Sound attenuation assembly for air-cooling apparatus

Abstract: A sound attenuation assembly (24;26) for a forced-draft, liquid-to-air cooling apparatus (10) having at least two rows of elongate cylindrical members (46) arranged across the air inlet (30) of the assembly (24;26) to provide a blockage to the line of sight of the air flow through the sound attenuation assembly (24;26) to provide a multiple barrier effect of frontal impact on a sound wavefront travelling through the assembly (24;26), the elongate members (46) being made of sound absorbing material, which members provide improved sound attenuation associated with the force-draft apparatus (10) while reducing back pressure losses in the air flow.

Description: The present invention provides a sound attenuation assembly for utilization with air-cooling apparatus. More specifically, the invention provides an assembly that is particularly adaptable for utilization on forced-draft, liquid-to-air cooling apparatus at either, or both, the air entry port or the air discharge port of the air cooling apparatus. Forced-draft, liquid-to-air cooling systems utilize air moving machinery, such as fans, which generate noticeable or significant noise. This noise at a certain decibel level is unacceptable in commercial buildings, urban settings and specific geographic regions or environments, such as Europe and Japan. Sound deflection barriers and sound absorbing members, which are referred to as attenuators, may be installed in the air flow path. Sound deflection barriers have limited application as they may disturb the aesthetic appearance of the building, structure or surroundings. In addition, these barriers have limited effect in reducing the noise level and frequently require structural reinforcements against the wind. The added barrier structures can increase the cost and the overall size of the cooling apparatus. The most frequently utilized devices to suppress an elevated decibel level are the sound absorbing members or attenuators. For sound abatement purposes, the sound absorbing members may be positioned at either the air inlet or air outlet side, or both, of the liquid-to-air cooling system. An exemplary attenuator system includes an enclosure with rectangular baffles therein of a sound absorbing material. One such system is disclosed in JP 52103050. Such attenuator systems are interposed in the air flow path either upstream of the air inlet or downstream of the air outlet for transmission of the air stream through the enclosure and baffle network. Generally these baffles have a rectangular configuration of a material, such as fiberglass. However, the baffles and their associated structure tend to be bulky and expensive. Further, use of the rectangular baffles increases significantly the static pressure losses along the air flow path. There are known sound absorption devices, which are mountable on or from ceilings and walls. However, these devices are considered to be relatively expensive in comparison to attainment of sound attenuation by means of a baffle and enclosure arrangement. A sound attenuation assembly for a forced-draft, liquid-to-air cooling apparatus constructed in accordance with the invention has the features given in claim 1. A plurality of elongate, substantially cylindrical members are arranged in at least two rows across the air flow path through the chamber with the elongate, substantially cylindrical members of the adjacent rows aligned with the gaps between adjacent elongate, substantially cylindrical members of a given row to block the line of sight through the chamber from a sound source to a sound receiver, the elongate substantially cylindrical members each having a varying cross-sectional diameter and an irregularly shaped surface from the top end to the bottom end of the member. The assembly is mountable at either the cooling apparatus air inlet port or air exhaust, or an assembly may be provided at both the air inlet port and the air exhaust port, to reduce the sound decibel level associated with air flowing into and discharging from a cooling apparatus. The surfaces of the elongate members are irregularly shaped from the top end to the bottom end of the cylinder. Therefore, there is a plurality of cylindrical diameters in each member. At.either location of the attenuation assembly with the cooling apparatus, there may be provided a coupling plenum extending a distance of at least twice-the smallest diameter of the largest elongate member in a row of members adjacent to the cooling apparatus port coupled to the attenuation member aperture. In the Figures of the drawings, like reference numerals identify like components. An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure. 