Reflux condensation occurs in a vertical tube when there is an upward core flow of vapour (or gas-vapour mixture) and a downward flow of the liquid film. The understanding of this condensation configuration is crucial in the design of reflux condensers and in loss-of-coolant safety analyses in nuclear power plant steam generators. A range of modelling approaches exists for co-current film condensation from gas-vapour mixtures in parallel-plate channels and tubes. These methods are based on marching from the inlet down the tube and do not apply to the reflux condensation. In this research, however, a two-dimensional two-phase model was developed that solves the steady, full elliptic governing equations in both the film and the gas-vapour core flow on a non-orthogonal mesh that dynamically adapts to the phase interface. Gas-vapour shear and heat and mass transfer at the interface were accounted for fundamentally. This modelling is a big step ahead of current capabilities by removing the limitations of previous reflux condensation models which inherently cannot account for the detailed local balances of shear, mass, and heat transfer at the phase interface. The model was developed and applied for co-current and counter-current flows in vertical parallel-plate channels, followed by vertical tubes. In each stage, the model results were compared against the available experimental and numerical data for validation purposes. A wide range of boundary conditions and geometries have been studied to examine the details of co-current and counter-current condensation phenomena. Velocity, temperature, pressure, and gas mass fraction profiles along with the axial variation of various parameters such as local Nusselt number, film thickness, interface and centre-line temperature and gas mass fraction are presented in parametric studies. / February 2017

The present thesis deals with soil resistivity and especially the suitability of replacing various soil models with a two-layer horizontal model. First, the factors that influence soil resistivity as well as the methodology of its measuring are described, and various soil models are introduced. Then, the Ansys program was used to create several soil models: a vertical model with perpendicular or oblique division, a model with a pronounced inhomogeneity and a three-layer model. In all of these models, a Wenner measurement simulation was performed, followed by a two-layer horizontal replacement model. Then the size of the error that was created by replacing the actual model with a two-layer horizontal model was examined.

Implementing a nonlinear gravity wave (GW) parameterization into a mechanistic middle and upper atmosphere model, which extends to the lower thermosphere (160 km), we study the response of the atmosphere in terms of the circulation patterns, temperature distribution, and migrating terdiurnal solar tide activity to the upward propagating smallscale internal GWs originating in the lower atmosphere. We perform three test simulations for the Northern Hemisphere winter conditions in order to assess the effects of variations in the initial GWspectrum on the climatology and tidal patterns of the mesosphere and lower thermosphere. We find that the overall strength of the source level momentum flux has a relatively small impact on the zonal mean climatology. The tails of the GW source level spectrum, however, are crucial for the lower thermosphere climatology. With respect to the terdiurnal tide, we find a strong dependence of tidal amplitude on the induced GW drag, generally being larger when GW drag is increased.

Implementing a nonlinear gravity wave (GW) parameterization into a mechanistic middle and upper atmosphere model, which extends to the lower thermosphere (160 km), we study the response of the atmosphere in terms of the circulation patterns, temperature distribution, and migrating terdiurnal solar tide activity to the upward propagating small scale internal GWs originating in the lower atmosphere. We perform three test simulations for the Northern Hemisphere winter conditions in order to assess the effects of variations in the initial GW spectrum on the climatology and tidal patterns of the mesosphere and lower thermosphere. We find that the overall strength of the source level momentum flux has a relatively small impact on the zonal mean climatology. The tails of the GW source level spectrum, however, are crucial for the lower thermosphere climatology. With respect to the terdiurnal tide, we find a strong dependence of tidal amplitude on the induced GW drag, generally being larger when GW drag is increased.