Добірка наукової літератури з теми "Liquid diffusion length"
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся зі списками актуальних статей, книг, дисертацій, тез та інших наукових джерел на тему "Liquid diffusion length".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Статті в журналах з теми "Liquid diffusion length":
1
Khrapak, Sergey A. "Self-Diffusion in Simple Liquids as a Random Walk Process." Molecules 26, no. 24 (December 11, 2021): 7499. http://dx.doi.org/10.3390/molecules26247499.
Анотація:
It is demonstrated that self-diffusion in dense liquids can be considered a random walk process; its characteristic length and time scales are identified. This represents an alternative to the often assumed hopping mechanism of diffusion in the liquid state. The approach is illustrated using the one-component plasma model.
2
Pham Huu, Kien, Linh Nguyen Hong, Hien Pham Xuan, Linh Nguyen Thi Thuy, Quang Phan Dinh, and Trang Giap Thi Thuy. "Molecular dynamics simulation for structural heterogeneity and diffusion process in liquid GeO2." Journal of Science Natural Science 66, no. 1 (March 2021): 42–48. http://dx.doi.org/10.18173/2354-1059.2021-0005.
Анотація:
In this paper, we perform a simulation about liquid GeO2. The structure and diffusion process are analyzed through the radial distribution function, the distribution of GeOx (x = 4, 5, 6) structural units, length distribution, angle distribution, and data visualization. Simulation results show that the structure of liquid GeO2 composes clusters of GeO4, GeO5, or GeO6. These clusters have sizes depending on pressure and are distributed heterogeneously in space. This result confirms the origin of dynamical heterogeneity in the liquid oxide systems. In addition, the diffusion coefficient of Ge and O decreases upon pressure. We show that the diffusion relates to the breaking bond Ge-O.
3
Senn, S. M., and D. Poulikakos. "Multiphase Transport Phenomena in the Diffusion Zone of a PEM Fuel Cell." Journal of Heat Transfer 127, no. 11 (June 20, 2005): 1245–59. http://dx.doi.org/10.1115/1.2039108.
Анотація:
In this paper, a thorough model for the porous diffusion layer of a polymer electrolyte fuel cell (PEFC) is presented that accounts for multicomponent species diffusion, transport and formation of liquid water, heat transfer, and electronic current transfer. The governing equations are written in nondimensional form to generalize the results. The set of partial differential equations is solved based on the finite volume method. The effect of downscaling of channel width, current collector rib width, and diffusion layer thickness on the performance of polymer electrolyte membrane (PEM) fuel cells is systematically investigated, and optimum geometric length ratios (i.e., optimum diffusion layer thicknesses, optimum channel, and rib widths) are identified at decreasing length scales. A performance number is introduced to quantify losses attributed to mass transfer, the presence of liquid water, charge transfer, and heat transfer. Based on this model it is found that microchannels (e.g., as part of a tree network channel system in a double-staircase PEM fuel cell) together with diffusion layers that are thinner than conventional layers can provide substantially improved current densities compared to conventional channels with diameters on the order of 1 mm, since the transport processes occur at reduced length scales. Possible performance improvements of 29, 53, and 96 % are reported.
4
Dong, F. T., Xiang Yi Xue, Hong Chao Kou, Jun Wang, C. X. Niu, and J. S. Li. "Diffusion Bonding of Fe-Based Amorphous Ribbon to Crystalline Cu." Materials Science Forum 745-746 (February 2013): 788–92. http://dx.doi.org/10.4028/www.scientific.net/msf.745-746.788.
Анотація:
A copper rod/FeSiB amorphous ribbon/copper rod sandwich laminated composite material has been successfully fabricated by co-pressing at temperatures within supercooled liquid region. The bonding interface has been characterized by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Results showed that a good bonding interface could be obtained only when the initial surface were carefully polished. The diffusion zone confirmed by EDS is about 60nm, indicating the bonding is in atomic metallurgical level via limited diffusion. The present results show that even the diffusion length is very small, diffusion bonding in the supercooled liquid region could be an effective way for fabricating Fe-based metallic glass/Cu laminated composites
5
Pratt, F. L., F. Lang, S. J. Blundell, W. Steinhardt, S. Haravifard, S. Mañas-Valero, E. Coronado, B. M. Huddart, and T. Lancaster. "Studying spin diffusion and quantum entanglement with LF-µSR." Journal of Physics: Conference Series 2462, no. 1 (March 1, 2023): 012038. http://dx.doi.org/10.1088/1742-6596/2462/1/012038.
Анотація:
Abstract LF-µSR studies have previously been used to study the diffusive 1D motion of solitons and polarons in conducting polymers. This type of study was also applied to investigating the diffusive motion of spinons in spin-1/2 antiferromagnetic chains. Recently the method has been extended to examples of 2D layered triangular spin lattices which can support quantum spin liquid states, such as 1T-TaS2 and YbZnGaO4. These systems are found to show spin dynamics that matches well to 2D spin diffusion, such a model being found to provide a much better fit to the data than previously proposed models for spin correlations in such systems. In YbZnGaO4 the diffusion rate shows a clear crossover between classical and quantum regimes as T falls below the exchange coupling J. That the spin diffusion approach works well in the high T classical region might be expected, but it is found that it also works equally well in the low T quantum region where quantum entanglement controls the spin dynamics. Measurement of the diffusion rate allows a T dependent length scale to be derived from the data that can be assigned to a quantum entanglement length ξ E. Another entanglement measure, the Quantum Fisher Information F Q can also be obtained from the data and its T dependence is compared to that of ξ E.
