Method and apparatus for producing fluid cavitation

Details Method and apparatus for producing fluid cavitation Method and apparatus for producing fluid cavitation

2002-04-02

2004-03-16

Bagnell, David (Department: 3679)

Wells

Processes

Vibrating the earth or material in or being placed in the...

C166S304000, C166S312000, C166S177600, C166S177700

Reexamination Certificate

active

06705396

ABSTRACT:

FIELD OF THE INVENTION
This invention pertains to hydrodynamics predominantly related to an oil and gas industry and also this invention can be used for other purposes such as eliminating of microbiological objects, cleaning of surfaces from deposits, erosive breaking (pitting) of metals, promoting of chemical reactions, dispersing of solid particles or high molecular compounds into liquid, making emulsions of non-soluble compounds, and in other processes to improve effectiveness of internal mass transfer.
PRIOR ART
A method of cavitation of a liquid is known (I. S. Pearsall, Cavitation, Mills & Boon Ltd., London, 1972, pp. 9-16) which is referred to as vibrational method. It comprises an oscillating body (for example, a magnetostriction vibrator) that generates waves of pressure and decompression in the ambient fluid. At certain magnitude of acceleration (oscillation frequencies) the pressure during the decompression phase reduces down to atmospheric thus providing a rupture of the fluid continuity and a cavitational cavity is formed which collapses during the counter phase.
The main shortcomings of such prior art method are the following:
1. The cavitation zone (i.e. zone of the fluid discontinuity) is localized in the disturbance area adjacent to the oscillating body, though the pressure oscillations spread far remotely to the liquid;
2. The cavitation zone is stationary;
3. As the hydrostatic (external) pressure grows the fluid rupture becomes impossible.
Another method of cavitation of a liquid known as hydrodynamical method (R. T. Knapp, J. W. Daily, F. G. Hammitt, Cavitation, McGraw Hill Book Comp., N.-Y., 1970, pp. 13-35) comprises placing into a fluid flow of a barrier (for example, a body having a shape poorly followed by the flow) at the downstream part of which a zone of reduced pressure is formed. At certain critical speed of the fluid flow the pressure in this zone decreases down to the atmospheric one resulting in generation of bubbles filled by gas or vapor and, further then, a cavity. When the bubbles or cavities coming off the cavitator they pass into the higher pressure zone where they implode releasing some energy which can be usefully applied, for example, for cleaning of inner surface of a conduit from a corrosion layer or carbonate deposit.
This method of cavitation of a liquid is the most relevant by its implementation to the presently claimed one and therefore it is considered as a prior art prototype.
The main shortcomings inherent to the said prototype are the following:
1. The cavitation zone is formed, according to the cavitation number, at certain magnitudes of the flow speed and ambient hydrostatic pressure;
2. The cavitation zone (cavity) is localized and formed along the flowed body (cavitator) and is stationary;
3. It is impossible to rupture the fluid (produce a discontinuity cavity) at higher hydrostatic pressures, for example, the ones that are typical for deep wells.
The devices are known to cavitate a fluid flow (U.S. Pat. No. 4262757, E 21 B 7/18, 1981; “Oil and Gas J.”, 1977,31/X, v. 75, N 45, pp. 129-146) that are made in form of a barrier rigidly fixed in the direction of a flow (transverse bar, curved blade, cone directed counter flow, extensions of the duct into the flow, etc.). Such devices could be considered as analogs. Main shortcomings inherent to these devices are as follows:
1. According to the cavitation number
 &sgr;=2(
P−Pv
)/&rgr;
V
2
or &sgr;=2(
P+&ggr;z−Pv
)/&rgr;
V
2
where P and Pv are, respectively, the pressure values in non-disturbed and disturbed flow; &rgr;—fluid gravity; z—depth (hydrostatic pressure); V—velocity of the non-disturbed flow respectively to the cavitator, &ggr;=pg, where g is free falling acceleration.
It follows that too high fluid pumping rate is required to provide a rupture of a flow continuity which rates are difficult to obtain, especially in deep wells or long pipelines;
