In empty ball mill power consumption is more or filled why?

In a ball mill, the power consumption is varied according to the shifting of the centre of gravity in the internal volume of the mill.when the mill is empty, the fraction of volume occupied by the grinding media is more. but when the mill is filled with some feed, as the centre of gravity of grinding media shifts up,the fraction of volume occupied by the grinding media decreases. so power consumption is less.

• Power =0.285*d(1.073-j)m*n

d - internal diameter of mill

j - fraction of mill volume occupied by media

m - mass of grinding media in tonnes

n - number of rotations of the mill