6
Gomez, Houari Cobas, Jéssica Gonçalves da Silva, Jocasta Mileski Machado, Bianca Oliveira Agio, Francisco Jorge Soares de Oliveira, Antonio Carlos Seabra, and Mario Ricardo Gongora-Rubio. "LTCC 3D FLOW FOCALIZATION DEVICE FOR LIQUID-LIQUID PARTIAL SOLVENT EXTRACTION." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2016, CICMT (May 1, 2016): 000111–17. http://dx.doi.org/10.4071/2016cicmt-wa23.
Анотація:
Abstract The present work shows a ceramics microfluidic device for partial solvent extraction scheme. The technology used for device fabrication was Low Temperature Cofired Ceramics (LTCC) which allows us for complex and chemical resistant 3D microfluidic devices. The proposed system aims to partially extract the solvent present in a mixture containing aqueous and organic phases. This scheme uses a 3D flow focalization in order to improve the solvent diffusion into the external aqueous phase. The device is composed by three different parts, the input channels distribution, the main channel and the output channels distribution. The designed input channels distribution ensures a centered 3D focalized solvent stream along the main channel. The focalized solvent mixes with the surrounding water thanks to diffusion. Projected output channels take the central fluid out separately from the surrounding. Thus the device has two different outputs, one for the focalized fluid and another one for the waste fluid, which is the aqueous phase plus solvent. For a device concept proof, acetone and water were used as organic and aqueous phases, respectively. COMSOL Multiphysics was used for device microfluidics and chemical transport simulation. The extraction efficiency was the variable used as indicator for device performance validation. The flow rate ratio between phases, total flow rate, main channel length and focalized stream channel output hydraulic diameter (ODH) were used as process variables for simulation purposes. A factorial experimental planning was used in order to analyze the extraction efficiency taking into account process variables effects. From simulation results it was determined main channel length and ODH as the variables with stronger effect on extraction efficiency. Obtained simulated efficiencies were as high as 80.6%. Considering previous results observations a microfluidic device was fabricated with a main channel length of 21,4 mm and ODH of 214,63 μm. Gas chromatography was used to measured acetone concentration in outputs samples and from here the extraction efficiency. Experimental results were in agreement with simulation, returning extraction efficiencies in the order of 80.8% ± 2.2%.
7
Zhang, Guoyan, Shengyong Liu, Jie Lu, Jiong Wang, and Yongtao Ma. "Numerical Simulation of Diffusion Absorption Refrigerator." E3S Web of Conferences 233 (2021): 01044. http://dx.doi.org/10.1051/e3sconf/202123301044.
Анотація:
Based on Fluent software, a mathematical model of thermosyphon pump is established and numerical simulation is carried out to study the influence of riser tube length, tube diameter and immersion ratio on liquid lifting capacity and efficiency. The results showed that: the liquid lifting volume increased with the increase of immersion ratio, whereas the lifting efficiency showed a trend of increasing followed by decreasing. The highest lifting efficiency for a 340mm long, 6mm diameter riser achieved when the immersion ratio is 0.35. With the increasing of the height in riser, the velocity of the gas phase close to the wall in the thermosyphon pump was higher than the velocity along the radial direction. In order to enhance fluid interchange, corners of the refrigeration box were designed to be arc-shaped with a higher corner speed and lower temperature.
8
Ward, P., N. Collings, and N. Hay. "A Comparison of Simple Models of Turbulent Droplet Diffusion Suitable for Use in Computations of Spray Flames." Journal of Engineering for Gas Turbines and Power 107, no. 3 (July 1, 1985): 690–94. http://dx.doi.org/10.1115/1.3239790.
Анотація:
An exact analysis of the diffusion of droplets in turbulent flow, taking account of the random nature of the flow and the range of length and time scales, is very involved and the equations derived are not necessarily solvable. For this reason spray models have usually not included liquid turbulent diffusion effects. Simpler models of turbulent diffusion of droplets are compared in this paper and equations suitable for insertion into existing spray models that require little extra computational effort are derived.
9
Suwannakham, Parichart, and Kritsana Sagarik. "Dynamics of structural diffusion in phosphoric acid hydrogen-bond clusters." RSC Advances 7, no. 35 (2017): 21492–506. http://dx.doi.org/10.1039/c7ra01829k.
Анотація:
For protonated H3PO4 clusters, the Eigen–Zundel–Eigen mechanism is enhanced by fluctuations in the H-bond chain length and local-dielectric environment, and can proceed without the reorientation of H3PO4 molecules as in the case of neat liquid H3PO4.
10
Jüngling, E., K. Grosse, and A. von Keudell. "Propagation of nanosecond plasmas in liquids—Streamer velocities and streamer lengths." Journal of Vacuum Science & Technology A 40, no. 4 (July 2022): 043003. http://dx.doi.org/10.1116/6.0001669.
