TRANSPORT PHYSICS / DIMENSIONLESS RATIO
Compare thermal diffusion with molecular mass diffusion using two explicitly identified diffusivities from one state.
METHOD / WORKED EXAMPLE
Compare thermal diffusion with molecular mass diffusion using two explicitly identified diffusivities from one state. The ratio becomes dimensionless only when every property uses coherent units and one physical state.
WORKED DEFAULT
Thermal diffusivity 1.43e-7 m^2/s divided by mass diffusivity 1e-9 m^2/s gives Le = 143.
READ THE RESULT
The ratio compares thermal and species diffusion rates; it does not solve coupled temperature or concentration fields.
ASSUMPTIONS AND LIMITS
Cross-diffusion, reaction, phase change, property variation, and transport correlations remain outside this ratio.
COMMON QUESTIONS
Use one coherent SI unit system, physical state, geometry, and documented characteristic scale across every input. Both diffusivities apply to one phase and state. The mass diffusivity identifies the relevant species pair. Confirm whether each property belongs to the fluid, solid, interface, particle, or transported quantity named by the formula. Mixed conventions can produce a plausible number whose physical meaning is wrong.
The ratio compares thermal and species diffusion rates; it does not solve coupled temperature or concentration fields. A dimensionless group compares selected mechanisms under a stated model; it does not prove a regime, transition, instability, similarity, or safe design. Geometry, boundary conditions, property variation, measurement uncertainty, and the validity range of downstream correlations still require separate review.
No. This educational calculator performs displayed arithmetic on supplied SI values; it is not simulation, experimental validation, a correlation selector, material data, or engineering approval. Cross-diffusion, reaction, phase change, property variation, and transport correlations remain outside this ratio. Retain source values, units, property temperatures, geometry definitions, and uncertainty, then obtain qualified review before using the result for design or safety decisions.
RELATED TOOLS
Use boundary
Express thermal and mass diffusivity in the same units, then divide thermal diffusivity by mass diffusivity.
Le = alpha / D.