Patent Application
20090162720
The present invention relates to a fluid transfer device for causing a fluid to travel along a channel, and more specifically, to a fluid transfer device for use in an electronic apparatus, and a fuel cell and an electronic apparatus using the same.
Air blowers using the flexural vibration of piezoelectric ceramics and the like have been conventionally known (see for example Japanese Patent Application Laid-Open Nos. 2000-186699 and 2000-120600).
In the above-discussed air blower 1000, an AC voltage of a frequency equal to the resonant frequency of the vibrating plate 101 is applied to each of the piezoelectric ceramics 103 and 104. The control is such that it expands the piezoelectric ceramic 103 while contracting the piezoelectric ceramic 104, thereby allowing the vibrating plate 101 to vibrate greatly at the other end according to the polarity of the AC voltage. This causes the vibrating plate 101 to vibrate like a fan to generate air flow.
In the air bower 1100, AC voltages of frequencies equal to the resonant frequencies of the vibrating plates 111a and 111b are respectively applied in phase to the piezoelectric ceramics 113a to 113d and 114a to 114d. Then, the piezoelectric ceramics 113a, 113c, 114a and 114c are allowed to contract in phase while the piezoelectric ceramics 113b, 113d, 114b and 114d are allowed to contract in phase. Further, the piezoelectric ceramics 113a, 113c, 114a and 114c, and the piezoelectric ceramics 113b, 113d, 114b and 114d are allowed to contract in opposite phase to each other. This generates standing waves in the vibrating plates 111a and 111b respectively as indicated by reference numerals A, A′, B and B′ in
The above-discussed air blowers 1000 and 1100 according to the first and second examples of the conventional art are not only intended for use in cooling of LSIs, CPUs and the like arranged inside compact electronic apparatuses, but are also expected to serve as air suppliers for supplying air into fuel cells for use in compact electronic apparatuses (see for example Japanese Patent Application Laid-Open No. 2004-214128).
A top plate 205 is arranged over the cathode 204b. A first channel 201 with an inlet 201a and an outlet 201b is defined between the top plate 205 and the cathode 204b. A bottom plate 207 is arranged under the anode 204c. A second channel 206 with an inlet 206a and an outlet 206b is defined between the bottom plate 207 and the anode 204c.
In the fuel cell 1200, an oxidizing fluid such as air or oxygen is supplied from the inlet 201a toward the outlet 201b of the first channel 201, and a fuel fluid such as hydrogen or methanol is supplied from the inlet 206a toward the outlet 206b of the second channel 206. The oxidizing fluid and the fuel fluid are thereby supplied to the cathode 204b and the anode 204c of the MEA 204, respectively. This generates electrochemical reaction in the MEA 204, thereby taking electricity out of the cathode 204b and the anode 204c to the outside.
The air blowers 1000 and 1100 according to the first and second examples of the conventional art may be arranged near the inlet 201a of the first channel 201, or near the inlet 206a of the second channel 206, thereby enhancing respective capacities to supply a fuel fluid and an oxidizing fluid. As a result, higher output of the fuel cell is obtained.
However, in both the above-discussed air blowers 1000 and 1100 according to the first and second examples of the conventional art, the vibrating plates 101, and 111a and 111b are required to increase in amplitude in order to supply a fuel fluid and an oxidizing fluid in large quantities. This disadvantageously results in the increase of device size and the increase in energy loss, resulting in inefficient supply of air. When the above-discussed air blowers 1000 and 1100 according to the first and second examples of the conventional art are applied to the above-discussed conventional fuel cell 1200 for use in a compact electronic apparatus, the efficiency of supplying a fuel fluid and an oxidizing fluid is low. This disadvantageously results in insufficient output. Further, with reduced amounts of supply of a fuel fluid and an oxidizing fluid, CO2 and H20 generated by the reaction of a fuel fluid and an oxidizing fluid are likely to be accumulated on a surface of the MEA 204. This inhibits electrolytic chemical reaction, disadvantageously resulting in the difficulty of obtaining a high output.
It is one object of the present invention to provide a compact fluid transfer device capable of causing a fluid to efficiently travel at a high flow rate. It is another object of the present invention to provide a compact fuel cell capable of efficiently providing high electric power generation. It is still another object of the present invention to provide an electronic apparatus exhibiting excellence in power efficiency or cooling capability.
In a fluid transfer device according to the present invention, a vibrating plate for generating an acoustic wave and a reflection wall for reflecting the acoustic wave face each other at opposite sides of a channel along which a fluid is to be caused to travel, with the channel being held therebetween. The fluid is caused to travel by a sound pressure gradient formed in the channel by the vibration of the vibrating plate. An acoustic wave means a wave motion generated by vibration and propagates in a medium.
Acoustic streaming is the steady flow of a fluid generated by an acoustic field. When the vibrating plate and the reflection wall are arranged to face each other and vibration is applied to the vibrating plate to generate an ultrasonic standing wave, air column resonance is generated between the vibrating plate and the reflection wall. This generates eddy acoustic streaming between the vibrating plate and the reflection wall.
The principles of acoustic streaming generation are introduced in some theses such as “Acoustic streaming and radiation pressure”, Technical report of IEICE (The Institute of Electronics, Information and Communication Engineers), US96-93, EA96-97 (January, 1997), or “Mechanism for generating acoustic streaming”, Journal A of The Institute of Electronics, Information and Communication Engineers, Vol. J80-A, No. 10, pp. 1614-1620 (October, 1997), for example. However, a technique for stably generating acoustic streaming to cause a fluid to travel by means of this acoustic streaming has not been known.
In the above-discussed fluid transfer device according to the present invention, an acoustic wave generated in the vibrating plate is subjected to multiple reflection in the channel between the vibrating plate and a reflector to increase sound pressure in the channel. This forms acoustic streaming in the channel to generate a force to move a fluid in the channel. As a result, a fluid is caused to travel along the channel. In the present invention, “acoustic streaming” is considered as an idea meaning steady flow of a fluid generated by a sound pressure gradient in an acoustic field.
