GB2348377A

GB2348377A - In-line fluid mixer with venturi defined by oscillating spherical member or ball

Info

Publication number: GB2348377A
Application number: GB9907487A
Authority: GB
Inventors: Kelly Libby
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-03-31
Filing date: 1999-03-31
Publication date: 2000-10-04
Also published as: CA2302196A1; GB9907487D0

Abstract

The venturi comprises a cylindrical body or tube 2, having inlet and outlet ends 8,10, with a spherical member 12 (eg a ball bearing) loosely confined therein and having an external diameter slightly less than the internal diameter of the cylindrical body. The longitudinal movement of the spherical member within the cylindrical body is limited (eg by coil springs 18,20) so that the spherical member oscillates thereby inducing cavitation within the venturi throat around the circumference of the spherical member. The internal surface 4 of the cylindrical body may be spirally grooved. The mixer may be used in the fuel line of an internal combustion engine (Fig 1) or for the oxygenation of water (Fig 3).

Description

VENTURI APPARATS, AND IN-LINE MIXER INCORPORATING SAME The invention relates to in-line, self powered mixing devices for liquids, with or without the admixture of gases, and to venturi apparatus for use in constructing such devices.

In such a device, the energy required to operate the device and provide the mixing action is derived from the liquid itself by virtue of pressure required to pass the liquid through the structure of the mixer. This structure may be static, or may include elements that oscillate or rotate under the influence of the passing liquid.

It is known that mixing, if sufficiently vigorous, can result in physical and chemical changes to the characteristics of the liquid being treated. For example, weak bonds in molecular chains may be broken, free radicals generated, immiscible liquids or liquid/gas mixtures may be emulsified, or gas may be adsorbed by liquids, particularly when the mixer subjects the liquid being treated to extreme mechanical stresses.

One known type of device capable under suitable conditions of applying such extreme mechanical stresses is the so called cavitating venturi, in which liquid is passed through a venturi under conditions such that the pressure drop at the venturi is so extreme and occurs at such a rate that cavitation occurs, generating micro bubbles that collapse in a mixing chamber downstream of the venturi, generating shock waves which subject the liquid to the extreme mechanical stresses referred to above. It should be understood that, throughout this specification, explanations of physical phenomena occurring during the mixing process are based upon the applicant's present best understanding of the physical mechanisms involved, and should not be regarded as limitative except where utilized to delimit the invention by way of functional limitation.

U. S. Patent No. 3,937,445 (Agosta) discloses the use of a cavitating venturi for emulsifying non-miscible liquids.

U. S. Patent No. 5,647,201 (Hook et al) discloses a cavitating venturi for low flow, low Reynolds number flows, and its use to condition fuel in a bipropellant rocket thruster.

U. S. Patent No. 5,492,654 (Kosjuk et al) discloses the production of a free disperse system utilizing a cavitating venturi produced by a baffle body within a channel and producing a cavitation field downstream of the body.

U. S. Patent No. 5,431,346 (Sinaisky) discloses the use of a cavitating venturi in a nozzle for atomizing a liquid. The forces produced by the collapse of cavitation bubbles are said to break atomic, molecular and crystalline bonds in the liquid.

U. S. Patent No. 5,125,582 (Surjaatmadja et al) discloses a cavitating jet or venturi with a cylindrical surge section downstream providing a surge volume within which the cavitation is contained.

U. S. Patent No. 5,749,945 (Beck) discloses cavitating venturi apparatus adapted for degassing and decontaminating liquids, in which cavitation bubbles are allowed to coalesce and separate.

U. S. Patent No. 3,647,176 (Usry) discloses a cavitating throttling valve in which flow is metered between a metering plug and valve seat.

Proposals have also been made to enhance the action of mixers by engendering oscillation of mixing elements or of liquid flows being mixed, at up to ultrasonic frequencies, and the application of shear forces to liquids being mixed. U. S. Patent No. 4,832,500 (Brunold et al) discloses a mixer in which bodies within a tubular chamber oscillate longitudinally relative to stationary annular configurations on the wall of the chamber, which configurations have sharp extremities and may be helical in form, such as to apply shear to fluid passing through the annular passage between the bodies and the annular configurations.

U. S. Patent No. 4,000, 086 (Stoev et al) discloses emulsification apparatus in which fluids are passed through serial vibrated emulsification cells.

