Inertial filter

Abstract

An inertial filter for separating a suspended matter from a fluid includes a plurality of drainage channels. The suspended matter may be a solid particulate matter, a liquid droplet, or a combination of the solid particulate matter and the liquid droplet. The fluid may be a gas or a liquid. The plurality of drainage channels allow captured liquid to drain from the inertial filter and allow a wash liquid to remove captured suspended matter from the inertial filter.

Description

[0001] Inertial Filter

[0002] I. Related Applications

[0003] This application is entitled to priority from U.S. Provisional Patent Application 63 / 688,097 filed August 28, 2024 by the inventors herein, which is hereby incorporated by reference as if set forth in full herein. PCT application PCT / US24 / 34846 filed June 20, 2024 also is hereby incorporated by reference as if set forth in full herein.

[0004] II. Background of the Invention

[0005] A. Field of the Invention

[0006] An inertial filter for separating a suspended matter from a fluid includes a plurality of drainage channels. The suspended matter may be a solid particulate matter, a liquid droplet, or a combination of the solid particulate matter and the liquid droplet. The fluid may be a gas or a liquid. The plurality of drainage channels allows captured liquid to drain from the inertial filter and allows a wash liquid to remove captured suspended matter from the inertial filter.

[0007] B. Statement of the Related Art

[0008] Separation of suspended matter from a fluid is important for many industries and applications, including: cleaning and washing processes using sprays of water and other solutions; cooling solids via spray cooling with water or other coolants; gas cooling & conditioning wherein droplets may condense from air streams; coating applications using liquid droplets; dust control; fire protection applications where sprays of fire retardants and fire extinguishing materials are of interest; humidification where water droplet sprays humidify air, but may require capture of these droplets; lubrication tank cleaning using droplet sprays; spray drying; NOx control using droplet sprays; sulfur burning; vacuum distillation processes that may require droplet capture; marine fire suppression using nozzles that reduce droplets of water or other fire retardant materials; deluge spray; gas scrubbing applications using chemically active droplets; odor control using chemically active droplets; precision lubrication using droplet sprays; foam control using spray foams; air inlet cooling; aeration / air stripping; cleaning / washing processes in general; coating processes in general, which use droplet sprays; metal descaling; disinfecting processes using droplet sprays of hot liquids or chemically active liquids; general mist elimination; snowmaking processes; pasteurization; pickling; roll cooling; particle-liquid separations; particle, liquid, and gas separations and others.

[0009] The prior art does not teach the apparatus, system and method of the Invention.

[0010] III. Brief Description of the Invention

[0011] The filter of the present invention removes suspended matter from a stream of a fluid. The suspended matter may be solid particulate matter, liquid droplets, or a combination of solid particulate matter and liquid droplets. The fluid may be a liquid or a gas. The filter is composed of a substrate having a front side and an opposing back side. The substrate defines a plurality of perforations through the substrate from the front side to the back side. Each perforation has a perforation wall defined by the substrate. Each perforation wall defines a flow path. The stream of the fluid flows through the flow path defined by the perforation wall from the front side to the back side.

[0012] The perforation wall defines at least one change of direction for the flow path as the fluid travels through the perforation from the front side to the back side. When the stream of fluid changes direction, inertia causes the suspended matter to resist the change in direction and may bring the suspended matter in contact with the perforation wall. If the suspended matter contacts the wall, the suspended matter may be absorbed into the substrate by capillary forces or may adhere to the wall by electrostatic forces or by Van der Waals forces.

[0013] The filter may be oriented so that when the filter is in operation the collected suspended matter will drain from the substrate by gravity, as by giving the length or width of the drainage channel a generally vertical orientation. The wash liquid may be introduced to the drainage channels at an uppermost side of the substrate so that the liquid wash will drain by gravity through the substrate. Alternatively, a pump or blower may move accumulated suspended matter from the substrate.

[0014] The substrate may be a unitary, monolithic structure, and may be complete with the drainage channels and perforations, and may be made by additive manufacturing, as by 3D printing. Alternatively, the filter may be composed of a plurality of layers of the substrate stacked one on another. Holes penetrate the multiple layers so that when the multiple layers are stacked, the holes in combination align to define the perforations and hence the flow paths. Some or all of the multiple layers may be spaced apart by a separation distance to define the drainage channels. The separation distance between adjacent layers defines the thickness of the drainage channel and the length and width of the adjacent layers defines the length and width of the drainage channel. A plurality of spacers may be interposed between adjacent layers to maintain the separation distance between the adjacent layers. As a first alternative, dimples may be defined by the surface of a layer and the dimples may extend proud from the surface to maintain the separation distance between that layer and an adjacent layer. As a second alternative, the separation distance between adjacent layers may be defined by removing substrate from a layer, as by cutting or etching the surface of the layer.

