WO2012079141A1

WO2012079141A1 - Discharge acoustic muffler for a refrigeration compressor

Info

Publication number: WO2012079141A1
Application number: PCT/BR2011/000476
Authority: WO
Inventors: Claudio De Pellegrini; Daniel Henri Bedatty Hofmann; Edson Correa Miguel; Paulo Henrique Mareze
Original assignee: Whirlpool SA; Universidade Federal de Santa Catarina
Current assignee: Whirlpool SA; Universidade Federal de Santa Catarina
Priority date: 2010-12-15
Filing date: 2011-12-15
Publication date: 2012-06-21
Anticipated expiration: 2013-06-15
Also published as: BRPI1005459A2

Abstract

The acoustic muffler (F) is mounted to a discharge tube (10) of the compressor and comprises a tubular body (20) which is internally divided, by a dividing wall (23): in a first chamber (C1) connected, by a first discharge tube portion (11), to a gas outlet (1) of the compressor; and, in a second chamber (C2) maintained in fluid communication with the first chamber (C1) through a passage (23a) in the dividing wall (23) and connected, by a second discharge tube portion (12), to a refrigeration system (2). The second chamber (C2) has a volume which is only a fraction of the volume of the first chamber (C1), so as to produce, through the passage (23a), impedance differences capable of reflecting at least part of the pulsation energy to be attenuated in the compressor operating frequencies.

Description

DISCHARGE ACOUSTIC MUFFLER FOR A REFRIGERATION COMPRESSOR Field of the Invention

The present invention refers to an acoustic muffler for attenuating the pulsation generated by the pressure transients in the gas discharge of a refrigeration compressor, for example of the reciprocating type.

Background of the Invention

Reciprocating compressors used in refrigeration systems are generally provided with pulsation attenuators or acoustic mufflers positioned in the gas discharge. Said acoustic mufflers have the purpose of attenuating the pulsation resulting from the pressure transients generated by the process of compression and discharge of the gas to an associated refrigeration system. These acoustic mufflers also allow reducing the noise irradiated, by the compressor, to the external ambient. The pulsation of the gas being compressed and pumped by the compressor generates an excitation in the compressor shell and in the ducts and components of the refrigeration system to which the compressor is coupled, resulting in high noise levels of the compressor, and also of the assembly formed by the compressor and by the refrigeration system.

The attenuation of the pulsations in the gas discharge of a compressor is generally carried out: by restricting the refrigerant fluid flow being pumped, by reducing the diameter of the flow conduct, obtaining pulsation attenuation by restricting the path of the acoustic energy; or by providing one or more expansion volumes disposed in series with the discharge tube, making the discontinuity of the acoustic impedance to reflect pulsation acoustic waves existing in said tube, thereby attenuating the pulsation transmitted.

The pulsation attenuation by restricting the gas flow has the serious inconvenience of producing load losses in the discharge flow, causing an inevitable and undesirable loss of energy efficiency in the compressor. In view of the inconvenience mentioned above and associated with the pulsation attenuation by restricting the discharge gas flow, there were proposed different discharge acoustic mufflers, to be mounted to the gas discharge tube of the compressor and comprising, as common constructive aspects, two chambers presenting substantially equal dimensions and which are connected in series by a tube which projects to the interior of each of said chambers, through a common dividing wall, a portion of the discharge tube, coming from the compressor, being open to the first chamber, whilst the second chamber is open to a portion of the discharge tube which leads to the refrigeration system with which the compressor is operatively associated.

Although said discharge acoustic muffler, comprising two chambers in series with substantially equal volumes, provides positive results in terms of pulsation attenuation, with acceptable levels of load loss, it is not efficient enough to attenuate medium and high frequencies, for example, in frequencies above about 2kHz. Thus, in these known constructions exemplified in patent documents US 4,111,278 and US 5,196,654, the high pulsation levels, in frequencies above 2kHz, are not adequately attenuated.

In these known constructions, when the pulsation reaches the chambers of the acoustic muffler, part of the pulsation energy is reflected due to the impedance difference found, another part of the energy is dissipated by the volumes of the two chambers and the remaining energy is transmitted to the constituent elements of the compressor and of the associated refrigeration system.

However, since the volumes of the two chambers are substantially equal in said known constructions, in frequencies generally above 2kHz, the impedance difference produced in both chambers is not sufficient to reflect a substantial part of the pulsation energy, allowing a greater portion of the latter to be transmitted to the elements of the compressor and refrigeration system.

Due to the limited efficiency of the known acoustic mufflers comprising two chambers in series and with substantially equal volumes, it is desirable to provide an acoustic muffler which allows obtaining improved levels of attenuation of pulsation noise in the discharge gas of the compressor, in medium and high frequencies, generally above 2kHz.

