the y-axis represents the width of the channel, and the z-axis represents the height of the channel. The left end of the x-axis corresponds to the position of the water inlet, and the right end of the x-axis corresponds to the position of the water outlet. The plane of "z = 0" indicates the plane on which graphene is installed, and electromotive force was measured for each position in the x-axis direction. In the figure, the water flow velocity in the channel is color-coded, and for convenience, some of the flow velocities are shown in five categories: "a>b>c>d>e" from the fastest to the slowest.

[0021] FIG. 4 is an example of a graph showing the change in water flow velocity over time in this case, where the horizontal axis represents time t (s) and the vertical axis represents the water flow velocity v in the x-axis direction. ｘ (1) to (6) show the change in flow velocity over time at positions "x = 4 mm," "x = 7 mm," "x = 14 mm," "x = 20 mm," "x = 27 mm," and "x = 30 mm," respectively, when a position slightly away from the inlet toward the outlet is set as the reference position "x = 0 mm."

[0022] Looking at these graphs, we can see that the state of water flow changes depending on the position within the flow channel, and that the water velocity distribution and time change are particularly turbulent near the inlet, but tend to stabilize as it progresses downstream (towards the outlet).

[0023] FIG. 5 is an example of a graph showing the change in electromotive force over time in this case, where the horizontal axis represents time t (s) and the vertical axis represents electromotive force per unit flow path area (μV / mm ２ ) are shown. (1) to (6) show the electromotive forces at the respective positions "x = 4 mm," "x = 7 mm," "x = 14 mm," "x = 20 mm," "x = 27 mm," and "x = 30 mm." In this example, the electromotive forces are shown when water introduction is started at "t = 5 (s)," stopped at "t = 10 (s)," started again at "t = 20 (s)," and stopped at "t = 25 (s)." This graph shows that the stability of the voltage signal and the amount of electromotive force vary depending on the distance from the inlet. Specifically, it can be seen that the stability of the voltage signal is low and the electromotive force is relatively small near the inlet and outlet. On the other hand, there are positions within the flow channel where the electromotive force is maximum, and it can be seen that the voltage signal is also stable at those positions.

[0024] FIG. 6(1) is a graph showing the electromotive force at each position in the flow path, and FIG. 6(2) is a graph showing its dispersion. Here, the results of a simulation performed with two flow velocities set to "245 mm / s" and "147 mm / s" are shown. In FIG. 6(1), the horizontal axis represents the position "x" and the vertical axis represents the electromotive force per unit flow path area (μV / mm ２ ) In FIG. 6(2), the horizontal axis indicates the position "x" and the vertical axis indicates the dispersion of the electromotive force "σ ２ " is shown. In each figure, the upper part shows the results when the flow velocity is set to "245 mm / s", and the lower part shows the results when the flow velocity is set to "147 mm / s". Looking at this graph, it can be seen that at any flow velocity: - There is a position in the flow channel where the electromotive force is maximum - The electromotive force is small near the inlet and outlet parts - The electromotive force is less stable (large variance) near the inlet and outlet parts. In this result, the position in the flow channel where the electromotive force is maximum is approximately near the center of the flow channel.

[0025] Based on these results, the inventors of the present invention placed graphene at a position approximately near the center of the flow channel and conducted an experiment to examine how the electromotive force changes when the state of the water flow is changed.

[0026] FIG. 7 shows an example of the configuration of the flow channel used in the experiment. In this example, the position corresponding to the inlet was set to "x = 0 mm" and the position corresponding to the outlet was set to "x = 37 mm." Graphene was also installed near the center of the flow channel (on the substrate). A buffer region was also configured to communicate with the inlet of the flow channel on the left side of the drawing, allowing water stored in the buffer region to be introduced into the flow channel. By storing water in the buffer region and then allowing it to flow into the flow channel, water with a highly spatiotemporally stable flow state is introduced into the flow channel. On the other hand, when water is introduced from the outlet side on the right side of the drawing, for example, water with a less spatiotemporally stable flow state is introduced into the flow channel without the buffer region.

