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Novel Heat Removal Enhancement and Reduction Methods and Optimized Surface Treatments for Several Engineering Applications

  • Author(s): Haghighi, Arman
  • Advisor(s): Vafai, Kambiz
  • et al.
Abstract

Metallic foams have increasingly gained attention due to their superior structural, acoustic, mixing and filtering characteristics. To further enhance the thermal features of these materials, a single or an array of metallic porous structures of various geometries are introduced on the inside surface of the partially heated wall of a channel with laminar flow. The challenge is to enhance the forced convection heat transfer rate from the heated wall to the working fluid while minimizing the pressure drop penalty caused by implementing these structures. Forced convective heat transfer rate from the heated wall to the fluid, as well as the average pressure drop along the channel are numerically studied with respect to the case with no structural extensions.

Various Aluminum metallic foams with different structural parameter values of Porosity (ɛ), Pore diameter (dp*), Darcy number (Da) are studied for the most common working fluids used in practical applications. Accordingly, the optimum geometrical conditions of the system is extensively explored considering geometrical parameters such as block’s height, width and spacing between them. Our results demonstrate that the optimum conditions yield considerable Nu enhancement ratios compared to the case of a channel with no metallic structural foam mounted inside. As such, thermal performance of metal foams can be substantially enhanced for heat removal in applications for solar collectors, compact heat exchangers, electronic cooling, etc. for only a modest increase in the pressure drop.

The second part of this thesis, addresses the issue of natural convection in cavities which is widely found in cooling electronics devices, heat exchangers, solar thermal collectors, heating and ventilating applications and energy conservation in refrigeration units. Implementations of the insulating features in a cavity is a solution for the goal of reduction in the overall heat transfer through the cavity. Therefore, heat transfer reduction capabilities of a vertical or a horizontal adiabatic partial partition fixed in a differentially heated cavity with insulated top and bottom walls are analyzed and compared. The effects of length and location of the partition is taken into account for aspect ratios from 1 to 4 and for Rayleigh numbers from 103 to 106. Different characteristics of square and higher aspect ratio cavities are compared and a comprehensive correlation of the heat transfer reduction is introduced, incorporating all the pertinent parameters. Furthermore, the optimized configurations and features for insulating purposes are established and discussed. Based on our results, vertical baffles more efficiently reduce heat transfer, in most cases.

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