This computer simulation study carried out by classical the molecular dynamics technique (MD) investigates structural phase transitions of various atomic and molecular condensed matter systems. Particularly, our attention is focused on the signals for their observation. Classical nucleation theory is briefly reviewed in relation to the present study. An overall review is made on the methodology of the MD simulation technique such as the integration of the equations of motion, the rotational motion of molecules which is dealt with the four-component quaternion, and other various techniques involved with the simulation of atomic clusters, the simulation of bulk molecular systems using periodic boundary conditions, and isobaric molecular dynamics. There are also reviews on measurements of thermodynamic quantities which are monitored during the simulation including the pressure, the kinetic energy, and the potential energy as well as their corrections due to the spherical cutoff. In addition, various analysis techniques for the observation of the signals of structural phase transitions are discussed. All the potential functions used in this study are of the pairwise additive atom-atom Lennard-Jones interaction for both the atomic and the molecular systems. A small cluster of a binary mixture of krypton and argon atoms is studied by triggered breathing motions to investigate anharmonic motion which involves the structural phase transitions. A small cluster of krypton atoms is also simulated and discussed in detail concerning the very first moment of nucleation in relation to five-fold symmetric structures. In simulations of sulphurhexafluoride molecule systems, artifacts of finite size and periodic boundary conditions are investigated. Freezing the system by MD is investigated since it is known to supercool in computer simulations. Furthermore, accelerating the nucleation process by various methods such as shear flow, accelerated layer, inclusion of defect molecules, and pressure fluctuations is investigated.

A comprehensive theoretical and experimental study is made of the following condensation processes, occurring in cocurrent downwards flow within a single vertical tube and with negligible shear effects at the vapour-liquid interface. 1. Condensation of a vapour in the presence of a non-condensable gas. 2. Condensation of binary vapours of miscible liquids. 3. Multicomponent condensation of the vapours of miscible liquids in the presence of a non-condensable gas. 4. Condensation of binary vapours of immiscible liquids where the vapours are not at eutectic conditions. 5. Condensation of vapours of immiscible liquids in the presence of a non-condensable gas. Condensation of binary vapours or vapour-gas mixtures has been widely investigated and processes I and 2 are studied in this work to test existing design methods particularly the evaluation of heat and mass transfer coefficients and the enhancement of transfer rates due to the presence of the condensate. The experimental and theoretical procedures of this work are validated to provide a firm basis for the new studies. Multicomponent condensation of the vapours of miscible liquids has been a subject of several recent studies. New data are presented and the following models of multicomponent mass transfer are compared. 1. The linearised theory of Toor (1964) 2. The matrix method of Krishna and Standart (1976) 3. Simple effective diffusivity models. Particular emphasis is given to the significance of diffusional interactions and conditions under which the simple effective diffusivity model is adequate are identified. Little work is reported in the literature on condensation of the vapours of immiscible liquids and these studies are limited to binary eutectic mixtures. In this work extensive new data are reported on condensation of non-eutectic mixtures and multicomponent mixtures containing a non-condensable gas. The data are compared with existing correlations of the heat transfer coefficients of immiscible liquid films. New methods are reported to allow design of condensers carrying immiscible liquids. where the vapour is of non eutectic composition or contains a non-condensable gas. These methods are considered in relation to the experimental data.

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