Fine and ultra-fine bubbles - technical information
Fine and ultra-fine bubbles
Modern bubble nomenclature can be confusing with the terms 'microbubble' and 'nanobubble' being used interchangeably, even in print.
In order to contribute to the recognition of a common standard, Aeration&Mixing© have adopted the terms used by Japan's Fine Bubble Industries Association (FBIA) who have greatly advanced international understanding in many areas of bubble research; see this video link... =lQkmFiJFnGI
At Aeration&Mixing in accordance with FBIA we class fine bubbles as those with diameters from 1µm to 50µm, and ultra-fine bubbles as those with diameters of less than 1µm.
Nikuni KTM pumps are precision made devices which can create consistent fine bubble discharges in a carrier fluid at an average fine bubble diameter of 25µm. Smaller fine bubbles can be produced by these pumps with additional equipment provided by A&M©.
Fine bubbles at a diameter of only 25µm have many uses particularly because, they not only provide an excellent bubble-to-particle ratio for DAF and IAF/IGF applications, but they are small enough to enable good mass-transfer of gasses to liquids.
Fine bubbles are best applied in tanks and vessels rather than in open lagoons or lakes, as their action is essentially gentle rather than the creating strong mixing needed for the treatment of active sludges.
A fine bubble in tap water at circa 15°C has a life of approximately 2 minutes, after which it disappears. It should be noted that the rate of bubble collapse will vary according to water or other fluid temperature and viscosity.
When a fine bubble disappears however, one of two states will have occurred;
a) it may have collapsed and the gas dissolved into the carrier liquid or: b) it may have split into a very large number of ultra-fine bubbles, sometimes called nano-bubbles.
Ultra-fine bubbles, which can only be measured with special instrumentation, have been measured with diameters as small as circa 100nm. These resilient tiny spheres are completely invisible to the human eye and only visible in clusters under the backscattering of green laser light.
One of the challenges in measuring ultra-fine bubbles is differentiating between a bubble and other particles present in a sample fluid. One method is to note the characteristics evident under green laser light, as particles present in a fluid will reflect light whereas fine and ultra-fine bubbles will refract light.
It should be noted that whereas fine bubbles have a life rarely extending beyond two minutes, ultra-fine bubbles can exist for many months and, in some special cases, can remain intact for years. This means that care should be taken in applications to ensure that where an ATEX rated gas is being sheared into fine bubbles and allowed to collapse, provision is made for the safe venting of any latent gas.
Current international research is seeking ways of collapsing ultra-fine bubbles at a time of a user's choosing, an area of research in which A&M is active.
The principal current uses of fine bubbles include:
Injecting gasses into liquids
Changing the state of fluids
Separating particles of waste by flotation e.g. DAF/IGF etc.
Cleaning and sterilization
Medical treatments and procedures
Future uses of ultra-fine bubbles include:
Advanced drug delivery
Further new medical treatments
Significant new cleaning techniques
Major advances in sterilization techniques and CIP technologies
Food and drink sector product developments
Fine bubble technologies are a fascinating area of science constantly evolving yielding new discoveries.