BUBBLE GENERATOR

Abstract

The present invention is a novel bubble generator that can be used in many different industrial applications. The design of the bubble generator of the invention allows its user to selectively generate gas bubbles in a liquid having a wide range of diameters in the range from microns to millimeters simply by changing the ratio of the flow rate of the gas to that of the liquid. The bubbles are generated at low liquid and gas supply pressure values. The bubble generator of the invention is able to create an unstable liquid flow regime having large amplitudes and frequencies for liquid containing bubbles without the use of moving mechanical parts and drives.

Claims

1. A bubble generator that has no moving parts and is configured to generate gas bubbles having a wide range of diameters in a liquid simply by changing the ratio of the flow rate of the gas to that of the liquid, the bubble chamber comprising: a. a vortex chamber having a cylindrically shaped wall that defines a vortex chamber cavity; b. openings in the cylindrically shaped wall through which the liquid is introduced tangentially into the vortex chamber cavity; c. a cylindrical bushing with a blind gas channel that is coaxial with the vortex chamber; and d. orifices at the lower end of the gas channel in the bushing through which low-velocity gas jets are radially injected into the liquid flow near the center of the vortex chamber cavity.

2. The bubble generator of claim 1, comprising: a. a body having a hollow side arm near its top through which liquid is introduced into the bubble chamber; b. a cavity hollowed out of the interior of the upper part of the body into which the bushing and vortex chamber is inserted; c. a cavity hollowed out of the interior of the lower part of the body, the cavity having the shape of an inverted cone that acts as an exhaust diffuser; d. a space between the wall of the vortex chamber and the interior wall of the body, which is in fluid communication with the side arm and forms a liquid reservoir from which liquid flows tangentially through the openings in the vortex chamber wall into the vortex chamber cavity; and e. an opening at the bottom of the vortex chamber cavity that forms an outlet nozzle through which the two-phase medium leaves the vortex chamber and passes into the exhaust diffuser.

3. The bubble generator of claim 1, wherein there are n openings in the cylindrically shaped wall that are equally spaced around the circumference of the vortex chamber, wherein the n openings each have diameter d.sub.t, length L.sub.t, and their centers are offset from the center of the vortex chamber by distance R.

4. The bubble generator of claim 3, wherein the n openings are arranged in at least two layers separated by vertical distance L.

5. The bubble generator of claim 1, wherein the orifices at the bottom of the blind gas channel are equally spaced around the circumference of the bushing and have diameters d.sub.a.

6. The bubble generator of claim 5, wherein the orifices are arranged in at least two layers that are separated by vertical distance L between centers and vertical distance Δ between the edges of orifices in two adjacent layers.

7. The bubble generator of claim 2, wherein the opening at the bottom of the vortex chamber cavity is comprised of a conical section having a cone angle α, which is coupled to the outlet nozzle having radius r.sub.n by means of a curved wall portion having radius of curvature r, and the outlet nozzle is connected to the exhaust diffuser by a tapered section of wall having maximum radius r.sub.d.

8. The bubble generator of claim 7, wherein α is in the range 45 degrees to 120 degrees.

9. The bubble generator of claim 7, wherein the ratio r:r.sub.n is in the range 0.8-1.0.

10. The bubble generator of claim 2, wherein the ratio of the tangential flow velocity to the axial flow velocity of the two phase gas-liquid medium as it flows through the outlet nozzle of the vortex chamber is determined by a parameter $A=\frac{R.Math.r_n}{n.Math.r_t^2}.$

11. The bubble generator of claim 10, wherein the value of A is in the range of 4 to 6.

12. The bubble generator of claim 10, wherein the radius of the tip lateral surface the bushing at the location of the orifices is given by the equation:
r.sub.b≧r.sub.n.Math.√{square root over (1/φ)} where: r.sub.b=the radius of the tip of the bushing; r.sub.n=the radius of the vortex chamber nozzle; φ=a parameter, defined by the characteristic A of the vortex chamber, according to the following equation: $A=\frac{\sqrt{2}.Math.\left(1-\varphi \right)}{\varphi .Math.\sqrt{\varphi }}.$

13. The bubble generator of claim 2, wherein when the ratio of the volume flow rate of water Q.sub.w to air Q.sub.air are in the range 22≦Q.sub.w/Q.sub.air≦28 air bubbles with diameter 10-20 μm are obtained.

