Experimental and simulation studies on performance of a compact gas/liquid separation system

The need of exploiting the offshore oil reserves and reducing the equipment costs becomes the motivation for developing new compact separation techniques. In the past years, the development of compact separators has almost solely focused on the cyclonic type separators made of pipes, because of their simple construction, relatively low cost of manufacturing and being able to withstand high pressures. Considerable effort has been put into the separator test program and qualification, and consequently notable advances in the compact separation technique have been made. However the application has been held back due to lacking of reliable predicting and design tools. The objectives of this study were threefold. Firstly, an experimental study was carried out aiming at understanding the separation process and flow behaviours in a compact separator, named Pipe-SEP, operating at high inlet gas volume fraction (GVF). Secondly it is to gain insight of the gas and liquid droplet flow in the compact separator by means of Computational Fluid Dynamics (CFD) simulations. Last but not least, the understanding and insight gained above were used to develop a comprehensive performance predictive model, based on which, a reliable optimizing design procedure is suggested. An experimental study was carried out to test a 150-mm Pipe-SEP prototype with a water-air mixture. Three distinct flow regimes inside the Pipe-SEP were identified, namely swirled, agitated, and gas blow-by. The transition of the flow regimes was found to be affected by inlet flow characteristics, mixture properties, geometry of the separator, and downstream conditions. A predictive model capable of predicting the transition of flow regimes and the separation efficiency was developed. A comparison between the predicted result and experiment data demonstrated that the model could serve as a design tool to support decision-making in early design stages ... [cont.]

Research on Bubble Separation and Elimination for Hydraulic System

博士(工学)法政大学 (Hosei University

Sustainable humidification-dehumidification desalination system using low-grade heat source

Humidification-dehumidification desalination (HDH) cycle is one of the methods for producing freshwater from seawater or saline water for small-scale and low-cost applications. Major energy source of the desalination system is thermal energy that can be provided from any available low-grade heat sources such as industrial waste heat or solar thermal collectors. The working principle of HDH system is very similar to the rain cycle which air is humidified in by evaporation of seawater. Then the humidified air moved by wind streams to cooler places where it condenses to water droplets. In this project, at first mathematical thermodynamic based models for different types of the HDH cycle are developed, and the effect of operational parameters such as temperatures and flow rates on cycle performance parameters like gain output ratio (GOR) and recovery ratio (RR) are studied.  Also, the heat and mass transfer analysis of the cycle is conducted to examine the behavior of key performance parameters such as temperatures, flow rates, surface area, and air velocity on the heat and mass transfer rate. Further, a new concept of using a heat pump is investigated to simultaneously provide heating and cooling load requirements of the HDH system in an optimized way. A mathematical model is developed to investigate the optimum operating condition of the HDH system for fully coupled condition operation.  Experimental investigations of the cycle performance and potential of water production at different operating conditions, including the effect of temperatures, feed salinity, air to seawater flow rate ratios, and freshwater to seawater flow rate ratios studied. The experimental findings validated with the mathematical model. To reach an environmentally sustainable solution in HDH system, brine recirculation method is proposed, mathematically modelled, and experimentally investigated.  It is found that the brine recirculation method is practically feasible and can significantly reduce the rejected brine volume

Activities in nuclear engineering at M.I.T.

