| Abstract: | The dynamics of fluid systems which consist of a suspended material in a Newtonian continuous phase is investigated theoretically. Criteria are derived to predict conditions under which the strength of a flow, i.e. a measure of the form and magnitude of the velocity gradient tensor, is sufficient to induce significant deformation and/or orientation of the fluid microstructure, that is, the elements which collectively comprise the suspended phase. The development relies upon the choice of a model to describe the microstructure, and the form of the criteria reflects this choice. Once the choice is made, however, the detailed material properties of a particular fluid system enter only as parameters in the resulting equations, and thus, the results encompass a large class of systems, including particulate suspensions and macromolecular solutions. Two microstructure models are investigated here. When the microstructure is characterized by a vector, the flow strengths of all linear flows are displayed in a single figure from which the strength of a particular flow can be evaluated directly. A comparison is then made for selected flows between these results and those for the case where an irreducible second order tensor is employed to describe the microstructure. A significant difference between the two models derives from the fact that the “volume” of the microstructure must be conserved in the second-order tensor case. The criteria are finally used to predict the degree of macromolecular stretching in a model turbulent flow and the breakup of immiscible liquid drops in simple shear flow. A comparison between the flow strength predictions and experimental data yields good qualitative agreement in the latter case. |
