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Laminar forced convection in viscous, non-Newtonian polymeric liquids that exhibit pseudoplastic or shear-thinning behavior is characterized. The fluid rheology is characterized by a new asymptotic power-law (APL) model, which appropriately represents extensive data for apparent viscosity variation with shear rate - from the low-shear constant-viscosity plateau to shear thinning at high shear rates. This is contrasted with the traditional Ostwald-de Waele or power-law (PL) model that invariably over-extends the pseudoplasticity in the very low shear-rate region. The latter's limitations are demonstrated by computationally obtaining frictional loss and convective heat transfer results for fully developed laminar flows in a circular pipe maintained at uniform heat flux. The Fanning friction factor and Nusselt number, as would be anticipated from the rheology map of pseudoplastic fluids, are functions of flow rate with the APL model unlike the Newtonian-like constant value obtained with the PL model. Comparisons of the two sets of results highlight the extent of errors inherent in the PL rheology model, which range from 23%-68% for frictional loss and 3.8%-13.7% for heat transfer. The new APL rheology model is thus shown to be the more precise characterization of viscous shear-thinning fluids for their thermal processing applications with convective heat transfer.

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To predict liquid-gas two-phase flow, accurate tracking of the evolving liquid-gas interface is required. Volume-of-Fluid (VoF) method has been used for computationally modeling such flows where a single set of governing equations are solved for both phases along with an advection equation for the volume fraction. Properties in each cell are determined by a linear weighted average of the properties of the two fluids based on the phase fraction. While the method predicts water-air flows well, the predictions tend to deviate significantly from experiments for liquids with high viscosity. A new property averaging technique is proposed, which is shown to provide accurate results for high viscosity liquids. Computational predictions using open source VoF solver interFoam and the proposed method are compared with experimental data for multiple two-phase applications. Four different problems, viz., suspended drop, jet breakup, drop impact on thin films, and on liquid pools, are considered to extensively validate the new method. Data for aqueous solutions of propylene and ethylene glycol are used to cover a range of surface tension (72 - 36 mN/m) and viscosities (1 - 40 mPa.s). For all cases, the modified VoF solver is observed to perform significantly better than original VoF method. It reduces spurious currents in simulations of drop suspended in air. For the cases of drop impacting on a pool and during drop generation from liquid jets, the time progression of the surface tension governed dynamics is improved from the slower estimate of interFoam solver.