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Numerical Investigation of Formation and Growth of Steam Condensing Droplets on Nanostructured Superhydrophobic Surface Using Lattice Boltzmann Method

Ashrafi Habibabadi, Amir | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48238 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Moosavi, Ali
  7. Abstract:
  8. Condensation is one of the main processes in environment and engineering systems, including thermal power plants, desalination systems and air conditioners. Thus, improvement of its performance can lead to decrease of energy consumption and the resulting air pollutions. Recently, using nanotechnology and new coating methods, there have been great researches on stable superhydrophobic surfaces and using theme as condensing surfaces which because of jumping droplet phenomena can increase condensation performance. Because of the great influence of wetting and structure properties of surfaces on condensation, in this study nucleation and growth of condensing droplets on smooth and structured surfaces is investigated using lattice Boltzmann method. Using Shan-Chen proposed model and thermal passive scalar approach, a double distribution function code with the ability of modelling phase change is developed and is validated using several theoretical solutions. Next, condensation on completely smooth surface is investigated and different mechanisms which cause dropwise and filmwise condensation are studied which shows the presence of Jakob model for condensation on smooth surfaces. The effect of chemical and thermal heterogeneities is also investigated and the positive effect of these parts on condensation is seen. The effect of different space between chemical heterogeneities and their difference with entire surface is also analyzed and it is seen that with an optimum space between them the maximum condensation performance can be achieved. Next, the condensation on smooth gradient wettability surface and the effect of different gradients and contact angle of core region on condensation is studied. Condensation on rough and structured surface is next investigated and it is seen that on these surfaces the nucleation starts on the edge of surface roughness which shows the presence of Tammann and Boebme model for condensation near surface roughness. Next, the effect of surface structures at different surface contact angles on nucleation and growth is studied. Finally, droplet condensation and jumping on smooth, structured and hybrid superhydrophobic surfaces is investigated and using non-dimensional parameters of this phenomena, a method for designing of such structured surfaces is presented
  9. Keywords:
  10. Consolidation ; Superhydrophobic Surfaces ; Phase Changing Methods ; Lattice Boltzmann Method ; Droplet Formation ; Numerical Investigation ; Droplet Jumping

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