14. The bubble generator of claim 2, comprising at least one pin inserted into the exhaust diffuser to generate oscillations having a given frequency and amplitude in the two phase gas-liquid medium flowing out of the bubble chamber.

15. The bubble generator of claim 14, wherein the at least one pin protrudes into the exhaust diffuser a distance 0.3r.sub.inst≦L.sub.p≦0.5r.sub.inst, where r.sub.inst is the radius of the cavity at the location of the at least one pin.

16. The bubble generator of claim 14, wherein the diameter d.sub.p of the at least one pin is related to the radius r.sub.inst by the equation 0.3r.sub.inst≦d.sub.p≦0.5r.sub.inst.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 is a vertical cross-sectional view that schematically shows the bubble generator of the invention;

[0043] FIG. 2 is a schematic horizontal cross-sectional view of the bubble generator of the invention in a plane passing through the orifices in the gas channel inside the vortex chamber cavity;

[0044] FIG. 3 is a schematic horizontal cross-sectional view of the vortex chamber;

[0045] FIG. 4 is a schematic horizontal cross-sectional view of the vortex chamber showing the design of the vortex chamber exit nozzle;

[0046] FIG. 5 schematically shows a cross-sectional view of the bushing used to introduce gas into the vortex chamber cavity;

[0047] FIG. 6 is two photographs taken at an exit tube connected to a prototype generator of the invention;

[0048] FIG. 7 is a graph showing the dependence of air bubbles diameter on the liquid/air volume ratio;

[0049] FIG. 8 schematically shows an embodiment of the bubble generator of the invention that is adapted to produce an unstable flow regime with a given frequency of fluctuations; and

[0050] FIG. 9 is a record of the pressure fluctuations at the output of the bubble generator of FIG. 8.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0051] The present invention is a novel bubble generator that can be used in many different industrial applications. The design of the bubble generator of the invention allows its user to selectively generate gas bubbles in a liquid having a wide range of diameters simply by changing the ratio of the flow rate of the gas to that of the liquid. The bubbles are generated at low liquid and gas supply pressure values. Amongst the advantages of this generator is the fact that, at the location of the liquid and gas interaction, the liquid has maximal value of the tangential velocity and has pressure equal to the exit pressure of the medium from the bubble generator. This allows creation of bubbles with minimum diameter of less than 20 μm to bubbles having diameters of several mm at low gas supply pressure. Another advantage of the bubble generator of the invention is the ability to create an unstable liquid flow regime having large amplitudes and frequencies for liquid containing bubbles without the use of moving mechanical parts and drives.

[0052] The key technical problems that are solved by the design of the bubble generator of the invention are: producing air bubbles in a wide range of sizes according to the user's choice, including the bubbles with outer diameters on the order of tens of microns and producing unsteady flow with oscillation having user selected amplitudes and frequency; while, at the same time, raising the velocity of the liquid relative to the gas and decreasing the gas and liquid supply pressures in the region of their interaction.

[0053] FIG. 1 is a vertical cross-sectional view that schematically shows the bubble generator 10 of the invention. Bubble generator 10 is comprised of a body 12, which in cross-section essentially has the shape of an upside down “T” and in three dimensions is cylindrically symmetric around symmetry axis 13—with the exception of side arm 16 located near its top. The interior of the upper part of body 12 is hollowed out to form a cavity into which a vortex chamber 20 is inserted. Vortex chamber 20 is held in place inside body 12 by means of bushing 22. The interior of vortex chamber 20 is vortex chamber cavity 26. The interior of the lower part of body 12 is hollowed out to form a cavity having the shape of an inverted cone that acts as an exhaust diffuser 14.