[0027] FIG. 8 is an example of a graph showing the flow velocity dependency of the electromotive force in this case, and is a diagram showing an example of the results of measuring the electromotive force while changing the flow velocity. The horizontal axis represents the flow velocity (mm / s), and the vertical axis represents the electromotive force per unit flow area (μV / mm ２ ) is shown. The circular plots show the electromotive force when water is introduced into the flow path through the buffer region, and the rectangular plots show the electromotive force when water is introduced into the flow path without passing through the buffer region. Looking at this graph, we can see that: - Regardless of the flow rate, the electromotive force is relatively larger when water is introduced without passing through the buffer region than when water is introduced through the buffer region.

[0028] From these results, the inventors of the present application thought that in order to obtain a large electromotive force, a transition in the flow state of the water flowing through the flow path is necessary, and more specifically, an irregular flow is necessary in the upstream section.

[0029] In the following, "developed flow" may refer to a state of liquid flow in which spatial changes with respect to time and flow direction have become sufficiently small (a state of flow that can be regarded as such). It may also be considered a state of liquid flow in which spatial turbulence with respect to time and flow direction has become sufficiently small and stable. However, it is not necessary for the spatial changes with respect to time and flow direction to reach a state of "0" (this state may also be called "fully developed flow"). Laminar flow may be considered to be included in this developed flow. Furthermore, "irregular flow" may refer to a state of liquid flow that has not yet reached developed flow (or a state of flow that can be regarded as such).

[0030] FIG. 9A shows an example of the structure of a device (hereinafter referred to as the "irregular flow generating device") 20 devised as a device for generating an irregular flow. In this example, the irregular flow generating device 20 is configured by forming, for example, a narrowed circular outlet 21a on the bottom surface of a cylindrical member (hereinafter referred to as the "cylindrical member") 21, and joining this outlet 21a to a truncated conical member (hereinafter referred to as the "frustum-shaped member") 22. The truncated conical member 22 has a hollow upper surface 22a that fits into the outlet 21a and a hollow bottom surface 22b that fits into the inlet of the flow path. Water flows inside the cylindrical member 21, encounters resistance at the circular outlet 21a on its bottom surface, flows into the truncated conical member 22, and expands, generating an irregular flow. The water containing the irregular flow is introduced into the flow path from the hollow bottom surface 22b through the inlet of the flow path. Water containing irregular flow is introduced into a channel, and as it flows through the channel, the spatial and temporal variations gradually decrease, eventually resulting in a developed flow.

[0031] It should be noted that, for example, the size of the outlet 21a of the cylindrical member 21 (the size of the upper surface 22a of the truncated cone-shaped member 22) and the size of the bottom surface 22b of the truncated cone-shaped member 22 can be designed to any size. Also, for example, the shape of the member joined to the cylindrical member of the irregular flow generating device 20 may be changed and is not limited to a truncated cone-shaped member.

[0032] 9(2) is a diagram showing an example of the structure of a general device 30 for comparison with the above-mentioned irregular flow generating device 20. In this example, the device 30 has an end of a flow path joined to the bottom of a cylindrical member (hereinafter referred to as "cylindrical member") 31. Water flows vertically down inside the cylindrical member 31 and is introduced directly into the flow path.

[0033] FIG. 10 is an example of a graph showing the flow velocity dependency of the electromotive force in this case, and shows an example of the results of measuring the electromotive force by changing the flow velocity using the irregular flow generating device 20 and the device 30. The horizontal axis represents the flow velocity (mm / s), and the vertical axis represents the electromotive force per unit flow area (μV / mm ２ ) is shown. The circular plots indicate the electromotive force when water is supplied to the flow path using the irregular flow generating device 20, and the rectangular plots indicate the electromotive force when water is supplied to the flow path using the device 30. Looking at this graph, it can be seen that: regardless of the flow velocity, the electromotive force is relatively larger when water is supplied to the flow path using the irregular flow generating device 20 than when water is supplied to the flow path using the device 30.