"List of theses"--Pages 157-167Progress report; October 197

Design and characterisation of fluidised bed cooling towers

This thesis discusses the operating characteristics and design of fluidised bed cooling towers (FBCT), which may be used to cool hot water for industrial purposes. Limited data exist for such a three-phase fluidised bed acting as a cooling tower. This motivated some early workers to investigate its usefulness in cooling tower applications and they showed that the FBCT produces heat and mass transfer rates much higher than in conventional fixed-bed towers. Despite this advantage, the FBCT has not been commercially exploited to date. An extensive experimental study is presented using up-to-date instrumentation to determine the thermal and hydraulic characteristics with a view to establishing a design criteria for full-scale FBCTs. Experimental tests were performed to account for the effect of the plenum chamber and the spray zone region upon the thermal performance of the FBCT. Data analysis was performed so that the effect of the fluidised bed alone as well as the plenum chamber could be known. A prototype was designed and built incorporating nine calibrated Platinum Resistance Thermometers for fluid temperature measurements with one located just below the fluidized bed itself while another was positioned below the plenum chamber to measure outlet water temperatures. Two differential pressure transducers and an electronic water flowmeter were used to measure air pressures and water flow rates respectively. All instruments were connected to a data-logger linked to a personal computer. Two different software packages were written and installed on the computer, to automatically retrieve experimental data from the rig during test runs and to automatically process the retrieved variables for analysis. Nine independent variables were measured in order to determine the tower thermal-hydraulic performance. Water and air flow rates ranged from 0.5 - 5 and 0.5 - 4 kg/s m2 respectively giving liquid/gas mass flux ratios that ranged from about 0.1 - 6. The inlet hot water temperature ranged from about 25 - 55°C while the inlet air wet-bulb temperature averaged about 18°C. Four different spherical packing arrangements were studied at static bed heights that ranged from about 25 to 400 mm. The spray nozzle height from the distributor grid ranged from 400 - 1500 mm. Data analysis was performed for thermal-hydraulic performance using both dimensional analysis and the Merkel approach. A least-square multiple regression analysis carried out on dimensionless and dimensional groups that resulted from this analysis showed that correlations derived are in good agreement with other experimental data. Correlations were derived for the prediction of the bed air pressure drop and hence the power requirement, the tower thermal performance, the minimum fluidisation velocity, and the expanded bed height. Correlations used to design a full-scale FBCT are presented. Novel work included measurements of local radial and axial temperature variations within the fluidised bed. Thermal performance decreased as the liquid/gas mass flux ratio was increased while it increased as the particle size was decreased. High density particles gave a higher bed air pressure, and hence a higher power requirement than low density ones. Minimum fluidization gas velocity was independent of the static bed height. Expanded bed height increased as the liquid and gas mass fluxes were increased. Thermal performance was found to increase when the effect of the plenum chamber was included in the analysis as compared to the fluidised bed itself. Methodological criteria for the design of a full scale FBCT have been developed. Design analysis suggests that FBCTs can be several times smaller in size than conventional cooling towers, and that they may operate with a similar or lower power requirement than the latter

Index to NASA Tech Briefs, 1972

Abstracts of 1972 NASA Tech Briefs are presented. Four indexes are included: subject, personal author, originating center, and Tech Brief number

Humidification strategy for polymer electrolyte membrane fuel cells – A review

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.apenergy.2018.08.125 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/Polymer electrolyte membrane fuel cells are promising power sources because of their advantage such as high efficiency, zero emission and low operating temperature. Water management is one of the critical issues for polymer electrolyte membrane fuel cells and has received significant attention. The membrane within the fuel cell needs to stay in hydrated state to have high ion conductivity and durability, which requires proper humidification. Both internal and external methods have been utilized to humidify the polymer electrolyte membrane. Numerous studies on fuel cell humidification have been conducted in the past decades, especially in recent years. This review aims to summarize the main humidification methods and the related studies. The internal humidification methods are classified as physical methods and chemical methods. The external humidification methods include gas bubbling humidification, direct water injection, enthalpy wheel humidification, membrane humidifiers, and exhaust gas recirculation. The working principle and performance of each method are introduced and the advantage and drawback are summarized. Further, the humidification methods for alkaline anion exchange membrane fuel cells are also briefly reviewed, because of more recent studies showing their potential of using non-precious metal catalysts. This review can help to choose proper humidification strategy for specific polymer electrolyte membrane fuel cell application and may inspire further investigations.National Natural Science Foundation of China ["51706153"]Natural Science Foundation of Tianjin City ["17JCZDJC3100"]Natural Sciences and Engineering Research Council of Canad

Simultaneous removal of SO2 and NOx by a new combined spray-and-scattered-bubble technology based on preozonation: from lab scale to pilot scale