[0054] Side arm 16 is hollow forming a liquid channel 18 through which liquid is introduced the space between the exterior wall of vortex chamber cavity 26 and the interior wall of body 12, as will be described with respect to FIG. 2 this space forms a liquid reservoir from which the liquid enters vortex chamber cavity 26.

[0055] The interior of bushing 22 is hollow until its lower end; the hollow interior forming a blind gas channel 24 having a circular cross-section. In the side of gas channel 24 at its lowest end there are a number of small orifices 28 that allow gas flowing through gas channel 24 to enter radially into vortex chamber cavity 26. An opening at the bottom of vortex chamber cavity 26 forms an outlet nozzle 30, through which the two-phase medium leaves the vortex chamber and passes into the exhaust diffuser 14.

[0056] FIG. 2 is a schematic horizontal cross-sectional view of the bubble generator 10 in a plane passing through the orifices 28 in the gas channel 24 inside vortex chamber cavity 26. Liquid that flows into the bubble generator through liquid channel 18 in side arm 16 flows into liquid reservoir 19 of the bubble generator body 12 surrounding the wall 34 of vortex chamber 20. In the wall 34 are created a number of equally spaced openings 36 that are shaped such that liquid flowing openings 36 will flow from reservoir 19 into vortex chamber cavity 26 in a direction tangential to the inner side 32 of wall 34. Note that in the embodiment of vortex chamber 20 shown in the figures there are four openings 36; however there can be more or less of these openings—in this embodiment there are actually eight openings 36 arranged in two layers (see FIG. 4)—as long as certain dimensional constraints described herein below are satisfied.

[0057] At the center of vortex chamber cavity 26 can be seen the lower end of the wall of bushing 22, the gas channel 24, and some of the equally spaced orifices 28 through which gas flows in a radial direction into vortex chamber cavity 26. Note that in the embodiment of vortex chamber 20 shown in the figure there are four orifices 28 visible; however there can be more or less of these orifices—in this embodiment there are actually eight orifices 28 arranged in two layers (see FIG. 5)—as long as certain dimensional constraints described herein below are satisfied.

[0058] The bubble generator of the invention is designed such that the tangential flow velocity of the fluid increases and the pressure of the fluid decreases as the distance from wall 32 increases. As a result the necessary pressure head for injecting the gas into the vortex chamber is minimal, while turbulence is maximal. These conditions enable generation of gas bubbles at low pressure values and with low air flow rates.

[0059] Since the diameters of the gas bubbles decrease with increasing relative velocity between liquid and gas, the radial injection of low-velocity gas jets into the liquid flow near the center of the vortex chamber cavity provide for the production of small diameter gas bubbles at chosen operating parameters. Note that the design of the bubble generator 10 enables low values of the operating parameters, i.e. the gas and liquid supply pressures, to be reached.

[0060] FIG. 3 schematically shows a horizontal cross-sectional view of the vortex chamber 20. FIG. 4 schematically shows a vertical cross-sectional view of the vortex chamber cavity 24, showing the design of the vortex chamber exit nozzle 30.

[0061] In the inner wall 32 of vortex chamber tangential openings 36 allow fluid to flow into the interior of vortex chamber cavity 26. Openings 36 have diameter d.sub.t and are displaced from the symmetry axis 13 by distance R. The two phase mixture of liquid and dissolved gas bubbles exits the vortex chamber cavity 26 through outlet nozzle 30, which has diameter d.sub.n=2r.sub.n. In order to reduce hydraulic losses the end wall of the vortex chamber cavity on the outlet nozzle side has a conical shape tapering down to radius r.sub.n before again gradually increasing to radius r.sub.d=d.sub.d/2. The cone angle α of the vortex chamber end wall is in the range 45°-120°.sup.°. In order to reduce pressure losses the conical vortex chamber wall is coupled to outlet nozzle 30 by a curved portion having radius of curvature. The ratio r/r.sub.n is in the range r/r.sub.n=0.8-1.

