CA2965249A1 - Dampener for a fluid accelerator such as a pneumatic blower - Google Patents

Abstract

Disclosed is a dampener that can eliminate or reduce noise from fluid flow, where the fluid has been accelerated by equipment. A typical kind of equipment that may do such a thing is a pneumatic blower, which takes in ambient air and discharges the air at a higher velocity. The discharged fluid may be passed through the dampener, which includes a noise-absorbing spool structure and a reflective head. Noise that is not absorbed by the noise-absorbing spool structure may be reflected back on the direction of the noise-absorbing spool structure The combination of noise absorption with noise reflection can result in the dampener efficiently dampening noise with comparatively little adverse effect on fluid flow.

Description

DAMPENER FOR A FLUID ACCELERATOR SUCH AS A PNEUMATIC BLOWER
FIELD
The present disclosure is directed to apparatus used for movement of fluids such as gases, and more particularly, an apparatus to eliminate, reduce or prevent the formation or transmission of sonic or oscillatory waves from the apparatus to the environment or between parts of the apparatus.
BACKGROUND
There are numerous types of apparatus that generate streams of accelerated fluid.
One such apparatus is a pneumatic blower. In simple terms, a pneumatic blower takes in air at one or more intakes (inputs) and blows air out at one or more discharges (outputs), typically with a high output velocity. Pneumatic blowers have hundreds of applications. Some of those applications entail moving gases, such as air, and nothing else.
Other applications may involve using gases as a vehicle for moving solids, such as sand, wood chips or grain.
Accelerating gases by apparatus such as a pneumatic blower can result in the generation of noise. Some of the noise is attributable to the sounds made by the accelerated gases that are being drawn into the intake or expelled from the discharge of the pneumatic blower.
Noise is, by its nature, generally undesirable. In some circumstances, noise is not merely a nuisance, but noise becomes a hazard or a safety concern. The hazard can be in the form of potential damage to people's hearing, for example, or disruptive vibrations, or masking sounds (such as alarms or other communications) that are important to hear.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of an assembled dampener.
FIG. 2 is an exploded view of the dampener of FIG. 1.
FIG. 3 is a cross-section of an illustrative reflective head, with attached fins and discharge element.
FIG. 4 is a plan view of an illustrative fin.
FIG. 5 is a perspective view of a cross-section of a dampener depicting fluid flow and streamlines.

2 DETAILED DESCRIPTION
The present disclosure describes apparatus for eliminating, or reducing, or preventing the formation of, or preventing the transmission of sonic or oscillatory waves (generally, "noise") that may otherwise be generated by fluid-accelerating apparatus, such as a pneumatic blower. For purposes of the discussion that follows, such noise reduction may be referred to as "silencing," even if it does not eliminate all of the noise, or "dampening."
Pneumatic blowers may be of many variant configurations, having different shapes, different sizes, and different apparatus to accelerate a gas. For purposes of simplicity, it will be assumed that the gas being accelerated is air, although the concepts described here are not limited to air.. The accelerated air may be air only, or it may be air mixed with other materials (such as solids or liquids or particulates), with the air serving as the vehicle for accelerating and moving the materials.
For purposes of describing the context of the concepts and various features and potential advantages thereof, it will be assumed that the fluid-accelerating apparatus is a pneumatic blower, and that the pneumatic blower is a rotary lobe roots-type blower, useful in applications such as mills for blowing wood chips. Such blower systems may be medium pressure, medium volume systems. Rotary lobe roots-type blowers tend to discharge accelerated air in pulses, rather than a continuous stream of air at a steady rate, and the pulses may generate pulsation noise. The noise can be significant enough to be a safety concern. The concepts described herein may be useful with such a blower system, and may have been subjected to experimentation with such a blower system. The concepts are not necessarily limited to application to such a blower system, however. The concepts may be applied to other kinds of blowers or fluid-accelerating apparatus, such as high frequency screw compressors, high pressure high volume applications like air compressors, and low

