Patent Application
20090142212
1. Field of the Invention
The present invention relates generally to the field of mechanical vacuum pumps and blowers used in industrial and municipal applications, and more particularly relates to double rotor multi-lobe type blowers commonly known as positive displacement rotary blowers or simply Roots blowers, and more specifically relates to a Noise Abatement jacket enclosure for reducing noise transmission from rotary blowers.
2. Description of the Prior Art
Rotary blowers are widely used in industrial and municipal applications such as for loading a bulk truck by pneumatic conveying bulk materials or for cleaning municipal sewer lines by vacuum suction. They are desired because of its unique performance characteristics inherent from its rotary positive displacement nature: it delivers an almost constant flow at varying vacuum levels. The ability of varying pressure or vacuum at constant flow makes rotary blowers the ideal tools for pneumatic conveying applications where material clogging can be quickly cleared with the increase of the discharge pressure or suction vacuum while maintaining the transfer capability.
Rotary blowers for use in municipal sewer cleaning applications, especially when used in residential areas, are required to meet stringent noise level requirements, such as those prescribed by OSHA. Rotary blowers tend to be very noisy, sometimes as high as 90-105 dBA if untreated, because of the sharp discharge flow pulsations and engagement of timing gears at high speed. The later is generally of high frequency and radiates from blower body. From a system point of view, the primary source of noise generation in a blower package is the rotary blower. In addition to the Rotary blower, there is an array of secondary sources of noise, such as the motor, the valves, and the silencer body. But they are all about 10-20 dBA less than the noise level of the blower.
Noise generated by the aforementioned sources is propagated either by air or by structure. By introducing upstream and downstream silencers, been widely used in the industry, air borne noise transmitted through air stream is greatly reduced. Effort are also made to reduce the noise level by lowering the pulsation inside the blower, such as the method disclosed in U.S. Pat. No. 4,215,977 to Weatherston by self-cancelling a portion of the pulsation with de-phasing. The commercial application of this technology is, for example, Roots WhispAir as explained in publication “Roots Whispair Blowers”. However, its effectiveness is limited, only achieving 5-10 dBA reduction. Moreover, to reduce the structure borne noise and the air borne noise radiated from blower surface itself, one way is to increase the mass and stiffness of the blower. Such modification of the structure of the blower is expensive and can affect manufacturability of the blower. Another way is to enclose the blower system in a room-like sound enclosure usually consisting of 6 sided wall panels with sound absorbent material and hard reflection surfaces. Sound enclosure built in this fashion is generally very effective, reducing the noise levels up to 25 dBA, but it is expensive, heavy and bulky, especially not practical for mobile applications.
What is therefore needed is a device capable of achieving a high damping and reduction of noise emitted from blower surfaces while being kept light in mass, small in size and suitable for mobile application. It would further be preferable if the device could also serve to enhance the heat transfer from the blower outer surfaces, so that they could operate more quietly, reliably and be used for mobile applications.
Accordingly, it is an object of the present invention to provide a noise abatement jacket enclosure, with a shape generally conforming to blower outer contours, for reducing noise transmission from a rotary blower while maintaining small size, light weight and suitable for mobile application.
It is a further object of the present invention to provide a noise abatement jacket enclosure for a rotary blower which comprises a forced air cooling jacket with a shape generally conforming to blower outer contours to enhance the heat transfer from the blower outer surfaces, so that they could operate more quietly, reliably and be used for mobile applications.
It is a further object of the present invention to provide a noise abatement jacket enclosure for a rotary blower which comprises a sound absorbent layer comprising an inner and outer surface, the inner surface in contact with the blower outer surface, and a sound barrier layer comprising an inner surface in contact with the outer surface of the sound absorbent layer.
It is a further object of the present invention to provide a noise abatement jacket enclosure for a rotary blower which comprises a forced air cooling jacket comprising an inner and outer cover, a sound absorbent layer comprising an inner and outer surface, the inner surface in contact with the blower outer cooling surface, and a sound barrier layer comprising an inner surface in contact with the outer surface of the sound absorbent layer.
