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Title:	Stability analysis of natural and thermocapillary convection in a fluid layer heated from below
Authors:	Haliza Othman (P42608)
Supervisor:	Ishak Hashim, Prof. Dr.
Keywords:	Thermal analysis Universiti Kebangsaan Malaysia -- Dissertations Dissertations, Academic -- Malaysia
Issue Date:	18-Sep-2018
Description:	Thermal instabilities in a fluid layer heated from below play an important role in industry, engineering processes and nature. Control mechanisms are important in order to stabilise, delay or alter complex flow patterns due to the steady or oscillatory Marangoni and Bénard convections. The ability to control the convections will enable a deeper understanding into the dynamics of flow for better material processing and achieve the optimum outcomes. Some of the control mechanisms are investigated comprehensively in this thesis. A fluid layer of finite depth is assumed heated sufficiently strongly from below. The upper free surface is open to the ambient air. The lower horizontal bottom boundary is rigid. There are four main problems being considered as discussed in this thesis. In the first problem, the onset of Marangoni convection with a non-uniform temperature gradient is considered. In the second problem, combined Marangoni and Bénard convections in a micropolar fluid are considered. Effects of a cubic basic temperature gradient are taken into account. In the internal heat generation problem, feedback control is applied to control the thermocapalillary instability is discussed in problem three. The effect of rotation on the onset of convection in an anisotropic porous layer saturated with viscoelastic fluid is investigated in the last problem. Explicit analytical expressions for the marginal stability curve are presented for both the conducting and insulating cases in the first problem. The influences of various parameters on the onset of convection are analysed. The temperature gradient has a stabilising effect on the fluid layer when the lower boundary is insulating to temperature perturbations. The presence of micron-sized suspended particles delays the onset of convection in the second problem. Meanwhile in third problem, an exact solution for marginal stability owing to an exchange of stabilities is reported in the internal heat generation problem. It was found that there exists a critical value of crispation number below which the feedback control has a drastic stabilising effect with wave number and below which the feedback control has a minute effect on critical Marangoni number with zero wave number. In the other hand, the internal heating is found to have a destabilising effect. Finally in the porous medium problem, the governing equation was solved analytically by performing linear and nonlinear analyses. The effect of increasing the values of Taylor number, inter-phase heat transfer coefficient and ratio of diffusivities are found to stabilise the system while increasing the value of porosity modified conductivity ratio is to advance the convection.,'Certification of Master's/Doctoral Thesis' is not available,Ph.D.
Pages:	119
Call Number:	QD79.T38H335 2018 tesis
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Science and Technology / Fakulti Sains dan Teknologi

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