Анотація:
Nanosecond plasmas in liquids are often generated by applying a short high voltage pulse to an electrode immersed in a liquid for biomedical or environmental applications. The plasmas appear as streamers that propagate through the liquid. The understanding of the ignition of these nanosecond plasmas in liquids, however, is an open question. The occurrence of any traditional gas phase ignition mechanism is unlikely, because the formation of a gas bubble prior to ignition is suppressed by the inertia of the liquid. Therefore, either electron multiplication inside nanopores that are induced by an electric field pressure gradient or field effects at the tip and at the ionization front of the liquid streamer may act as electron generation mechanisms. A deeper understanding can be achieved by comparing the velocity and dynamic of the plasma propagation with modeling, where the individual mechanisms and transport coefficients can be analyzed. Here, we are using intensified charge-coupled device imaging to investigate the time dependence of the streamer dynamic and compare this with a 1D fluid code for negative voltages. It is shown that the maximum streamer length scales with the applied electric field, indicating that an electric stability field in the liquid streamer channel is important, as known for gas streamers. The 1D fluid code can reproduce the proper streamer velocities, if transport coefficients for hydrated electrons are chosen. The model suggests that the propagation of liquid streamers is dominated by the local ionization rate at the ionization front rather than by advection or diffusion of electrons as in gases. This also explains the finding that positive and negative streamers exhibit almost identical electron densities.
Дисертації з теми "Liquid diffusion length":
1
Sachi, Savya. "Coupling solidification model with CALPHAD data for the prediction of macrosegregation and solidification structures." Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0086.
Анотація:
Le présent travail vise à affiner les modèles existants dans SOLID® pour une meilleure prédiction des macroségrégations et des structures de solidification. Les modèles de solidification mis en œuvre dans le code SOLID® sont multiphasiques et multiéchelles. Les équations de transport qui le constituent sont fermées par des termes de transfert interphase régis par des relations constitutives microscopiques. Ces termes de transfert interphase reposent sur la représentation aussi précise que possible des phénomènes microstructuraux tels que la morphologie des grains,le profil des solutés dans les phases, et les équilibres thermodynamiques aux interfaces solide-liquide. Ce travail se concentre sur deux aspects : i) le couplage du modèle de solidification avec la thermodynamique des alliages multiconstitués et ii) l'incorporation d'un nouveau modèle de longueur de diffusion pour la phase liquide intervenant dans les termes de transfert interphase. Une méthodologie est proposée pour incorporer les données du diagramme de phase dans le modèle de solidification du code SOLID®. Les exemples présents dans le littérature concernant le couplage d'un modèle de solidification avec des progiciels thermodynamiques (de type CALPHAD) ont été réalisé en considérant : soit le couplage direct entre les logiciels, soit une technique de tabulation permettant ensuite le calculs des grandeurs thermodynamiques par interpolation. Le couplage direct prend beaucoup de temps, tandis que l'approche par tabulation devient impossible avec l'augmentation du nombre de constituants de l'alliage. Nous présentons une nouvelle approche consistant à mettre en oeuvre des réseaux de neurones pour obtenir à partir de données thermodynamiques issus de codes de type CALPHAD, des relations de régression. Ces relations de régression peuvent ensuite être facilement couplées à un modèle de solidification de type de celui implémenté dans le code SOLID®. Cette approche est beaucoup plus efficace sur le plan informatique que les méthodes mentionnées ci-dessus. La procédure de couplage est décrite et validée à partir de comparaisons avec des calculs CALPHAD sur des cas simples de solidification. D'autres simulations ont été effectuées sur le cas de référence Hebditch & Hunt ainsi que sur un lingot industriel. Les résultats obtenus par le modèle, tout en améliorant la prédiction de la ségrégation, mettent également en évidence les paramètres critiques du diagramme de phase, ce qui nous permet de proposer des valeurs modifiées de ces paramètres pour les simulations qui les supposent constants. Deuxièmement, la relation de longueur de diffusion dans la phase liquide proposée par Martorano et al. a été étendue pour tenir compte de la convection de la phase liquide. La simulation du lingot industriel avec cette nouvelle relation de longueur de diffusion montre un impact significatif sur la taille et la morphologie des grainsThe present work aims at refining existing models in SOLID® by developing capabilities for improved prediction of the solidification process. Multiphase solidification models incorporate transport equations, which are closed by interphase transfer terms that are governed by microscopic constitutive relationships. These analytical relationships rely on the accurate representation of the microstructural phenomena such as the grain morphology and solute profile in the phases, along with the assumptions of diffusion-controlled solidification with thermodynamic equilibria at the solid-liquid interfaces. This work focuses on two aspects: i) coupling solidification model with the thermodynamics of multicomponent alloys and ii) incorporating a new liquid diffusion length model for improved prediction of solute profile in the liquid phase. A methodology is proposed for incorporating phase diagram data into multiphase volume average solidification models. Previous instances of coupling the model with thermodynamic software packages include direct coupling with the software and a tabulation and interpolation technique. Direct coupling is time-consuming, whereas the tabulation approach becomes infeasible with increasing number of components in the system. We present a novel approach of using Artificial Neural Networks - Multi-layer perceptron (ANN-MLP) on tabulated thermodynamic data to obtain regression relationships, which can be easily coupled with the solidification model. This approach is computationally much more efficient than the above mentioned methods. The coupling procedure is described and validated with Thermo-Calc® Scheil solidification. Further simulations were performed on the Hebditch & Hunt benchmark case as well as an industrial ingot. Results obtained from the model, while improving the segregation prediction, also highlight the critical phase diagram parameters which help us propose modified values of these parameters for simulations which assume them to be constant. Secondly, the liquid diffusion length relationship proposed by Martorano et al. was extended to account for liquid convection. Simulation of the industrial ingot with the new diffusion length relationship shows significant impact on the grain size and grain morphology
2
Chahine, Gilbert. "Propriétés remarquables et dynamique lente de cristaux liquides nanoconfinés." Rennes 1, 2010. http://www.theses.fr/2010REN1S200.
