Abstract:
An apparatus for reducing distortion of air flow entering the inlet of a fan. The device includes a perforated body member that has a first end that is attachable to the inlet end of the fan and a second end. The apertures in the body member are arranged in a plurality of circumferential rows. Preferably, the apertures in each successive row from the first end to the second end increase in diameter with the apertures in the row adjacent the first end being smaller in diameter than the apertures in the row adjacent the second end. The body member can be frustoconical, cylindrical or ellipsoidal in shape. In addition, the body member can be equipped with an apparatus for reducing airflow noise.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 08/730,925, filed Oct. 18, 1996, now U.S. Pat. No. 5,979,595. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to air moving apparatuses and, more particularly, is directed to a device for reducing the distortion of air entering the inlet of a fan and the noise created thereby. 
     2. Description of the Invention Background 
     Over the years, a variety of devices have been developed for moving air and other gases. For example, various types of fans have been created for moving air for heating, ventilating and cooling purposes in residential and industrial structures alike. Virtually all refrigerators, freezers and air conditioners are equipped with a fan for moving air across their heat-exchanger coils. Fans are also frequently used in industrial applications for moving process air and contaminated air through filtration and pollution control systems. Electronic equipment may require cooling fans to prevent “hot spots” from developing within the equipment which could damage sensitive electrical components. Machines used to dry raw and processed materials use fans for circulating heated air to the product and for carrying moisture away from the materials. Air support structures require fans to inflate them and maintain their supporting pressure. 
     Fans are generally classified by the nature of the airflow through their impellers. Axial flow, radial flow (centrifugal), mixed flow and cross flow are types of fan impellers commonly employed. Perhaps the two types of fans that are most commonly employed are centrifugal fans and axial fans. The construction of a centrifugal fan and an axial fan are fundamentally different. The impeller of a centrifugal fan usually includes a front rim that has a centralized opening therein and a backplate that is attached in spaced-apart parallel relation to the rim by a series of radial blades. The impeller assembly is rotatably supported within a housing which has an inlet that corresponds with the opening in the impeller rim. As the impeller is rotated within the housing, air is drawn in through the inlet and into the center of the impeller. The centrifugal force developed by the impeller causes the air to be discharged radially out of the impeller and through an outlet formed in the housing; hence the name “centrifugal fan”. 
     An axial fan is typically equipped with a “propellertype” impeller that is rotatably supported within an air passage opening. For example, an axial fan may be mounted in a wheel or rim that is attached within an opening in a housing. As the impeller is rotated, air is drawn into or out of the housing depending upon the orientation of the impeller blades. Other axial fans are mounted within housings that can form portions of ductwork for carrying air for heating, ventilation and air conditioning purposes. 
     The selection of a particular size and type of fan for a particular application typically involves aerodynamic considerations, economic considerations and functional stability considerations. Axial fans are desirable air moving devices in most systems due to their relatively small sizes and high efficiencies. System design and fan applications, however, can be limited due to the axial fan&#39;s sensitivity to inlet air conditions. Axial fans often impart an air swirl at their inlets which can lead to an uneven velocity profile of inlet air immediately in front of the fan. 
     In addition, due to design considerations, the preferred configuration of many systems would require a change in air direction immediately in front of or at the rear of the air moving device. However, any obstruction or change in direction of airflow immediately in front of the fan can cause even more inlet air distortion which can result in a reduction in the fan&#39;s operating efficiency as well as impart cyclical stresses on the blades. 
     These undesirable conditions can also be caused when system components such as heat exchanging coils, sound attenuators, moisture eliminators, filters, etc. are located in close proximity to the fan inlet. It is common practice, therefore, to oversize such components to reduce the airflow distortion created thereby. Of course, such oversizing adds to equipment costs, operating costs and maintenance costs. Distortion of inlet air can also be caused by directing high velocity return air into a mixing device located in close proximity to the fan inlet. Existing building structure and design requirements also sometimes dictate that structural components (i.e., beams, joists, pipes, walls, etc.) pass through the fan inlet stream which can result in further airflow distortion. 
