JP3259305B2 - Method for forming uniform droplets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for generating a droplet having a uniform size and maintaining the droplet for a certain period of time.

[0002]

2. Description of the Related Art There is a process for producing uniform solid particles from a solution of a composition by drying. To perform such a process, first generate uniform droplets of the solution,
It is then necessary to maintain this for a certain period of time, during which time the solvent is removed.

As a technique for generating uniform liquid droplets, there is known a method in which a liquid is ejected from a nozzle and the nozzle is vibrated. The vibration is given by using a sound wave or an ultrasonic generator (for example, a speaker), or by using electrostatic strain.

The problem is how to maintain the generated uniform droplets. As the droplets fall through the gas, Karman vortices are generated behind them, which tend to attract and coalesce the droplets. This phenomenon is
This is remarkable when the distance between the droplets is 1.5 mm or less. In addition, even if it is a uniform droplet, it is inevitable that a certain degree of particle size distribution occurs, and the difference in particle size causes a difference in terminal drop speed, so that there is a possibility that the preceding and following droplets collide during falling. .

For this reason, even if a uniform droplet is dropped from the nozzle, when the falling distance reaches 40 to 50 cm, considerable coalescence of the droplets occurs, and in many cases, the uniformity of the droplets is increased. Is lost. However, in general, it has been desired to maintain the uniformity of the droplet over at least the falling distance of the order of the meter.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved droplet formation technique as described above to maintain droplet uniformity over a sufficiently long drop distance.
An object of the present invention is to provide a method for forming uniform droplets.

[0007]

According to the method of forming uniform droplets of the present invention, as shown in FIG. 1, liquid is ejected from a nozzle which is given a vibration to form droplets of uniform size. While the droplets are falling at substantially equal intervals, gas is blown from the lateral direction onto the droplets to disperse the droplets in the lateral direction, thereby preventing coalescence due to collision of the droplets. Consisting of

The nozzle for ejecting the liquid is preferably a jet nozzle, and any type such as a pipe-shaped nozzle or a nozzle having a hole in a plate can be used. The diameter of the nozzle may be appropriately selected according to the size of the target droplet. For example, in order to obtain a droplet having a diameter of about 200 μm to 1.5 mm, it is preferable to use a nozzle having a nozzle diameter of about 150 μm to 1.3 mm.

To apply vibration to the nozzle, conventional means such as mechanical, electroacoustic, and electromagnetic vibration can be used.
Specifically, sound waves and ultrasonic vibrations caused by electric vibration using a speaker, a piezoelectric vibrator or an electrostrictive vibrator are examples.

The direction in which the gas is sprayed is preferably in a range of 90 ° to the flow of the vertically falling droplets, that is, an inclined range of 60 ° obliquely upward or downward from horizontal. It is a matter of course that gas can be blown by a method using a single nozzle or a method using a plurality of nozzles.

The atmosphere for generating droplets and the blowing gas are as follows:
In many cases, air is sufficient, but an inert gas or the like can be used if necessary, and a gas or steam at an elevated temperature can be used if necessary for drying or the like.

[0012]

In the experimental apparatus shown in FIG. 1, the liquid (1) is sent out of the tank (2) by the pressure of the compressed air, and is supplied to the droplet generating nozzle (3) through a flow meter and a filter to form droplets. And fall. The nozzle (3) is vibrated by a speaker (4) driven by a high frequency generated by an oscillator and amplified by an amplifier.

When gas is blown from the gas blowing nozzle (6) to the flow of the falling droplet (5), the droplet is dispersed in the horizontal direction and continues to fall. By properly choosing the direction, flow and velocity of the gas, the flow of the droplets does not disperse excessively, but the horizontal distance between the droplets is kept large enough to fall, so that the Karman vortex described above The attraction between the droplets is so weak that it hardly causes any problem, and the possibility of coalescence due to the collision of the droplets before and after based on the difference in the terminal drop speed is significantly reduced.

By such a mechanism, the uniform droplets generated in the nozzle (3) continue to maintain the uniformity.
The situation was confirmed by photographing the liquid droplets with a video camera (8) using a flash emitted from a strobe (7) and performing data processing with an image processing device (9).

[0015]

【Example】

Example 1 Water droplets were formed using the apparatus shown in FIG. However, as a droplet generator, as shown in FIG.
A single nozzle with an inner diameter of 300 μm and a length of 10 mm is provided at the tip of a container having a diameter of 8 mm and a length of 30 mm.
The one given a vibration of 100 Hz was used. The flow rate of the water exiting the nozzle is 1.5 m / sec.

A liquid column having a length of about 10 mm is formed at the tip of the nozzle,
The tip was cut and the droplet fell. 100 from nozzle end
The droplet diameter distribution at a position below mm was as shown in the graph of FIG. 4, and substantially uniform droplets concentrated at (550 ± 50) μm were generated.

