AIR PURIFIER

Abstract

An air purifier system characterized by a housing, a fan, and a motor, as well as a docking ring located at the outer edge of the inlet side of the air purifier system, a seat below the housing, a prefilter or barrier upstream of the fan, and a filter downstream of the fan. An air purifier system characterized by an upstream-to-downstream airflow path that includes an axial fan, a diffuser, and a filter, in that relative order, with an electric motor held along the centerline of the housing by one or more supports and/or guide vanes. A docking ring that facilitates attachment of a screen-like, mesh-like, cloth-like, or paper-like filter to a machine capable of air purification, characterized by having a large hole through which air passes and by attachment to the machine utilizing any tongue and groove system, for which installation and removal of the docking ring is achieved, in whole or in part, by rotation of said docking ring relative to the machine.

Claims

1. (canceled)

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4. (canceled)

5. (canceled)

6. (canceled)

7. (canceled)

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9. (canceled)

10. (canceled)

11. (canceled)

12. (canceled)

13. (canceled)

14. (canceled)

15. (canceled)

16. (canceled)

17. (canceled)

18. (canceled)

19. (canceled)

20. (canceled)

21. An air purifier system, the air purifier system comprising: (a) a housing; (b) an axial fan; (c) a motor; (d) a prefilter; (e) a filter; (f) a docking ring; and (g) a seat; (h) where the prefilter is located upstream of the axial fan, (i) where the filter is located downstream of the axial fan, (j) where the axial fan is placed inside the housing, (k) where the seat rests below the housing.

22. The air purifier system according to claim 21, (a) the air purifier system further comprising: (i) a plurality of motor supports; and (b) wherein the motor comprises: (i) an output shaft; (c) where the axial fan is mounted on the output shaft of the motor, (d) where the motor supports attach the motor to the housing, (e) where the motor supports hold the motor along the centerline of the housing.

23. The air purifier system according to claim 21, (a) the air purifier system further comprising: (i) a plurality of guide vanes; and (b) wherein the motor comprises: (i) an output shaft; (c) where the axial fan is mounted on the output shaft of the motor, (d) where the guide vanes attach the motor to the housing, (e) where the guide vanes hold the motor along the centerline of the housing.

24. The air purifier system according to claim 21, the air purifier system further comprising: (a) a filter housing, the filter housing comprising: (i) a lid; and (ii) a groove; (b) where the filter housing is located downstream of the axial fan, (c) where the filter slides into the filter housing and is held in-place by the filter housing groove.

25. The air purifier system according to claim 21, the air purifier system further comprising: (a) a filter housing, the filter housing comprising: (i) a first filter housing part; (ii) a second filter housing part; and (iii) at least one snap; (b) where the first filter housing part and the second housing part are held together by the at least one snap, (c) where the filter is held in-place between the first filter housing part and the second housing part, (d) where the filter housing is located downstream of the axial fan.

26. The air purifier system according to claim 21, the air purifier system further comprising: (a) a diffuser; (b) where the diffuser is located between the housing and the filter.

27. The air purifier system according to claim 21, the air purifier system further comprising: (a) a horn-shaped inlet; (b) where the horn shaped inlet is located downstream of the docking ring, (c) where the prefilter is held between the docking ring and the horn-shaped inlet.

28. The air purifier system according to claim 24, the air purifier system further comprising: (a) a safety cage; (b) where the safety cage slides into the filter housing and is held in-place by the filter housing groove.

29. The air purifier system according to claim 21, the air purifier system further comprising: (a) a carry handle; (b) where the carry handle is located above the housing.

30. An improved air purifier system, the improved air purifier system comprising: (a) a housing; (b) an axial fan, comprising: (i) a plurality of fan blades; (c) a tapered diffuser; (d) a filter; (e) a motor; (f) a plurality of guide vanes; (g) a filter housing; and (h) a seat; (i) where the diffuser is located between the housing and the filter, (j) where the filter is located downstream of the axial fan, (k) where the motor is held along the centerline of the housing, (l) where the filter housing is located downstream of the axial fan, (m) where the seat rests below the housing.