     In the past, the above-mentioned conditions were somewhat alleviated through the use of an “inlet leveling screen.” An inlet leveling screen typically comprises a flat plate that has a plurality of perforations therethrough that comprise approximately fifty percent of the plate area. While such a device causes the inlet air to be more evenly distributed across the screen and thus reduces the distortion of the air as it enters the fan, it creates added airflow resistance which places a greater load on the fan motor often requiring larger, more expensive motors to be used thereby adding to equipment and operating costs. In this device, the airflow remains in an axial direction and thus objects such as heat exchanger coils, noise attenuators, filters, etc. that are placed immediately in front of the screen can limit its effectiveness. 
     The effectiveness of prior air inlet level screens is also limited by the screen&#39;s surface area. Thus, traditional inlet leveling screens are typically constructed with a “round-to-square” transition member attached to the inlet end of the fan housing which enables the screen area to be somewhat maximized. Such arrangements, however, are usually very large and cumbersome which makes them expensive to build and difficult to install. Further, such devices usually cannot be used in applications where space is limited. 
     Other fan inlet devices have been developed and are disclosed in U.S. Pat. No. Re 31,258 to De Baun, U.S. Pat. No. 3,483,676 to Sargisson, U.S. Pat. No. 3,519,024 to Johnson et al., U.S. Pat. No. 3,871,844 to Calvin, Sr., U.S. Pat. No. 5,099,879 to Baird and U.S. Pat. 5,405,106 to Chintamani et al. Devices of the types disclosed above are typically expensive to produce and install. In addition, such devices often require the use of large motors for operating the fan. Moreover, those prior devices often occupy large amounts of building space which might otherwise be used for other purposes. 
     Other fan-related problems exist in air distribution systems for buildings and commercial structures. Such systems typically comprise discrete functional elements coupled together in series at a central location in a building. Such a system usually includes an input plenum for mixing outside and “return” air, filters, heat exchanging coils, a fan and noise attenuation apparatus for reducing the noise created by the airflow. Because such components typically occupy large amounts of building space when linearly-aligned, it often becomes necessary to arrange components in non-linear orientations. For example, structure design considerations sometimes require that inlet ducts for fans be orientated at right angles relative to the fan inlet. In addition, because relatively high airflow velocities are required to service large buildings, sound attenuating apparatuses must be employed. However, prior sound attenuating apparatuses are typically large and expensive and difficult to manufacture and install or they are relatively small devices which undesirably restrict airflow which increases airflow distortion. 
     Thus, there is a need for a device for reducing distortion of airstream entering the inlets of fans without greatly adding to the airflow resistance. 
     There is a further need for an airflow inlet device that is small and relatively easy to install and inexpensive to produce. 
     There is yet another need for a fan inlet device that can be used in close proximity to coils, filters, etc. and effectively minimize the airflow distortion entering the fan&#39;s inlet. 
     There is still another need for a device that can reduce the distortion of an airstream in a system to such a degree such to enable axial fans to be used in applications where their uses would have otherwise been prohibited. 
     Another need exists for a compact air handling system that can provide airflows similar to airflows typically achieved by prior systems that occupy large spaces. 
     Yet another need exists for an air handling system with improved silencing characteristics. 
     SUMMARY OF THE INVENTION 
     In accordance with a particular preferred form of the present invention, there is provided an airflow inlet apparatus for reducing distorltion of air entering an inlet end of a fan assembly. In a preferred form, the inlet apparatus comprises a hollow body member that has a first and second end. The first end is attachable to the inlet end of the fan assembly. An end member is attached to the second end of the body and has a plurality of substantially uniformly distributed first apertures therethrough. A plurality of substantially uniformly distributed second apertures are provided in the hollow body member such that the second apertures adjacent the first end of the body member are smaller in diameter than the diameters of the second apertures adjacent the second end of the body member. The body member can be cylindrical, frusto-conical or ellipsoidal in shape. In another embodiment, the hollow body member houses airflow silencing apparatus for reducing noise generated by the air flowing through the body member. 
