Abstract:
A flow control device having no moving parts that controls fluid flow along a fluid pathway in such a way that flow rate remains constant irregardless of environmental changes. The device achieves a constant flow rate by taking advantage of the properties of the fluid moving along the fluid pathway and maintains the constant flow rate irregardless of changes in viscosity due to changes in temperature.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to fluid flow control devices for controlling the flow of fluid along fluid flow pathways. More particularly, the invention concerns a highly novel fluid flow control device that has no moving parts and uniquely controls fluid flow by taking advantage of the properties of the fluid moving along the fluid flow pathway.  
         [0003]     2. Discussion of the Prior Art  
         [0004]     Various types of fluid flow control devices have been suggested in the past. Typically, these prior art devices use flow regulators, valves, diaphragms and like constructions all employing moving parts to achieve flow rate stabilization. Such constructions tend to be complex, costly and often of questionable reliability, particularly when used in medical applications.  
         [0005]     Exemplary of a prior art flow regulator that embodies a deflectable beam placed within the fluid flow path is that described in U.S. Pat. No. 5,163,920 issued to Olive. The Olive device comprises a beam structure that is placed in the fluid flow path between an inlet and an outlet in a miniaturized housing. A flow gap defined between the beam and the housing provides a pressure differential between the faces of the beam which causes deflection and thus varies the fluid flow through the gap.  
         [0006]     U.S. Pat. No. 3,438,389 issued to Lupin describes a flow metering orifice with automatic compensation for change in viscosity. Compensation for changes in viscosity in the Lupin device is effected by a movable valve element that shifts to increase the effective flow area as the viscosity of the fluid increases and to decrease the effective flow when the viscosity decreases.  
         [0007]     The thrust of the present invention is to provide a highly novel flow control device that is of simple construction and design and is significantly more reliable than prior art flow control devices of conventional design. More particularly, the device of the present invention uniquely achieves flow rate stabilization by taking advantage of the properties of the moving fluid alone. In this regard, it is known that under certain circumstances eddy currents are generated as fluid moves past obstacles in the fluid flow path and the shape and magnitude of such eddies depend on the viscosity of the fluid. Further, it has been observed that the eddies themselves can be responsible for impeding the flow of fluid. Thus, arranging the size and position of obstacles in the fluid flow path can serve to provide viscosity dependent resistance to the flow of fluid. Therefore, the present inventor has determined that it is possible to design the fluid path so that the fluid flowing along the fluid path will generate its own regulation.  
         [0008]     With the forgoing in mind, it is apparent that the method of flow rate stabilization contemplated by the present invention is fundamentally different in character from the prior art flow rate regulators that embody moving parts. Advantageously, because the devices of the present invention have no moving parts their manufacture is substantially easier and less expensive than conventional prior art flow rate stabilization devices.  
         [0009]     An example of one form of a flow rate stabilization system contemplated by present invention comprises a device having a simple set of veins or collars protruding from the sides of otherwise straight channels to provide for the delivery of fluid at a rate independent of viscosity. The veins or collars of the device either have dimensions (primarily the dimension perpendicular to the current flow) or elastic constants relatively large so that under normal operating conditions their position and dimensions are constant. Advantageously, these types of veins are quite easy to incorporate into an injection molded fluidic chip in which the veins are merely an especially molded feature protruding from the walls of the fluid flow channel.  
       SUMMARY OF THE INVENTION  
       [0010]     It is an object of the invention to provide a flow control device having no moving parts that controls fluid flow along a fluid pathway in such a way that flow rate remains constant irregardless of environmental changes.  
         [0011]     Another object of the invention is to provide a device of the aforementioned character that achieves flow rate stabilization by taking advantage of the properties of the fluid moving along the fluid pathway.  
         [0012]     Another object of the invention is to provide a device as heretofore described that maintains flow rate irregardless of changes in viscosity due to changes in temperature.  
         [0013]     Another object of the invention is to provide a flow control device of the class described that includes means for generating eddy currents in the fluid to provide viscosity dependent resistance to fluid flow along the fluid pathway.  
         [0014]     Another object of the invention is to provide strategically placed fixed obstacles within the fluid flow path for the purpose of controllably producing eddies.  
         [0015]     Another object of the invention is to provide a flow control device of the character described in the preceding paragraph in which the means for generating eddy currents comprise a stationary vein protruding from a wall of a channel that defines the fluid pathway.  
         [0016]     Another object of the invention is to provide a micro-fluidic device that includes a rigid vein of a character that is easy to incorporate into a fluidic chip having a fluid pathway in the form of a microchannel.  