Summary of the Invention

As a function of the above, the present invention has the object of providing an acoustic muffler, to be mounted to the gas discharge of a refrigeration compressor and which presents a compact and small-size construction, and which is capable of attenuating the noises generated by the pulsations in the gas discharge, in medium and high frequencies, generally above 2kHz, without producing load losses sufficient to impair, in a relevant manner, the energy efficiency of the compressor.

The object mentioned above is attained by the provision of a discharge acoustic muffler for a refrigeration compressor of the type provided with a gas outlet which is connected to a refrigeration system by a discharge tube, said acoustic muffler being mounted, in series, to the discharge tube and comprising a tubular body, with closed ends, which is internally and transversally divided by a dividing wall: in a first chamber, to the interior of which an outlet end of a first discharge tube portion is open, an inlet end of said discharge tube being connected to the gas outlet of the compressor; and in a second chamber, which is maintained in fluid communication with the first chamber, through a passage in the dividing wall, and to the interior of said second chamber being open an inlet end of a second discharge tube portion, an outlet end of the latter being connected to the refrigeration system. According to the invention, the second chamber has a volume which represents only a fraction of the volume of the first chamber, said fraction being capable of producing, through the passage of the dividing wall, impedance differences which are sufficient to reflect at least part of the pulsation energy to be attenuated, in the frequencies produced by the compressor operation. Generally, but not compulsorily, the volume of the second chamber is 9% to 10% of the volume of the first chamber, the attenuation of the pulsation energy being obtained in compressor operating frequencies lying above about 2kHz. The construction defined above allows, by means of a simple and cost-efficient construction and with an adequate dimensional ratio between the volumes of the first chamber and the second chamber of the tubular body of the acoustic muffler, obtaining high levels of attenuation of the pulsation noises of the discharge gases of the compressor, even in frequencies above 2kHz. Brief Description of the Drawings

The invention will be described below, with reference to the enclosed drawings, given by way of example of an embodiment of the invention and in which:

Figure 1 is a perspective view of the present acoustic muffler when mounted, in series, to the discharge tube of a compressor;

Figure 2 is a longitudinal sectional view of the acoustic muffler illustrated in figure 1, with the second discharge tube portion, which is defined downstream of the acoustic muffler, being only partially illustrated; Figure 3 is a graph illustrating the pulsation attenuation curves, in frequencies above 2kHz, related to a prior art acoustic muffler and to the acoustic muffler of the present invention;

Figure 4 is a graph illustrating the curves representing the imaginary part and the real part of the impedance calculated in the connection region between the two chambers of the acoustic muffler; Figure 5 is a graph illustrating the different pulsation levels measured in the compressor discharge, in different frequencies, considering a prior art discharge and a discharge using the acoustic muffler of the present invention; and

Figure 6 is a graph illustrating the different noise levels measured in the compressor discharge, in different frequencies, considering a prior art discharge and a discharge using the acoustic muffler of the present invention.

Description of the Invention

As already mentioned, the present invention refers to an acoustic muffler F to be applied to a refrigeration compressor (not illustrated) , for example of the reciprocating type and which is provided with a gas outlet 1 connected to a refrigeration system 2 by a discharge tube 10 which presents a first discharge tube portion 11, having an inlet end 11a connected to the gas outlet 1 of the compressor, and an outlet end lib connected to the acoustic muffler F. The discharge tube 10 further comprises a second discharge tube portion 12, having an inlet end 12a connected to the acoustic muffler F, and an outlet end 12b connected to the refrigeration system 2, in a well known prior art arrangement.

The first discharge tube portion 11 and the second discharge tube portion 12 are formed in any adequate material as, for example, steel or copper metal alloys. Although not illustrated in the drawings, it should be understood that the outlet end 12b of the second discharge tube portion 12 can be connected to the refrigeration system 2 by means of different tubular connecting elements, well known from the prior art such as, for example, a discharge outlet tube disposed through a wall of the shell of a refrigeration compressor of the hermetic type.

As illustrated in figures 1 and 2, the acoustic muffler F, object of the present invention, comprises a tubular body 20, constructed in any adequate material as, for example, metal sheet or injected plastic, being closed by end walls 21, 22 and internally and transversally divided, by a dividing wall 23, in a first chamber CI and in a second chamber C2, preferably with a cylindrical shape and coaxial to each other, which are maintained in fluid communication with each other, through a passage 23a, medianly provided in the dividing wall 23. The passage 23a presents the form of a through hole, preferably circular and disposed in the center of the dividing wall 23.