Although specific embodiments of the present invention will now be described with reference to the drawings, it should be understood that such embodiments are by way of example only and merely illustrative of but a small number of the many possible specific embodiments which can represent applications of the principles of the present invention. Various changes and modifications obvious to one skilled in the art to which the present invention pertains are deemed to be within the spirit, scope and contemplation of the present invention as further defined in the appended claims.
As a brief introduction, the present invention rotary blower with a noise abatement jacket enclosure includes an inner enclosed casing having a flow suction port and a flow discharge port and an internal bearing support structure, and an outer multi-layered cover, the noise abatement jacket enclosure, comprising a forced air cooling jacket layer, a sound absorbent layer, the inner surface in contact with the blower outer cooling layer, and a sound barrier layer comprising an inner surface in contact with the outer surface of the sound absorbent layer. The noise abatement jacket enclosure is shaped to surround the blower and to conform generally to its body contours, but is oversized to provide adequate cooling spaces between outer skin and the blower.
The present invention rotary blower with noise abatement jacket enclosure also includes two parallel multi-lobe rotors mounted on two parallel rotor shafts respectively, where the rotor shafts are supported by the internal bearing support structure of the inner casing and interconnected through a set of timing gears to rotate the rotors in synchronization for propelling flow from the suction port to the discharge port. Cooling fans are mounted on one of the two rotor shafts at locations adjacent to the inlet and outlet openings of the outer cover for circulating cooling air through the space between the outer cover and the inner casing.
It is therefore an object of the present invention to teach the construction of a noise abatement jacket enclosure for reducing the radiation noise from blower outer surfaces. More specifically, the noise abatement jacket enclosure of the present invention is a multi-layered apparatus constructed to engage in contact with a rotary blower so as to both reduce noise propagation and to act as a cooling path on the blower outer surfaces. The present invention rotary blower with noise abatement jacket enclosure is capable of achieving lower noise level while maintaining being effectively cooled, light weight and compact size, thereby improving the blower application range for mobile and residential areas.
Referring to
As an important novel and unique feature of the present invention, a noise abatement jacket enclosure, is conformingly surrounding the rotary blower 10 of the present invention, and its cross-section is illustrated in
When a rotary blower 10 is surrounded by the noise abatement jacket enclosure 50 of the present invention comprised of the forced air cooling layer 52 in contact with the sound absorbent layer 54 which is in contact with the sound barrier layer 56, there exists both a reduction in the noise transmitted from the rotary blower to ambient as well as an improvement in the cooling provided to the rotary blower.
The theory of operation underlying the noise abatement jacket enclosure 50 of the present invention is as follows. The vibrating inner surfaces 20 of the rotary blower 10 first is reflected by the cover 28, which is also used to guide the cooling air around the blower outer contours. Then the vibrating surfaces 28 of the rotary blower 10 sets the sound absorbent layer 54 in vibration and the vibration induced mechanical energy is turned into heat. It is of note that sound absorbent layer 54 exhibit low stiffness, and as such, act as a decoupler between the sound barrier layer 56 and the rotary blower casing 28. It is the purpose of the sound barrier layer 56 to again reflect sound waves back and forth between the sound barrier layer 56 and the rotary blower 28 thereby increasing the dissipation of sound energy.
In the event that the rotary blower 10 outer surface 20 temperature is not very high (typically lower than 120° F.), there is no need to have the forced air cooling layer 52 to carry the heat away. In that case, the forced air cooling layer 52 is not needed and the rotary blower 10 outer surface 20 is immediately followed by a sound absorbent layer layer 54 which is itself surrounded by a sound barrier layer 56. In such an instance, the combination of the sound absorbent layer 54 and the sound barrier layer 56 is sufficient to achieve the goal of the present invention.
It is apparent that there has been provided in accordance with the present invention a noise abatement jacket enclosure for reducing noise transmission in rotary blower. While the present invention has been described in the context of specific embodiments thereof, other alternatives, modifications, and variations will become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications, and variations as fall within the broad scope of the appended claims.
