In fluid dynamics, Sauter mean diameter (SMD) is an average measure of particle size.
It was originally developed by German scientist Josef Sauter in the late 1920s.
[1][2] It is defined as the diameter of a sphere that has the same volume/surface area ratio as a particle of interest.
The equation may be simplified further as: This is usually taken as the mean of several measurements, to obtain the Sauter mean diameter (SMD): This provides intrinsic data that help determine the particle size for fluid problems.
The SMD can be defined as the diameter of a drop having the same volume/surface area ratio as the entire spray.