Thermal stability of nanofluids in superimposed fluid-porousdomain

• Main Authors: Chi-Miao Hsueh, 學其妙
• Other Authors: Falin-Chen
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/2qc39x

碩士 === 國立臺灣大學 === 應用力學研究所 === 105 === In this paper, a system of nanofluid is used to fill the fluid layer and the porous layer. By using the double diffusion convection effect of Brownian motion and thermal convection coupling of nanofluid, the double layer system is the natural mechanism that affects the heat transfer. This mechanism is related to the physical properties and geometric conditions of the heat transfer, and these physical parameters can be used to design the enhanced electronic kit cooling mechanism, to enhance the CPU computing power and DRAM access speed have substantial effect. For the current full development of the electric car motor cooling, but the analysis of this paper from the right angle coordinates into cylindrical coordinates to meet the axle shape of the design. We study the linear stability theory and discuss the influence of thickness ratio and concentration difference on the instability of this system. When the thickness is relatively small, the long wave is unstable than the short wave, and the convection mainly occurs in the porous medium layer. As the depth ratio becomes larger, the short wave is unstable than the long wave , and the convection mainly occurs in the fluid layer, so-called modal conversion. The number of vortex also become more, so that the vortex become shape as finger, that is, the so-called finger convection . In addition to the modal conversion, the t the Rayleigh number of the fluid layer and of the porous media layer are changed with the thickness ratio. With the increase of the thickness ratio, the Rayleigh number of the fluid layer is greatly increased. In addition, according to the double diffusion theory, only when the board concentration is high, there will be oscillation frequency, and in the conversion mode, the oscillation frequency is particularly low, when the thickness ratio increases, the oscillation frequency will increase significantly. To design the appropriate size, we fixed the total length to explore the different thickness than the temperature difference required to produce turbulence. To get the depth of the heat transfer in the industrial application, the different oscillation frequency should also have different effects. The larger thickness ratio more prone to turbulence , but the main occurrence of convection in the fluid layer. The relatively small flow of convection area is relatively small, the overall cooling effect is not necessarily better, so the need to achieve double-layer system has a heat dissipation and the minimum temperature difference should be converted to modal thickness it is good.