31. The improved air purifier system according to claim 30, the improved air purifier system further comprising: (a) a motor cover, comprising: (i) an open-end; and (ii) a closed end, comprising: (1) air vents; and (b) wherein the axial fan further comprises: (i) a hub dome, comprising: (1) hub beams; (2) hub sidewalls; and (3) air vents; (c) where the motor cover has a continuous surface of continuous slope, (d) where the open-end of the motor cover is attached to the guide vanes.

32. The improved air purifier system according to claim 30, the improved air purifier system further comprising: (a) a prefilter or a barrier; (b) where the prefilter or the barrier is located upstream of the axial fan.

33. The improved air purifier system according to claim 30, wherein the filter housing comprises: (a) a lid; and (b) a groove; (c) where the filter slides into the filter housing and is held in-place by the filter housing groove.

34. The improved air purifier system according to claim 30, wherein the filter housing comprises: (a) a first filter housing part; (b) a second filter housing part; and (c) at least one snap; (d) where the first filter housing part and the second housing part are held together by the at least one snap, (e) where the filter is held in-place between the first filter housing part and the second housing part.

35. The improved air purifier system according to claim 30, (a) where the filter is made from pleated filter paper or pleated cloth.

36. The improved air purifier system according to claim 30, the improved air purifier system further comprising: (a) a docking ring; (b) where the docking ring is connected to the housing.

37. The improved air purifier system according to claim 36, the improved air purifier system further comprising: (a) a horn-shaped inlet; (b) where the prefilter is held between the docking ring and the horn-shaped inlet.

38. The improved air purifier system according to claim 30, the improved air purifier system further comprising: (a) at least one height and tilt adjuster; (b) where the at least one height and tilt adjuster is connected to the seat.

39. An improved docking ring, comprising: (a) a plurality of grooves; (b) an inner surface; (c) where the improved docking ring grooves are located on the inner surface of the improved docking ring.

40. The improved docking ring according to claim 39, further comprising: (a) a plurality of slots; (b) where the improved docking ring slots are located on the inner surface of the improved docking ring.

41. The improved docking ring according to claim 39, (a) where the improved docking ring has substantially annular shape.

42. The improved air purifier system according to claim 30, the improved air purifier system further comprising: (a) a docking ring, comprising: (i) a plurality of grooves; and (ii) an inner surface; and (b) a horn-shaped inlet, comprising: (i) a plurality of tongues; and (ii) an outer surface; (c) where the horn-shaped inlet tongues are located on the outer surface of the horn-shaped inlet, (d) where the docking ring grooves are located on the inner surface of the docking ring, (e) where the horn shaped inlet is located downstream of the docking ring, (f) where the docking ring grooves lock into the horn-shaped inlet tongues, (g) where the horn-shaped inlet is connected to the housing.

43. The improved air purifier system according to claim 42, (a) wherein the horn-shaped inlet further comprises: (i) a plurality of protruding parts; and (b) wherein the docking ring further comprises: (i) a plurality of slots; (c) where the horn-shaped inlet protruding parts are located on the outer surface of the horn-shaped inlet, (d) where the docking ring slots are located on the inner surface of the docking ring, (e) where the horn-shaped inlet protruding parts snap into the docking ring slots.

44. An advanced air purifier system, the advanced air purifier system comprising: (a) a housing; (b) an axial fan, comprising: (i) a plurality of fan blades; (c) a tapered diffuser; (d) a filter; (e) a motor; (f) a plurality of motor supports; (g) a filter housing; and (h) a seat; (i) where the filter housing is located downstream of the axial fan, (j) where the motor is held along the centerline of the housing, (k) where the filter is located downstream of the axial fan, (l) where the diffuser is located between the housing and the filter, (m) where the seat rests below the housing.

45. The advanced air purifier system according to claim 44, wherein each fan blade comprises: (a) a leading edge; (b) a trailing edge; (c) a root; (d) a tip; and (e) a plurality of cylindrical airfoils; (f) where the planar projection of each fan blade leading edge is parabolic, (g) where the planar projection of each fan blade trailing edge is parabolic, (h) where the planar projection of each fan blade root is semi-circular, (i) where the planar projection of each fan blade tip is semi-circular, (j) where each cylindrical airfoil has a camber-line that is a parabola projected onto a cylindrical surface.

