A constitutive theory for ferrofluids

A constitutive theory for paramagnetic ferrofluids based on a rational thermodynamic theory with Lagrange multipliers is developed. It is shown that the 44 scalar coefficients of a general constitutive theory are reduced to 20 scalar coefficients through the exploitation of the entropy principle. By imposing: i) that the thermomechanical quantities are decoupled from the magnetic quantities; and ii) that the magnetization contributes only to the antisymmetrical part of the stress tensor, the 20 scalar coefficients are reduced to five e. g. the coefficients of thermal conductivity, shear and bulk viscosity and two relaxation times related to magnetic relaxation effects of the ferrofluid. Received May 1, 1999