     In yet another preferred embodiment, the present invention comprises an airflow inlet apparatus for reducing noise generated by air entering an inlet end of a fan assembly. In a preferred form, the inlet apparatus comprises a perforated housing member and a perforated inlet duct centrally disposed within the housing member. The inlet duct is attachable to the inlet end of the fan assembly. A plurality of radially extending silencing members extend between the inlet duct and the housing and are attached thereto such that when air flows through the housing and the inlet duct to the fan assembly, the noise generated thereby is reduced by the silencing members. 
     Accordingly, the present invention provides solutions to the aforementioned problems encountered when using prior inlet leveling screens and sound attenuation apparatuses. The reader will appreciate that it is an object of the present invention to provide an inlet device for a fan that is relatively compact, inexpensive to produce and install and effectively reduces distortion of air flowing into the inlet of a fan. 
     It is another object of the present invention to provide an inlet device having the above-mentioned attributes that is also capable of reducing airflow noise. 
     It is still another object of the present invention to provide an inlet device that can be used in connection with air moving devices such as axial fans that would permit the use of such devices in applications wherein, due to airflow distortion, they could not have been otherwise used. 
     Thus, the present invention solves many of the problems encountered when moving air through structures. However, these and other details, objects and advantages will become further apparent as the following detailed description of the present preferred embodiment thereof proceeds. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, there are shown present preferred embodiments of the invention wherein like reference numerals are employed to designate like parts and wherein: 
     FIG. 1 is a side elevational view of a preferred airflow inlet device of the present invention attached to a fan assembly; 
     FIG. 2 is an end elevational view of the airflow inlet device of FIG. 1; 
     FIG. 3 is an enlarged side view of an enlarged side view of the airflow inlet device of FIGS. 1 and 2 with a portion of the skin thereof removed for clarity; 
     FIG. 4 is a partial side view of a preferred attachment arrangement for attaching a preferred airflow inlet device to a fan inlet member; 
     FIG. 5 is a partial exploded side view of another preferred attachment arrangement including a fastening clamp shown in cross-section for attaching a preferred airflow inlet device to a fan inlet member; 
     FIG. 6 is another partial side view of the attachment arrangement of FIG. 5 with the fastening clamp thereof installed around the attachment flanges of the airflow inlet member and the inlet duct; 
     FIG. 7 is a partial end view of the fastening clamp of FIGS. 5 and 6; 
     FIG. 8 is a side elevational view of another preferred airflow inlet device of the present invention attached to a fan assembly; 
     FIG. 9 is an end elevational view of the airflow inlet device of FIG. 8; 
     FIG. 10 is an enlarged side view of the airflow inlet device of FIGS. 8 and 9 with some of the skin thereof removed for clarity; 
     FIG. 11 is a side elevational view of another preferred airflow inlet device of the present invention attached to a fan assembly; 
     FIG. 12 is an end elevational view of the airflow inlet device of FIG. 10; 
     FIG. 13 is an enlarged side view of the airflow inlet device of FIGS. 11 and 12; 
     FIG. 14 depicts the airflow inlet device of FIGS. 1-3 attached to a fan assembly that is housed within a duct system wherein inlet airflow is at right angles to the airflow inlet device; 
     FIG. 14A is a side elevational view of another preferred airflow inlet device of the present invention; 
     FIG. 15 is a cross-sectional side view of an airflow system employing a preferred inlet device of the present invention; 
     FIG. 16 is a plan view of a preferred silencing assembly of the present invention; 
     FIG. 17 is a cross-sectional side elevational view of the silencing assembly of FIG. 16 taken along line XVII—XVII in FIG. 16; 
     FIG. 18 is a cross-sectional view of a preferred acoustical panel of the present invention; 
     FIG. 19 is a plan view of the silencing assembly of FIG. 16 adapted to receive airflow from three different directions; 
     FIG. 20 is a plan view of the silencing assembly of FIG. 16 adapted to receive airflow from two different directions; and 
     FIG. 21 is a plan view of the silencing, assembly of FIG. 16 adapted to receive airflow from one direction. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings for the purposes of illustrating present preferred embodiments of the invention only and not for purposes of limiting the same, the Figures show an axial fan assembly generally designated as  10 . While the present invention will be described herein in connection with axial fan assemblies, the skilled artisan will readily appreciate that the subject invention could be effectively employed in a variety of other air moving systems. Accordingly, the scope of protection afforded to the subject invention should not be limited to use with axial fan arrangements. 