In the fluid transfer device according to the present invention, a sound pressure gradient is formed in the channel to generate uniform acoustic streaming from the entrance toward the exit of the channel, thereby causing a fluid to travel. Thus, a fluid supply mechanism as an external device to be connected to the channel is not required, therefore, the fluid transfer device is composed by defining the channel by the vibrating plate and the reflection wall, and simply providing the vibrating plate with a vibrating application part such as a piezoelectric element. As a result, the fluid transfer device according to the present invention is a compact device with a simple structure and low power consumption, and can be suitably applied as a fluid transfer device of a fuel cell to be built into a compact electronic apparatus. In addition to a fuel cell, the applicability of the fluid transfer device of the present invention includes electronic circuits, cooling means for use in systems such as solar panels or projection systems, insect repellant devices, air blowers for use in systems such as humidifiers or aspirators, refreshing means for removing materials deposited on sensors and the like to restore sensitivity, propelling means of micromachines, or fluid feed means for use in Lab-on-a-chip devices.
In the fluid transfer device according to the present invention, a fluid is allowed to travel in a fixed direction by acoustic streaming. Therefore, unlike an air blower using the curvature movement of a vibrating plate, the vibrating plate is not required to be increased in amplitude. This easily realizes reduction in size of the device configuration while efficiently causing a fluid to travel. Further, even with a small capacity of the channel, a fluid can be efficiently caused to travel at a high flow rate. As a result, it is possible to obtain a compact fluid transfer device capable of efficiently causing a fluid to travel at a high flow rate. An acoustic wave used in the present invention is preferably a so-called ultrasonic wave with a frequency in a range of about 20 kHz to about 200 kHz. In this case, the acoustic wave has a short wavelength of some centimeters or shorter. This allows size reduction of the device configuration while efficiently generating acoustic streaming, thereby causing a fluid to travel at low energy. As the frequency of the acoustic wave goes out of a human audible range, the influence upon the human body exerted by the acoustic wave can be suppressed.
In the fluid transfer device according to the present invention, five forms given below are employed as the specific structures of a mechanism for generating a sound pressure gradient in order to reliably cause a fluid to travel in the channel in the predetermined direction along the channel.
According to a first form, the vibrating plate for generating an acoustic wave and the reflection wall for reflecting this acoustic wave are arranged so that the distance therebetween is greater on the side of the exit than on the side of the entrance of the channel. According to this form, the channel has a dimension greater on the side of the exit than on the side of the entrance. Thus, the travel of a fluid in the channel toward the exit results in lower pressure loss than the travel toward the entrance. As a result, the fluid is discharged through the exit of the channel with greater dimension while being sucked in through the entrance with smaller dimension.
In the fluid transfer device in the first form, the vibrating plate is preferably arranged so that the distance from the reflector gradually increases in the direction from the entrance toward the exit. According to this configuration, the dimension of the channel is easily made greater on the side of the exit than on the side of the entrance, while the cross section is gradually changed along the channel. As a result, pressure loss is reduced to cause a fluid to travel more effectively.
In this fluid transfer device, a standing wave of acoustic waves is preferably generated in the channel. According to this configuration, the generation of a standing wave increases further sound pressure in the channel to cause a fluid to travel more effectively.
In this fluid transfer device, a standing wave is preferably generated in the channel on the side of the entrance with smaller dimension. According to this configuration, sound pressure is greater on the side of the entrance of the channel with smaller dimension than on the side of the exit with greater dimension. A sound pressure gradient is thereby formed in which sound pressure decreases in the direction from the entrance toward the exit of the channel. As a result, a fluid in the channel is more easily caused to travel from the entrance toward the exit.
In this fluid transfer device, the vibrating plate is preferably excited at a resonant frequency of the vibrating plate or at a frequency close to the resonant frequency. According to this configuration, the vibrating plate is allowed to increase in amplitude by resonance to increase further sound pressure in the channel.
Preferably, the acoustic field resonant frequency of an air column in the channel and the resonant frequency of the vibrating plate are the same to efficiently generate air flow.
In this fluid transfer device, a vibration application part is preferably provided on a surface of the vibrating plate. According to this configuration, the vibrating plate can be easily caused to vibrate to generate an acoustic wave.
According to a second form of the fluid transfer device of the present invention, the vibrating plate has lower bending stiffness and/or mass on the side of the entrance of the channel, and higher bending stiffness and/or mass on the side of the exit of the channel. The bending stiffness of the vibrating plate is defined by the product of a second moment of area I and a modulus of elasticity E in a particular cross section.
More specifically, the vibrating plate has a lower second moment of area on the side of the entrance of the channel, and a higher second moment of area on the side of the exit of the channel. In other words, the vibrating plate has a lower modulus of elasticity on the side of the entrance of the channel, and a higher modulus of elasticity on the side of the exit of the channel.
In the fluid transfer device in the second form, an ultrasonic standing wave is generated in the vibrating plate to thereby generate air column resonance between the vibrating plate and the reflection wall. The vibrating plate has lower bending stiffness and/or mass on the side of the entrance of the channel, and higher bending stiffness and/or mass on the side of the exit. Thus, the vibrating plate vibrates with greater amplitude on the side of the entrance of the channel, while vibrating with smaller amplitude on the side of the exit of the channel. This makes sound pressure in the channel higher on the side of the entrance, and lower on the side of the exit. As a result, a sound pressure gradient is formed in which sound pressure decreases in the direction from the entrance toward the exit of the channel, thereby forming acoustic streaming in the channel from the entrance toward the exit to cause a fluid in the channel to flow from the entrance toward the exit.
According to a third form of the fluid transfer device of the present invention, the vibrating plate projects outwards from the reflection wall on the side of one of end portions of the channel to define a region that does not face the reflection wall.
In the fluid transfer device in the third form, an ultrasonic standing wave is generated in the vibrating plate to thereby generate air column resonance between the vibrating plate and the reflection wall. The vibrating plate projects outwards from the reflection wall on the side of the exit of the channel to define a region that does not face the reflection wall. Thus, the sound pressure in an acoustic field defined by this region is lower than that in an acoustic field defined by a region between the vibrating plate and the reflection wall facing each other. As a result, a sound pressure gradient is formed in which sound pressure decreases in the direction from the entrance toward the exit of the channel, thereby forming acoustic streaming in the channel from the entrance toward the exit to cause a fluid in the channel to flow from the entrance toward the exit.