46. The advanced air purifier system according to claim 45, wherein each fan blade further comprises: (a) a thickness; (b) where the thickness of each fan blade is constant in the circumferential direction, (c) where the thickness of each fan blade is linearly-tapered in the radial direction.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0026] FIG. 1 is a schematic drawing of a simple embodiment of the air purifier system in an exploded perspective view.

[0027] FIG. 2 depicts the previous embodiment in an assembled perspective view.

[0028] FIG. 3 is a schematic drawing of the fan, motor, motor cover, and guide vane assembly in an exploded perspective view.

[0029] FIG. 4 is an assembled version of FIG. 3.

[0030] FIG. 5 is an inlet-side schematic drawing of the fan.

[0031] FIG. 6 is a left side view of FIG. 5.

[0032] FIG. 7 is an inlet-side fan blade plot with the leading edge, trailing edge, root, and tip labeled.

[0033] FIG. 8 is a perspective plot of one fan blade, with a cylindrical airfoil labeled.

[0034] FIG. 9 is a schematic drawing of a high-efficiency embodiment of the air purifier system in an exploded perspective view.

[0035] FIG. 10 is a perspective view showing the assembled structure of the FIG. 9 embodiment.

[0036] FIG. 11 is a front-view of the FIG. 10 embodiment.

[0037] FIG. 12 shows a sectional view of the front-view of FIG. 11 taken at the sectioning place and in the direction indicated by section lines 12-12.

[0038] FIG. 13 is a schematic view of the air purifier system installed with a flexible wind-blocking sheet.

[0039] FIG. 14 depicts an embodiment of the air purifier system installed with a glass wind-blocking sheet.

[0040] FIG. 15 is a schematic diagram of the installed flexible wind-blocking sheet.

[0041] FIG. 16 is a side view of another height and tilt adjustment mechanism for the air purifier system.

[0042] FIG. 17 is a perspective schematic structural view of the air purifier system's safety cage.

[0043] FIG. 18 is a radial pressure distribution graph corresponding to early embodiments of the air purifier system.

[0044] FIG. 19 is an exploded perspective view of a high-efficiency embodiment appropriate for mass-production.

[0045] FIG. 20 is a perspective view of the FIG. 19 embodiment from the front with legs retracted.

[0046] FIG. 21 is a perspective view of the FIG. 20 embodiment from the rear with legs partially-extended.

[0047] FIG. 22 depicts an embodiment tongue-and-groove connection between the inlet and docking ring.

[0048] FIG. 23 illustrates an example locking mechanism for an inlet+docking ring connection.

DETAILED DESCRIPTION OF THE INVENTION

(1) Definitions

[0049] The term air purifier is understood to include: air purifiers, ventilation purifiers, air filtration systems, and all other machines capable of filtering particulate matter out of air.

(2) List of Symbols

[0050] 1carry handle; 2lid; 3filter housing; 4docking ring; 5motor supports/guide vanes; 6fan; 7inlet; 8speed adjustment knob; 9prefilter; 10electrical control box cover; 11height and tilt adjuster; 111height adjustment mechanism; 112tilt adjustment mechanism; 12electrical control box; 13motor; 14motor cover; 141air vents (on the motor cover); 15housing; 16filter; 17inner ring; 18outer ring; 19electrical conduit; 20wind-blocking sheet; 21window frame; 22damper/stiffener; 23seat; 24diffuser; 25hub; 28blade leading edge; 29blade trailing edge; 30blade root; 31blade tip; 32blade airfoils; 33hub ring; 34hub dome; 341vents (on the hub dome); 35air inlet hole; 36connecting ring; 37safety cage; 38hose; 39timer control knob; 40windowsill/stand; 41snaps; 42skirt; 43side-panels; 44threaded elements; 45rotary switch; 46capacitor; 47tongue; 48groove; 49 protruding part; 50slot, 51hub beams; 52hub sidewall.