Анотація:
Les effets de désordre gelé ont été largement étudiés sur des transitions de second ordre de fluides complexes confinés, tel que les cristaux liquides, mais restent mal compris pour des transitions de premier ordre. Dans ce travail de thèse, nous étudions les propriétés structurales et dynamiques du 12CB en volume et confiné dans des matrices à porosité unidirectionnelle. Nous montrons que le confinement dans l’alumine poreuse n’affecte pas le caractère premier ordre de la transition isotrope-smectique bien qu’une transition de configuration smectique apparait après un cycle de cristallisation/fusion. En revanche, nous mettons en évidence des effets du désordre gelé, induits par la rugosité interne des pores de silicium, et qui remplacent la transition par une mise en ordre smectique à courte portée. Toutefois, ce désordre anisotrope n’éteint pas complètement le caractère premier ordre vu le maintient d’un fort couplage nématique-smectique. Par ailleurs, nous montrons qu’une dynamique locale domine dans la fenêtre temporelle sondée en volume, et que des légers effets de ralentissement et d’hétérogénéité apparaîssent sous nanoconfinement anisotropeThe effects of quenched disorder were widely studied on second order transitions of confined complex fluids such as liquid crystals. Meanwhile they a still poorly understood in the case of first order transformations. In this work, we study the structural and dynamical properties of bulk and confined 12CB in matrices with unidirectional porosity. We show that confinement in porous alumina does not affect the first order isotropic-smectic transition; although, a transition of smectic configuration appears after a crystallization/melting cycle. On the contrary, we demonstrate that the effects of quenched disorder, induced by the roughness of silicon pore surface, replaces the transition by a continuous growth of a short range ordered smectic phase. However, this strong anisotropic disorder does not switch off completely the first order character of the transition where a nematic-smectic coupling remains strong. Moreover, we show that in the bulk, local dynamics dominate in the probed time window. In silicon and silica pores, we revealed weak effects of slowing down and heterogeneity of molecular dynamics which are mainly influenced by interfacial effects
3
Lettat, Abdelkader. "Adsorption multi-composant dans les zéolithes. Caractérisation par méthode cyclique de la co-diffusion d'isomères mono- et di-branchés de l'hexane sur silicalite en présence d'un composé à cinétique lente." Thesis, Vandoeuvre-les-Nancy, INPL, 2008. http://www.theses.fr/2008INPL099N/document.
Анотація:
L’objectif de cette thèse est de développer une méthode expérimentale permettant de mesurer simultanément des coefficients de co-diffusion dans les zéolithes, pour des mélanges de paraffines en C6 mono et di-branchées, dont les cinétiques de diffusion sont très différentes. Les espèces sont le 2- et le 3-methyl-pentane (2MP et 3MP) et le 2-2- et le 2-3-dimethyl-butane (22DMB et 23DMB) et l'adsorbant est une silicalite. Cette méthode est basée sur la réponse en sortie d’un lit fixe d’adsorbant à une variation cyclique de la composition à son entrée. La conception d’un modèle faisant intervenir des paramètres cinétiques et thermodynamiques a également être effectuée afin de simuler les courbes de perçages des différents constituants en mélange et sur plusieurs cycles. Les conditions expérimentales sont proches des conditions industrielles, à savoir en phase liquide et à fort taux de remplissage de l’adsorbant (185°C et 35 bars) L’écriture d’un modèle de diffusion, basé sur l’équation de Maxwell-Stefan appliquée au "Dusty Gas Model", dans ces conditions de fonctionnement, implique d’introduire des grandeurs volumiques qui permettent de redéfinir les contraintes liées à la saturation de l'adsorbant. De plus, tout en conservant la simplicité du modèle "Single File Diffusion" (pas de contre-diffusion microporeuse), nous avons montré que la prise en compte d’un flux volumique relatif associé au solide permet de conserver l’indépendance des coefficients de diffusion dans le cristal. Les simulations des courbes de perçage – sur un seul cycle pour les molécules rapides et sur plusieurs cycles pour les molécules lentes – indiquent que les coefficients de diffusion des différents isomères suivent l'ordre suivant : D3MP ˜ D2MP > D23DMB > D22DMB, avec un écart de trois ordres de grandeurs entre le 3MP et le 22DMB, ce qui laisse supposer qu'un procédé de séparation basé sur une sélectivité diffusionnelle peut être envisagé. Cependant, les tests de perçage en condition cyclique permettant de caractériser de manière plus précise le système, il a été possible de mettre en évidence une très lente accumulation du 22DMB au cours des cycles sous certaines conditions opératoires, phénomène qui peut s'avérer indétectable sur un faible nombre de cycles et/ou sur le profils de concentration des autres espèces. Ce phénomène a pour conséquence de diminuer les performances de l'adsorbant, aussi bien d'un point de vue capacitif que d'un point de vue sélectifThe aim of this work is to develop a new experimental method in order to determine simultaneously co-diffusion coefficients in zeolites for mixtures of single- and di-branched