A new technology (called here, spray-and-scattered-bubble technology) based on preozonation was designed and tested for simultaneous removal of SO2 and NOx from power plant flue gas. It combines the advantages of the common spray tower and the jet bubble reactor, in which the flue gas experiences an initial SO2/NOx removal in the spray zone and then undergoes further removal in the bubble zone. Factors that affect the simultaneous removal of SO2/NOx were investigated through lab-scale experiments, by varying the O3/NO molar ratio, liquid/gas ratio and the immersion depth. The results showed the removal of SO2 and NOx can be significantly improved as compared to a separate spray column or bubble reactor, by as much as 17%, for the spray column and 18% for the bubble reactor for NOx and 11% for the spray column, and 13% for the bubble reactor for SO2, for liquid/gas ratio of 4 dm3/m3 or immersion depth of 100 mm. The O3/NO molar ratio had little effect on the SO2 removal, but it strongly affected the removal efficiency of NOx especially when it was less than 1.0. Both the liquid/gas ratio and immersion depth demonstrated a positive correlation with the removal efficiency. However, a balance must be maintained between efficiency and economics, since the liquid/gas ratio directly influences the performance and number of the circulating pumps, and the depth is closely related to the flue gas pressure drop, and both factors affect energy requirements. To further confirm its industrial feasibility, a 30 h test using real coal-fired flue gas was conducted in a pilot-scale experimental facility (flue gas volume of 5000 Nm3/h). Increasing SO2 concentration in flue gas can promote the removal efficiency of NOx, but the SO2 removal was almost complete under all conditions tested. Finally, taking a 300 MW unit as an example,- the total energy cost of this new technology is estimated as being 10% lower than that of the common spray tower technology, based on an analysis using Aspen Plus™, with the largest difference reflected in the energy requirements of the circulating pumps and the ozonizer. Over all, the new technology offers the joint advantages of reducing emissions and saving energy

Noninvasive Submillimeter-Precision Brain Stimulation by Optically-Driven Focused Ultrasound

High precision neuromodulation is a powerful tool to decipher neurocircuits and treat neurological diseases. Current non-invasive neuromodulation methods offer limited millimeter-level precision. Here, we report an optically-driven focused ultrasound (OFUS) for non-invasive brain stimulation with submillimeter precision. OFUS is generated by a soft optoacoustic pad (SOAP) fabricated through embedding candle soot nanoparticles in a curved polydimethylsiloxane film. SOAP generates a transcranial ultrasound focus at 15 MHz with a lateral resolution of 83 micrometers, which is two orders of magnitude smaller than that of conventional transcranial focused ultrasound (tFUS). Effective OFUS neurostimulation in vitro with a single ultrasound cycle is shown. Submillimeter transcranial stimulation of mouse motor cortex in vivo is demonstrated. An acoustic energy of 0.02 J/cm^2, two orders of magnitude less than that of tFUS, is sufficient for successful OFUS neurostimulation. By delivering a submillimeter focus non-invasively, OFUS opens a new way for neuroscience studies and disease treatments.Comment: 36 pages, 5 main figures, 13 supplementary figure

Experimental and Theoretical Analyses of Adiabatic Two-phase Flows in Horizontal Feed Pipes

