• By assuming that the particles are spherical , you have two unknowns : the number of particles and the the mean radius. However, you have two equations: one for surface area and the other for volume ( volume depends on SG). Two unknown and two equation; solve and found the unknowns

a brilliant answer, dear Ahmed Mancy Mosa

I don't think there is an accurate way to achieve what you want. The surface area is calculated by assuming a range of particle sizes. Thus it will all depend on the selected ranges.

Dr. Zheng

there are specific surface and specific gravity of one type of ash. the question is how we can find the mean particle size by knowing these two parameters. or is there any relation between these two and mean particle size