Gas separation: apparatus – Degasifying means for liquid – With control means responsive to sensed condition
Reexamination Certificate
2000-11-17
2002-10-29
Smith, Duane S. (Department: 1724)
Gas separation: apparatus
Degasifying means for liquid
With control means responsive to sensed condition
C096S167000, C096S171000
Reexamination Certificate
active
06471756
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bubble-removing apparatus, and more particularly to an apparatus for removing bubbles entrained in a liquid such as industrial water, oil and chemical solutions.
2. Background Information
Various fluids are used for various purposes. In such use, inconvenience is often caused when bubbles are entrained in the fluids. For example, during a cleaning step of a semiconductor production process, a cleaning solution consisting of acid-based chemicals or alkaline-based chemicals contained in a constant mixing ratio is circulated in a cleaning bath in a predetermined amount to conduct automatic cleaning of semiconductor substrates. In this case, in order to realize the cleaning effects with good stability and reproducibility, it is important to maintain a constant mixing ratio of chemicals, and for this purpose, a stable supply of chemicals in a predetermined amount is required. The bubbles entrained in a liquid of the kind described must be removed therefrom because they cause damage to equipment, increase compressibility of the liquid, cause vibration and noise, result in poor product quality, and cause deterioration and change in the quality of the liquid.
Various methods have been used for measuring a supplied amount of a cleaning solution which is supplied automatically. Recently, an ultrasonic flow meter having the advantages of facilitating miniaturization of a measurement apparatus and varying pressure has been widely used. This ultrasonic flow meter has the further advantage that the supplied amount of cleaning solution can be readily changed and the mixing ratio of chemicals can thereby be simply adjusted automatically. However, the ultrasonic flow meter is susceptible to the influence of bubbles in the cleaning solution, and accurate measurement can not be made without eliminating the bubbles. These bubbles are formed, for example, during a change of canisters containing chemicals or during operation of the pump (e.g., a diaphragm pump). For this reason, various types of conventional bubble-removing apparatuses have been proposed and employed. However, in many cases, when bubbles are discharged, the solution is entrained in the bubbles and are both discharged together in a large amount. Furthermore, with such conventional bubble-removing apparatuses, additional equipment, such as a suction pump or a tank, must be provided to insure proper liquid/gas separation and subsequent discharge of the gas, thereby increasing the overall size of the apparatus. Accordingly, an operation where only a small amount of cleaning solution is discharged can not be achieved.
A bubble-removing apparatus has been known in which a liquid is fluidized by mixing it (e.g., by rotation) in a vessel and the bubbles are collected at the central portion for removal in order to use the apparatus even when the flow amount is small. For example, one such apparatus is disclosed in JP-A-11-19406. According to the disclosure in JP-A-11-19406, the bubble-removing apparatus can be used even in a case where the flow amount of liquid is low, and the apparatus is constructed to separate bubbles and collect the bubbles towards the central axis of a vessel by a rotating flow and to discharge the bubbles through a discharge outlet provided at the central axis of the vessel. At the discharge outlet of this apparatus, an automatic ON-OFF valve is disposed. The ON-OFF valve has a mechanism wherein a spherical discharge valve float is raised by the buoyancy of the liquid to shut the discharge outlet, and when bubbles are collected, the discharge valve float is released by its own weight and a spring to discharge the bubbles through the outlet.
However, in the case of the automatic ON-OFF valve of the abovementioned apparatus, since it is necessary to use the spring to securely open the discharge outlet when the liquid comprises chemicals such as acid or alkali, it is difficult to maintain a stable performance for a long period of time. Further, operation of the valve varies depending upon the balance of, for example, the discharge valve float's own weight, the spring force of the spring and the buoyancy of the discharge valve float. Accordingly, when the internal pressure inside the vessel largely changes by the flow amount of the liquid which flows into the vessel, the operation of the valve can not accurately follow the change. For this reason, with such type of apparatus alone, it has not been possible to treat a liquid which is to be used for the case where the flow amount is widely varied.
A bubble-removing apparatus has been known wherein an air vent which has a ball element instead of a spring is disposed at the discharge outlet. However, in such apparatus, the ball element is unstable, and when the flow amount increases, the ball element will float in the air vent and the liquid will flow out together with the bubbles. Further, when the ball element is raised and shuts the discharge outlet of the air vent, the liquid containing bubbles will flow out from the outflow port of the bubble-removing apparatus, thereby preventing the removal of bubbles. In addition, since the ball element has a spherical surface, when the ball element moves only a little, the liquid flows into the air vent and the air vent becomes filled with the liquid, whereby the ball is made further unstable and it becomes difficult to keep balance with the flow amount.
Further, a pump is used in order to permit the liquid to flow into a cleaning bath or the like through the above bubble removing apparatus. Usually, however, the pump does not necessarily create a constant pressure at all times. Particularly, with diaphragm pumps, air-actuated pumps and the like, the pressure can not be kept constant and pulsations are generated, whereby the flow amount becomes unstable due to transfer of such pulsations. As a result, problems may sometimes arise when the above liquid is used, for example, in a subsequent cleaning step.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a bubble-removing apparatus for removing bubbles entrained in a fluid regardless of the flow amount of fluid or a fluctuation in the flow amount.
Another object of the present invention is to provide a bubble-removing apparatus by which bubbles entrained in a fluid can be removed from a bubble discharge outlet without permitting the fluid to flow out from the discharge outlet.
Another object of the present invention is to provide a bubble-removing apparatus which does not require additional equipment, such as a suction pump or a tank, for the effective removal of bubbles from a liquid and the subsequent discharge of the bubbles.
Still a further object of the present invention is to provide a bubble-removing apparatus by which the internal pressure can be controlled and by which pulsations of fluid flowing out from a discharge outlet can be buffered while bubbles are removed from the fluid.
The foregoing and other objects of the present invention are carried out by a bubble-removing apparatus comprising a main body having a main chamber comprised of a first chamber portion, a second chamber portion and a third chamber portion connecting the first chamber portion in fluid communication with the second chamber portion. A stationary rod or bar is disposed in the main chamber along a central axis thereof. At least one inflow port is disposed in the main body for introducing a fluid containing entrained bubbles tangentially into the main chamber so that the fluid is caused to rotate in the first, second and third chamber portions about the central axis of the main chamber to thereby cause the bubbles to separate from the fluid and collect around the bar.
The main body has an outflow port for discharging the fluid whose entrained bubbles have been separated, and a discharge outlet for discharging the bubbles separated from the fluid. A valve chamber is disposed between the discharge outlet and the first chamber portion of the main chamber. A block member is disposed in the
Adams & Wilks
Satoh Jushi Kogyo Co., Ltd.
Smith Duane S.
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