Moisture recovery is important in the operation of many fuel cell systems, especially proton exchange membrane (PEM) fuel cells. The exhaust of a PEM fuel cell is a moderate temperature, pressurized humid air stream. A system that recovers liquid water condensate from the pressurized humid exhaust stream of a PEM fuel cell would markedly increase the effectiveness of such a system. The recovered water could be used to hydrate the fuel cell membrane, and it could supply a hydrocarbon reformer used for generating hydrogen. This project investigated and documented moisture recovery from the simulated humid exhaust stream of a 25 kW fuel cell with an improved axial flow separator. An axial flow centrifugal separator design was chosen as the best candidate due to its high efficiency and low pressure drop and a prototype was designed and constructed. The separator was then integrated into an experimental test system. First, the stream was simulated by heating compressed air and then humidifying it with superheated steam. Then, after expanding through the turbine section of an automotive turbocharger, the humid stream was passed through the moisture separator where liquid water condensate was removed from the flow. Results are presented for varying turbine inlet conditions at three separate separation lengths. It is shown that the separation efficiency for the improved design was 40% higher and the pressure drop was only 1/3 that of the conventional separator.

In order to explain the observed time-dependent salinity variations in seafloor hydrothermal vent fluids, quasi-numerical and fully numerical fluid flow models of the NaCl-H2O system are constructed. For the quasi-numerical model, a simplified treatment of phase separation of seawater near an igneous dike is employed to obtain rough estimates of the thickness and duration of the two-phase zone, the amount of brine formed, and its distribution in the subsurface. For the fully numerical model, the equations governing fluid flow, the thermodynamic relations between various quantities employed, and the coupling of these elements together in a time marching scheme is discussed. The fully numerical model is benchmarked against previously published heat pipe and Elder problem simulation results, and is shown to be largely in agreement with those results. A number of simulation results are presented in the context of two-phase flow and phase separation within the framework of the single pass model. It is found that a quasi-stable two-phase (liquid + vapor) zone at depth below the hydrothermal discharge outlet gives rise to vent fluid with lower than normal seawater salinity. Additionally, it is shown that increasing the spatial extent of the two-phase zone can lower vent fluid salinity. The numerical approach used in this thesis is able to generate salinity patterns predicted by a widely held conceptual model of vent fluid salinity variation, and may be able to explain the vent fluid salinities and temperatures found at the Main Endeavour Vent Field on the Juan de Fuca Ridge, as this approach is able to produce simulated vent fluid salinities that match observed values from the Endeavour Field vents Dante and Hulk.

This study focuses ontransient heat flow behavior in which centralizing energy on themetal makes metal surface come to aheat molten state with centralized heat source . This flow field is two-dimensional transient model, using Phase-field method and Two-phase flow to simulatemetal surface. In this study is under considerations of the mass conservation equation, momentum equation, energy equation and the level-set equation, regardless of the impact due to the concentration diffusion. At last it will show the flow of the molten zone caused by temperature, and the flows in molten zone forced by thermocapillary which is caused byvariation of temperature.

This thesis investigates the refrigerant (R-134a) flow in three minichannels having different geometries experimentally. During the last 40 years heat transfer in small scales has been a very attractive research area. Improvements in heat transfer in the refrigeration applications by means of usage of micro/minichannels provide significant developments in this area. Also it is known that experimental studies are very important to constitute a database which is beneficial for new developments and research. During the two-phase flow experiments conducted in the minichannels, low mass flow rates and constant wall temperature approach, which are the conditions in the evaporators of the refrigerator applications were applied because one of the purposes of this study is to determine the most ideal minichannel among the tested minichannels for usage in the evaporator section of the refrigerators. Two-phase flow experiments were made with refrigerant R134a in the three minichannels having hydraulic diameters of 1.69, 3.85 and 1.69 mm respectively. As distinct from the others, the third minichannel has a rough inner surface. Comparison of the experimental results of the three minichannels was made in terms of forced convection heat transfer coefficients and pressure drop at constant quality and mass flux values. As a result of the experiments, the most ideal minichannel among the tested minichannels was determined for the evaporator applications in the refrigerators.

