General Part

Abstract

The term “viscosity” is already quite old. It describes the internal friction of an object, in most cases a fluid. Heraclitus already spoke about pantha rei (everything flows), no doubt not only in connection with the transitoriness of earthly things. In the eighteenth century Newton (1642–1727) described the basic correlation between viscosity, shear force, and shear rate. The discovery of the laws governing the flow of liquids in tubes was made in the year 1839 by the construction engineer Hagen [412] in Berlin and in 1842 by the Parisian medical practitioner Poiseuille [702]. Further studies by Hagenbach [413] in 1860 led to the formulation of the law named after Hagen and Poiseuille. The Hagen- Poiseuille law states that the quantity of fluid flowing through a capillary in a certain time (flow rate) under constant pressure is directly proportional to the pressure and to the fourth power of the radius of the capillaries and indirectly proportional to the viscosity of the liquid and the capillary length.