A new method of in situ extraction of alcohols from fermentation broth was investigated. The extraction method exploited the latent advantages of the non-equilibrium phase interaction of the fluid system in the flash tank to effectively recover the alcohol. Carbon dioxide gas ranging from 4.2L/min to 12.6L/min was used to continuously strip 2 and 12% (v/v) ethanol solution in a fermentor with a recycle. Ethanol and water in the stripped gas was recovered by compressing and then flashing into a flash tank that was maintained at 5 to 70bar and 5 to 55oC where two immiscible phases comprising CO2-rich phase (top layer) and H2O-rich phase (bottom layer) were formed. The H2O-rich bottom layer was collected as the Bottoms. The CO2-rich phase was continuously throttled producing a condensate (Tops) as a result of the Joule-Thompson cooling effect. The total ethanol recovered from the extraction scheme was 46.0 to 80% for the fermentor containing 2% (v/v) ethanol and 57 to 89% for the fermentor containing 12% (v/v) ethanol. The concentration of ethanol in the Bottoms ranged from 8.0 to 14.9 %(v/v) for the extraction from the 2 %(v/v) ethanol solution and 40.0 to 53.8 %(v/v) for the 12% (v/v) fermentor ethanol extraction. The Bottoms concentration showed a fourfold increase compared to the feed. The ethanol concentration of the Tops were much higher with the highest at approx. 90% (v/v) ethanol, however the yields were extremely low. Compression work required ranged from 6.4 to 20.1 MJ/kg ethanol recovered from the gas stream in the case of 12% (v/v) ethanol in fermentor. The energy requirement for the 2% (v/v) extraction was 84MJ/kg recovered ethanol. The measured Joule-Thompson cooling effect for the extraction scheme was in the range of 10 to 20% the work of compressing the gas. The lowest measured throttle valve temperature was -47oC at the flash tank conditions of 70bar and 25oC. Optimization of the extraction scheme showed that increasing the temperature of the flash tank reduced the amount of ethanol recovered. Increasing the pressure of the flash tank increased the total ethanol recovered but beyond 45bar it appeared to reduce the yield. The 12.6L/min carbon dioxide flow rate favored the high pressure(70bar) extraction whiles 4.2L/min appeared to favor the low pressure(40bar) extraction. The studies showed that the extraction method could potentially be used to recover ethanol and other fermentation products. / Master of Science

Este trabalho estuda o fenômeno de evaporação rápida em jatos de líquidos superaquecidos ou metaestáveis numa região 2D. O fenômeno se inicia, neste caso, quando um jato na fase líquida a alta temperatura e pressão, emerge de um diminuto bocal projetando-se numa câmara de baixa pressão, inferior à pressão de saturação. Durante a evolução do processo, ao cruzar-se a curva de saturação, se observa que o fluido ainda permanece no estado de líquido superaquecido. Então, subitamente o líquido superaquecido muda de fase por meio de uma onda de evaporação oblíqua. Esta mudança de fase transforma o líquido superaquecido numa mistura bifásica com alta velocidade distribuída em várias direções e que se expande com velocidades supersônicas cada vez maiores, até atingir a pressão a jusante, e atravessando antes uma onda de choque. As equações que governam o fenômeno são as equações de conservação da massa, conservação da quantidade de movimento, e conservação da energia, incluindo uma equação de estado precisa. Devido ao fenômeno em estudo estar em regime permanente, um método de diferenças finitas com modelo estacionário e esquema de MacCormack é aplicado. Tendo em vista que este modelo não captura a onda de choque diretamente, um segundo modelo de falso transiente com o esquema de \"shock-capturing\": \"Dispersion-Controlled Dissipative\" (DCD) é desenvolvido e aplicado até atingir o regime permanente. Resultados numéricos com o código ShoWPhasT-2D v2 e testes experimentais foram comparados e os resultados numéricos com código DCD-2D v1 foram analisados. / This study analyses the rapid evaporation of superheated or metastable liquid jets in a two-dimensional region. The phenomenon is triggered, in this case, when a jet in its liquid phase at high temperature and pressure, emerges from a small aperture nozzle and expands into a low pressure chamber, below saturation pressure. During the evolution of the process, after crossing the saturation curve, one observes that the fluid remains in a superheated liquid state. Then, suddenly the superheated liquid changes phase by means of an oblique evaporation wave. This phase change transforms the liquid into a biphasic mixture at high velocity pointing toward different directions, with increasing supersonic velocity as an expansion process takes place to the chamber back pressure, after going through a compression shock wave. The equations which govern this phenomenon are: the equations of conservation of mass, momentum and energy and an equation of state. Due to its steady state process, the numerical simulation is by means of a finite difference method using the McCormack method of Discretization. As this method does not capture shock waves, a second finite difference method is used to reach this task, the method uses the transient equations version of the conservation laws, applying the Dispersion-Controlled Dissipative (DCD) scheme. Numerical results using the code ShoWPhasT-2D v2 and experimental data have been compared, and the numerical results from the DCD-2D v1 have been analysed.