[0034] <Power Generation Element> Next, an example of a power generation element according to the present invention configured based on the above principle will be described.

[0035] 11A is an example of a schematic plan view of a microflow chip (microchannel chip) 1, which is an example of a power generation element in this embodiment. The microflow chip 1 includes, for example, a substrate 11, graphene 12, a spacer 13, an inlet 15, a channel formed by the spacer 13 through which water introduced from the inlet 15 flows, and an outlet 16 for discharging the water from the channel.

[0036] The substrate 11 is a basic component of the microflow chip 1 and is formed, for example, from a light-transmitting or non-light-transmitting material. For example, when detecting or observing the state inside the flow path portion using light, a material that is highly transparent to light may be used. Examples of light-transmitting materials that can be used include resin and glass. Examples of resins that can be used as the light-transmitting material for forming the substrate 11 include acrylic resin, methacrylic resin, polypropylene, polycarbonate resin, cycloolefin resin, polystyrene resin, polyester resin, urethane resin, silicone resin, and fluorine-based resin.

[0037] Graphene 12 is placed on the substrate 11. For example, graphene is synthesized by CVD on a copper foil base, and polymethyl methacrylate (PMMA) is formed as a support film on the graphene. The copper foil base is then removed by wet etching, and the graphene is transferred onto the substrate 11. Then, the PMMA film is removed by, for example, immersion in acetone.

[0038] A spacer 13 is sandwiched between the substrate 11 and the graphene 12, and a flow path is formed by the spacer 13. The spacer 13 may be, for example, a silicon spacer. The height and width of the spacer 13 correspond to the cross-sectional area of ​​the flow path.

[0039] The substrate 11 is covered with, for example, a top plate (not shown), and the inlet 15 and outlet 16 are configured to introduce water into the flow path through through holes provided in the top plate. A top plate with spacers 13 may be placed on the substrate 11 on which the graphene 12 is placed.

[0040] The inlet 15 may be configured to introduce water into the flow path by an irregular flow generating device 20 (similar to that shown in FIG. 9(1)) shown in FIG. 11(2) connected to a predetermined tube. The outlet 16 has, for example, a pump (such as a syringe pump), and the water that has flowed through the flow path is discharged from the outlet 16.

[0041] Although not shown in the figure, a pair of electrodes may be installed on the graphene 12 at an arbitrary distance d along the water flow direction, and may be connected to a voltmeter and a variable resistor via, for example, a coaxial cable from an electrical connection port on the top plate, so that the potential difference across the graphene 12 during application of water flow can be measured. In this case, the electrodes may be installed outside the spacer 13 that forms the flow path to prevent contact with the water.

[0042] Furthermore, a plurality of inlet portions 15 and outlet portions 16 may be provided. Also, a plurality of flow paths may be provided.

[0043] As described above, the irregular flow generating device 20 allows water containing irregular flows to flow into a flow channel. As the water flows through the flow channel, the spatiotemporal changes in the flow channel gradually decrease, eventually resulting in a developed flow. The flow then becomes a fully developed flow. In this embodiment, the graphene 12 is installed across a region of the water flowing through the flow channel that includes irregular flows and a region that includes developed flows. In this case, for example, the graphene 12 may be installed so that at least a portion of the range of positions within the flow channel during the transition process (transition process) from irregular flows to fully developed flows is included within a range that is computationally determined as a range that is effective for increasing electromotive force (details will be described later). Conceptually, the region containing irregular flows may include a region in the flow channel where irregular flows are observed, and the region containing developed flows may include a region in the flow channel where developed flows are observed.

[0044] The placement position of the graphene 12 will be described in detail below. Here, a method based on a numerical index introduced by the inventors of the present application will be described.

