Williams spray equation
In combustion, the Williams spray equation, also known as the Williams–Boltzmann equation, describes the statistical evolution of sprays contained in another fluid, analogous to the Boltzmann equation for the molecules, named after Forman A. Williams, who derived the equation in 1958. == Mathematical description == Source: The sprays are assumed to be spherical with radius r {\displaystyle r} , even though the assumption is valid for solid particles(liquid droplets) when their shape has no consequence on the combustion.