When the flow of the droplet is freely dropped,
The droplet distribution at a position 5000 mm below the nozzle end is:
As shown in FIG. 5, the range was expanded to the larger side, and it was found that coalescence of the droplets occurred.

According to the invention, approximately 150 mm from the nozzle end
At the lower position, an air flow having a flow rate of 5 m / sec was blown from the horizontal direction. Similarly, the particle size distribution of the droplet measured at a position below 5000 mm is as shown in FIG. 6, and it was confirmed that collision of the droplet was avoided and uniformity of the generated droplet was maintained.

Embodiment 2 A container having a diameter of 8 mm and a length of 30 mm and a single nozzle having an inner diameter of 500 μm and a length of 10 mm was provided at the tip, and the frequency of the speaker was changed to 660 Hz. In the same manner as described above, water droplets were formed.
The liquid column from the nozzle end is 20mm long and 10
The droplet diameter measured at the position of 0 mm was uniform within the range of (950 ± 50) μm as shown in FIG.

Similarly, the flow of the free-falling droplet was measured at a position 5000 mm below the nozzle, and the result shown in FIG. 8 was obtained. The droplets which were blown with air to maintain uniformity as in Example 1 had the particle size distribution shown in FIG.

Example 3 A double nozzle having the structure shown in FIG. 3 was used. The inner tube of the nozzle portion has an inner diameter of 140 μm and an outer diameter of 240 μm, and the inner diameter of the outer tube is 400 μm. A water stream having a flow rate of 1.5 m / sec was jetted from both the inner and outer pipes, and 830 Hz vibration was applied by a speaker.

A liquid column having a length of about 10 mm was formed from the end of the nozzle, and thereafter it was cut off and dropped as a droplet. The particle size distribution was uniform as shown in FIG. 10 in the range of (650 ± 50) μm.

As in Examples 1 and 2, the nozzle 50
The particle size distribution of the droplet under 00 mm was measured in the case of free fall and the case of blowing 10.5 m / sec air, and the data shown in FIGS. 11 and 12, respectively, were obtained.

[0024]

By forming droplets according to the method of the present invention, the uniformity of the droplets can be maintained over a long drop distance and therefore for a relatively long time. Accordingly, during that time, it is easy to carry out drying in the droplets, to cause polymerization and other reactions, and it is possible to obtain various products having a uniform particle size.

Thus, the present invention has potential application in a variety of fields where products with a uniform particle size are desired, such as plastic beads.

[Brief description of the drawings]

FIG. 1 is a conceptual explanatory view showing the configuration of an apparatus used for experimenting the method of the present invention.

FIG. 2 is a sectional view showing the structure of an example of a droplet generation nozzle used in an embodiment of the present invention.

FIG. 3 is a sectional view showing the structure of another example of the droplet generation nozzle used in the embodiment of the present invention.

FIG. 4 is a graph showing data of Example 1 and showing a particle size distribution of droplets falling from a nozzle.

FIG. 5 is a graph showing the particle size distribution of droplets that are freely dropped at a distance of 5000 mm from a nozzle as comparative data of Example 1.

FIG. 6 is a graph showing the particle size distribution of liquid droplets sprayed and dispersed according to the present invention at a position 5000 mm below the nozzle, which is the data of Example 1.

7 is a graph corresponding to FIG. 4, which is data of Example 2. FIG.

8 is a graph corresponding to FIG. 5, which is comparison data of Example 2. FIG.

FIG. 9 is a graph corresponding to FIG. 6, which is implementation data of the second embodiment.

FIG. 10 is a graph corresponding to the data of Example 3 obtained by combining FIGS. 4 and 7;

FIG. 11 is a graph showing comparison data of Example 3 and corresponding to FIGS. 5 and 8;

FIG. 12 is a graph corresponding to FIG. 6 and FIG. 9, which is implementation data of the third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid 2 Tank 3 Droplet generating nozzle 4 Speaker 5 Droplet 6 Gas blowing nozzle 7 Strobe 8 Video camera 9 Image processing device

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-179006 (JP, A) JP-A-3-125944 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 2/04 B29B 9/00

Claims (2)

(57) [Claims] 1. A liquid is ejected from a vibrating nozzle to form droplets of a uniform size, and while the droplets are falling at substantially equal intervals, a gas is supplied from a lateral direction. A method of forming uniform droplets by spraying the droplets and dispersing the droplets in the horizontal direction to prevent coalescence due to collision of the droplets. 2. A gas spraying direction is within a range of 90 ° ± 60 ° with respect to a dropping direction of a droplet.
Of forming uniform liquid droplets.