Lopez, Vincent (8083 Stonebrook Parkway #1207, Frisco, TX, 75034, US)
Guanghua WU. (3121 Devonshire Drive, Plano, TX, 75075, US)
Lopez, Vincent (8083 Stonebrook Parkway #1207, Frisco, TX, 75034, US)
| 1. | A flow restrictor comprising a piece of foil, wherein: the flow restrictor has a first end and a second end; the piece of foil includes grooves that extend substantially from the first end of the flow restrictor to the second end of the flow restrictor. |
| 2. | The flow restrictor of claim 1, further comprising a pin, wherein the piece of foil surrounds the pin. |
| 3. | The flow restrictor of claim 1, further comprising a sleeve, wherein the piece of foil lies within the sleeve. |
| 4. | The flow restrictor of claim 1, wherein, under the grooves, the piece of foil has a thickness in a range of approximately 1020 mils. |
| 5. | The flow restrictor of claim 1, wherein each of the grooves has a depth in a range of approximately 717 mils. |
| 6. | The flow restrictor of claim 1, wherein, each of the grooves has a width in a range of approximately 4050 mils. |
| 7. | The flow restrictor of claim 1, wherein each of the grooves and the flow restrictor have substantially the same length. |
| 8. | The flow restrictor of claim 1, wherein: the piece of foil further comprises dividers lying between the grooves; and each of the dividers has a width in a range of approximately 1015 mils. |
| 9. | An apparatus comprising a flow restrictor, wherein: the apparatus has a designed flow direction through the flow restrictor; the flow restrictor includes a piece of foil; and the piece of foil includes grooves that extend substantially along the flow direction. |
| 10. | The apparatus of claim 9, further comprising a pin, wherein the piece of foil surrounds the pin. |
| 11. | The apparatus of claim 9, further comprising a sleeve, wherein the piece of foil lies within the sleeve. |
| 12. | The apparatus of claim 9, wherein, under the grooves, the piece of foil has a thickness in a range of approximately 1020 mils. |
| 13. | The apparatus of claim 9, wherein each of the grooves has a depth in a range of approximately 7 17 mils. |
| 14. | The apparatus of claim 9, wherein, each of the grooves has a width in a range of approximately 4050 mils. |
| 15. | The apparatus of claim 9, wherein the grooves and the flow restrictor have substantially the same length. |
| 16. | The apparatus of claim 9, wherein: the piece of foil further comprises dividers lying between the grooves; and each of the dividers has a width in a range of approximately 1015 mils. |
| 17. | The apparatus of claim 9, further comprising an inner wall of a flow path and a wire, wherein the wire lies between an inner wall and the flow restrictor. |
| 18. | The apparatus of claim 9, further comprising a flow path, wherein: a portion of the flow path has a taper; and the flow restrictor has an outer surface that corresponds to the taper. |
| 19. | The apparatus of claim 9, wherein the apparatus is a mass flow controller. |
| 20. | A process for fabricating an apparatus comprising: obtaining a piece of foil, wherein; the piece of foil includes grooves; the grooves extend partially into the piece of foil; and each of the grooves has a length that extends from one edge of the piece of foil to an opposing edge of the piece of foil; attaching the piece of foil to a pin, wherein the pin has a first end and second end; and wrapping the piece of foil around the pin so that the grooves extend substantially from the first end of the pin to the second end of the pin. |
| 21. | The process of claim 20, further comprising inserting the piece of foil and the pin into a sleeve. |
| 22. | The process of claim 20, wherein, before inserting the piece of foil and the pin into the sleeve, an outer diameter of a combination of the piece of foil and the pin is greater than an inner diameter of the sleeve. |
| 23. | The process of claim 20, further comprising, after wrapping the piece of foil, attaching one end of the foil to another part of the foil. |
| 24. | The process of claim 20, further comprising attaching wires to the outside of a flow restrictor, wherein the pin and the piece of foil is at least part of the flow restrictor. |
| 25. | The process of claim 20, further comprising inserting the flow restrictor into the apparatus, wherein the apparatus is a mass flow controller. |
60/472,699 filed May 23,2003, which is assigned to the current assignee hereof and incorporated herein by reference in its entirety. This application is related to Patent Cooperation Treaty Patent Application No. PCT/US03/16493 entitled"Slotted Flow Restrictor and Methods of Fonning and Using the Same"by Tison et al. filed May 23,2003, which is assigned to the current assignee hereof and incorporated herein by reference in its entirety.
