THEORIES OF VISCOSITY

Abstract

Among the theories of viscosity (a measure of internal friction) of fluids, those related to gases are well developed compared to the situation of liquids. In a gas, momentum transfer occurs due to collisions between the molecules, while forces between the closely packed molecules cause the momentum transfer in liquids. Because of the complexities involved in the liquid momentum transfer mechanisms - including those due to dispersive and electrostatic forces - there has been no simple basis for the estimation of liquid viscosities. The simplicity of approach adopted in the kinetic theory applied to gas viscosity, which is of natural interest to the development of the theories on liquid viscosity will be dealt first in our discussion. This will be followed by the theories on the viscosities of dense gases and liquids.