Es wurde ein neues Zweifluidmodell entwickelt, um Nichtgleichgewichtseffekte in kritischen und nahkritischen Ein-komponenten-Zweiphasenströmungen von anfänglich unter-kühlten oder siedenden Fluiden durch Rohre und Düsen zu untersuchen. Das vorgeschlagene Sechs-Gleichungsmodell besteht aus den phasenbezogenen Erhaltungsgleichungen für Masse und Impuls, der Bilanzgleichung für die thermische Energie der flüssigen Phase sowie einer zusätzlichen Transport-gleichung für die volumetrische Blasenanzahl. Zur Lösung des Systems aus partiellen Differentialgleichungen wird ein semi-implizites Finite-Differenzen-Zeitschrittverfahren angewendet. Die Schließung des Gleichungssystems wird durch Einbindung thermodynamischer Beziehungen und konstitutiver Gleichungen, die den strömungsformabhängigen Impuls-, Wärme- und Stofftransport beschreiben, erreicht. Für Strömungssysteme mit spontaner Entspannungsverdampfung aus dem rein flüssigen Zustand (Flashing) werden verschiedene Keimbildungsmodelle eingesetzt, die den Anfangszustand der verzögerten Dampfbildung beschreiben. Auf diese Weise werden thermodynamische Nichtgleichgewichtszustände als Folge von Zuständen mit für die Aktivierung von Keimstellen benötigtem Energieüberschuß, eingeschränkt vorhandener Phasengrenzfläche sowie begrenzter Wärmeübertragung zwischen den Phasen betrachtet. Abweichungen vom fluid-dynamischen Gleichgewicht (Phasenschlupf) ergeben sich aufgrund unterschiedlicher Trägheitseigenschaften und verschieden stark ausgeprägter mechanischer Kopplung zwischen den Phasen. Die mit diesem Modell erhaltenen numerischen Ergebnisse stimmen gut mit experimentellen Werten für Zweiphasen-strömungen mit unterschiedlichen Eintrittsbedingungen und Kanalgeometrien überein. / A new two-fluid flow model has been developed in order to examine non-equilibrium effects in critical and near-critical one-component two-phase flows of initially subcooled or saturated fluids through pipes and nozzles. The six-equation model proposed consists of the phasic conservation equations of mass and momentum, the liquid thermal energy, and of an additional transport equation for the bubble number density. To solve for the unknowns of the system of partial differential equations, a semi-implicit finite difference time-marching method is utilized. The closure of the set of equations is accomplished by thermodynamic relationships and additional constitutive equations describing momentum transport, interphase heat, and mass transfer which account for different flow regimes. For fluid flow systems undergoing a sudden change of phase from the pure liquid state (flashing), distinct nucleation models are included to describe the initial state of delayed vapor generation. In this way thermal non-equilibrium states are considered to be the consequence of excessive energy states required to activate nucleation sites, of restricted interfacial area and limited heat transfer between the phases. Deviation from fluid-dynamic equilibrium (phasic slip) results from different inertial properties and from distinct strength of mechanical coupling between the phases. The numerical results obtained with this model agree quite well with experimental data for two-phase flows with various inlet conditions and channel geometries.