         [0017]     Another object of the invention is to provide a flow control device of the type descried in the preceding paragraphs which, because of the absence of moving parts, can be manufactured more inexpensively that conventional prior art flow control devices. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a generally perspective view of a fluid system embodying one form of the flow control device of the present invention.  
         [0019]      FIG. 2  is a greatly enlarged cross-sectional view taken along lines  2 - 2  of  FIG. 1 .  
         [0020]      FIG. 3  is a top plan view of an alternate form of the flow control device of the present invention.  
         [0021]      FIG. 4  is a cross-sectional view taken along lines  4 - 4  of  FIG. 3 .  
         [0022]      FIG. 5  and is a greatly enlarged, generally diagrammatic view of fluid flow channel of an alternate form of flow control device.  
         [0023]      FIG. 6  is a top plan view of still another form of flow control device of the present invention.  
         [0024]      FIG. 7  is a cross-sectional view taken along lines  7 - 7  of  FIG. 6 .  
         [0025]      FIG. 8  is a cross-sectional view taken along lines  8 - 8  of  FIG. 7 .  
         [0026]      FIG. 9  is a greatly enlarged, longitudinal cross-sectional view of still another form of the flow control device of the present invention.  
         [0027]      FIG. 10  is a cross-sectional view taken along lines  10 - 10  of  FIG. 9 .  
         [0028]      FIG. 11  is a generally graphical representation of fluid flow rate plotted against pressure. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0029]     Referring to the drawings and particularly to  FIGS. 1 and 2 , one form of the flow control device of the present invention is there illustrated and generally designated by the numeral  14 . The flow control device  14 , which is here shown as a fluidic micro-chip, is disposed within a fluid conduit  16 , having a first end  16   a  that is interconnected with a source of fluid “S” and having a second end  16   b  that is interconnected with a conventional luer connector  18 . Source “S” can be any type of a source of fluid, such as, by way of non-limiting example, a device for dispensing medicinal fluids, that delivers fluid under pressure into conduit  16  and through device  14  along a fluid pathway  22  in the direction of the arrow  19  ( FIG. 2 ). Disposed within fluid pathway  22 , which here comprises a microchannel, is means for achieving flow rate stabilization, which means is here shown as a pair of spaced-apart obstacles comprising stationary veins  24 .  
         [0030]     As illustrated in the drawings, microchip  14  includes a housing  14   a  having top and bottom walls  14   b  and  14   c . As best seen in  FIG. 2 , veins  24 , which are interconnected with top and bottom walls  14   b  and  14   c , extend into the fluid pathway  22  at an acute angle generally designated by the numeral  25 . Angle  25  can vary depending upon the use to be made of the flow control device, but preferably is between about 15 and about 75 degrees. In this embodiment, veins  24  are about 3 μm wide, 30 μm long and make an angle of about 45° with respect to the channel walls. The direction of flow is from left to right in the direction of the arrow.  
         [0031]     It is to be understood that for any range of operating conditions the lengths of the veins, the thickness of the veins, the taper of the veins, the cross-sectional profile of the veins, the angle the veins make with respect to the channel walls, their physical properties (for example, elastic moduli), will be selected. Further, the number of veins per unit length or density of veins per unit area will also be chosen to provide the desired stabilization for the range of environmental conditions under which the particular device is to operate.  
         [0032]     In the embodiment of the invention illustrated in  FIGS. 1 and 2 , veins  24  function to achieve flow rate stabilization by providing viscosity dependent resistance to fluid flow along fluid pathway  22 . More particularly, veins  24  are uniquely constructed and arranged so as to produce eddy currents within the fluid flowing along said fluid pathway, which eddy currents provide viscosity dependant resistance to the flow of fluid along the fluid flow path.  
         [0033]     Turning to  FIGS. 3 and 4  of the drawings, an alternate form of flow control device of the invention is there shown and generally designated by the numeral  28 . This device is similar in many respects to the previously described device and comprises a fluidic micro-chip  30  having top and bottom walls  30   a  and  30   b  which cooperate to define a fluid flow path, here depicted as a micro-channel  30   c . In this alternate form of flow control device, only a single vein  34  extends into the flow path  30   c . As best seen in  FIG. 4 , vein  34  is of a specially configured, tapered construction. Single vein  34  can be specially configured for particular end-use applications, but preferably has a length of between about 25 μm and about 1,000 μm and a thickness of between about 5 μm and about 100 μm. Various methods for forming vein  34  will be discussed in the paragraphs which follow.  
         [0034]     It is to be understood that the thickness, length and taper of vein  34  may be varied to provide desired results. The angle at which the vein meets the wall of the channel can also be adjusted to produce the desired flow properties of the channel. The shape of the vein need not be of the simple geometric form as shown in  FIG. 4  but could take any shape that the designer believed would produce the desired flow rates under conditions of the environmental parameters.  
