Second Law Analysis of Adiabatic and Non-Adiabatic Pipeline Flows of Unstable and Surfactant-Stabilized Emulsions

Rajinder Pal

doi:10.3390/e18040113

Abstract

Entropy generation, and hence exergy destruction, in adiabatic flow of unstable and surfactant-stabilized emulsions was investigated experimentally in different diameter pipes. Four types of emulsion systems are investigated covering a broad range of the dispersed-phase concentration: (a) unstable oil-in-water (O/W) emulsions without surfactant; (b) surfactant-stabilized O/W emulsions; (c) unstable water-in-oil (W/O) emulsions without surfactant; and (d) surfactant-stabilized W/O emulsions. The entropy generation rate per unit pipe length is affected by the type of the emulsion as well as its stability. Unstable emulsions without any surfactant present at the interface generate less entropy in the turbulent regime as compared with the surfactant-stabilized emulsions of the same viscosity and density. The effect of surfactant is particularly severe in the case of W/O emulsions. In the turbulent regime, the rate of entropy generation in unstable W/O emulsions is much lower in comparison with that observed in the stable W/O emulsions. A significant delay in the transition from laminar to turbulent regime is also observed in the case of unstable W/O emulsion. Finally, the analysis and simulation results are presented on non-adiabatic pipeline flow of emulsions.

Highlights

A significant portion of the electrical energy produced in the world is consumed by pumping systems [1]
They are widely treated as homogeneous fluids when it comes to defining their macroscopic flow behavior [6]
Conclusions with and without the presence of surfactant at the droplet interface, the following conclusions can be made: (a) in the absence of any surfactant at the droplet interface, the unstable emulsions generate less entropy as compared with single-phase Newtonian fluids of the same viscosity and density in the turbulent regime. This indicates that pumping of unstable emulsions is more efficient thermodynamically provided that the flow regime is turbulent; (b) the entropy generation rate in unstable water-in-oil (W/O) emulsions is significantly lower than that in unstable oil-in-water (O/W)

Summary

Introduction

A significant portion of the electrical energy produced in the world is consumed by pumping systems [1]. The amount of work lost due to irreversibilities in the process is related to the total exergy destruction and total entropy generation in the process [2,3,4,5] as follows:. Where W lost is the rate of lost work and Ψ D,total is the total rate of exergy destruction in the process, including both the internal destruction within the control volume and the external destruction outside the control volume, To is the temperature of the surroundings, and SG,total is the total rate of entropy generation. Equation (1) is the Gouy-Stodola theorem [5] which states that the total rate of exergy destruction in the process is linearly proportional to the total rate of entropy production in the system and the surroundings. The higher the rate of exergy destruction, the higher is the amount of energy

Results

Discussion

Conclusion