Although the passage 23a of the dividing wall 23 is illustrated in the form of a through hole, it can take the form of a tubular extension (not illustrated) , passing through the dividing wall 23 and axially projecting to the interior of the first chamber CI and of the second chamber C2. Nevertheless, it was observed that the use of a passage 23a in the form of a tubular extension tends to limit the versatility of the acoustic muffler F in attenuating pulsations of the discharge gas, in compressor operating frequencies above 2kHz.

The fixation of the dividing wall 23 in the interior of the tubular body 20 can be effected by different manners, with the desired axial positioning, defined by project, being guaranteed by an inner circumferential step formed by the difference between the inner contours of the first chamber CI and of the second chamber C2, or by an alignment of inner radial projections spaced from each other and which can be obtained by deforming the material with which the tubular body 20 is formed. The fixation of the dividing wall 23 in the interior of the tubular body 20 can be obtained, for example, by welding or gluing. At least one of the end walls 21, 22 can be formed in a piece separated from the tubular body 20 and affixed to the latter by gluing, welding or any other adequate means .

According to the invention, the second chamber C2 is dimensioned to have a volume which represents only a fraction of the volume of the first chamber CI, which fraction is capable of producing, through the passage 23a of the dividing wall 23, impedance differences sufficient to reflect at least part of the pulsation energy to be attenuated, in the frequencies produced by the compressor operation, avoiding said part of the pulsation energy from being transmitted to the elements of the compressor and of the refrigeration system 2.

In general, the volume of the second chamber C2 is 9% to 10% of the volume of the first chamber CI, so as to obtain the desired impedance difference in frequencies above 2kHz and the consequent pulsation attenuation in this frequency band.

Figure 3 of the drawings illustrates a graph of the attenuations obtained by the present acoustic muffler, in frequencies above 2kHz, upon a unitary excitation in the inlet of the discharge system and with the pressure being measured in the outlet of said system for each frequency step. The curves in the graph, which are representative of the measurements in a conventional discharge acoustic muffler and in a discharge acoustic muffler according to the present invention, show the expected yield of the proposed muffler.

It should be understood that the specific dimensioning of the volume of the first chamber CI and of the second chamber C2 is carried out as a function of the particularities of the compressor project and of the attenuation effect to be obtained. The variations of the volume ratio between the two chambers CI and C2 generate impedance differences in the communication region therebetween defined by the passage 23a of the dividing wall 23. The impedance differences generated in the region of the passage 23a are capable of blocking a substantial part of the pulsation energy, reducing the part of said energy which, otherwise, would be transmitted to the compressor and to the refrigeration system.

Figure 4 illustrates the effect mentioned above, representing the imaginary part and the real part of the impedance calculated in the region of the passage 23a which makes the connection between the first chamber CI and the second chamber C2. It should be noted that the imaginary part increases considerably from 2kHz.

Besides the difference of volume between the first chamber CI and the second chamber C2, the acoustic muffler F of the present invention has the outlet end lib of the first discharge tube portion 11 axially projecting to the interior of the first chamber CI, through the adjacent end wall 21 of the tubular body 20.

Preferably, the extension of the first discharge tube portion 11, which projects to the interior of the first chamber CI, is aligned with the passage 23a and has the outlet end lib positioned in a region of the first chamber CI, in which the acoustic nodes are found, that is, the locations with low acoustic pressure level, for the frequency bands considered of interest in the compressor project. The main acoustic modes of the first chamber CI are located at the region in which the outlet end lib is provided. Thus, the excitation coming from the compressor is not amplified by the acoustic mode of the first chamber CI, guaranteeing a low energy level transmitted to the following chamber, that is, to the second chamber C2.

The axial alignment of the extension of the first discharge tube portion 11, internal to the first chamber CI, with the passage 23a, and the fact that the outlet end lib thereof maintains, from the passage 23a, a reduced distance in relation to the length of the first chamber CI, allow reducing the load loss caused by the acoustic muffler in the discharge gas flow, when compared with the load loss in the mufflers in which the first discharge tube portion does not project to the interior of the first chamber CI. The small dimension of the chamber C2, its geometry and the fact of being coaxial in relation to the first chamber CI and to the passage 23a, result in two main benefits, besides the impedance difference in the frequencies of interest:

1 - The acoustic modes of the second chamber C2 are in extremely high frequencies, above 7000Hz, in which there is little pulsation energy;

2- All the acoustic modes of the second chamber C2 have their acoustic nodes in the center thereof, which is the region where the passage 23a and also the inlet end 12a of the second discharge tube portion 12 are located.

Thus, the excitations are not amplified by the acoustic modes present in the second chamber C2.

The difference between the volumes of the first and of the second chamber CI, C2 and the dimensioning of the cross-section of the passage 23a, in the dividing wall 23, allow selecting the frequencies to be attenuated by the present acoustic muffler.

