WO2004046563A1 - Variable flow resistance element - Google Patents

Abstract

The invention relates to a variable flow resistance element comprising a fluid inlet (20), a fluid outlet (22) and a closed fluid conduit (16) of a fixed length, which connects the fluid inlet (20) to the fluid outlet (22), allowing the passage of said fluid. Said element also comprises a unit for varying the flow cross-section of the fluid conduit (16) over a predetermined length of said conduit, in order to adjust the flow resistance that is defined by the fluid conduit. The ratio of the predetermined length of the fluid conduit (16) to the characteristic diameter of said conduit is > 500 and the unit for varying the flow cross-section is configured to exert an external pressure on wall sections of the fluid conduit, said pressure being independent of the pressure of a medium in the fluid conduit.

Description

 Variable flow resistance

description

The present invention relates to a variable flow resistance and in particular to a variable flow resistance which is suitable for use as a control component in a fluid system.

Active fluid valves are known from the prior art, in which an elastic membrane can be deflected by means of a suitable actuating device in order to open or close a valve opening. Valves of this type generally have an open state and a closed state, but do not allow the flow resistance supplied by them to be adjusted.

P. Cousseau, et al., "Improved Micro-Flow Regulator For Drug Delivery Systems", 2001 IEEE, pages 527-530, disclose a flow regulator that provides a constant flow rate despite pressure differential within a predetermined operating pressure range. The flow regulator includes one in one membrane formed through the first substrate, through which an inlet opening is provided in the center, a fluid chamber having an outlet opening is formed in a second substrate, a spiral, upwardly open, capillary channel is formed in the underside of the fluid chamber, the two substrates are connected to one another in such a way that the membrane closes off the fluid chamber formed in the second substrate If pressure is exerted on the membrane, it is first deflected in the center until it hits the bottom of the fluid chamber in the center the inlet opening through the membrane with the inner end of the channel formed in the bottom, so that di e inlet opening and the channel are fluidly connected. With increasing deflection of the membrane, the membrane forms together with the channel a flow resistance, the length of which increases with increasing deflection of the membrane. In this way, a uniform flow rate can be maintained despite pressure difference differences due to the increasing fluid resistance.

Furthermore, according to the prior art, capillaries produced with the aid of microsystem technology serve as fluidic resistors in microfluidics and are used for generating pressure-controlled, low flows. Relevant applications are found primarily in medical technology, but also in analytics.

DE 60000109 T2 relates to elastomeric micro- and microvalve systems, in which two intersecting channels with a membrane arranged between them define a valve.

EP 1215426 A2 discloses an electrostrictive valve for modulating a fluid flow, which comprises a valve body in the form of a cannula, in which a valve element in the form of a viscoelastic material is arranged.

DE 69415683 T2 discloses a flow regulator which has a channel formed in a substrate which, together with a membrane, defines a fluid line which connects an inlet opening to an outlet opening. A liquid, the flow of which is to be regulated through the channel, acts on the membrane from both sides, so that the fluid line is closed with increasing pressure.

The object of the present invention is to provide a flow resistance, the flow resistance of which can be varied continuously to be suitable as a control component for a fluid system, and which has a simple structure, and a method for controlling a fluid flow. This object is achieved by a variable flow resistance according to claim 1 and a method according to claim 13.

The present invention provides a variable flow resistance with the following features:

a fluid inlet;

a fluid outlet;

a closed fluid line of fixed length which fluidly connects the fluid inlet to the fluid outlet; and

a device for varying the flow cross section of the fluid line over a predetermined length thereof for setting the flow resistance defined by the fluid line, the ratio of the predetermined length of the fluid line to the characteristic diameter thereof being> 500, the device being designed for varying the flow cross section, to exert a pressure on the wall sections of the fluid line from the outside which is independent of the pressure of a medium in the fluid line.

The present invention further provides a method of controlling fluid flow using a variable flow resistance having a fluid inlet, a fluid outlet, and a fixed length closed fluid conduit that fluidly connects the fluid inlet to the fluid outlet, the method comprising the step of:

Applying a pressure, which is independent of the pressure of a medium in the fluid line, from the outside to wall sections of the fluid line and thereby varying the flow cross-section of the fluid line over a predetermined length thereof to adjust the flow resistance defined by the fluid line, thereby thereby during the application of a defined pressure on the fluid line to control the fluid flow through the fluid line, the ratio of predetermined length of the fluid line to its characteristic diameter is> 500.