The majority of technical separation processes for fluid mixtures utilize the principle of rectification. If a two-phase mixture is fed into the column, possibly undesirable flow morphologies or severe droplet carry-over may occur, which detrimentally affect separation efficiency and equipment integrity. Currently, the two-phase flow behavior in feed pipes is hardly predicable and mostly based on empirical or heuristic methods, which do not properly account for a broad range of possible fluid properties and plant dimensions. As a consequence, costly safety margins are applied. Feed pipes to separation columns are often characterized by horizontal inlet nozzles, small length-to-diameter ratios and complex routing, involving elbows or bends. The pipe lengths are too short to enable the two-phase flow to fully develop, which thus, enters the column with unknown flow morphology. Since developing flows have rarely been studied, today’s engineering practice relies on existing predictive methods for fully developed two-phase flows. Graphical methods can hardly represent gradual transitions between flow regimes. Analytical models provide only simplified flow representations of the two-phase flow that have not yet been qualified for developing pipe flow. In this work, a comprehensive experimental database of horizontal water-air flows in two test sections with nominal pipe diameters of D = 50 mm and D = 200 mm and feed pipe lengths in the range 10 < L/D < 75 was established. This way, the data cover developing pipe flows with entrance lengths typical for two-phase feeds of separation columns and more developed flows that are comparable with the extensively studied reference system water-air. A particular focus was put on the effect of pipe bends on the flow morphology up- and downstream. The flow morphology was captured using imaging wire-mesh sensors. A 4D fuzzy algorithm was applied to objectively identify the flow two-phase morphologies. Based on their fuzzy representation, the flow morphologies were classified and a novel 2D visualization technique is proposed to discuss the flow development along the feed pipes. Undesired flow morphologies (intermittent flow and entrainment) during the operation of two-phase feeds are hardly predictable by conventional design tools. The inception of intermittent flows was analyzed using the experimental data. Consequently, the inception criteria based on the required liquid levels for fully developed intermittent flows were adapted for short entrance lengths. The characteristic dynamics of flow morphologies that are known to cause the onset of entrainment were analyzed. Based on wave frequencies, a predictive criterion for the susceptibility of wavy flows for the onset of entrainment is introduced and applied to straight feed pipes and horizontal 90° bends. Among the dozens available, 66 reduced-order models for the prediction of the void fraction were tested for straight feed pipes and horizontal 90° pipe bends. Thereof, the ones most suitable for variable operating conditions and pipe geometries were identified and adapted. Complementary 3D simulations were performed to verify the applicability of numerical codes (VoF, AIAD) for flows with free interfaces. The flow morphologies were successfully reproduced at macroscopic scale, however, the simulation results rank behind reduced-order models considering their quantitative predicting capabilities.:Abstract II Kurzfassung IV Acknowledgement VI Nomenclature VIII Table of Contents XIII 1 Introduction 1 1.1 Thermal separation in view of the 21st century 1 1.2 Engineering and design of rectification plants 2 1.3 Outline of the thesis 4 2 State of the art 5 2.1 Two-phase feeds in thermal separation 5 2.1.1 Feed condition as adjustable parameter 5 2.1.2 Thermohydraulic optimization 8 2.1.3 Hydrodynamic conditioning 9 2.2 Hydrodynamics of two-phase feeds 11 2.2.1 Flow morphologies in feed pipes 11 2.2.2 Droplet entrainment 14 2.2.3 Flow regime maps 17 2.2.4 Consequences for