[0015] The substrate may be absorbent and may retain the collected suspended matter within the substrate by capillary action. Alternatively, the substrate may be non-absorbent and the collected suspended matter may adhere to the surface of the substrate.

[0016] The perforation may define a taper between the front side of the substrate and the back side of the substrate, with the cross-sectional area of the perforation normal to the flow path at the front side being larger than the cross-sectional area at the back side, and with the cross-sectional area of the perforation through which the fluid passes reducing as the fluid moves from the front side to the back side. The result is an increase in velocity of the fluid as the fluid moves through the perforation. For a perforation having a constant change in direction through the substrate, such as a helical perforation, the suspended matter experiences increasing inertial forces as the suspended matter advances so that larger and heavier suspended matter collides with the perforation wall and is collected toward the front side where the cross-sectional area is larger. Smaller and lighter suspended matter collides with the perforation wall and is collected toward the back side where the cross-sectional area is smaller.

[0017] While the cross section of the perforation normal to the flow path may be circular, the cross section also may be other than circular. For example, the cross section of the perforation normal to the flow path may be triangular, pentagonal, star-shaped, irregular, or any other shape. A circular cross section presents the smallest possible circumference for a given cross-sectional area, and hence the smallest surface for the collection of the suspended matter. Cross-sectional shapes other than circular present larger circumferences for a given cross-sectional area, and hence larger surfaces for the collisions and collection of suspended matter. Cross-sectional shapes other than circular present geometries useful for liquid transport, including interior corners that will preferentially transport liquid into the interior feature via capillary forces and may preferentially transport liquid through the vertical axis of the interior corner.

[0018] The cross-sectional shape of a perforation may change between the entrance to the perforation on the front side and the exit from the perforation on the back side. For example, the cross-sectional shape proximal to the front side may be circular while the cross-sectional shape proximal to the back side may be star-shaped (or any other non-circular shape). The star-shaped perforation provides a larger surface area per unit of cross-sectional area than the circular perforation and thus presents more opportunities for inertial forces to cause the suspended matter to collide with the perforation wall. The star-shaped perforation presents including interior corners that will preferentially transport liquid into the interior feature via capillary forces and may preferentially transport liquid through the vertical axis of the interior corner.

[0019] The at least one change in direction of the flow path between the front wall and back wall may define any shape, including one or more angles, irregular shapes, or a helix. The flow path may define a flat spiral having a decreasing radius of curvature as the fluid flows between the front side and the back side or a conical helix having a decreasing radius of curvature between the front side and the back side. Assuming a constant cross-sectional area and hence constant velocity along the flow path, the decreasing radius of curvature causes an increase in the inertial forces acting on the suspended matter as the suspended matter advances through the substrate, initially collecting larger and heavier suspended matter and subsequently collecting smaller and lighter suspended matter as the fluid advances through the substrate.

[0020] The at least one change in direction of the flow path may define a branched flow path having a primary perforation starting at the first side, the primary perforation branching into two or more secondary perforations at a branch location intermediate to the front and back sides. The secondary perforations communicate from the branch location to the back side. The cross sectional areas of the secondary perforations normal to the flow paths are less than the cross sectional area normal to the primary flow path. The secondary perforation may maintain flow velocities higher than that of the primary perforation and may maintain radii of curvature that are smaller than that of the primary perforation, all for improved collection of small and light suspended matter as the suspended matter advances along the flow path from the front side to the back side.

[0021] The filter may utilize electrostatic attraction between the suspended matter and the perforation walls to cause the suspended matter to collide with the perforation walls and to be captured by the substrate. The substrate may be provided with an electrostatic charge by an electrode attached to the substrate. As a first alternative, the substrate may acquire an electrostatic charge by the fluid passing through the substrate and carrying electrons from the substrate away in the fluid. As a second alternative, the substrate may be an electret material provided an electrostatic charge during manufacture. The suspended matter may be provided an opposite electrostatic charge by electrodes disposed in the fluid stream upstream of the filter.

[0022] IV. Brief Description of the Drawings

[0023] Fig. l is a perspective view of an inertial filter.