In der vorliegenden Arbeit wird der Einsatz von Positronenemittern zur Bestimmung der Dichte eines zweiphasigen Mediums beschrieben. Zur Messung wird die Dichteabhängigkeit der Positronenreichweite ausgenutzt. Die Realisierbarkeit des Verfahrens wird zunächst in einer Computersimulation geprüft. Danach werden Experimente an einem hochauflösenden PET-Scanner vorgestellt. Bei diesen Experimenten wird die Dichteabhängigkeit der Reichweite von Positronen anhand von Modellmedien aus festen Schaumstoffen untersucht. Dabei werden die in der Computersimulation erzielten Ergebnisse bestätigt. Aus den experimentellen Ergebnissen wird ein Modell zur Beschreibung der Abnahme der Koinzidenzrate in Abhängigkeit von der Entfernung des Detektors von der Positronenquelle und der Mediendichte entwikkelt. Auf der Basis des Modells erfolgt die Konzipierung einer für die Dichtemessung optimierten Detektoranordnung. Die Funktionsweise dieses Detektorsystems wird in Form technischer Unterlagen und experimenteller Ergebnisse beschrieben. Mit dem optimierten Detektorsystem werden die Untersuchungen an den Modellmedien nochmals durchgeführt, wobei die bisherigen Ergebnisse bestätigt werden. Das beschriebene Meßverfahren dient der Bestimmung der mittleren Dichte in einem überwiegend gasförmigen Medium, wobei eine Mittelwertbildung über das Meßvolumen erfolgt. Das Verfahren kombiniert die Vorteile bekannter densitometrischer Meßmethoden auf der Basis einer Schwächung von Strahlung, indem die hohe Dichtesensitivität der Positronenstrahlung mit der relativ geringen Absorption der energiereichen Annihilationsquanten kombiniert wird.

A significant percentage of computational time in compositional simulations is spent performing flash calculations to determine the equilibrium compositions of hydrocarbon phases in situ. Flash calculations must be done at each time step for each grid block; thus billions of such calculations are possible. It would be very important to reduce the computational time of flash calculations significantly so that more grid blocks or components may be used. In this dissertation, three different methods are developed that yield fast, robust and accurate phase behavior calculations useful for compositional simulation and other applications. The first approach is to express the mixing rule in equations-of-state (EOS) so that a flash calculation is at most a function of six variables, often referred to as reduced parameters, regardless of the number of pseudocomponents. This is done without sacrificing accuracy and with improved robustness compared with the conventional method. This approach is extended for flash calculations with three or more phases. The reduced method is also derived for use in stability analysis, yielding significant speedup. The second approach improves flash calculations when K-values are assumed constant. We developed a new continuous objective function with improved linearity and specified a small window in which the equilibrium compositions must lie. The calculation speed and robustness of the constant K-value flash are significantly improved. This new approach replaces the Rachford-Rice procedure that is embedded in the conventional flash calculations. In the last approach, a limited compositional model for ternary systems is developed using a novel transformation method. In this method, all tie lines in ternary systems are first transformed to a new compositional space where all tie lines are made parallel. The binodal curves in the transformed space are regressed with any accurate function. Equilibrium phase behavior calculations are then done in this transformed space non-iteratively. The compositions in the transformed space are translated back to the actual compositional space. The new method is very fast and robust because no iteration is required and thus always converges even at the critical point because it is a direct method. The implementation of some of these approaches into compositional simulators, for example UTCOMP or GPAS, shows that they are faster than conventional flash calculations, without sacrificing simulation accuracy. For example, the implementation of the transformation method into UTCOMP shows that the new method is more than ten times faster than conventional flash calculations.

Heat transfer and pressure drop during condensation of propane flowing through minichannels is investigated in this study. Studies of condensation of hydrocarbons are important for applications in the petrochemical industry. Insights into the mechanisms of propane condensation are required for accurate design of heat transfer equipment for use in hydrocarbon processing. At present, there is very little research on vertical condensation, especially of hydrocarbons, for the tube sizes and flow conditions of interest to the present study. An experimental facility was designed and fabricated to measure the frictional pressure drop and heat transfer coefficients during condensation of propane in plain tubes with an inner diameter of 1.93 mm. Measurements were taken across the vapor-liquid dome in nominal quality increments of 0.25 for two saturation temperatures (47°C and 74°C) and four mass flux conditions (75 – 150 kg m‾² s‾¹). The data were compared to the predictions of relevant correlations in the literature. The data from this study were also used to develop models for the frictional pressure drop and heat transfer coefficient based on the measurements and the underlying condensation mechanisms. These results and the corresponding correlations contribute to the understanding of condensation of hydrocarbons in vertical minichannels.