     More particularly and with reference to FIG. 1, there is shown an axial fan assembly  10  that includes a conventional fan member  12  that is housed within a housing member  14 . Those of ordinary skill in the art will understand that a variety of different axial fan assemblies are commercially available. Thus, the exact construction and operation of such fan assemblies will not be discussed herein. As can be further seen in FIG. 1, a curved inlet duct  16  is preferably attached to one end of housing member  14 , although inlet duct  16  may not be necessary in all applications, and a discharge duct  18  is attached to the other end of the housing member  14 . The direction of airflow through the fan assembly is represented by arrow “A”. Again the skilled artisan will appreciate that such a fan assembly  20  can be employed in a variety of different systems. For example, the fan assembly could be integrally attached to supply and discharge ducts or it could be received and mounted within the ducts. 
     A preferred airflow inlet device  30  is shown in FIGS. 1-3. As will be discussed in further detail below, a preferred airflow inlet device  30  comprises a body member  32  and an end plate  60 . In this embodiment as can be most particularly seen in FIG. 3, the body member  32  has a frusto-conical shape. In particular, the body member  32  preferably has a first flanged end  34  and a second end  36  wherein the first end  34  is larger in diameter than the second end  36 . In a preferred embodiment, body member  30  is fabricated from a perforated material such as steel or aluminum; however, other suitable perforated materials could also be successfully employed. 
     As can be further seen in FIG. 3, the apertures  40  that are adjacent the second end  36  are preferably larger in diameter than the apertures  53  that are adjacent the first end  34 . The skilled artisan will appreciate that the diameters of the first and second ends ( 34 ,  36 ) of the body member  32  will be dictated by the size of the fan inlet member  16 . For example, the subject invention is well-adapted for use in connection with fans having eighteen inch diameter inlets to fans having eighty-four inch diameter inlets. However, the subject invention is not limited by fan diameter and could conceivably be successfully used in connection with any size of fan inlet. 
     By way of example, for a fan inlet having an approximate diameter of forty-two inches, a preferred fan inlet device  30  would have the characteristics discussed below. As can be seen in FIG. 3, the body portion  32  includes a conically-shaped frame member  31  that is fabricated from structural steel members. The outer skin, generally designated as  33 , is fabricated from segments of perforated sheet metal that have been formed to conform to a corresponding segment of the frame  31 . Preferably, the skin  33  has three segments ( 35 ,  37 ,  39 ). Segment  35  is provided with a plurality of equally distributed perforations therein that preferably comprise approximately fifty-one percent of the surface area of the skin segment  35 . Likewise, segment  37  is provided with a plurality of equally distributed perforations that preferably comprise about fifty-eight percent of the surface area of the skin segment  37 . Segment  39  also has a plurality of equally distributed perforations therethrough that comprise approximately sixty-three percent of the surface area of the skin segment  39 . Segments ( 35 ,  37 ,  39 ) are welded together at their adjoining edges and are also preferably welded to the frame  31 . A solid end plate  60  is also preferably welded to the end of frame  31 . Preferably, the combination of apertures in the body member  32  comprise about sixty percent of the surface area of the inlet device  30 . Although the sizes, numbers of apertures per row and the number of rows may be varied, it will be appreciated that the fan inherently induces a higher negative pressure adjacent to the first end  34  which gradually decreases along the length of the body member  32 . The arrangement of apertures in the above-described pattern (i.e., apertures gradually reducing in diameter from the second end to the first end) insures a substantially uniform airflow and velocity of radial inlet air along the length of the body member  32 . 