(3) Simple Embodiment

[0051] The present invention is directed to an air purifier system, for which FIGS. 1, 2, 13, and 14 depict a simple embodiment. This simple embodiment includes an axial fan (6), a housing (15), a motor (13), and motor supports (5). For the embodiment in FIG. 1, the motor supports (5) are radially-oriented bars that connect to a central ring onto-which the motor is secured using screws such that the motor (13) is fixed at the center of the housing (15) with its shaft-axis normal to the vertical plane. One of the motor supports (5) is modified to allow electrical wires to safely run from the electrical control box (12) to the motor (13); this support is called the electrical conduit (19). The electrical control box (12) has a cover (10) and a speed adjustment knob (8), as well as a timer control knob (39).

[0052] The fan (6) is mounted on the output shaft of the motor (13). There is a prefilter (9) upstream of the fan (6), which can consist of a stainless-steel screen, and a filter (16) located downstream of the fan. The filter (16) is not limited to a HEPA filter, but a HEPA filter is preferred. Toward the outer edge of the prefilter (9) there is a docking ring (4). The docking ring (4) can maintain tension in the prefilter (9) and be used to connect the prefilter (9) to the housing (15). The air purifier system rests on a seat (23), which is located below the fan (6). Height and tilt adjusters (11) connect to the seat (23). The four threaded elements can be turned to provide minute adjustment of the height and tilt of the air purifier system, allowing the docking ring (4) to be easily aligned with a connecting ring (36) during installation at a window, when desired. For special circumstances and applications, the height adjustment mechanism may consist of two tubes that can slide relative to one-another, increasing the total height adjustment range. In this embodiment the docking ring (4) has an annular shape, but the docking ring (4) in-general is not limited to an annular shape.

[0053] During simultaneous ventilation and forced filtration air from outside is sucked through the prefilter (9). The prefilter (9) causes a loss of flow energy, but it also reduces turbulence in the outside air. Turbulence reduction partially offsets energy lost through the prefilter because it improves the aerodynamic efficiency of the fan (6). The prefilter (9) is also an important component because it prevents premature clogging of the filter (16) due to insects, fibers, and large dust particles, and it protects both the fan (16), and people's fingers.

[0054] The simple embodiment has a square filter housing (3) to accommodate a standard square-shaped filter. The filter housing (3) has a lid (2) with a front lip that covers the front edges of the filter to hold it in place and to prevent dirty air from bypassing the filter (16), leaking into the building, and reducing overall air quality. For the simple embodiment of FIG. 1 the lid (2) conveniently hinges about the carry handle (1) and is recessed to provide space for the filter (16).

[0055] The filter (16) can be easily installed into and removed from the filter housing (3) for replacement or cleaning by opening the lid (2) and sliding the filter (16) in or out. For example, the filter housing (3) can have a U shape whose inner-side has a groove for the filter (16) to slide into. The lid (2) is above the filter housing (3). The carry handle (1) is on the upstream side of the lid (2). The filter (16) can be removed to provide high flow-rate pure ventilation, which is useful when the outside air is relatively clean and rapid indoor ventilation is desired, or when the indoor temperature is less comfortable than the outdoor temperature. If there are small children or pets in the home then a safety cage (37) can replace the filter in the filter housing (3). The air purifier system can also include additional filters. Examples include more than one prefiltration layer or a non-mesh type prefilter upstream of the filter (6), as well as an activated carbon filter downstream of the filter (6), which is used to absorb odors and harmful chemical vapors. Further, the air purifier system may include an electrical heating device to increase comfort during cold weather use. The air purifier system can be removed from the window and used on a desktop for pure filtration without ventilation, making it extremely versatile. Users are cautioned that the preferred technique is to filter incoming air before it enters a building, not after it has diffused throughout the building; the former is much more effective and efficient than the latter.

[0056] The simple embodiment has an axial fan (6) with a small hub-to-tip ratio. Planar projections of a blade's leading (28) and trailing edge (29), as viewed from downstream looking-in, (FIG. 5, 7) produce parabolas and the blade's root (30) and tip (31) are semi-circular. The blade airfoils are constructed using parabolic camber-lines projected onto cylindrical surfaces coaxial with the centerline of the hub dome (34). The blades are of constant thickness in the circumferential direction and linearly-tapered in the radial direction (32).

