Search results for "Convection"
showing 10 items of 332 documents
Dry-Season Precipitation in Tropical West Africa and Its Relation to Forcing from the Extratropics
2008
Abstract Precipitation is a major socioeconomic factor in the Guineo-Soudanian zone of tropical West Africa with its distinct summer rainy season from May to October. Albeit rare, precipitation during the dry season can have substantial impacts on the local hydrology and human activities reaching from the rotting of harvests to improved grazing conditions. This study provides an observationally based synoptic and dynamical analysis of an abundant rainfall event during the dry season of 2003/04 that affected the countries of Nigeria, Benin, Togo, and Ghana. The results point to a forcing of the rainfalls from the extratropics in the following ways: 1) Upper-level clouds and moisture to the e…
The simulation of morphology of dissimilar copper–steel electron beam welds using level set method
2010
Abstract In present work, the simulation of morphology and velocity field in dissimilar electron beam welds formed between the metals with limited solubility is described by the example of copper–stainless steel couple. Finite element software COMSOL Multiphysics 3.5 has been employed due to its flexibility in solving of coupled multiphysical problems. The domination of horizontal flows allows reducing the model to two dimensions. Level set method has been used to determine the position of the interface between immiscible components basing on coupled heat transfer and fluid flow pseudo-stationary solution. The evolution of the shape, fluid flow and mixing pattern in function of operational …
Influence on the macrosegregation of binary metallic alloys by thermoelectromagnetic convection and electromagnetic stirring combination
2014
International audience; Influence of a slowly rotating 0.5 T transverse magnetic field on the directionally solidified metallic alloy has been experimentally studied in this work. Main idea is to study an influence on the melt flow and material structure caused by the simultaneous electromagnetic stirring and thermoelectromagnetic convection with comparable magnitudes. Electromagnetic stirring and thermoelectromagnetic convection intensities have been estimated analytically to find optimal experimental parameters. It is experimentally demonstrated that with such an interaction it is possible to modify component macrosegregation of Sn-10 wt% Pb alloy. Helical macrosegregation within cylindri…
Impacts of Varying Concentrations of Cloud Condensation Nuclei on Deep Convective Cloud Updrafts—A Multimodel Assessment
2021
AbstractThis study presents results from a model intercomparison project, focusing on the range of responses in deep convective cloud updrafts to varying cloud condensation nuclei (CCN) concentrations among seven state-of-the-art cloud-resolving models. Simulations of scattered convective clouds near Houston, Texas, are conducted, after being initialized with both relatively low and high CCN concentrations. Deep convective updrafts are identified, and trends in the updraft intensity and frequency are assessed. The factors contributing to the vertical velocity tendencies are examined to identify the physical processes associated with the CCN-induced updraft changes. The models show several c…
Two-Dimensional Modeling of a Flat-Plate Photocatalytic Reactor for Oxidation of Indoor Air Pollutants
2007
In this paper we present a two-dimensional (2-D) analysis of a narrow-slit, flat-plate, single-pass, flow-through photocatalytic reactor for air purification. The continuity equation for convection and diffusion in two dimensions, under un-steady-state conditions, was coupled with radiation field modeling and photocatalytic reaction kinetics to model the transient and steady-state behavior of the reactor. The model was applied to the photocatalytic oxidation of trichloroethylene (TCE) in humidified air streams under different experimental conditions. The kinetic parameters determined by a three-dimensional (3-D) computational fluid dynamics model of the reactor were used in the 2-D model si…
Breakdown of Burton-Prime-Slichter approach and lateral solute segregation in radially converging flows
2005
A theoretical study is presented of the effect of a radially converging melt flow, which is directed away from the solidification front, on the radial solute segregation in simple solidification models. We show that the classical Burton-Prim-Slichter (BPS) solution describing the effect of a diverging flow on the solute incorporation into the solidifying material breaks down for the flows converging along the solidification front. The breakdown is caused by a divergence of the integral defining the effective boundary layer thickness which is the basic concept of the BPS theory. Although such a divergence can formally be avoided by restricting the axial extension of the melt to a layer of fi…
Design and Experimental Test of a Thermomagnetic Motor
2012
Abstract This paper presents a Thermomagnetic Motor. The design of the motor is based on a thermal-magnetic coupled dynamic model, which is obtained by assuming the use of a ferromagnetic material working at temperatures near the curie point. The motor is modeled in terms of both its magnetic as well thermal properties (magnetic permeability and thermal conductivity) and the thermal processes are supposed to be influenced by the thermal conductivity, the convection and the advection. An analytical expression of the generated torque, which links this quantity to the magnetic, thermal and geometrical parameters of the generated torque is given. A design of a machine, based on this theory is p…
The 2007 eruption of Stromboli volcano: Insights from real-time measurement of the volcanic gas plume CO2/SO2 ratio
2009
Abstract The recent eruption of Stromboli in February–April 2007 offered a unique chance to test our current understanding of processes driving the transition from ordinary (persistent Strombolian) to effusive activity, and the ability of instrumental geophysical and geochemical networks to interpret and predict these events. Here, we report on the results of two years of in-situ sensing of the CO 2 /SO 2 ratio in Stromboli's volcanic gas plume, in the attempt to put constraints on the trigger mechanisms and dynamics of the eruption. We show that large variations of the plume CO 2 /SO 2 ratio (range, 0.9–26) preceded the onset of the eruption (since December 2007), interrupting a period of …
Onset of Convection in an Inclined Anisotropic Porous Layer with Internal Heat Generation
2019
The onset of convection in an inclined porous layer which is heated internally by a uniform distribution of heat sources is considered. We investigate the combined effects of inclination, anisotropy and internal heat generation on the linear instability of the basic parallel flow. When the Rayleigh number is sufficiently large, instability occurs and a convective motion is set up. It turns out that the preferred motion at convection onset depends quite strongly on the anisotropy ratio, &xi
A versatile model of steady state O2 supply to tissue. Application to skeletal muscle
1990
A model of combined convective and diffusive O2 transport to tissue is suggested which allows for the calculation of PO2 distributions in a cuboid tissue region with arbitrary microvascular geometries and blood flows. Carrier-facilitated O2 diffusion in the erythrocytes and in the tissue and red blood cell reaction kinetics are considered. The model is based on analytical descriptions of the PO2 fields of single erythrocytes surrounded by carrier-free layers in an infinite three-dimensional space containing an O2 carrier such as myoglobin. These PO2 fields are overlaid to obtain a solution of the differential equation of diffusion in respiring tissue. The model has been applied to a situati…