FIELD OF THE INVENTION This invention relates in general to flow restrictors and apparatuses including flow restrictors, and more particularly, to flow restrictors that allow fluid flow through the restrictor and apparatuses having those flow restrictors.
DESCRIPTION OF THE RELATED ART Mass flow controllers that operate on heat transfer principles have been widely adopted. The mass flow controllers typically have a small diameter tube (for sensing) in parallel with a primary flow path through the controller. Typically, a partial fluid flow blockage along the primary flow path is used to divert some of the fluid flow to the secondary flow path where sensing may occur.
One attempt to address the flow diversion is to use a solid flow restrictor within a primary flow path.
The flow restrictor may be generally cylindrical with a slight taper that may reside within a tube having a similar taper. The flow restrictor may be held in position through a press-fit mounting mechanism. A solid restrictor may cause too much pressure drop and too much fluid (s) to flow through the secondary flow path. Consequently, the sensor output will no longer be linear or even no longer be single value function.
Another attempt to address the problem is to use the flow restrictor as previously described with holes drilled along the length of the flow restrictor. FIG. 1 includes a cross-sectional view of a flow restrictor 10 having generally circular, cylindrical holes 12 extending through it. To maintain a laminar flow, the diameter of the holes should be very small. To make many small holes is time- consuming and expensive.
SUMMARY OF THE INVENTION A flow restrictor can comprise a piece of foil with grooves. The foil can include a pattern of grooves and dividers lying between the grooves. The flow restrictor can further comprise a pin and a sleeve.
The flow restrictor may be modified relatively easily by removing a foil-pin combination and changing the diameter of the pin, the foil, the sleeve, or any combination thereof. The restrictor may be less expensive to fabricate and more flexible in design adaptation compared to other flow restrictors that allow at least part of the flow to pass through the flow restrictor.
In one set of embodiments, a flow restrictor can comprise a piece of foil. The flow restrictor can have a first end and a second end, and the piece of foil can include grooves that extend substantially from the first end of the flow restrictor to the second end of the flow restrictor.
In another set of embodiments, an apparatus can comprise a flow restrictor. The apparatus may have a designed flow direction through the flow restrictor. The flow restrictor can include a piece of foil.
The piece of foil can include grooves that extend substantially along the flow direction.
In still another set of embodiments, a process for fabricating an apparatus can comprise obtaining a piece of foil. The piece of foil can includes grooves, the grooves can extend partially into the piece of foil, and each of the grooves may have a length that extend from one edge of the piece of foil to an opposing edge of the piece of foil. The process can also comprise attaching the piece of foil to a pin, wherein the pin has a first end and second end. The process can further comprise wrapping the piece of foil around the pin so that the grooves extend substantially from the first end of the pin to the second end of the pin.
The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as defined in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS The present invention is illustrated by way of example and not limitation in the accompanying figures.
FIG. 1 includes an illustration of a cross-sectional view of a flow restrictor having generally circular, cylindrical holes.
FIG. 2 and 3 include illustrations of top and cross-sectional views, respectively, of a portion of a piece of foil, wherein the foil includes a pattern of grooves and dividers.
FIG. 4 includes an illustration of a perspective view of a pin for use with the foil of FIGs. 2 and 3.
FIG. 5 includes an illustration of a perspective view of a sleeve for use with the foil of FIGs. 2 and 3 and the pin of FIG. 4.
FIG. 6 includes an illustration of a top view of the foil of FIGs. 2 and 3 and the pin of FIG. 4 during an attachment operation of the foil to the pin.
FIG. 7 includes an illustration of a perspective view of a combination of the foil and pin after the attachment operation shown in FIG. 6.
FIG. 8 includes an illustration of a perspective view of the foil-pin combination of FIG. 6 and the sleeve of FIG. 5 before the combination is inserted into the sleeve.
FIG. 9 includes an illustration of a perspective view of a flow restrictor after the insertion operation shown in FIG. 8.
FIG. 10 includes an illustration of a side view of a flow restrictor of FIG. 9 having wires welded to the outer surface of the flow restrictor.
FIG. 11 includes an illustration of a schematic diagram of a mass flow controller including a flow restrictor in accordance with one embodiment.
FIG. 12 includes an illustration of a cross-sectional view of the mass flow controller of FIG. 11 within the tapered portion of the mass flow controller.
FIG. 13 includes an illustration of a cross-sectional view of a portion of a foil that can be used to form a flow restrictor with corrugated internal portion in accordance with an alternative embodiment.
FIG. 14 includes an illustration of a side view of a flow restrictor using the foil of FIG. 13.
FIG. 15 includes an illustration of a cross-sectional view of a portion of another foil that can be used to form a flow restrictor with corrugated internal portion in accordance with an alternative embodiment.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS Reference is now made in detail to the exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts (elements).
A flow restrictor may comprise a pin, a piece of foil wrapped around the pin, and a sleeve. The foil may include a pattern of grooves and dividers lying between the grooves. The flow restrictor can be modified relatively easily by removing the foil-pin combination and changing the diameter of the pin, the foil, the sleeve, or any combination thereof. The restrictor may be less expensive to fabricate and more flexible in design adaptation compared to other flow restrictors that allow at least part of the flow to pass through the flow restrictor.
As used herein, the terms"comprises, ""comprising, ""includes,""including,""has,""having"or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, process, article, or apparatus that comprises a list of elements is not necessarily limited only those elements but may include other elements not expressly listed or inherent to such process, process, <BR> <BR> article, or apparatus. Further, unless expressly stated to the contrary, "or"refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).
FIG. 2 includes a top view of a portion of a piece of foil 30. Foil 30 may comprise a material that is compatible to fluid (s) that may come in contact with the foil. Exemplary materials include 316L
stainless steel, Monel, or the like. Foil 30 may have a thickness in a range of approximately 0.25-0. 51 mm or 10-20 mils thick. The width of the piece of foil may be substantially as wide as the flow restrictor is long. In one non-limiting example, the width may be a range of approximately 18-20 mm or 0.7-0. 8 inches. The length of foil 30 depends in part on the application of the flow restrictor. For example, if foil is designed to be used in a nominal 55 standard liters per minute ("slpm") mass flow controller ("MFC"), the length may be in a range of approximately 108-230 mm or 7-9 inches. For a 100 slpm MFC, the length may be in range of approximately 300-360 mm or 12-14 inches.
Foil 30 may be patterned using conventional lithographic techniques to form grooves 32 and dividers 34. In one example, a resist material (not shown) may be formed over foil 30 and patterned to leave exposed portions of foil 30 where grooves 32 will be formed. Wet chemical or dry plasma etching may be performed to etch away portions of foil 30 to leave the grooves. If dry plasma etching is used, grooves 32 may have more of a rectilinear shape as shown in FIG. 2. If wet chemical etching is used, grooves 32 may have more of a"U"shape. After reading this specification, skilled artisans appreciate that they can use wet etching, dry etching, or a combination of them to achieve a desired shape for grooves 32. After etching, the remaining resist is removed using a conventional technique.
In FIG. 2, the width of foil 30 extends beyond the top to the bottom as illustrated, and the length of foil 30 extends beyond the sides as illustrated. Note that grooves 32 and dividers 34 extend in a direction substantially parallel with the width of foil 30 and tenninate substantially at the opposing edges of foil 30. As will be explained later, the fluid flow is substantially parallel to grooves 32 and the width of foil 30.
In an alternative embodiment (not shown), grooves 32 and dividers 34 may extend in a direction other vertical as shown in FIG. 2. For example, the direction may be approximately 10 degrees from vertical as shown in FIG. 2. The grooves 32 and dividers still extend substantially to the opposing edges of foil 30. When wrapped around a pin, the fluid flow though a groove would be helical.
The dimensions of groove width 42 and groove depth 44 of grooves 32 and width 48 of dividers 24 may vary depending upon application, fluid properties (e. g. , viscosity), and flow rate. The dimensions should be chosen such that flow through grooves 32 is laminar and entrance and exit effects for grooves 32 are not unacceptable to the user. Exemplary, non-limiting dimensions include groove widths 42 in a range of approximately 1.0-1. 3 mm or 40-50 mils, groove depths 44 in a range of approximately 0.25-0. 51 mm or 10-20 mils, and divider widths in a range of approximately 0.18- 0. 43 mm or 7-17 mils. These dimensions may be particularly well suited for nominal 50-100 slpm MFCs.