(4) High Efficiency Embodiment

[0057] A high efficiency embodiment is shown in FIGS. 9-12. It has additional parts: the inlet (7), diffuser (24), motor cover (14), a novel axial fan (6), and novel guide vanes (5). The novel axial fan (6) and guide vanes (5) are described at the end of this section. The structure and function of the inlet (7), diffuser (24), motor cover (14) and guide vanes (26) are described as follows.

[0058] The inlet (7) has a streamlined horn-like shape and it is located between the prefilter (9) and the housing (15). The inlet (7) accelerates the flow and allows the air to flow smoothly into the housing (15) preventing flow separation and reattachment near the housing's (15) otherwise sharp corners, which is called vena contracta. Vena contracta reduces the aerodynamic efficiency of the fan blades (6) near their tips. The net result of the inlet (7) is an improvement in system efficiency on the order of a few percent. The docking ring (4) here is the same as for the simple embodiment.

[0059] The high efficiency embodiment includes a diffuser (24) located between the housing (15) and the filter (16). The diffuser (24) is tapered; It has a smaller cross-sectional area on the housing (15) side and a larger cross-sectional area, which may be round, square, or some other shape, on the filter (6) side. The diffuser's (24) smallest cross-section should expand smoothly to its largest cross-section. If the diffuser (24) is too short then flow separation will result, leading to reduced efficiency. If the diffuser (24) is too long then the air purifier system will not balance over a windowsill/shelf without fixing or fastening its legs to the windowsill or shelf. In general, the greater the diffusion area ratio (outlet area divided by inlet area) the greater the required length to avoid flow separation. The diffusion area ratio can be increased without changing the outlet area by increasing the inlet area, which is essentially an annulus from the hub diameter of the fan (6) to the inner diameter of the housing (15). Diffuser (24) considerations encourage a smaller fan (6) hub diameter and a larger tip diameter than might otherwise be used. The diffuser's (24) length is selected ensure that fully-attached flow is maintained on the walls of the diffuser as the flow expands from the smallest cross-section to the largest cross-section of the diffuser (24). For this high efficiency embodiment, the diameter of the upstream circular part of the diffuser (24) is no bigger than that of a side-length on the downstream side. The ultimate effect of the diffuser (24) is to increase the total volumetric flow rate of air through the air purifier system (all else being equal). A logical material choice for the diffuser (24) is plastic. For the high efficiency embodiment of FIGS. 9-12, the filter housing (3) and lid (2) are plastic, and the lid (2) snaps in-place.

[0060] This high efficiency embodiment utilizes a half ellipsoidal motor cover (14) whose open-end attaches to the guide vanes (5) and whose closed end has air vents (141), which allow motor cooling air to flow out. The flow rate of cooling air is very small, so it does not significantly reduce the efficiency of the entire air purifier system. The motor cover (14) has a continuous surface of continuous slope to avoid flow separation, helping the air downstream of the fan (6) to flow smoothly around the motor (13), thereby reducing flow resistance. Plastic is a logical material choice for the motor cover (14), as well as the other aerodynamic surfaces. Using a rounded hub dome (34), as opposed to a flat hub face, can improve the efficiency of the fan blades near their roots (30).

[0061] Vents (341, 141) are placed in the hub dome (34) and the motor cover (14) to allow a small amount of air to flow over the motor (13) for cooling, and to prevent flow separation near the outer downstream face of the motor cover (14). Cooling air flow is driven by suction created just behind the hub dome (34) that arises due to the rotation of radially-oriented hub beams (51) (FIG. 3) that induce centrifugal forces within the flow causing air to enter through the vents (341) and spiral outward toward the hub sidewalls (52) then downstream and around the motor (13). Hub beams (51) also serve as structural members.

