Modelagem matemática do processo de mudança de fase de materiais semissólidos

Abstract

During production shutdowns on offshore oil platforms, whether due to scheduled maintenance or emergency stops, oil becomes confined within the pipeline. The lower temperature of the marine environment compared to the oil triggers a heat transfer process. As the oil reaches the initial crystallization temperature, paraffin crystals begin to precipitate. Once a certain concentration of solid paraffin is reached, the oil gelifies. This phenomenon is accompanied by volumetric contraction, which can result in the formation of voids. The presence of voids influences the mechanical properties of the material, rendering assumptions such as uniform yield stress and incompressible material invalid. This study aims to develop a mathematical model and implement a numerical simulation of a phase change process. It also seeks to evaluate different numerical parameters and boundary conditions on the final solidification profile. The numerical implementation was performed using the commercial software Ansys Fluent, employing the VOF and enthalpy-porosity methods. An analysis of the effects of surface tension is presented. An appropriate value for the porosity parameter is determined. The effects of the cooling rate on the final solidification profile are investigated. A brief discussion on fluid flow during solidification is included. Finally, it is concluded that the model successfully captured both the solidification process and the interface between the paraffin and the air.