BACKGROUND

[0001] When designing an air filter, it is generally preferred for the face of the filter to be normal to the direction of airflow.

SUMMARY

[0002] When a filter is designed to be used in a predetermined volume, it may be impractical to orient the filter so that the face of the filter is normal to the direction of airflow. Inability to orient the face of the filter to be normal to the direction of airflow may result in any or all of efficiency, life, or pressure loss of the filter being inadequate. WO 2020/060981 is an example of a device that includes a filter designed to be used in a predetermined volume.

[0003] Also, a single type of filtration media (e.g., one of a fibrous media or carbon media) may not provide filtration that can adequately filter all of the potential contaminants from an air source. Gas and debris generated from a laser etching or cutting process, such as could be generated by the device disclosed in WO 2020/060981, may be difficult to filter adequately using only one of a fibrous media or a carbon media.

[0004] At least one embodiment disclosed in the present application solves one or more of these problems.

[0005] A filter assembly comprises a housing with an inlet and an outlet; a pleated filter within the housing, the pleated filter including an upstream face; and a carbon filter within the housing. The inlet and the outlet respectively define an inlet direction and an outlet direction that are parallel but opposite. The pleated filter is upstream of the carbon filter. The upstream face is transverse to the inlet direction.

[0006] The housing may include an internal flow path that is J-shaped.

[0007] The housing may include an internal flow path where flow direction reverses between the pleated filter and the carbon filter.

[0008] A cross-sectional area of a flow path between a downstream face of the pleated filter and an upstream face of the carbon filter may increase toward the upstream face of the carbon filter. The flow path may be configured so that flow direction changes from the inlet direction to the outlet direction between the pleated filter and the carbon filter.

[0009] An angle between the upstream face and the inlet direction may be 175°.

[0010] An angle between a downstream face of the pleated filter and the inlet direction may be 5°. [0011] The pleated filter may include a downstream face parallel to the upstream face, the housing may include an interior passage with parallel walls, the upstream face and the downstream face may be between the parallel walls, and a first distance normal to and between the upstream face and the downstream face may be 60% to 80% of a second distance normal to and between the parallel walls.

[0012] An outlet face of the carbon filter may be normal to the outlet direction, and an inlet face of the carbon filter may be normal to the outlet direction.

[0013] Flow through the housing between the inlet and the pleated filter is along the inlet direction, and flow through the housing immediately after the pleated filter is along the inlet direction.

[0014] The housing has a first side at the inlet and a second side opposite the inlet, and the outlet may be offset from the inlet toward the second side.

[0015] The inlet and the outlet may be parallel.

[0016] An area of the outlet may be three to five times, preferably 4.2 times, that of an area of the flow passage normal to the inlet direction at a most upstream edge of the pleated filter.

[0017] An area of the upstream face may be eleven to twelve times that of an area of the flow passage normal to the inlet direction at a most upstream edge of the pleated filter.

[0018] Other aspects, features, and advantages of this technology will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of this technology.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Fig. 1 illustrates a bottom perspective view of a filter assembly.

[0020] Fig. 2 illustrates an exploded view of a filter assembly.

[0021] Fig. 3 illustrates an exploded view of a filter assembly.

[0022] Fig. 4 illustrates a cross-section including a flow path of a filter assembly.

[0023] Fig. 5 illustrates a side view of a filter assembly.

[0024] Fig. 6 illustrates a front view of a filter assembly.

[0025] Fig. 7 illustrates a rear view of a filter assembly.

[0026] Fig. 8 illustrates a bottom view of a filter assembly.

[0027] Fig. 9 illustrates a partial cross-section with an alternative orientation of a pleated filter. DETAILED DESCRIPTION OF EMBODIMENTS

[0028] The following description is provided in relation to several examples which may share common characteristics and features. It is to be understood that one or more features of any one example may be combinable with one or more features of the other examples. In addition, any single feature or combination of features in any of the examples may constitute additional examples.

