Patent ID: 12203493

DETAILED DESCRIPTION

FIG.1shows a schematic view of a fluid flow device5, which may be in the form of a mass flow controller10according to one exemplary embodiment of the present disclosure. The mass flow controller10comprises a flow restrictor12, an upstream pressure sensor14, a downstream pressure sensor16, a control valve18, and a temperature sensor20. It will be appreciated that in other examples, one or more of the above components can be omitted. For example, either of the pressure sensors14,16may be omitted in some configurations. In another configuration, the control valve18may be positioned downstream of the flow restrictor12. In yet other configurations, the fluid flow device5may be configured as a mass flow meter, and thus may not include a control valve18. Additionally, it will be noted that there can be other components in the mass flow controller10that are not depicted inFIG.1. For example, isolation valves (e.g., shut off valves) may be provided in the flow path on either side of the assembly ofFIG.1to isolate the fluid flow device5, and/or a purge line valve may be outfitted downstream of the restrictor to allow purge gas to flow through the fluid flow device5to a purge line.

As shown inFIG.1, flow restrictor12typically includes a collar12A and backing plate12B which sandwich and secure a stack S of sheets21. Although seven sheets21are depicted inFIG.1, it will be appreciated that a different number of sheets may be provided, as discussed below. The sheets21include first sheets22and second sheets24which alternate throughout the stack S. An end-to-end restrictor flow path through the restrictor is depicted by the fluid flow arrows, and extends from a restrictor inlet12C on an upstream side to a restrictor outlet12D on a downstream side of the restrictor12, although the restrictor can be used for flow in either direction (i.e., bidirectional flow). Within the end-to-end restrictor flow path, first sheets22each define an in-sheet flow path26athat allows fluid to flow from an interior region of the restrictor, radially outward to a peripheral end of the first sheet22. Once the fluid flows out of the flow paths26ain first sheets22in stack S, it is guided along the end-to-end flow path to the restrictor outlet12D by external structures, as shown.

FIG.2Ashows a schematic, planar view of a conventional disk422of a flow restrictor comprising a flow passage426that spirals from a hole434of the disk422. It will be appreciated that the flow passage426maintains its spiral shape in the peripheral areas of the disk422. A problem with the restrictor design depicted inFIG.2Ahas been discovered, namely that uncertainty in the flow rates measured through this restrictor is too high under certain flow conditions. It is thought that geometrical uncertainties at the end of the flow passages due to manufacturing tolerances might contribute to this flow rate uncertainty.

FIG.2Bshows a schematic, perspective view of the flow restrictor12of the exemplary embodiment ofFIG.1comprising a first sheet22including a flow passage26aand a second sheet24stacked on the first sheet22. The term sheet is used herein to refer to a structure with a thickness that is substantially less than its lateral dimensions (e.g., horizontal and vertical dimensions in the view ofFIG.2C). Although circular sheets21are shown, the perimeters of the sheets21may be of other shapes, such as polygons. Although sheets21of uniform thickness are shown, the sheets21may alternatively be of non-uniform thickness. The sheets21may alternatively be referred to as plates.FIG.2Cshows a schematic, planar view of the flow restrictor12. The first sheet22and the second sheet24can be fabricated as circular disks with an opening in the middle. The first sheet22and the second sheet24can be made of metals including but not limited to stainless steel or superalloys comprising oxidation-corrosion-resistant materials. To stack the second sheet24on the first sheet22, the first sheet22and the second sheet24can be fused via diffusion bonding, for example. Other adhesion techniques may alternatively be used. Or, in some cases, additive manufacturing may be used to form the flow paths described herein in a monolithic block of material.

FIG.2Dshows a schematic, planar view of the first sheet22in isolation. A circular hole34is provided in a center of the first sheet22. The flow passage26aincludes a groove cut into a surface of the first sheet22that communicates with an outer expansion zone28at a peripheral area of the first sheet22. In this example the flow passage26ais one of a plurality of flow passages26that are uniformly radially distributed around the hole34. Each flow passage26acan include a corresponding groove that spirals from the hole34to a corresponding outer expansion zone28at the peripheral area of the first sheet22. Spiral shaped grooves have the technical advantage of lengthening the flow path within the restrictor, which can be advantageous. However, although spiral shaped grooves are illustrated, it will be appreciated that the grooves may have another shape, such as linear or curved in a non-spiral shape. The outer expansion zone28typically has a cross-sectional area perpendicular to a flow direction that is larger than the cross-sectional area perpendicular to the flow direction within the flow passage26a. As viewed from above inFIG.2D, a width W1of the outer expansion zone28is larger than a width W2of flow passage26a. Typically, the width W1of the outer expansion zone28can be 20%, 50%, 100% or even 500% larger than the width W2of the flow passage26a.