According to a fourth form of the fluid transfer device of the present invention, the reflection wall has a higher acoustic impedance on the side of the entrance of the channel, and a lower acoustic impedance on the side of the exit of the channel.
In the fluid transfer device in the fourth form, the reflection wall has a higher acoustic impedance on the side of the entrance of the channel, and a lower acoustic impedance on the side of the exit of the channel. Thus, higher sound pressure is generated on the side of the entrance of the channel while lower sound pressure is generated on the side of the exit of the channel. As a result, a sound pressure gradient is formed in which sound pressure decreases in the direction from the entrance toward the exit of the channel, thereby forming acoustic streaming in the channel from the entrance toward the exit to cause a fluid in the channel to flow from the entrance toward the exit.
According to a fifth form of the fluid transfer device of the present invention, a surface of the reflection wall that faces the vibrating plate has a lower acoustic absorption coefficient on the side of the entrance of the channel, and a higher acoustic absorption coefficient on the side of the exit of the channel.
In the fluid transfer device in the fifth form, the surface of the reflection wall that faces the vibrating plate has a lower acoustic absorption coefficient on the side of the entrance of the channel, and a higher acoustic absorption coefficient on the side of the exit of the channel. Thus, the strength of a reflected wave is higher on the side of the entrance of the channel, and is lower on the side of the exit of the channel. As a result, a sound pressure gradient is formed in which sound pressure decreases in the direction from the entrance toward the exit of the channel, thereby forming acoustic streaming in the channel from the entrance toward the exit to cause a fluid in the channel to flow from the entrance toward the exit.
In a fuel cell according to the present invention, an anode and a cathode are arranged on opposite sides of an electrolytic membrane to form a membrane electrode assembly (MEA). A fluid transfer device is arranged on a surface of the MEA that causes at least either a fuel fluid or an oxidizing fluid to travel.
In this fuel cell, the fluid transfer device of the present invention is used to transfer at least either a fuel fluid or an oxidizing fluid to the MEA. This easily realizes reduction in size of the fuel cell while causing a fuel fluid and an oxidizing fluid to travel effectively. Further, even with a small capacity of the channel, a fuel fluid and an oxidizing fluid can efficiently be caused to travel at high flow rates. As a result, a compact fuel cell capable of efficiently providing high electric power generation is obtained.
In the fuel cell according to the present invention, the vibrating plate and the reflection wall are preferably arranged over the MEA to face each other in the direction parallel to a surface of the MEA. This allows sound pressure in the channel to be controlled by the distance between the vibrating plate and the reflection wall, and by the area of the vibrating plate or the reflection wall. Thus, the dimension of the channel in the direction perpendicular to the surface of the MEA, namely, the dimension of the channel in the direction of the thickness of the MEA can be arbitrarily changed. This allows the reduction in dimension of the channel in the direction of the thickness of the MEA, leading to the reduction in thickness of the fluid transfer device. As a result, the fuel cell can be reduced further in size.
In the fuel cell according to the present invention, the vibrating plate is preferably arranged to face the MEA, and a surface wall of the MEA is preferably used as the reflection wall. This allows space defined between the vibrating plate and the MEA to serve as a channel, thereby realizing simpler configuration of the fuel cell while easily reducing the fuel cell in size. Further, as a result of the action of an acoustic wave on the surface of the MEA, CO2 and H2O generated by electrochemical reaction of a fuel fluid and an oxidizing fluid become hard to stick to the surface of the MEA. This suppresses reduction in the output of the fuel cell.
An electronic apparatus according to the present invention is provided with an electronic circuit section and a fluid transfer device for causing a fluid to travel along a channel that extends along a surface of the electronic circuit section. The fluid transfer device according to the present invention is adapted for use as the fluid transfer device in this electronic apparatus.
Another electronic apparatus according to the present invention is provided with a fuel cell that comprises a membrane electrode assembly with an electrolytic membrane, and an anode and a cathode arranged on opposite sides of the electrolytic membrane. The fuel cell with the above-discussed fluid transfer device according to the present invention is adapted for use as the fuel cell in this electronic apparatus.
In the fluid transfer device 100 according to the first embodiment of the present invention, a reflector 2 in the form of a flat plate and formed from a acrylic plate, and a vibrating body 3 are arranged to face each other with a channel 1 held therebetween and at positions over and under the channel 1. The vibrating body 3 includes a vibrating plate 3a in the form of a flat plate and formed from an Al plate (A5052), and a PZT element 3b (“C203” produced by Fuji Ceramics Corporation) provided on the vibrating plate 3a. The PZT element 3b is an example of a “vibration application part” of the present invention.
As shown in
In the vibrating body 3, the PZT element 3b has a rectangular shape with a length L3 of about 3 mm, a width W2 of about 30 mm, and a thickness t3 of about 1 mm. The PZT element 3b is arranged on the vibrating plate 3a while being spaced a distance L4 of about 7 mm away from the end portion of the vibrating plate 3a on the side of the outlet 1b. The fluid transfer device 100 according to the first embodiment of the present invention is configured in this manner.
In the fluid transfer device 100 according to the first embodiment of the present invention, an AC voltage of about 70 kHz is applied to the PZT element 3b using an AC power supply (not shown), thereby causing the PZT element 3b to expand and contract in the direction of the length L3 to excite the vibrating plate 3a. This generates an acoustic wave in the vibrating plate 3a. The generated acoustic wave is subjected to multiple reflection in the channel 1 between the reflector 2 and the vibrating plate 3a to increase sound pressure in the channel 1. As a result, acoustic streaming is formed in the channel 1 which generates a force to move air inside the channel 1. Air is an example of a “fluid” of the present invention. The channel 1 is so formed that the height of the channel 1 is greater on the side of the outlet 1b than on the side of the inlet 1a. Thus, the travel of air in the channel 1 toward the outlet 1b results in lower pressure loss than the travel toward the inlet 1a. As a result, air is discharged through the outlet 1b at which the channel 1 has a greater height while being supplied into the channel 1 through the inlet 1a at which the channel 1 has a smaller height.