No description available.

The extensive experimental results presented in this report provide a high-quality database for air-/water flows in a vertical pipe with a nominal diameter of 200 mm. This database can be used for the development and validation of CFD-like models for two-phase flows, e.g. for bubble coalescence and fragmentation. In particular, the investigations aim on the evolution of the two-phase flow along the pipe height. Therefore, up to 18 single measurements with varying distances between the gas injection and measurement plane were realised for each of the 92 combinations of gas and water flow rates. The pressure at the position of the activated gas injection was kept constant at 0.25 MPa(a). This boundary condition has the advantage that the measured data represent exactly the evolution of the flow along the pipe, i.e. they reflect a configuration at which the gas injection is at a fixed height position, while the measurement plane varies. Important results of this test series are time averaged radial profiles of the gas fraction, and the gas velocity, as well as the time and cross-section averaged bubble size distributions. Furthermore, gas fraction data resolved regarding the bubble size and spatial distribution are presented. As in previous test series, flow patterns were analysed, whereby the classification results from the bubble size. A substantial part of these new air/water experiments were quality and plausibility checks of the measured data. In the result, a clear and consistent trend regarding their evolution with increasing distance from the position of the gas injection was found. Comparisons of the trend of time and cross section averaged gas volume fraction along the pipe height with the theoretically expected values were carried out. The influence of the orifice diameter of the gas injection on flow patterns is also discussed in the report.

Die im Rahmen dieser Versuchsserie erzielten umfangreichen experimentellen Ergebnisse bilden eine hochwertige Datenbasis für Luft-Wasser-Strömungen in einem vertikalen DN200-Rohr, die für die Entwicklung und Validierung von CFD-Modellen, beispielweise bzgl. Blasenkoaleszenz und -fragmentierung, genutzt werden können. Besonderes interessant ist die Untersuchung der Entwicklung der Zweiphasenströmung über der Rohrhöhe. Aus diesem Grund wurden für jede der 92 betrachteten Kombinationen aus Gas- und Wasser-Volumenstromdichten bis zu 18 Messungen mit variablen Abständen zwischen Gaseinspeisung und Messebene durchgeführt. Dabei wurde der Druck an der Gaseinspeisestelle konstant auf 0,25 MPa(a) gehalten. Diese Randbedingung bietet den Vorteil, dass die so gemessenen Daten die Entwicklung der Strömung über der Rohrhöhe widerspiegeln, d.h. eine Konfiguration beschreiben, bei der das Gas an einer festen Höhenposition eingespeist wird und die Messungen in verschiedenen darüberliegenden Ebenen erfolgen. Wesentliche Ergebnisse dieser Messserie sind radiale zeitgemittelte Profile für den Gasgehalt und die Gasgeschwindigkeit sowie zeit- und querschnittsgemittelte Blasengrößenverteilungen. Außerdem liegen blasengrößen- und ortsaufgelöste Gasgehaltsdaten vor. Wie bereits bei früheren Versuchsserien wurden auch in diesem Fall die Strömungsformen analysiert, wobei die Klassifizierung anhand der Blasengröße erfolgte. Ein wesentlicher Bestandteil dieser neuen Luft/Wasser-Versuche war die Qualitäts- und Plausibilitätsprüfung der Messdaten. Es konnte festgestellt werden, dass die Daten einen eindeutigen, widerspruchsfreien Trend bzgl. ihrer Entwicklung mit zunehmendem Abstand von der Gaseinspeisung aufweisen. Zur Plausibilitätsprüfung wurden Vergleiche des Gasgehaltsverlaufes über der Rohrhöhe mit theoretisch zu erwartenden Kurven durchgeführt. Zusätzlich zu diesen Ergebnissen enthält der Bericht eine Einschätzung des Einflusses des Bohrungsdurchmessers an der Gaseinspeisung auf die sich einstellende Strömung.