[0024] Fig. 2 is a perspective view of an inertial filter having drainage channels.

[0025] Fig. 3 is a perspective section view of an inertial filter having drainage channels.

[0026] Fig. 4 is a perspective section view of the inertial filter having drainage channels and having perforations penetrating the drainage channels.

[0027] Fig. 5 is a detail perspective section view of the inertial filter having drainage channels extending to the perimeter of the substrate.

[0028] Fig. 6 is a schematic view of an inertial filter with spacers separating layers of the substrate to create the drainage channels.

[0029] Fig. 7 is a schematic view of an inertial filter with dimples separating the layers of substrate to create the drainage channels.

[0030] Fig. 8 is a schematic view of an inertial filter with substrate removed from adjacent layers by etching or cutting to define the drainage layers.

[0031] Fig. 9 is a schematic view of an inertial filter in operation with wash liquid and gravity drainage.

[0032] Fig. 10 is a perspective view of example changes of direction of the liquid flow path.

[0033] Fig. 11 is a perspective view of example cross sectional shapes of the perforation and flow path.

[0034] Fig. 12 is a perspective view of an example tapered flow path.

[0035] Fig. 13 is a perspective view of an example branched flow path.

[0036] Fig. 14 is a perspective view of an example flat spiral flow path. Fig. 15 is a perspective view of an example conical helix flow path.

[0037] Fig. 16 is a perspective view of an example flow path that morphs from one cross- sectional shape to another cross-sectional shape.

[0038] Fig. 17 is a perspective view of an example of electrostatic attraction to the substrate.

[0039] Fig. 18 is a perspective view of a second example of electrostatic attraction of suspended matter to the substrate.

[0040] V. Description of an Embodiment

[0041] The present invention is an inertial filter for separation of a suspended matter from a stream of a fluid. An example inertial filter is shown by Fig. 1. As shown by Fig. 1, the suspended matter, which may be a solid particulate matter, liquid droplets or a combination of solid particulate matter and liquid droplets, is carried by the fluid, which may be a gas or liquid. The inertial filter is comprised of a substrate that has a front side and a back side and is penetrated by perforations that communicate between the front side and the back side. The substrate defines perforation walls that define flow paths through the substrate.

[0042] From Fig. 1, the perforation walls of each perforation define at least one change in direction of the flow path as the fluid and suspended matter flow through each perforation. As the stream of fluid changes direction within the flow path, the inertia of the suspended matter causes the suspended matter to resist the change in flow path direction, which may cause the suspended matter to contact the perforation walls. The substrate may be composed of either an absorbent material or a non-absorbent, non-porous material. An absorbent substrate may absorb suspended matter that contacts the walls by capillary action. Suspended matter that contacts a non-absorbent wall may adhere to the wall by adhesive (wetting) forces, electrostatic forces or by van der Waals forces.

[0043] From Figs. 2 through 9, the inertial filter of the Invention may include drainage channels to remove the captured liquid droplets and particulate matter from the substrate. The substrate defines a substrate perimeter and defines a substrate thickness between the front side and the back side of the substrate. A plurality of drainage channels are disposed within the substrate. Each drainage channel has a length, a width and a thickness. The thickness of each drainage channel is small compared to the length and width. The thickness of each drainage channel is aligned with the thickness of the substrate and the length and width of each drainage channel is generally parallel to the front side or the back side of the substrate. As shown by Figs. 2, 3 and 5, the length and width of each drainage channel may extend to the substrate perimeter. As shown particularly by Fig. 4, the perforations may penetrate the plurality of drainage channels.

[0044] From Fig. 4, the substrate, and hence the drainage channels and the perforations, may be a unitary, monolithic structure comprising a single piece, such as a monolithic structure created by additive manufacturing, an example of which is 3D printing. Alternatively, and as shown by schematic Figs. 6, 7 and 8, the substrate may be a composite structure composed of a plurality of substrate layers laid one on another.

[0045] From Fig. 6, one or more of a plurality of layers of the substrate may be stacked with a separation distance thereinbetween. The separation distance, where present, between two adjacent layers defines a drainage channel. In the example of Fig. 6, the separation distance between adjacent layers is maintained by a plurality of spacers disposed between the adjacent layers of the substrate to form a plurality of drainage channels. As shown by Fig. 6, the perforation, and hence the flow path of the fluid with the suspended matter, may penetrate the plurality of drainage channels.

