Resumen de Numerical simulation of frost growth and densification using deformable and static grids
The present thesis aims at developing a basis for the numerical simulation of the growth and densification of macroscopic frost sheets. Notwithstanding the fact that icing has still a long way to fully understand its physics, this work is potentially important, since a broad range of empirical correlations as well as the implementation of formerly neglected physical effects are studied herewith. In particular, this research is focused on developing methodologies for three-dimensional meshes, capable to predict the frost growth and densification of complex geometries.
This work comprises five chapters. The first one is an introduction to icing and frost formation. The main motives that urge to numerically simulate frosting are detailed. Moreover, the different methods and approaches to model frosting are presented. From these, the main objectives and outline of the thesis are derived.
The next two chapters are the core of this dissertation, which comprehend the two developed methods.
In detail, the second chapter introduces a model that simulates the frost growth and densification using a moving mesh method. First, the most relevant empirical correlations used to describe the frost layer conductivity and diffusivity among others are tested by means of parametric studies. A thorough discussion on the performance of such parameters is made, emphasizing the fact of using diffusion resistance factors above 1.0 in order to capture the frost growth. The best-fitted solutions validate the model input combinations which give good agreements against experimental data under certain experimental conditions. Furthermore, the method is tested against a 2D numerical case, highlighting the main advantages of using a deformable grid, i.e. the accurate tracking of the air-frost interface.
The third chapter introduces a fixed-grid-porous-media method capable of simulating the growth and densification of frost sheets. In pursuance of finding out possible explanations to the needed artificially enhanced diffusion resistance factors, a velocity field is calculated across all the domain. A porous media treatment is given to the frost layer, whereas the transported temperature and vapour density are used to define the thermophysical state of each cell, which might enable phase change. The method is tested with a study case of a duct flow with a non-homogeneously cooled lower boundary. The influence of accounting for the convection, as well as the enhanced diffusion resistance factors within the frost layer, are studied.
The last two chapters contain the concluding remarks, as well as ideas on how the present work could be continued.