Este trabalho estuda o fenômeno de evaporação rápida em jatos de líquidos superaquecidos ou metaestáveis numa região 2D. O fenômeno se inicia, neste caso, quando um jato na fase líquida a alta temperatura e pressão, emerge de um diminuto bocal projetando-se numa câmara de baixa pressão, inferior à pressão de saturação. Durante a evolução do processo, ao cruzar-se a curva de saturação, se observa que o fluido ainda permanece no estado de líquido superaquecido. Então, subitamente o líquido superaquecido muda de fase por meio de uma onda de evaporação oblíqua. Esta mudança de fase transforma o líquido superaquecido numa mistura bifásica com alta velocidade distribuída em várias direções e que se expande com velocidades supersônicas cada vez maiores, até atingir a pressão a jusante, e atravessando antes uma onda de choque. As equações que governam o fenômeno são as equações de conservação da massa, conservação da quantidade de movimento, e conservação da energia, incluindo uma equação de estado precisa. Devido ao fenômeno em estudo estar em regime permanente, um método de diferenças finitas com modelo estacionário e esquema de MacCormack é aplicado. Tendo em vista que este modelo não captura a onda de choque diretamente, um segundo modelo de falso transiente com o esquema de \"shock-capturing\": \"Dispersion-Controlled Dissipative\" (DCD) é desenvolvido e aplicado até atingir o regime permanente. Resultados numéricos com o código ShoWPhasT-2D v2 e testes experimentais foram comparados e os resultados numéricos com código DCD-2D v1 foram analisados. / This study analyses the rapid evaporation of superheated or metastable liquid jets in a two-dimensional region. The phenomenon is triggered, in this case, when a jet in its liquid phase at high temperature and pressure, emerges from a small aperture nozzle and expands into a low pressure chamber, below saturation pressure. During the evolution of the process, after crossing the saturation curve, one observes that the fluid remains in a superheated liquid state. Then, suddenly the superheated liquid changes phase by means of an oblique evaporation wave. This phase change transforms the liquid into a biphasic mixture at high velocity pointing toward different directions, with increasing supersonic velocity as an expansion process takes place to the chamber back pressure, after going through a compression shock wave. The equations which govern this phenomenon are: the equations of conservation of mass, momentum and energy and an equation of state. Due to its steady state process, the numerical simulation is by means of a finite difference method using the McCormack method of Discretization. As this method does not capture shock waves, a second finite difference method is used to reach this task, the method uses the transient equations version of the conservation laws, applying the Dispersion-Controlled Dissipative (DCD) scheme. Numerical results using the code ShoWPhasT-2D v2 and experimental data have been compared, and the numerical results from the DCD-2D v1 have been analysed.

Es wurde ein neues Zweifluidmodell entwickelt, um Nichtgleichgewichtseffekte in kritischen und nahkritischen Ein-komponenten-Zweiphasenströmungen von anfänglich unter-kühlten oder siedenden Fluiden durch Rohre und Düsen zu untersuchen. Das vorgeschlagene Sechs-Gleichungsmodell besteht aus den phasenbezogenen Erhaltungsgleichungen für Masse und Impuls, der Bilanzgleichung für die thermische Energie der flüssigen Phase sowie einer zusätzlichen Transport-gleichung für die volumetrische Blasenanzahl. Zur Lösung des Systems aus partiellen Differentialgleichungen wird ein semi-implizites Finite-Differenzen-Zeitschrittverfahren angewendet. Die Schließung des Gleichungssystems wird durch Einbindung thermodynamischer Beziehungen und konstitutiver Gleichungen, die den strömungsformabhängigen Impuls-, Wärme- und Stofftransport beschreiben, erreicht. Für Strömungssysteme mit spontaner Entspannungsverdampfung aus dem rein flüssigen Zustand (Flashing) werden verschiedene Keimbildungsmodelle eingesetzt, die den Anfangszustand der verzögerten Dampfbildung beschreiben. Auf diese Weise werden thermodynamische Nichtgleichgewichtszustände als Folge von Zuständen mit für die Aktivierung von Keimstellen benötigtem Energieüberschuß, eingeschränkt vorhandener Phasengrenzfläche sowie begrenzter Wärmeübertragung zwischen den Phasen betrachtet. Abweichungen vom fluid-dynamischen Gleichgewicht (Phasenschlupf) ergeben sich aufgrund unterschiedlicher Trägheitseigenschaften und verschieden stark ausgeprägter mechanischer Kopplung zwischen den Phasen. Die mit diesem Modell erhaltenen numerischen Ergebnisse stimmen gut mit experimentellen Werten für Zweiphasen-strömungen mit unterschiedlichen Eintrittsbedingungen und Kanalgeometrien überein. / A new two-fluid flow model has been developed in order to examine non-equilibrium effects in critical and near-critical one-component two-phase flows of initially