[0046] Fig. 7 is a second example of one or more of a plurality of layers of the substrate that may be stacked with a separation distance thereinbetween to define one or more drainage channels. In the example of Fig. 7, the surface of each layer defines one or more dimples that stand proud of the surface of the layers. The dimples cause the separation of the adjacent layers that defines the one or more drainage channels. As shown by Fig. 6, the perforations penetrate the drainage channels.

[0047] Fig. 8 is a third example of one or more layers of the substrate that may be stacked to create the drainage channels. In the example of Fig. 8, a portion of a surface of one or more layers of the substrate is removed, as by cutting or etching. The resulting relief of each stacked layer defines the drainage channel. In the example of Fig. 8, the perforations do not penetrate the drainage channels.

[0048] From Fig. 9, the inertial filter may be oriented to assist in drainage of the captured suspended matter by the force of gravity. The front side and back side of the substrate may be oriented generally in a vertical direction. The pull of gravity will then pull captured liquid from the filter. The inertial filter also may utilize a blower or a pump to remove captured liquid from the substrate.

[0049] Also from Fig. 9, the inertial filter may utilize a wash liquid to remove the captured liquid and captured particulate matter from the substrate. The liquid wash may be introduced at the top of the substrate and flow through the vertically-oriented drainage channels to entrain and remove the particulate matter and captured liquid from the substrate.

[0050] From Figs. 10, and 12 through 15, the change in direction of the perforation may be any suitable shape. Fig. 10 illustrates that any change in direction of the flow path may cause the suspended matter in a stream of fluid to contact the walls of the perforation due to inertia acting on the suspended matter. Fig. 12 illustrates that the perforation may be tapered with a reducing cross-sectional area as the perforation advances from the front side to the back side. The reducing cross section area of the perforation causes an increase in the velocity of the stream of fluid and hence an increase in the inertial forces acting on the suspended matter as a result of a change in direction of the stream of fluid. For a given change in direction, the tapered perforation allows perforation proximal to the first side to collect relatively larger, heavier suspended matter and the perforation proximal to the second side to collect smaller, lighter suspended matter.

[0051] Fig. 13 shows a primary perforation that branches into two or more secondary perforations. Each of the secondary perforations has a smaller cross sectional area than the primary perforation. The smaller cross sectional areas of the secondary perforations allows the secondary perforations to undergo changes of direction with smaller radii of curvature and with increased surface area compared to the larger primary perforations and allows the secondary perforations to collect smaller and lighter suspended matter than the primary perforation.

[0052] Fig. 14 shows a perforation in the shape of a flat spiral with a decreasing radius of curvature as a stream of fluid progresses from the front side to the back side. For a constant cross sectional area and hence a constant flow velocity through the perforation, the inertial forces acting on the suspended matter increase as the stream of fluid progresses. Larger, heavier suspended matter is collected proximal to the first side and smaller, lighter suspended matter is collected toward the back side.

[0053] Fig. 15 shows a perforation in the shape of a conical helix. The conical helix also has a decreasing radius of curvature as the perforation extends from the front side toward the back side. As for the flat spiral of Fig. 14, and for a constant cross-sectional area of the perforation, the decreasing radius of curvature causes increased inertial forces on the suspended matter as the suspended matter progresses from the front side to the back side. The result is that larger, heavier suspended matter is collected proximal to the front side and smaller, lighter suspended matter is collected proximal to the back side. Figs. 11 and 16 illustrate that the cross-sectional shape of the perforation may be any shape. A circle is the cross-sectional shape having the smallest circumference for any given cross-sectional area and that also results in the the smallest perforation surface area for a given cross-sectional area. A larger perforation surface area for a given cross-sectional area provides more perforation wall area with which suspended matter may collide and therefore improved suspended matter collection. The Invention contemplates that at least a part of the perforation may have a surface area greater than what its surface area would be if the cross sectional area of the perforation was a circle.

[0054] Fig. 16 shows that the cross-sectional shape may morph from a first shape to a second or even a third or fourth shape over the length of the perforation. For example, and as shown by Fig. 16, the cross-sectional shape may start as a circle at the front side and may morph into a triangle (or any other shape, for example a star shape) at the back side. For a given cross- sectional area, the triangle has a larger circumference, and hence larger surface area than a circle. If the cross-sectional areas are the same for the circle and the triangle, the velocity of the fluid will be the same; however, for a given change in direction the circular cross section portion of the perforation will collect larger and heavier suspended matter and the triangular (or other) -shaped portion of the perforation will collect smaller and lighter suspended matter.

