ウルトラファインバブル生成器の革新的技術

ナノバブルの作り方

気泡を作るときは液体の中に気体を入れます。気泡は気体の中の液体である液滴の一種です。 気泡および液滴ファミリーのもう 1 つのメンバーは、気体または液体中の固体である粒子です。 これら 3 つの用語を互いに区別することが重要です。 気泡を作るには、流体力学的、音響的、光学的、および粒子キャビテーションによる方法がいくつかあります。 ウルトラファインバブルを作るための最も費用対効果が高く、最も効率的な方法は流体力学です。 流体力学は、流体上の運動と、流体に浸され、流体に対して運動する固体に作用する力を扱う物理学の分野です。 気泡を作るには簡単に言うと、動く液体が必要で、気体を加えて気体と液体に力を加えると気泡が発生します。 日常生活において、缶ビールやコーラを開けると、圧力の変化（力）によって泡が発生し、それが目と音でわかります。

ナノバブルに関する記事が初めて出版されたのは 1982 年で、最近までナノバブルの存在は激しく議論されていましたが、最近のウルトラファインバブル技術またはナノバブル技術の誇大宣伝は 2 つの要因によって引き起こされています。第一に、現在では、次のようなことができる機器が市販されています。 ウルトラファインバブルのサイズと密度を測定し、現在ではほとんどの科学者がナノバブルが存在することに同意しています。 第二に、この測定装置の大きな利点は、ウルトラファインバブルメーカーがウルトラファインバブル発生装置をさらに開発、最適化し、アプリケーションをさらに開発できるようになったということです。

ナノバブルの発生技術には大きく分けて2種類あり、1つは気体・水循環型のナノバブル発生装置です。 2つ目は、加圧溶解型ナノバブル発生器とも呼ばれるガス・水加圧・減圧方式です。 ほとんどのユニットは、どちらかの原則、または両方の組み合わせに基づいています。

ファインバブルの製造方法には次のようなものがあります。 最初の 4 つの方法について詳しく説明します。

1. 加圧溶解
2. 回転流
3. 乱流スタティックミキサー
4. エジェクターノズル（微細孔式）
5. 超音波（超音波振動）
6. 発振器
7. ベンチュリ
8. 混合蒸気直接接触凝縮

Pressurized dissolution method

This method of ultrafine bubble generation is based on the principles of Henry's Law, which relates the concentration of a gas to the partial pressure. This means that more gas can be dissolved into a solution at a higher pressure. The principle of the ultrafine bubble generator is as follows: Via a venturi system the liquid and the gas are mixed together, in the next step in the mixing box the gas is melted into the water via pressurization. In the last step via a nozzle the water and gas is discharged. Due to drastic drop in pressure of the supersaturated liquid gas solution, the gas is expelled as fine bubbles and ultrafine bubbles in the liquid. The figure illustrates the process.

1. Liquid is pumped into the unit under pressure.
2. By narrowing the size of the pipe, the speed of the incoming liquid flow is increased, which converts most of the pump pressure into dynamic pressure, thus reducing static pressure and air being suctioned through negative pressure.
3. After the liquid and suctioned gas become saturated with bubbles, the liquid/gas flow is sent through a wider pipe to reduce the speed of the flow, where dynamic pressure is converted back to static pressure and the process of pressurized dissolution of gas takes place.
4. After the gas is completely dissolved into the liquid, the liquid/gas is ejected at once using atmospheric pressure, causing the liquid to become over-saturated, and massive ultra fine nanobubbles are released.

Rotational flow

Rotational flow is also often called Swirl Method or Spiral Flow. This fine bubble generator generates bubbles according to the Bernoulli's principle. In fluid dynamics, Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy. The principle is named after Daniel Bernoulli, who published it in his book "Hydrodynamica" in 1738. Centuries later, fine bubble generators are made based on this principle. The first product based on this technology is the Ranque-Hilsch Vortex Tube in 1933. Followed 50 years later by the Swirling jet flame. In the mid-nineties, the first swirling type micro-bubbles was invented in Japan.

The principle of the fine bubble generator is as follows: water is put into a cylindrical tank from the top-side and made to flow in a spiral downwards. From the center bottom of the cylinder, the gas is sucked in. The rotating water is sheared to the top of the cylinder, producing fine bubbles. However, it's generally acknowledged in the ultrafine bubble industry that the bubble concentration of the pressurized dissolution method is higher than the rotational flow.

Turbulent Static Mixer

The static mixer has its origin from mixing two liquids, the first patent for a static mixer was filed in 1965. Instead of mixing two liquids, there is also the possibility of mixing a liquid and a gas. This technology is based on the principle of creating a vortex and bringing into the vortex a gas very effectively. Due to the turbulent flow gas will break the vortex and the collisions  between water and gas creates the nanobubbles. The benefits of the static mixers are that they have a relative simple design, and they can treat large volumes of water at once with relative little energy compared to many of the other above nanobubble generators. Finally, they are not sensitive to clogging. The acniti Turbiti technology is a combination of the turbulent static mixer and the Ejector Nozzle.

Ejector Nozzle

In the ejector nozzle nanobubble generator type, liquid flow channels in the cylindrical generator are designed to shrink and stepwise enlarge. The gas is brought in under negative pressure at the most reduced pressure point and reduced to a number of nanobubbles by cavitation. In this device, the water flow is highly turbulent, and the gas is reduced to nanobubbles by cavitation. Ejector nozzles are closely related to hydrodynamic cavitation generators, with this method cavitation is generated by the flow of liquid through a simple geometry under controlled conditions. In this nanobubble generator, when the pressure falls below the vapor pressure of the liquid, the liquid flashes, generating a number of cavities. The cavities collapse when the pressure recovers. The collapse of the cavitation bubbles starts some physicochemical effects such as shock waves, shear forces and chemical reactions. Free radicals are sometimes generated by the these processes.

Hammermill Rotation

The hammermill rotation concept is a unique concept compared to all the other nanobubble generation techniques, as it does not use a pump to generate nanobubble. Instead, it uses a motor with hammers mounted on the shaft. The motor turns at a velocity of 3400 rotations per minute in a tube. The tube fills with water from the top, and the gas injection is also from the top. The hammers on the shaft dissolve the gas and crushes the gas into nanobubble at the bottom of the unit the nanobubbles come out. The hammer rotation concept is the most energy friendly way to generate nanobubbles as it is not moving large amounts of water and doesn’t need a high pressure but uses all its energy to crush the gas. The lineup of hammermill rotation nanobubble generators is called the microStar nanobubble generator. This unit is suitable for ozone gas and for use in seawater environments.