subcooled or saturated fluids through pipes and nozzles. The six-equation model proposed consists of the phasic conservation equations of mass and momentum, the liquid thermal energy, and of an additional transport equation for the bubble number density. To solve for the unknowns of the system of partial differential equations, a semi-implicit finite difference time-marching method is utilized. The closure of the set of equations is accomplished by thermodynamic relationships and additional constitutive equations describing momentum transport, interphase heat, and mass transfer which account for different flow regimes. For fluid flow systems undergoing a sudden change of phase from the pure liquid state (flashing), distinct nucleation models are included to describe the initial state of delayed vapor generation. In this way thermal non-equilibrium states are considered to be the consequence of excessive energy states required to activate nucleation sites, of restricted interfacial area and limited heat transfer between the phases. Deviation from fluid-dynamic equilibrium (phasic slip) results from different inertial properties and from distinct strength of mechanical coupling between the phases. The numerical results obtained with this model agree quite well with experimental data for two-phase flows with various inlet conditions and channel geometries.

The present research is an experimental investigation of the atomization of a superheated pressurized liquid jet that is exposed to the ambient pressure due to a sudden depressurization. This phenomena is called flashing and occurs in several industrial environments.<p><p>Liquid flashing phenomena holds an interest in many areas of science and engineering. Typical examples one can mention: a) the accidental release of flammable and toxic pressure-liquefied gases in chemical and nuclear industry; the failure of a vessel or pipe in the form of a small hole results in the formation of a two-phase jet containing a mixture of liquid droplets and vapor, b) atomisation improvement in the fuel injector technology, c) flashing mechanism occurrence in expansion devices of refrigerator cycles etc. The interest in flashing events is especially true in the safety field where any unexpected event is undesirable. In case of an accident, flammable or toxic gas clouds are anticipated in close regions of the release because of the sudden phase change .Due to the non-equilibrium nature of the flow in these near field regions, conducting accurate data measurements for droplet size and velocity is a challenging task resulting in scarce data in the very close area.<p><p>This research has been carried out at the von Karman Institute (VKI) within the 5th framework of European Commission to fulfill the goal of understanding of source processes in flashing liquids in accidental releases. The program is carried out under name of FLIE (Flashing Liquids in Industrial Environments)(Contract no: EVG1-CT-2000-00025). The specific issues that are presented in this thesis study are the following:a) a comprehensive state of art of the jet break up patterns, spray characteristics and studies related to flashing phenomena; b)flashing jet breakup patterns and accurate characterization of the atomized jet such as droplet diameter size, velocity and temperature evolution through carefully designed laboratory-scale experiments; c) the influence of the initial storage conditions on the final atomized jet; d) a physical model on the droplet transformation and rapid evaporation in aerosol jets.<p><p>In order to characterize the atomization of the superheated liquid jet, laser-based optical techniques like Particle Image Velocimetry (PIV), Phase Doppler Anemometry (PDA) are used to obtain information for particle diameter and velocity evolution at various axial and radial distances. Moreover, a high-speed video photography presents the possibility to understand the break-up pattern changes of the simulating liquid namely R-134A jet in function of driving pressure, superheat and discharge nozzle characteristics. Global temperature measurements with an intrusive technique such as thermocouples, non-intrusive measurements with Infrared Thermography are performed. Cases for different initial pressures, temperatures, orifice diameters and length-to-diameter ratios are studied. The break-up patterns, the evolution of the mean droplet size, velocity, RMS, turbulence<p>intensity and temperature along the radial and axial directions are presented in function of initial parameters. Highly populated drop size and velocity count distributions are provided. Among the initial storage conditions, superheat effect is found to be very important in providing small droplets. A 1-D analytical rapid evaporation model is developed in order to explain the strong temperature decrease during the measurements. A sensitivity analysis of this model is provided.<p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished