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Numerical Simulation of Two-Phase Annular Flow in Horizontal Tubes

Harati, Mohammad Ali | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40293 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Nouri Borujerdi, Ali
  7. Abstract:
  8. Two-phase flows are widely used in petrochemical industry, chemical processes, boilers, nuclear reactors, cooling systems and air conditioning equipment. Since the problem of earth’s ozone layer and global warming, the analysis of flow characteristics in evaporators are necessary to improve performance of refrigerating systems and saving the environment. Most of the researchers have been studied the evaporation of two phase flow refrigerant through experimental studies and numerical analysis has less attention in the literature. In this Thesis, a mathematical model based on the two-phase separated flow model is developed to simulate the evaporation of pure refrigerant under constant heat flux , with mass flow rate G, saturation pressure , and saturated vapor quality x, diameter D, and length L, flowing in a horizontal tube. The finite difference form of governing equation of annular flow model is derived from the conservation of mass, energy and momentum. The numerical results are validated by comparing it with the experimental data. This model can be use to investigate the axial distributions of pressure drop, velocities, heat transfer coefficient and temperature of various refrigerants. In this study number of parameters such as mass flux, inlet pressure, inlet flow quality, tube diameter and heat flux were varied to investigate their effects on the pressure drop, quality change, velocity, heat transfer coefficient and evaporation rate along the tube. It is found that the saturated pressure and temperature of refrigerant decrease along the tube due to the tube wall friction and the flow acceleration of refrigerant. The liquid heat transfer coefficient increases with the axial length due to the reducing thickness of the liquid film. Both liquid film and vapor core velocities increase with increasing axial length and vapor core velocity is higher than liquid velocity due to its lower viscosity and density. The results show that there are no significant differences between numerical and experimental data which are also obtained (pressure, vapor quality, fluid and wall temperature) with deviation of less than 4%. Highest percentage of error for the pressure drop is equal to 3.29% and the lowest percentages of error for calculate the mean temperature of the liquid phase is equal to 0.06%.

  9. Keywords:
  10. Numerical Analysis ; Evaporation ; Two Phase Flow ; Annular Flow ; Coolant ; Evaporators

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