FIG. 4 includes an illustration of a perspective view of pin 50 that may provide a base material around which foil 30 may be wrapped. Pin 50 can comprise any of the materials as listed for foil 30. In one non-limiting embodiment, pin 50 may comprise 316L stainless steel. Pin 50 may have a substantially cylindrical shape. The diameter of pin 50 may be in a range of approximately 2.3-2. 5 mm or 90-125 mils. The length of pin 50 may be in a range of approximately 18-20 mm or 0.7-0. 8 inches. In one embodiment, the length of pin 50 is at least as long as the width of foil 50 to reduce the likelihood of foil 30 being folded over the end of pin 50. Such folding may cause an undesired effect with fluid flow through grooves 32.
FIG. 5 includes an illustration of a perspective view of sleeve 60 for holding foil 30 and pin 50.
Sleeve 60 can comprise any of the materials as listed for foil 30. In one non-limiting embodiment, sleeve 60 may comprise 316L stainless steel. Sleeve 60 may have a substantially cylindrical shape with a slight taper along the outer surface of its length. More detail regarding the tape is described later in this specification.
The outer diameter of sleeve 60 depends upon the inner diameter of the tube it resides. In on embodiment, it is in a range of approximately 16.3-16. 5 mm or 640-650 mils. One or both ends of sleeve 60 may have rounded outer edges 62 that have a radius of curvature in a range of approximately 0.5-1 mm or 20-40 mils. The outer edges 62 help during a subsequent insertion operation that may be performed when fabricating an MFC. Sleeve 60 can also include chamfer 64 having an angle in a range of approximately 13-17 degrees. The inner diameter of the sleeve 60 depends upon the designed flow rate. For example, a 55 slpm MFC may have an inner diameter in a range of approximately 10.2-10. 7 mm or 0.40-0. 42 inches, and a 100 slpm MFC may have an inner diameter in a range of approximately 13.2-14. 2 mm or 0.52-0. 56 inches. The length of sleeve 60 should be the same as the foil width and the pin length, which is approximately 18-20 mm or 0.7-0. 8 inches.
Although many dimensions have been given for foil 30, pin 50, and sleeve 60, dimensions outside these ranges may be used. The actual dimensions used may be a function of linearity requirement of the application, flow rate, sensor specification, and potentially other factors. Additional information regarding the flow restrictor and its use within a MFC is described later in this specification.
Attention is now directed to a process for fabricating the restrictor and an MFC using the restrictor.
Foil 30 may be attached to pin 50 as illustrated in FIG. 6. Spot welds 72 may be used. Alternatively, attaching may be performed using screws, nail, epoxies, or the like. The dimensions of the flow restrictor and purity concerns may favor one attaching methodology over the other. With the small
dimensions of pin 50 and purity concerns, spot welds 72 may be the easiest to use. As illustrated in FIG. 6, portions of foil 30 left of pin 50 have their grooves facing away from pin 50 (i. e. , extending into the page.
After attaching, foil 30 is wrapped around pin 50 to form foil-pin combination 80 that may have at least one and possibly multiple layers of foil 30 around pin 50 as illustrated in FIG. 7. The end of foil 30 may be attached to another part of foil 30 to keep foil 30 from unraveling. The outer diameter of combination 80 may be slightly larger than the inner diameter of sleeve 60 in which combination 80 will be inserted.
Foil-pin combination 80 can be inserted into sleeve 60 as illustrated in FIG 9. The chamfer 64 helps to guide the combination 80 into sleeve 60. Because combination 80 has a slightly larger diameter compared to the inner diameter of sleeve 60, the combination 80 may be held in place by friction.
While some deformation of foil 30 may occur, it is not to such a degree to substantially affect the flow characteristics through most of grooves 32 within foil 30.
After the insertion operation, a flow restrictor 100 has been formed as illustrated in FIG. 9. The flow restrictor 100 comprises pin 50, sleeve 60, and foil 30 lying between pin 50 and sleeve 60. The flow restrictor 100 can be characterized by an internal overall open cross-sectional area. The area should be close to the sum of the cross-sectional areas (width 42 times depth 44) of grooves 32 as shown in FIG. 3.
FIG. 10 includes a side view of a flow restrictor 100 after attaching wires 112 and 114 using spot welds 1122 and 1142, respectively. In one embodiment, there are four wires attached to the restrictor.