     To attach the member  30  to the inlet member  16  of the fan assembly  10 , a flange  70  is preferably attached to the first end  34  of the body member  32 . The flange  70  is of typical construction and is sized to mate with a flange  17  on the inlet member  16 . In a preferred embodiment, the flanges ( 17 ,  70 ) are then bolted together with bolts  72 . See FIG.  4 . In another preferred embodiment, a commercially available circumferential flange clamp  80  is employed to connect the flanges ( 17 ,  70 ). More particularly and with reference to FIGS. 5-7, circumferential flange clamp  80  has a body portion  82  that is sized to fit around the circumference of flanges ( 17 ,  70 ) when the clamp  80  is in an open position. After the body portion  82  has been fitted over the flanges ( 17 ,  70 ), the clamp  84  is activated to draw the body portion  82  tightly around the flanges ( 17 ,  70 ). Those of ordinary skill in the art will appreciate, however, that other known methods of connecting flanges ( 17 ,  70 ) could also be employed. 
     Another preferred embodiment is depicted in FIGS. 8-10. Although this air inlet device  130  is depicted in connection with a fan assembly  10  of the type and construction described above, it will be appreciated that the inlet device  130  can be successfully employed with other air moving apparatuses, including centrifugal fans. As can be seen in FIGS. 8 and 9, the device  130  preferably has a cylindrically-shaped body portion  132  that has a first end  134  and a second end  136  which are substantially equal in diameter. Body portion  132  contains a plurality of apertures therethrough that are arranged in circumferentially-extending rows in the manner described above. That is, the smallest diameter apertures are adjacent to the first end  134  and the apertures gradually increase in diameter by row such that the largest diameter apertures are adjacent the second end  134 . See FIG.  10 . 
     For example, for a fan inlet having an approximate diameter of forty-two inches, a preferred fan inlet device  130  would have the characteristics described below. The diameter of the first and second ends ( 134 ,  136 ) of the body member  132  would preferably be approximately fifty-five inches. As can be seen in FIG. 10, the body member  132  includes a cylindrical-shaped frame member  131  that is fabricated from structural steel members. The outer skin, generally designated as  133 , is preferably fabricated from segments of perforated sheet metal that have been formed to conform to the frame  131 . Preferably, the skin  133  has three segments ( 135 ,  137 ,  139 ) that are preferably of equal width. Segment  135  is provided with a plurality of equally distributed perforations therein that preferably comprise approximately fifty-one percent of the surface area of the skin segment  135 . Likewise, segment  137  is provided with a plurality of equally distributed perforations that preferably comprise about fifty-eight percent of the surface area of the skin segment  137 . Segment  139  also has a plurality of equally distributed perforations therethrough that comprise approximately sixty-three percent of the surface area of the skin segment  139 . Segments ( 135 ,  137 ,  139 ) are preferably welded together at their adjoining edges and are also preferably welded to the frame  131 . 
     An end plate  160  is also attached to the second end  134  of the body member  132 . The preferred arrangement and densities of the apertures in the device are identical to those densities and arrangements described above. However, the skilled artisan will appreciate that exact aperture size and distribution will be dictated by the application. In addition, the device  130  is preferably provided with a flange  170  for attachment to the flange  17  of the fan assembly inlet  16  in a manner described above. 
     Another preferred embodiment of the present invention is shown in FIGS. 11-13. In this embodiment, the inlet device  230  has a body member  232  that has an,elliptical shape as shown in FIG.  10 . Body member  232  has a first end  234  and a second end  236 . A flange member  270  is attached to the first end  234  to facilitate attachment of the device  230  to the inlet  16  of fan assembly  10  in the manner described above. For example, for a fan inlet having an approximate diameter of forty-two inches, a preferred fan inlet device  230  would have the characteristics described below. The diameter of the first end  234  of the body member  32  would preferably be approximately 55 inches. As can be seen in FIG. 13, the body member  232  includes an elliptical-shaped frame member  231  that is fabricated from structural steel members. The outer skin, generally designated as  233 , is preferably fabricated from segments of perforated sheet metal that have been formed to conform to the frame  231 . Preferably, the skin  233  has three segments ( 235 ,  237 ,  239 ) that are preferably equal in width. Segment  235  is provided with a plurality of equally distributed perforations therein that preferably comprise approximately fifty-one percent of the surface area of the skin segment  235 . Likewise, segment  237  is provided with a plurality of equally distributed perforations that preferably comprise about fifty-eight percent of the surface area of the skin segment  237 . Segment  239  also has a plurality of equally distributed perforations therethrough that comprise approximately sixty-three percent of the surface area of the skin segment  239 . Segments ( 235 ,  237 ,  239 ) are preferably welded together at their adjoining edges and are also preferably welded to the frame  131 . 
