TS 2439 ISO 31-12

TS 2439 ISO 31-12 is a terminology standard for the names and symbols of characteristic numbers used to describe transport phenomena. In practical engineering language, it harmonises how these dimensionless quantities are identified in fluid mechanics, heat transfer, and mass transfer; it is not a calculation method or a design rule, but a standard for consistent naming and notation.

Where characteristic numbers matter in engineering

In general technical use, characteristic numbers compare the relative strength of competing physical effects. Numbers such as Reynolds, Prandtl, Nusselt, and Sherwood provide a compact, standardised way to describe flow regime, heat-transfer behaviour, or the dominant mechanism in mass transfer. They are widely used when reporting experiments, comparing results across sources, and communicating engineering models with precision.

What this standard covers

• Provides names and symbols for characteristic numbers used in the description of transport phenomena.
• Supports terminology consistency within the quantities-and-units family of standards.
• Addresses the designation of the quantities, not the underlying physical models or equations.

This listing reflects the TSE edition based on ISO 31-12:1992 and Amendment 1, and it has since been withdrawn. It therefore serves as a historical reference for terminology and symbols, especially when interpreting older engineering documents and literature.