# Dimensionless Number

Dimensionless numbers play an important role in analysing fluid dynamics and heat and mass transfer problems. They provide a method by which complex phenomena can be characterised, often by way of a simple, single number comparison. This article provides a summary of dimensionless numbers and the formulae used to calculate them.

Dimensionless numbers play an important role in analysing fluid dynamics and heat and mass transfer problems. They provide a method by which complex phenomena can be characterised, often by way of a simple, single number comparison. This article provides a brief overview of the derivation and use of dimensionless numbers.

The Sherwood number is a dimensionless number that represents the ratio of convective mass transfer to the rate of diffusive mass transport and is used in the analysis of mass transfer systems such as liquid-liquid extraction. This article describes the Sherwood number and typical formulations.

The Schmidt number is a dimensionless number that describes the ratio of momentum diffusivity to mass diffusivity that is commonly used in analysis of mass transfer systems. This article describes the Schmidt Number and typical formulations.

The Mach number is the ratio of the relative velocity of a fluid to the local speed of sound. This article provides the equation for the calculation of the Mach number and a discussion of its uses.

The Prandtl number is a dimensionless number named after the German physicist Ludwig Prandtl. It represents the ratio of molecular diffusivity of momentum to the molecular diffusivity of heat.

The Reynolds number is dimensionless and describes the ratio of inertial forces to viscous forces in a flowing fluid. It is used in many fluid flow correlations and is used to describe the boundaries of fluid flow regimes (laminar, transitional and turbulent). This article will show you how to calculate and interpret the Reynolds number.