[0045] FIG. 12 is a diagram showing an example of velocity distribution in a flow channel. This diagram shows the velocity distribution at "0<z<300 μm" (z: height of the flow channel) at position x in the flow direction in the flow channel, determined by simulation. Here, it is assumed that the water flow is fully developed at "x=30". In this case, at an arbitrary position (x ｉ , z ｊ ) (flow direction position x = i, height z = j) and position (x ３０ , zｊ ) (position x = 30 in the flow direction, height z = j) and calculate the flow velocity ratio in the x direction. The average value in the z direction is u(z). i (Equation (1)).

[0046] Also, this u(z) ｉ Using this, the fully developed flow (= u(z) ３０ An index value Δu(z) (here, the unit is %) indicating how close the object is to the target object is defined as, for example, equation (2).

[0047] Fig. 13 is a graph showing the relationship between the position x and the index value Δu(z) in this case, with the horizontal axis representing the position x [mm] and the vertical axis representing the index value Δu(z) [%]. Fig. 14 is a graph showing an example of the relationship between the index value Δu(z) and the electromotive force, with the horizontal axis representing the index value Δu(z) [%] and the vertical axis representing the electromotive force EMF [μV / mm 2 ] are shown. As an example, the results are shown here when a water flow with a flow velocity of 245 mm / s is applied to a flow path (width 3.4 mm, height 0.3 mm) with the shape shown in FIG. 15. The upstream to downstream of the flow path shown in FIG. 15 corresponds to the right to left in FIG. 14, and the corresponding position x on the horizontal axis in FIG. 13 is shown in association with each plot. The plot of "Δu(z) = 0" on the left side of the graph corresponds to the position of "x = 30".

[0048] 14, it can be seen that as the index value Δu(z) decreases (from upstream to downstream in the flow path), the electromotive force increases significantly from Δu(z) approximately 1% (corresponding to x=7).Then, the increase in the electromotive force becomes gentler from Δu(z) 0.1% (corresponding to x=14), the electromotive force reaches a maximum when Δu(z) is slightly larger than 0.01% (corresponding to x=20), and then the electromotive force decreases rapidly from that point.

[0049] For example, the range indicated by the double arrow in Figure 14 indicates the range that is effective for increasing the electromotive force within the range (index of) the transition process from an irregular flow to a fully developed flow. Specifically, it is advisable to place the graphene 12 at a position in the flow channel corresponding to a range where Δu is greater than 0.01% and less than 1%, which is effective for increasing the electromotive force. In this case, it is not necessary for all of the graphene 12 to be within this range, but at least a portion of the graphene 12 must be placed in this region.

[0050] <Power Generation Device> It is also possible to configure a power generation device including the power generation element described above. Fig. 16 is a diagram showing an example of the schematic configuration of a power generation device 100. The power generation device 100 is configured to include, for example, the microflow chip 1, a control unit 110, a solenoid valve 120, and a voltmeter 130.

[0051] The control unit 110 is a control unit that performs overall control of the power generation device 100, and is configured to include, for example, a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), and processing circuits such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array).

[0052] The solenoid valve 120 is attached to a pipe that introduces water into the microflow chip 1, and is a device for adjusting the flow rate of the introduced water. The solenoid valve 120 may be, for example, a proportional control solenoid valve. The control unit 110 changes the control signal sent to the proportional control solenoid valve, thereby continuously controlling the flow rate of water introduced into the microflow chip 1, for example, within a range of "0% to 100%."

[0053] The voltmeter 130 is connected to a pair of electrodes 19 a and 19 b connected to the graphene 12 of the microflow chip 1 , measures the electromotive force generated by the graphene 12 , and outputs the measurement result to the control unit 110 .

[0054] Under the control of the control unit 110, the solenoid valve 120 adjusts the flow rate of, for example, water flowing into the irregular flow generating device 20 of the microflow chip 1. Because the cross-sectional area of ​​the piping is fixed, controlling the flow rate controls the flow rate of the irregular flow introduced into the flow path via the irregular flow generating device 20.