[0062] The possibility of obtaining the desired ratio between the tangential and the axial flow velocities in the exit nozzle is determined by the value of a parameter A, which is a parameter that represents the geometrical characteristic of a vortex chamber [Dityakin Y. F., Klyachko L. A., Novikov B. V., Yagodkin V. I., Liquid Spraying, Moscow, Mashinostroenie, pp. 25-32, 1977].

[0063] A is determined by the equation:

[00003]$A=\frac{R.Math.r_n}{n.Math.r_t^2}$

[0064] where,

[0065] A—geometrical characteristic of a vortex chamber;

[0066] R—the distance of the tangential cannel axis from axis of the vortex chamber;

[0067] r.sub.n—the radius of the vortex chamber nozzle;

[0068] r.sub.t=d.sub.t/2—the radius of the tangential liquid channels;

[0069] n—the number of tangential liquid channels.

[0070] Since small air bubbles can be obtained at a large ratio between the tangential and axial water velocities at the vortex chamber outlet nozzle the value of A is taken to be between 4 and 6.

[0071] Since the liquid in the vortex chamber moves according to the equation VR=constant, where V is the liquid velocity in the tangential openings 36, the tangential velocity of the liquid increases with decreasing radius, and has a maximum value at a radius equal to the radius of the gas cavity r.sub.φ. At radius r.sub.φ the pressure is equal to the value of exit pressure of the two phase solution at the outlet nozzle 30. Therefore, outflow through the outlet nozzle 30 has an annular cross-section with the thickness of the ring equal to the distance between the radius of the gas cavity and the radius of the vortex chamber outlet nozzle 30, i.e. r.sub.n-r.sub.φ.

[0072] The radius of the tip lateral surface the bushing 22 at the location of the orifices 24 is given by the equation:

r.sub.b≧r.sub.n.Math.√{square root over (1−φ)}

[0073] where: r.sub.b=the radius of the tip of the bushing; [0074] r.sub.n=the radius of the vortex chamber nozzle; [0075] φ=a parameter, defined by the characteristic of A of the vortex chamber, according to the following equation:

[00004]$A=\frac{\sqrt{2}.Math.\left(1-\varphi \right)}{\varphi .Math.\sqrt{\varphi }}.$

[0076] The internal measurements of the vortex chamber should be as small as possible since it is necessary to keep the liquid rotating in the chamber and if the volume of the chamber is large then the value of the tangential velocity will be reduced together with the effectiveness of the of gas and liquid interaction.

[0077] For a bubble generator designed for large water flow the inventors propose creating the vortex chamber with an arrangement of tangential openings 36 arranged in several rows—see FIG. 4, which shows two rows separated by distance L—while maintaining the value of its characteristic A within the above specified range of values. In this way the number of tangential channels is increased which allows their diameters to be reduced while preserving the overall cross-sectional area of the openings and maintaining the distance R (FIG. 2). Thus the diameter of the vortex chamber cavity can be reduced. The total length of the tangential openings must be sufficiently long in relation to their radius, i.e. the ratio Lt/r.sub.t, in order to produce the desired flow in the tangential direction inside the vortex chamber cavity, therefore, increasing the number of openings allows the diameter of the individual openings to be decreased and, for a given value of the ratio Lt/r.sub.t allows their length L.sub.t, i.e. the thickness of wall 34 of the vortex chamber, to be reduced. From experimental flow investigations the inventors have found that the optimum ratio of the axial line length of the openings 36 L.sub.t to their radius r.sub.t should obey the relation L.sub.t/r.sub.t≧1.5÷2.

[0078] In addition the inventors have found that the distance between the rows of tangential openings L should obey the relation L≧d.sub.t in order to obtain the minimal height of the vortex chamber. The height of the vortex chamber is connected with the diameter d.sub.t of the tangential openings and the number of rows by the equation:

L.sub.vor=d.sub.t*n+Δ*(n−1)

[0079] where,

[0080] L.sub.vor=the vortex chamber height;

[0081] n=the number of rows of tangential openings; and

[0082] Δ=the vertical distance between openings in each row [see FIG. 4]

[0083] To produce small air bubbles in a liquid flowing with a large flow rate, the orifices for the entrance of the gas into the vortex chamber cavity also are arranged in levels separated by distance L.sub.0≧d.sub.a, where d.sub.a is the diameter of the air supply orifices 28 located at the center of the vortex chamber cavity 26 (FIG. 5).

