Entropy Generation in Flow of Highly Concentrated Non-Newtonian Emulsions in Smooth Tubes

Entropy generation in adiabatic flow of highly concentrated non-Newtonian emulsions in smooth tubes of five different diameters (7.15–26.54 mm) was investigated experimentally. The emulsions were of oil-in-water type with dispersed-phase concentration (φ ) ranging from 59.61–72.21% vol. The emulsions exhibited shear-thinning behavior in that the viscosity decreased with the increase in shear rate. The shear-stress (τ ) versus shear rate (γ ) data of emulsions could be described well by the power-law model: n Kγ τ  = . The flow behavior index n was less than 1 and it decreased sharply with the increase in φ whereas the consistency index K increased rapidly with the increase in φ . For a given emulsion and tube diameter, the entropy generation rate per unit tube length increased linearly with the increase in the generalized Reynolds number ( n Re_ ) on a log-log scale. For emulsions with φ 15 . 65 ≤ % vol., the entropy generation rate decreased with the increase in tube diameter. A reverse trend in diameter-dependence was observed for the emulsion with φ of 72.21% vol. New models are developed for the prediction of entropy generation rate in flow of power-law emulsions in smooth tubes. The experimental data shows good agreement with the proposed models.