[0029] Fig. 1 is a bottom perspective view of a filter assembly 100 with a case 105 that includes an inlet 110 and an outlet 115. From two opposite sides, the case 105 can be characterized as having an L-shaped profile. From all other sides, profile of the case 105 is substantially rectangular. Through the inlet 110, a side of a pleated filter 120 (e.g., a first filter) is visible. The outlet 115 is illustrated with a grid or course mesh. The case 105 has a first side at the inlet 110 and a second side opposite the inlet (see, e.g., Fig. 4), and the outlet 115 is offset from the inlet 110 toward the second side. The inlet 110 and the outlet 115 may be characterized as parallel planes.

[0030] Fig. 2 is also a bottom perspective view but the case 105 is illustrated separated into two halves 105 A and 105B. Most of the pleated filter 120 and a carbon filter 125 (e.g., a second filter) are visible. As will be discussed further below, the pleats of the pleated filter are not arranged to face the inlet 110. As is evidence from this and other figures, both the pleated filter 120 and the carbon filter 125 have overall envelopes that are rectangular prisms, but the two overall envelopes are different.

[0031] Fig. 3 is a further bottom perspective view but various components are separated in an exploded view. The most significant differences in this view are that the elements of the carbon filter 125 are separated and less of the pleated filter 120 is obscured compared to Fig. 2.

[0032] The carbon filter 125 includes carbon media 130, which is illustrated as a solid rectangular prism for simplicity. The prism is representative of container walls as well as media; however, it will be appreciated that the carbon media 130 may be in a granular or pellet form. Two grates 135 A, 135B, along with pass-through media 140, provide retention of the carbon media 130. Note that only one pass-through media 140 is illustrated, but preferably one pass-through media is associated with each of the grates 135A, 135B. The pass-through media allows gas (and contaminants) to pass through while retaining the carbon media 130 and thus may be a fibrous media, either woven or non-woven, that readily allows gas to pass there through while retaining the carbon media 130. If the carbon media 130 is somehow retained together (e.g., fused or sintered) instead of being in particle or pellet form, the pass-through media 140 and/or the grates 135A, 135B may be omitted.

[0033] Fig. 4 is a cross-section that illustrates the relative positions of the pleated filter 120 and carbon filter 125 within the case 105 as well as a simplified representation of flow represented by arrows. Gas to be filtered enters the case 105 substantially normal to the inlet 110 and then enters an upstream face 120 A of the pleated filter 120 and exits a downstream face 120B. The upstream face 120 A is an imaginary surface corresponding to where a flat surface could rest on the upper folds of the pleated filter 120 in this figure. Similarly, the downstream face 120B is an imaginary surface corresponding to where the lower folds would rest on a surface. The flow immediately before and immediately after the pleated filter is along the inlet direction.

[0034] It will be appreciated that flow through the pleated filter 120 is more complex than the simplified representation. The simplified representation through the filter may be characterized as the desired direction of flow instead of an accurate model.

[0035] The pleated filter 120 is oriented so that the angle between the upstream face 120A and the inlet direction is 175°. Thus the downstream face 120B is also at a 175° angle with respect to the inlet direction. The walls adjacent to the upstream face 120A and the downstream face 120B are parallel to the inlet direction. Thus an included angle between the faces and the walls is about 5° and could be decreased to about 3° (however, turbulence may be noticeably greater at about 4°). Larger angles are preferable when the volume of the filter is not predetermined, but here the angle between the upstream face 120A and the inlet direction minimizes turbulent flow and minimizes pressure drop. If, for example, the angle were zero (i.e., parallel to the inlet direction), additional space between the inlet face 120A and the adjacent wall would be required to allow flow to equalize across the inlet face 120 A. If the upstream face 120 A were oriented parallel to the inlet 110, the filter could be much thicker (i.e., taller pleats) but this would result in greater pressure loss through the pleated filter 120. Also, taller pleats would require a reduction in pleat density and result in lower effective surface area of the filtration media. Alternatively, shorter pleats could be used if the angle were zero, but shorter pleats would decrease filtration capacity.

