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Faghih-Naini, Sara:
Theory and Numerics for Convective Heat Transport in Nanofluids.
Erlangen
,
2019
(Masterarbeit,
2019
, Friedrich-Alexander-Universität Erlangen-Nürnberg)
Abstract
Nanotechnology has drawn the interest of many researchers for some years and is considered to be one of the significant forces that drive the next major industrial revolution of this century. Since thermal conductivity of conventional heat transfer fluids such as water, oil and ethylene glycol is a primary limitation in the construction of e.g. compact engineering electronic devices with high performance, there exists a strong motivation to develop advanced heat transfer fluids with substantially higher conductivities to enhance thermal characteristics. The central problem addressed in this thesis is a convective heat transport model for nanofluids, specifically a thermodynamically consistent version of the celebrated Buongiorno model. We propose a semi–discretization in time that fully decouples the subproblems. Also for this semidiscrete problem, an energy estimate can rigorously be shown. Based on this energy estimate it is proved that solutions of the semi–discrete problem converge to a weak solution of the system.
We use the time discretization to define an effective, fully discrete finite element scheme. Simulations are performed for a nanofluid flowing through a pipe that is heated periodically in time at one lateral wall and a lid driven cavity with a triangular heat source placed within. Careful inspection of the computational results reveal the mechanisms of enhanced heat transfer by nanofluids through thermophoresis: the temperature gradient at the wall leads to a reduced concentration of nanoparticles. This reduces the concentration dependent viscosity of the suspension close to the boundary, which in turn leads to a stronger convective transport.