A model of the fluid flow in a thin walled continuous caster is proposed. The stability of the flow is considered when the viscosity is temperature dependent. Mathematically the model can be described as a Hele-Shaw cell with heat loss. A condition for the growth of an uneven flow distribution in the cell is derived. This condition is related to the change in viscosity with the temperature of the liquid metal being cast, and the rate at which it is being cooled. An unstable flow distribution in the mould makes the continuous casting process difficult to control and can cause ‘lock-ups’ and ‘breakouts’.
Using SPH (smoothed particle hydrodynamics), the motion of a lobe pump under load was simulated in order to predict the level of shear stress experienced by a protein solution. By varying the gap size between the lobes and pump housing, variations in pump efficiency and shear stress were determined. The simulations indicated that pump shear was dependent on gap size, with shear stress levels (0-40 Pa) correlating with those estimated in previous albumin-pumping studies. As gap size increased, the number of fluid particles experiencing low shear (<10 Pa) increased, whereas those experiencing high shear (>20 Pa) showed a decreasing trend. The pump efficiency, however, decreased with gap size, requiring more lobe revolutions to pass a unit volume. Taken together, these observations indicate that lobe pumps operated with increased gaps between the rotors and the housing result in larger number of particles within the fluid experiencing shear stresses. Moreover, the simulations indicate that it is best to use larger lobe pumps operated at high efficiency to transfer protein-containing solutions.
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