Rotary kinetic fluid motors or pumps – With sound or vibratory wave absorbing or preventing means...
Reexamination Certificate
1999-06-30
2001-04-17
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
With sound or vibratory wave absorbing or preventing means...
C415S208200, C454S187000
Reexamination Certificate
active
06217281
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a low-noise fan-filter unit used in a clean room, and particularly relates to a fan-filter unit applicable in a clean room or hospital for providing filtered airflow at pre-defined cleanliness and flow quality. The unit performs at a very low noise level.
BACKGROUND OF THE INVENTION
The fan-filter unit of the invention is an air filtration device incorporating a centrifugal fan and a filter, and provides purified air to the space of a room. Fan-filter units have been widely used in the industry, medical and research facilities. They are especially popular for their characteristics of space-saving, energy-saving and easy installation. However, existing fan-filter units often generate high levels of noise in operation and may psychologically or mentally annoy the personnel within the room where precise and delicate manufacturing processes are being handled. Therefore, there is a need for a clean room fan-filter unit to operate and generate noise at a low level.
A fan-filter unit usually incorporates a centrifugal fan. The airflow drawn into the unit is guided by interior air passageways to the filter in the unit. After passing through the filter, the air is propelled into the designated environment, such as a clean room. The construction of the fan-filter unit makes less space in the axial direction of the fan than in the radial direction. The limited space increases the difficulty of incorporating noise reduction constructions into the fan-filter unit. For example, in a conventional fan-filter unit, for the airflow from the inlet to the outlet, the contact area of the airflow to some sound-absorbing materials is so limited that it performs low effectiveness.
People have been trying to solve the serious problem of the high noise levels of conventional fan-filter units. An exemplary prior art for reducing the noise of a clean room fan-filter unit is disclosed in U.S. Pat. No. 5,803,721. It provides a fan-filter unit having a perforated plate situated within the airflow path in the fan-filter unit housing such that the perforations diffuse the airflow before it passes through a filter and exits the housing. The uniform airflow provided by the perforated plate produces a reduced noise level.
SUMMARY OF THE INVENTION
The primary objective of the present invention is therefore to provide a low-noise fan-filter unit and to reduce the noise influence to the environment.
To achieve the aforesaid objective, a fan-filter unit according to the present invention includes a housing having at least an air inlet and a coaxial air outlet; a centrifugal fan installed in the housing for drawing air from the air inlet into the housing and propelling it out of the air outlet; a filter attached with or inserted into the housing for removing impurities from the air; and noise reduction means installed along the air passageway between the fan and the filter. The housing includes a front wall, a back wall, a right wall, a left wall and an upper wall. The front, back, right and left walls are in the direction parallel to the axis of the fan. The air inlet is on the upper wall. The centrifugal fan is installed in the interior of the housing and positioned under the air inlet. The noise reduction means are installed in the housing along the air passageway between the fan and the filter.
The noise reduction means include at least a tortuous air passageway formed by a flow-guiding plate and a noise-reduction plate, and sound-absorbing materials furnished on walls of the air passageway. The flow-guiding plate is positioned under the fan and extends in the radial direction of the fan. The noise-reduction plate, which can be in one piece or two separate pieces, attaches to the left and right walls of the housing, and extends to the front and the back walls. The position of the noise-reduction plate in the axial direction of the fan is between the flow-guiding plate and the filter. Therefore, the tortuous air passageway is formed among the flow-guiding plate, the noise-reduction plate and the filter. The flow-guiding plate first guides the discharged airflow moving in the radial direction of the fan. The airflow turns into direction parallel to the axial direction of the fan after reaching the walls of the housing. Then, the airflow is further guided by the noise-reduction plate extending inward in the general direction parallel to the radial direction of the fan. And finally, the airflow passes through the opening of the noise-reduction plate, diffuses into the cavity under the noise-reduction plate and exhausts through the filter into a clean environment. Hence, the airflow turns several times in the tortuous air passageway before passing through the filter. The tortuous and extended air passageway, together with the sound-absorbing materials furnished along the air passageway, increases the contact area of the airflow to the sound-absorbing materials, and enhances noise reduction.
An exemplary embodiment of the sound-absorbing materials in the noise reduction means according to the present invention is foam pads furnished on the surface of the air passageway. The foam pads have a wavy or wedged-like surface to absorb noise in the air passageway.
Another exemplary embodiment of the sound-absorbing materials in the noise reduction means according to the present invention is perforated plates mounted along the surface of the air passageway and separated by a clearance with aforementioned plates and walls. Acoustic waves penetrating into the clearance would reflect therein and dissipate into heat, and, thereby, the noise is reduced. Meanwhile, the surfaces of the perforated plates are preferably smooth so that friction losses can be minimized.
For an embodiment of the present invention, in a sectional view taken along a plane parallel to the axis of the fan, the height of the tortuous air passageway should be the same as or close the height at the outlet of the fan, but the opening in or between the noise-reduction plate should be at least twice of the width of the aforementioned height, so that the pressure drop in the air passageway can be minimized.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 3783969 (1974-01-01), Pall
patent: 4410065 (1983-10-01), Harvey
patent: 4560395 (1985-12-01), Davis
patent: 5470363 (1995-11-01), Leader et al.
patent: 5720274 (1998-02-01), Brunner et al.
patent: 6030186 (2000-02-01), Tang
patent: 406159752 (1994-06-01), None
patent: 8-86297 (1996-04-01), None
patent: 11-37525 (1999-02-01), None
Chen Lai-Fu
Chou Ya-Wen
Jeng Ming-Shan
Tasu Fang-Hei
Tseng Pen-Chang
Birch & Stewart Kolasch & Birch, LLP
Industrial Technology Research Institute
Look Edward K.
McDowell Liam
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