ISO 21910-2:2025

Overview

ISO 21910-2:2025 - "Fine bubble technology - Characterization of microbubbles - Part 2: In‑situ dynamic image analysis method" defines the principles, instrumentation and operating procedures for measuring bubble size distribution of microbubbles using an in‑situ dynamic image technique. The standard applies to bubbles from 1 μm up to 500 μm (microbubbles: ≥1 μm to <100 μm; also covers 100–500 μm) dispersed in transparent liquid media (primarily water). It specifies how to capture real‑time images of moving bubbles submerged in the liquid and how to process those images to produce reliable size and distribution data.

Key technical topics and requirements

• Measurement principle: Submersible optical path, light source and image acquisition are immersed in the liquid to capture rapid‑exposure images of bubbles in situ.
• Size range & resolution: System must cover 1 μm–500 μm; image resolution no less than 0.5 μm/pixel and include a certified calibration ruler with minimum scale 2 μm.
• Frame rate & exposure: Image capture at ≥60 frame/s (typically several hundred fps); shutter/strobe timing chosen to minimize motion blur using the relation a = v · t (bubble image center displacement).
• Optics & lighting: Colourless transparent glass, parallel beam illumination, and acceptable depth of field for sharp edge segmentation.
• Image analysis functions: Distortion correction, transmitted light analysis, adjustable thresholds, discrimination of bubbles from contaminants, automated extraction of bubble parameters (area, perimeter), and statistical size reporting (min, max, mean, standard deviation).
• Setup & calibration: Iterative determination of magnification and acquisition time; ensure smallest bubble has sufficient pixel representation and that the largest bubble fits within image frame constraints.
• Environment & operation: Designed for still or laminar natural flow conditions; Annex B provides guidance for open water use (rivers, lakes, seas). Standard also covers measurement errors and required test reporting.

Practical applications and users

ISO 21910-2:2025 is intended for professionals and organizations needing accurate, real‑time microbubble characterization:

• Instrument manufacturers designing or certifying in‑situ dynamic image analysers
• Research labs studying microbubble dynamics, aeration, or cavitation
• Environmental monitoring of aeration, remediation or natural water bodies
• Aquaculture and agriculture optimizing oxygenation and irrigation systems
• Food, chemical and process industries controlling gas‑liquid processes
• Wastewater treatment and mineral processing where bubble size affects performance

Using this standard helps ensure reproducible bubble size distributions, supports process optimization and enables consistent reporting across studies and instruments.

Related standards

• ISO 21910 series (other parts on fine bubble technology)
• Referenced terminology and imaging standards cited within the document (for example ISO 13322‑1:2014, ISO 26824:2022, ISO 20480‑1:2017). Check the ISO catalogue for the latest cross‑references.