2. It appears to be impossible to obtain cavitation due to such devices at high hydrostatic pressure values, for example in deep wells.
The devices are also known, for example (J. W. Daily and D. F. Harleman, Fluid Dyamics, Addison-Wesley Ltd., Ontario, 1966, pp. 418-424) comprising a cavitator in the form of a ball rigidly fixed on a rode placed in the downstream part of the flow which device could be considered as a prior art prototype due to that it is the most close by its designing principles to the presently claimed ones.
Main shortcomings inherent to this prior art prototype are:
1. Ball closes less than 0.8 of the cross-section area of the conduit and is motionless, and therefore either very high fluid pumping rates or the corresponding narrowing of the conduit (as it is usually employed in hydrodynamic setups to model the cavitation) is required to obtain cavitation and produce a cavitation cavity;
2. If a cavitation is obtained and the cavitation cavity is formed, such cavity will not come off the cavitator since it is stationary, and as a result, it is impossible to provide the effective action of cavitation on the surrounding bodies at a phase of imploding of the bubbles and cavities;
3. Applying of excessive external or internal pressure results in degeneration of cavitation (boiling of the liquid behind the cavitator), where just an underpressure zone will take place only.
SUMMARY OF THE INVENTION
The present method of cavitation of a flow of liquid appears to be the hydrodynamical one by its nature. The method is realized under the following conditions: the flow in a given cross-section of the higher pressure delivery conduit is to be accelerated to a velocity at which Re>Re
cr
, where Re—Reynolds number, Re
cr
—critical Reynolds number, and then the flow is interrupted during a time less than duration of a half of semi-period of the liquid hammer. Due to such interruption, full or partial, a rupture of the fluid flow is provided. The selection of the interrupt time less than semi-phase of a liquid hammer excludes the liquid hammer that is potentially harmful for the pressure part (manifold) of the conduit. To facilitate the fluid flow rupturing at higher hydrostatic pressure the nuclei of cavitation can be introduced into the pumped fluid such as gas bubbles or dispersion of solid particles or emulsion of an insoluble liquid.
The claimed device to cavitate the fluid flow in the delivery conduit comprises a cavitator made in the form of a working body placed in the channel of the conduit and said body has an opportunity to move in a radial direction of the conduit (casing) and is restricted to move along the axial direction of the conduit, and maximal area of cross section of the working body in a plane, perpendicular to axis of the conduit is more than 0.8 of the cross-section of the conduit but not equal to it.
The claimed method of cavitation employs the kinetic energy of a fluid flow that, as it is known, is a function of a mass and velocity of a moving liquid. At a bigger length of a pipeline the force applied to rupture a fluid can reach very high values thus enabling the solution of a task to obtain cavitation at higher hydrostatic pressure. In wells of 3000-5000 m by depth the hydrostatic pressure is equal to 300-500 kg/sq.cm and more, and it is practically impossible to produce cavitation under such conditions due to vibrations or just high pumping rates. Similar conditions of high hydrostatic pressure can take place in the on-land pipelines also.
The free turbulent vortexes nucleate the cavitation, i.e. create in the flowing liquid the local underpressure zones. These vortexes concentrate the gas dissolved in the liquid thus promoting the development of cavitation. Injection into a fluid of gas bubbles, solid particles or emulsions of an insoluble liquid boost the said effect.


REFERENCES:
patent: 3373752 (1968-03-01), Inoue
patent: 3528704 (1970-09-01), Johnson
patent: 3536263 (1970-10-01), Parker
patent: 3545552 (1970-12-01), Angona
patent: 3807632 (1974-04-01), Johnson, Jr.
patent: 3905553 (1975-09-01), Bradley et al.
patent: 4262757 (1981-04-01), Jo

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