C6 paraffins, with totally different diffusion kinetics. The species are 2- and 3-methyl-pentane (2MP and 3MP) and 2-2- and 2-3-dimethyl-butane (22DMB and 23DMB) and the adsorbent is a silicalite. This method is based on the output measurement of an adsorbent column subjected to cyclic variations of its input concentration. The analysis of the mixture experimental breakthrough curves, on several cycles, is carried out using a mathematical model, based on Maxwell-Stefan theory of multi-component diffusion, allowing an estimation of thermodynamic and kinetic parameters. The experimental conditions are close to industrial constraints, i.e. at very high adsorption loading, and in the liquid phase (185°C and 35 bars). This requires to develop a modified Maxwell-Stefan diffusion model, applied to the "Dusty Gas Model", including volume constraints in the crystal which implies to redefine the adsorbent saturation. Moreover, while preserving the simplicity of the "Single File Diffusion" model (no counter-diffusion), a relative volumetric flow of the solid is taken into account, allowing to ensure the independence of the diffusion coefficient of each component in the adsorbent. The Maxwell-Stefan diffusion coefficients for the different isomers, obtained from breakthrough curves simulations – on one cycle for fast diffusing species and several cycles for slow molecules – are in the sequence : D3MP ˜ D2MP, > D23DMB > D22DMB, with a difference of three orders of magnitude between 3MP and 22DMB. This implies that a separation process based on kinetic selectivity can be considered. The cyclic breakthrough experiments, allowing a better characterization of the system, highlight a very slow accumulation of the 22DMB isomer during cycles for specific operating conditions, which may be undetectable on a small number of cycles and on the profiles of the other components.. This phenomenon involves a decrease of the adsorbent performances, in terms of capacity as well as selectivity
Частини книг з теми "Liquid diffusion length":
1
Doraiswamy, L. K. "Microphase-Assisted Reaction Engineering." In Organic Synthesis Engineering. Oxford University Press, 2001. http://dx.doi.org/10.1093/oso/9780195096897.003.0032.
Анотація:
A relatively recent concept in organic reaction engineering is the use of submicron particles to enhance the rate of a reaction. These are usually microparticles of solids, but can also be microdroplets of liquids, or even microbubbles of gases. They can be external agents, participating reactants, or precipitating solids. In this chapter, we cover the role of small particles as a whole, which may be regarded as constituting an additional colloid-like phase normally referred to as the microphase. We begin by classifying the microphase in terms of its mode of action and then proceed to an analysis of the following categories of importance in organic technology: microslurry of (1) catalyst or adsorbing particles in a reactive mixture; (2) solid reactant particles in a continuous phase of the second reactant; and (3) solid particles precipitating from reaction between two dissolved reactants, one of which can be a solid dissolving and reacting simultaneously with the other reactant. The microphase in the first case is externally added, whereas that in the last two cases is a reactant or a product. The field is still developing (with many unproven theories), and hence we restrict the treatment to a simple analysis of selected situations based on reasonable assumptions (thus avoiding often unjustified complexity). A microphase can be described as an assemblage of very small dispersed phase particles with average size (dp) much less than the diffusional length scale of the solute. Usually dp < l0μm, compared to the diffusional length scale which is of the order of 50-60 μm. Although the microphase is a distinct phase, the phase in which it is present is commonly regarded as pseudohomogeneous. In a stricter sense, however, it should be regarded as a microheterogeneous phase. Indeed, several studies have been reported on modeling heterogeneous microphase systems (Holstvoogd et al., 1986, 1988; Yagi and Hikita, 1987). In view of the ability of the particles of such a system, pseudohomogeneous or pseudoheterogeneous, to get inside the fluid film, they can enhance the transport rate of the solute through the film. Experimental observations in typical gas-liquid and slurry systems have clearly demonstrated (see Ramachandran and Sharma, 1969; Uchida et al., 1975; Sada et al., 1977a,b, 1980; Alper et al., 1980; Pal et al., 1982; Bruining et al., 1986; Bhaskarwar et al., 1986; Bhagwat et al., 1987; Mehra et al., 1988; Mehra and Sharma, 1988a; Hagenson et al., 1994) the enhancing role of a microphase made up of fine particles. The case of a second liquid phase acting as a microphase or of a solid product performing a similar function has also been studied and found to enhance the reaction rate (Janakiraman and Sharma, 1985; Mehra and Sharma, 1985, 1988b; Anderson et al., 1998). Mehra et al. (1988) and Mehra (1990a,b, 1996) presented a detailed account of the role of different types of microphases in rate enhancement. In all these cases, either a microphase is separately introduced or one of the reactants or products acts as a microphase.
