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Title: Simulation of drying for multilayer investment casting shells
Author: Harun, Zawati
Awarding Body: Swansea University
Current Institution: Swansea University
Date of Award: 2007
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The number of interacting variables influencing the drying of ceramic shells is large and to explore by experimental means is prohibitive. Therefore, the main advantage of the proposed theoretical model in this work, is that the effect of the drying conditions on their other important parameters (such as saturation, temperature, gas pressure) and transport properties (permeabilities, diffusivity) that control final properties of a multilayer ceramic shell can be investigated without extensive experimentation. This is very important in avoiding shell failure due to incomplete drying. Due to the fact that a porous ceramic body is a three phase system (solid, liquid and gas), modelling its transport and thermodynamic behaviour involves a complex solution due to the highly nonlinear physics that capture their evolution. A twodimensional numerical model based on the fundamental equations of heat, mass and gas transport was developed to establish the drying and thermodynamic response of the ceramic shell system. This complete coupled set is based on Whitaker's model that includes the mass, momentum and energy equation which also embodies the constitutive diffusion and capillary flow theory and its evaporation-condensation term in the flow phases; conduction, convection and latent heat of evaporation in the energy equation; along with the gas transport equation. The most widely implemented numerical solution (the fully implicit backward time stepping scheme) in the area of multiphase flow and drying in porous media was chosen for the temporal solution. The finite element method was employed for the spatial solution, due to its flexibility in dealing with complex geometries, and also it shows an ideal approach to employ in the solution of this class of problem. Both of the temporal and spatial numerical solutions for the theoretical solution were implemented into a computational code by using the Fortran programming language. This simulation scheme has been benchmarked against thermal test cases (to confirm the correct functioning of the thermal analysis) and for the first time the brick drying benchmark by Stanish in which it is demonstrated to provide the best solution. The scheme was then extended to address the drying of a single ceramic layer and compared with the published work, again showing good agreement. For the first time a simulation approach for the drying of a multilayer system that includes the impact of wet layer addition is proposed. The principles of an ab initio scheme are demonstrated that again show good agreement with experimental trends. Further work is required to obtain a better match with experimental data, but to do so will require improvements in deriving a compatible material data set that is appropriate for this simulation approach. The scheme set out in this thesis may be used to guide the test selection tofacilitate derivation of these material properties.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available