[0084] Measurements carried out on a prototype of the bubble generator of the invention show that it can create air bubbles in water having diameters in a large range from less than 20 μm to several mm at low water and air supply pressure (FIG. 6). The experiments were carried out using Laser Doppler Velocimetry (LDV) measurement technique for measurements of bubbles with diameters in the micron range and a high speed photo camera (Canon D1100 with lenses 18-55 f 4.5 and speed 1/4000 sec) for measurements of bubbles with mm dimensions. The diameters of the bubbles generated by the bubble generator of the invention are determined by the ratio of the volumetric flow rates of the liquid to gas.

[0085] FIG. 6 shows two photographs taken at an exit tube connected to a prototype generator of the invention. In these experiments the liquid was water and the gas air. In the photograph on the left the ratio of the flow rates=Q.sub.w/Q.sub.air=14 and the measured diameter of the bubbles is d.sub.b=0.5 mm. In the photograph on the right the ratio of the flow rates=Q.sub.w/Q.sub.air=7.2 and the measured diameter of the bubbles is d.sub.b=2.0 mm. It should be noted that this refers to the diameters of the majority of bubbles. And along with the given diameter, there are bubbles having diameters larger and smaller than the indicated values. In these experiments the diameters of the bubbles were determined using a program “Measuring tools.exe”. This program assumes insignificant optical distortion when processing the images and determines the diameters of the observed air bubble d.sub.b by measuring the diameters of the bubbles in the images and comparing the diameters to those of a standard bubble having diameter d.sub.o=1 mm.

[0086] FIG. 7 is a graph showing the dependence of the diameter of air bubbles on the liquid/air volumetric flow ratio. From a much larger number of measurements than those shown in FIG. 7 it has been found that for creating air bubbles with diameter 10-20 μm the ratio of the volume flow rates of water to air must be in the range 22≦Q.sub.w/Q.sub.air≦28.

[0087] To create an unstable flow regime with a given frequency of fluctuations in the output of the bubble generator cavity, one or more cylindrical pins 40 are inserted into the exhaust diffuser 14 as shown in FIG. 8. The pin/s protrude into the exhaust diffuser a distance

0.3r.sub.inst≦L.sub.p≦0.5r.sub.inst

[0088] where r.sub.inst is the radius of the cavity at the location of the pin/s. Since a large pin diameter decreases the cross section of the liquid flow, and therefore creates large hydraulic resistance, it has been found experimentally that the best results are obtained when the diameter d.sub.p of the pins is connected to the radius r.sub.inst by the equation

0.3r.sub.inst≦d.sub.p≦0.5r.sub.inst.

[0089] Introduction of one or more pins 40 into exhaust diffuser 14 interferes with the orderly rotation of the liquid with dissolved bubbles at the generator's exit, creating intense vortexes, which generate oscillations having a given frequency and amplitude. Changing the diameter of the pin, the number of pins, the location at which they are installed, and the distance that they protrude into the exhaust diffuser of the generator changes the characteristics of the oscillations of the flow in the exhaust diffuser. FIG. 9 shows a plot of flow pulsations generated by the generator in an experimental study carried out with the following parameters: water flow rate Q.sub.w=1.0 l/min, air flow rate Q.sub.a=1.9×10.sup.−3 l/min, bubble diameter in the range d.sub.b=1.5 mm, and obtained frequency of oscillations 6.5 Hz.

[0090] The bubble generator of the invention is simply constructed, has no moving parts, allows creating liquid flow with dissolved air bubbles having a range of diameters at low energy consumption, and also can be adapted to create an unstable flow regime without complicating the design and the introduction of additional movable elements controlled by various types of actuators.

[0091] Although embodiments of the invention have been described by way of illustration, it will be understood that the invention may be carried out with many variations, modifications, and adaptations, without exceeding the scope of the claims.