The spiral shape of the groove in the illustrated embodiment terminates at an inner diameter30of the outer expansion zone28. Inside the outer expansion zone28, the shape of flow passages26inside the outer expansion zone28can be linear as shown, or can continue in a curved shape. The groove can be manufactured by chemical etching, laser micro-machining, or a combination of both. Alternatively, the groove can be manufactured by other techniques in which the material of the first sheet22is not cut entirely through the sheet (i.e., is cut to form a bottomed groove).

It will be appreciated that an outer peripheral edge27of the second sheet24(seeFIG.2E) contacts the first sheet22in the outer expansion zone28between an inner diameter30and an outer diameter32of the expansion zone28. Here, the outer expansion zone28is received by one end of the flow passage26a. A thickness of the first sheet22can be 10 to 100 μm. A length of the flow passage26acan be 100 to 1000 times the thickness of the first sheet22. A width of the flow passage26acan be about 5 to 100 times the thickness of the first sheet22.

By providing an outer expansion zone28in the outer peripheral area of the first sheet22, the uncertainty in flow restriction performance can be reduced compared to a conventional restrictor including the conventional disk422ofFIG.2A.

An inner expansion zone28′ can also be provided in an inner peripheral area of the first sheet22, as illustrated inFIG.2D. The inner expansion zone28′ can be provided to the first sheet22additionally or alternatively to the outer expansion zone28. The flow passage26aincluding the groove cut into the surface of the first sheet22can also communicate with an inner expansion zone28′ at an inner peripheral area of the first sheet22. The corresponding groove of each flow passage26aspirals from the outer expansion zone28in the outer peripheral area of the first sheet22, into the inner expansion zone28′ adjacent the hole34. An inner peripheral edge27′ of the second sheet24(seeFIG.2E) contacts the first sheet22in the inner expansion zone28′ between an inner diameter30′ and an outer diameter32′ of the inner expansion zone28′. By providing inner expansion zone28′ in the inner peripheral area of the first sheet22, the uncertainty in flow restriction performance can be reduced compared to a conventional restrictor including the conventional disk422ofFIG.2A. Like the outer expansion zone28, the inner expansion zone28′ typically has a cross-sectional area perpendicular to a flow direction that is larger than the cross-sectional area perpendicular to the flow direction within the flow passage26a. As viewed from above inFIG.2D, a width W3of the inner expansion zone28′ is larger than a width W2of flow passage26a. Typically, the width W3of the inner expansion zone28′ can be 20%, 50%, 100% or even 500% larger than the width W2of the flow passage26a.

FIG.2Eshows a schematic, planar view of the second sheet24in isolation. A hole25is provided in a center of the second sheet24. In this example, the second sheet24has no flow passages.

FIG.2Fshows a schematic, exploded view of the flow restrictor12formed by the first sheet22, a top second sheet24a, and a bottom second sheet24b.

FIG.2Gis a prophetic bar chart based on simulation data comparing the uncertainty in the performance of flow restrictor12of the exemplary embodiment ofFIGS.2B-2Fto conventional flow restrictors for some combinations of upstream pressure (P1) and downstream pressure (P2), with pressure measured in kPa. The results inFIG.2Gwere obtained with computational-fluid-dynamics (CFD) simulations using a CFD model that agrees with experimental data within experimental uncertainty. The uncertainty depicted inFIG.2Gis the sensitivity of the molar flow rate ratio of sulfur hexafluoride and nitrogen to a worst-case-scenario restrictor-geometry variation. As can be seen inFIG.2G, the configuration of the outer expansion zone28at the peripheral area of the first sheet22of the flow restrictor12reduces uncertainty compared to flow restrictors of the prior art, including conventional disk422. It is thought that this technical effect is achieved by mitigating the geometrical uncertainty and the end of the flow passages.

