JPH07795A - Method and device for forming uniform and minute droplet group - Google Patents

Abstract

PURPOSE:To form a uniform and minute droplet group stabilized for a long time by regularly vibrating a liq. jet flowing out from a nozzle. CONSTITUTION:This device is provided with a liq. material inlet 2, a nozzle part 4 having plural nozzles for discharging the introduced material, means 8 and 10 for vibrating a jet discharged from the nozzle part 4 connected to the nozzle part 4 and a part 9 for detecting the flow rate of the liq. material supplied to the nozzle part 4. Further, the injection rate for each nozzle is calculated from the flow rate of the material detected by the part 9, and a means 11 for controlling the vibrating means 8 and 10 so that a frequency to be applied to the jet is adjusted in accordance with the calculated rate is furnished.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of producing a uniform droplet group having a uniform droplet diameter and a producing apparatus used therefor.

[0002]

2. Description of the Related Art Conventionally, for the purpose of generating a group of droplets having a uniform size, a smooth liquid jet ejected from a nozzle is regularly vibrated to divide the jet into uniform droplets. Methods for generating droplets of a size have been studied (eg, Japanese Examined Patent Publication No. 64-2414 and Japanese Examined Patent Publication No. 3973
No. 0 bulletin). The principle of these methods is Rayleigh, L. (Pr.
oc.London Math. Soc., 10 4,1878) and other studies on the stability of liquid columns. That is, the minute initial turbulence generated in the liquid column grows with the passage of time, and when the amplitude of the turbulence exceeds the radius of the liquid column, the liquid column is divided, and thereby droplets corresponding to the wavelength of the turbulence are generated. It is generated. Therefore, by applying regular vibration to the surface of the liquid columnar jet, it is possible to generate uniform droplets having uniform particle diameters.

[0003]

However, in the method of producing droplet groups of uniform size using the conventional technique, the jet velocity changes with time for the purpose of industrial mass production. As a result, there is a problem that the generated droplets are not uniform. The present invention has been made in view of the above circumstances, and provides a method for producing a uniform microdroplet group that can stably produce a uniform droplet group for a long time, and an apparatus for producing the same. The purpose is to

[0004]

According to a first aspect of the present invention, there is provided a method for producing fine droplets in which a droplet group is generated by applying regular vibration to a liquid jet flowing out from a nozzle hole. This is a method of generating a group of microdroplets, which detects the velocity and the frequency applied to the jet, and adjusts the frequency applied to the jet according to changes in the jet velocity.

According to the second aspect of the present invention, a nozzle portion having an inlet for the raw material liquid and a plurality of nozzle holes for flowing out the introduced raw material liquid, and a nozzle portion connected to the nozzle portion and discharged from the nozzle portion. A vibration generating unit that applies vibration to the jet flow, a flow rate detection unit that detects the flow rate of the raw material liquid supplied to the nozzle unit,
Based on the flow rate detection value of the raw material liquid detected by the flow rate detection unit, the ejection velocity per nozzle hole is calculated, and the vibration generating means is controlled so as to adjust the frequency of the jet flow according to the calculated velocity. And a control means for performing the same.

In the present invention, the condition of the frequency at which droplets having uniform droplet diameters can be generated is determined by the physical properties of the raw material liquid to be atomized, the nozzle hole diameter and the jet velocity. That is, the present invention utilizes the universal relationship found between the physical properties of the liquid to be atomized and the jet velocity and the frequency applied to the jet to generate uniform microdroplet groups. By controlling the vibration generating means so as to adjust the frequency of the vibration applied to the liquid column-shaped jet in accordance with the change in the jet velocity, droplets of stable and uniform size are generated.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a droplet generation device used in the method for producing uniform microdroplet groups of the present invention. In FIG. 1, the droplet generating device includes a nozzle plate 1 having a plurality of nozzle holes on its lower surface and a raw material supply port 2 as an inlet for a raw material liquid, and a nozzle holder 3 connected to the nozzle plate 1. The nozzle portion 4 and the raw material liquid tank 5 for storing the raw material liquid L1, the pressure in the raw material liquid tank 5 is kept constant, and the raw material liquid L1 is supplied to the nozzle holder 3 through the conduit 6.
Pressure regulator 7 for pressure feeding to the nozzle holder 3, a vibration generator 8 that is connected to the nozzle holder 3 and vibrates the nozzle portion 4, and the raw material supply flow rate in the pipeline 6 is detected, and the detected flow rate value is used as a flow rate signal. A flow meter 9 as an output flow rate detecting unit, and an oscillator 10 that is connected to the flow meter 9 and receives a flow rate signal.
It mainly comprises a control device 11 as control means for controlling the vibration signal sent from the vibration generator 8 to the vibration generator 8. The controller 11 is composed of a microcomputer and controls the vibration signal according to a program written in a ROM (not shown). Also,
The vibration generator 8 and the oscillator 10 function as vibration generating means.