(5) Mass Production Embodiment

[0062] The high efficiency embodiment depicted in FIG. 9 is modular to illustrate different aerodynamics-related parts and their functions. It also serves as a useful rapid-prototyping embodiment for part-by-part experimental optimization. An embodiment suitable for mass-production is depicted in FIGS. 19-21. The mass-production embodiment is made using compression molding and assembled with screws.

[0063] For the guide vanes (5) of FIG. 19 camber and twist have been omitted to facilitate removal from a mold. As a result, they can be described as flat-plate guide vanes (5). These guide vanes (5) retain their effectiveness because their trailing edges align with the desired axial flow direction and they are sufficiently numerous to impose their geometry on the flow.

[0064] The lid (2) has been omitted in favor of using snaps (41) attached to the filter housing (3a, 3b) for installation and removal of the filter (16). A skirt (42) has been added to cover the height and tilt adjusters (11) and two side-panels (43) have been included to further improve the aesthetics of the air purifier. Threaded elements (44) are embedded in the seat (23a, 23b) to mate with the height and tilt adjusters (11). A rotary switch (45) and capacitor (46) are also shown.

[0065] The docking ring (4) for all embodiments is the part used to hold the prefilter (9) or barrier in-place; it may or may not be used to facilitate installation of the air purifier system at a window. In practice, the docking ring (4) can have a wide variety of shapes and need-not be annular. In the example embodiment of FIG. 25 the docking ring (4) can be turned approximately 10 degrees to unlock it from the inlet (7) using a tongue (47)-and-groove (48) type design. A protruding part (49) located on the outer surface of the inlet (7) snaps into a slot (50) on the docking ring (4), as depicted in FIG. 23. This allows a prefilter (9) to be quickly and easily rinsed-clean and reinstalled. The docking ring (4) design also facilitates convenient access to the fan (6), motor (13), and housing (15) so they can be wiped-clean with a damp cloth after accumulating dust.

[0066] Many discrete parts from the FIG. 9 embodiment have been combined to reduce the number of manufacturing steps and the overall cost of production. For example: the carry handle (1), guide vanes (5), electrical control box cover (11), electrical control box (12), motor cover (14), housing (15), and half of the seat (23b) can all be stamped-out as one piece of continuous plastic (FIG. 19). One can imagine other embodiments in which various groups of parts are combined in a similar way. For example, the docking ring (4), inlet (7), and prefilter (9) or barrier could be combined into one continuous piece that attaches and detaches directly to-and-from the housing (15). Such embodiments are understood to fall within the scope of the present invention.

(6) Installation

[0067] Installation of the air purifier system may include a wind-blocking sheet (20). The wind-blocking sheet (20) has an air inlet hole (35) and may include a connecting ring (36) applied around the air inlet hole (35) that mates in a temporary, easily-removable, fashion with the docking ring (4). The docking ring (4) can also have a locking connection with the connecting ring (36) in a variety of ways, including using: glue, double-sided tape, snaps, screws, magnets, etc. Height and tilt adjusters (11) are used to align the docking ring (4) with the connecting ring (36).

[0068] The function of the wind-blocking sheet (20) is to cover the window, allowing ventilation only through the air inlet hole (35). Preferred materials for the wind-blocking sheet are transparent, and may include: glass, rigid plastic, or a flexible material made from a relatively thin film. For a do-it-yourself installation using a thin flexible material the material can be received in a roll with the air inlet hole (35) pre-cut and the connecting ring (36) already attached. The sheet (20) could be cut to the necessary frame-size using scissors. After removing an existing window screen its rubber strip and groove can be utilized to tension and mount the flexible wind-blocking sheet (20). Tape can used to help keep the rubber strip in-place, and a transverse stiffener or damper (22), as depicted in FIGS. 16 and 18, can be used when the wind-blocking sheet (20) is too flexible or weak relative to the applied wind-loading. This situation is likely to occur when the area of the window is large and/or the area is particularly windy. For cases where a permanent installation is desired it is recommended to use glass, as seen in FIG. 17.

[0069] After installing the wind-blocking sheet (20) the air purifier system is set on a corresponding windowsill or stand (40). A no-cost installation of an excellent ventilation purifier has been achieved without the need to drill any holes or install complicated room-to-room ducting. There is no damage to the window, its frame, or any other part of the building. To return the window to its original condition simply remove the unit and reinstall the old window screen.