An acoustic wave generated in the vibrating plate 3a is subjected to multiple reflection in the channel 1 between the reflector 2 and the vibrating plate 3a. Thus, an acoustic wave is allowed to resonate if the height of the channel 1 and the wavelength of the acoustic wave satisfy a condition for resonance. Under the condition where the vibrating plate 3a is arranged in parallel with the reflector 2, and under the same conditions as those employed in the above-discussed fluid transfer device 100 except for the varying height of the channel 1, examination has been performed to find out the distance between the reflector 2 and the vibrating plate 3a that allows the resonance of an acoustic wave in the channel 1. The result is that the resonance of an acoustic wave occurs if the distance between the reflector 2 and the vibrating plate 3a is about 3 mm. Accordingly, under the condition where the height of the channel 1 increases in the direction of the length L1 as in the first embodiment of the present invention, an acoustic wave is considered to resonate in the channel 1 on the side of the inlet 1a at which the channel 1 has a height of about 3 mm. In this case, a standing wave of acoustic waves is generated in an area of the channel 1 on the side of the inlet 1a, thereby increasing further sound pressure in the channel 1 on the side of the inlet 1a. As a result, air can be caused to more efficiently travel along the channel 1 from the inlet 1a toward the outlet 1b.
In the first embodiment of the present invention, the vibrating body can be excited in various vibration modes by changing the frequency of an AC voltage applied to the PZT element 3b. Here, relationships between resonant frequencies and vibration modes have been found out when the vibrating plate 3a is excited at frequencies in a range of about 20 kHz to about 200 kHz. The result is shown in Table 1.
As seen from Table 1, the vibrating plate 3a is allowed to resonate at various resonant frequencies and in various resonant modes. Thus, the vibrating plate 3a is allowed to increase further in amplitude by being excited at resonant frequencies, thereby increasing sound pressure in the channel 1 to a greater degree. As a result, air can be caused to more effectively travel along the channel 1 from the inlet 1a toward the outlet 1b. The vibrating plate 3a increases in amplitude as its vibration frequency gets closer to the resonant frequencies. In the case that the vibrating plate 3a is excited at a frequency in a range of about 500 Hz with respect to the resonant frequencies, the vibrating plate 3a considerably increases in amplitude. This increases sound pressure in the channel 1 to realize efficient travel of air.
As seen from Table 1, the vibrating body of the fluid transfer device 100 according to the first embodiment of the present invention can resonate at several resonant frequencies. Some of these resonant frequencies (about 70 kHz, about 117 kHz and about 134 kHz) allow the vibrating body to resonate in a mode of vibration (mode of stripes) that generates resonance in the direction in which the height of the channel 1 increases as indicated by dashed lines in
As discussed above, in the first embodiment, the vibrating plate 3a is arranged so that the distance from the reflector 2 gradually increases in the direction from the inlet 1a toward the outlet 1b. Thus, the dimension of the channel 1 is easily made greater on the side of the outlet 1b than on the side of the inlet 1a, while the cross section is gradually changed along the channel 1. As a result, pressure loss is reduced to cause a fluid to travel more effectively.
In the fluid transfer device 100 according to the first embodiment, the tilt angle θ between the vibrating plate 3a and the reflector 2 is set at about 2 degrees. This angle θ may be suitably changed according to the shapes of the reflector 2 and the vibrating plate 3a, or to resonant frequencies, in a preferable range of about 0.1 degree to about 5 degrees. Further, the distance between the reflector 2 and the vibrating plate 3a preferably falls within a range of about 0.1 mm to about 5 mm.
In the fluid transfer device 100 according to the first embodiment, the reflector 2 and the vibrating plate 3a are tilted with respect to each other so that the height of channel 1 gradually increases in the direction from the inlet 1a toward the outlet 1b. Accordingly, an acoustic wave travels in the channel 1 from the inlet 1a toward the outlet 1b while being reflected between the reflector 2 and the vibrating plate 3a. This realizes more efficient use of acoustic streaming, leading to more efficient travel of air.
In the fluid transfer device 100 according to the first embodiment, the vibrating plate 3a is supported at an end side of the vibrating plate 3a at which a node is formed when the vibrating plate 3a vibrates in a mode of stripes. Thus, the vibration damping of the vibrating plate 3a is unlikely to occur, thereby realizing efficient travel of air.
First Exemplary Configuration of Fuel Cell
The fuel cell 200 of the first exemplary configuration comprises an MEA 14 including an electrolytic membrane 14a containing Nafion and the like, and a cathode 14b and an anode 14c formed of a metal material with a mesh or porous structure and the like that are respectively arranged on upper and lower surfaces of the electrolytic membrane 14a. The fuel cell 200 is not limited to the form of a stack in which a plurality of MEAs 14 are stacked, but may also preferably be in the form of a planer module in which these MEAs 14 are arranged on a plane. There are provided on the upper surface of the cathode 14b a reflector 12 and a vibrating plate 13 containing a resin material and the like such as ABS resin or polycarbonate resin. The reflector 12 and the vibrating plate 13 are arranged so that the direction in which they are facing each other is parallel to the upper surface of the MEA 14, thereby defining a first channel 11. A top plate 15 containing a resin material and the like such as ABS resin or polycarbonate resin is provided to cover the cathode 14b, the reflector 12 and the vibrating plate 13. The vibrating plate 13 has the same structure as that of the vibrating body used in the fluid transfer device 100 according to the first embodiment. But a PZT element is not shown in
A bottom plate 17 containing a resin material and the like such as ABS resin or polycarbonate resin is arranged under the lower surface of the MEA 14, thereby defining a second channel 16 with an inlet 16a and an outlet 16b. The MEA 14 and the bottom plate 17 are fixed by respective support members not shown. The fuel cell 200 of the first exemplary configuration according to the first embodiment of the present invention is configured in this manner.
In the fuel cell 200 of the first exemplary configuration, the reflector 12 and the vibrating plate 13 arranged on the side of the cathode of the MEA 14 constitute a fluid transfer device 110 according to the first embodiment. Thus, an oxidizing fluid such as air or oxygen to travel along the channel 1 can be sucked in through the inlet 11a, while being discharged through the outlet 11b.
An oxidizing fluid is supplied to the first channel 11 while a fuel fluid such as hydrogen or methanol is supplied by a structure not shown through the inlet 16a to travel in the second channel 16. This generates electrochemical reaction of the oxidizing fluid and the fuel fluid in the MEA 14, thereby taking electricity out of the cathode 14b and the anode 14c to the outside.
