Patent Grant
7879301
1. Field of the Invention
The present invention relates in general to a fluid element, and more particularly to a fluid element which is useful for treatment of a micro quantity of liquid in chemical analysis devices, medical devices, biotechnology devices, and the like. In particular, the present invention relates to a fluid element which is applied to microanalysis systems (μTAS: Micro Total Analysis Systems) for effecting chemical analysis or chemical synthesis on a chip, and more particularly to a fluid element which is applied to defusement (or making harmless) of harmful substances generated in the μTAS or the like, recovery and reuse of a raw material from a waste liquid, decomposition, dissolution, reaction acceleration, and the like.
2. Related Background Art
In recent years with development of three-dimensional microprocessing techniques, the systems attracting attention are those which have fluid elements such as a fine flow path, a pump, and a valve, and a sensor integrated on a substrate such as of glass or silicon, and conduct chemical analysis on the substrate. Such a system is called a microanalysis system, a μ-TAS (Micro Total Analysis System), or Lab on a Chip. The miniaturization of the chemical analysis system enables decrease of void volume and remarkable reduction in sample amount.
The miniaturization also enables shortening of the analysis time and a decrease in power consumption of the entire system. Further, the miniaturization is promising for price reduction of the system. Furthermore, the μ-TAS is promising in medical services such as home medical care and bedside monitoring, and biotechnology such as DNA analysis and proteomics analysis because it enables the miniaturization and price reduction of a system, and a remarkable shortening in analysis time.
Japanese Patent Application Laid-open No. H10-337173 discloses a micro-reactor capable of implementing a sequence of biochemical experiment steps of mixing solutions to cause reaction, analyzing quantitatively the reaction product, and separating the product, by using combination of cells. The micro-reactor has isolated reaction chambers each closed tightly with a flat plate on a silicon substrate. This micro-reactor has a reservoir cell, a mixing cell, a reaction cell, a detection cell, and a separation cell combined with each other. By providing such a reactor in plurality on a substrate, many biochemical reactions can be allowed to proceed simultaneously concurrently. Furthermore, not only the analysis but also material synthesis such as protein synthesis can also be conducted in the cells.
On the other hand, in circumstances in which tackling environmental issues becomes essential, a waste liquid treating technique using supercritical water has been proposed as a technique enabling harmful organic substances such as dioxin to be perfectly decomposed.
There is disclosed a technique for effectively making a waste liquid harmless without increasing a quantity of heavy metal ions by utilizing a waste liquid treating method in which an aqueous waste liquid containing an organic substance capable of forming a water-soluble complex with heavy metal ions is heated together with oxygen under pressure using a container made of titanium such that the temperature becomes 375° C. or more, and the partial pressure of water becomes 230 atm or more (see Japanese Patent Application Laid-open No. H03-113858).
In addition, a technique is proposed in which a waste liquid containing tetramethylammonium hydrooxide (TMAH) is subjected to supercritical water oxidation by using oxygen or hydrogen peroxide as an oxidizer under the conditions of a reaction temperature of 550 to 650° C. and a reaction pressure of 23 to 25 MPa, thereby effectively decomposing the indecomposable TMAH contained in a waste liquid from a semiconductor manufacturing plant (see Japanese Patent Application Laid-open No. H11-221583).
In addition, a chemical decontamination waste liquid treating method is proposed in which an organic acid separated and concentrated at an anode, especially, a chelating agent is decomposed using supercritical water (see Japanese Patent Application Laid-open No. H06-201898).
Also, a method of treating an analysis waste liquid is proposed in which an analysis waste liquid and an emulsifying agent are mixed with each other to form an emulsion, and the resultant emulsion is then discomposed using supercritical water (see Japanese Patent Application Laid-open No. 2003-164750).
