Couple-stress effect on the effective viscosity of magnetic fluids

The presence of nanostructure in a fluid causes the collision and friction between nanoparticles and between nanoparticles and walls when it is flowing; that is, the couple stresses in a fluid are present. It is desirable to understand the effect of couple stresses on the effective viscosity of magnetic fluids. In this study, we propose the modifications in momentum balance of magnetic fluids with nanostructure and derive a magnetoviscosity expression coming from the effective-field method, which describes the nonNewtonian behaviour of magnetic fluids. Results reveal that the effective viscosity is greater than the viscosity of non-couplestress fluids. However, the magnetic response and the shear-thinning non-Newtonian behavior are reduced.