| Summary: | 碩士 === 國立中興大學 === 化學工程學系所 === 101 === Nanofluid is the base liquid containing dispersed particles which size is below 100nm, which have large application value of heat transfer, lubricants, and medical treatment. But we also need to face the problem that the shear stress would increase leading to wear pipeline in the same time when we added nanoparticles into the base fluid. Therefore we built an unsteady state and 3-D concentric Couette flow containing TiO2 nano-particles dispersing in the ethylene glycol fluid (EG) to analyze effects of parameters on the shear stress and the heat flux respectively. In this study, we took angular speed of the inner tube, volume fraction of particle, secondary average particle size, and wall temperature as the variables. We exploited L9(34) orthogonal array to design experiments, in which, the viscosity and thermal conductivity of nano-fluid were proposed by Chen et al [17, 18], and the density and specific heat capacity of nano-fluid were deduced by Pak and Cho [39]. The volume of fluid (VOF) and finite volume method (FVM) associated with pressure implicit with splitting of operators (PISO) were then applied to solve the volume fraction equation and conservation equations for simulating the momentum and heat transfer of nano-fluids in a gap between circular double pipes. Finally, we used static smaller-the-better ratio and static larger-the-better ratio of signal to noise (S/N ratio) in Taguchi method to obtain the factor effect on shear stress and heat flux respectively.
In comparison, the resulting velocity and shear stress profiles were consistent with the theoretical value in the radial direction, which may be used to improve the reliability of the computational fluid dynamics (CFD) in this work. Furthermore, as known from the analysis of S/N ratio in Taguchi method, it was found that influence degrees of angular speed of the inner tube, the particle volume fraction, the particle aggregation, and the wall temperature, are 32%, 27%, 23%, and 17% on the shear stress, as well as 7%, 32%, 9%, and 52% on the thermal flux, respectively.
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