Acoustics – Sound-modifying means – Muffler – fluid conducting type
Reexamination Certificate
1997-11-21
2001-09-04
Dang, Khanh (Department: 2837)
Acoustics
Sound-modifying means
Muffler, fluid conducting type
Reexamination Certificate
active
06283245
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the attenuation and reduction of machinery and gas flow noise and turbulence in duct systems including, but not restricted to, heating, ventilating and air conditioning air duct systems.
2. Background Information
Conventional sound attenuators used in duct systems use resistance provided by filler material when sound travels through pores of the filler material. Typically FIBERGLASS, ROCKWOOL, foam and other fibrous materials are used for this purpose. Perforated sheets are used to increase the access of the sound from flow passage to filler material. The filler material that is used to attenuate sound creates some new problems. At higher gas flow velocities the filler material gets eroded into small particles and gets entrained in airflow contaminating indoor air of a facility. The filler materials produce some toxic gases, cause microorganisms to grow or release some hazardous products when they come in contact with some other chemicals. These problems make the use of filler material in sound attenuators dangerous. Pat. No. 4,287,962 Packless Silencer, Ingard et al, Sep. 8, 1981 addresses the above mentioned problems associated with the filler material of fibrous nature. Ingard et al uses sound attenuators with acoustic resistance provided by resistive sheets or perforated face sheets. While sound attenuators having perforated sheets were an improvement, they did not include benefits that round and oval passages inherently have over flat sheets or rectangular shapes. The entrance and exit were not designed optimally and this causes flow noise to increase and often results in turbulence of flow. Turbulent flow increases the energy required to maintain gas flow. These disadvantages led to a less than optimal acoustical and flow performance. As will be seen in the subsequent description, the present invention overcomes these disadvantages of the prior art.
SUMMARY OF THE INVENTION
The present invention is a media free sound attenuator that reduces machinery and gas flow noise and turbulence in duct systems. The present invention uses acoustic impedance of perforated passages and cavities, shape factors of the round/flat-oval passage elements and transitions to effectively reduce machinery and gas flow noise and turbulence in duct systems instead of using fibrous filler material. The present invention includes a metallic shell and at least one perforated liner element that acts like a flow passage. For optimum performance, the liner element is a spriral element. The shell and the liner elements are separated by divider plates, transitions are placed at the entrance and exit of the media free sound attenuator to reduce pressure drop and increase acoustic performance. The expansion chamber is an area discontinuity inside the sound attenuator that adds to the attenuation by reflecting the noise in the lower frequencies. The shape factor of the round and flat-oval passage elements adds to broad band noise attenuation, also the transitions at the entrance and exit are also effective in noise attenuation. All these factors enhance the performance of the sound attenuator in terms of insertion-loss, pressure drop and gas flow generates noise. Also, the improvements included in the present invention reduces turbulence of flow, which reduces horsepower required to maintain then flow. The present invention includes an optional expansion chamber that adds to the acoustic impedance of the sound attenuator.
REFERENCES:
patent: 4055231 (1977-10-01), Martinez
patent: 4287962 (1981-09-01), Ingard et al.
patent: 4418788 (1983-12-01), Gorchev et al.
patent: 5473124 (1995-12-01), Yazici et al.
Coday Roger M.
Mysore Prabhanjan
Thurman William E.
Dang Khanh
Morgan George
Price Gary
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