The present invention is based on the finding that fluidic resistors based on fluid lines, which can be produced, for example, with the aid of microsystem technology, can be constructed in such a way that they can be varied continuously in a defined range and thus as a control component, for example as Control valve can be used by the fluid line is formed such that the cross section thereof between a fluid inlet and a fluid outlet is variable over a predetermined length.

Such a fluid line has a defined fluidic resistance for liquids of a defined viscosity, which is characterized by the ratio of channel length to characteristic channel diameter. According to the invention, the fluidic resistance can be adjusted by the flow cross-section, and thus the characteristic diameter, being adjustable over a predetermined length, the ratio of the predetermined length to the characteristic diameter being> 500 (in the initial state in which the flow cross-section is not varied).

In addition to the predetermined length of a variable flow cross section, an adjustable resistance according to the invention can also have sections with a fixed flow cross section. Furthermore, the predetermined length with variable flow cross section can be provided by a plurality of sections with variable flow cross section. Furthermore, a plurality of sections with a fixed flow cross section can be provided. The total resistance results from the sum of the partial resistances defined by the respective sections.

Depending on the application, the ratio of predetermined length to characteristic diameter can be higher than> 500, and for example> 1000, in order to be able to implement a desired fluid resistance.

The term characteristic diameter is used in fluid technology to denote the diameter that a fluid channel with a round flow cross section should have in order to provide a flow cross section which is equivalent to a fluid line of any flow cross section under consideration. The determination of this characteristic diameter for any flow cross sections is known in the art.

According to a preferred exemplary embodiment of the variable flow resistance according to the invention, this can be achieved in that the fluid line is formed by a channel formed in the surface of a substrate and a membrane covering the channel. By deflecting the membrane, the flow cross-section of the fluid line and thus the flow resistance supplied by the same can be varied.

In order to use the variable flow resistance according to the invention as a control component, a system can be used in which a defined pressure is specified via the fluid line forming the flow resistance, which pressure results in a flow dependent on the viscosity of the fluid and the fluidic resistance of the fluid line. The flow area that can be covered is defined by the system geometry, i.e. the cross section and the length of the fluid line, and the viscosity of the fluid used.

The present invention can be used in all areas of microfluidics and is also particularly suitable for applications in medical technology or analysis. With a sufficient reduction in the flow cross-section of the fluid line, for example to 30% of the original flow cross-section, it can have such a high flow resistance that the invented flow resistance according to the invention represents a closed valve. In such a case, the leakage behavior is comparable to that of conventional microvalves, for example those in which an opening is closed by a membrane. Known micro valves of this type have a leakage of a few μl per day due to trapped particles, leaks, etc. However, the structure according to the invention has an increased particle tolerance compared to known micro valves, since known micro valves typically do not allow particles that are larger than about 500 nm , Due to the simple structure, the fluidic resistance according to the invention is extremely durable. Furthermore, the fluidic resistance according to the invention allows a valve and a throttle, ie a fluid resistance, to be combined in one component. Defined flows can be realized by means of the variable flow resistance according to the invention using analog controls.

Preferred exemplary embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. Show it:

Figure 1 is an exploded schematic view of an embodiment of a variable flow resistance according to the invention.

2 and 3 are schematic cross-sectional views for explaining the variable flow resistance according to the invention;

4 shows a schematic representation of a system for flow control using a variable flow resistance according to the invention; and

Figure 5 is a graph showing the flow rate versus pressure on the fluid line. As shown in FIG. 1, an embodiment of a variable flow resistance according to the invention comprises a substrate 10, a holding element 12 and a membrane element 14. A channel 16 is formed in the upper surface of the substrate 10, which in the embodiment shown shows a channel for space-saving reasons has a meandering course.