FIG.2His a prophetic chart based on simulation data illustrating the reduction of uncertainty in flow restrictor performance shown inFIG.2G.FIG.2Hplots the molar flow rate per flow path of sulfur hexafluoride versus that of nitrogen for three cases. Ideally, restrictors could be manufactured with infinitesimal precision, as illustrated for the benchmark case inFIG.2H. But in practice, there is a manufacturing tolerance which is taken into account. It will be noted inFIG.2Hthat the seem (standard cubic centimeter per minute) deviation from the ideal is smaller with the configuration of the outer expansion zone28at the peripheral area of the first sheet22of the flow restrictor12, compared to flow restrictors with a conventional disk422. This achieves the potential advantage of reducing the uncertainty in flow restrictor performance as illustrated inFIG.2G.

FIG.3Ashows a cross-sectional side view of a conventional flow restrictor512. The direction of the fluid flow is indicated with arrows flowing from a flow inlet536, through the flow restrictor512, and into the flow outlet538. First sheets522a,522b,522cand second sheets524a,524b,524c,524dare stacked in an alternating manner. In the conventional flow restrictor512, the fluid flows radially outwards between the second sheets524a,524band through the flow paths of the first sheets522a,522b. However, in other conventional flow restrictors, the fluid flow can alternatively flow radially inwards between the second sheets524a,524band through the flow paths of the first sheets522a,522b. In this example, the fluid does not flow through the second sheets524a-d.

FIG.3Billustrates a cross-sectional side view of a flow restrictor112in an exemplary embodiment of the present disclosure. The direction of the fluid flow is indicated with arrows flowing through the flow restrictor112from a restrictor flow inlet12C, through a sheet flow inlet136, out of a sheet flow outlet138, and eventually being guided to flow out of a restrictor flow outlet12D. First sheets122a,122b,122cand second sheets124a,124b,124c,124dare stacked alternately to form a restrictor stack S. The first sheets122a,122b,122care provided with flow passages126a,126b,126c, respectively. The flow restrictor112comprises an upstream flow passage126aconnected to an upstream end of the restrictor stack112. A downstream flow passage126cis connected to a downstream end of the restrictor stack.

In the flow restrictor112of this example, two of the second sheets124b,124cinclude slits140a,140bpenetrating through an entire thickness of the second sheets124b,124c, respectively. The slit140afluidically communicates the flow passage126aof first sheet122awith the flow passage126bof first sheet122b. The slit140bfluidically communicates the flow passage126bof first sheet122bwith the flow passage126cof first sheet122c.

Accordingly, the first sheets122a,122b,122cand second sheets124a,124b,124c,124dare stacked and aligned to form a continuous flow path from the sheet flow inlet136, through the flow passages126a,126b,126cand slits140a,140bof the flow restrictor112, and into the sheet flow outlet138, so that the continuous flow path forms a serpentine shape extending along a thickness direction of the second sheets124a-cas viewed in a vertical cross section of the second sheets124a-c. In this example, the fluid flow passes through the flow passage126a, slit140a, flow passage126b, slit140b, and flow passage126c, in this order as the fluid flow from the sheet flow inlet136, through the flow restrictor112stack S, to the sheet flow outlet138. By increasing the effective length of the flow path inside the flow restrictor112and by passing the fluid flow through a plurality of first sheets122a,122b,122c, the uncertainty in flow restriction performance can be reduced compared to the conventional flow restrictor512.

FIG.4Aillustrates a schematic, exploded view of a stack S of a flow restrictor212in an exemplary embodiment of the present disclosure, in which eight first sheets222a-hand nine second sheets224a-iare stacked alternately to comprise a restrictor stack. Like the exemplary embodiment ofFIG.3B, the first sheets222a-hare provided with flow passages226a-h, respectively, and the second sheets224a-icomprise slits240a-i, respectively, which penetrate through an entire thickness of the second sheets224a-i, respectively. It will be appreciated that the number of first sheets and second sheets stacked alternately is not particularly limited to the number depicted inFIG.4A, and may be more or less than this number depending on the application of the mass flow controller incorporating the flow restrictor212. A typical range for a number of sheets in stack S is between 3 and 99, and more typically is between 5 and 15.

