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Numerical and Analytical Investigation of Unequal Size Droplets Generation Process in Micro and Nano Channels

Bedram, Ahmad | 2015

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 47234 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Moosavi, Ali; Kazemzadeh Hannani, Siamak
  7. Abstract:
  8. In this paper, we introduced two methods for producing unequal sized droplet from an initial one that don’t have the disadvantages of the available methods. We developed a comprehensive analytical theory for the T-junction with valve method. Also the geometry was simulated using a VOF algorithm and a comparison was performed between numerical and analytical results and very good agreement was observed. The accuracy of numerical results was confirmed by doing the grid independency and time step independency and comparing the results with two analytical benchmarks. We derived accurate analytical relations for calculating the droplet volume ratio, droplet length (L1, L2 and Lwhole) and pressure drop of the system. We observed that if the valve ratio becomes less than a specific value (0.65) the system enters the non-breakup region. Both the analytical theory and the numerical results showed that by decreasing (increasing) the valve ratio the droplet length of branch 1 decreases (increases) and droplet length of the branch 2 increases (decreases) and whole length of the droplet remains constant. The results showed that the system pressure drop does not depend on the time and decreases by increasing the valve ratio, namely, leading the geometry to a symmetric T-junction. Also we proposed a novel method for producing unequal sized droplets (intelligent system) that reduces the dependency of the droplets volume ratio to the inlet velocity of the system up to 26 percent. The employed method for investigating the proposed system relies on 3D numerical simulation using the VOF algorithm and the results have been obtained in various valve ratios for both the micro- and nanoscale. The results indicated that the droplet length during the breakup process increases linearly with the time. It has been shown that the maximum local capillary number in this system is 2.5 times the average capillary number. Therefore one can use the analytical theories based on the low capillary number assumptions for investigating the intelligent system
  9. Keywords:
  10. Drop Breakage ; Analytical Solution ; Numerical Investigation ; Analytical Approach ; Micro/Nanochannel ; Unequal Size Droplets

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