Loading...
Search
| Friend's email | |
| Your name | |
| Your email | |
| enter code | |
This page was sent successfuly
Digital Object List
Bookmark
Review List
75 viewed
شبیه سازی عددی جریان متقابل حرارتی ابرسیال هلیوم
یوسفی، حمید Yousefi, Hamid
- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 58832 (08)
- University: Sharif University of Technology
- Department: Mechanical Engineering
- Advisor(s): Afshin, Hossein
- Abstract:
- In this study, counterflow heat transfer around a rotating cylinder, heated and cooled cylinders, as well as through converging and diverging channels with hyperbolic, elliptical, and forward- and backward-facing step geometries, is numerically investigated. The simulations are performed using the two-fluid model based on the Gorter–Mellink formulation, with the primary objective of achieving a deeper understanding of superfluid helium behavior and improving the design of thermal heat exchangers. To this end, a novel algorithm is developed to couple the momentum equations of the two components with the pressure field. Unlike many previous studies, common simplifying assumptions are avoided, and the numerical results are validated through four independent verification stages. In the first phase, the effects of rotation and imposed heat flux on flow separation angles, drag and lift coefficients, and overall flow patterns around the cylinder are examined. The results reveal that, unlike classical fluids, superfluid flow behavior does not follow general or universal trends. Rotation and cooling or heating significantly influence flow separation and hydrodynamic forces; however, their effects vary markedly across different configurations and may even be contradictory. In some cases, rotation increases the separation angle, while in others it completely suppresses flow separation. Consequently, the drag coefficient exhibits diverse behavior, increasing from approximately 0.7 to nearly 1.4 in one case, while decreasing from about 0.8 to nearly 0.1 in another. In addition, rotation leads to a drag coefficient of approximately 1.3 in one configuration. A potential approach for component separation is also proposed, where in one case the rotation of the cylinder results in the separation of nearly 86% of the superfluid component. Overall, cooling reduces both the separation angle and drag coefficient, whereas heating increases them. In the subsequent stage, the thermal and hydrodynamic performances of different channel geometries with identical length and volume are analyzed and compared in terms of maximum temperature difference, thermal resistance, effective thermal conductivity, pressure drop, maximum Reynolds number, velocity difference between the two components, and density ratio. The results indicate that the simple channel exhibits the lowest thermal resistance and the highest effective thermal conductivity. When the use of a simple channel is not feasible, the elliptical channel is identified as a more suitable alternative. It is also shown that placing the heat flux on the smaller cross-sectional area and employing stepped geometries yield better performance compared to nozzles and diffusers. The maximum temperature difference in the nozzle and elliptical channels is approximately 16.8 and 3.8 times higher than that of the simple channel, respectively. Although pressure drop generally increases in all geometries relative to the simple channel, an exception is observed in the hyperbolic geometry, where pressure drop is reduced by approximately 18.1% in some cases due to the suppression of vortices and oscillatory flow. Overall, when minimizing pressure drop is a priority, the hyperbolic channel is a more favorable option. The largest velocity difference and intercomponent friction are observed in the converging channel, while higher average temperatures and an increased contribution of the normal component are found in the nozzle and backward-facing step geometries
- Keywords:
- Counterflow Burner ; Rotation ; Superfluid System ; Circular Cylinder ; Numerical Simulation ; Helium
-
محتواي کتاب
- view