[0036] With all of the elements of the filter assembly 100, including the size, material and orientation of the filter, the face velocity of flow entering the upstream face 120A is below 5.33 cm/sec with a flow rate of about 18 cubic feet of air per minute (cfm) flowing through the filter assembly 100. The total surface area of the media for the pleated filter is about 250 square inches and the material is suitable for a HEPA filter. The height of the pleats is 1.063 inches (e.g., about one inch) and the distance between walls adjacent to the pleats is 1.56 inches (e.g. about 1.5 inches). Thus the distance normal to and between the upstream face 120A and the downstream face 120B is 68% of the distance normal to and between the parallel walls, but these distances may be changed varied between 60% and 80%, more preferably 65% to 75% and most preferably 68%. With these parameters, the volume upstream of the upstream face 120 A and the volume downstream of the downstream face 120B function as an inlet and outlet plenum sufficient to nominalize the flow on both sides of the filtration media guaranteeing utilization of the entire pleated media surface.

[0037] For the most effective filtration, the periphery of the pleated filter 120 should be sealed so that gas does not flow around the pleated filter 120 (e.g., around the perimeter of the upstream face 120A and past the perimeter of the downstream face 120B) but instead is forced through the media of the pleated filter 120. Any sealing process may be used, but this configuration may be particularly suited to an encapsulating (potting and/or gluing) process. The media is a sheet of material (e.g., a laminate) that has limited resistance to force before it collapses. Sealing the edge using encapsulation may preclude collapsing the media, preserving the pleated structure and providing the greatest possible tolerance window for assembly. Media encapsulation of this type is most convenient when the surface where the encapsulating material is applied is horizontal because commonly used encapsulating material (e.g., adhesive such a hot melt adhesive, a polyurethane adhesive or an acrylic adhesive) is low and the encapsulating material should encapsulate the entire series of pleat ends. To facilitate this method, the case 105 includes two halves 105 A and 105B with a split longitudinally along the central axis. One of the halves 105 A and 105B can have the encapsulating material applied and the ends of the pleats can be pressed downward against the encapsulating material. After an appropriate amount of time for the encapsulating material to cure, the process can be repeated for the other half. The halves 105 A and 105B may include dovetail bosses 160 and corresponding grooves 165 oriented parallel to the assembly direction to facilitate alignment (see, e.g., Fig. 3).

[0038] After exiting the downstream face 120B the flow continues along, or parallel to, the inlet direction and then encounters a U-turn 145 within the case 105 that results in the flow being substantially normal to the outlet 115 as the flow passes through the carbon filter 125. Thus considering Fig. 4, the flow passage may be characterized as U-shaped or J-shaped where the flow direction reverses between the pleated filter 120 and the carbon filter 125. The U-turn 145 includes a relative expansion of the cross-sectional area of the flow path between a downstream face 120B of the pleated filter 120 and an upstream face of the carbon filter 125 (and thus acts as a plenum or expansion volume), which reduces flow velocity and ensures that the flow velocity is substantially equal across the upstream face of the carbon filter 125 (e.g., the grate 135B). Thus the flow path is configured so that flow direction changes from the inlet direction to the outlet direction between the pleated filter 120 and the carbon filter 125. As the flow begins to enter the carbon media 130, contaminant gases create a flow front with a large difference between the contaminant gas density upstream of the flow front and downstream of the flow front (e.g., an isotherm).