Тези доповідей конференцій з теми "Liquid diffusion length":
1
Kockmann, Norbert, Michael Engler, Claus Fo¨ll, and Peter Woias. "Liquid Mixing in Static Micro Mixers With Various Cross Sections." In ASME 2003 1st International Conference on Microchannels and Minichannels. ASMEDC, 2003. http://dx.doi.org/10.1115/icmm2003-1121.
Анотація:
Micro mixers are an integral part of several micro fluidic devices like micro reactors or analytical equipment. Due to the small dimensions, laminar flow is expected a priori in those devices while the mass transfer is supposed to be dominated by diffusion. A detailed numerical CFD-study by CFDRC-ACE+ of simple static mixers shows a significant deviation from strictly laminar flow in a wide range of Reynolds numbers Re, channel dimensions, and types of cross sections (square, rectangular, trapezoidal). With increasing flow velocity and Re number the flow starts to form vortexes at the entrance of the mixing channel. The vortexes are symmetrical to the symmetry planes of the mixing channel, both for the rectangular and the trapezoidal cross sections investigated here. With further increasing velocity the flow tends to instabilities, which causes a breakup of the flow symmetry. These instabilities are generally found in T-shape mixers with symmetrical flow conditions, but not always in Y-shape mixers or with asymmetrical flow conditions. Within the laminar flow regime diffusive mass transfer is dominant. In this case the mixing quality at constant channel length becomes worse with increasing velocity. This effect can almost be equalized by the onset of the vortex regime, which enhances the mass transfer by convective transport. This paper shows the mixing quality at a certain length for different geometrical parameters and flow conditions.
2
Ishii, Eiji, Toru Ishikawa, and Yoshiyuki Tanabe. "Simulation of Liquid Jet Breakup Using a Combination of Particle and Grid Methods." In ASME 2005 Fluids Engineering Division Summer Meeting. ASMEDC, 2005. http://dx.doi.org/10.1115/fedsm2005-77001.
Анотація:
Fine atomization of the liquid jet from a fuel injector in an automobile engine lowers engine emissions and improves fuel efficiency. The breakup length of liquid films and the lengths of ligaments near the injector outlet after the breakup of liquid films are important parameters for predicting the atomization. These parameters have been predicted mainly using the Eulerian-grid method. (We refer to this as the ‘grid method’.) However, the grid method causes a loss of the liquid film with numerical diffusion, and it requires a large amount of computation time in practical engineering aspect because fine meshes smaller than the ligaments must be used. On the other hand, the particle method, an alternative (particle-based) method for representing the continuum Navier-Stokes equation which can simulate a ligament using a group of particles, does not cause numerical diffusion. However, a large number of particles are needed to simulate the entire computational domain within the injectors. In this study, we have focused on the flow field only near the injector outlet, and have tried to simulate the breakup of liquid films by using groups of particles in the particle method. In the simulation, the particle method was applied only to the liquid film and the grid method was used in other regions to shorten the computation time. Furthermore, we tried to integrate Brackbill’s surface-tension model, which is widely used in the grid method, into the particle method. To evaluate this approach, we compared the breakup lengths obtained for a cylindrical liquid jet in a uniform air stream with measurements done by Arai and Hashimoto; the breakup lengths agreed well with their measurements. We then simulated the breakup of a liquid film near the outlet of a fuel injector used for automobile engine, and found that our hybrid method could simulate the breakup of the liquid film into ligaments.
3
Kissick, Sean M., and Hailei Wang. "Numerical Modeling for a Supercritical CO2-Liquid Sodium Hybrid Compact Heat Exchanger." In ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-86682.
Анотація:
As research continues into the generation IV advanced nuclear reactors, exploration of liquid sodium as a coolant, or Sodium Fast Reactors (SFRs), coupled to supercritical CO2 (sCO2) Brayton cycles are currently underway. Liquid sodium offers unique and beneficial fluid properties that can achieve higher efficiencies and longer equipment lifespans compared to conventional water cooled reactors. Coupling sodium with sCO2 matches well with sodium’s temperature profile and is less reactive with sodium when compared to water used in standard Rankine cycles. To achieve commercial viability, methods for developing diffusion-bonded Hybrid Compact Heat Exchangers (H-CHX) to couple SFRs with sCO2 Brayton cycles are being developed. This paper includes thermal-hydraulic analysis of these fluids to quantify thermal and pressure stresses within the H-CHX for use in determining a structurally sound design. Two models for predicting the temperature profiles within a practical H-CHX channel design are presented. The first is a 1-D heat transfer model employing heat transfer correlations to provide both bulk fluid and wall temperatures. The second is a 3-D computational fluid dynamics model (CFD) providing a three-dimensional temperature profile, but at a significantly increased simulation time. By comparing the results of the two models for specific design conditions, significant temperature deviation is shown between the models at a short channel length of 10 cm. However, for longer channel lengths, although the 1-D model neglected the strong axial conduction on the sodium side, it generally shows good agreement with the CFD model. Thus, for any practical H-CHX designs, the findings reveal both simulation methods can be used to extrapolate the temperature gradient along the channel length for use in designing a H-CHX, as well as predicting the overall size and mass of the heat exchanger for component costing.
