Abstract: A rotor-stator assembly includes a rotor and a stator, each of which includes at least one surface having a plurality of grooves defining a plurality of ridges and valleys. The grooves are located so that material in the rotor grooves is caused to collide with material in the stator grooves or vice versa. Ideally, the grooves have a curved cross section so that material is caused to spin in the grooves. Material spinning in a stator groove is caused to collide with material spinning in a rotor groove and vice versa. The number of times that particles are caused to collide depends on the number and length of the grooves in relation to the depth of the grooves. Shear zones are located between the grooves on the stator and the grooves on the rotor.