two-phase feeds 19 2.3 Modelling of two-phase feeds 23 2.3.1 Basic definitions 23 2.3.2 Fundamentals of the two-fluid model 25 2.3.3 The interfacial level gradient 29 2.3.4 Analytical models 32 2.3.5 CFD simulations for commercial feed pipes 34 2.4 Objectives of this thesis 36 3 Experimental method and algorithms for flow characterization 37 3.1 Experimental setups 37 3.2 Wire-mesh sensors 40 3.3 Experimental procedure 42 3.4 Data processing 44 3.4.1 Fuzzy flow morphology classification 45 3.4.2 Power spectral density 48 3.5 Measurement uncertainty 49 4 Flow morphologies in different feed pipe geometries 53 4.1 Developing two-phase flow in straight pipes 53 4.2 Effect of pipe curvatures on the flow morphology 55 4.3 Morphology recovery 57 4.4 Conclusions 60 5 Prediction of undesirable flow morphologies in feed pipes 61 5.1 Initiation of intermittent flows 61 5.2 Onset of droplet entrainment 62 5.2.1 Vulnerable flow morphologies 62 5.2.2 Derivation of a criterion for onset of entrainment 64 5.2.3 Adjustment of the criterion for the investigated pipe geometries 67 5.3 Conclusions 70 6 Reduced-order modelling of two-phase feeds 71 6.1 Prediction of void fraction 71 6.2 Liquid levels 75 6.3 Conclusions 78 7 CFD modelling of two-phase feeds 79 7.1 Simulation setup 79 7.2 Multiphase models 82 7.3 Comparison with experimental data 83 7.3.1 Straight pipes 83 7.3.2 Horizontal 90° bends 85 7.4 Conclusions 88 8 Summary and recommendations for future work 89 8.1 Summary 89 8.2 Recommendations for future work 91 References 94 List of figures 113 List of tables 118 Appendix i Scientific publications and contributions xxxiii Eidesstattliche Erklärung xxxviiDie meisten technischen Verfahren zur Trennung von Flüssigkeitsgemischen beruhen auf dem Prinzip der Rektifikation. Wird ein Zweiphasengemisch in die Trennkolonne eingespeist, können unerwünschte Strömungsmorphologien oder ausgeprägte Tröpfchenverschleppung auftreten, welche sich nachteilig auf die Trennleistung und die Integrität einzelner Anlagenkomponenten auswirken. Derzeit lässt sich das Verhalten solcher Zweiphasenströmungen in Einspeiseleitungen kaum vorhersagen und basiert meist auf empirischen oder heuristischen Methoden, die ein breites Spektrum möglicher Stoffeigenschaften und Anlagendimensionen nicht angemessen berücksichtigen. Infolgedessen müssen kostspielige Sicherheitszuschläge angewendet werden. Einspeiseleitungen von Trennkolonnen sind häufig durch horizontale Eintrittsstutzen, ein geringes Länge-zu-Durchmesser-Verhältnis und eine komplexe Leitungsführung mit Bögen und anderen Normteilen gekennzeichnet. Typische Rohrlängen sind zu kurz, um eine vollständig entwickelte Zweiphasenströmung auszubilden, welche daher mit unbekannter Strömungs-morphologie in die Trennkolonne eintritt. Da derartige Strömungen jedoch bisher nur selten untersucht wurden, verlässt man sich gegenwärtig in der technischen Praxis auf bestehende Vorhersagemethoden für voll entwickelte Zweiphasenströmungen. Grafische Methoden können jedoch die allmählichen Übergänge zwischen Strömungsformen kaum darstellen. Analytische Modelle liefern nur vereinfachte Näherungswerte der Zweiphasenströmung, die noch nicht für sich entwickelnde Rohrströmung qualifiziert wird. In dieser Arbeit wurde eine umfangreiche experimentelle Datenbasis horizontaler Wasser-Luft-Strömungen in zwei Versuchsstrecken mit Rohrinnendurchmessern von D = 50 mm und D = 200 mm und Einlauflängen im Bereich 10 < L/D < 75 erstellt. Auf diese Weise decken die Daten sowohl sich entwickelnde Rohrströmungen mit typischen Einlauflängen für Einspeiseleitungen ab, als auch weiter (in axialer Richtung) entwickelte Strömungen, die mit dem umfangreich untersuchten Referenzsystem Wasser-Luft vergleichbar sind. Die Auswirkung von Rohrbögen auf die Strömungsmorphologie stromauf- und stromabwärts wurde gezielt untersucht. Die Strömungsmorphologie wurde mit bildgebenden Gittersensoren erfasst. Ein 4D-Fuzzy-Algorithmus wurde zur objektiven Identifizierung der Strömungsmorphologien