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Developing a 3D-DSMC Solver to Simulate Supersonic Rarefied Gas Flows over Micro/Nanosensors

Mosayebi, Ghasem | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44111 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Darbandi, Massoud
  7. Abstract:
  8. Use of micro/nanoelectromechanical systems has become increasingly prevalent in recent years. Therefore, the development of technologies and understanding of fundamental physics associated with them is necessary.In micro-and nano-scale different behavior is often observed and it is due to Knudsen number that forms different types of flow regimes. When the flow is considered to be continuum; for it is in the slip-flow regime, for it is called the transition-flow regime. When , the flow is considered to be free molecular and is sufficiently rarefied to allow molecular collisions to be completely neglected in analysis. For continuum and slip flow regime the Navier-Stokes equations with adequate boundary conditions deliver accurate results. But for transinal and free molecular regimes it is necessary to utilize a particle-based method like Molecular Dynamics and Direct Simulation Monte Carlo. The Direct Simulation Monte Carlo (DSMC) method is an alternative to CFD that has been used widely and successfully to simulate high Knudsen number gas flow in transional regime. DSMC method is based on separation of particles movement and collisions. Particle movements are completely deterministic and collisions are modeled stochastic. At first part of this study for simulating of micro and nano gas flows a new DSMC code is developed that is called MONIR-DSMC. It has been implemented with c++ programming language using object-oriented scheme and advanced data structure. Then it used to simulate hypersonic, supersonic and subsonic rarefied flows in macro and micro scale. The results are compared to other available results and validated with different cases. Microsensors can be used in macro or micro devices such as micropropulsion. These can be located on microchannel or microvalves to construct a flow control system. Thermal flow sensors, which considered for simple structure, uses heat transfer laws for flow measurement. In the second part of present study MONIR-DSMC code has been used to simulate the performance of micro hotwire as thermal flow sensor to rarefied gas measurement. This sensor works on basis of heat transfer from heated resistance and usually operates on constant temperature or constant power modes. If the sensitivity of the sensor be great, it can also measure the smaller variation. In the current research a simple two dimensional model is used to assess the hotwire sensor, however the effects of different parameters on sensors have been studied. The results show that as hotwire diameter decreases probe dissipated energy reduces. The results also shows when Khudsen number increases the slope of Nu-Re relation in logarithmic scale from 0.5 in continuum regime close to 1in free molecular regime. It also shows in supersonic flow heat transfer decreases when Mach number increases. Three dimensional simulation of sensor also confirms the previous two dimensioanal results
  9. Keywords:
  10. Direct Simulation Monte Carlo (DSMC)Method ; Rarefied Gas ; Supersonic Flow ; Micro/Nanoelectromechanical System

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