Abstract

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: τ=K˙γn. 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 ( Re_n ) on a log-log scale. For emulsions with Φ ≤65.15 % 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.

Highlights

  • According to the Gouy-Stodola theorem, the rate of loss of work or available energy in a process is directly proportional to the total rate of entropy generation within and outside the control volume

  • Gouy-Stodola theorem is expressed mathematically as [1]: W lost = To S G,total where W lost is the rate of lost work, To is the surroundings temperature, and S G,total is the total rate of entropy generation within and outside the control volume

  • The greater the rate of entropy generation due to internal and external irreversibilities, the greater is the amount of energy that becomes unavailable for work [2,3,4]

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Summary

Introduction

According to the Gouy-Stodola theorem, the rate of loss of work or available energy in a process is directly proportional to the total rate of entropy generation within and outside the control volume. This article is related to entropy generation in flow of highly concentrated non-Newtonian emulsions of oil-in-water type in smooth tubes. The oil-in-water (designated as O/W) emulsions consist of oil droplets dispersed in a continuum of aqueous phase Such emulsions are very important industrially [5]. To facilitate the flow of highly viscous crude oils in pipelines, it is necessary to reduce their viscosity This can be achieved by forming emulsions of O/W type with crude oil as the dispersed phase. Concentrated O/W emulsions are known to exhibit non-Newtonian shear-thinning behavior

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