Surface Roughness Rigid Particles

The most significant effects of surface roughness on flow past a particle occur in the critical range (see Chapter 5). Achenbach (A2) investigated this 

---

In analyzing surface effects of ultra fine polymer particles, we calculated the surface area and volume using Connolly s contact-reentrant method [231-233]. The contact-reentrant surface (molecular surface) uses a rigid hard sphere with a spherical probe that can trace molecular shape while in contact with the van der Waals surface. The van der Waals surface treats a CH2 bead as a rigid hard sphere equal to the van der Waals radii. The union of the spheres is considered the volume. Connolly s method provides a smooth surface by patching the space between the probe radius and the probed molecule. For our surface area and volume calculations, the van der Waals radius for the PE particles is set at 1.89 C for CH2 beads and the probe radius at 1.4 C to mimic the H2O molecule. Using the molecular surface, we also computed the fractal dimension D to determine roughness of the surface.. The value of D can be calculated by... 

Additives lor the Modification of Surface Prop0Tths. Additives that increase the roughness at the materials surface are sometimes necessary to reduce the contact surface between specimens and also their gloss. Such an effect is obtained by introducing small rigid or rubbery particles in the polymer, that helps to easily separate the latter from the metallic walls of the processing machine. 

---