|
|
|
SIMULATION HYBRID METHOD CLÁSICO-CUÁNTICOS OF VIBRATIONAL RELAXATION OF MOLECULES IN SOLUTIONAuthor: CRUZ VALCÁRCEL CARLOS. Year: 2005. University: MURCIA [ www.um.es]. Place of defense: FACULTAD DE QUÍMICA. Place of preparation: FACULTAD DE QUÍMICA. Summary: The inability to perform in practice a rigorous quantum description of the vibrational relaxation processes in liquid due to the large number of particles involved, is the need to use approximate methods. The classical Molecular Dynamics offers the simplest approach, but it has serious limitations for the study of the vibrational relaxation processes, to ignore the inherent quantum nature of the movement of vibration. Alternatively, in this thesis proposing the development of hybrid method clásico-cuánticos where there is a quantum description of the vibrational motion, while the rest of degrees of freedom are described classically. Among them we can distinguish two groups. First treatments based on the golden rule of Fermi, nature perturbativa. In the second place to treatment in which a temporary joint spread of the classical and quantum subsystems, which allows a detailed analysis of the flow of energy between the solute and solvent. Within this second group are the method of Field East, and those of Jumping between Cuánticos States. First, we have deducted an algorithm that ensures jump, in the absence of hops energetically forbidden, stock identity classical and quantum of quantum states, simulations using the break between Cuánticos States. On the other hand we propose a modification of the method Field East to attain equilibrium vibrational populations, given by the Boltzmann distribution. We have applied these methods to the study of the vibrational relaxation of the molecule liquid xenon and iodine cyanide ion in water, where we analyze the role of the solvent in the transitions between the vibrational states of the solute. Our results for these systems, so different in nature, agree well with experimental measures, which in the absence of exact theoretical results is a valuable testament to the ability of these methods to study vibrational relaxation processes in liquids.
NUMERICAL METHODS FOR RADIATIVE HEAT TRANSFER.Summary: The main objective of the present thesis is to study the energy transfer by means of radiation. Therefore, the basic phenomenology of radiative heat transfer has been studied. However, considering the nature of the equation that describes such energy transfer, this work is focussed on the numerical methods which will allow us to take radiation into account, for both transparent and participating media. Being this the first effort within the CTTC (âCentre Tecnològic de Transferència de Calorâ) research group on this subject, it is limited to simple cartesian and cylindrical geometries. For this purpose, chapter 1 contains an introduction to radiative energy transfer and the basic equations that govern radiative transfer are discussed. These are the radiative transfer equation, formulated in terms of the absorption and scattering coefficients, and the energy equation. It is also given a discussion on when this mode of energy transfer should be considered. In this chapter are also defined all of the magnitudes and concepts used throughout this work. It ends with a brief description of some approximate methods to take radiation into account. The Radiosity Irradiosity Method is introduced in chapter 2. In this chapter it is also described a numerical method to calculate the view factors for axial symmetric geometries. The main results obtained in such geometries are also presented. Although a little disconnected from the rest of the present thesis, the algorithm used to handle âde factoâ' three dimensional geometries with computation time just a little longer than two dimensional cases, with no additional memory consumption, is considered worthy enough to be included in this work. In chapter 3, the Discrete Ordinates Method (DOM) is detailed. The fundamental aspect of this method is the choice of an ordinate set to integrate the radiative transfer equation. The characterization of such valuable ordinate sets is laid out properly. The discretization of the radiative transfer equation is explained in detail. The direct solution procedure is also outlined. Finally, illustrative results obtained with the DOM under several conditions are presented. In the moment we wish to solve real problems, we face the fact that the absorption and scattering coefficients depend strongly on radiation wavelength. In the present thesis, special emphasis has been placed on studying the radiative properties of real gases in chapter 4. This interest resulted on a bibliographical research on how the wavenumber dependence of the absorption coefficient is modeled and estimated. Furthermore, this bibliographical research was focussed also on numerical models able to handle such wavenumber dependence. Several methods are discussed, and two of them, namely the Weighted Sum of Gray Gases (WSGG) and the Spectral Line Weighted sum of gray gases (SLW), have been implemented to perform non gray calculations. Some significant results are shown. Plenty of tests have been performed to the numerical code that resulted from the elaboration of this thesis. According to the results obtained, the objectives proposed in this thesis have been satisfied. As a demonstration of the usefulness of the implemented code, it has been succesfully integrated to a general purpose computational fluid dynamics code (DPC), fruit of the effort of many researchers during many years. Results of the above integration lead to the resolution of combined heat transfer problems, that are analyzed in chapters 5 and 6, where radiative heat transfer is coupled to convection heat transfer. The effect of radiation on the total heat transfer is studied in chapter 5, which has been published as International Journal of Heat and Mass Transfer, volume 47 (issue 2), pages 257--269, year 2004. In chapter 6, the impact of some parameters of the SLW model on a combined heat transfer problem is 8 analyzed 289 .
|
|
|