As discussed above, the fuel cell of the first exemplary configuration comprises the fluid transfer device 110 of the first embodiment. This easily realizes the size reduction of the device configuration and efficient travel of oxidizing fluid. Even with a small capacity of the channel 11, efficient travel of an oxidizing fluid is realized at a high flow rate. As a result, a compact fuel cell capable of efficiently providing high electric power generation is obtained.
As discussed above, in the fuel cell of the first exemplary configuration, the reflector 12 and the vibrating plate 13 of the fluid transfer device 110 are arranged over the MEA 14 to face each other in the direction parallel to the upper surface of the MEA 14. According to this configuration, since sound pressure in the channel can be controlled by the distance between the vibrating plate 13 and the reflector 12, the dimension of the channel in the direction perpendicular to the upper surface of the MEA 14, namely, the height of the first channel 11 in the direction of the thickness of the MEA 14 can be arbitrarily changed. This allows the reduction in height of the channel in the direction of the thickness of the MEA 14, leading to the reduction in thickness of the fluid transfer device 110. As a result, the size reduction of the fuel cell 200 can be realized.
Second Exemplary Configuration of Fuel Cell
In the fuel cell 300 of the second exemplary configuration according to the first embodiment of the present invention, a vibrating body is arranged over the MEA 14 to face the MEA 14, in a way that the vibrating body is tilted at an angle θ with respect to the MEA 14 to define a channel 21. The distances d1 and d2 are defined between the vibrating body and the MEA 14 respectively on the side of an inlet 21a and an outlet 21b. The vibrating body has the same structure as that of the vibrating body used in the fluid transfer device 100 of the first embodiment. But the PZT element is not shown In
In the fuel cell 300 of the second exemplary configuration, an acoustic wave generated in the vibrating plate 3a by the excitation of the vibrating body 3 is reflected by the MEA 14. Thus, the vibrating body 3 and the MEA 14 used in place of a reflector constitute a fluid transfer device 120. This realizes travel of an oxidizing fluid in the channel 21 in the direction in which the distance between the vibrating body 3 and the MEA 14 increases.
Like in the fuel cell 200 of the first exemplary configuration, a fuel fluid is supplied through the second channel 16 to the lower surface of the MEA 14. This realizes electrochemical reaction of an oxidizing fluid and a fuel fluid in the MEA 14, thereby taking electricity out of the cathode 14b and the anode 14c to the outside.
In the second exemplary configuration, the MEA 14 is used in place of a reflector, and space (channel 21) between the vibrating body and the MEA 14 is applied as a channel. This provides simpler configuration and ease of size reduction of the fuel cell 300.
In the second exemplary configuration, as a result of the action of an acoustic wave on the surface of the MEA 14, CO2 and H20 generated by the above-discussed electrochemical reaction are hard to stick to the surface of the MEA 14. This suppresses reduction in the output of the fuel cell 300.
In the above-discussed first embodiment, the excitation of the vibrating body is realized by the excitation of the PZT element 3b serving as a vibration application part attached to the vibrating plate 3a that is a non-piezoelectric material. Alternatively, in the present invention, an elastic plate may be caused to vibrate directly that is formed of a piezoelectric material such as piezoelectric ceramics including PZT, lithium tantalate (LiTaO3), lithium niobate (LiNbO3), lithium tetraborate (Li2B4O7) and the like, or crystal. In this case, the excitation of the elastic plate formed of a piezoelectric material is realized directly by applying a voltage in a polarization direction of the piezoelectric material. Still alternatively, like in a SAW device adapted for use as a high-frequency filter and the like, a pair of interdigitated electrodes may be formed on a surface of an elastic plate formed of a piezoelectric material. By the formation of electrodes on a surface of a piezoelectric material, a surface acoustic wave is generated on the surface of the piezoelectric material.
In the above-discussed fluid transfer device according to the first embodiment, the reflector 2 and the vibrating plate 3a are both in the form of a flat plate, and the vibrating plate 3a is tilted at the angle θ with respect to the reflector 2. Alternatively, in the present invention, for example at least either the reflector 2 or the vibrating plate 3a may be of a stepped shape.
In a fluid transfer device 400 shown in
In the discussion given above, the reflector 32 is shown to have a stepped shape. Alternatively, in the present invention, the vibrating plate 3a may be of a stepped shape as shown in
In the first embodiment discussed above, the vibrating plate is caused to vibrate in a mode of vibration (mode of stripes) that generates resonance in the direction in which the height of the channel 1 increases. Alternatively, in the present invention, as long as a sound pressure gradient is formed from one side to the other side of the channel 1, the vibrating plate may vibrate in any mode.
In the first embodiment discussed above, air is caused to travel along the channel 1. The present invention may also realize travel of other gases or liquids. Further, a solid such as a powder can also be caused to travel by being dispersed into a fluid.
In the above-discussed first and second exemplary configurations of the fuel cell according to the first embodiment, the fluid transfer devices 110 and 120 are intended to supply an oxidizing fluid to the MEA 14 on the side of the cathode 14b. Alternatively, in the present invention, the first and second exemplary configurations may be used to supply a fuel fluid to the MEA 14 on the side of the anode 14c. Still alternatively, the first and second exemplary configurations may be used to supply both fluids to the MEA 14 on respective sides.
In the above-discussed first and second exemplary configurations of the fuel cell according to the first embodiment, one fluid transfer device 110 or 120 is provided in corresponding relationship with the MEA 14. Alternatively, in the present invention, a plurality of fluid transfer devices may be provided to one MEA 14 as shown in
As shown in
The vibrating plate 42 has a cuneal shape in cross section with a minimum thickness T1 at an end portion 42a (left end portion in
In this fluid transfer device 4, the distance between the vibrating plate 42 and the surface of the MEA 14 is set at a height of resonance (for example in a range of 0.1 to 5 mm) at which air column resonance is generated. An ultrasonic standing wave is generated in the vibrating plate 42 by the piezoelectric vibrating body 43 to generate air column resonance between the vibrating plate 42 and the surface of the MEA 14. The vibrating plate 42 has a smaller thickness on the side of the entrance of the channel 40 and thus has lower bending stiffness thereat while having a greater thickness on the side of the exit of the channel 40 and thus has higher bending stiffness thereat. As a result, as indicated by arrows with dashed lines in the figure, the vibrating body 42 vibrates with greater amplitude on the side of the entrance of the channel 40, while vibrating with smaller amplitude on the side of the exit of the channel 40. This makes sound pressure in the channel 40 high on the side of the entrance, and low on the side of the exit.