The operation of the droplet generating device having such a configuration is as follows. First, the raw material liquid L1 to be atomized, which is stored in the raw material liquid tank 5, is pressurized by the compressed gas adjusted to an appropriate pressure by the pressure adjuster 7 and supplied to the nozzle portion 4. Next is the nozzle holder 3
The raw material liquid L1 supplied from the raw material supply port 2 is ejected vertically downward as a liquid columnar jet L2 from a large number of nozzle holes provided in the nozzle plate 1. At the same time, the nozzle plate 1 is excited in the vertical direction by the vibration generator 8 together with the nozzle holder 3, whereby the vibration is transmitted to the liquid column jet L2, and as a result, the liquid column jet L2 is regularly formed into droplets L3. Split. At this time, the flow rate signal detected by the flow meter 9 is sent to the control device 11, and the control device 11 converts the flow rate signal into the jet velocity per nozzle hole and determines the optimum range of the relational expression described later. The oscillator 10 is controlled so that the vibration generator 8 generates a frequency.

The condition of the frequency generated by the vibration generator 8 will be described below with reference to FIGS. Tables 1 and 2 show the sample physical properties and nozzles used to determine the frequency range in which droplets of uniform diameter are obtained. The range is as follows. Density ρ: 0.89 to 1.20 g / cm ³ , viscosity of raw material liquid μ: 0.89 to 37 mPa.S, surface tension σ: 25 to 72 mN
/ m, nozzle diameter d: 0.1 to 2.0 mm.

[0010]

[Table 1]

[0011]

[Table 2]

Also, FIG. 2 uses an aqueous solution of 60% ethanol.
Nozzle diameter d is 0.1, 0.5, 1.0 mm respectively
Of the ejection velocity u on the frequency f when it is changed
Is shown. Upper limit vibration regardless of nozzle diameter d
Number f_H And the lower limit frequency f _L The slope of the line is almost
It is “1”. The upper limit frequency f_H And lower limit
Frequency f_L Is the line obtained by the least squares method.
It Summarizing those results, the upper limit frequency f_H and
Lower limit frequency f_L And the ejection velocity u are expressed by the following equation.
To be done.

[0013]

[Equation 2]

FIG. 3 shows that an aqueous solution of 20% ethanol is used.
It is the upper limit frequency f _H and the lower limit frequency f _L when the jet velocity u is 4 m / s, and shows the influence of the nozzle diameter on the frequency. As the nozzle diameter increases, the straight lines f _H and f _L decrease with almost the same inclination. The same tendency was obtained under other conditions,
From these results, the upper limit frequency f _H and the lower limit frequency f
The relationship between _L and the nozzle diameter d is expressed by the following equation.

[0015]

[Equation 3]

Further, FIG. 4 shows the influence of the viscosity on the frequency. FIG. 5 shows the effect of surface tension on the frequency. The influence of these surface forces on the frequency f is considerably small, and the relationship between the upper limit frequency f _H and the lower limit frequency f _L and the surface tension is expressed by the following equation.

[0017]

[Equation 4]

The above-mentioned physical properties of the sample, the nozzle diameter, the ejection speed, and the frequency are summarized as follows.

[0019]

[Equation 5]

From these results, dimensional analysis was performed on the upper limit frequency f _H and the lower limit frequency f _L to derive a non-dimensional empirical formula. Then, the following formula was obtained for the upper limit frequency f _H.

[0021]

[Equation 6] Similarly, the following equation was obtained for the lower limit frequency f _L.

[0022]

[Equation 7] Therefore, the frequency range for obtaining a uniform diameter droplet can be expressed by the following equation.

[0023]

[Equation 8]

According to the frequency f satisfying this relationship, droplets of uniform size can be generated. According to the above relational expression, in the case of industrially producing a large amount of droplets, even if the supply amount of the raw material liquid changes with time, it can be obtained by the above relational expression according to the change of the jet velocity. By controlling the operation of the vibration generator 8 within the frequency range, it becomes possible to stably generate a droplet group having a uniform size for a long time. As the liquid to be miniaturized, various inorganic / organic solutions, metal melts, slurries containing fine solid particles insoluble or hardly soluble in them, and the like can be used.