The holding element 12 has an essentially frame-shaped structure which defines a recess 18 over an essential area of the channel 16. Furthermore, a fluid inlet opening 20 and a fluid outlet opening 22 are formed in the holding element 12. The recess 18 is preferably formed such that the membrane element 14 can be introduced into it and thus covers the upper side of the channel 16 which is formed in the substrate 10, with the exception of a first and a second end 24 and 26 of the channel which are arranged below the frame structure. A closed fluid line of a predetermined length is thus defined by the channel 16 and the membrane element 14 applied to the upper side of the substrate 10, the holding element 12 being used to fix the position of the membrane element. In the finished state, the fluid inlet opening 20 of the holding element 12 is in fluid communication with the first end 24 of the channel 16, while the fluid outlet opening 22 is in fluid communication with the second end 26 of the channel 16.

The substrate 10 can consist of any suitable carrier material, for example silicon, plastics or metals. The channel 16 can be formed by any suitable method in the upper side of the substrate 10, for example by etching methods, chip processing, laser ablation methods, injection molding methods, stamping techniques, eroding or lithography methods etc. This channel 16 which is open at the top is capped by applying the membrane element 14, the membrane element 14 can be an elastomer membrane, a metal membrane or the like. Furthermore, the membrane 14 can also consist of silicon and bonded to substrate 10 using known methods, such as silicone fusion bonding. Alternatively, the membrane element 14 can be attached to the substrate 10 by another method, for example welding, gluing and the like, the frame element shown in FIG. 1 being optional.

A capillary structure can be formed by the channel 16 and the membrane 14 closing it off at the top. A capillary structure is defined by the fact that capillary forces dominate in the same, whereby capillaries, depending on the surface tensions involved, which in turn depend on the fluids used, can fill under ambient conditions due to capillary forces without the introduction of additional forces.

Flow cross sections of fluid lines used according to the invention can lie, for example, in a range between 50 μ ² and 1500 μ ² , a typical value for the duct cross section being 820 μm ² , for example. The length of the fluid line 16 can be, for example, in a range between 0.05 m and 1.5 m, typically around 1 m, in order, for example, to set a suitable flow resistance of the fluid line assuming a viscosity of water at room temperature. However, the actual dimensions can deviate from the dimensions mentioned and depend on the flow resistance to be implemented and the fluid for which the same is to be implemented.

In the embodiment shown in FIG. 1, by applying a defined force to the side of the membrane element 14 facing away from the channel 16, this membrane element can be pressed into the channel, for example by 2-38 μm, so that the cross section of the channel changes, whereby it however, it is usually not closed completely. However, a complete closing can be realized by matching the cross-sectional shape of the channel to the shape of the membrane is adjusted in the deflected state. By regulating the force, the cross section, and thus the flow resistance supplied by the fluid line, can be varied within defined limits. Pneumatic systems are particularly suitable for applying a defined force to the side of the membrane element 14 facing away from the channel. Alternatively, however, other drives are also conceivable by means of which the membrane can be deflected accordingly, for example electrostatic, piezoelectric or electromagnetic drives.

As an alternative to the exemplary embodiment shown in FIG. 1, the closed fluid line with an adjustable flow cross section can be formed by a channel formed in a flexible substrate, which is covered by a rigid or likewise flexible cover. In such a case, too, pneumatic systems can preferably be provided in order to exert pressure on the flexible substrate or the flexible substrate and the flexible cover from the outside in order to reduce the flow cross section. For this purpose, the arrangement can be arranged in a pressure chamber, for example.

Two schematic cross-sectional views, which represent flow cross sections of two exemplary embodiments of channels formed in a silicon substrate 30, are shown in FIGS. 2 and 3. FIG. 2 shows a fluid line cross section 32 etched in dry chemical chemistry in silicon, while FIG. 3 shows a fluid line cross section 34 etched in wet chemical chemistry in silicon. Furthermore, FIGS. 2 and 3 each show an elastic cover 36, which is preferably supplied by a respective membrane element.

As can also be seen from FIGS. 2 and 3, the depth of the respective channel is D, while the width facing the elastic cover 36, ie maximum width, of the respective channel is w. In Figures 2 and 3 is furthermore, a state is shown in each case in which the elastic cover has penetrated by the depth d into the channel cross section 32 or 34 formed in the substrate 30.

With reference to FIG. 3, it is explained below how the flow resistance can be set in the case of a flow resistance which has such a fluid line with a variable flow cross section. In the example described below only as an illustration, the flow resistance in the initial state has a triangular cross section, so that the following equations refer to such a triangular cross section.