A sound pressure gradient is thereby formed in which sound pressure decreases in the direction from the entrance toward the exit of the channel 40. This generates acoustic streaming in the channel 40 from the entrance toward the exit to generate uniform air flow in the channel 40 from the entrance toward the exit. As a result, air is supplied to the MEA 14 to generate electricity in the MEA 14.
In the fuel cell of the first exemplary configuration shown in
Like in the first exemplary configuration, in this second exemplary configuration, the vibrating plate 42 is also actuated by the piezoelectric vibrating body 43 to vibrate with greater amplitude on the side of the entrance of the channel 40 while vibrating with smaller amplitude on the side of the exit of the channel 40. A sound pressure gradient is thereby formed in which sound pressure decreases in the direction from the entrance toward the exit of the channel 40. This generates acoustic streaming in the channel 40 from the entrance toward the exit to generate uniform air flow in the channel 40 from the entrance toward the exit.
a), (b) and (c) each show a fluid transfer device provided in a fuel cell of a third exemplary configuration. As shown in
In this configuration, the vibrating plate 42 has a lower modulus of elasticity on the side of the entrance of the channel 40 and thus has lower bending stiffness thereat while having a higher modulus of elasticity on the side of the exit and thus has higher bending stiffness thereat. This causes the vibrating plate 42 to vibrate with greater amplitude on the side of the entrance of the channel 40, while being caused to vibrate with smaller amplitude on the side of the exit of the channel 40, thereby making sound pressure high on the side of the entrance and low on the side of the exit. As a result, acoustic streaming is generated in the channel 40 from the entrance toward the exit to generate uniform air flow in the channel 40 from the entrance toward the exit as indicated by arrow A in the figure.
In this fluid transfer device 4, the vibrating plate 42 is formed into a disc and accordingly has lower bending stiffness at the periphery than that at the center. Thus, by the actuation of the piezoelectric vibrating body 43, vibration with greater amplitude is generated at the periphery of the vibrating plate 42 while vibration with smaller amplitude is generated at the center. As a result, a sound pressure gradient is formed in the channel 40 in which sound pressure decreases in the direction from the periphery toward the center. This generates acoustic streaming from the entrance toward the exit. At the same time, as indicated by arrows A in the figures, air is introduced through openings on opposite sides of the cover 5 serving as entrances, and is then discharged to the outside through the central opening 44 of the vibrating plate 42 serving as an exit to the outside.
Another configuration shown in
Still another configuration shown in
In order to prove the effect of the fluid transfer device according to the second embodiment of the present invention, there have been built a prototype of the fluid transfer device of the second exemplary configuration shown in
In the example of comparison, while lycopodium powder moves before and after the application of a voltage to the piezoelectric vibrating body 43, air does not flow uniformly and it is difficult to control the direction of air flow. In contrast, in the example of the present invention, it has been found that lycopodium powder uniformly travels from the entrance toward the exit of the channel 40 before and after the application of a voltage to the piezoelectric vibrating body 43, making the control in the flow direction easy.
The amounts of displacement have been measured that are obtained by the vibration of the respective vibrating plates of the example of the present invention and the example of comparison, and distributions of the amounts of displacement of both vibrating plates have been compared. As for the vibrating plate in the example of comparison, an aluminum plate (A5052) with a width of 30 mm, a length of 20 mm and a thickness of 1 mm has been employed. The same aluminum plate (A5052) is also used as the vibrating plate in the example of the present invention, except that this aluminum plate has a thickness of 1 mm at the section in the form of a thick plate, a thickness of 0.5 mm at the section in the form of a thin plate, and the thickness change from 1 mm to 0.5 mm occurs at a point of 10 mm in the length direction. Further the piezoelectric vibrating body 43 was caused to vibrate at a frequency of about 36 kHz.
The results are that, with regard to the vibrating plate of the example of the present invention, a large difference of about 1.1 μm is generated in the amount of displacement between the section in the form of a thick plate and the section in the form of a thin plate as shown in
As discussed above, in the fuel cell with the fluid transfer device according to the second embodiment of the present invention, the fluid transfer device 4 has a structure to serve to cause air in the channel 40 that extends along the MEA 14 to travel based on the principles of acoustic streaming. Therefore, a fluid supply mechanism as an external device to be connected to the channel 40 is not required, thus the fluid transfer device 4 is of a simple configuration in which the channel 40 itself is defined by the vibrating plate 42 and a reflection wall, and the piezoelectric vibrating body 43 is arranged on the vibrating plate 42. Thus, the fluid transfer device 4 is capable of realizing reduction in size and power consumption, and can be suitably applied as a fluid transfer device of a fuel cell for use in a compact electronic apparatus.
Especially in the configuration of the fuel cell adopting the fluid transfer device according to the second embodiment of the present invention, an acoustic wave generated by the vibration of the vibrating plate 42 acts on a surface wall of the MEA 14. Thus, water deposited on a surface of the cathode 14b, or carbon dioxide deposited on a surface of the anode 14c can spread out into the channel 40. This enhances the performance of the fuel cell.
A configuration shown in
In this fluid transfer device 4, the distance H between the vibrating plate 42 and the MEA 14 is set at a height of resonance (for example in a range of 0.1 to 5 mm) at which air column resonance is generated, and an ultrasonic standing wave is generated in the vibrating plate 42 by the piezoelectric vibrating body 43, thereby generating air column resonance between the vibrating plate 42 and the surface of the MEA 14.
The distance S of projection of the end region 48 of the vibrating plate 42 is set at a suitable distance that is for example about half the wavelength of a standing wave generated in the vibrating plate 42 (for example, in a range of 0.5 to 5 mm). This generates a sound pressure gradient in which sound pressure decreases in the direction from the entrance toward the exit of the channel 40. Acoustic streaming is thereby formed in the channel 40 from the entrance toward the exit to generate uniform air flow in the channel 40 from the entrance toward the exit as indicated by arrows A. As a result, air is supplied to the MEA 14 to generate electricity in the MEA 14.