1 is an elevational side view of an exemplary cooling tower in proximity to a structure or building; Figure 2 illustrates a diagrammatic attenuation chamber coupled to a liquid-to-air cooling apparatus; Figure 3 shows an elevational view of a wall absorber; Figure 4 shows an oblique of a horizontally hung absorber; Figure 5 illustrates an oblique view of a,vertically hung absorber; Figure 6 illustrates oblique top and bottom views a ceiling tile absorber; Figure 7 is a diagrammatic illustration of an attenuation chamber according to the prior art in a partial cutaway with some of the cylindrical baffles arranged in two rows; Figure 8 illustrates an exemplary right cylindrical baffle according to the prior art in elevational view; Figure 9 illustrates an end view of the cylindrical baffle shown in Figure 8; and, Figure 10 illustrates the embodiment of the present invention showing irregularly shaped, but generally cylindrical baffles. In Figure 1, a classical liquid-to-air cooling apparatus 10, which may include cooling towers or evaporators or condensers, is illustrated in proximity to an associated structure which would generally be a commercial facility such as an office building 12. Apparatus 10 has a cooling tower 14 with an air moving device 16, such as a fan, air inlet port 18 and an exhaust port 20 with sound barrier 22 interposed between structure 12 and exhaust port 20 to suppress the decibel level of the noise emanating from the air flow from exhaust port 20. Figure 1 is an exemplary illustration of an alternative configuration showing attenuation assemblies 24 and 26 positioned at inlet port 18 and exhaust port 20, respectively. Figure 2 shows an enlarged view and representation of attenuation assembly 24, which is representative of such assemblies. As assemblies 24 and 26 are similar in structure and operation only assembly 24 will be described but it will be understood that the description is applicable to assembly 26. In this Figure 2, attenuation assembly 24 is coupled to tower 14 at inlet port 18, Assembly 24 is shown with a generally rectangular housing 25, but the shape of the housing is not a limitation but merely an illustration. Assembly 24 has chamber 28 with air inlet 30, air outlet 32 and a plurality of baffles 34 longitudinally mounted in chamber 28 in the direction of air flow, as shown by the arrow. Individual baffles 34 in any row are separated by a gap 36 between adjacent baffles 34, although there is nothing that dictates such gaps 36 must be equal across cross-section 'x' of air inlet 30. Air inlet 30 has cross-section or cross-sectional area 'x', and baffles 34 have a generally rectangular shape, which typically occupy between about 55% to 65% of cross-sectional area 'x'. Elongate baffles 34 are usually formed from a sound. absorbing material, such as fiberglass. However, baffles 34 are bulky, generally expensive and impose significant pressure losses in the air flow through chamber 28. Other sound suppressing devices, as illustrated in Figures 3 to 6, are known in the sound attenuation art. In Figure 3, elongate, semielliptical shapes 38 of a sound-absorbing material are mountable on a wall in an ordered or linear array. In Figure 4, a pair of the semielliptical shapes 38 are joined at their outer edges to form a pipe-like component 40 with a hollow passage 42 and a baffle 44 therein. Component 40 is suspended and hung horizontally to absorb the sound. Figure 5 illustrates sound absorber component 40 arranged vertically. In Figure 6, the sound-absorbing shapes 38 are noted with their sides either convex up or concave up, which shapes 38 are mountable on a ceiling to absorb the sound. Although these absorbing shapes can be effective in confined spaces where air movement is only nominal, the cost of the sound suppressing devices as well as the installation cost are considered to be expensive for use in a forced air moving environment. In Figure 7, exemplary cylindrical baffles 46 are arranged in a first row 48 and a second row 50 across cross-sectional area 'x' in chamber 28. In this array, baffles 46 in each of rows 48 and 50 have a gap 52 between adjacent baffles 46. The air flow direction is through chamber 28 between inlet air port 30 and exhaust port 32. Baffles 46 of second row 50 are generally aligned with gap 'y', which is between baffles 46 of first row 48. Similarly baffles 46 of first row 48 are about aligned with gaps 'y' between baffles 46 of second row 50. Figure 10 shows the embodiment of the present invention, wherein the substantially cylindrical form is a non-circular shape having a cross-sectional view different from the one shown in Figure 9, for example such different form could be elliptical, oval or