Overview
EN ISO 80000-11:2020 - Quantities and units - Part 11: Characteristic numbers (ISO 80000-11:2019) is the CEN-adopted European version of the ISO technical specification that standardizes the names, symbols and definitions of characteristic numbers used to describe transport and transfer phenomena. Characteristic numbers are physical quantities of unit one (commonly but incorrectly called “dimensionless”) that express relationships such as ratios of forces, energies or characteristic times. This edition supersedes EN ISO 80000-11:2013 and expands the list of items substantially (from 25 to 108 entries).
Key topics
- Scope and structure
- Provides standardized names, symbols and worded definitions for characteristic numbers used in momentum, heat and mass transfer, magnetohydrodynamics and related processes.
- Organized in Clauses 4–9 (Momentum transfer; Transfer of heat; Transfer of matter in a binary mixture; Constants of matter; Magnetohydrodynamics; Miscellaneous).
- Examples of characteristic numbers covered
- Reynolds number (Re) - ratio of inertial to viscous forces for fluid flow (used to estimate laminar vs turbulent flow).
- Euler number (Eu) - relates pressure drop to kinetic energy per unit volume.
- Froude number (Fr) - ratio of inertial to gravitational forces for free-surface flows.
- Grashof number (Gr), Weber number (We), Mach number (Ma), Knudsen number (Kn) and many others - each with definitions, symbols and contextual remarks.
- Definitions and cross-references
- Links to other ISO 80000 parts (e.g., quantities and units for mass density, viscosity, temperature, speed of sound) to ensure consistent use of symbols and units across standards.
Applications
- Engineering design and analysis
- Fluid mechanics, aerodynamics, hydraulic engineering, process engineering - use characteristic numbers for scaling, similarity analysis and to predict transitions (e.g., laminar→turbulent).
- Computational modeling and simulation
- Non-dimensionalization of governing equations in CFD and heat/mass transfer models to improve numerical stability and comparability.
- Experimental reporting and test standards
- Clear, standardized terminology and symbols for test reports, research papers and technical specifications.
- Education and documentation
- Teaching transport phenomena and producing technical documentation that aligns with international standards.
Who uses this standard
- Mechanical, chemical and civil engineers; CFD and simulation specialists; researchers in fluid/thermal sciences; standards bodies; test laboratories; authors of technical publications and regulatory documents seeking consistent, authoritative nomenclature.
Related standards
- Part of the ISO 80000 series (Quantities and units). Cross-references include other parts such as ISO 80000-3, -4, -5 and -8 for basic quantities (length, mass density, viscosity, temperature, speed of sound) used in the definitions.
Using EN ISO 80000-11:2020 helps organizations and practitioners achieve clarity, interoperability and reproducibility when working with characteristic (dimensionless) numbers in transport and transfer phenomena.
