Practically, in most operations relevant to process engineering numerous fluids are handled. Fluids of all sorts constitute raw materials and finished products in industries as diverse as the chemical industry, the biotechnology industry, the mining industry, and the food industry. Newtonian theory provides the simplest cases of viscous behavior, in which the stresses are related to the velocity gradients existing at time of the observation. The different theoretical aspects needed to understand the operating principles of all the mechanical operations employed in separating components in two-phase and multiphase systems can be facilitated. Within the context of particle technology, the most relevant application of centrifugation is centrifugal clarification since it follows theoretical principles of dynamics of particles submerged in fluids. By far, the most understood behaviors are those of Newtonian fluids and time-independent non-Newtonian suspensions. A series of flow equations and charts have been developed in order to predict their flow characteristics.