semi-annular. Rather, the cylindrical forms could be oblique or erratic, as shown in an exaggerated format, for emphasis, in Figure 10. In these erratic or oblique shapes, the cylinder 46 has a multitude of varying cross sectional diameters. The separation distance between the adjacent rows 48 and 50 is at least the smallest cross-sectional dimensional diameter of the baffle members 46 in the adjacent rows. The separation gap 'y' is between about seventy percent and ninety-five percent of the smallest diameter of the baffle members 46 defining the gap 'y'. Housing 25 in Figure 7 is illustrated with first row 48 and second row 50 of baffles 46, however, it is understood that there may be any number of rows of baffles arranged across chamber 28. The connection of housing 25 to either air inlet port 18 or air discharge port 20 of tower 14 is arranged to provide a plenum distance 'z'. This separation distance is provided between baffles 46 and air inlet port 18, or between baffles 46 and discharge port 20 to minimize the air pressure losses along the air flow path. In operation, at least two rows of baffles 46 block the line-of-sight from the sound source to the sound receiver. More specifically, in Figure 7 air flows into chamber 28 through air inlet 30 for discharge into tower 14 at air-inlet port 18. However, the air passes through chamber 28 around baffles 46, through plenum 'z' and air outlet 32, and into air-inlet port 18. In this configuration, the line of sight of the air flow through chamber 28 from air inlet to air outlet is obscured. More particularly, air inlet 30 has a first cross-sectional area across chamber 28 and about normal to the direction of air-flow. The baffles 46 in rows 48 and 50 effectively provide an insertion loss, which is the decrease in sound power level measured at the location of the receiver when a sound attenuating element is inserted in the transmission path between the sound source and the receiver. In the present invention, the insertion loss is considered to be manifested by a combination of the following two phenomena: 1) a multiple barrier effect of at least two rows of attenuators; and, 2) a sound absorption effect of the attenuator material. The multiple barrier effect is the frontal impact of the attenuators imposed on the sound front travelling from the sound source toward the receiver. As a consequence, the sound energy is reduced by being partially absorbed by the encountered surface of the attenuators and by being reflected into and dissipated in space 26. Sound absorption is provided by the acoustical materials of the attenuators. These materials naturally act to absorb sound. The elements which account for the dissipation of the sound energy within the acoustical materials are small, air-filled pores formed between material fibers or felted minerals. As an example, substantially cylindrical attenuators formed from layers of fiberglass with tiny fibers and interconnecting pores between the fibers have been utilised in certain applications. The air static pressure loss associated with the sound attenuators of the present invention is less than the pressure loss with elongate baffles 34. As the substantially cylindrical attenuator assembly has an over-all larger open area exposed to the air flow, that is in each cross-section the open area is narrowed only in spaces 'y' between adjacent cylinders. Even in the narrowed spaces 'y', the preferred spacing is larger than in known systems with rectangular baffles. Further, the narrow spaces 36 between baffles 34 in Figure 2, have led to high velocity air channelling precluding smooth access of air to the intakes of fan 16, and consequently to additional pressure losses in the air flow. In the present invention substantially cylindrical attenuators render a streamlined surface to the air flow that expands downstream in a plenum between the attenuator row of baffles adjacent to inlet port 18, which results in a reduced inlet pressure loss. Thus, the reduced cost substantially cylindrical baffles 46 reduce the air flow pressure losses, which results in a reduction in the use of energy by air moving devices 16 as well as in a reduced noise level from the operation of the apparatus 10. Preferably, the plenum 'Z' extends a distance between the air outlet 32 and the air-inlet port 18 of at least twice the smallest outside diameter of the largest elongate member in the row adjacent the air outlet 32. Alternatively, the plenum 'Z' extends a distance between the air outlet 32 and an air moving device 16 positioned either in the assembly housing 25 or the air inlet port 18 of at least twice the smallest outside diameter of the largest elongate member in the row adjacent the air outlet 32.