[0055] Of course, any of the foregoing configurations for the perforation may be combined as needed for a particular fluid stream, particular suspended matter, and particular application.

[0056] Figs. 17 and 18 illustrate that the inertial filter may include electrostatic precipitation to augment the inertial filter. The substrate may be provided an electrostatic charge by an electrode, shown by Fig. 17. Alternatively, where the inertial filter is to be used in low humidity applications, the material from which the substrate is composed may be selected from polyester, nylon, rubber, or other electrical insulators that will acquire a static charge from friction from the fluid flowing through the filter. As a second alternative, the substrate may be composed of an electret material that is given an electrostatic charge during manufacture. For each alternative, the incoming suspended matter may be provided with an opposite static charge by an electrode, shown by Fig. 17. Electrostatic attraction causes the charged particles of the suspended matter to be attracted to and adhere to the walls of the perforation, shown by Fig. 18, augmenting the inertial effects. Electrostatic attraction is particularly effective for the collection of very small and light particles of the suspended matter. The inertial filter may be used in a variety of applications. These include:

[0057] General liquid-gas chemical operations using chemically active sprays to capture gaseous species from air, including water vapor, alcohols, CO2, NOX, SOX, H2S, formaldehyde, volatile organic compounds, chlorides, fluorides, and others.

[0058] A water vapor capture device may be implemented in an HVAC (heating, ventilation, & air conditioning) system to reduce latent loads.

[0059] A particle capture device enabled by liquid sprays and multiplexed inertial coalescence filters may be used in HVAC filtration and other filtration systems.

[0060] A particle capture device enabled by liquid sprays and the inertial filter filters may be used as a standalone filtration device.

[0061] The material composition of the inertial filter may be engineered to embed chemically active substances in the substrate. These substances may be capable of promoting a variety of liquid-solid reactions directly at the substrate surface, enabling new capabilities. By incorporating, for example, catalytic materials or reactive compounds into the filter matrix, the inertial filters can facilitate high-temperature reactions, such as catalytic oxidation or thermal decomposition processes, as well as low-temperature reactions, like adsorption or surface catalysis.

[0062] A liquid-gas spray reactor using an inertial filter that is designed for CO2 capture, wet gas filtration (water vapor filtration), and sour gas filtration (H2S filtration).

[0063] A liquid-gas spray reactor using an inertial filter that is designed for pathogen capture and inactivation, including viruses, bacteria, fungus, mold, etc.

[0064] An inertial filter used in liquid-solid filtration, for example, lithium and bromine filtration out of brines. Centrifugal forces in the multiplexed inertial coalescence filters may increase precipitation rates for lithium and bromine from solution.