[Test Example] A 10 wt% aqueous solution of ethanol was used as the liquid to be atomized, and the nozzle hole diameter was 100 μm.
m was formed to have a diameter of 100 mm and the number of nozzle holes was 500, and an electrodynamic vibration generator was used as the vibration generator 8 to configure the droplet generation device shown in FIG. FIG. 6 shows a frequency range in which a droplet of uniform diameter obtained from the above relational expression is obtained for the solution. Droplets of uniform diameter are generated within the range indicated by the diagonal lines in the figure.

Using this device, the control device 11 was set so that the frequency f was within the range of the hatched lines shown in FIG. 6 even if the jet velocity changed. Then, when 10 wt% ethanol aqueous solution was supplied so that the jet velocity was 1.3 m / s,
The control device 11 controls the oscillator 10 so that the frequency f becomes 500 Hz (point A in FIG. 6), and as a result, a droplet group having a droplet diameter of 1 mm is generated.

Next, when the jet velocity of the 10 wt% aqueous solution of ethanol was changed to be 3 m / s, the controller 1
1 is controlled so that the frequency f is 1200 Hz (see FIG. 6).
As a result, it was possible to generate a droplet group having a droplet diameter of 1 mm.

[Comparative Example] Ethanol 10 wt% under the same conditions (point A in FIG. 6) as in the example except that the control condition of the vibration due to the change of the jet velocity was not set in the controller 11.
An aqueous solution was produced. Next, when the jet velocity of the 10 wt% ethanol aqueous solution was changed so as to be 3 m / s (point C in FIG. 6), droplet groups having irregular droplet diameters were generated. Although the control device of the present invention is implemented by software using a microcomputer, it may be implemented by a dedicated hardware circuit that performs those functions.

[0029]

As is apparent from the above description,
According to the first and second aspects of the present invention, it is possible to stably generate a uniform droplet group for a long time even if the jet velocity changes with time.

[Brief description of drawings]

FIG. 1 is a block diagram of a uniform droplet generation device used in an example of the present invention.

FIG. 2 is a graph showing the relationship between the frequency and the ejection speed according to the embodiment.

FIG. 3 is a graph showing the relationship between the frequency and the nozzle diameter according to the embodiment.

FIG. 4 is a graph showing the relationship between frequency and viscosity according to the example.

FIG. 5 is a graph showing the relationship between the frequency and the surface tension according to the example.

FIG. 6 is a graph showing a region of jet velocity and frequency for generating uniform droplets according to an example.

FIG. 7 is a cross-sectional view showing a nozzle diameter dimension according to an embodiment.

[Explanation of symbols]

 1 Nozzle Plate 2 Raw Material Liquid Supply Port 3 Nozzle Holder 4 Nozzle Part 5 Raw Material Liquid Tank 6 Pipeline 7 Pressure Regulator 8 Vibration Generator 9 Flowmeter 10 Oscillator 11 Control Device

Claims (3)

[Claims] 1. A method for producing fine droplets, in which a droplet group is generated by applying regular vibration to a liquid jet flowing out from a nozzle hole, wherein a jet velocity and a frequency applied to the jet are detected, and A method for producing a uniform group of microdroplets, characterized in that the frequency of vibration applied to the jet is adjusted according to a change in jet velocity. 2. A nozzle portion having a feed port for the raw material liquid and a plurality of nozzle holes for flowing out the introduced raw material liquid, and a jet stream connected to the nozzle portion and flowing out from the nozzle portion is vibrated. A vibration generating means for applying, and a flow rate detecting section for detecting a flow rate of the raw material liquid supplied to the nozzle section,
The ejection velocity per one nozzle hole is calculated based on the flow rate detection value of the raw material liquid detected by the flow rate detection unit, and the vibration is adjusted to adjust the frequency applied to the jet flow according to the calculated velocity. A uniform microdroplet group generation apparatus comprising: a control unit that controls the generation unit. 3. The frequency f applied to the jet flow is represented by the following equation expressed by a nozzle diameter d, a jet velocity u, a liquid viscosity coefficient μ, a liquid surface tension σ, and a liquid density ρ. The method or apparatus according to claim 1 or 2, characterized in that