In the exemplary embodiments ofFIGS.3B and4A, a plurality of successively measured fluid flow rates through the restrictor divided by a number of the plurality of first sheets divided by a number of flow passages per first sheet can average a Mach number of less than 0.1. Here, the average Mach number is defined as mass flow rate divided by the product of the following: average density in the restrictor, the flow path cross-sectional area, the sound speed in the gas, and the total number of flow paths. Based on this definition, the Mach number can be reduced to less than 0.1 by increasing the average density in the restrictor, increasing the flow path cross-sectional area, and/or increasing the total number of flow paths, for a fixed mass flow rate. In the embodiments ofFIGS.3B and4A, the total number of flow paths can be increased by increasing the number of first sheets and second sheets that are stacked alternately to comprise a restrictor stack, so that the average Mach number is less than 0.1.

In the exemplary embodiment ofFIG.3Bwith three first sheets122a-cand one flow passage per first sheet, a plurality of successively measured fluid flow rates through the restrictor112divided by three divided by one can average a Mach number of less than 0.1. In the exemplary embodiment ofFIG.4Awith eight first sheets222a-hwith twelve flow passages per first sheet, a plurality of successively measured fluid flow rates through the restrictor212divided by three divided by twelve can average a Mach number of less than 0.1.

FIG.4Bshows a prophetic chart based on simulation data illustrating the reduction of uncertainty in the performance of the flow restrictor with an increasing number of first sheets, which is due to an averaging process. AsFIG.4Bindicates, the uncertainty in the performance of the flow restrictor is reduced as the number of first sheets increases because of an averaging process.FIG.4Bshows theoretical results using a simplified physics-based model that agrees well with CFD and experimental data. For this chart, the measured uncertainty is the sensitivity of the molar flow rate ratio of sulfur hexafluoride and nitrogen to random variations of the width of the first sheets. Many representative operating conditions were used to obtain the results inFIG.4B.

FIG.4Cshows a prophetic chart based on simulation data illustrating the uncertainty in the performance of the flow restrictor as a function of average Mach number for a vast number of flow path geometries and process gases. Results were obtained with a simplified physics-based model that agrees well with CFD results and experimental data. The uncertainty is defined as inFIG.2G, where it is depicted as the sensitivity of the molar flow rate ratio of sulfur hexafluoride and nitrogen to a worst-case-scenario restrictor-geometry variation. However, unlikeFIG.2G, the chart ofFIG.4Cuses flow rate ratios using different gases besides sulfur hexafluoride.FIG.4Cindicates that the uncertainty can be reduced by keeping the average Mach number to less than about 0.1, as indicated by ‘1e-1’ in the chart ofFIG.4C.

FIG.5Ashows a schematic, planar view of a conventional disk622of a flow restrictor comprising a flow passage626that radiates from a hole634of the disk622. It will be noted that the shape of the flow passage626is rectangular.

FIG.5Bshows a schematic, exploded view of a flow restrictor312of an exemplary embodiment of the present disclosure. As illustrated inFIG.5B, the flow restrictor312comprises a first sheet322comprising a flow passage326; and a second sheet324stacked on the first sheet322. A hole325is provided in a center of the second sheet324. The flow passage326is a serpentine groove cut through a thickness of the first sheet322and forming a serpentine shape along a surface of the first sheet322as viewed from above.

FIG.5Cshows a schematic, planar view of the first sheet322in isolation. A hole334is provided in a center of the first sheet322. The flow passage326includes a plurality of serpentine grooves cut into a surface or through the thickness of the first sheet322. Each of the plurality of serpentine grooves of the flow passage326includes a pair of radial sections326a,326bextending in radial directions and a plurality of arcuate sections326c-kdefining a flow path between the plurality of radial sections326a,326b. By increasing the effective length of the flow path inside the flow restrictor312, the uncertainty in the performance of the flow restrictor312can be reduced compared to a conventional flow restrictor with a conventional disk622.

FIG.5Dis a prophetic data plot based on simulation data comparing the uncertainty in the performance of flow restrictor312of the exemplary embodiment ofFIGS.5B-Cto conventional flow restrictors with a conventional disk622for some combinations of upstream pressure (P1) and downstream pressure (P2), with pressure measured in kPa. The experimental results inFIG.5Dwere obtained with CFD simulations using a CFD model that agrees with experimental data within experimental uncertainty. The uncertainty depicted inFIG.5Dis the sensitivity of the molar flow rate ratio of sulfur hexafluoride and nitrogen to a worst-case-scenario restrictor-geometry variation. As can be seen inFIG.5D, the configuration of a flow passage326including a plurality of serpentine grooves cut into a surface of the first sheet322reduces uncertainty compared to flow restrictors of the prior art, including conventional disk622. The present inventors demonstrated through CFD simulations that the pressure drops at the corners of the serpentine grooves would be minimal and contribute little to uncertainty.