[0039] The shape and volume of the carbon media 130 is chosen so that, the isotherm moves through the carbon, the interaction of contaminants and the carbon media 135 are maximized and the contaminants move uniformly through the carbon media 135, so all the carbon media 135 is utilized. About 245 cubic centimeters are available for the carbon media. The specific type of carbon media 135 should be chosen based upon contaminants to be filtered. For example, carbon is particularly well suited for removing organic vapors (e.g., 12x20 mesh high activity Organic Vapor carbon). If carbon dioxide needs to be filtered, Hopcolite may be used. A formaldehyde carbon can be included to filter contaminants caused by using a laser on plastics such as acetal plastics. More than one, or all, of the types of carbon media 135 may be included if the contaminants are unknown or variable.

[0040] In the pleated filter 120, extra filtration media enhances particulate filter life providing more surface area to accumulate particulates. However, the carbon media functions, and is chosen, differently. The volume of carbon media 130 is preferably chosen to control the adsorption of gas from the air-stream. As gas contaminants enter the carbon a concentration differential is created between where the contaminated gas contacts the carbon media 130 and where the contaminated gas has not contacted the carbon media 130. The volume of the carbon media 130 is preferably designed to maximize the efficiency of the gas exchange and provide as much filter life as possible within the space constraints of the case. Unlike the pleated filter 120 where surface area is a primary design factor, the time in which the contaminated gas contacts the carbon media 130 (e.g., increasing the kinetic potential of the gas flowing across the carbon particles) is a primary factor in designing the volume (i.e., size and shape) of the carbon media.

[0041] After the pleated filter 120 is installed as described above, the carbon media 135 can be filled on top of the grate 135B and the pass-through media 140 using known filling methods. A second pass-through media 140 and the grate 135 A are then placed to retain the carbon media 130. [0042] Fig. 5 is a side view of the filter assembly 100, which illustrates the generally L-shaped profile. The offset between the inlet 110 and outlet 115 are apparent.

[0043] Fig. 6 is front view which shows the relative size and shape of the inlet 110 and the outlet 115. Due to the orientation of the pleated filter, the effective area of the flow passage is an area of the flow passage normal to the inlet direction at a most upstream edge of the pleated filter (see, e.g., Fig. 4), which approximately corresponds to the area of dense lines toward the top of Fig. 6. The area of the outlet 115 is larger than the area of the flow passage normal to the inlet direction at the most upstream edge of the pleated filter, preferably three to five times that of the area of the flow passage normal to the inlet direction at the most upstream edge of the pleated filter. As illustrated, the area of the outlet is about 4.2 times that of the area of the flow passage normal to the inlet direction at the most upstream edge of the pleated filter. However, as is apparent at least from Fig. 4, the area of the upstream face 120A is considerably larger than the area of the flow passage normal to the inlet direction at the most upstream edge of the pleated filter. As illustrated, the area of the upstream face 120A is about eleven to twelve (e.g., 11.5) times that of the area of the flow passage normal to the inlet direction at the most upstream edge of the pleated filter. This allows velocity through the filter to be sufficiently low (e.g, below 5.33 cm/sec) for adequate filtration while also allowing for the flow passage for the pleated filter to be in a condensed space as compared to conventional techniques where the upstream face 120 A would be oriented normal to the flow direction.

[0044] Fig. 7 is a rear view in which a handle 150, in the form of a rectangular recess, is illustrated. The depth of the handle 150 is illustrated in Fig. 4.

[0045] Fig. 8 is a bottom view in which a retention feature 155 is visible. The retention feature 155 includes two cantilevered projections with lobes at the end to engage with recesses in the corresponding receptacle (not shown).

[0046] Fig. 9 is a partial cross-section view corresponding to a portion of Fig. 4. The pleated filter 120 is oriented in a manner that is a mirror image (about the inlet direction) of Fig. 4.

[0047] With at least one embodiment of the present technology, a combination of a pleated filter and a carbon filter can be provided in a compact space with a relatively small volume of carbon media while minimizing loss through the pleated filter and maximizing efficiency of the pleated filter and carbon media.

[0048] While the present technology has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the present technology is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.