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

Rajinder Pal

doi:10.3390/e16105178

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]

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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Conclusion