FIG.6is a prophetic bar graph based on simulation data comparing a gas-ratio dispersion of a conventional flow restrictor with smooth first and second sheets to gas-ratio dispersions of flow restrictors of exemplary embodiments in which the second sheet has a rougher surface than the first sheet. In the exemplary embodiments ofFIG.6, the ratios of the roughness parameter (Ra) and the flow path thickness were 1 to 5%. In other words, for the exemplary embodiments described above, the second sheet can have a roughened surface relative to a surface of the first sheet. In other words, a roughness parameter of the second sheet can be greater than a roughness parameter of the first sheet. The roughness parameter can be a profile roughness parameter or an area roughness parameter.

The gas-ratio dispersion ofFIG.6is defined as the maximum variation of the flow rate ratio of helium and nitrogen at some conditions. The larger this dispersion is, the larger the uncertainty in the performance of the flow restrictor is. The results inFIG.6were obtained with CFD simulations using a CFD model that agrees with experimental data within experimental uncertainty.

In principle, it was conventionally thought that roughening the walls of the second sheets would increase the uncertainty in the performance of the flow restrictor, because parameters characterizing the roughness would add to the uncertainty. As a result, using second sheets with smooth walls has been the norm in flow restrictor design. For example, ratios of the roughness parameter (Ra) and the flow path thickness are typically less than about 1%.

However, the unexpected results inFIG.6indicate that the roughening of the second sheets results in a reduction of uncertainty that is out of proportion to the effect of merely changing the roughness parameters. Therefore, the unexpected results ofFIG.6show that roughening the walls can significantly reduce flow restrictor uncertainty, at least for the operating parameters considered above. The roughening of the surfaces of the first and second sheets can be achieved in different ways. One is the mechanical abrasion of the metal sheets used to make the second sheets. Another one is to cycle temperature and pressure during the diffusion-bonding of first sheets and second sheets in a way to roughen the walls.

It will be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible.

For example, the features of the exemplary embodiment ofFIGS.2B-Fcan be combined with the features of the exemplary embodiment ofFIG.4Ato incorporate expansion zones into a restrictor stack with a plurality of first and second sheets with an average Mach number of less than 0.1. The features of the exemplary embodiment ofFIGS.2B-Fcan be combined with the features of the exemplary embodiment ofFIG.3Bto incorporate expansion zones into flow restrictors with serpentine flow paths extending along a thickness direction of the second sheets.

Alternatively, the features of the exemplary embodiment ofFIGS.5B-Ccan be combined with the features of the exemplary embodiment ofFIG.4Ato incorporate serpentine grooves on the first sheets of restrictor stack with a plurality of first and second sheets with an average Mach number of less than 0.1. The features of the exemplary embodiment ofFIGS.5B-Ccan be combined with the features of the exemplary embodiment ofFIG.3Bto incorporate serpentine grooves on the first sheets of flow restrictors with serpentine flow paths extending along a thickness direction of the second sheets. Further, the features of the exemplary embodiment ofFIG.3Bcan be combined with the features of the exemplary embodiment ofFIG.4Ato incorporate serpentine flow paths extending along a thickness direction of the second sheets into a restrictor stack with a plurality of first and second sheets with an average Mach number of less than 0.1.

In accordance with the present disclosure, uncertainty in the performance of the flow restrictors of mass flow controllers is decreased, so that the quality of fluid delivery can be increased in various industrial applications.

The subject disclosure includes all novel and non-obvious combinations and subcombinations of the various features and techniques disclosed herein. The various features and techniques disclosed herein are not necessarily required of all examples of the subject disclosure. Furthermore, the various features and techniques disclosed herein may define patentable subject matter apart from the disclosed examples and may find utility in other implementations not expressly disclosed herein.

It will be appreciated that “and/or” as used herein refers to the logical disjunction operation, and thus A and/or B has the following truth table.

ABA and/or BTTTTFTFTTFFF

To the extent that terms “includes,” “including,” “has,” “contains,” and variants thereof are used herein, such terms are intended to be inclusive in a manner similar to the term “comprises” as an open transition word without precluding any additional or other elements.