4
Raju, Mandhapati P., and James S. T’ien. "Heat and Mass Transports in Porous Wicks Driven by a Gas-Phase Diffusion Flame." In ASME 2005 Summer Heat Transfer Conference collocated with the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems. ASMEDC, 2005. http://dx.doi.org/10.1115/ht2005-72202.
Анотація:
A one dimensional stagnation point diffusion flame stabilized next to a porous wick is studied using a numerical model. The bottom end of the one-dimensional wick is dipped inside a liquid fuel (ethanol) reservoir. The liquid is drawn towards the surface of the wick through capillary action against gravity. The model combines heat and mass transfer equations in the porous media with phase change and gas-phase combustion equations to investigate steady-state flow structure in the porous wick and flame characteristics in the gas phase. In one-dimensional system, the only steady solution in the porous wick that is stable is found to be in the funicular regime. There are two regions in the wick: a vapor-liquid two-phase region near the surface exposed to the flame and a purely liquid region deep inside the wick. The physics behind the two-phase flow driven by capillarity and evaporation has been studied in detail. The coupling between the flame and the porous transport involves three different length scales: flame standoff distance, wick height above the reservoir and capillary rise. Attempt is made to study the effect of the non-dimensional numbers that contains these scales. In the limit of fast chemical kinetics (large Damkohler number), the computed results depend only on two non-dimensional ratios: the ratio of wick height to capillary rise and the ratio of wick height to flame standoff distance. Thus, a simplified similitude has been identified.
5
Sasabe, Takashi, Shohji Tsushima, Shuichiro Hirai, Katsunori Minami, and Keiji Yada. "Liquid Water Visualization in an Operating PEMFC by Soft X-Ray Radiography." In ASME 2009 7th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2009. http://dx.doi.org/10.1115/fuelcell2009-85135.
Анотація:
Liquid water distribution in the operational PEMFC was visualized by soft X-ray radiography. To achieve a maximum sensitivity towards liquid water, low electron beam energy in soft X-ray range was chosen. As a result, the spatial resolution of 1 μm and the temporal resolution of 0.5 sec were obtained. In addition, a correlation between the accumulation of water and the reduction of performance in higher current density range was observed. At low current densities, liquid water accumulation was observed under the ribs, because the longer diffusion length for the rib area conduced to a less effective water removal into the vapor phase. With increase of current density, liquid water was also observed under the channels and the reduction of performance with time was observed. These results suggested that the current density under the rib is much less than under the channel and the anisotropy of GDL and the geometry of flow field had a heavy impact on the liquid water distribution and the cell performance.
6
Kawaguchi, Tatsuya, Yasuhiko Sakai, Kouji Nagata, Osamu Terashima, and Shoichi Takaku. "Characteristics of the Scalar Field in a Turbulent Liquid Jet and a Fundamental Study on the Micro Scale Concentration Measurements by the Optical Fiber LIF Method." In ASME-JSME-KSME 2011 Joint Fluids Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajk2011-21015.
Анотація:
In this study, the characteristics of the scalar field in an axisymmetric turbulent water jet are investigated experimentally. In the experiments, the axial velocity, the concentration of the dye solution and the temperature of the fluid are measured by the hot-film probe, the fiber sensor and the cold-firm probe, respectively. In particular, the difference of statistics between scalars (concentration and temperature) with the different molecular diffusion coefficients is discussed. The Schmidt number of the diffusing matter is 3,800, and the Prandtl number of temperature is 7. As regarding the mean values, the r.m.s values and distribution of PDF, we cannot find any difference between the concentration field and temperature field. However, in the spectrum, it is found that the temperature spectrum shows the −5/3 law almost in the same range as the velocity spectrum, on the other hand, the concentration spectrum shows the −5/3 law in the wider range than the velocity spectrum. This means that the shape of spectrum depends on the diffusion coefficient. In order to make the higher resolution measurement of concentration, a new optical probe based on the LIF method is designed. This probe consists of the two optical fibers, the tip of which is processed like the shape of a lens. By the effect of lens, the laser beam can be focused on the narrower area in comparison with the past LIF measurements. In the present design, the width of focus of laser beam is set to 0.6 micrometers, and the focal length is set to 7.3mm. It is shown that this probe has the resolution less than the Batchelor scale at x / d ≥30 in the condition of present jet diffusion field (d = 4mm, Re = 20,000). Further, a new system to adjust the position of the optic fiber probe exquisitely is developed.
7
Franc¸ais, Olivier, Marie Caroline Jullien, Lionel Rousseau, Patrick Poulichet, Serge Desportes, Jean Pierre Lefevre, Assia Chouai, and Jacques Delaire. "A Thermally-Driven Micromixer Based on Fluid Volume Variation." In ASME 8th Biennial Conference on Engineering Systems Design and Analysis. ASMEDC, 2006. http://dx.doi.org/10.1115/esda2006-95276.
Анотація:
In microfluidics, flows are laminar due to low Reynolds number (<1). Consequently, mixing between two liquids is mainly obtained by natural diffusion which may take a long time or equivalently requires centimetre length channels. However, it is possible to generate chaotic-like flows either by modifying the channel geometry or by creating an external perturbation of the flow. In this paper, an active micromixer is presented consisting on thermal actuation with heating resistors. In order to disturb the liquid flow, an oscillating transverse flow is generated by heating the liquid. Depending on the value of boiling point, either bubble expansion or volumetric dilatation controlled the transverse flow amplitude. The configuration is identical to the one of Dodge et al. [7], but the transversal oscillating flow is created by thermal actuation instead of pneumatic ones. A chaotic like mixing is then induced under particular conditions depending on volume expansion, liquid velocity, frequency of actuation… This solution presents the advantage to achieve mixing in a very short time (1 s) and along a short channel distance (channel width). It can also be integrated in a more complex device due to actuator integration with microfluidics.
8
Premasiri, A., G. Happawana, and A. Rosen. "Porous Media Tumor Model for Light Penetration and Oxygen Diffusion During Photodynamic Therapy." In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-66480.
Анотація:
Photodynamic therapy (PDT) is an FDA approved, effective, and minimally invasive cancer treatment modality with few side effects. PDT requires three major components; photosensitizing agent, activation light, and molecular oxygen. Optimization of PDT for an individual patient requires good therapeutic selectivity and high efficacy, where the design of such an effective protocol is based on the understanding of the interaction of key therapeutic components with tumor tissue. Tumor models expressive of changes during the growth of tumor along with the behavior of PDT components facilitate the above requirement. In this study we have developed a mathematical model considering tumor as a porous medium of solid of and liquid that enables to express characteristics of a growing tumor. The characteristic lengths and the volumes that can be changed in the model represent the dynamic changes during the growth of the tumor. An energy based light transport model is superimposed with the porous media model to yield an analytical equation of light penetration in turbid media. In addition a molecular diffusion model combined with the porous media tumor model provides a second analytical equation yielding molecular oxygen diffusion during PDT. Experimentally available physiological and photophysical data are used to obtain the results from the developed models. The commonly used wavelength for PDT, 635nm and corresponding photophsical parameters for a healthy tissue are used for the calculations. The modeling results reveal an exponential decay of optical power along the direction of light penetration and the characteristic changes in oxygen diffusion during PDT. Further observations include the time dependent changes in photosensitizer photobleaching and the corresponding increase in oxygen diffusion length. The modeling results in both cases show a promising accordance with the available experimental results in literature. The model calculations also reveal the effect of light penetration on oxygen diffusion in PDT milieu adding to the expression of its usefulness.
9
Cai, Qingjun, Chialun Tsai, Jeff DeNatale, and Chung-Lung Chen. "Fluid Mixing in Micro Scale Channel Patterned Hydrophobic/Hydrophilic Surface." In ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-13739.
Анотація:
Micro scale fluid control or mixing is critical for chemistry and life sciences. Successful performance of on-chip biochemical analysis processes, such as DNA hybridization and PCR amplification, highly depend on rapid mixing of multiple fluid species. In this paper, a set of initial designs is developed for flow mixing. In micro channels with 100 and 200μm width, alternating regions of hydrophobic/hydrophilic surface are created on silicon surfaces by photolithography and dry etch techniques. Experimental results show that in the micro channels with 20mm length, effective mixing is observed on the device patterned by incline hydrophobic/hydrophilic grilles in which eddy diffusion mixes two liquids. In contrasts, slight mixing is caused by the development of liquid instability induced by alternating hydrophobic/hydrophilic patterns orthogonal to the flow direction.
10
Graham, Owen, Nicholas Magina, A. J. Wickersham, Fei Han, Sebastiano Sorato, and Sven Bethke. "Thermo-Acoustic Analysis of a Realistic Liquid-Fueled GT Combustor." In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-91547.
Анотація:
Abstract Thermo-acoustic instabilities are an important consideration in the design of modern power generation gas turbine combustors. While the design process must consider many competing requirements, such as temperature profiles, emissions, robustness to auto-ignition and flameholding, thermoacoustics is one of the most challenging to predict, and therefore design for. This is particularly true in the case of liquid-fueled systems, where the phenomenon results from a complex system of coupled multi-physics phenomena: fuel atomization and transport, mixing, reactive kinetics and acoustics. Nevertheless, emissions-compliant liquid fuel capability is becoming increasingly important to GT operators, thus it is critical to be able to predict the thermoacoustic instabilities of these combustors. In this work we present an approach to model the thermoacoustic feedback loop for a realistic liquid fuel nozzle in a single burner configuration. The approach is based on an analytical liquid-fuel diffusion flame model to provide the fluctuating heat release response to inflow perturbations. This is coupled with a 3D FEM description of the acoustic response of the single burner rig through a time-domain Green’s function model to predict the growth and saturation of pressure oscillations. The necessary flame model parameters are calibrated based on a range of test data obtained from the single burner rig with a tunable combustor length. The results are shown to compare well with test data across a range of operating conditions, and for two different nozzle geometries.