Gas and liquid contact apparatus – Fluid distribution – Pumping
Reexamination Certificate
2000-03-17
2002-03-26
Bushey, C. Scott (Department: 1724)
Gas and liquid contact apparatus
Fluid distribution
Pumping
C261S081000, C261SDIG004
Reexamination Certificate
active
06361024
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to equipment for visualizing airflow and, more particularly, to a hand-held ultrasonic fog generator for visualizing laminar airflow in contamination sensitive areas such as clean rooms.
2. Description of the Prior Art
Integrated circuit chips (ICs) are manufactured in hyper clean environments termed clean rooms. Even the smallest of particulates in a clean room can contaminate the wafer under process by introducing, e.g., short circuits that result in a failed IC and a consequent lower yield. Ventilation or air ducts and other such equipment are notorious particulate carriers. For this reason, it is critical to control the airflow in clean rooms. Fog generators are used in clean rooms to visualize laminar airflow emanating from ventilation and air ducts or other such equipment.
There are generally four types of visual vapor or fog generators on the market today. Carbon dioxide (CO
2
) fog generators generate a visual fog using a solid block of CO
2
—dry ice—dropped into a super heated—140 deg F or higher—bath of deionized (DI) water. CO
2
fog generators require an alternating current (AC) power source to heat the DI bath. Once the DI bath is heated, however, the CO
2
fog generator can be disconnected from its AC power source. One disadvantage of the CO
2
fog generator is that the fog quantity it produces is unregulated. That is, the fog quantity cannot be tuned to the particular application because the fog it produces is largely based on the size of the block of dry ice. As the dry ice melts, the quantity of fog output from the fog generator diminishes. Another disadvantage is that CO
2
fog generators must be reconnected to its AC power source after each use to reheat the DI water bath. Yet another disadvantage is that CO
2
fog generators are large taking up valuable floor space in the clean room. CO
2
fog generators are also unwieldy being difficult to move around the clean room.
Helium (He) bubble generators, as the name implies, generate small He filled bubbles of water that float in the air at almost neutral buoyancy. The primary disadvantage with He bubble generators is that they only produce a small quantity of bubbles that do not easily visualize laminar airflow.
Ultrasonic fog generators create a fog by vibrating a bath of DI water using ultrasonic sound. Ultrasonic fog generators use an AC power source. One disadvantage of ultrasonic fog generators is that the unit must be kept stationary to operate properly because if the fog generator is tipped from a horizontal position, the transducers are exposed causing them to burnout and fail prematurely.
The ultrasonic fog generator disburses the water vapor through a long hose. The long hose causes the DI water vapor fog to condense on the inside and drip out the end of the hose creating a possible safety hazard by dripping on the clean room floor. If the ultrasonic fog generator is used over a chemical bath, the hose drippings may additionally contaminate the bath or wafer being fabricated therein. Much like the CO
2
fog generators, ultrasonic fog generators are large and unwieldy.
DI fog generators generate a fog by using steam from boiling DI water. The DI water is heated until boiling produces water bubbles. The bubbles are passed through a bath of liquid nitrogen (N
2
) creating a super cooled fog that visualizes airflow. An example of a DI fog generator is described in U.S. Pat. Nos. 4,771,608 and 4,875,340 to Liu et al., incorporated herein by reference. As shown in both the above-mentioned Liu patents, DI fog generators are unusually large. DI fog generators are either fixedly installed or wheeled to the site. Another disadvantage of DI fog generators is that they require an AC power source and liquid N
2
. DI fog generators are very expensive to own and operate. DI fog generators are the most hazardous of all the above-listed fog generators because they require both a boiler to heat the DI water and extremely cold liquid N
2
to operate.
Accordingly, a need remains for an ultrasonic fog generator that is hand-held, portable, battery operated, reliable, and inexpensive to own and operate.
SUMMARY OF THE INVENTION
An object of the present invention is to overcome the disadvantages associated with prior art fog generators for visualizing airflow in clean rooms.
Another object of the present invention is to provide a hand-held and portable ultrasonic fog generator.
Yet another object of the present invention is to provide an ultrasonic fog generator that is battery operated allowing for ease of movement.
Yet another object of the present invention is to provide an ultrasonic fog generator that allows the user to choose between a battery pack and a remote power source.
Yet another object of the present invention is to provide an ultrasonic fog generator that includes easily accessible trigger switches for turning the fog vapor on and off.
Yet another object of the present invention is to provide an ultrasonic fog generator that delivers fog without dripping condensation from a fog exit or barrel.
Yet another object of the present invention is to provide an ultrasonic fog generator that includes sensors to prevent the operation of transducers without a predetermined level of water covering the transducers thereby eliminating transducer burnout and failure.
Yet another object of the present invention is to provide an ultrasonic fog generator that includes circuitry to prevent battery over charging and discharging.
Yet another object of the present invention is to provide an ultrasonic fog generator that is reliable and inexpensive to own and operate.
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patent: 4771608 (1988-09-01), Liu et al.
patent: 4875340 (1989-10-01), Liu et al.
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Bushey C. Scott
Marger & Johnson & McCollom, P.C.
PWC Technologies, Inc.
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