Lewis number

The Lewis number is a dimensionless quantity used in chemical engineering and physics to compare how fast heat and mass transfer occur within a substance. Specifically, it is the ratio of thermal diffusivity (how quickly heat spreads) to mass diffusivity (how quickly a substance's particles spread). A high Lewis number means heat moves faster than mass, while a low number indicates mass transfer is quicker. Understanding this ratio helps engineers predict how mixtures will behave in processes like combustion, cooling, or chemical reactions, aiding in efficient design and safety assessments.