Microbubble,Nanobubble,Micro nano bubble

Microbubbles,Nanobubbles,Micro nano bubbles/about micro bubbles


The technique of blowing air into liquid has been practiced for years in various fields including waste water treatment, but in most cases, the bubbles were as big as several centimeters or tens of centimeters in diameter.
There is no problem to proceed with large bubbles for your operational process. But the recent focus on the environment and energy efficiency and the rising demand for more efficient and functional process technologies are turning the spotlight on these tiny bubbles.

Ultra fine bubbles are called in several ways such as “micro bubbles,” “nano bubbles,” or “micro-nano-bubbles” with a prefix indicasting the bubble size, but their definitions vary from each researchers and companies.

On ultra fine bubbles, many studies have been published to date, most of which generally agree that bubbles smaller than 50μm in diameter have properties different from larger ones. Researchers are beginning to suggest that bubbles smaller (assuming 1μm or 0.1μm as a threshold) than that have even more unique properties, which remain not yet fully explained.

We refrain from using the designation of “nano bubbles” (bubbles with diameters of tens or hundreds of nano meters in our definition), because we have not yet established a method to directly measure and verify a bubble diameter of that class:
we use instead designations such as “micro bubbles” or “micro-nano-bubbles” to indicate a broader definition,
since we can only infer, based on bubble distribution charts summarizing optically verified bubbles, that there must be a certain share of bubbles under our current limit of measurement (i.e. smaller than 1μm).

Although many academic institutions and companies have been working on the research, many aspects are yet unknown to wait for future study.
Here, we will show you the general characteristics of micro/nano bubbles and their advantages.

1.Sustained effects over a wide area

The buoyancy of a bubble is proportional to the volume of air contained in it.
Smaller bubbles have smaller buoyancy. Thus, micro/nano bubbles have minimal buoyancy and able to survive underwater longer than larger bubbles.

Force of buoyancy: F = pVg (p: Fluid density, V: Volume of the object, g: Gravitational acceleration)

2.Better reactivity (larger contact area between air and liquid)

When one square mm of water is filled with micro bubbles (1μm in diameter), the contact area between water and bubbles are 1000 times as large as that in water filled with normal bubbles (1mm diameter). The increase in the contact area dramatically enhances aerobic bacteria activities in the liquid and the efficiency of chemical reaction between the supplied gas and liquid ingredients.

3.Promotion of separation by floatation

As bubbles float up to the surface, they catch solids (contaminants) suspended in the liquid and bring them up to the surface. Since suspended solids are not uniform in size and shape, large bubbles often fail to catch and bring them up to the surface. On the other hand, micro/nano bubbles can penetrate into small dents of a contaminant and enclose it entirely in a ball of tiny bubbles, making it buoyant.

4.Lower surface tension (higher detergency from better soaking)

The surface tension of liquid is proportional to the density of the liquid. Introducing micro/nano bubbles into liquid lowers the apparent density of the liquid, resulting in better soaking and detergency.

Other features

■High internal pressure (difference between internal and external pressures: ⊿p)
※Calculated from the Young–Laplace equation (⊿p is in inverse proportion to the radius) and the surface tension of water.
■High solubility of gas
It is suggested that micro bubbles within 50μ naturally disappear (collapse) in the end after repeating the process of gas dissolution (gas dissolves → the bubble shrinks → internal pressure rises → gas dissolves).
■Laminar flows as fluid
Bubbles of uniform spherical shapes rarely create turbulent flows but make laminar flows.
■Lower frictional force
It is suggested that the formation of laminar flows of gas and liquid results in lower frictional force between a solid and liquid.
(Application example: ships)
■Electrically charged micro/nano bubbles
It is suggested that the external surfaces of micro/nano bubbles are negatively charged, and the charging tendency is proportionately greater when pH is greater. Charged bubbles can electrostatically attract contaminants and metal ion.


Generating types
Principles and features
a.Collapse (impulse wave) This type utilizes the sharp change in pressure caused by ultrasonic waves, impulse waves etc. However, unless some anti-coalescence agent is used, bubbles coalesce or disappear soon after generated. In certain cases, screw revolutions or ultrasonic waves reduce the pressure sharply even to a level below the saturated vapor pressure, causing the liquid to boil and the dissolved air to separate out, which may leave bubbles to collapse afterwards.
b.Shearing (turbulent flow) Bubbles are produced by cutting gas with turbulent flows in a mixture of gas and liquid. Turbulent flows are produced by a venturi tube or swirl flows. Simply shaking a bottle of a mixture of gas and liquid also falls under this category.。
c.Pressurized dissolution Gas is forcibly dissolved into liquid with a compressor etc., and then the supersaturated solution is rapidly depressurized or taken out to a normal pressure liquid, to separate out the supersaturated gas.
d.Microporous (sintered material) These types blow pressurized gas through a sintered or loosely bonded glass, metal, and ceramic with micro/nano scale open pores or a glass tube extended into a small diameter in the liquid to generate bubbles.
e.Solid trapping Bubbles are generated when gas trapped in ice or a semi-solid material dissolves into liquid.
f.Electrolysis Part of the gas generated at an electrolysis electrode makes micro/nano bubbles.
g.Chemical reaction Gas is generated by a chemical reaction. Example: an insoluble gas such as carbon dioxide is generated by mixing acid with a carbonate.
h.Shrinking Larger bubbles are made smaller by some physical or chemical method (Example: pressurization or cooling)

Principal types of commercialized micro/nano bubble generation systems include the following four types:
a.Collapse (impulse wave) type systems
b.Shearing (turbulent flow) type systems
c.Pressurized dissolution (supersaturation & separation) systems, and
e.Solid trapping systems

d.Since the microporous (sintered) material type can hardly generate micro/nano bubbles, they are used mostly for generating millimeter or centimeter scale bubbles in tropical fish aquariums or aeration in waste water treatment processes.

We are primarily focuse on a and b type systems to apply for our main products.