Home About us Contact
|
Home About us Contact | ||
|
|
||
Transfer Phenomena (transfer + phenomenon)
Kinds of Transfer Phenomena Selected AbstractsRecent Advances in Mathematical Modeling of Flow and Heat Transfer Phenomena in Glass FurnacesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2002Manoj K. Choudhary This paper reviews significant advances in the mathematical modeling of flow and heat transfer phenomena in glass furnaces during the period 1996,2000. It describes developments in both the fundamental/scientific and practical aspects of modeling. The topics reviewed include developments in (a) model formulation and modeling techniques, (b) postprocessing modeling of glass quality and environmental emissions, (c) measurement of thermodynamic and transport properties of melt relevant to modeling, and (d) incorporation of model-based knowledge into process control schemes. These developments are critically examined and assessed from an industrial perspective, and topics needing further research and development efforts are identified. [source] Hybrid Simulation of Miscible Mixing with Viscous FingeringCOMPUTER GRAPHICS FORUM, Issue 2 2010Seung-Ho Shiny Abstract By modeling mass transfer phenomena, we simulate solids and liquids dissolving or changing to other substances. We also deal with the very small-scale phenomena that occur when a fluid spreads out at the interface of another fluid. We model the pressure at the interfaces between fluids with Darcy's Law and represent the viscous fingering phenomenon in which a fluid interface spreads out with a fractal-like shape. We use hybrid grid-based simulation and smoothed particle hydrodynamics (SPH) to simulate intermolecular diffusion and attraction using particles at a computable scale. We have produced animations showing fluids mixing and objects dissolving. [source] Study of Joule heating effects on temperature gradient in diverging microchannels for isoelectric focusing applicationsELECTROPHORESIS, Issue 10 2006Brian Kates Abstract IEF is a high-resolution separation method taking place in a medium with continuous pH gradients, which can be set up by applying electrical field to the liquid in a diverging microchannel. The axial variation of the channel cross-sectional area will induce nonuniform Joule heating and set up temperature gradient, which will generate pH gradient when proper medium is used. In order to operationally control the thermally generated pH gradients, fundamental understanding of heat transfer phenomena in microfluidic chips with diverging microchannels must be improved. In this paper, two 3-D numerical models are presented to study heat transfer in diverging microchannels, with static and moving liquid, respectively. Through simulation, the temperature distribution for the entire chip has been revealed, including both liquid and solid regions. The model for the static liquid scenario has been compared with published results for validation. Parametric studies have showed that the channel geometry has significant effects on the peak temperature location, and the electrical conductivity of the medium and the wall boundary convection have effects on the generated temperature gradients and thus the generated pH gradients. The solution to the continuous flow model, where the medium convection is considered, shows that liquid convection has significant effects on temperature distribution and the peak temperature location. [source] Heat and mass transfer phenomena in magnetic fluidsGAMM - MITTEILUNGEN, Issue 1 2007Th. Völker Abstract In this article the influence of a magnetic field on heat and mass transport phenomena in magnetic fluids (ferrofluids) will be discussed. The first section is dealing with a magnetically driven convection, the so called thermomagnetic convection while in the second section the influence of a temperature gradient on the mass transport, the Soret effect in ferrofluids, is reviewed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Solute transport in sand and chalk: a probabilistic approachHYDROLOGICAL PROCESSES, Issue 5 2006E. Carlier Abstract A probabilistic approach is used to simulate particle tracking for two types of porous medium. The first is sand grains with a single intergranular porosity. Particle tracking is carried out by advection and dispersion. The second is chalk granulates with intergranular and matrix porosities. Sorption can occur with advection and dispersion during particle tracking. Particle tracking is modelled as the sum of elementary steps with independent random variables in the sand medium. An exponential distribution is obtained for each elementary step and shows that the whole process is Markovian. A Gamma distribution or probability density function is then deduced. The relationships between dispersivity and the elementary step are given using the central limit theorem. Particle tracking in the chalky medium is a non-Markovian process. The probability density function depends on a power of the distance. Experimental simulations by dye tracer tests on a column have been performed for different distances and discharges. The probabilistic approach computations are in good agreement with the experimental data. The probabilistic computation seems an interesting and complementary approach to simulate transfer phenomena in porous media with respect to the traditional numerical methods. Copyright © 2006 John Wiley & Sons, Ltd. [source] Carbothermal synthesis of vanadium nitride: Kinetics and mechanismINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2006A. Ortega Constant rate thermal analysis (CRTA) has been used for the first time to study the kinetics of the carbothermal reduction of V2O5 in nitrogen to obtain vanadium nitride. It is noteworthy to point out that CRTA method allows both a good control of pressure in the sample surroundings and the use of reaction rates low enough to keep temperatures gradients at a negligible level to avoid any heat or mass transfer phenomena. This method allows one to control the texture and the structure of many materials through kinetic control of the thermal treatment of the precursors. The precise control of the external parameters of the reaction shows that CRTA is an attractive method for kinetic studies and leads to more reliable kinetic data. It has been shown that the carbothermal synthesis of vanadium nitride is best described by a three-dimensional diffusion kinetic model (the Jander equation) with an activation energy which falls in the range of 520,540 kJ/mol. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 369,375, 2006 [source] The impact of flow field pattern on concentration and performance in PEMFCINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2005A. Su Abstract In this study, we present a rigorous mathematical model, to treat prediction and analysis of proton exchange membrane fuel cells gas concentration and current density distribution in mass transfer area and chemical reaction area performed in 3-D geometry. The model is based on the solution of the conservation equations of mass, momentum, species, and electric current in a fully integrated finite-volume solver using the CFDRC commercial code. The influences of fuel cell performance with two kinds of flow channel pattern design are studied. The gas concentration of the straight flow pattern appears excessively non-uniform, resulting in a local concentration polarization. On the other hand, the gas concentration is well distributed for the serpentine flow pattern, creating a better mass transfer phenomena. The performance curves (polarization curves) are also well correlated with experimental data. Copyright © 2005 John Wiley & Sons, Ltd. [source] Fundamental heat transfer mechanism between bed-to-membrane water-walls in circulating fluidized bed combustorsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 9 2003B.V. Reddy Abstract In the present work, the fundamental mechanism between bed-to-membrane water-walls in the riser column of a circulating fluidized bed (CFB) combustor is presented. The bed-to-membrane water-wall heat transfer depends on the contributions of particle heat transfer, dispersed phase heat transfer and radiation heat transfer. The fundamental mechanism of particle heat transfer and the effect of fraction of wall exposed to clusters and gas gap thickness between cluster and wall on particle heat transfer coefficient and bed-to-wall heat transfer coefficient are investigated. The influence of operating parameters like cross-sectional average volumetric solids concentration and bed temperature on particle and bed-to-wall heat transfer are also reported. The present work contributes some fundamental information on particle heat transfer mechanism, which is responsible for increasing the bed-to-wall heat transfer coefficient (apart from dispersed phase convection and radiation heat transfer). The details on particle heat transfer mechanism will enable to understand the basic heat transfer phenomena between bed-to-membrane water-walls in circulating fluidized bed combustors in a detailed way, which in turn will aid for better design of CFB combustor units. The particle heat transfer mechanism is significantly influenced by the fraction of wall exposed to clusters and gas gap thickness between clusters and wall. Copyright © 2003 John Wiley & Sons, Ltd. [source] Simulation of heat transfer during rotational moldingADVANCES IN POLYMER TECHNOLOGY, Issue 4 2003A. Greco Abstract In rotational molding, polymer powders are subjected to heating, melting, cooling, and subsequent solidification in biaxially rotating molds. Heat transfer phenomena during rotational molding are significantly affected by the presence of endothermic and exothermic transitions. In this paper instead of using the traditional moving interface method, a new approach is presented which is applicable to semicrystalline materials like linear low-density polyethylene. Melting is described by a statistical model and crystallization by a kinetic model. The model parameters are determined from differential scanning calorimetry measurements. The one-dimensional unsteady heat conduction equation is solved by a finite difference method. The numerical predictions are in good agreement with experimental data. The overall heat transfer model can be used for process optimization purposes. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 271,279, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10055 [source] MASS TRANSFER IN PACIFIC HAKE (Merluccius australis) PACKED IN REFRIGERATED MODIFIED ATMOSPHEREJOURNAL OF FOOD PROCESS ENGINEERING, Issue 6 2001R. SIMPSON ABSTRACT The objective of this research was to develop, and experimentally validate a fully mathematical model, to predict mass transfer phenomena in Pacific Hake (Merluccius australis) packed in refrigerated modified atmosphere. A mathematical model to predict mass transfer of CO2, O2, N2 and water vapor was developed and validated. The diffusion model was developed utilizing Fick's second law, considering fish fillet as an infinite slab and applied to Pacific Hake (lean fish species) under refrigeration conditions. CO2 diffusivity of Pacific Hake was determined by an inverse procedure at OC and resulted in a value of 5.19 × 10,10 [m2/s] that is in accordance with values reported in the literature. However, postmortem variations of pH could affect solubility and diffusivity of CO2 in fish muscle. [source] A chaos-based iterated multistep predictor for blast furnace ironmaking processAICHE JOURNAL, Issue 4 2009Chuanhou Gao Abstract The prediction and control of the inner thermal state of a blast furnace, represented as silicon content in blast furnace hot metal, pose a great challenge because of complex chemical reactions and transfer phenomena taking place in blast furnace ironmaking process. In this article, a chaos-based iterated multistep predictor is designed for predicting the silicon content in blast furnace hot metal collected from a pint-sized blast furnace. The reasonable agreement between the predicted values and the observed values indicates that the established high dimensional chaotic predictor can predict the evolvement of silicon series well, which conversely render the strong indication of existing deterministic mechanism ruling the dynamics of complex blast furnace ironmaking process, i.e., a high-dimensional chaotic system is suitable for representing the blast furnace system. The results may serve as guidelines for characterizing blast furnace ironmaking process, an extremely complex but fascinating field, with chaos in the future investigation. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Recent Advances in Mathematical Modeling of Flow and Heat Transfer Phenomena in Glass FurnacesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2002Manoj K. Choudhary This paper reviews significant advances in the mathematical modeling of flow and heat transfer phenomena in glass furnaces during the period 1996,2000. It describes developments in both the fundamental/scientific and practical aspects of modeling. The topics reviewed include developments in (a) model formulation and modeling techniques, (b) postprocessing modeling of glass quality and environmental emissions, (c) measurement of thermodynamic and transport properties of melt relevant to modeling, and (d) incorporation of model-based knowledge into process control schemes. These developments are critically examined and assessed from an industrial perspective, and topics needing further research and development efforts are identified. [source] Saturation transfer in human red blood cells with normal and unstable hemoglobin,NMR IN BIOMEDICINE, Issue 1 2003Masaru Sogami Abstract Saturation transfer phenomena from irradiated protein protons to observed water protons in packed human red blood cells (RBCs) with normal or unstable hemoglobin (Hb), i.e. Hb Yokohama and Hb Koeln, were studied using intermolecular cross-relaxation rates [CR; 1/TIS(H2O)], action spectra {[1 ,(I,/I0)] vs f2 (ppm), where I0 and I, are the longitudinal magnetization of observed water protons before and after long-time f2 -irradiation, respectively}, CR spectra [CR vs f2 (ppm)] and CR ratio vs f2 (ppm) with f2 -irradiation from ,100 to 100,ppm at ,H2/2, of 69 or 250,Hz. RBCs (Hb Yokohama) exhibited many large Heinz bodies and strongly impaired filterability, while RBCs (Hb Koeln) showed few microscopically typical Heinz bodies and virtually normal filterability. However, increases in CR values for RBCs (Hb Koeln) and RBCs (Hb Yokohama), monitored by f2 -irradiation below ,,6 and above ,14,ppm, clearly indicated marked increases in association or aggregation of unstable Hb in RBCs compared with those in normal RBCs. CR values, monitored between ,0 and ,10,ppm, were related to not only association or aggregation of unstable Hb but also amounts of water in RBCs. Aggregation or association of unstable Hb exhibited greater effects on CR values compared with those of methemoglobin formation. Copyright © 2003 John Wiley & Sons, Ltd. [source] Effects of tool-embedded dielectric sensors on heat transfer phenomena during composite curePOLYMER COMPOSITES, Issue 2 2007A.A. Skordos The present study examines the effects that placement of tool-mounted dielectric sensors in the composite cure assembly has on the local thermal and degree-of-cure fields. A nonlinear heat transfer model, incorporating appropriate thermoset cure and thermal property submodels, is used to simulate the cure of carbon and glass composites of various thicknesses. The model is validated against experimental data obtained during the cure of composite samples in a resin-transfer molding tool. The results of the simulations show that embedding a sensor can have a significant effect on the thermal field, because of the thermal conductivity mismatch between the metal tool and the sensor substrate material. In the heating-up stage of the cure profile, sensors embedded in the heated tool side intensify thermal gradients, which causes a corresponding lag in the progress of the reaction in the area adjacent to the sensor. Exothermic effects are also intensified by the sensor presence, especially in the case of thick composite curing. These results suggest that control strategies based on the utilization of embedded sensors should take these effects into account. POLYM. COMPOS., 28:139,152, 2007. © 2007 Society of Plastics Engineers. [source] Analysis of heat transfer in autoclave technologyPOLYMER COMPOSITES, Issue 5 2001Vincenza Antonucci In autoclave technology, polymer based composites are manufactured under the application of pressure and heat. The heat transferred between the energy carrying fluid and the bag-composite-tool element activates exothermic curing reactions, leading to composite consolidation. The convective heat transfer mechanism is the most relevant aspect controlling the rate of chemical and physical transformations associated with composite curing. Moreover, the fluidodynamic regime that results from the interactions between the autoclave and the tool geometry, even if totally predictable in theory, is unattainable in practice. In this study, the heat transfer phenomena occurring during the autoclave manufacturing cycle have been analyzed. The assumption of a negligible through-the-thickness thermal gradient led to simplified energy balance equations. In this case, the thermal evolution of the manufacturing elements has been completely determined by two parameters: the global convective heat exchange coefficient, setting the rate of the heat transfer between the autoclave environment and the bag-composite-tool element, and the adiabatic temperature rise, establishing the relevance of the polymerization exotherm. A scaling analysis has been performed in order to identify the dimensionless parameters controlling the autoclave process. The developed semitheoretical methodology has been extensively tested by comparison with experimental data from an industrial autoclave. [source] | ||||||||||||||||