In the fluid transfer device 4 of the first exemplary configuration shown in
Like in the first exemplary configuration, in this second exemplary configuration, ultrasonic standing waves are also generated in the vibrating plates 42a by the piezoelectric vibrating bodies 43a to generate acoustic streaming in each channel 40a from the entrance toward the exit. This generates uniform air flow in each channel 40a from the entrance toward the exit.
A reflector 46 is provided between the channels 40b, 40b in upright position with respect to the surface of the MEA 14. The reflector 46 terminates near the exits of the channels, thereby causing each vibrating body 42b to project by a certain distance S from the reflector 46. This defines the regions 48 that do not face the reflector 46. A configuration shown in
In the above-discussed fluid transfer device 4, ultrasonic standing waves are generated in the vibrating plates 45, 45 by the piezoelectric vibrating bodies 43b, 43b. This generates air column resonance between each vibrating plate 45 and the reflector 46 to form acoustic streaming. At this time, a sound pressure gradient is formed in the channels 40b, 40b in which sound pressure decreases in the direction from the entrances toward the exits of the channels 40b, 40b. This generates uniform air flow in the channels 40b, 40b from the entrances toward the exits as indicated by arrows A. As a result, air is supplied to the MEA 14 to generate electricity in the MEA 14.
The vibrating plates 51, 51 respectively have the regions 48 defined on the sides of the exits (left and right sides of
In the above-discussed fluid transfer device 4, ultrasonic standing waves are generated in the vibrating plates 51, 51 by the piezoelectric vibrating bodies 43c, 42c to generate air column resonance between each of the vibrating plates 51 and the surface of the MEA 14. By the presence of the regions 48 of the vibrating plates 51, 51 that do not face the surface of the MEA 14, a sound pressure gradient is generated in which sound pressure degreases in the direction from the entrance toward the both of the exits of the channel 40c. This generates acoustic streaming in the channel 40c from the entrance toward the both exits. Thus, air introduced through the entrance of the channel 40c is divided to generate uniform air flow toward the both exits as indicated by arrows A. As a result, air is supplied to the MEA 14 to generate electricity in the MEA 14.
To prove the effect of the fluid transfer device according to the third embodiment of the present invention, there have been built a prototype of the fluid transfer device of the first exemplary configuration shown in
In the built prototypes of the fluid transfer device 4, an aluminum plate (A5052) with a width of 30 mm, a length of 30 mm and a thickness of 1 mm is used as the vibrating plate 42, a PZT element (“C203” produced by Fuji Ceramics Corporation) with a width of 7 mm, a length of 30 mm and a thickness of 1 mm is used as the piezoelectric vibrating body 43, and an acrylic plate with a width of 30 mm, a length of 30 mm and a thickness of 1 mm is used as a reflector. The channel 40 has a height H of 0.5 mm, and the end region 48 of the vibrating plate 42 has a distance S of projection set at 2.5 mm. Further, the piezoelectric vibrating body 43 has been caused to vibrate at a frequency of about 34 kHz.
In the example of comparison, while lycopodium powder moves before and after the application of a voltage to the piezoelectric vibrating body 43, air does not flow uniformly and it is difficult to control the direction of air flow. In contrast, in the example of the present invention, it has been found that lycopodium powder uniformly travels from the entrance toward the exit of the channel 40 before and after the application of a voltage to the piezoelectric vibrating body 43, making the control in the flow direction easy.
As discussed above, in the fuel cell with the fluid transfer device according to the second embodiment of the present invention, the fluid transfer device 4 has a structure to serve to transfer air in the channel 40 that is provided along the MEA 14 based on the principles of acoustic streaming. Therefore, a fluid supply mechanism as an external device to be connected to the channel 40 is not required, thus the fluid transfer device 4 is of a simple configuration in which the channel 40 itself is formed by the vibrating plate 42 and a reflection wall, and the piezoelectric vibrating body 43 is arranged on the vibrating plate 42. Thus, the fluid transfer device 4 is capable of realizing reduction in size and power consumption, and can be suitably applied as a fluid transfer device of a fuel cell for use in a compact electronic apparatus.
Especially in the configuration of the fuel cell adopting the fluid transfer device according to the present invention, the vibration of the vibrating plate 42 generates the vibration of a surface wall of the MEA 14. Thus, water deposited on a surface of the anode 14c, or carbon dioxide deposited on a surface of cathode 14b the can spread out into the channel 40. This enhances the performance of the fuel cell.
In the fluid transfer device 4 according to the fourth embodiment, the surface wall 18 of the MEA 14 responsible for the reflection of an acoustic wave has a higher acoustic impedance on the side of the entrance of the channel 40, and a lower acoustic impedance on the side of the exit of this channel 40. This generates higher sound pressure on the side of the entrance of the channel 40 and lower sound pressure on the side of the exit of the channel 40. As a result, a sound pressure gradient is formed in which sound pressure decreases in the direction from the entrance toward the exit of the channel 40. Thus, acoustic streaming is generated in the channel 40 from the entrance toward the exit to cause a fluid to flow in the channel 40 from the entrance toward the exit.
In the fluid transfer device 4 according to the fifth embodiment, a surface of the surface wall 18 of the MEA 14 responsible for the reflection of an acoustic wave has a lower acoustic absorption coefficient on the side of the entrance of the channel 40, and a higher acoustic absorption coefficient on the side of the exit of the channel 40. Thus, the strength of a reflected wave is higher on the side of the entrance of the channel 40, and is lower on the side of the exit of the channel 40. As a result, a sound pressure gradient is formed in which sound pressure decreases in the direction from the entrance toward the exit of the channel 40. Thus, acoustic streaming is generated in the channel 40 from the entrance toward the exit to cause a fluid to flow in the channel 40 from the entrance toward the exit.