         [0035]     In the embodiment of the invention shown in  FIGS. 3 and 4 , the taper of the vein (the difference in thickness between the end of the vein at the wall and its free end) is about 10 μm at the wall and about 6 μm at the free end.  
         [0036]     Turning to  FIG. 5 , this Figure depicts a longitudinal section along the axis of the cylindrically symmetric channel  36  formed in an alternate form of flow control device of the invention. In this instance, because of the axial symmetry of the channel, the vein  37  shown in  FIG. 5  may be properly termed a “collar”. However, when this “collar” is viewed sliced through its axis of symmetry it appears as two veins in  FIG. 5 .  
         [0037]     The various dimensions identified in  FIG. 5  can be adjusted to provide for the desired flow rates at given input pressures. As depicted in  FIG. 5 , the first segment, which contains the vein comprises the stabilizer unit is identified as L 1 . Similarly: 
        L 2 =length of the second segment     L 3 =length of the third segment     R 1 =radius of the first segment     R 2 =initial radius of the second segment     R 3 =radius of the third segment; and     D 1 =distance to the vein.        
 
         [0044]     The graphs below display the results of computations on systems similar to those above with various structural and environmental parameters listed below. 
        L 1 =length of the first segment=1000 μm     L 2 =length of the second segment=42000 μm     L 3 =length of the third segment=60000 μm     R 1 =radius of the first segment=80 μm to 110 μm     R 2 =radius of the entrance to the second segment=85 μm to 115 μm     R 3 =radius of the third segment=800 μm     D 1 =distance to the vein=500 μm     L v =length of the vein=80 μm     t b =thickness of the vein at its base=10 μm     t e =thickness of the vein at its end=6 μm     φ=angle the vein makes with the wall of the channel=33°    Pressure=4.5 to 12.5×10 +3  N/m 2       Viscosity=5.5 or 11.0×10 −4  Kg/m·sec        
 
         [0058]     It is to be understood that the various dimensions identified in the preceding paragraph are merely exemplary and can be adjusted to provide for the desired flow rates at given input pressures.  
         [0059]     Turning to  FIGS. 6, 7  and  8  of the drawings, still another form of flow control device of the invention is there shown and generally designated by the numeral  40 . This device is similar in many respects to the devices described in the preceding paragraphs and comprises a fluidic micro-chip  42  having walls  42   a  and  42   b  which cooperate to define a fluid flow path, here depicted as a micro-channel  42   c . In this alternate form of flow control device, a plurality of transversely spaced-apart veins  44  extend from bottom wall  42   a  into the flow path, or micro-channel  42   c  ( FIGS. 7 and 8 ). Like single vein  34 , veins  44  can be specially configured for particular end-use applications, but preferably have a length of between about 25 μm and about 1,000 μm and a thickness of between about 5 μm and about 100 μm. It is to be understood that veins  44  can be symmetrically or randomly positioned along the flow path.  
         [0060]     Referring next to  FIGS. 9 and 10 , yet another alternate form of flow control device of the invention is there shown and generally designated by the numeral  48 . This device, unlike the previously described devices, comprises a larger, generally tubular-shaped housing  50  having a sidewall  52  that defines a fluid flow path  54 . In this latest form of flow control device, a plurality of longitudinally spaced-apart pairs of veins or collars  56  extend from side wall  52  into the fluid flow path  54 . Like single vein  34 , veins  56  can be specially configured for particular end-use applications. Although the array of veins depicted in  FIG. 9  is well-ordered this is not an essential feature of the invention and the designer might wish to populate the walls of the channel with veins in a random fashion.  
         [0061]     Referring now to  FIG. 11 , this Figure displays the results of computations on systems similar to those described in the preceding paragraphs above and plots of flow rate vs. pressure.  
         [0062]     It is apparent that the information contained in the graph of  FIG. 11  can readily be used to design elements in a micro-fluidic network. For example, if one wanted the flow rate control device to deliver fluid at a flow rate of 1 ml/min, then reading directly from the graph of  FIG. 11  one could choose a radius for the regulator of 80 μm and a pressure of 12.5×10 3  N/m 2  or a regulator with a radius of 85 μm and a pressure of 8.5×10 3  N/m 2 . The fractional difference in flow rates for these two cases is 4×10 −2  vs. 3×10 −2 . This is not a great difference in the flow rate with respect to changes in viscosity so either would be a reasonable choice.  