     Another preferred fan inlet device  30 ′ is depicted in FIG.  14 A. As can be seen in that FIG., preferred airflow inlet device  30 ′ comprises a body member  32 ′, that is fabricated from wire wound around a conically-shaped frame  33 ′. In a preferred embodiment, 0.25 inch diameter steel wire is used; however, other types and sizes of wire could be successfully employed. The frame member  33 ′ preferably has a first flanged end  34 ′ and a second end  36 ′ wherein the first end  34 ′ is larger in diameter than the second end  36 ′. By way of example, the first end  34 ′ may have a diameter of 42.75 inches (represented by arrow “B′”) and the diameter of the second end may be 20 inches (represented by arrow “C′”). 
     As can be further seen in FIG. 14A, the body member  32 ′ may be segmented into three segments (represented by “D′”, “E′”, “F′”). In a preferred embodiment, all three segments (“D′”, “E′”, “F′”) are equal in length and for the present example are 11.75 inches long. Preferably, in segment “D′”, there is 0.159 inches between each wire wrap. Thus, in segment “D′” there is approximately thirty-nine percent open space. In segment “E′”, there is preferably 0.240 inches between each wire wrap and approximately forty-eight percent of segment “E′” is open. In segment “F′”, there is approximately 0.318 inches between each wire wrap and approximately fifty-six percent of segment “F′” is open. 
     Also in the preferred embodiment, an endcap  60 ′ is attached to the second end  36 ′ of the frame  33 ′. Endcap is fabricated from steel or aluminum and preferably has no perforations therethrough. It will also be appreciated that the flanged end  34 ′ is adapted to be attached to fan assembly in the manners described above. Those of ordinary skill in the art will further appreciate that the body member  32 ′ could be configured in a variety of different conical sizes that are compatible with the sizes and types of air moving devices being employed. Thus, the scope of this embodiment should not be limited to inlet devices having the same diameters, lengths and wire spacing. 
     The skilled artisan will understand that the above-described fan inlet devices solve many of the problems encountered when using prior inlet leveling screens. The unique designs of the present invention convert inlet airflow from an axial direction to a radial direction which significantly reduces air velocity and eliminates air swirl and turbulence in front of the fan inlet. This results in a substantially even airflow distribution through a coil  92  or any other system component such as a filter or sound attenuator mounted within a system of ductwork  90 . See FIG.  14 . In addition, due to their compact nature, the inlet devices of the present invention enable the fan assembly  10  to be located at right angles to the inlet area of a duct system as shown in FIG.  14 . Thus, the devices of the present invention enable axial fans to be used in applications wherein, due to airflow distortion, they could not previously be used. Another benefit of the fan inlet devices such as ( 30 ,  130 ,  230  and  30 ′) is that they improve the efficiency of any noise attenuators, coils and/or filters placed in proximity therewith because they provide more uniform airflow through such devices. 
     Another preferred airflow system  300  is shown in FIG.  15 . As can be seen in that FIG., a fan  310  is mounted in a section of ductwork  302  that is preferably square or rectangular in cross-section. Fan  310  has an inlet side  312  and an outlet side  314 . Attached at right angles to duct  302  is a cross-duct  304 . A filter  306  and a heat exchanger coil  308  are, for the purposes of this example, mounted in the cross-duct  304 . Arrows “T” represent the airflow through the filter  306 , coil  308  and through a preferred air inlet device  30  of the type and construction that was described hereinabove. However, in this embodiment, a silencing assembly  320  is provided within the interior of the inlet device  30 . 