Claims

CLAIMSWhat is claimed is:Claim 1. A filter for separating a suspended matter from a fluid, the suspended matter being a solid particulate matter, a liquid droplet, or a combination of a solid particulate matter and a liquid droplet, the fluid being a gas or a liquid, the filter comprising: a) a substrate, the substrate having a front side and an opposing back side; b) a perforation communicating between the front side and the back side, wherein when the front side and the back side are both immersed in the fluid and the front side is exposed to a pressure of the fluid that is greater than the pressure of the fluid on the back side, a stream of the fluid will flow from the front side to the back side along a flow path defined by the perforation, the perforation having a perforation wall defined by the substrate; c) at least one change in direction of the flow path defined by the perforation wherein an inertia of the suspended matter urges the suspended matter toward the perforation wall as the stream of the fluid moves through the at least one change in direction; d) a plurality of drainage channels defined by the substate, each of the drainage channels having a drainage channel length, width, and thickness, the drainage channel thickness being small compared to the drainage channel length and width, the drainage channel length and width being generally parallel to the substrate front side or substrate back side, the substrate defining a substrate perimeter, the length and width of each of the plurality of drainage channels extending substantially to the substrate perimeter.Claim 2. The inertial filter of claim 1 wherein the flow path intersects each of the plurality of drainage channels.Claim 3. The filter of claim 2 wherein the substrate length or width is oriented so that a liquid will drain through the plurality of drainage channels under a force of gravity when thefluid is passing through the filter and the filter is separating the suspended matter from the fluid.Claim 4. The filter of claim 3, the filter further comprising: a wash liquid, the substrate being configured so that the wash liquid introduced to the substrate will flow through the drainage channels and will exit the substrate while carrying the suspended matter with the wash liquid.Claim 5. The filter of claim 4 wherein the configuration of the substrate is such that the wash liquid will flow through the drainage channels comprising: the substrate being oriented so that when the fluid is flowing through the perforation from the front side to the back side, the front side and the back side have a generally vertical orientation and the drainage channel length or width has the generally vertical orientation.Claim 6. The filter of claim 2 wherein the substrate is a monolith.Claim 7. The filter of claim 2 wherein the substrate is composed of a plurality of layers, each of the plurality of layers being separated from another of the plurality of layers by a separation, the separation defining a one of the plurality of drainage channels.Claim 8. The filter of claim 7 further comprising: a plurality of spacers disposed between the plurality of layers, the plurality of spacers maintaining the separation between each of the plurality of layers and another layer, wherein the plurality of spacers maintain the plurality of drainage channels.Claim 9. The filter of claim 7 further comprising: a plurality of dimples defined by a surface of each of the plurality of layers, each of the plurality of dimples being proud of the surface of the corresponding layer, wherein the plurality of dimples maintain the separation between each of the plurality of layers and another layer, wherein the dimples maintain the plurality of drainage channels.Claim 10. The filter of claim 7 wherein a surface of each of the plurality of layers is etched or cut to define a relief, the relief defining the separation.Claim 11. The filter of claim 2 wherein at the substrate is porous and configured to absorb the liquid.Claim 12. The filter of claim 2 wherein at least some substrate is non-absorbent and not configured to absorb the liquid.Claim 13. The filter of claim 1 wherein the perforation wall defines a cross-sectional area of the perforation normal to the flow path at each location along the flow path from the front side to the back side, the cross-sectional area being tapered for at least a portion of the flow path from the front side to the back side wherein the cross-sectional area of the perforation wall normal to the flow path proximal to the front side is greater that the cross sectional area normal to the flow path proximal to the back side so that a velocity of the fluid increases as the fluid flows from the front side to the back side through the tapered portion of the perforation.Claim 14. The filter of claim 1 wherein the perforation wall defines a cross-sectional shape normal to the flow path at a location along the flow path from the front side to the back side, the perforation wall defining an actual cross-sectional circumference and an actual cross-sectional area at the location, wherein a reference circle having a reference circle area equal to the actual cross-sectional area at the location has a reference circle circumference, and wherein the actual cross-sectional circumference at the location is greater than the reference circle circumference.Claim 15. The filter of claim 14 wherein the location along the flow path is a first location and the cross-sectional shapes is a first cross-sectional shape and wherein the perforation wall defines a second cross-sectional shape at a second location, wherein the stream of the fluid flows through the perforation at the first location before flowing through the second location when the fluid flows from the front wall to the back wall, and wherein the actual cross-sectional circumference of the first cross-sectional shape is less than the actual cross-sectional circumference of the second cross-sectional shape.Claim 16. The filter of claim 15 wherein the cross sectional area of the perforation at the first location is substantially equal to the cross sectional area of the perforation at the second location.Claim 17. The filter of claim 1 wherein the at least one change in direction comprising: a radius of curvature defined by at least a portion of the flow path, the radius of curvaturedecreasing between the front side and the back side so that at least the portion of the flow path defines a spiral.Claim 18. The filter of claim 17 wherein the spiral defines a conical helix.Claim 19. The filter of claim 17 wherein the spiral is a flat spiral.Claim 20. The filter of claim 1 wherein the perforation at the front wall is a primary perforation that branches into two or more secondary perforations at a branch location intermediate to the front side and the back side, the secondary perforations communicating between the branch location and the back wall, and wherein the flow path extends from the front wall through the primary perforation to the branch location and from the branch location to the back wall through the secondary perforations, the primary perforation having a primary perforation cross-sectional area normal to the flow path in the primary perforation, each secondary perforation having a secondary perforation cross-sectional area normal to the flow path in each of the secondary perforations, the primary perforation cross-sectional area being greater than the secondary perforation cross-sectional area.Claim 21. The filter of claim 1 wherein the substrate has a first electrostatic charge when the fluid flows through the perforation, the suspended matter having an opposite second electrostatic charge, wherein the suspended matter is electrostatically attracted to the filter.Claim 22. The filter of claim 21 wherein the first electrostatic charge is applied to the filter by a first electrode and the opposite second electrostatic charge is applied to the suspended matter by a second electrode.Claim 23. The filter of claim 21 wherein the substrate is a composed of an electret material having the first electrostatic charge, the filter further comprising: an electrode configured to apply the second electrostatic charge to the suspended matter.

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