         [0063]     On examination of the graph of  FIG. 11  one should conclude that any particular flow rate can be achieved by many different geometries and pressures. For example, the graph indicates that flow rates of 1, 2 and 3 ml/min can be achieved using the range of pressures and geometries explicitly shown in the graph. In addition it is obvious that the lines defined by flow rates vs. pressures for any given geometry can be extrapolated to other pressures to define systems that deliver fluid at pressures other than those explicitly shown in the graph.  
         [0064]     The details of the construction of the flow rate stabilizing device and the various methods of making the flow rate stabilizing device will now be considered. With respect to the materials to be used in constructing the chip, medical grade polymers are the materials of choice. These types of polymers include thermoplastics, duroplastics, elastomers, polyurethanes, acrylics and epoxies. In other variations, the materials used for the flow rate stabilizing device may be made of glass, silica, or silicon. In further variations, the flow control component may be made of metals or inorganic oxides.  
         [0065]     Using the foregoing materials, there are several ways that the flow rate stabilizing device can be made. These include injection molding, injection-compression molding, hot embossing, casting, laser ablation and like techniques well known to those skilled in the art. The techniques used to make the imbedded fluid channels are now commonplace in the field of microfluidics, which gave rise to the lab-on-a-chip, bio-MEMS and micro-total analysis systems (μ-TAS) industries. Additionally, depending on the size of the fluid channels required for a given flow rate, more conventional injection molding techniques can be used.  
         [0066]     The first step in making the channel and veins using an injection molding or embossing process is a lithographic step, which allows a precise pattern of channels to be printed on a “master” with lateral structure sizes down to 0.5 μm. Subsequently, electroforming is performed to produce the negative metal form, or mold insert. Alternatively for larger channel systems, precision milling can be used to make the die mold insert directly. Typical materials for the mold insert or embossing tool are nickel, nickel alloys, steel and brass. Once the mold insert is fabricated, the polymer of choice may be injection molded or embossed to yield the desired part with imprinted channel and veins.  
         [0067]     Alternatively, channels and veins can be made by one of a variety of casting processes. In general, a liquid plastic resin, for example, a photopolymer can be applied to the surface of a metal master made by the techniques described in the preceding paragraph and then cured via thermal or ultraviolet (UV) means. After hardening, the material is then “released” from the mold to yield the desired part. Additionally, there are similar techniques available that utilize CAD data of the desired channel configuration and direct laser curing of a liquid monomer to yield a polymerized and solidified part with imbedded channels. This process is available by contract from, by way of example, MicroTEC, GmbH of Duisburg, Germany.  
         [0068]     In order to seal the flow channel, a planar top plate may be used. In this instance, the channel system may be sealed with a top plate, which is here defined as any type of suitable cover that functions to seal the channels. The top plate may be sealably interconnected with the base plate which contains the flow channel by several means, including thermal bonding, sonic welding, laser welding, adhesive bonding with vacuum application and other bonding techniques using plasma deposition.  
         [0069]     Thermal bonding may be performed by using a channel base plate material and planar top cover that are made of similar polymeric materials. In this case the two substrates are placed in contact with one another, confined mechanically and heated to 2-5° C. above their glass transition temperature. Following a holding period sufficient enough for the polymer molecules of the two surfaces to interpenetrate with one another, the temperature is slowly reduced and a stress-free bonded interface with imbedded micro channel and veins is yielded.  
         [0070]     Additionally, the top plate may be bonded to the base plate through the use of one or more suitable bonding materials or adhesives. The bonding material or adhesive may be of the thermo-melting variety or of the liquid or light curable variety. For thermo-melting adhesives, the adhesive material is melted into the two opposed surfaces, thereby interpenetrating these surfaces and creating a sealed channel structure.  
         [0071]     Further, liquid curable bonding materials or adhesives and light curable bonding materials or adhesives may be applied to one of the surfaces, for example the top plate. Subsequently, the other surface is brought into contact with the coated surface and the adhesive is cured by air exposure or via irradiation with a light source. Liquid curable bonding materials or adhesives may be elastomeric, for example, thermoplastic elastomers, and natural or synthetic rubbers, polyurethanes, and silicones. Elastomeric bonding materials may or may not require pressure to seal the channel system. They may also provide closure and sealing to small irregularities in the opposed surfaces by conforming to the substrates of the channel system.  
         [0072]     A channel system may also be formed and sealed in cases where two surfaces are being joined and one of the surfaces has one or more apertures. In order to promote bonding between these two surfaces, a vacuum may be applied to the apertures. Bonding may then be accomplished by thermal methods or after previously having applied a bonding material or adhesive.  
         [0073]     Having now described the invention in detail in accordance with the requirements of the patent statutes, those skilled in this art will have no difficulty in making changes and modifications in the individual parts or their relative assembly in order to meet specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention, as set forth in the following claims.