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Numerical Investigation of Nitrogen Condensation in a Two-phase Vortex Tube

Mirjalili, Mohamad Reza | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55128 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Ghorbanian, Kaveh
  7. Abstract:
  8. The Ranque-Hilsch vortex tube (RHVT) has no moving parts through which a high-pressure fluid gains on rotational velocity by passing radially through the inlet nozzles and then enters the vortex chamber. Subsequently, the high-pressure fluid becomes divided into two relatively distinctive hot and cold axial flows. Today, while RHVT is of great industrial interest due to its simplicity in manufacturing and operation; however, the mechanism of energy dissociation, which is dominated by the complex coupled interaction of the viscous thermo-fluid characteristics and geometrical properties, is not fully understood and no clear theory has been proposed to explain the energy dissociation so far. The focus of this dissertation is to better understand the transient thermo-fluid processes in a vortex tube through numerical investigation.An axisymmetric numerical investigation is performed for a vortex tube at a cold mass fraction equal to 0.44. The results reveal a close agreement with past numerical and experimental data from open literature. The distribution of axial, radial, and tangential velocities as well as the stagnation pressure and temperature are examined at different positions for different time steps. The results indicate that the tangential velocity is the most significant velocity component and dominates the heat transfer and energy conversion processes. In addition, it is evident that the core of the cold end experiences the highest pressure gradient along with almost zero tangential and radial velocities. The maximum axial velocity appears close to the inlet and its value increases with higher cold mass fractions due to higher pressure gradient which may lead to the enlargement of the inner vortex. The impact of different cold mass fractions at various tube length ratios and different time steps are examined. The results indicate that there is relatively no vortex decomposition near the cold outlet.Further, nitrogen at both ambient and cryogenic temperatures in a RHVT is studied. While the results indicate similar energy separation process; however, the magnitude of temperature difference at cryogenic condition is smaller than at ambient condition. In this regard, the condensation phenomenon is simulated by using equilibrium multiphase model and Soave-Redlich-Kwong equation of state with different turbulence models at different inlet pressures and temperatures. The results indicate of an increase of nitrogen density with increasing inlet pressure and decreasing inlet temperature. Finally, the effect of RHVT divergence is investigated. The results reveal a negative effect on nitrogen condensation; however, at small divergence angles, the vortex tube cooling performance increases at the cold outlet.
  9. Keywords:
  10. Vortex Tubes ; Energy Separation ; Two Phase Flow ; Numerical Simulation ; Natural Gas Liquefaction ; Liquefaction Process ; Ranque-Hilsch Vortex Tube (RHVT)

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