(7) Fan Design

[0070] The fan (6) is designed such that incoming air approaches nearly tangent to its blade leading edges and flows smoothly over the blades without separation. The precise shape of the blades is designed to maximize efficiency. As air passes through the fan it undergoes a necessary rise in static pressure, which ultimately drives flow through the filter (16). Due to its rotation, the fan (6) also introduces a circumferential velocity component, which is undesirable as it does not contribute to axial flow through the filter.

[0071] An embodiment of the fan (6) is depicted in FIGS. 5 through 8. Said fan (6) is custom-designed with parabola-based airfoil camber-lines that are projected onto cylindrical surfaces. These cylindrical airfoils (32) are shown in FIG. 8, where the X axis represents a substantially circumferential direction, Y a substantially radial direction, and Z the axial direction (air flows from high to low Z). The blades are forward-swept; their thickness is constant in the circumferential direction and linearly-tapered in the radial direction. The leading (28) and trailing (29) edges of each blade are parabolic when projected onto a vertical plane, as seen in FIGS. 5 and 7, as given by: x.sub.LE=1.972y.sub.LE.sup.2+0.115y.sub.LE0.005 and x.sub.TE=3.615y.sub.TE.sup.2+0.945y.sub.TE0.005. Leading and trailing edges are rounded. Under the same vertical-plane projection the root (30) and tip (31) of each blade is a semi-circle (FIGS. 5 and 7). The blade design of the fan (6) differs from conventional designs. Conventional axial fans with a diameter of approximately 25 cm, a hub diameter of approximately 10 cm, and rotational speeds of approximately 1200 RPM, may have root-to-tip pitch angles of about 15.1 to 38.7 degrees for a total twist of about 23.6 degrees. For the custom fan of FIGS. 5-8 pitch angles vary from 69.3-74.7 degrees for a total twist of 5.4 degrees. Comparing experimentally-determined efficiencies for the simple embodiment of FIG. 1 (in watts per cubic meter per minute, a national standard) the custom fan design improved system performance by approximately 28%.

[0072] Embodiments with longer diffusers can tolerate higher fan hub-to-tip ratios without flow separation, allowing higher static pressures and flow rates to be achieved. Such embodiments can also be designed to operate well over a broader range of flow speeds by utilizing more-complex airfoils with non-uniform thickness distributions. For such embodiments the axial fan becomes relatively heavy, and its mass is distributed further away from the axis of rotation. As a result, such fans can be difficult to balance.

(8) Guide Vane Design

[0073] For the high efficiency embodiment depicted in FIG. 11, the motor supports (5) have been replaced with guide vanes (5). As air leaves the fan blades it approaches these guide vanes (5), which are optimally designed when the oncoming flow approaches tangent to a vane's leading edge and exits the vane's trailing edge in the purely axial direction. Guide vanes (5) for the FIG. 9 embodiment utilize NACA 4-digit series airfoils with maximum camber located at three-tenths of the chord-length aft of the airfoil leading-edge. The chord-length tapers linearly from vane tip-to-root while vane thickness is held constant, except at the rounded leading and trailing edges. Guide vanes (5) improve efficiency by recovering swirl energy downstream of the fan (converting unproductive circumferential velocity into axial velocity). To design the guide vanes two unique equations were derived having the following parameters: m is maximum airfoil camber in tenths of chord, V is axial flow speed, Vc is post-fan circumferential flow speed, p is the static pressure rise across the fan, is air density, and U is the velocity of the rotating fan blade, which is a function or radial position and fan rotation rate. The first unique equation is: m=0.105.Math., where

[00001]$=a.Math..Math.\tan \left(\frac{V_0}{V}\right)$

and the other equation was derived to estimate the post-fan circumferential flow speed, as:

[00002]$V_{c}0.154.Math.\frac{.Math..Math.p}{.Math.U}.$

Shape details for the guide vanes (5) (beyond having the proper inlet and outlet angles) are not as important as those of the fan (6). The guide vanes (5) are stationary, causing the flow speed over them to be relatively low. As a result, their shape-effect on system efficiency is reduced. The number of guide vanes (5) is selected to ensure three criterion: (1) that they successfully impose their geometry on the flow, (2) that they adequately support the weight of all mounted components, and (3) that their material use is not excessive. One of the guide vanes (5) is hollow with a thick symmetric airfoil; it serves as the electrical conduit (19) that allows electric wires to run safely from the electric control box (12) to the motor (13) without creating a flow disturbance. The electrical conduit's (19) trailing edge is left open for ease of assembly.

