RU2344874C1 - Method for dispersion of liquids, their mixtures and solid substance suspensions in liquids - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: method includes preliminary mixing of liquid with stabiliser and further homogenisation. Circulating liquid flow is formed, periodically cut off, and part of cut off flow is taken and separated into two or more paired flows. In every pair flows are transformed into high-speed jets and sent opposite to each other to provide periodic head-on impact with frequency equal to frequency of circulating flow cut off. In order to control extent of dispersion, length and speed of circulating flow motion are changed.

EFFECT: higher extent of medium dispersion.

4 cl, 4 dwg

Description

The invention relates to the field of processing liquid media and can be used to obtain liquid composite materials, including nanostructured liquids.

The technology for producing liquid composite materials includes a certain sequence of operations, while the primary and determining operation is the dispersion of liquid or solid components. At the stage of dispersion, an ensemble of particles with a certain average statistical size is obtained. In this case, the degree of dispersion is significant, which can correspond to the mastered microlevel or belong to a more promising nanolevel.

In liquid media, a collision effect is usually used for dispersion, which leads to crushing of the colliding particles. To assess the probability of dispersion of a fluid particle, the Weber number We, which expresses the ratio of inertia to surface tension forces, is used (see, for example, Povkh I.L. Technical hydromechanics. Leningrad, publishing house Mechanical Engineering, 1969, p. 263):

where ρ is the density of the colliding particle;

V is the relative velocity of the colliding particles;

d is the particle diameter;

σ is the interfacial surface tension.

The above ratio shows that the degree of dispersion in a liquid depends mainly on the speed of collision of a particle with an obstacle. As an obstacle, the vessel wall or another moving particle of liquid can act. With the value of We = 10, each drop is divided into 2 particles, and when We = 14 is reached, each drop is divided into 10 parts. A further increase in the number of Weber leads to an increase in the number of crushed particles (Volynsky M.S. Unusual life of an ordinary drop. M., Knowledge, 1986, p. 67).

Collisions of fluid particles are used in various dispersion methods. Known, for example, methods of dispersing fuel mixtures based on the mixing of liquids (homogenization) and the subsequent atomization of the mixture using a nozzle. When passing through the nozzle orifices, particles experience collisions that cause atomization of the liquid. The size of the particles atomized by the nozzle, as experience shows, is tenths of a millimeter and cannot be significantly reduced due to the speed limits of the colliding drops.

More effective methods of dispersing liquids are based on the use of cavitation phenomena. When cavitation dispersion in a liquid medium creates the conditions for the emergence of the negative pressure necessary for the development and subsequent collapse of cavitation cavities. As a result of the collapse of the cavitation cavity, the local pressure increases sharply, a shock wave arises, which causes dispersion of the fluid particles or the grinding of solid particles located in the zone of the collapsing cavity. The dispersible particle experiences a powerful shock collision with the wall of the collapsing cavity, the local pressure pulse at the moment of the collapse of the cavity reaches 10 ⁶ atmospheres.

Cavitation dispersion as a method of processing liquid media is used to create a variety of technological processes. As an example, we can cite methods for producing water-coal fuel (application No. 2003123237) and water-fuel emulsions (patent No. 2208043), methods for processing monodisperse cream emulsions (patent No. 2240782) and silicon organolipid microcapsules for medical and cosmetic preparations (patent No. 2173140), separation methods ( application No. 20011114277) and degassing of liquid media (patent No. 2254913) in the food, chemical, mining industries.

These methods can be used as analogues of the invention. A common disadvantage of the above analogues is the low degree of dispersion of the components associated with the limitation of the rate of collapse of the cavitation cavity.

The prototype of the invention is a method for the operation of an acoustic emitter described in patent RU No. 2149713 C1, B06B 1/18. The principle of operation of the acoustic emitter is illustrated in Fig.4. In an acoustic emitter, the liquid medium passes through periodically overlapping channels of the rotor and stator, which have a cylindrical shape and a coaxial arrangement. A distinctive feature of the prototype is the flow of the processed fluid from the outer surface of the rotor to the center.

The prototype operates as follows. At the moment of periodic coincidence of the channels of the rotor and stator, the processed fluid passes into the internal cavity of the stator, where there is a receiving chamber and an outlet pipe. At the moment of blocking of the stator channels in the liquid located in the cavity of the channels, a negative pressure is created, due to which cavitation cavities arise and collapse. The movement of fluid from the edge to the center promotes the concentration of cavitation cavities and the occurrence of acoustic vibrations inside the stator cavity, which leads to the intensification of dispersion processes.

The main disadvantage of the prototype is the lack of impact interaction between the flows passing through the stator channels.

The aim of the present invention is to eliminate the above disadvantages and increase the degree of dispersion of liquids, their mixtures and suspended solids. The goal is achieved in the following way.