U. S. Patent No. 5,836, 683 (Moon et al) disclose mixing apparatus in which fluid is passed through an annulus around a resonant element.

U. S. Patent No, 4,784,218 (Holt) discloses an arrangement in which a core rod has on its surface an array of interrupter structures for disrupting fluid boundary layers at the wall of the apparatus, the structures being spaced such that wake interference occurs between the vortices produced by the interrupter structures.

U. S. Patent No. 4,071,225 (Holt) discloses a structure in which one of two closely spaced walls is caused to oscillate relative to the other at an ultrasonic frequency so as to disperse, emulsify, dissolve, mix or deagglomerate a fluid passing through the mixer.

It is an object of the invention to provide venturi apparatus that may be utilized in mixing apparatus and other applications.

It is a further object of the present invention to provide a self-powered in-line mixer of simple and durable construction which is capable of applying to a liquid (this term being taken to include a mixed phase fluid exhibiting primarily liquid flow characteristics) extremely intense disruptive forces while permitting a reasonable flow through the mixer without excess pressure drop. Such a mixer has a utility for example as a conditioner of liquid fuels for internal combustion engines or other applications, in the preparation of emulsions and suspensions, in improving the adsorption of gases by liquids, and in improving the activity of components to be reacted in the liquid phase.

According to the invention, venturi apparatus comprises a cylindrical body having an inner wall with an internal diameter and inlet and outlet ends, a spherical body loosely confined within the chamber and having an external diameter slightly less than the internal diameter of the cylindrical body, and means to limit longitudinal movement of the spherical body within the cylindrical body towards the outlet end. In a preferred embodiment, the apparatus includes means to induce turbulence in a chamber defined by the cylindrical chamber between the spherical body and the outlet end. In one embodiment, the inner wall is spirally grooved at least adjacent the spherical body.

According to the invention in a further aspect, there is provided an in-line mixer comprising a generally cylindrical tubular body having an internal diameter extending between two opposite ends and inlet passage to the interior of the body at one upstream end and an outlet passage from the body at the other downstream end, a spherical body contained within the tubular body and having an external diameter slightly less than the internal diameter of the body, the spherical body dividing space enclosed by an inside wall of the cylindrical body into an inlet chamber communicating with the inlet passage and an outlet chamber of communicating with the outlet passage, structure projecting inwardly of the cylindrical body upstream and downstream of the spherical body to limit movement of the latter body longitudinally of the cylindrical body and to control the length of the outlet chamber, and means for maintaining turbulence and creating back pressure in the outlet chamber; the clearance between the bodies, the length of the outlet chamber, and the back pressure creating means being selected so that when a liquid for which the mixer is designed is passed through the mixer at at least a predetermined rate, the spherical body will oscillate.

In one embodiment, the interior wall of the cylindrical chamber adjacent the spherical body has channels provided by single or multiple short helical thread on the inside wall of the tubular body. The structure to limit movement of the spherical body may be formed by helical coils engaged with the thread or threads and having radially inward extending end portions spaced by more than the diameter of the spherical body, or by other equivalent structures providing the function of delimiting the extent of axial movement of the spherical body within the tubular body.

The means for maintaining turbulence and creating back pressure in the outlet chamber may include means for generating a retention vortex in the chamber, static mixer elements, or further venturi apparatus as set forth above.

Where different constituents are to be mixed, the inlet chamber may have separate ports for these constituents.

The invention extends to methods of treating liquids using apparatus as set forth above.

Further features of the invention will become apparent from the following description of exemplary embodiments thereof with reference to the accompanying drawings.

SHORT DESCRIPTION OF THE DRAWINGS Figure 1 is a longitudinal section through one exemplary embodiment of the invention; Figure 2 is a corresponding section through the same embodiment of the invention, set up for treating a different liquid; Figure 3 is a longitudinal section through a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figures 1 and 2, there is shown an in line mixer device intended for connection into a fuel line of an internal combustion engine, with a view to conditioning the fuel of the vehicle prior to use. More specifically, the device is connected into the pressure line of a fuel injection system as close as possible to the injection pump.