(9) Experimental Results

[0074] To verify the performance of the air purifier system an initial simple, high efficiency, and manufacturing embodiment were produced and tested alongside a commercial desktop filter. The method for comparison was volumetric flow rate through the filter divided by power consumption in watts, which is an industry standard. This is not a very fair comparison between desktop purifiers and ventilating purifiers, as the technique of filtering incoming air is much more efficient than the technique of letting dirty air enter and then trying to clean it using a desktop filter (after it has diffused throughout a space).

[0075] Table 1 compares three embodiments of the air purifier system during experimental operation, where mean power consumption is presented in watts (W). Supply voltage from the local grid (in China) fluctuates, so values are adjusted to correspond to 220V. The mass production embodiment uses a more efficient electrical motor and has four power-settings (not three).

TABLE-US-00001 TABLE 1 Average power consumption (W) Power setting 1 (low) 2 (medium) 3 (high) Simple embodiment of the air purifier 22.9 26.5 35.0 system (FIG. 1) High-efficiency embodiment of the air 22.1 26.4 35.2 purifier system (FIG. 9) Mass production embodiment of the air 20.3 21.1, 22.0 25.2 purifier system (FIG. 19)

[0076] Table 2 compares the performance of different air purifier systems having the same nominal power and voltage for their motors. Niu Kee is a typical commercially-available desktop filtration system utilizing an axial fan.

TABLE-US-00002 TABLE 2 Flow-rate (m3/min) through a HEPA filter for systems with the same nominal power Power setting 1 (low) 2 (medium) 3 (high) Niu Kee purifier (HEPA filter only) 1.00 best tested HEPA strapped to a desktop 1.23 fan combination Simple embodiment of the air purifier 1.44 1.82 2.18 system (FIG. 1) High-efficiency embodiment of the air 2.11 2.62 3.06 purifier system (FIG. 9) Mass production embodiment of the air 1.97 2.78, 3.38 3.97 purifier system (FIG. 19)

[0077] FIG. 18 shows pressure distribution along the radial direction at power-setting 2. Radial distance from the center of the fan is given along the x-axis in mm. Pressure difference across the filter (16) is given on the y-axis in Pa. The thick solid line corresponds to the high efficiency embodiment, while the thick dotted line corresponds to the simple embodimentboth at power-setting 2. Vertical dashed lines denote key radial positions: r=48.5 is the radius of the fan hub, r=127.5 is the radius of the fan blade tips, r=130 is the inner radius of the housing (15), r=141 is the perpendicular distance between the shaft center and one side of the square-shaped filter housing (3), r=199.4 mm is the distance from the shaft center to a corner of the square-shaped filter housing (3).

[0078] The flow speed through the filter is proportional to the pressure difference across it, as given on the y-axis of FIG. 18. Integration of the pressure difference across the entire frontal area of the filter yields the total volumetric flow rate of air passing through the filter. A higher-pressure difference, all-else being equal, implies better system performance. Pressure distribution uniformity is desirable because more uniform particle capture is associated with longer filter life. Optimization was completed for the mass production embodiment, which has a significantly higher and nearly flat pressure-distribution line (between 30 and 35 Pa, not shown) corresponding to extremely good performance.

[0079] While the foregoing written description of the invention enables a person having ordinary skill in the art to make and use what is considered presently to be the best mode thereof, those of ordinary skill in the art will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, process, and examples herein. The invention should therefore not be limited by the above described embodiments, processes, and examples, but by all embodiments and processes within the scope and spirit of the invention.