Only two wires can be seen in FIG. 10. The flow restrictor 100 may have a diameter (width) 1162 at one end that is larger than the diameter (width) 1164 at the other end of the restrictor 100 as illustrated in FIG. 10. The taper of the width may be in a range of approximately 1-5 degrees.
The wires 112 and 114 extend along the length of the flow restrictor 100. The wires 112 and 114 can have a diameter in a range of approximately 0.13-0. 43 mm or 5-17 mils, and usually, in a range of approximately 14-16 mils. The wire can aid in the alignment of the restrictor 100 within a tube and can offset the restrictor 100 from the inner wall of a tube in which it is to reside. A more detailed description of the wires during an insertion operation is later in this specification.
FIG. 11 includes a schematic view of mass flow controller 120 including inlet 1222, main body 1224, and outlet 1226. Main body 1224 can include primarily flow path 1244 and secondary flow path 1246. Flow restrictor 100 lies within tapered portion 1245 of the primary flow path 1244. The inner
wall of portion 1245 defines the taper, and outer surface 104 of flow restrictor 100 has a shape that corresponds to the taper of portion 1245 (i. e. , effectively parallel to each other). Secondary flow path 1246 typically has a smaller diameter compared to the primary flow path 1244. Secondary flow path 1246 provides a parallel flow path to primary flow path 1244 and can be used to measure the flow of the gas through mass flow controller 120. Electronic controller 126 is connected to valve 1242 and sensor 1248.
Depending on the flow rate through mass flow controller 120, the annular area between restrictor 100 and tapered portion 1245 can be adjusted for that flow rate. Referring to FIG. 12, portion 1245 has outer wall 132 and inner wall 134. The flow characteristics in the annular area between outer surface 104 of restrictor 100 and inner wall 134 the tapered portion 1245 are a function of distance 136.
Initially, distance 136 is approximately the same as the diameters of wires 112 and 114. During an insertion operation, as the pressure used to insert restrictor 100 into tapered portion 435 increases, wires 112 and 114 can start to flatten and reduce distance 136. Therefore, wires 112 and 114 may comprise a material that is the same hardness or softer than the materials used for restrictor 100 and the portion 1245. It also should be compatible with the fluid (s) the restrictor may contact. Exemplary materials may include 316 L stainless steel, nickel, and the like. In some situations, the force used during insertion may be approximately 500 newtons or several hundred pounds. In this manner, mass flow controller 120 can be tuned to the mass flow rate for which it is designed by varying the pressure used during the insertion exercise.
The flow of fluids at the restrictor 100 may also be affected by the design of pattern (grooves 32 and dividers 34) of foil 30 within restrictor 100 and width of wires 112 and 114. As the ratio of the overall open cross-sectional area increases, a higher flow rate through restrictor 100 may be achieved.
Conversely, if the overall open cross-sectional area decrease, a lower flow rate may be achieve. The design can be affected by changing the thickness of foil 30 and the dimensions of grooves 32 and dividers 34.
Wires 112 and 114 can provide an annulus between the flow restrictor 100 and the tapered inner wall of portion 1245. If the ratio of the flow rate through primary flow path 1244 needs to be increased relative to the flow rate through flow path 1246, wires 112 and 114 may have a larger diameter, less pressure may be used during insertion, or a combination of the two. If the ratio of the flow through primary flow path 1244 is to be decreased relative to secondary flow path 1246, a smaller diameter of wires 112 and 114 may be used, less pressure may be used during insertion, or a combination of the two.
In one particular embodiment, a combination of methods can be used to adjust the flow around a restrictor. For example, the design of foil 30 (thickness and dimensions of grooves 32 and dividers 34) may be used as a coarse adjustment, and the insertion pressure when fabricating the MFC may be used as a fine adjustment.
In still further embodiments, corrugated flow restrictors may be made by using materials, which when wrapped around themselves, appear as a corrugated material when inserted into sleeve 60. FIG. 13 includes an illustration of a cross-sectional view of foil 130 having a substrate 132 and a saw-tooth pattern 134. Foil 130 may be obtained from PCM Products, Inc. (Part number 332346). In addition to the saw-tooth pattern, other patterns, such as semicircles may be used. Unlike a prior embodiment, pin 50 and attaching foil 30 to pin 50 may be eliminated. Foil 130 may be wrapped around itself and inserted into sleeve 60. FIG. 14 includes an illustration of a flow restrictor 140 including foil 130 surrounded by sleeve 60.