[0055] <Actions and Effects of the Embodiment> According to the present embodiment, in a microflow chip 1 (an example of a power generation element), graphene 12 (an example of a carbon material) is provided on the surface of a flow path through which water (an example of a liquid) flows, and this graphene 12 is provided across a region in which the water flowing through the flow path includes an irregular flow and a region in which the water flowing through the flow path includes a developed flow. By providing the carbon material across a region in which the liquid flowing through the flow path includes an irregular flow and a region in which the liquid flowing through the flow path includes a developed flow, it is possible to achieve effective power generation using the carbon material and obtain a larger electromotive force than conventional methods.

[0056] In this case, the irregular flow generating device 20 may be provided at a position where water flows into the flow path. By providing a device that generates an irregular flow at a position where liquid flows into the flow path, it is possible to introduce liquid containing an irregular flow into the flow path.

[0057] The carbon material may be, for example, graphene, which is a type of nanocarbon, and the liquid may be, for example, water.

[0058] The flow channel may be, for example, a micro-flow channel, which allows for continuous introduction of liquid, thereby realizing continuous power generation using a carbon material.

[0059] Furthermore, a power generating device 100 may be configured that includes the above-described microflow chip 1 and a control unit 110 that controls the flow rate of the irregular flow. This makes it possible to control the flow rate of the irregular flow introduced into the power generating element.

[0060] The power generation element of this embodiment is expected to be utilized in the energy harvesting market, and can be expected to be applied to, for example, storage batteries, sensors (for example, sensors that monitor the flow state of pipes, etc., or sensors that estimate the flow state from electromotive force), etc.

[0061] <Modifications> (1) Carbon Material In the above embodiment, graphene, a type of nanocarbon, is used as the carbon material, but this is not limiting. Nanocarbon is preferable because it has high in-plane conductivity, and in addition to graphene, carbon nanotubes, carbon nanofibers, etc. may also be used. Furthermore, various other conductive carbon materials may also be used, such as graphite, which is a laminate of graphene, or amorphous carbon (carbon black, carbon fiber, etc.).

[0062] In place of the carbon material, for example, molybdenum disulfide (MoS), which is a type of sulfide, may be used. ２ ) may be used.

[0063] (2) Liquid In the above embodiment, water is used as an example of the liquid flowing through the flow path, but this is not limiting. A polar liquid (solvent) other than water may also be used as the liquid. Furthermore, an electrolyte solution, specifically, a solution in which an ionic substance is dissolved in a polar solvent, may also be used as the liquid. Furthermore, an ionic liquid may also be used as the liquid.

[0064] (3) Flow Channel In the above embodiment, a microchannel is used as the flow channel, but this is not limiting. The flow channel does not necessarily have to be configured as a microchannel. For example, a flow channel of a size other than the above-mentioned flow channel having a height (depth) of 1 mm or less may be configured. Even in this case, power generation using a carbon material can be realized.

[0065] REFERENCE SIGNS LIST 1 Microflow chip 11 Substrate 12 Graphene 13 Spacer 15 Inlet section 16 Outlet section 20 Irregular flow generating device 100 Power generation device

Claims

1. A power generation element in which a carbon material is placed on the surface of a flow path through which a liquid flows, wherein the carbon material is placed across a region in which the liquid flowing through the flow path includes an irregular flow and a region in which the liquid includes a developed flow.

2. The power generating element according to claim 1, wherein a device for generating an irregular flow is provided at a position where the liquid flows into the flow path.

3. The power generating element according to claim 1, wherein the carbon material is nanocarbon.

4. The power generating element according to claim 1, wherein the liquid is one of a polar liquid, an electrolyte solution, and an ionic liquid.

5. The power generating element according to claim 1, wherein the flow path is a micro flow path.

6. A power generating device comprising: a power generating element according to any one of claims 1 to 5; and a control unit that controls the flow rate of the irregular flow.

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