ISO 80000-11:2008

Overview

ISO 80000-11:2008, "Quantities and units - Part 11: Characteristic numbers", defines the names, symbols and concise definitions for dimensionless (characteristic) numbers used to describe transport phenomena. The standard clarifies notation, the coherent unit for these quantities (the dimensionless number 1), and provides recommended symbols and definitions for commonly used dimensionless numbers in momentum, heat and mass transport, and related material constants.

Key topics and technical content

• Scope and purpose: standardizes terminology and symbols for characteristic (dimensionless) numbers used in fluid mechanics, heat transfer and mass transfer.
• Dimensionless unit: all characteristic numbers are quantities of dimension one; the unit symbol 1 is the coherent unit and is normally omitted in expressions.
• Tables of quantities: includes names, English/French equivalents, recommended symbols and short definitions for each number. The scalar/vector/tensor character is identified where relevant.
• Momentum transport numbers (examples):
  • Reynolds number (Re) - ratio of inertial to viscous forces
  • Mach number (Ma), Froude (Fr), Weber (We), Knudsen (Kn), Strouhal (Sr)
  • Notes on deprecated alternate definitions (e.g., variations in Euler and Froude definitions)
• Heat transport numbers (examples):
  • Fourier (Fo), Péclet (Pe), Rayleigh (Ra), Nusselt (Nu), Biot (Bi), Stanton (St)
• Mass transfer numbers: mass-transfer analogues such as Sherwood (Sh) (Nusselt for mass), mass-transfer Péclet and Stanton numbers, Grashof for mass transfer.
• Constants of matter: dimensionless property ratios such as Prandtl (Pr), Schmidt (Sc) and Lewis (Le).
• Normative references: links to related ISO/IEC 80000 parts for space/time, mechanics, thermodynamics, electromagnetism, acoustics and physical chemistry.

Practical applications

ISO 80000-11 is practical for:

• Engineers and scientists performing dimensional analysis, similarity scaling and model testing in fluid dynamics, aerodynamics, HVAC, turbomachinery and naval architecture.
• Practitioners in heat transfer and mass transfer applications (process engineering, heat exchanger design, drying, evaporation).
• Developers of CFD software, instrumentation, technical documentation and standards, ensuring consistent naming and symbols across reports, papers and regulatory documents.
• Educators and students as a reference for consistent definitions of common dimensionless numbers.

Related standards

• ISO 80000 parts: Part 3 (Space and time), Part 4 (Mechanics), Part 5 (Thermodynamics), Part 8 (Acoustics), Part 9 (Physical chemistry)
• IEC 80000-6 (Electromagnetism)

Keywords: ISO 80000-11:2008, characteristic numbers, dimensionless numbers, Reynolds number, Nusselt number, Péclet number, Prandtl number, transport phenomena, fluid mechanics, heat transfer, mass transfer.