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Experimental Investigation of Surfactant Effects on Drop Formation of Shear-thinning Liquids

Dastyar, Peyman | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52171 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Firoozabadi, Bahar; Afshin, Hossein
  7. Abstract:
  8. In this research, the characteristics of non-Newtonian, shear-thinning drop formation containing surfactant from a needle are investigated experimentally. The ambient fluid is air and all experiments have been conducted in a constant flow rate of drop phase fluid. Images of forming drop are taken using a high-speed camera and by processing them, important parameters in drop formation such as length of drop, minimum neck thickness, formation time and the size of satellite drops have been studied. Three non-Newtonian and three Newtonian fluids are considered in a way that the initial viscosity of non-Newtonian fluids would be equal to the viscosity of their corresponding Newtonian fluids. afterwards, their drop formation in different surfactant concentrations in terms of critical value have been investigated. Non-Newtonian fluids are solutions of Carboxymethyl cellulose (CMC) and water at the CMC weight fraction of 0.5%, 0.75%, and 1% and their corresponding Newtonian fluids are solutions of glycerine and water at the glycerine weight fraction of 90.1%, 92.3%, and 94.5% respectively. According to our research, the formation of Newtonian and non-Newtonian drops in the presence of surfactant is under the influence of different factors so that, distinguishing the effects of shear-thinning is impossible. Therefore, the formation process of water and CMC solutions with different concentrations of surfactant that have equal initial viscosity are compared and has been discussed about the role of shear-thinning effect and the presence of surfactant in the process. Results indicate that increasing the shear-thinning feature of drop phase fluid, leads to the reduction of limiting length of drop and increase in the thinning rate of neck thickness and satellite drop size. Also, the obtained results suggest that enhancement of surfactant concentration in the drop causes limiting length of the drop to increase, reduces the thinning rate of neck thickness and although in the case of non-Newtonian fluids, is effective in the increment of satellite drop size. Furthermore, the whole process of drop formation is divided into two stages and is stated that the effect of surfactant addition on the duration of each stage is different, whereas shear-thinning and in general viscosity, doesn’t have a significant effect on first stage’s duration
  9. Keywords:
  10. Droplet Formation ; Shear Thining Fluid ; Surfactants ; Experimental Investigation ; Carboxymethyl Cellulose

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