Claims: A sound attenuation assembly (24;26) for a forced-draft, liquid-to-air cooling apparatus (10) having a forced draft apparatus with an air moving device (16), an air flow duct with an air inlet port (18), means for transferring heat (14), and an air exhaust port (20) downstream of said heat transfer means (14), wherein air flows from said air inlet port (18) through said apparatus to said air exhaust port (20), said sound attenuation assembly (24;26) comprising: a housing (25) having a wall, said wall having an inner surface, an outer surface and defining a chamber (28), an air-entry aperture (30) and an air-exit aperture (32), said housing (25) couplable to said apparatus (10) for communication of said air flow through said air-entry aperture (30), said chamber (28) and said air-exit aperture (32) to either an air flow duct port (18) or the atmosphere; a plurality of elongate members (46), each said member (46) having an outer surface and a longitudinal axis, at least a first row (48) of said elongate members and a second row (50) of said elongate members, which first (48) and second (50) rows are adjacent rows and separated by an interval distance (52), said elongate members (46) in each said first (48) and second (50) rows having a separation gap (Y) between adjacent members in said respective first (48) and second rows (50); said first (48) and second (50) rows mounted in said chamber (28) and having said longitudinal axes substantially parallel to and transverse to said air flow direction through said chamber (28), one (48) of said first (48) and second (50) rows of elongate members (46) in proximity to said air-entry aperture (30), and the other (50) of said first (48) and second (50) rows in proximity to said air-exit aperture (32), said rows (48,50) arranged to provide said separation gaps (Y) with said first row (48) substantially aligned with the elongate members of said second row (50) to block a line of sight through said chamber (28) from a sound source to a sound receiver, said elongate members (46) being arranged to provide a multiple barrier effect of frontal impact of said member (46) outer surfaces to a sound wavefront travelling from a source of sound in a direction through said sound attenuation assembly (24;26) to a receiver of said sound, said barrier effect combining with sound absorption by the member material; said attenuation assembly (24;26) mountable either at said air inlet port (18) or said air exhaust port (20) to receive and discharge air in said air flow and operable to reduce a decibel sound level associated with air flowing into and discharging from a cooling apparatus (10); characterised in that each elongate member (46) is substantially cylindrical and has a varying cross-sectional diameter, and in that the surface of each elongate member is irregularly shaped from the top end to the bottom end of the cylinder. A sound attenuation assembly as claimed in claim 1, wherein said separation gap (Y) between adjacent elongate members (46) within each of said rows (48,50) being between substantially seventy percent and substantially ninety-five percent of the smallest cross-sectional diameter of said member (46). A sound attenuation assembly as claimed in any preceding claim, wherein said interval distance (52) between said adjacent rows (48, 50) is at least the smallest cross-sectional diameter of said members (46) in said adjacent rows (48, 50). A sound attenuation assembly as claimed in any preceding claim, wherein said elongate member material is a sound absorbing material. A sound attenuation assembly as claimed in any preceding claim, comprising a plurality of rows (48,50) of said elongate members (46) mounted in said chamber (28), each said row (48;50) having its elongate members (46) generally aligned with the separation gaps (Y) in the adjacent rows (48,50). A sound attenuation assembly as claimed in any preceding claim, wherein said sound attenuation assembly air-exit aperture (32) is couplable to an air inlet port (18) of a forced-draft, liquid-to-air cooling apparatus (10), said assembly (24) further comprising a coupling plenum (Z) positioned in use between said air-exit aperture (32) and said air inlet port (18), which coupling plenum (Z) extends a distance between said air-exit aperture (32) and said air inlet port (18) of at least twice the smallest outside diameter of the largest elongate member (46) in the row (50) of said members (34;46) adjacent to said air-exit aperture (32). A sound attenuation assembly as claimed in any of claims 1 to 5, wherein said sound attenuation assembly air-exit aperture (32) is couplable to an air inlet port (18) of a forced-draft, liquid-to-air cooling apparatus (10), said assembly (24) further comprising a coupling plenum (Z) positioned in use between said air-exit aperture (32) and said air inlet port (18), which coupling plenum (Z) extends a distance between said row (50) of elongate members (46) adjacent to said air-exit aperture (32) and an air moving device (16) positioned either in said assembly housing (25) or said air inlet port (18), which plenum (Z) is at least twice the smallest outside diameter of the largest elongate member (46) in the row (50) of said members (46) adjacent to said air-exit aperture (32). A sound attenuation assembly as claimed in any preceding claim, wherein said elongate member is made from hardened fiberglass. A forced-draft, liquid-to-air cooling apparatus having a forced draft apparatus with an air moving device (16), an air flow duct with an air inlet port (18), means for transferring heat (14), and an air exhaust port (20) downstream of said heat transfer means (14), wherein air flows from said air inlet port (18) through said apparatus to said air exhaust port (20), wherein a first sound attenuation assembly (24) is coupled at said air inlet port (18) and a second assembly (26) is coupled to said apparatus (10) at said air exhaust port (20), wherein at least one of said sound attenuation assemblies (24,26) is as previously claimed.

Inventors: KAPLAN VLADIMIR, KAPLAN, VLADIMIR
Applicants: BALTIMORE AIRCOIL CO INC, BALTIMORE AIRCOIL COMPANY, INC.
Application year: 1996
Main classification: F28C1
IPC codes: F28C1, G10K11