As previously stated, in a fluid line system having an anisotropically etched channel in 110 silicon as shown in Fig. 3, the fluid resistance of the element can be changed by reducing the effective channel height, i.e. by using an elastic cover material 36 which is pressed into the channel of depth D by a depth of, for example, d. The fluid resistance of a channel with a triangular flow cross section, as shown in FIG. 3, results in a flow q, which is defined by the following equation 1:

where Δp represents the pressure gradient across the fluid line, η represents the viscosity of the fluid whose flow is to be controlled, ξ is a correction factor which is determined from the ratio of channel depth to channel width, takes into account the geometric influence of a non-circular cross section and is described experimentally, where ξ = 0.84 applies here, L is the length of the fluid line and w is the maximum width thereof, ie the width thereof in the region of the surface of the substrate 30. The width w is defined by the depths d and D according to the following equation 2:

w (d) = tan (54.7) • (D - d) * -v / 2 ^• (D - d) G1.2

Hence, for the flow as a function of d according to equation 3:

The deflection of the elastic cover 36 to obtain a given flow can thus be calculated as follows:

The deflection d is achieved by applying a force F to the elastic material that is used as the channel cover 36. The local deflection d (x) where x is the position over the deflectable membrane area can be described approximately as follows:

Here, p is the pressure exerted on the side of the cover 36 facing away from the channel, E the modulus of elasticity of the membrane and I _y the surface moment perpendicular to x. The area torque I _y is defined by the channel length L and the membrane thickness H _M :

H:

G1.6

12 A certain deflection into the channel and thus an adjustment of the flow resistance can thus be brought about by correspondingly exerting a force on the elastic material or by correspondingly applying a pressure thereon. If the flow cross section of the fluid line with a triangular cross section is reduced by a percentage of, for example, 70% at a predetermined pressure, the flow resistance of the fluid line is increased in such a way that the flow resistance acts like a closed valve, ie with leakage rates which are below the range of conventional micro valves , ie in the range of a few nl per day.

The present invention is therefore suitable for realizing flow control mechanisms using an analog variation of the flow cross section of a fluid line.

An exemplary embodiment for carrying out an analog control of continuous flows in a fluid line 50 using a variable flow resistance 52 according to the invention, which has a fluid line with a variable flow cross section, is shown in FIG. 4. The fluid line of the variable flow resistance according to the invention is connected into the fluid line 50, for example by connecting the fluid inlet opening and fluid outlet opening shown in FIG. 1 to respective connections of the fluid line 50. Furthermore, a flow meter 54 is located in the fluid line 50 can act any conventional fluid flow meter. Furthermore, FIG. 4 shows a device 56 for applying a predetermined pressure to the fluid line, ie for generating a defined pressure difference between the inlet and outlet of the fluid line, this device 56 being a pump, for example. Alternatively, the device 56 can be formed by a pressure reservoir. The pressure on the pressure in the fluid line 50 Sensitive fluid can only be caused by gravitational forces.

The output signal of the flow meter 54 is fed to a control device 60 which compares the output signal with a predetermined value. The control device 60 is also connected to a pressurization device 62, by means of which, for example, the membrane element 14 shown in FIG. 1 can be subjected to a force in order to vary the flow cross section of the fluid line of the variable flow resistance 52. Depending on the comparison of the detected flow rate, the controller 60 controls the pressurization device 62 in order to provide a flow resistance of the variable flow resistance 52 required for a desired flow. The present invention thus enables analog control of continuous flows in a microfluidic system using a variable flow resistance which has a fluid line with a variable flow cross section.

Although the flow meter 54 is shown in FIG. 4 in front of the variable flow resistor 52, it is clear that this is not limited to this position, but can also be arranged behind the variable flow resistor, for example.

Because of its simple structure, the present invention is also particularly suitable for use in a drug metering system. The variable flow resistance according to the invention can also be used as a valve, since with a sufficient reduction in the flow cross section of the fluid line, the same acts as a closed valve.