FIG. 15 illustrates an alternative pattern for a corrugated flow restrictor. FIG. 15 includes corrugated foil 150. Unlike foil 130, foil 150 has a pattern on both sides. Foil 150 may be formed by crimping a flat foil sheet, and therefore, may be economical to form. Similar to foil 130, foil 150 may not require pin 60. After reading this specification, skilled artisans appreciate that other foil patterns may be used.
Example A specific non-limiting example is given to illustrate some dimensions and design considerations. A mass flow controller has a nominal flow rating of 55 standard liters per minute for nitrogen (N2) gas.
The flow restrictor may have an overall length of approximately 19 mm or 0.75 inches and a diameter at the larger end of approximately 16.4 mm or 0.647 inches. The taper is approximately 2 degrees overall.
Foil 30 has a width of approximately 19 mm or 0.75 inches and a length of approximately 200 mm or 8 inches. Each of the grooves has a depth of approximately 0.30 mm or 12 mils and a width of approximately 1.0 mm or 40 mils. Each of dividers 34 has a width of approximately 0.3 mm or 12 mils.
Pin 30 has a diameter of approximately 2.4 mm or 0.094 inches and a length of approximately 19 mm or 0.75 inches. Sleeve 60 may have an inner diameter of approximately 10 mm or 0.41 inches, an outer diameter of approximately 16.4 mm or 0.647 inches and a length of approximately 19 mm or 0.75 inches.
Wires may be attached to the flow restrictor, and each wire may have a diameter of approximately 0.38 mm or 15 mils. After preparing the restrictor and wires, the combination may be inserted into the mass flow controller. The rest of the fabrication and calibration of the mass flow controller can be performed using a conventional method.
The flow restrictor 100 may be used in nearly any flow apparatus including a mass flow controller, mass flow meter, or any other device that controls, measures, or regulates the flow of fluids, whether gasses or liquids. The flow restrictor may also be used in other fluid flow applications. For example, the flow restrictor may be used to divert some of a liquid stream from a primary flow path to a secondary flow path. The concepts described herein can be used to design properly the flow restrictor with slots extending from an external surface of the flow restrictor.
The flow restrictor 100 has advantages over the conventional flow restrictors as illustrated in FIGs. 1 and 2. The design of restrictor 100 can be modified to meet system requirements. In some applications, pressure drop across the flow restrictor 100 may be important and need to be kept to a certain value, for example, no greater than 7 torr. Also, to achieve a linear relationship between pressure drop and flow rate, the fluid flow should be kept laminar. Given a specific fluid material (density and viscosity) and flow rate, the overall open cross sectional area of restrictor 100 may be designed to keep the pressure drop from becoming too high. The adjustment of the overall open cross sectional area of restrictor 100 can be achieved by changing the inner diameter of sleeve 60, outer diameter of pin 50, or both. The adjustment of the overall open cross sectional area of restrictor 100 can also be achieved by changing the pattern of the grooves on the foil. But in this case, the linearity of the restrictor will also be changed.
When changing the design of restrictor 100, the foil-pin combination 80 may be removed and a different sleeve, pin, foil, or combination of them may be used. Therefore, restrictor 100 can be easily modified from a higher flow apparatus to a lower flow apparatus. The restrictors seen in FIGs.
1 and 2 are not as easily adapted when going from high flow conditions to lower flow conditions.
Restrictor 100 is relatively inexpensive to fabricate and does not require expensive, complex machining tools. Conventional lithographic methodology can be used to pattern the foil. Lasers or electronic milling machines are not needed. Restrictor 100 may be integrated in a number of different fluid flow apparatuses without undue complication.
The flow restrictor 100 can be used to change the flow ratio between the primary and second flow paths 1244 an 1245. Different variables as previously described can be used to achieve the desired flow ratios for the designed flow conditions (e. g. , gas, pressure, total flow rate, etc.).
In a further alternative embodiment, a different number of wires (similar to wires 112 and 114) may be used. For example, instead of four wire lengths along the flow restrictor only three wire lengths may be used. Also, more wire lengths may be used, but the amount of area that they occupy may become greater than desired. In yet a further alternative embodiment, no wires are required.
In the foregoing specification, the invention has been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention.
Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any element (s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or element of any or all the claims.
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