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Numerical Simulation and Shape Optimization of Supersonic Ejectors for Refrigeration Applications

Aligolzadeh, Farid | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51049 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Hakkaki-Fard, Ali
  7. Abstract:
  8. Due to an increasing need for refrigeration systems and consequently increasing in electricity usage and greenhouse gases production, using ejector refrigeration systems would be a suitable substitution for conventional cooling systems. Main drawback of ejector refrigeration systems is their low coefficient of performance. The key component to improve the cycle performance is the ejector. Prerequisite of improving ejector performance is an accurate CFD simulation for predicting entrainment ratio. In this study, a two dimensional, axisymmetric, steady state, compressible flow CFD simulation of a supersonic ejector is presented. CFD results are validated with experimental data. Furthermore, the influences of applying different types of equations of state and turbulence models are studied. The k-ε realizable turbulence model and Soave-Redlich-Kwong equation of state have been applied for further simulations. In the second part of this study, geometrical optimization of the simulated ejector for two objective functions has been investigated. First, the objective function was entrainment ratio. The optimization has led to 53% relative improvement in entrainment ratio with a negligible decrease in critical pressure. Second, the objective function was exergy efficiency in which the optimization has showed 39.6% relative increase. In third part of this study, a methodology for designing multi-ejector refrigeration system is described to tackle the main defect of single-ejector refrigeration system which is low seasonal coefficient of performace. A case study has been performed to evaluate the performance of the multi-ejector system. It has been shown that the system seasonal coefficient of performance can be improved up to 72.8% compared to single-ejector refrigeration system
  9. Keywords:
  10. State Equation ; Turbulence Model ; Shape Optimization ; Computational Fluid Dynamics (CFD) ; Supersonic Ejector ; Multi-Ejector Refrigeration System

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