Such systems normally have a pressure line and a return line for excess fuel, the flow rate in the pressure line and thus through the device being substantially constant. The device comprises a cylindrical body 2 having an internal surface 4 formed with a thread 6. Internally threaded counterbores in each end of the body receive unions 8,10 by which upstream and downstream ends of the cylinder are connected into a fuel line (not shown). Within the bore formed by the surface 4 is a spherical body, conveniently formed by a ball bearing 12.

Typically the cylindrical body has an external diameter of 2.5cm and an internal diameter just larger than that of the ball bearing which may be llmm in diameter. The difference in diameter between the ball bearing and that of the inner crowns of threads may be about 0.25mm. The bearing is positioned in this embodiment between inturned end tabs 14, 16 on helical coil springs 18,20 screwed into the threads of the bore. The tabs on these springs are positioned in accordance with the viscosity and volatility of the liquid to be treated such that a flow rate through the device similar to that existing in the pressure line of an automotive fuel system will cause the ball to oscillate, given a fuel supply at about 2.8kPa with about 0.2 kPa. The length of chamber 22 downstream of the ball affects the operation of the device, and the stop 16 should be about 2cm from the downstream end of the bore for diesel fuel (Figure 1), and about 3cm for gasoline (Figure 2).

Referring now to Figure 3, the apparatus shown is intended for oxygenation of water. It consists of a tubular body 30, in an upper end of which is located a spherical body in the form of a ball bearing 32, which normally rests on an upper end of a spindle 34 carrying a plurality of spaced baffle plates 36 each having a thickness of about 6.25mm and four equally spaced bores of about 6.25mm diameter, outward of the spindle, the bores in adjacent baffle plats being relatively circumferentially displaced. An elbow 38 at the bottom of body 30 conducts water to an outlet hose connector 40. A stem of a tee 42 conducts water from an inlet hose connector 44. The tee 42 also connects to the body 30 and supports an air inlet pipe 46 terminating in a nozzle 48 just above the ball bearing 32, the nozzle having lateral openings 50.

In an exemplary application, the body 30 has an internal diameter of 3.00cm and a length of about 30cm and the ball bearing 32 has a diameter of 2.86cm. The air nozzle 48 has a diameter of 4mm and is spaced from the ball bearing by about 3.5mm. Water is supplied to the hose connection 44 at a rate of about 9 litres per minute at a pressure of 145 kPa, and air is supplied through the pipe 46 at a somewhat higher pressure and a flow rate of about 150 litres per minute.

Water leaving the unit exhibits a dissolved oxygen content of about 10 parts per million. Similar apparatus may be used for emulsification, with immiscible liquids being introduced through the connection 44 and the nozzle 48, or for the treatment of water and other liquids without the admission of gas or secondary liquids.

The following theory of the operation of the device is offered by way of explanation only, and is not to be regarded as limitative. The phenomena occurring within the device are complex, interactive and not as yet fully understood. It is known from the prior art that the application of extreme and very rapidly varying stresses to liquids can result in disruption of the structure of the liquid at a molecular level, breaking weak bonds and forming free radicals.

While, as stated, the operation of devices in accordance with the invention is not fully understood, various phenomena appear to be involved. The spherical body (or ball) interacts with the tubular body (or tube) to define an annular venturi in which a very narrow throat can be provided without unduly restricting flow through the device because of the large perimeter of the ball. Since the latter can move laterally within the clearance to the tube, the width of this throat at points around the circumference of the ball varies as the ball moves. The helical channels, if provided, on the inside surface of the tube provide an elongated path for a portion of the flow through the throat, thus extending the effective length of the throat, and imparting vortical motion to the flow. Longitudinal movement of the ball, if permitted, will cause variation in the circumferential position of this bypass and will also move the edges of the channels relative to the ball, creating a shear zone. These phenomena, together with the severe pressure drop and very high liquid velocities occurring at the throat of the venturi, tend to induce the formation of cavitation microbubbles.

When the ball oscillates within the tube, the width of the throat at any point around the circumference of the ball will vary rapidly over a substantial range, accompanied by the application of shear forces to the liquid. This is likely to advance the onset of cavitation within the throat, thus enabling a cavitation to be set up at lower flow rates and under less severe conditions than would normally be required.