     As can be seen in FIG. 15, a preferred silencing  320  assembly comprises a housing member  322  that is fabricated from perforated steel or aluminum; however, other perforated material could also be used. In a preferred embodiment, perforations  324  are {fraction (3/32)} inches in diameter and comprise twenty-three percent of the surface area of the housing member  322 . Housed within the housing member  322  is fiberglass fill material  326  having a preferred density of 2 pounds per cubic foot. However, other acoustical absorbent materials could also be used. The silencing assembly  320  is cylindrical and is disposed within the member  30 . The diameter of assembly  320  is preferably similar to that of the hub of fan  312 . To further reduce airflow noise, other silencing assemblies  400  are preferably positioned as shown in FIG. 15 within the cross-duct  304 . 
     A preferred silencing assembly  400  is shown in FIGS. 16 and 17. As can be seen in those FIGS., assembly  400  preferably comprises a housing member  402  that is sized to fit within the cross duct  302 . The housing member has a top section  410  and a bottom section  430  and perforated side walls  404 . The top section  410  has a centrally disposed ring member  412  that defines a circular-shaped open area  414 . As can be seen in FIG. 17, the top section has an outer skin  418  that is preferably fabricated from 18 gauge metal. In addition, an inner skin  420  is arranged in spaced-apart relationship with respect to the outer skin  418 . Inner skin  420  is preferably fabricated from 22 gauge perforated sheet metal. The perforations are approximately {fraction (3/32)} inches in diameter and collectively comprise approximately about twenty-three percent of the surface area of the inner skin  420 ; however, other sizes and densities of perforations could also be used. Housed between the inner skin  420  and the outer skin  418  is fiberglass insulation preferably having a density of two pounds per cubic foot; however, other acoustically absorbent materials could be successfully used. 
     The bottom portion  430  is preferably similarly constructed with an outer skin  432  fabricated from 18 gauge material and an inner skin  434  fabricated from 22 gauge perforated material. 2.25 inch thick insulation is preferably used between the inner skin  434  and outer skin  432 . In addition, a centrally-disposed portion  436  is removably attached to the bottom section  430  for removal therefrom to enable the assembly  400  to be used in applications wherein air is flowing in at least two axial directions. 
     Also in a preferred embodiment, a plurality of radially extending panels  440  are preferably attached to the top section  410  and the bottom section  430  as shown in FIGS. 16-18. As can be seen in FIG. 18, the walls  442  of panels  440  are fabricated from a perforated material and the ends  444  are fabricated from a non-perforated material of equal thickness. Each panel  440  is preferably filled with an acoustically absorbent material  446  (preferably 2 PCF fiberglass insulation). In a preferred embodiment, the ring member  412  is formed from a channel and is adapted to receive the ends of the panels  440  therein. See FIG.  19 . The other ends of the panels  440  are attached to the outer walls by similarly arranged channel members (not shown); however, other types of fastening arrangement may be successfully employed. 
     In this embodiment, inlet air is adapted to pass through opening  412  and into the fan. As air passes into through opening  412 , the noise generated thereby is substantially absorbed by the radially extending panels  440  and optionally the attenuated cylinder  320  mounted within. FIGS. 20-22 illustrate other airflow arrangements with which the device  400  can be used. In particular, FIG. 20 illustrates the use of device  400  in an application where air can enter from three directions. FIG. 21, illustrates the use of device  400  in an application where air can enter from two directions. FIG. 22 illustrates the use of device  400  in an application where air can enter from one direction. In all cases, the unique radial arrangement of the panels  440  serves to reduce airflow noise without occupying the amount of space that is typically required by prior sound attenuation devices. 
     Accordingly, the present invention provides solutions to the aforementioned problems associated with prior air inlet screens and silencing devices. In particular, the unique designs of the present devices are more compact and efficient than prior air inlet screens. Furthermore, although the present invention is equally effective when used in connection with centrifugal fans, the present invention enable axial fans to be used in applications, where due to large amounts of airflow distortion, could not be previously used. In addition, the present invention provides for effective sound attenuation in compact applications wherein conventional sound attenuation devices could not be used. It will be understood, however, that various changes in the details, materials and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.