3 pressure, high volume applications such as fans. Some such systems may generate significant noise other than pulsation noise. The concepts may further be applied to systems that are not conventionally thought of as blowers, such as exhaust systems for diesel engines for generators or vehicles, or other systems that generate noise when discharging an accelerated fluid.
For simplicity, however, the concepts will be discussed in context with a pneumatic blower.
Pneumatic blowers generally include one or more intakes. The intakes are the sites where the air is drawn into the pneumatic blower. Typically, a pneumatic blower creates internally a pressure that is lower than the ambient air pressure, such that ambient air at a higher pressure tends to move through the intake into the blower with its lower internal pressure. The drawn air moves in rapidly and may be accelerated further by the blower.
Pneumatic blowers also generally include one or more discharges that expel the accelerated air. Air moving through the intakes and the discharges can create noise.
Structures that reduce the noise may adversely affect the flow of the air. In other words, some noise reduction structures may reduce the speed of the airflow, or may require the pneumatic blower to draw more energy to draw air into an intake or expel air from a discharge at a desired speed, or both.
The concepts described below are directed to silencing noise at an intake or a discharge, or both, without substantially compromising air flow speed or significantly increasing energy consumption. Once again, for simplicity, the concepts will be discussed in the context of air accelerated from a discharge.
When air is accelerated by a pneumatic blower, the accelerated air exits the blower through a discharge in a stream. The noise generated at the discharge is not localized in the

4 stream but radiates outward in all directions.
FIG. 1 is an isometric view of a dampener 100 illustrative of the concepts described herein. The dampener 100 is shown in FIG. 1 in an assembled state, and later drawings will illustrate some of the internal components of the dampener 100. The dampener 100 is in an elongated shape with most of its length being substantially uniform circular cross-sections.
The dampener 100 includes a first end 102 and second end 104. For purposes of explanation, it will be assumed that the first end 102 is physically coupled to a discharge of a pneumatic blower (not shown), such that air expelled by the discharge moves into the first end 102 of the dampener 100. The air moves out of the dampener 100 at the second end 104, and may thereafter move into the ambient atmosphere or into additional apparatus (not shown). Although the air may be discharged linearly from the dampener 100, any other type of discharge, such as radial discharge, is also possible.
The dampener 100 includes a first head 106 (or first head ring 106) near the first end 102, which physically couples the dampener 100 to the discharge or manifold of the blower.
The first head ring 106 may be physically coupled to the blower in any fashion, including bolted or welded. In FIG. 1, the first head ring 106 includes holes 108, that may accommodate bolts or other fasteners to hold the first head ring 106 to the blower. Ordinary, the first head ring 106 would be physically coupled to the blower in a very secure fashion, though not necessarily a permanent fashion. The first head ring 106 may typically be attached to the blower like a collar, such that virtually all of the air exiting from the blower discharge is directed into the dampener 100, with no leaks.
In the case of a dampener 100 at the intake of a blower, the first head ring 106 would be physically coupled to the blower. Thus, for a dampener 100 at the intake, air would move into the second end 104 and out of the first end 102 and into the blower; but for a dampener 100 at the discharge, air would move out of the blower into the first end 102 and out of the second end 104.
A second head 110 is near the second end 104. The second head 110 may include structures such as holes 112 that may accommodate bolts or other fasteners to hold the second head 110 to another piece of equipment, such as a tube.
Near the first end 102 is a spool structure 114, which will be shown in more detail in FIG. 2. The components of the spool structure 114 may be welded together for strength and durability, and so the spool structure may be described in some embodiments as a spool weldment 114. The first head 106 is a part of the spool structure 114.
An outer cylinder 116 surrounds the dampener 100 and encloses internal components to be described below.
The rigid or most physically durable parts of the dampener 100 may be constructed from any number of materials or combinations of materials, including but not limited to metals, plastics, and ceramics. For purposes of simplicity, however, the rigid or physically durable parts of the dampener 100 may be constructed from steel. As will be mentioned below, some components of the dampener 100 are not rigid and may be made from more flexible materials.
FIG. 2 shows an exploded view of the dampener 100 shown in FIG. 1.
Near the first end 102 is the spool structure 114. The spool structure includes the first head 106 and a mid head 118, which resemble the flanges of a spool, with a drum 120 between the flanges. Although the first head 106, mid head 118, and drum 120 may be constructed as separate components, they are typically physically coupled to form a a spool structure 114 that behaves as a single unitary element. The center of the drum 120 may be hollow. The drum 120 may have a circular cross-section, though this is not essential. The walls of the drum 120 may be constructed of a mesh-like material. The mesh-like material may resemble a screen or a sieve, or may be embodied as a solid material with perforations, for example. Perforations, if used, need not be in any pattern, and may be randomly distributed; the perforations may be any openings in the solid material of any number, shape, or size. Surrounding the drum 120, and disposed between the first head 106 and the mid head 118 and encased by the cylinder 116, is an absorptive material 122. A
small section of the absorptive material 122 is shown in FIG. 2; in practice, the drum 120 would ordinarily be fully surrounded by a torus of absorptive material 122.
Absorptive material 122 is absorptive of sound. Absorptive material 122 may be composed of packed polyester, for example. Other types of materials, such as fiberglass and/or ceramics'and/or other polymers and/or combinations thereof may also be used; but polyester has been found by experimentation to work well and has a low risk of breaking down. High density polyester is optimal for sound absorption and cohesion.
Cohesion of the absorptive material is important, as any fractured fiberglass or ceramic material, for instance, can damage the blower, pump, fan or other impeller, and if downstream, can contaminate a conveyed material.
In a variation, the drum 120 may be formed in cooperation with the absorptive material 122. The mesh-like material may be reduced or eliminated such that the walls of the drum 120 through which air passes would be formed, perhaps in part, by the absorptive material 122.
In a further variation, there may be no drum, but rather an absorbent material may be formed against the interior surface of the dampener in order to defin a longitudinal hole through which gasses, usually air, may pass. The interior wall of the absorbent material itself may form a retaining barrier.

In operation, most air passing through the drum moves through the center of the drum 120. The air has variations in air pressure or compression, however, which generate or convey sound or noise. The variations in compression enable some air to transmit sound through the mesh of the drum 120 into the absorptive material 122. Though air does not flow through the absorptive material 122, the variations in compression of the air may be conveyed to the absorptive material 122. The noise is less easily transmitted though the absorptive material 122 than it is through air, and so the absorptive material 122 acts as a dampener to reduce or eliminate some of the noise.
The spool structure 114 with absorptive material 122, encased by the cylinder 116, forms a first dampening section of the dampener 100.
The center of the drum 120 may be thought of as defining an axis, along which the air traveling through the drum 120 generally follows. Air exiting from the drum 120 of the spool structure 114 flows toward a second dampening structure, which will now be described.
The air exiting from the drum 120 encounters a reflective head 124, mounted to one or more fins 126. The reflective head 124 is near the second end 104, that is, nearer to the second end 104 than to the first end 102. The fins 126 are nearer the 138 end 104 than is the reflective head 124.
The reflective head 124 is disposed coincident with the axis of the drum 120.
The reflective head 124, though generally not strictly planar, may define a plane that is orthogonal to the axis of the drum 120. For example, an outer edge of the reflective head 124 may be thought of as defining a plane, and the axis defined by the drum 120 would be at or very close to a right angle where the axis intersected that plane.
The fins 126 may be planar, and the planes of the fins 126 may be parallel to or coincident with the axis defined by the drum 120. In other words, the planes of the fins 126 are generally orthogonal to the plane defined by the reflective head 124.
Optimally, the fins 126 are disposed radially about the axis of the drum 120, and are attached at one end to the reflective head 124 and at the other end to the second end 104.
In the embodiment shown in FIG. 2, six fins 126 are used, although not all of the six fins 126 can be seen. The fins 126 are arrayed with approximately sixty degrees of separation between adjacent fins. The reflective head 124 and the fins 126 are physically coupled to one another in a fixed arrangement. The reflective head 124 and the fins 126 may be formed from a single piece of material, or may be joined or physically coupled together by a fastening technique such as welding.
Surrounding the reflective head 124 and fins 126 is a liner 128. Neither the reflective head 124 nor the fins 126 are physically coupled to the liner 128, except through intermediate elements as will be discussed below. As shown in FIG. 2, the liner 128 is almost a cylinder, but for a gap 130. The liner 128 has a diameter smaller than the diameter of the cylinder 116.
The liner 128 fits inside the cylinder 116 and is physically coupled to the cylinder 116; the physical coupling of the liner 128 to the cylinder 116, however, need not be rigid in all places.
In one embodiment, the liner 128 is welded to the cylinder 116 in a select number of attachment sites. FIG. 2 shows an illustrative welding spot attachment site 132 and shows five similar attachment sites; the concept is not limited to that number of attachment sites, nor the disposition of the sites.
The less-than-fully-rigid attachment of the liner 128 to the cylinder 116, and the geometrical features of the liner 128 such as the gap 130, give some limited freedom of the liner 128 to move relative to the cylinder 116. This limited freedom of movement may allow the liner 128 to act as a dampening element. It has been discovered that a less-than-fully-rigid attachment of the liner 128 to the cylinder 116 is better at absorbing sound than a more rigid attachment.
The air exiting from the drum 120 cannot pass through the reflective head 124, and must flow around the reflective head 124. Accordingly, the air stream exiting from the drum 120 may change from a column of air to a tube of air (or to several columns of air) as the air flows around the reflective head 124. The cross-sectional circular area of the center of the drum 120 may be (but need not be) comparable to the cross-sectional area of the ring-shaped area around the reflective head 124. As a result, the air may change from a columnar flow to a tubular flow without major changes in speed or pressure, and laminar flow may be largely maintained, with slight loss. In another variant, the air may change from a single columnar flow to multiple columnar flows by fins 126.
Due to the natural viscosity of air, a boundary layer of air may be expected to form next to the reflective head 124. The boundary layer does not move (or does not move very much) with respect to the reflective head 124. In other words, the boundary layer does not form part of the airstream around the reflective head 124.
Experimentation has shown that noise resulting from the moving airstream does not necessarily follow the airstream. It has been discovered through experimentation that, as the airstream flows around the reflective head 124, some of the noise in the airstream, in the form of variations in air pressure and compression, is conveyed in a more-or-less straight line thorough the boundary layer and into the reflective head 124. The reflective head 124 reflects this noise back toward the spool structure 114.
FIG. 3 shows a cross-section of an illustrative reflective head 124. In FIGS.
2 and 3, the reflective head 124 is depicted as a concave structure (that is, concave in relation to, or viewed from the point of view of, the first end 102) such as a spherical reflector. The reflective head 124 may be shaped to be any kind of reflector, such as a concave elliptical i0 reflector, a concave parabolic reflector, a corner reflector, a concave conical reflector, a concave frustro-conical reflector, or a combination of reflectors, or any other shape of (typically non-planar) reflector. Planar reflectors and convex reflectors have been found to be typically less effective than other shapes selected to reflect sound back in the general direction it came from.
Reflected noise may, to some extent, interfere constructively or destructively with non-reflected noise. The geometry of the dampener 100, such as the distance between the mid head 118 and the reflective head 124, may be selected to improve noise cancellation by destructive interference, though this is not essential to the concept.
Basically, noise is reflected back to the spool structure 114, where the noise may be absorbed by the absorptive material 122. In other words, noise that did not get absorbed by the absorptive material 122 on the first pass may reflected back for a second chance at absorption.
It has been discovered by experimentation that reflection of noise does not result in appreciable resistance to the airstream. It has further been discovered that the change from a columnar flow of air to a tubular flow (or to multiple columnar flows) adds fairly little resistance, so that the amount of additional energy expended to push the air through the dampener 100 is manageable and not a serious impediment. It has further been discovered through experimentation that the noise reduction achieved as described above can also be achieved if the air is moving in the opposite direction (as it may be when a dampener 100 is disposed at an intake for a pneumatic blower).
Further noise dampening may occur before the air exits the dampener 100. After flowing in a column from the drum 120, and flowing around the reflective head 124, the air may be divided into columns once again. The fins 126 may break the airstream into multiple columnar flows.

FIG. 4 is a plan view of an illustrative fin 126. The fin 126 is perforated.
Two kinds of perforations are illustrated in FIG. 4. The fin 126 may have one or more holes 134. In FIG. 4, there are three such holes 134 and they are circular. A molecule one side of a fin 126 could pass through a hole 134 and, be on the other side of the same fin. Another kind of perforation is a core cutout 136, which enables a molecule proximate to any fin to pass through and be proximate to any other fin. These perforations are merely for illustration.
The concept is not restricted to any number or shape or arrangement of perforations.
Perforations, if used, need not be in any pattern, and may be randomly distributed. The perforated fins 126 also may assist in noise dampening.
As shown in FIG. 3, the fins 126 are physically coupled to a discharge element 138.
Illustrative attachment sites 140, where fins 126 are physically coupled to the discharge element 138, are shown in FIG. 3. The fins 126 may be physically coupled to a binding ring 142, shown in FIG. 2. Attachment may be by welding, for example. The binding ring 142 may include one or more perforations 144, which may have any of several sizes and shapes and distributions. The second head 110 may be a fixed component of the discharge element 138, as shown in FIG. 2. The discharge element 138 may also include a flange 146 that may be physically coupled to the cylinder 116. By physical connections such as these, the reflective head 124, which is physically connected to the fins 126, may be held in a fixed place within the dampener 100.
FIG. 5 is a perspective view of a cross-section of a dampener 100. FIG. 5 shows illustrative streamlines 148, which are paths traced out by representative fluid elements (such as "particles" of air). The streamlines 148 through the dampener 100 are roughly the same regardless of which direction the air is moving.
As shown. in FIG. 5, about two-thirds of the length of the dampener 100 includes the spool structure 114 with the absorptive material 122, and about one-quarter of the length of the dampener 100 includes the reflective head 124, fins 126, and discharge element 138.
These proportions are for purposes of illustration, and other proportions are also possible. As shown in FIG. 5, there is a gap or displacement 150 between the end of the spool structure 114 and the reflective head 124. The gap 150 may be selected to obtain a desired balance of fluid flow and noise dampening. Disposing the reflective head 124 closer to the spool structure 144 may result in more noise reflection and thus more noise reduction. Disposing the reflective head 124 closer to the spool structure 144 may also result, however, in more constrictions in airflow and more energy needed to move air through the dampener 100.
The disclosed apparatus may realize one or more potential advantages, many of which were discovered or verified by experimentation and some of which have been mentioned already.
The dampener 100 has been found by experimentation to significantly reduce the noise generated by some very noisy pieces of equipment. Further, the noise reduction may typically come at a cost (it generally takes more energy to move a fluid through a dampener than not to do so), but the cost is low in comparison to other known dampening techniques.
Experimentation has indicated that the concepts described above are more efficient in dampening noise with less air resistance. Tests suggest that, in comparison to other dampeners, the apparatus disclosed here can cut the noise by half or more, while maintaining a comparable fluid flow.
The dampener 100 can be adapted to a number of different types of equipment by adjustment of its dimensions. The dampener 100 may be sturdy and need not include any mechanical moving parts, making it durable.
The subject silencer or dampener 100 has been shown through acoustic modeling and the construction of prototypes and test models to significantly reduce noise without adversely affecting air flow. The net effect of the subject silencer is to drastically reduce the operating noise of silenced machinery, while not adversely affecting airflow, therefore allowing machinery to run at lower HP requirements than with existing silencers, which substantially affect the airflow in order to reduce noise levels. This results in significantly lower power use in plants, mills or factories using the subject silencer.
The embodiments described above are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments without departing from the scope of the concept, which is defined by the claims appended hereto.

Claims (12)

What is claimed's.

1. An elongated dampener comprising a first end and a second end, the dampener comprising.
a drum defining an axis; and a reflective head near the second end, the reflective head defining a plane, wherein the axis is orthogonal to the plane, and wherein the reflective head is shaped to reflect sound reflect sound back in the general direction the sound came from.

2. The elongated dampener of claim 1, wherein the drum comprises a wall, and wherein the wall comprises a mesh-like structure.

3. The elongated dampener of claim 2, wherein the mesh-like structure comprises a solid material having perforations.

4. The elongated dampener of claim 1, wherein the drum is surrounded by an absorptive material.

5. The elongated dampener of claim 4, wherein the absorptive material comprises polyester.

6. The elongated dampener of claim 1, wherein the drum is physically coupled to a first head and a mid head to form a spool structure.

7. The elongated dampener of claim 6, wherein the spool structure is near the first end.

8. The elongated dampener of claim 1, further comprising a plurality of fins physically coupled to the reflective head.

9. The elongated dampener of claim 8, wherein the fins are planar, and wherein the planes of the fins are orthogonal to the plane defined by the reflective head.

10. The elongated dampener of claim 1, wherein the reflective head has a concave structure, in relation to the first end

11. The elongated dampener of claim 10, wherein the concave structure of the reflective head comprises a spherical reflector.

12. An elongated dampener comprising a first end and a second end, the dampener comprising An absorptive material disposed about the longitudinal axis on the interior of said dampener and deifing a longitudinal hole through said absorptive material; and a reflective head near the second end, the reflective head defining a plane, wherein the axis is substantially orthogonal to the plane, and wherein the reflective head is shaped to reflect sound reflect sound back in the general direction the sound came from.