According to the exemplary embodiment described with reference to FIG. 1, a fluid inlet 20 and a fluid outlet 22 are formed in the holding element 12. Similarly, a fluid inlet and a fluid outlet could each be in the sub- Strat 10 may be provided, for example penetrating the same to the rear. Again, alternatively, the membrane element 14 could completely cover the substrate 10, wherein a fluid inlet or a fluid outlet could be formed in the membrane 14 opposite the first or the second end 24 or 26 of the channel 16.

Although a fluid line, which is formed by a channel in a substrate and an elastic cover, has been described above with reference to a preferred exemplary embodiment, the present invention is not limited to such a case. For example, a variable flow resistance according to the invention could have a tubular fluid line with elastic walls, which is arranged in a pressure chamber, so that the flow cross section thereof can be varied by varying the pressure in the pressure chamber. In addition to the cross-sectional shapes specified above, the fluid line used according to the invention can have any cross-sectional shapes, for example a round cross-section, a polygonal cross-section, a polygonal cross-section with rounded corners, etc.

As shown in FIG. 5, according to the invention the flow rate decreases with increasing pressure acting on the fluid line or the channel from the outside.

Claims

claims 1. Variable flow resistance (52) with the following features: a fluid inlet (20); a fluid outlet (22); a closed, fixed length fluid conduit (16) fluidly connecting the fluid inlet (20) to the fluid outlet (22); and means (62) for varying the flow cross-section of the fluid line (16) over a predetermined length thereof for adjusting the flow resistance defined by the fluid line, the ratio of the predetermined length of the fluid line (16) to the characteristic diameter thereof being> 500, wherein the device for varying the flow cross section is designed to exert a pressure from outside on wall sections of the fluid line, which pressure is independent of the pressure of a medium in the fluid line. 2. Variable flow resistance according to claim 1, wherein the fluid line is formed by a channel (16, 32; 34) formed in the surface of a substrate (10; 30) and a membrane (14; 36) covering the channel. 3. Variable flow resistance according to claim 2, wherein the device (62) for varying the flow cross section of the fluid line comprises a device for deflecting the membrane (14; 36). 4. Variable flow resistance according to claim 3, wherein the device for deflecting the membrane a Einrich- device for pressurizing the membrane. 5. Variable flow resistance according to one of claims 2 to 4, wherein the substrate (10; 30) consists of silicon or plastic. 6. Variable flow resistance according to one of claims 2 to 5, in which the channel is formed by isotropic or anisotropic etching, by injection molding, embossing or by lithography. 7. Variable flow resistance according to one of claims 1 to 6, further comprising a control device (54; 60) to control the device (62) for varying the flow cross-section to generate a predetermined flow through the fluid line. 8. Variable flow resistance according to one of claims 1 to 7, further comprising a fluid contacting member (12) in which an inlet opening (20), which is fluidly connected to a first section (24) of the fluid line, and an outlet opening (22), which is connected to a second section (26) of the fluid line, spaced from the first section is fluidly connected, are formed. 9. A variable flow resistance according to claim 8, wherein the fluid contacting member (12) is further configured to positionally position a membrane element (14) on the substrate (10). 10. Variable flow resistance according to one of claims 1 to 9, wherein the means for varying the flow cross-section is designed to effect such a reduction in the flow cross-section that the fluid line is such a flow resistance that at a given pressure with which a Fluid is applied in the fluid line, essentially no flow takes place through the fluid line. 11. Variable flow resistance according to one of claims 1 to 10, in which the cross-section varies substantially uniformly over the entire length by the device for varying the flow cross-section. 12. Use of a variable flow resistance according to claim 10 as a valve. 13. A method of controlling fluid flow using a variable flow resistance (52) having a fluid inlet (20), a fluid outlet (22) and a closed fluid line (16) of fixed length connecting the fluid inlet (20) to the fluid outlet ( 22) fluidly connects, the method comprising the following step: Applying a pressure, which is independent of the pressure of a medium in the fluid line, from the outside to wall sections of the fluid line and thereby varying the flow cross-section of the fluid line over a predetermined length thereof to adjust the flow resistance defined by the fluid line (16), thereby thereby the application of a defined pressure on the fluid line to control the fluid flow through the fluid line, the ratio of the predetermined length of the fluid line and its characteristic diameter being> 500. 14. The method of claim 13, wherein the flow cross-section is varied substantially uniformly over the entire length by the application of the pressure.