eingesetzt. Auf Grundlage dieser Fuzzy-Darstellung der Strömung wurden die Strömungsmorphologien klassifiziert, und es wurde eine neuartige 2D-Visualisierungstechnik entworfen, mit der die Strömungsentwicklung entlang der Einspeiseleitungen diskutiert wurde. Unerwünschte Strömungsmorphologien (intermittierende Strömung und Tropfenmitriss) während des Betriebs zweiphasiger Einspeisungen sind mit herkömmlichen Auslegungswerkzeugen kaum vorherzusagen. Das Einsetzen intermittierender Strömungen wurde auf Grundlage der experimentellen Daten analysiert. Daraufhin wurden existierende Kriterien, basierend auf den notwendigen Mindestfüllständen, für das Einsetzen intermittierender Strömungen in Abhängigkeit von den untersuchten Einlauflängen angepasst. Die charakteristische Dynamik von Strömungsmorphologien, die Tropfenmittriss hervorrufen, wurde analysiert. Voraussagemethoden zur Vorhersage der Anfälligkeit welliger Strömungen für das Auftreten von Tropfenmitriss wurden auf der Grundlage von Wellenfrequenzen entwickelt und für gerade Einspeiserohre und horizontale 90°-Bögen angewandt. Von den zahlreichen verfügbaren Modellen zur Vorhersage des Gasanteils wurden 66 Modelle reduzierter Ordnung für gerade Einspeiseleitungen und horizontale 90°-Rohrbögen getestet. Davon wurden die für variable Betriebsbedingungen und Rohrgeometrien am besten geeigneten Modelle ermittelt und angepasst. Komplementäre 3D-Simulationen wurden durchgeführt, um die Anwendbarkeit numerischer Codes (VoF, AIAD) für Strömungen mit freien Grenzflächen zu bestätigen. Die Strömungsmorphologien wurden im makroskopischen Maßstab erfolgreich reproduziert, die Simulationsergebnisse bleiben jedoch hinsichtlich ihrer quantitativen Vorhersagekraft hinter den Modellen reduzierter Ordnung zurück.:Abstract II Kurzfassung IV Acknowledgement VI Nomenclature VIII Table of Contents XIII 1 Introduction 1 1.1 Thermal separation in view of the 21st century 1 1.2 Engineering and design of rectification plants 2 1.3 Outline of the thesis 4 2 State of the art 5 2.1 Two-phase feeds in thermal separation 5 2.1.1 Feed condition as adjustable parameter 5 2.1.2 Thermohydraulic optimization 8 2.1.3 Hydrodynamic conditioning 9 2.2 Hydrodynamics of two-phase feeds 11 2.2.1 Flow morphologies in feed pipes 11 2.2.2 Droplet entrainment 14 2.2.3 Flow regime maps 17 2.2.4 Consequences for two-phase feeds 19 2.3 Modelling of two-phase feeds 23 2.3.1 Basic definitions 23 2.3.2 Fundamentals of the two-fluid model 25 2.3.3 The interfacial level gradient 29 2.3.4 Analytical models 32 2.3.5 CFD simulations for commercial feed pipes 34 2.4 Objectives of this thesis 36 3 Experimental method and algorithms for flow characterization 37 3.1 Experimental setups 37 3.2 Wire-mesh sensors 40 3.3 Experimental procedure 42 3.4 Data processing 44 3.4.1 Fuzzy flow morphology classification 45 3.4.2 Power spectral density 48 3.5 Measurement uncertainty 49 4 Flow morphologies in different feed pipe geometries 53 4.1 Developing two-phase flow in straight pipes 53 4.2 Effect of pipe curvatures on the flow morphology 55 4.3 Morphology recovery 57 4.4 Conclusions 60 5 Prediction of undesirable flow morphologies in feed pipes 61 5.1 Initiation of intermittent flows 61 5.2 Onset of droplet entrainment 62 5.2.1 Vulnerable flow morphologies 62 5.2.2 Derivation of a criterion for onset of entrainment 64 5.2.3 Adjustment of the criterion for the investigated pipe geometries 67 5.3 Conclusions 70 6 Reduced-order modelling of two-phase feeds 71 6.1 Prediction of void fraction 71 6.2 Liquid levels 75 6.3 Conclusions 78 7 CFD modelling of two-phase feeds 79 7.1 Simulation setup 79 7.2 Multiphase models 82 7.3 Comparison with experimental data 83 7.3.1 Straight pipes 83 7.3.2 Horizontal 90° bends 85 7.4 Conclusions 88 8 Summary and recommendations for future work 89 8.1 Summary 89 8.2 Recommendations for future work 91 References 94 List of figures 113 List of tables 118 Appendix i Scientific publications and contributions xxxiii Eidesstattliche Erklärung xxxvi