The acoustic muffler F of the present invention further presents the inlet end 12a of the second discharge tube portion 12 axially projecting to the interior of the second chamber C2, through the adjacent end wall 22 of the tubular body 20. Preferably, the extension of the second discharge tube portion 12, which projects to the interior of the second chamber C2, is axially aligned with the passage 23a and has its inlet end 12a positioned in a region of the second chamber C2, in which are found the acoustic nodes, that is, the locations of low acoustic pressure level, for the frequency bands considered of interest in the compressor project, by the same reasons regarding the gain of load loss and noise attenuation described above in relation to the extension of the first discharge tube portion 11 in the interior of the first chamber CI.

In the preferred construction illustrated in the enclosed drawings, the two chambers CI, C2 are cylindrical and formed from the same tube, which facilitates their production and allow that the excitations and the effects produced thereby in the interior of the second chamber C2 occur in their regions in which the nodes of the acoustic mode occur, with the already previously commented advantages mentioned above.

The determination of the volume of each of the chambers CI, C2, of the dimensions of the extensions of the first and second discharge tube portions 11, 12, which axially project to the interior of the first and second chambers CI, C2, and also of the cross section of the discharge tube portions 11, 12 and of the passage 23a, is carried out as a function of the attenuation effect to be obtained and of the pulsation band to be attenuated in each compressor project.

Figure 5 illustrates a comparative graph of the pulsation levels measured at the outlet of the discharge system of a compressor of the type considered herein, with and without the acoustic muffler F of the present invention. Figure 6 of the enclosed drawings illustrates a comparative graph of the noise levels generated by the same compressor, with and without the acoustic muffler F of the present invention.

As it can be noted, the provision of a second chamber C2, with a much lower volume than that of the first chamber CI, allows the acoustic muffler F of the present invention to present a higher efficiency in terms of noise attenuation, without the occurrence of pulsation amplifications due to the resonances of the second chamber C2.

The acoustic muffler of the present invention leads to a considerable gain in noise attenuation in a wide frequency spectrum, particularly frequencies above 2kHz, which is not reached by the known acoustic mufflers.

Claims

1. A discharge acoustic muffler for a refrigeration compressor provided with a gas outlet (1) which is connected to a refrigeration system (2) by a discharge tube (10), said acoustic muffler (F) being mounted, in series, to the discharge tube (10) and comprising a tubular body (20), having closed ends and being internally and transversally divided, by a dividing wall (23) : in a first chamber (CI) to the interior of which is open an outlet end (lib) of a first discharge tube portion (11) which has an inlet end (11a) connected to the gas outlet (1) of the compressor; and, in a second chamber (C2) maintained in fluid communication with the first chamber (CI) , through a passage (23a) in the dividing wall (23) , and to the interior of said second chamber being open an inlet end (12a) of a second discharge tube portion (12) having an outlet end (12b) connected to the refrigeration system (2), the acoustic muffler (F) being characterized in that the second chamber (C2) has a volume which represents a fraction of the volume of the first chamber (CI), which fraction is capable of producing, through the passage (23a) of the dividing wall 23, impedance differences sufficient to reflect at least part of the pulsation energy to be attenuated in the frequencies produced by the compressor operation .

2- The muffler, as set forth in claim 1, characterized in that the volume of the second chamber (C2) is from 9% to 10% of the volume of the first chamber (CI), the attenuation of the pulsation energy being obtained in compressor operating frequencies above 2kHz.

3- The muffler, as set forth in any of claims 1 or 2, characterized in that the first discharge tube portion (11) axially projects to the interior of the first chamber (CI), through an adjacent end wall (21) of the tubular body (20), the outlet end (lib) of said first discharge tube portion (11) being positioned in acoustic nodes, with low pressure level in the interior of the first chamber (CI), in frequency bands of the discharge gas pulsation to be attenuated by the acoustic muffler (F) .

4. The muffler, as set forth in claim 3, characterized in that the extension of the first discharge tube portion

(11) , internal to the first chamber (CI), is axially aligned with the passage (23a) of the dividing wall (23).

5. The muffler, as set forth in any of claims 3 or 4, characterized in that the second discharge tube portion

(12) axially projects to the interior of the second chamber (C2), through an adjacent end wall (22) of the tubular body (20), the inlet end (12a) of said second discharge tube portion (12) being positioned in acoustic nodes, with low pressure level in the interior of the second chamber (C2), in frequency bands of the discharge gas pulsation to be attenuated by the acoustic muffler (F) .

6. The muffler, as set forth in claim 5, characterized in that the extension of the second discharge tube portion

(12), internal to the second chamber (C2), is axially aligned with the passage (23a) of the dividing wall (23) .

7. The muffler, as set forth in any of claims from 3 to 6, characterized in that the first and the second chambers (CI, C2) are cylindrical and coaxial to each other .