Currently, in the field of analysis, there is a tendency that works for analyzing harmful substances such as dioxin increase due to growing interest in the environmental issues, so that treatment of an analysis waste liquid containing harmful substances becomes an important task. However, in the conventional μTAS, the circumstance has been that any system including waste liquid treating means effective for decomposing the harmful substances has not been proposed, and hence the harmful analysis waste liquid has been difficult to dispose of. In addition, because the prior art treatment system utilizing supercritical water requires such a high temperature as 374° C. or more and such a high pressure as 22 MPa or more, the treatment system should be called a large equipment and hence is difficult to miniaturize.
On the other hand, WO 2004/009226 discloses a chemical analysis method of effecting chemical analysis and chemical synthesis using a plurality of liquids on a substrate having a flow path, a fluid element, and a detection element, in which the plurality of liquids are stirred and mixed with one another by utilizing expansion and shrinkage of bubbles. In the chemical analysis method disclosed in WO 2004/009226, bubbles are generated using a heating element. However, WO 2004/009226 does not disclose the formation of the supercritical state.
The present invention has been accomplished in the light of the prior art described above, and it is, therefore, an object of the present invention to provide a micro fluid element having a function of promoting decomposition treatment and defusement of harmful substances such as an analysis waste liquid generated in μTAS or the like.
According to one aspect of the present invention, there is provided a fluid element, comprising:
a flow path formed in a substrate for carrying a fluid; and
a heating means provided in the flow path for heating the fluid, wherein the fluid is heated using the heating means to form a supercritical state of the fluid.
In the present invention, it is preferred that the flow path has a high inertance for the heating means.
Further, it is preferred that the supercritical state is formed by applying to the heating means a voltage pulse with a pulse width t0 represented by the general equation (1):
t0<((2AShd0)/ΔP)0.5
where A represents an inertance of the flow path for the heating means; Sh represents an area of the heating means; d0 represents a fluid movement allowance and is 1 μm; and ΔP represents a pressure difference and is 22 MPa.
Moreover, it is preferred that the fluid element further comprises a liquid chamber containing the heating means and connected to the flow path, wherein the supercritical state is formed by applying to the heating means a voltage pulse with a pulse width t0 represented by the general equation (2):
t0<((2ρLd0G)/ΔP)0.5
where ρ represents a density of the fluid; L represents a length of the flow path; d0 represents a fluid movement allowance and is 1 μm; G satisfies the condition of G=Sh/S>1 (where Sh represents an area of the heating means and S represents a cross-sectional area of the flow path); and ΔP represents a pressure difference and is 22 MPa.
Further, it is preferred that the fluid element further comprises means for effecting heat storage/heat radiation connected to the heating means, wherein heat storage and heat radiation are repeatedly carried out to repeatedly form the supercritical state.
Moreover, it is preferred that the fluid element further comprises an insulating thin film provided in contact with the heating means, wherein the heating means comprises a resistor thin film, and wherein the insulating thin film has a thickness d fulfilling the general equation (3):
(vt0)0.5<d<4(vt0)0.5
where t0 represents a pulse width of a voltage pulse applied to the resistor thin film, and v represents a thermal diffusivity of the insulating thin film.
Further, it is preferred that the fluid element further comprises a first electrode and a second electrode in the flow path, wherein a voltage is applied between the first and the second electrodes to form an electric field in the flow path, thereby effecting heating.
Moreover, it is preferred that the fluid is held between a plurality of the heating means, and a pulse voltage is applied to the heating means, thereby forming the supercritical state.
The present invention will hereinafter be concretely described by giving preferred embodiments.
That is, the present invention offers an effect in which it is possible to provide a micro fluid element having, within the same substrate, a flow path and a heating means provided in the flow path, and including a function with which a supercritical state is formed by heating a fluid using the heating means, thereby making it possible to promote decomposition treatment and defusement of harmful substances such as an analysis waste liquid generated in the μTAS or the like. The reason is that because the fluid cannot immediately move during the heating in such a minute flow path as to be formed within the same substrate, the supercritical state can be attained without scaling up a system.