Initially form a circulating fluid flow in a closed loop with a given cross section and speed. Periodically, this flow is blocked and thereby provides conditions for increasing pressure due to the occurrence of water hammer. Part of the fluid is taken from the overpressure stream, which is divided into two or more paired streams. In each pair, the flows are directed to nozzles oriented towards each other. At the exit from the nozzles, high-speed oncoming jets are formed, which experience a periodic frontal collision in the receiving chamber with a frequency equal to the frequency of overlapping the circulating flow. As a result of a head-on collision, the jets are divided into many crushed particles and molecules, that is, liquid disperses.

High speed of the jet is provided due to hydropercussion increment of pressure in a circulating closed circuit, the magnitude of hydropercussion increment of pressure is calculated by the Zhukovsky formula:

Δp = aρΔV,

where a is the speed of sound in a liquid, and ΔV is the change in flow velocity.

The time of hydropercussion in a circulating circuit is determined by the formula:

t = 2l / a,

where l is the length of the pipeline from the feed pump to the point of shutoff of the flow (see figure 1).

From the above formulas it can be seen that the water hammer intensity and the pressure increment can be set in a closed circuit and controlled by changing the speed of the circulating flow, and change the time of the impact of hydroshock pressure by choosing the length of the supply pipe. In particular, the length of the supply pipe should be selected so that the duration of the hydropercussion exceeds the formation time of the high-speed jet.

Let us consider in more detail the physical picture of the phenomena occurring in a liquid after the collision of two jets. At the time of the collision, the mass of liquid ceases to move. First, the liquid layer that has reached the meeting line stops, and then the remaining layers gradually stop. A pressure wave propagates in the direction of motion, resulting in compression of the fluid. After the compression phase, the liquid expands, and the pressure wave begins to propagate in the opposite direction. The compression and expansion processes are repeated with high frequency and decaying amplitude. As a result of a damped oscillatory process, a periodic decrease in the liquid pressure is observed in the collision zone, which leads to the formation of cavitation cavities. Each of the cavitation cavities collapses and thereby enhances the dispersion effect. Thus, in the collision of high-speed jets, the dispersion process from the oncoming collision of particles is enhanced due to the emergence and collapse of cavitation cavities.

Let us make a numerical assessment of the maximum capabilities of the proposed method. Suppose that as a result of a collision with an obstacle, all of the kinetic energy of the water jet transforms into the potential energy of the compressed column of liquid. Suppose also that the potential energy reserve is sufficient for the compressed column of liquid to warm up and transfer from a liquid to a vaporous state, that is, to completely disintegrate into molecules. For the numerical calculation of the phenomenon, we use the known data: the specific heat of water c = 4182 J / kg · K and the specific heat of vaporization of water q = 2257 kJ / kg. Assuming that all kinetic energy of the jet is spent on heating and vaporization of the liquid column with an initial temperature t = 20 ° C, and also taking into account the equality

we find the linear velocity of the liquid column:

Upon reaching the obtained velocity value, the entire mass of the jet after collision with an obstacle is dispersed to a molecular level. For two oncoming jets, the obtained value is the relative speed of movement, therefore, to achieve a similar effect, the oncoming jets must be accelerated to a speed of V / 2 = 1140 m / s. Jet formation at such a high speed is a technically achievable result. To confirm the possibility of achieving the named speed, as well as the possibility of implementing the present invention, it is possible to cite the parameters of the hydraulic cutting process used in industry, in which a fluid pressure of up to 4000 atm is created, which provides a high-pressure jet with a speed of up to 1200 m / s.

Consider the possibility of technical implementation of the proposed method based on a rotary dispersant. To describe the method, we use the circuit shown in figures 1-3. Figure 1 shows the direction of fluid flow and the main parts of the dispersant; figure 2 - the relative angular position of the channels of the rotor and the stator in the dispersant, figure 3 is a sequence of basic operations of the method.

The dispersant (figure 1) consists of a rotating two-chamber rotor 1 and a fixed stator 2, between which a minimum working clearance L (along a cylindrical surface) is made. In the stator 2 there is an inlet pipe 3 for receiving the incoming fluid into the chamber 4. The rotor 1 is divided by a continuous partition 5 into two chambers: the storage chamber 6 is designed to receive and transfer circulating fluid through the pipe 7 (hollow rotor shaft), and the receiving chamber 8 is for collection of finished products and its output through the pipe 9.

The fluid is supplied from the chamber 4 of the stator 2 through the channel 10, from which the liquid enters either into the wide channel 11 (in Fig. 1, the dotted line indicates the location of the channel 11 at a certain angular position of the rotor) or into the narrow channel 12 with a transition to the nozzle 13 and receiving chamber 8.

The fluid flow is generated using a pump 14, the input of which feeds the processed liquid and through the pipe 16 the liquid from the accumulation chamber 6 through the pipe 7 is supplied to the inlet through the pipe 7. The finished product from the receiving chamber 8 through the pipe 9 is discharged through the pipe 17.

