Abstract
The influence of droplet size on exergy destruction rate in flow of highly concentrated oil-in-water emulsions was investigated experimentally in a cone and plate geometry. The oil concentration was fixed at 74.5% by volume. At this dispersed-phase (oil) concentration, two different droplet size emulsions were prepared: fine and coarse emulsions. The fine and coarse emulsions were mixed in different proportions to vary the droplet size distribution. Although the dispersed and matrix phases of the emulsions were Newtonian in nature, the emulsions exhibited a non-Newtonian (shear-thinning) behavior due to the high droplet concentration. The shear stress—shear rate data of the emulsions could be described adequately by a power law model. At low shear rates, the exergy destruction rate per unit volume of emulsion exhibited a minimum at a fine emulsion proportion of 35%. The results from the cone and plate geometry were used to simulate exergy loss in pipeline flow of emulsions. The pumping of emulsions becomes more efficient thermodynamically upon mixing of fine and coarse emulsions provided that the flow regime is maintained to be laminar and that the Reynolds number is kept at a low to moderate value. In the turbulent regime, the exergy loss generally increases upon mixing the fine and coarse emulsions.
Highlights
Emulsions are two-phase dispersions of oil and water [1–3]
The power-law parameters K and n vary with the droplet size and droplet size distribution of emulsions
When fine emulsion is mixed with the coarse emulsion, keeping the dispersed-phase concentration fixed, the consistency index K goes through a minimum and the power-law index n goes through a maximum at a certain proportion of fine emulsion content of the mixed fine and coarse emulsion
Summary
Emulsions are two-phase dispersions of oil and water [1–3]. One of the phases (oil or water) is dispersed as droplets in a continuum of the other phase. As pumping systems consume a significant portion of the total electrical energy used in the process, it is important to quantify the extent to which exergy is destroyed due to irreversibilities in the process. It is important from a practical point of view to find ways to minimize the destruction of exergy and reduce the pumping costs. One possible way to manipulate and control the rate of exergy destruction in emulsion flows is to vary the droplet size distribution. The analysis and interpretation of influence of droplet size and droplet size distribution on exergy destruction in emulsion flows is lacking. This is the first study on the influence of droplet size distribution on exergy destruction in isothermal flow of emulsions
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