The flow of liquid through the helical channels, if provided, will also tend to set up a vortical flow in the liquid entering the downstream chamber, and further turbulence will be set up by the wake effect of the downstream surface of the ball. Within this chamber, the turbulence prevent the cavitation bubbles induced in the throat from coalescing; instead they will collapse, subjecting the liquid to severe shock waves. It is known that collapsing cavitation bubbles are capable of generating extremely intense shock waves, to the extent that this phenomenon has been used in application such as rock-breaking (see U. S. Patents Nos. 4,610,321), and has been observed to be associated with photo-luminescence due to the generation of rapidly collapsing gas plasmas. The liquid being treated can thus be subjected to forces sufficient to disrupt intermolecular or even intramolecular bonds with the liquid, with the generation of free radicals and other phenomena tending at least temporarily to enhance the reactivity and bonding capabilities of the liquid molecules. Dissolved gases in the liquid will also tend to be drawn out of solution, while larger bubbles will be broken up, thus greatly increasing the area of the liquid/gas interface. The downstream chamber should be sized to maintain turbulence and permit collapse of the cavitation microbubbles and absorption of gases and vapours to occur, it being postulated that too short or too long a chamber may tend to suppress turbulence, resulting in more gradual collapse and possible coalescence of bubbles, thus reducing the effectiveness of the device.

In order for the device to operate effectively, the dimensions of the device and the flow past the ball should be such that the latter oscillates, With too low a flow rate or inappropriate dimensions, the ball will find an equilibrium position and not oscillate, rendering the device comparatively ineffective.

The annular configuration of the venturi formed around the ball is advantageous, both because it enables a very narrow venturi throat to be achieved while permitting a much greater flow than would be possible through a cylindrical throat of equal width, but because the annular exit flow will induce turbulence around the wake of the ball, and can be subjected to circumferential forces that tend to induce vortical flows extending the residence of liquid in the chamber downstream of the ball while subjecting it to intense turbulence.

The venturi apparatus of the invention may be utilized in other known applications for venturi apparatus, and if operated in cavitating mode, in other applications for cavitating venturi.

Claims

CLAIMS : 1. Venturi apparatus comprising a cylindrical body having an inner wall with an internal diameter and inlet and outlet ends, a spherical body loosely confined within the chamber and having an external diameter slightly less than the internal diameter of the cylindrical body, and means to limit longitudinal movement of the spherical body within the cylindrical body towards the outlet end.
2. Apparatus according to claim 1, wherein the cylindrical body defines a chamber downstream of the spherical member, and the apparatus includes means to enhance turbulence in the chamber and delay passage of liquid while microbubbles induced in the venturi collapse.
3. Apparatus according to claim 1 or 2, wherein the inner wall of the cylindrical body is spirally grooved at least adjacent the spherical body.
4. An in-line mixer, comprising a generally cylindrical tubular body having an internal diameter extending between two opposite ends and inlet passage to the interior of the body at one upstream end and an outlet passage from the body at the other downstream end, a spherical body contained within the tubular body and having an external diameter slightly less than the internal diameter of the body, the spherical body dividing space enclosed by an inside wall of the cylindrical body into an inlet chamber communicating with the inlet passage and an outlet chamber communicating with the outlet passage, structure projecting inwardly of the cylindrical body upstream and downstream of the spherical body and to control the length of he outlet chamber, and means for maintaining turbulence and creative back pressure in the outlet chamber ; the clearance between the bodies, the length of the outlet chamber, and the back pressure creating means being selected so that when a liquid for which the mixer is designed is passed through the mixer at at least a predetermined rate, the spherical body will oscillate.
5. An in-line mixer according to claim 4, wherein the turbulence maintaining means include channels in the inside wall of the cylindrical body adjacent the spherical body which extend a throat portion of an annular venturi formed between the cylindrical and spherical bodies, the channels having shear inducing edges at said inside wall.
6. An in-line mixer according to claim 4 or 5, wherein the back pressure creating means comprises in-line mixing elements downstream of the spherical body.
7. An in-line mixer according to claim 4 or 5, wherein the back pressure creating means comprises means to create a vortex in the outlet chamber.
8. An in-line mixer according to any one of claims 4-7, wherein the back pressure creating means comprise apparatus according to any one of claims 1-3.
9. Venturi apparatus substantially as hereinbefore described with reference to any one of the accompanying drawings.
10. An in-line mixer substantially as hereinbefore described with reference to any one of the accompanying drawings.