In addition, the present invention especially offers an effect in which it is possible to provide a micro fluid element including a function with which the micro fluid element has the high inertance flow path 4 having an intentionally reduced cross-sectional area for the heating means 2, through the presence of flow restrictors 4A, to more surely prohibit a fluid from immediately moving during the heating, thereby making it possible to promote decomposition treatment and defusement of harmful substances such as an analysis waste liquid generated in the μTAS or the like.
The expression “inertance”, as described in “IEEE Standard Dictionary of Electronics Terms”, generally represents a value which is obtained by dividing a potential difference such as a pressure difference by a change in flow rate related thereto. However, the term “inertance” as herein employed is intended to mean an inertial mass of a fluid, and more specifically, represents, for example, a value of ρL/S where ρ represents a density of a fluid; L represents a length of a flow path; and S represents a cross-sectional area of the flow path.
In addition, the present invention especially offers an effect in which it is possible to provide a micro fluid element having the resistor thin film heating means 2 with an area Sh, and the flow path having the inertance becoming at least A for the heating means, and including a function with which a voltage pulse of a pulse width t0 which, when a pressure difference ΔP=22 MPa and a fluid movement allowance d0=1 μm, satisfies the condition of t0<((2AShd0)/ΔP)0.5, more preferably the condition of t0<0.5((2AShd0)/ΔP)0.5 is applied to the resistor thin film heating means 2 to form a supercritical state to more surely prohibit the fluid from immediately moving during the heating, thereby making it possible to promote decomposition treatment and defusement of harmful substances such as an analysis waste liquid generated in the μTAS or the like.
Here, when the inertance of the flow path is assigned A, a flow resistance is assigned B, a volume displacement is assigned V, and a pressure difference is assigned ΔP, the motion in the flow path is approximately expressed by the equation:
Ad2V/dt2+BdV/dt=ΔP.
Thus, when it is supposed that dV/dt=0 is established at a time t=0, and ΔP=0 is established at a time t<0, the step response of the fluid system is expressed by the equation:
dV/dt=(ΔP/B)(1−exp(−t/τ)),
where a time constant τ is τ=A/B. When t˜0 is established, because the above equation is linearized as
dV/dt=(ΔP/B)(1/τ)t,
an amount of volume movement until a time t is expressed as follows:
V=0.5(ΔP/B)(1/τ)t2=ΔP/(2A)t2.
Consequently, it can be seen that in order to force the fluid into a supercritical state by utilizing the difficulty of the fluid to move resulting from the inertance of the flow path, if the heating is generally carried out at time intervals fulfilling the following equation, the fluid reaches a supercritical state before its volume expansion during the heating:
ΔP/(2A)t2/Sh<d0,
where d0 represents a fluid movement allowance in which fluid existing in the vicinity of a surface of a heater forms no bubbles.
Bubble formation at a surface is a phenomenon in which a liquid which exists in the vicinity (normally, a thickness of about 0.2 to 1.0 μm) of a surface of a heater and which is heated up to a vicinity of a spinodal boundary abruptly changes from liquid phase to gaseous with volume change. If it is supposed that the movement allowance d0 of the liquid is 1 μm, the liquid can hardly move for the heating within a time period determined by the above equation and hence cannot form any bubble, so that the injected heat energy is used for temperature rise and pressure increase, and thus the supercritical water state can be realized.
Here, when it is supposed that ρ=1,000 kg/m3, ΔP=22 MPa, L=500 μm, and G=1, the pulse width t0 of the voltage pulse is t0<0.213 μs and more preferably t0<0.1065 μs.
In addition, when it is supposed that G=Sh/S>1, an effect is obtained in which the pulse width is made larger without increasing the inertance. For example, when it is supposed that G=Sh/S=4, the pulse width t0 of the voltage pulse is t0<0.426 μs and more preferably t0<0.213 μs.
For example, when it is supposed that G=Sh/S=16, the pulse width t0 of the voltage pulse is t0<0.852 μs and more preferably t0<0.426 μs.
In this embodiment, each of the flow paths 4a and 4b is a flow path with a height of 10 μm and a width of 10 μm, and with a cross-sectional area S of 10 μm×10 μm, and the heater 2 has an area Sh of 40 μm×40 μm.
