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Simulation of Natural Convection Inside an Enclosure with Several Heated Bodies

Sepahi, Farzan | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49106 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Nouri, Ali
  7. Abstract:
  8. in this study, turbulent natural convection inside an air filled square cavity with several hot and cold internal bodies in the range of Rayleigh numbers between 1010 and 1012 has been investigated numerically. Vertical walls of the enclosure have been considered isothermal and horizontal walls are insulated in all cases. An appropriate arrangement of internal bodies in which the minimum heat transfer occurs is desired. For this purpose, two dimensional Reynolds-averaged Navier-Stokes equations have been solved with the finite volume discretization method in a staggered grid. In addition, two equation high-Reynolds-number model with standard wall functions is used to simulate the turbulence of the flow which is computationally more efficient than low-Reynolds-number models. A multi-domain structured mesh is generated based on the first cell size adjacent to the walls and the concentration factor of the mesh. The hybrid and central differencing schemes are also used to discretize the convective and diffusion terms of the equations, respectively. Since natural convection occurs at high Rayleigh numbers, unsteady approach is emeployed to capture all unsteadiness within the enclosure. Consequently, unsteady SIMPLE and PISO algorithms are implemented for velocity-pressure coupling. Time derivatives are discretized implicitly and the spatial derivatives are computed at new time level so that the final discretization leads to a system of linear algebraic equations that should be solved simultaneously. Line by line iterative method of TDMA and preconditioned iterative method of SIP are employed to solve the obtained algebraic systems of equations with a remarkable rate of convergence. The results indicate that in the case with one hot body inside the enclosure, the heat transfer of the body and walls of the cavity is minimum when the hot body is located horizontally on the upper left hand side of the cavity. In the cases with two hot and cold bodies, total heat transfer is minimum when the hot body is located above the cold body and more reduction in this heat transfer can be achieved by increasing the distance between the bodies and placing them horizontally. Moreover, in the mentioned case by increasing the number of bodies to four, the averaged heat transfer of bodies is reduced about 40 percent at all Rayleigh numbers. Our results have been validated with several experimental and numerical researches for natural convection inside cavities with or without internal bodies and are believed to be in a reasonable agreement with reported data of these works
  9. Keywords:
  10. Natural Convection ; Turbulence ; Finite Volume Method ; Numerical Analysis ; Computational Fluid Dynamics (CFD) ; Unsteady Flow ; Enclosure with Internal Bodies

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