Compressors are widely used across the all technical fields and current pressure on ecology increases the demand for more effective compressor with economical operation costs. The reasons for inefficiencies must be identified during the development process of a new compressor, where simulation tools might become very useful. There are many different tools for compressor analysis and choosing the right one is mostly dependent on the level of detail that must be analyzed. Models based on energy balance seem to be appropriate when the global parameters of a compressor are demanded. These models offer quick results with reasonable degree of accuracy in terms of basic compressor characteristics. The goal of this thesis is to develop such a simulation tool for a reciprocating compressor. The tool can predict compressor behavior based on compressor dimensions and valve properties. The processes inside the cylinder and heat transfer between the components of a compressor are analyzed using energy balance equation. Simulation tools were verified and experimentally validated using two different types of compressors, therefore they might be used for any reciprocating compressor under some conditions. Mathematical solution was developed in Matlab and therefore it is possible to add new sub-models or to couple the actual model with other simulation tools. This work also contains an analysis of heat transfer models used to predict heat transfer coefficient inside the cylinder and comparison with complex numerical approach. Impact of heat transfer on the compressor efficiency was evaluated too.

Parametric performance analyses and comparison of a basic geothermal heat pump, a heat pump cycle with motor cooling/refrigerant preheating, and a heat pump cycle utilizing an economizer with respect to first law is conducted through simulation. Changing compressor, pump, and motor efficiency, along with condenser pressure, evaporator pressure, degree of subcooling at the condenser exit and degree of superheating at the evaporator exit is investigated. Economizer arrangements yield the highest coefficient of performance and resilience to change in COP with variation in evaporator pressure, and degree of superheating and subcooling. The basic vapor compression and motor cooling/refrigerant preheating systems have the lowest COP throughout and greatest resilience to variation in compressor efficiency, motor efficiency and condenser pressure. Motor cooling/refrigerant preheating and economizers have advantages over basic vapor compression cycles. Motor cooling reduces ground loop heat exchanger length with similar COP, and economizers allow for an increase in COP compared to the basic cycle. / UOIT

In the work presented in this dissertation, extensive molecular dynamics (MD) simulations have been performed to investigate various physical problems related to the solid-liquid transitions over a wide range of supercooling and superheating temperatures in model Lennard-Jones systems. The major focus of this work is to investigate the thermodynamics, kinetics, and underlying mechanisms of these problems. There are five topics in this work: (1) The classical nucleation theory (CNT) was tested for both liquid supercooling and solid superheating via different solid-liquid coexistence models. It is found that the CNT is valid for liquid supercooling but invalid for solid superheating. The arising elastic energy plays a significant role in affecting the liquid nucleation in a superheated solid. A new nucleation theory was proposed for describing the internal liquid nucleation of solid superheating. (2) Based on CNT, a new and accurate method was developed for calculating the crystal-melt interfacial free energy and its anisotropy. Our result is very close to Turnbulls experimental results. (3) The face, temperature, and size dependences of the crystallization rate were investigated in this work. The results show that the crystallization rate decreases substantially with the increasing system size. Different from the conventional models, a new model is developed to describe these dependences. (4) Melting from internal nanovoids was investigated in this work. It is found that the mechanism of void melting is quite different from bulk melting and nanoparticle melting. There are four different stages and three local melting temperatures in void melting. The mechanism of the complex melting sequence is systematically explained. (5) The homogenous melting at the upper limit of superheating was investigated in this work. For the first time, the ring diffusion is found to take place in superheated crystals and causes the spontaneous melting. The prevailing instability theories are unsuitable to describe this type of melting. The mechanism of the diffusion-loop mediated melting is carefully discussed in this work.

Superheated water has been used successfully as an eluent in liquid chromatography and has been coupled to various modes of detection, ultraviolet (UV), fluorescence, and nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS). A number of compounds were examined on poly(styrene-divinylbenzene) (PS-OVB), polybutadiene (PBO), and octadecylsilyl bonded silica (OOS) column with isothermal and temperature programmes.

No description available.

We computationally explore the dynamics of superconductivity near the superheating field in two ways. First, we use a finite element method to solve the time-dependent Ginzburg-Landau equations of superconductivity. We present a novel way to evaluate the superheating field Hsh and the critical mode that leads to vortex nucleation using saddle-node bifurcation theory. We simulate how surface roughness, grain boundaries, and islands of deficient Sn change those results in 2 and 3 spatial dimensions. We study how AC magnetic fields and heat waves impact vortex movement. Second, we use automatic differentiation to abstract away the details of deriving the equations of motion and stability for Ginzburg-Landau and Eilenberger theory. We present calculations of Hsh and the critical wavenumber using linear stability analysis.

Dans la zone insaturée, l’altération des roches poreuses en condition de séchage est attribuée principalement aux sels qui cristallisent dans la solution porale lors de son évaporation. Ils exercent une pression (pression de cristallisation) contre les parois du pore dont le moteur est la sursaturation de la solution. Dans le même contexte, l’eau porale qui est retenue par capillarité dans les pores nanométriques est amenée sous pression négative. L’eau sous tension capillaire exerce une traction mécanique contre les parois du pore, mais aussi modifie les équilibres chimiques. Ces deux mécanismes, pression de cristallisation et traction capillaire, qui sont de nature physique, ont pour origine le déséquilibre chimique entre l’eau porale et l’air sec.Des expériences de cristallisation de sels (Na2SO4, NaCl) permettent 1/ de mettre en évidence des conditions favorables à l’expression de la pression de cristallisation, qui apparait comme un phénomène brutal et transitoire provoqué par la relaxation d’un état de déséquilibre (sursaturation), et 2/ de montrer que la tension capillaire, générée par une interface nanométrique, peut être transmise à un macrovolume dans un système géométrique particulier construit par les sels. L’état de tension y est métastable (l’eau est surchauffée) mais dure suffisamment longtemps pour observer les effets mécaniques (traction) et chimiques (dissolution) attendus. La relaxation brutale de l’état de surchauffe permet une rapide sursaturation, qui est le moteur de la pression de cristallisation.Ainsi, les cycles climatiques sont à l’origine d’évènements brutaux et transitoires qui marquent la relaxation d’un état de déséquilibre (surchauffe et sursaturation), contrôlés par la tension capillaire et la cristallisation des sels qui coopèrent pour altérer la roche en conditions de séchage. / The alteration of porous media in drying conditions is generally attributed to the pressure exerted by growing salts from the poral evaporating solution against the pore wall (crystallization pressure). In drying conditions, the water retained by capillarity in nanometric pores is under absolute negative pressure. Water under capillary tension exerts a mechanical traction against the pore walls but also modifies the chemical equilibria and so rock-fluid interactions. Crystallization pressure and capillary tension, which are physical processes, are both induces by the disequilibrium between poral water and dry air.Salt crystallization experiments in microtubes (Na2SO4, NaCl) show some favorable conditions for crystallization pressure - in terms of supersaturation and geometry – which is transient and brutal. A second series of experiments shows that capillary tension, generated by a nanometric liquid air interface, can be transmitted to a macrovolume of aqueous solution in a particular geometric system built with salts. The tensile state is metastable (superheated), but long enough to modify significantly the chemical budget of the system and to see mechanical effects. The brutal relaxation of the superheating state by vapor nucleation induces a rapid salt supersaturation which is the driving force of the crystallization pressure.The salt growth (during evaporation) and capillarity cooperate in drying conditions to alter porous media.During climate cycles (especially humidity) they control and induce transient and brutal events which mark the end of metastable states (superheating and salt supersaturation).