In particular, there is obtained an effect that it is possible to provide a micro fluid element having a heating means, flow paths each having a high inertance during the heating, and heat storage/heat radiation means connected to the heating means, and including a function with which rapid heating and heat radiation are repeatedly carried out to repeatedly form a supercritical state, thereby making it possible to promote decomposition treatment and defusement of harmful substances such as an analysis waste liquid generated in the μTAS or the like without increasing the temperature and pressure of the overall system.
In particular, when the heating means is the resistor thin film 2, and when a pulse width of a voltage pulse applied to the resistor thin film 2 is represented by t0 and the insulating thin film 9 (see
Here, when it is supposed that t0=0.4 μs, the insulating thin film 9 is an SiO2 film, and v=0.852 ×10−6 m2/s, the film thickness d of the insulating thin film 9 is 0.584 μm<d<2.336 μm.
Here, if the film thickness d of the insulating thin film 9 is large, there is a tendency to be hard to cool down, and thus the fluid causes volume expansion after passing through the supercritical state. That is, after passing through the supercritical state, the fluid is accompanied by bubble generation and elimination. When there are bubble generation and elimination after passing through the supercritical state, there is obtained an effect that the decomposition of harmful substances is promoted by cavitation.
On the other hand, if the film thickness d of the insulating thin film 9 is small, there is a tendency to be easy to cool down, and after passing through the supercritical state, there is a tendency for the temperature and the pressure to decrease before causing significant volume expansion. When the fluid is not accompanied by bubble generation and elimination, there is an effect that the surface of the heater is hard to be damaged by cavitation.
Here, the heater 2 is a TaN thin film with a thickness of about 50 nm, and a rectangular pulse voltage of 10 to 30 V is applied at a period of 1 to 100 kHz. In addition, the substrate 1 is a good conductor of heat and is a Si substrate in this embodiment.
Here, by way of precaution, the difference in principle of the bubble formation between the present invention and the technique disclosed in WO 2004/009226 or an ink jet recording apparatus using a heating element will be described with reference to
The key features of the present invention are such that the inertance when viewed from the heating surface is made very large, and pulses having a peak-to-peak with higher energy density than that in the ink jet recording apparatus is applied for a short period of time. In the present invention, as shown in the path A of
On the other hand, in the ink jet recording apparatus which employs a heating element in which an increase in pressure due to bubble formation at about 300° C. is utilized to discharge a liquid droplet, it is generally essential to effect a state change so as to follow the path B shown in
In particular, the fluid element of this embodiment is nearly the same as that of the first embodiment with the exception that the fluid element has the first electrode 41 disposed in the vicinity of the heating means within the flow path and the second electrode 42 disposed within the flow path and that a suitable voltage is applied between the first and the second electrodes 41 and 42 to form an electric field within the flow path to thereby collect an electrolyte in the vicinity of the heating means, and in this state the surface heating is carried out.
Because there is a tendency that the supercritical state is realized in the vicinity of the heating means where a high temperature is easy to obtain, when the electrolyte is collected in the vicinity of the first and the second electrodes 41 and 42 by means of the electric field formed within the flow path and the surface heating is carried out in this state, the decomposition treatment can effectively be carried out.
This application claims priority from Japanese Patent Application No. 2004-131569 filed Apr. 27, 2004, which is hereby incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-131569 | Apr 2004 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20040179427 | Yamazaki et al. | Sep 2004 | A1 |
| Number | Date | Country |
|---|---|---|
| 3-113858 | May 1991 | JP |
| 6-201898 | Jul 1994 | JP |
| 10-337173 | Dec 1998 | JP |
| 11-221583 | Aug 1999 | JP |
| 2002-113475 | Apr 2002 | JP |
| 2003-164750 | Jun 2003 | JP |
| 2004-053370 | Feb 2004 | JP |
| 2004-053545 | Feb 2004 | JP |
| WO 2004009226 | Jan 2004 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20050249639 A1 | Nov 2005 | US |