(Support Structure for Vibrating Plate)
When the PZT element 3b is actuated to cause the vibrating plate 3a to vibrate in a high order resonant mode, the vibration of the vibrating plate 3a forms antinodes and nodes at different positions as shown in
In place of four leg segments 64 shown in
As shown in
(Application to Electronic Apparatuses)
In this cellular phone, the fuel cell according to the present invention is built into the display casing 71 or into the operation part casing 72. Alternatively, as shown in FIG. 46, a fuel cell 9 according to the present invention is attached to the rear surface of the display casing 71. As shown in
If the cellular phone is of a configuration in which the high pressure side (the side of the inlet) of the fluid transfer device is arranged on the side of the hinge mechanism 73, since the casings 71 and 72 are given a high structural strength in a region near the hinge mechanism 73, sound pressure on the side of the hinge mechanism of the fluid transfer device can be set to a high level.
As shown in
When the drainage 77 is of a structure in which the water storage part 77a juts out toward the channel of air as shown in
Likewise, when the fluid transfer device is applied to the side of the anode, a fluid is caused to flow toward the outlet to thereby efficiently discharge carbon dioxide (unwanted substance) generated on the side of the anode of the fuel cell.
As shown in
In a cellular phone of a straight type shown in
In these structures in which the inlets 76a are located at lower positions (in the direction of the action of gravity) and the outlets 76b are arranged at higher positions in normal use (during telephone conversation), air in the channel is heated by the MEA to go higher in the channel by buoyancy. This allows efficient travel of air from the inlets 76a toward the outlets 76b. Thus, high power consumption during telephone conversation can be covered enough by electric power generation at the fuel cell. Likewise, in a cellular phone of a slide type in which a pair of casings are coupled together by a sliding mechanism, an inlet is arranged at a lower position and an outlet is arranged at a higher position in one of the casings in normal use.
With reference to the above-discussed support structures (see
Still alternatively, a sound absorbing sheet formed of urethane sponge, polyurethane foam and the like may be fixed to the inner surface of the cover 76 to face the vibrating plate 3a so that vibration of air in space other than the above-discussed channel such as the one defined between the cover 76 and the vibrating plate 3a is absorbed to thereby reduce noises attributed to the vibration of the casing.
The actuation of the PZT element 3b realizes gas supply to the MEA 14, and electric power generated therefrom is used to charge a secondary cell 81. A phone body 80 is actuated by using the secondary cell 81 as a power supply. The amount of electric power generated at the MEA 14 is fed back to the control circuit 8. Electric power generated at the MEA 14 may also be directly supplied to the phone body 80.
First, in step S1 shown in
Thereafter in step S5, the current value at present Ii is substituted for the current value in the past Iold, and another current value at present Ii is obtained. Then, the procedure returns to step S2 to compare the current value at present Ii and the current value in the past Iold. If it is determined that the current value Ii is smaller than the current value Iold in step S2, or if it is determined that the frequency f is equal to or greater than the maximum frequency fmax in step S3, the procedure is switched to DOWN mode.
In DOWN mode, the current value at present Ii and the current value in the past Iold are compared in step S7. If the current value Ii is greater than the current value Iold, the procedure proceeds to step S8 to compare the frequency f and a certain minimum frequency fmin. If the frequency f is greater than the frequency fmin, the frequency is decremented in step 9.
Thereafter in step S10, the current value at present Ii is substituted for the current value in the past Iold, and another current value at present Ii is obtained. Then, the procedure returns to step S7 to compare the current value at present Ii and the current value in the past Iold. If it is determined that the current value Ii is equal to or smaller than the current value Iold in step S7, or if it is determined that the frequency f is equal to or smaller than the minimum frequency fmin in step S8, the procedure is switched to UP mode.
The vibrating plate is thus capable of operating at a resonant frequency by being actuated in UP mode and DOWN mode.
This way of control is capable of constantly causing the vibrating plate to vibrate at a resonance point to generate large-scale acoustic streaming even if the frequency of the vibrating plate varies due to the generation of heat at the vibrating plate, deposition of impurities or the like. In addition, power consumption can be reduced further by burst driving.
In the above-discussed cellular phone, power consumption is low in a standby mode, and increases when a display is turned on or backlight is turned on. In response, the actuation control of the vibrating plate shown in
In the flip cellular phone shown in
In the cellular phone of a straight type as shown in
It is to be appreciate that each of the embodiments and each of the exemplary configurations discussed above are in all aspects illustrative and not restrictive. The scope of the present invention is defined not by the foregoing description of the embodiments and exemplary configurations, but is defined by claims. Further, the scope of the present invention includes meaning equivalent to claims and all changes within the scope of claims.
The applicability of the fuel cell according to the present invention is not limited to cellular phones. The fuel cell of the present invention may be also applied as a power supply in all types of electronic apparatuses such as chargers for charging cellular phones and the like, AV apparatuses such as video cameras, portable game machines, navigation systems, handy cleaners, electric power generators for professional use, robots, and the like. Further, the applicability of the fluid transfer device according to the present invention is not limited to the structure used in fuel cells. The fluid transfer device of the present invention may be also applied to other uses than a power supply in all types of electronic apparatuses such as those listed above. For example, the fluid transfer device of the present invention may be arranged along a surface of an electronic circuit section that constitutes an electronic apparatus, in which the fluid transfer device serves to carry air for cooling to provide cooling for the electronic circuit section. Such use of the fluid transfer device allows a fuel cell to be configured in the form of a flat module.
The drainage 77 is arranged to face the terminal portion of the channel of the fluid transfer device (the terminal portion of the channel defined between the vibrating plate and the MEA facing each other). Alternatively, the drainage 77 may be arranged at any positions in the vicinity of the terminal portion such as those between the terminal portion and the outlet 76b to realize the same drainage effect.
The normal use is described as a state of telephone conversation, which is given as an example in the cellular phone discussed in the present embodiment. In the case of AV apparatuses such as video cameras, the normal use corresponds to a state of recording still images or moving images, or a state of viewing captured still images or moving images, and in the case of portable game machines, the normal use corresponds to a state of execution of games. Further, in the case of stationary electronic apparatuses such as navigation systems or electric power generators for professional use, the normal use corresponds to a state where these apparatuses are installed. As discussed, the normal use differs between apparatuses, and is not limited to a state of telephone conversation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-315445 | Oct 2005 | JP | national |
| 2005-342684 | Nov 2005 | JP | national |
| 2005-342685 | Nov 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/321528 | 10/27/2006 | WO | 00 | 10/14/2008 |
