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Title: Finite element modelling of convective diffusive heat transfer and phase transformation with reference to casting simulation
Author: Usmani, A. S.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1991
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Finite element models have been developed for the analysis of transient laminar flow and heat transfer problems including the effects of phase change, in general, and for the analysis of the various aspects of the casting process in particular. These models were based upon a 2-D finite element program developed from discretising in space, the Navier-Stokes and the energy equations, using the Galerkin form of the weighted residual method. Temporal discretisation was implemented using finite difference formulas. Automatic time stepping schemes based upon the time truncation error, were used to solve several familiar problems for testing the code developed. Various techniques for including phase change effects in finite element programs were compared on the basis of a benchmark test. The preferred technique for modelling phase change was then implemented in the coupled flow and heat transfer code developed earlier, which was used to solve problems of solidification and melting in a square cavity including the effects of natural convection on the heat transfer. The modelling of flow into mould cavities was attempted next based upon the VOF (volume of fluid) method first used in finite differences for modelling free fluid fronts. A model was developed by coupling of the Navier-Stokes equation solver and a finite element discretisation of the pure advection equation. The velocities from the Navier-Stokes solution were used to advect a 'pseudo-concentration' function, a specific contour of which represents the liquid metal front. The modelling of mould filling was undertaken with the primary purpose of obtaining realistic initial thermal fields in a full casting, from which point the subsequent analyses of heat transfer etc. until solidification, may continue. The conventional Galerkin finite element method was found to generate oscillatory solutions for both the pseudo-concentration and the temperature fields due to advection dominated nature of the transport. Furthermore the backward Euler time stepping method employed, produced highly overdiffuse thermal fields. The Taylor-Galerkin method was used to alleviate these problems and much smoother solutions were achieved with sharp thermal boundary layers. An interface element was developed and applied to the mould filling model for improved control of heat transfer between the filling metal and the mould.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available