The angular position of the channels of the rotor and stator is illustrated in figure 2, which shows the cross section of figure 1 in the planes aa and bb. Section A-A (see FIG. 2A) shows the angular arrangement of the narrow channels 12 of rotor 1, and section BB — see Figure 2B) shows the location of the wide channels 11 of rotor 1 relative to channels 10 located on stator 2 From the diagrams shown in figure 2 it can be seen that the arrangement of the channels is selected so that the liquid periodically passes through the narrow channels 12 with the wide channels 11 closed, and when the narrow channels 12 are closed, it is directed into the wide channels 11. In figure 2, as an example two pairs of channels on the rotor and stator are shown, but the number of pairs can be measured Neno. In the General case, the number of channels or the rotor speed is selected so that the duration of hydropercussion exposure exceeds the time of rotation of the rotor by an angle between the wide and narrow channels. Observance of the aforementioned condition makes it possible to maintain hydroshock pressure in the time interval during which a high-speed jet is formed.

The method is implemented as follows. The rotor 1 is driven into rotation by an electric motor (not shown in the figures). Turn on the pump 14 and the inlet pipe 3 under a given pressure serves a liquid mixture (see figure 1). As a liquid mixture, for example, a mixture of hydrocarbon fuel 80-85%, water 15-20% and surfactant 1-2%, which is used to obtain a water-fuel composition, is used. Liquid under pressure fills the chamber 4 and the channel 10 of the stator 2 throughout the volume. Next, the process is built on a specific cycle, which is repeated every 90 degrees of the angular rotation of the rotor. The successive phases of the cycle are shown in FIG. In the first quarter of the cycle (Fig. 3, phase φ _1/4 ), the liquid is fed into the wide channels 11 of the rotor 1 and sent through the pipe 7 to the pipe 16, forming a circulating flow with a pump 14 at a high speed and a predetermined cross section. In the second phase, the rotor is rotated by 22.5 degrees (Fig. 3, phase φ _2/4 ) and the wide channels 11 of the rotor 1 are closed. At the same time, the hydrostatic pressure increase is necessary at the point of overlap, which is necessary for functioning in the next phase of the cycle. Then, when the rotor is rotated 45 degrees from the initial position (Fig. 3, phase φ _3/4 ), narrow channels 12 are opened and the liquid is sent under high pressure to the nozzle 13, with which a high-speed jet is formed. Two diametrically opposed nozzles form two high-speed jets directed towards each other. Oncoming jets experience a frontal impact, the liquid mixture is sprayed and discharged through the pipe 9 and pipe 17 into the container for the finished product. At the final stage, when the rotor rotates 67.5 degrees from the initial position (Fig. 3, phase φ _4/4 ), all channels of the rotor 1 are blocked, through the pipe 9 and the pipe 17 completely empty the container 8 for receiving oncoming jets in the next cycle.

The resulting effect of the proposed method is manifested in an increased degree of dispersion of the liquid due to a frontal impact of high-speed jets. In turn, a high jet velocity is ensured by dividing the flow into two components, in one of which the liquid is accelerated and a pressure shock increment is obtained, and in the other, the obtained pressure increment is used to increase the jet velocity and increase the degree of dispersion. Dividing the flow of the processed fluid into two components allows you to pump energy into the first (circulating) part of the stream having a large mass, and transfer the received energy to the second small part of the stream with a lower mass but a higher speed. The narrowing of the paired channels to the diameter of the nozzle also contributes to an increase in the flow rate.

In the collision of oncoming high-speed jets, in addition to the dispersion mechanism from impact collision, a cavitation dispersion mechanism is connected, which ultimately enhances the efficiency of the process and increases the degree of dispersion.

The advantage of the proposed method is the ability to control the process by changing the speed and length of the flow in the circulating circuit, which allows you to change the speed of the jet and select the desired degree of dispersion.

Assessment of the process’s ultimate capabilities shows that when high-speed oncoming jets collide, it is possible to ensure that the liquid transitions to a vapor state, that is, disperses down to the molecular level. This means that the method can be used to obtain particles of the nanometer range in the liquid phase, as well as to create nanostructured composite materials.

Claims (4)

1. A method of dispersing liquids, their mixtures and suspensions of solids in liquids, including pre-mixing the liquids, their mixtures and suspensions with a stabilizer (surfactant) and subsequent homogenization, characterized in that they form a circulating fluid flow with a given cross section and speed movements, the formed stream is periodically blocked and part of the blocked stream is taken, which is divided into two or more paired streams, in each pair the streams are converted into high-speed jets and direct them towards each other to ensure periodic frontal impact with a frequency equal to the frequency of overlapping of the circulating flow. 2. The method according to claim 1, characterized in that the degree of dispersion of the treated fluid is set by changing the speed of movement of the circulating fluid flow. 3. The method according to claim 1, characterized in that the duration of the hydroshock pressure in the circulating stream is set by changing its length. 4. The method according to claim 1, characterized in that the interruption frequency of the circulating stream and the number of paired flows are selected so that the duration of the hydropercussion exceeds the time interval from the moment the circulating stream is shut off until the formation of the high-speed jet is completed.

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