ISO 21910-2:2025
(Main)Fine bubble technology — Characterization of microbubbles — Part 2: In-situ dynamic image analysis method
Fine bubble technology — Characterization of microbubbles — Part 2: In-situ dynamic image analysis method
This document specifies the principle, devices and operations for measuring bubble size distribution of microbubbles in liquid media using the in-situ dynamic image method. This document is applicable to microbubbles, as well as to bubbles in the size range of 100 μm to 500 μm, dispersed in transparent liquid media, mostly in water.
Titre manque — Partie 2: Titre manque
General Information
Standards Content (Sample)
International
Standard
ISO 21910-2
First edition
Fine bubble technology —
2025-05
Characterization of microbubbles —
Part 2:
In-situ dynamic image analysis
method
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units. 2
5 Principle . 3
6 Instrumentation and image acquisition . 3
6.1 Instrumentation .3
6.2 Setup .4
6.2.1 Determine the image resolution .4
6.2.2 Determine the magnification and acquisition time .4
6.2.3 Calibration . . .4
6.2.4 Other notes .5
6.3 Image acquisition .5
7 Image analysis . 5
7.1 Size classification .5
7.2 Image edge determination .5
7.3 Bubble image characteristic .5
7.4 Bubble identification .5
7.5 Bubble diameter calculation .6
8 Measurement errors . 6
9 Test report . 6
Annex A (informative) Examples of in-situ dynamic image analyser designs . 8
Annex B (normative) Considerations for instrument usage in open water areas such as rivers,
lakes and seas. .11
Bibliography .15
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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This document was prepared by Technical Committee ISO/TC 281, Fine bubble technology.
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Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
Introduction
Fine bubbles are bubbles with volume equivalent diameters smaller than 100 μm in liquid. Fine bubbles are
divided into two subgroups: microbubbles with volume equivalent diameters in the range from equal or
greater than 1 μm to smaller than 100 μm and ultrafine bubbles with volume equivalent diameters smaller
than 1 μm.
In recent years, many unique properties related to microbubbles have been revealed related to their large
specific surface area, instability, and motion characteristics. Microbubble technology with bubbles formed
with various gases, such as air, oxygen and hydrogen, is widely used in the fields of agriculture, aquatic and
food industry, energy and minerals, processing and manufacturing, environmental, cleaning, and health, etc.
Many properties of microbubble dispersion systems in liquid depend largely on the composition, geometry
and size distribution of the bubbles. Because of their thermodynamic instability in a dynamic evolution
process, rapid in-situ data acquisition and accurate identification of bubbles is the key to character the
bubbles in the measurement locations and in real time. It is of great significance to track and measure bubble
size, size distribution and dynamic evolution of microbubbles in liquid in real time in order to understand
the properties of microbubbles and to optimize and control the microbubble generation process. The in-situ
dynamic image analysis is such a method to satisfy the above needs.
v
International Standard ISO 21910-2:2025(en)
Fine bubble technology — Characterization of
microbubbles —
Part 2:
In-situ dynamic image analysis method
1 Scope
This document specifies the principle, devices and operations for measuring bubble size distribution of
microbubbles in liquid media using the in-situ dynamic image method.
This document is applicable to microbubbles, as well as to bubbles in the size range of 100 μm to 500 μm,
dispersed in transparent liquid media, mostly in water.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
acceptable depth of field
region where the sharpness of the edges of the images reaches the pre-set optimum and is accepted for
segmentation
[SOURCE: ISO 26824:2022, 3.8.15, modified — "" has been removed, "depth with
respect to focal depth" has been revised to "region," "particle images" revised to "images" and Note 1 to
entry has been removed.]
3.2
binary image
digitized image consisting of an array of pixels (3.13), each of which has a value of 0 or 1, whose values are
normally represented by dark and bright regions on the display screen or by the use of two distinct colours
[SOURCE: ISO 13322-1:2014, 3.1.2]
3.3
bubble size
linear dimension of a bubble determined by a specified measurement method and under specified
measurement conditions
Note 1 to entry: Different methods of analysis are based on the measurement of different physical properties.
Independent of the bubble property actually measured, the bubble size is reported as a linear dimension, e.g. as the
equivalent spherical diameter.
[SOURCE: ISO 26824:2022, 3.1.9, modified — "particle size" has been revised to "bubble size", and Note 2 and
3 to entry have been removed.]
3.4
edge determination
method used to detect transition between objects and background
[SOURCE: ISO 13322-1:2014, 3.1.4, modified — "detection" has been revised to "determination", "methods"
has been revised to "method," and Note 1 to entry has been removed.]
3.5
field of view
field which is viewed by the viewing device
Note 1 to entry: The full image frame of a digital imaging device corresponds to its field of view.
[SOURCE: ISO 13322-1:2014, 3.1.6]
3.6
image analysis
processing and data reduction operation which yields a numerical or logical result from an image
[SOURCE: ISO 13322-1:2014, 3.1.8]
3.7
laminar flow
fluid flow characterized by the parallel movement of fluid layers (laminae) past one another in an orderly fashion
[SOURCE: ISO 8625-2:2018(en), 3.3.1]
3.8
microbubble
fine bubble with a volume equivalent diameter in the ranges from equal or greater than 1 μm to smaller
than 100 μm
[SOURCE: ISO 20480-1:2017, 3.4, modified — "range" has been revised to "ranges" and Note 1 to entry has
been removed.]
3.9
threshold
grey level value which is set to discriminate objects of interest from background
[SOURCE: ISO 13322-1:2014, 3.1.14, modified — Figure 1 has been removed.]
4 Symbols and units
Symbols Names Dimension Units
a moving distance of the centre of the bubble image metre m
n number of bubbles of diameter x dimensionless
i i
2 2
σ standard deviation of bubbles of diameter x metre squared μm
i
t strobe flash time or camera shutter time second s
v bubble moving velocity metre per second m/s
x bubble diameter metre μm
i
x average of x metre μm
mean i
A area of bubble projection metre squared μm
i
...
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